Researcher Database

Ewa Kowalska
Institute for Catalysis Photocatalysis Research Division
Associate Professor

Researcher Profile and Settings


  • Institute for Catalysis Photocatalysis Research Division

Job Title

  • Associate Professor


  • PhD(Gdansk University of Technology)


J-Global ID

Research Areas

  • Nanotechnology/Materials / Nanostructure chemistry

Academic & Professional Experience

  • 2012/11 - Today Hokkaido University Catalysis Research Center associate professor
  • 2009/09 - 2012/10 FAU & Ulm University, Germany Institute of Inorganic Chemistry Marie Curie fellow
  • 2005/04 - 2009/08 Hokkaido University Catalysis Research Center JSPS & GCOE fellow
  • 2004/05 - 2007/09 Gdansk University of Technology, Poland Faculty of Chemistry, Department of Chemical Technology researcher


  • 1998/10 - 2004/06  Gdansk University of Technology, Poland  Faculty of Chemistry  Ph.D. thesis “Investigations of photochemical degradation of organic compounds”, 28.06.2004
  • 2001/11 - 2002/08  University of Paris Sud, France  Department of Physical Chemistry  Marie Curie fellowship
  • 1993/09 - 1998/06  Gdansk University of Technology, Poland  Faculty of Chemistry  MSc in Environmental Protection, MSc thesis "Photochemical destruction of methoxychlor"

Research Activities

Published Papers

  • Kunlei Wang, Ewa Kowalska
    Frontiers in Chemistry 10 2022/09/23 [Refereed][Invited]
    Titania is probably the most widely investigated semiconductor photocatalyst because of various advantages, such as high activity, thermal and chemical stability, low price, abundance, and negligible toxicity. However, pristine titania is also characterized by charge carriers’ recombination, and thus lower quantum yields of photocatalytic reactions than theoretical 100%. Moreover, its wide bandgap, despite being recommended for excellent redox properties, means also inactivity under visible part of solar radiation. Accordingly, titania has been surface modified, doped and coupled with various elements/compounds. For example, platinum deposited on the surface of titania has shown to improve both UV activity and the performance under vis. Although the studies on titania modification with platinum started almost half a century ago, and huge number of papers have been published up to now, it is unclear which properties are the most crucial and recommended to obtain highly efficient photocatalyst. In the literature, the opposite findings could be found on the property-governed activities that could result from huge differences in the reaction systems, and also examined photocatalysts. Considering the platinum properties, its content, the size of nanoparticles and the oxidation state, must be examined. Obviously, the characteristics of titania also influence the resultant properties of deposited platinum, and thus the overall photocatalytic performance. Although so many reports on Pt/TiO2 have been published, it is hardly possible to give indispensable advice on the recommended properties. However, it might be concluded that usually fine platinum NPs uniformly deposited on the titania surface result in high photocatalytic activity, and thus in the low optimal content of necessary platinum. Moreover, the aggregation of titania particles might also help in the lowering the necessary platinum amount (even to 0.2 wt%) due to the interparticle electron transfer mechanism between titania particles in one aggregate. In respect of platinum state, it is thought that it is highly substrate-specific case, and thus either positively charged or zero valent platinum is the most recommended. It might be concluded that despite huge number of papers published on platinum-modified titania, there is still a lack of comprehensive study showing the direct correlation between only one property and the resultant photocatalytic activity.
  • Maya Endo-Kimura, Kunlei Wang, Zuzanna Bielan, Marcin Janczarek, Agata Markowska-Szczupak, Ewa Kowalska
    Surfaces and Interfaces 32 102125 - 102125 2468-0230 2022/08 [Refereed][Invited]
  • Oliwia Paszkiewicz, Kunlei Wang, Rafał Rakoczy, Marian Kordas, Grzegorz Leniec, Ewa Kowalska, Agata Markowska-Szczupak
    Chemical Engineering and Processing - Process Intensification 178 109010 - 109010 0255-2701 2022/08 [Refereed]
  • Kunlei Wang, Zhishun Wei, Christophe Colbeau-Justin, Akio Nitta, Ewa Kowalska
    Surfaces and Interfaces 31 102057 - 102057 2468-0230 2022/07 [Refereed][Invited]
  • Kenta Yoshiiri, Kunlei Wang, Ewa Kowalska
    Inventions 7 (3) 54 - 54 2022/06/30 [Refereed][Invited]
    Plasmonic photocatalysts have gained more and more attention because of possible applications for solar energy conversion, environmental decontamination, and water treatment. However, the activity under visible light is usually very low, and the property-governed activity as well as the mechanisms are not fully understood yet. Accordingly, this study examines four different titania photocatalysts (anatase and rutile with fine and large crystallites) modified with gold by photodeposition. Three kinds of samples were prepared, as follows: (i) gold-modified titania (Au/TiO2), (ii) physically mixed Au/TiO2 samples (Au/TiO2(1) + Au/TiO2(2)), and (iii) Au/(TiO2(1) + Au/TiO2(2)) samples, prepared by subsequent deposition of gold on the mixture of bare and gold-modified titania. In total, twelve samples were prepared and well characterized, including diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM). The photocatalytic activity was examined in three reaction systems: (i) methanol dehydrogenation during gold photodeposition under UV/vis irradiation, (ii) oxidative decomposition of acetic acid (UV/vis), and (iii) oxidation of 2-propanol to acetone under visible light irradiation (λ > 450 nm). It was found that during subsequent deposition, gold is mainly formed on the surface of pre-deposited Au nanoparticles (NPs), localized on fine titania NPs, through the electrostatic attractions (negatively charged gold resulting from photogenerated electrons’ accumulation). This gold aggregation, though detrimental for UV activity (many “naked” large titania with low activity), is highly beneficial for vis activity because of efficient light harvesting and increased interface between gold and titania (gold deposits surrounded by fine titania NPs). Moreover, it was found that rutile is more active than anatase for plasmonic photocatalysis, probably due to easier electron transfer from gold via titania to adsorbed oxygen (more negative conduction band), which might hinder the back reaction (electron transfer: Au→TiO2→Au).
  • Kenta Yoshiiri, Baris Karabiyik, Kunlei Wang, Zhishun Wei, Christophe Colbeau-Justin, Ewa Kowalska
    The Journal of Chemical Physics 156 (24) 244706 - 244706 0021-9606 2022/06/28 [Refereed][Invited]
    Commercial titania photocatalysts were modified with silver nanoparticles (NPs) by the photodeposition method in the presence/absence of methanol. The obtained photocatalysts were characterized by XRD, XPS, diffuse reflectance spectroscopy, STEM, and time-resolved microwave conductivity (TRMC) methods. The photocatalytic activity was tested under UV/vis irradiation for (i) methanol dehydrogenation (during silver deposition), (ii) oxygen evolution with in situ silver deposition, and (iii) oxidative decomposition of acetic acid, as well as under vis irradiation for 2-propanol oxidation. The action spectra of 2-propanol oxidation were also performed. It has been confirmed that modification of titania with silver causes significant improvement of photocatalytic activity under both UV and vis irradiation as silver works as an electron scavenger (TRMC data) and vis activator (possibly by an energy transfer mechanism). The obtained activities differ between titania samples significantly, suggesting that the type of crystalline phase, particle/crystallite sizes, and electron traps’ density are crucial for both the properties of formed silver deposits and resultant photocatalytic activity. It might be concluded that, under UV irradiation, (i) high crystallinity and large specific surface area are recommended for rutile- and anatase-rich samples, respectively, during hydrogen evolution, (ii) mixed crystalline phases cause a high rate of oxygen evolution from water, and (iii) anatase phase with fine silver NPs results in efficient decomposition of acetic acid, whereas under vis irradiation the aggregated silver NPs (broad localized surface plasmon resonance peak) on the rutile phase are promising for oxidation reactions.
  • Ewa Kowalska, Saulius Juodkazis, Patrycja Henkiel, Damian Kowalski
    ACS Applied Nano Materials 5 (6) 7696 - 7703 2574-0970 2022/06/24 [Refereed]
  • Tamer M. Khedr, Kunlei Wang, Damian Kowalski, Said M. El-Sheikh, Hany M. Abdeldayem, Bunsho Ohtani, Ewa Kowalska
    Journal of Environmental Chemical Engineering 10 (3) 107838 - 107838 2213-3437 2022/06 [Refereed][Invited]
  • Kunlei Wang, Kenta Yoshiiri, Ewa Kowalska
    Chem Catalysis 2 (5) 925 - 927 2667-1093 2022/05 [Invited]
  • Lei Wang, Tharishinny R. Mogan, Kunlei Wang, Mai Takashima, Bunsho Ohtani, Ewa Kowalska
    ChemEngineering 6 (3) 33 - 33 2022/04/20 [Refereed][Invited]
    Novel materials with a periodic structure have recently been intensively studied for various photonic and photocatalytic applications due to an efficient light harvesting ability. Here, inverse opal titania (IOT) has been investigated for possible enhancement of photocatalytic activity. The IOT films were prepared on a glass support from silica and polystyrene (PS) opals by sandwich-vacuum-assisted infiltration and co-assembly methods, respectively. The reference sample was prepared by the same method (the latter) but with PS particles of different sizes, and thus without photonic feature. The modification of preparation conditions was performed to prepare the films with a high quality and different photonic properties, i.e., photonic bandgap (PBG) and slow photons’ wavelengths. The morphology and optical properties were characterized by scanning electron microscopy (SEM) and UV/vis spectroscopy, respectively. The photocatalytic activity was evaluated (also in dependence on the irradiation angle) for oxidative decomposition of acetaldehyde gas under irradiation with blue LED by measuring the rate of evolved carbon dioxide (CO2). It has been found that PBG wavelength depends on the size of particles forming opal, the void diameter of IOT, and irradiation angle, as expected from Bragg’s law. The highest activity (more than two-fold enhancement in the comparison to the reference) has been achieved for the IOT sample of 226-nm void diameter and PBG wavelengths at 403 nm, prepared from almost monodisperse PS particles of 252-nm diameter. Interestingly, significant decrease in activity (five times lower than reference) has been obtained for the IOT sample of also high quality but with 195-nm voids, and thus PBG at 375 nm (prohibited light). Accordingly, it has been proposed that the perfect tunning of photonic properties (here the blue-edge slow-photon effect) with bandgap energy of photocatalyst (e.g., absorption of anatase) results in the improved photocatalytic performance.
  • Dionysios D. Dionysiou, Sami Rtimi, Ewa Kowalska, Changseok Han, Marcin Janczarek
    Catalysts 12 (5) 458 - 458 2022/04/20 [Refereed][Invited]
    Due to exponential industrialization and rapid population growth, the global energy crisis and environmental pollution have become two of the greatest humanitarian challenges of the 21st century [...]
  • Ying Chang, Jiayi Jiang, Zhishun Wei, Ewa Kowalska
    Catalysts 12 (4) 408 - 408 2022/04/07 [Refereed][Invited]
    Mesoporous monodisperse microballs of amorphous titania were prepared from solution of absolute ethanol, tetrabutyl titanate (TBOT) and potassium chloride via a sub-zero sol–gel route. The as-obtained microballs were used as the precursor in an alcohothermal (ethanol with a small amount of water) process to synthesize monodisperse mesoporous microballs built of decahedral anatase nanocrystals. FE-SEM observation and XRD analysis have confirmed that the formed decahedral anatase-rich powder retained the original spherical morphology of the precursor. Importantly, a hierarchical structure composed of faceted anatase has been achieved under “green” conditions, i.e., fluorine-free. Additionally, the hysteresis loops (BET results) have confirmed the existence of mesopores. Interestingly, faceted microballs show noticeable photocatalytic activity under UV/vis irradiation for hydrogen generation without any co-catalyst use, reaching almost forty times higher activity than that by famous commercial titania photocatalyst—P25. It has been proposed that enhanced photocatalytic performance is caused by mesoporous structure and co-existence of two kinds of facets, i.e., {001} and {101}, and thus hindered charge carriers’ recombination.
  • Zhenhao Li, Kunlei Wang, Jinyue Zhang, Ying Chang, Ewa Kowalska, Zhishun Wei
    Catalysts 12 (2) 130 - 130 2022/01/21 [Refereed][Invited]
    Visible-responsive photocatalysts for environmental purification and fuel generation are, currently, highly sought after. Among the possible candidates, Bi2WO6 (BWO) has been considered due to its efficient light harvesting, stability, and promising activities. Here, hierarchical BWO microballs have been prepared using a hydrothermal method, and additionally modified with deposits of noble metals (gold, silver, copper, palladium and platinum) by the photodeposition method. The structure, morphology, photoabsorption properties, and surface composition of bare and metal-modified BWO samples were investigated by XRD, SEM, DRS and XPS analyses. The photocatalytic activity was evaluated by the oxidative degradation of model dye (methyl orange (MO)) under UV/vis, and hydrogen generation under vis and/or UV irradiation. It was found that hierarchical morphology is detrimental for high photocatalytic activity in both tested systems, resulting in the improved degradation of MO (ca. 65% during 90 min of UV/vis irradiation), and hydrogen evolution (0.1 and 0.4 μmol h−1 under vis and UV/vis irradiation, respectively). Moreover, the type of noble metal and its properties influence the overall photocatalytic performance. It was found that, under UV/vis irradiation, only platinum accelerates hydrogen evolution, whereas under vis irradiation the activity follows the order: BWO < BWO/Cu < BWO/Ag < BWO/Pt < BWO/Pd < BWO/Au. It was concluded that zero-valent metal is recommended for high vis response, probably due to plasmonic photocatalysis, efficient light harvesting ability, and co-catalytic role.
  • Tamer M. Khedr, Said M. El-Sheikh, Ewa Kowalska, Hany M. Abdeldayem
    Journal of Environmental Chemical Engineering 9 (6) 106566 - 106566 2213-3437 2021/12 [Refereed]
  • Zhishun Wei, Tharishinny Raja Mogan, Kunlei Wang, Marcin Janczarek, Ewa Kowalska
    Energies 14 (21) 7223 - 7223 2021/11/02 [Refereed][Invited]
    In the past few decades, extensive studies have been performed to utilize the solar energy for photocatalytic water splitting; however, up to the present, the overall efficiencies reported in the literature are still unsatisfactory for commercialization. The crucial element of this challenging concept is the proper selection and design of photocatalytic material to enable significant extension of practical application perspectives. One of the important features in describing photocatalysts, although underestimated, is particle morphology. Accordingly, this review presents the advances achieved in the design of photocatalysts that are dedicated to hydrogen generation, with an emphasis on the particle morphology and its potential correlation with the overall reaction performance. The novel concept of this work—with the content presented in a clear and logical way—is based on the division into five parts according to dimensional arrangement groups of 0D, 1D, 2D, 3D, and combined systems. In this regard, it has been shown that the consideration of the discussed aspects, focusing on different types of particle morphology and their correlation with the system’s efficiency, could be a promising route for accelerating the development of photocatalytic materials oriented for solar-driven hydrogen generation. Finally, concluding remarks (additionally including the problems connected with experiments) and potential future directions of particle morphology-based design of photocatalysts for hydrogen production systems have been presented.
  • Zuzanna Bielan, Szymon Dudziak, Adam Kubiak, Ewa Kowalska
    Applied Sciences 11 (21) 10160 - 10160 2021/10/29 [Refereed][Invited]
    Semiconducting materials display unique features that enable their use in a variety of applications, including self-cleaning surfaces, water purification systems, hydrogen generation, solar energy conversion, etc. However, one of the major issues is separation of the used materials from the process suspension. Therefore, chemical compounds with magnetic properties have been proposed as crucial components of photocatalytic composites, facilitating separation and recovery of photocatalysts under magnetic field conditions. This review paper presents the current state of knowledge on the application of spinel and hexagonal ferrites in heterogeneous photocatalysis. The first part focuses on the characterization of magnetic (nano)particles. The next section presents the literature findings on the single-phase magnetic photocatalyst. Finally, the current state of scientific knowledge on the wide variety of magnetic-photocatalytic composites is presented. A key aim of this review is to indicate that spinel and hexagonal ferrites are considered as an important element of heterogeneous photocatalytic systems and are responsible for the effective recycling of the photocatalytic materials.
  • Marcin Janczarek, Zhishun Wei, Tharishinny R. Mogan, Lei Wang, Kunlei Wang, Akio Nitta, Bunsho Ohtani, Ewa Kowalska
    Symmetry 13 (9) 1682 - 1682 2021/09/12 [Refereed][Invited]
    Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.
  • Kunlei Wang, Kenta Yoshiiri, Lorenzo Rosa, Zhishun Wei, Saulius Juodkazis, Bunsho Ohtani, Ewa Kowalska
    Catalysis Today in press 257 - 264 0920-5861 2021/09 [Refereed][Not invited]
  • Marcin Janczarek, Ewa Kowalska
    Catalysts 11 (8) 978 - 978 2021/08/16 [Refereed][Invited]
    Pristine and modified/doped titania are still some of the most widely investigated photocatalysts due to its high activity, stability, abundance and proper redox properties to carry out various reactions. However, modifiers and/or dopants resulting in visible-light activity might be expensive or work as recombination centers under UV irradiation. It seems that defective titania, known as “self-doped” TiO2, might be the best solution since it can be obtained under mild conditions without the addition of expensive materials and methods. This review discusses various methods of defective titania preparation, characterization of defect types, their localization (surface vs. bulk) and their function, as well as proposed mechanisms of photocatalytic reactions in the presence of self-doped titania. Although many kinds of defective titania samples have already been prepared with different colors, color intensities and defect kinds (mainly Ti3+ and oxygen vacancies), it is difficult to conclude which of them are the most recommended as the preparation conditions and activity testing used by authors differ. Furthermore, activity testing under solar radiation and for dyes does not clarify the mechanism since bare titania can also be excited and sensitized, respectively, in these conditions. In many reports, authors have not considered the possible influence of some impurities originated from the synthesis method (e.g., H, Al, Zn, Cl, F) that could co-participate in the overall mechanism of photocatalytic reactions. Moreover, some reports indicate that defective titania, especially black ones, might decrease activity since the defects might work as recombination centers. Despite some unproven/unclear findings and unanswered questions, there are many well-conducted studies confirmed by both experimental and theoretical studies that defective titania might be a promising material for various photocatalytic reactions under both UV and visible-light irradiation. Based on available literature, it could be proposed that optimal defects’ concentration, the preferential role of surface defects, a higher surface-to-bulk ratio of defects in rutile than in anatase, and the beneficial impact of disordered surface are the most important aspects to be considered during the preparation of defective titania.
  • Tharishinny Raja-Mogan, Anais Lehoux, Mai Takashima, Ewa Kowalska, Bunsho Ohtani
    Chemistry Letters 50 (4) 711 - 713 0366-7022 2021/04/05 [Refereed]
    Here, we report a novel structured material, titania inverseopal photonic crystal with or without a single gold nanoparticle in each void, to provide a photoabsorption design strategy as enhanced photoreaction rates, only when wavelengths of photo-irradiation, photoabsorption (by gold nanoparticles or titania), and photonic-bandgap edge are trebly matched.
  • Ewa Kowalska
    Catalysts 11 (4) 410 - 410 2021/03/24 [Refereed][Invited]
    Plasmonic photocatalysts, i [...]
  • Marta Paszkiewicz-Gawron, Ewa Kowalska, Maya Endo-Kimura, Julia Zwara, Anna Pancielejko, Kunlei Wang, Wojciech Lisowski, Justyna Łuczak, Adriana Zaleska-Medynska, Ewelina Grabowska-Musiał
    Applied Surface Science 541 148425 - 148425 0169-4332 2021/03 [Refereed]
  • Marcin Janczarek, Maya Endo-Kimura, Zhishun Wei, Zuzanna Bielan, Tharishinny R. Mogan, Tamer M. Khedr, Kunlei Wang, Agata Markowska-Szczupak, Ewa Kowalska
    Applied Sciences 11 (5) 1982 - 1982 2021/02/24 [Refereed][Invited]
    Graphene, graphene oxide, reduced graphene oxide and their composites with various compounds/materials have high potential for substantial impact as cheap photocatalysts, which is essential to meet the demands of global activity, offering the advantage of utilizing “green” solar energy. Accordingly, graphene-based materials might help to reduce reliance on fossil fuel supplies and facile remediation routes to achieve clean environment and pure water. This review presents recent developments of graphene-based semiconductor photocatalysts, including novel composites with faceted particles, photonic crystals, and nanotubes/nanowires, where the enhancement of activity mechanism is associated with a synergistic effect resulting from the presence of graphene structure. Moreover, antimicrobial potential (highly needed these days), and facile recovery/reuse of photocatalysts by magnetic field have been addresses as very important issue for future commercialization. It is believed that graphene materials should be available soon in the market, especially because of constantly decreasing prices of graphene, vis response, excellent charge transfer ability, and thus high and broad photocatalytic activity against both organic pollutants and microorganisms.
  • Marcin Janczarek, Ewa Kowalska
    Catalysts 11 (2) 198 - 198 2021/02/03 [Refereed][Invited]
    Photocatalysis has been considered future technology for green energy conversion and environmental purification, including carbon dioxide reduction, water splitting, air/water treatment, and antimicrobial purposes. Although various photocatalysts with high activity and stability have already been found, the commercialization of photocatalytic processes seems to be slow; it is thought that the difficulty in scaling up photocatalytic processes might be responsible. Research on the design of photocatalytic reactors using computer simulations has been recently intensive. The computer simulations involve various methods of hydrodynamics, radiation, and mass transport analysis, including the Monte Carlo method, the approximation approach–P1 model, and computational fluid dynamics as a complex simulation tool. This review presents all of these models, which might be efficiently used for the scaling-up of photocatalytic reactors. The challenging aspects and perspectives of computer simulation are also addressed for the future development of applied photocatalysis.
  • Zuzanna Bielan, Ewa Kowalska, Szymon Dudziak, Kunlei Wang, Bunsho Ohtani, Anna Zielińska-Jurek
    Catalysis Today 361 198 - 209 0920-5861 2021/02 [Refereed][Not invited]
    Titanium(IV) oxide is one of the most widely investigated photocatalysts. However, separation of nano-sized particulate titania might result in profitless technologies for commercial applications. Additionally, bare titania is almost inactive under the Vis range of solar spectrum due to its wide bandgap. Therefore, the present study aims to prepare novel core-interlayer-shell TiO2 magnetic photocatalysts modified with metal nanoparticles (Pt, Cu), which exhibit both photocatalytic and magnetic properties, making it easily separable within the magnetic field. Accordingly, the core-shell structure of Fe3O4@SiO2/TiO2 was obtained in water/TX100/cyclohexane microemulsion. Platinum and copper were photodeposited on four TiO2 templates and characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), specific surface area (BET) measurement and diffuse refiectance spectroscopy (DR-UV/Vis). Photoactivity was studied in the reaction of phenol, acetic acid, and methanol degradation under UV/Vis irradiation, using both polychromatic and monochromatic irradiation (action spectrum analysis). The core-interlayer-shell structure of Pt and Cu modified magnetic photocatalysts was confirmed using scanning transmission electron microscopy (STEM). Magnetic photocatalysts modified with platinum and copper revealed improved photoactivity both in oxidation and reduction photocatalytic reactions, as compared to unmodified Fe3O4@SiO2/TiO2 photocatalysts. Finally, the correlation between physicochemical properties and photocatalytic activities of Fe3O4@SiO2/TiO2-Pt/Cu photocatalysts was investigated. For the first time, the effect of metals' loading on the efficiency of phenol degradation and mineralization (TOC removal), and quantum efficiency of reaction in the presence of magnetic photocatalysts were analyzed. It was found that phenol can be efficiently decomposed (ca. 100%) during 60 min of UV/Vis irradiation for the photocatalyst recovered within the magnetic field during three subsequent degradation cycles.
  • Paweł Mazierski, Juganta K. Roy, Alicja Mikolajczyk, Ewelina Wyrzykowska, Tomasz Grzyb, Pablo Nicolas Arellano Caicedo, Zhishun Wei, Ewa Kowalska, Adriana Zaleska-Medynska, Joanna Nadolna
    Applied Surface Science 536 147805 - 147805 0169-4332 2021/01 [Refereed][Not invited]
  • Kunlei Wang, Zuzanna Bielan, Maya Endo-Kimura, Marcin Janczarek, Dong Zhang, Damian Kowalski, Anna Zielińska-Jurek, Agata Markowska-Szczupak, Bunsho Ohtani, Ewa Kowalska
    Journal of Materials Chemistry A 9 (16) 10135 - 10145 2050-7488 2021 [Refereed]

    Stable and enhanced UV/vis photocatalytic activity via the Z-scheme mechanism of CuxO@TiO2 prepared by the microemulsion method.

  • Agata Markowska-Szczupak, Maya Endo-Kimura, Oliwia Paszkiewicz, Ewa Kowalska
    Nanomaterials 10 (10) 2065 - 2065 2020/10/19 [Refereed]
    Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.
  • Maya Endo-Kimura, Bariş Karabiyik, Kunlei Wang, Zhishun Wei, Bunsho Ohtani, Agata Markowska-Szczupak, Ewa Kowalska
    Catalysts 10 (10) 1194 - 1194 2020/10/16 [Refereed]
    Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Although zero-valent copper was deposited on the surface of titania, oxidized forms of copper, post-formed in ambient conditions, were also detected in dried samples. All samples could absorb visible light (vis), due to localized surface plasmon resonance (LSPR) of zero-valent copper and by other copper species, including Cu2O, CuO and CuxO (x:1-2). The photocatalytic activities of samples were investigated under both ultraviolet (UV) and visible light irradiation (>450 nm) for oxidative decomposition of acetic acid. It was found that titania modification with copper significantly enhanced the photocatalytic activity, especially for anatase samples. The prolonged irradiation (from 1 to 5 h) during samples’ preparation resulted in aggregation of copper deposits, thus being detrimental for vis activity. It is proposed that oxidized forms of copper are more active under vis irradiation than plasmonic one. Antimicrobial properties against bacteria (Escherichia coli) and fungi (Aspergillus niger) under vis irradiation and in the dark confirmed that Cu/TiO2 exhibits a high antibacterial effect, mainly due to the intrinsic activity of copper species.
  • Paweł Mazierski, Alicja Mikolajczyk, Tomasz Grzyb, Pablo Nicolas Arellano Caicedo, Zhishun Wei, Ewa Kowalska, Henry P. Pinto, Adriana Zaleska-Medynska, Joanna Nadolna
    Applied Surface Science 527 146815 - 146815 0169-4332 2020/10 [Refereed][Not invited]
  • Zhishun Wei, Marcin Janczarek, Kunlei Wang, Shuaizhi Zheng, Ewa Kowalska
    Catalysts 10 (9) 1070 - 1070 2020/09/17 [Refereed][Not invited]
    Plasmonic photocatalysts have been extensively studied for the past decade as a possible solution to energy crisis and environmental problems. Although various reports on plasmonic photocatalysts have been published, including synthesis methods, applications, and mechanism clarifications, the quantum yields of photochemical reactions are usually too low for commercialization. Accordingly, it has been proposed that preparation of plasmonic photocatalysts with efficient light harvesting and inhibition of charge carriers’ recombination might result in improvement of photocatalytic activity. Among various strategies, nano-architecture of plasmonic photocatalysts seems to be one of the best strategies, including the design of properties for both semiconductor and noble-metal-deposits, as well as the interactions between them. For example, faceted nanoparticles, nanotubes, aerogels, and super-nano structures of semiconductors have shown the improvement of photocatalytic activity and stability. Moreover, the selective deposition of noble metals on some parts of semiconductor nanostructures (e.g., specific facets, basal or lateral surfaces) results in an activity increase. Additionally, mono-, bi-, and ternary-metal-modifications have been proposed as the other ways of performance improvement. However, in some cases, the interactions between different noble metals might cause unwanted charge carriers’ recombination. Accordingly, this review discusses the recent strategies on the improvements of the photocatalytic performance of plasmonic photocatalysts.
  • Zuzanna Bielan, Ewa Kowalska, Szymon Dudziak, Kunlei Wang, Bunsho Ohtani, Anna Zielińska-Jurek
    Data in Brief 31 105814 - 105814 2352-3409 2020/08 [Refereed][Not invited]
    Surface modification of titania with noble and semi-noble metals resulted in significant enhancement of photocatalytic activity. Presented data, showing the photocatalytic properties of TiO2-M (where M is Pt and/or Cu) photocatalysts were further used as Fe3O4 @SiO2/TiO2-M magnetic nanocomposites shells in "Monoand bimetallic (Pt/Cu) titanium(IV) oxide core-shell photocatalysts with Vis light activity and magnetic separability" [1] . Platinum and copper were photodeposited on four different titania matrices (commercial and self-obtained ones). The prepared photocatalysts were characterized by X-ray diffraction (XRD) analysis, specific surface area measurements using the Brunauer-Emmet-Teller (BET) isotherm, diffuse reflectance spectroscopy (DR-UV/Vis) analysis as well as scanning transmission electron microscopy (STEM) analysis. Photocatalytic properties were investigated in three different reactions: H-2 generation, acetic acid oxidation to CO2, and phenol degradation. (C) 2020 The Author(s). Published by Elsevier Inc.
  • Maya Endo-Kimura, Ewa Kowalska
    Catalysts 10 (8) 824 - 824 2020/07/23 [Refereed][Not invited]
    Wide-bandgap semiconductors modified with nanostructures of noble metals for photocatalytic activity under vis irradiation due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively investigated over the last decade. Most literature reports discuss the properties and activities of plasmonic photocatalysts for the decomposition of organic compounds and solar energy conversion. Although noble metals, especially silver and copper, have been known since ancient times as excellent antimicrobial agents, there are only limited studies on plasmonic photocatalysts for the inactivation of microorganisms (considering vis-excitation). Accordingly, this review has discussed the available literature reports on microbiological applications of plasmonic photocatalysis, including antibacterial, antiviral and antifungal properties, and also a novel study on other microbiological purposes, such as cancer treatment and drug delivery. Although some reports indicate high antimicrobial properties of these photocatalysts and their potential for medical/pharmaceutical applications, there is still a lack of comprehensive studies on the mechanism of their interactions with microbiological samples. Moreover, contradictory data have also been published, and thus more study is necessary for the final conclusions on the key-factor properties and the mechanisms of inactivation of microorganisms and the treatment of cancer cells.
  • Tharishinny Raja-Mogan, Bunsho Ohtani, Ewa Kowalska
    Catalysts 10 (8) 827 - 827 2020/07/23 [Refereed][Not invited]
    Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports have already been published, discussing the optimal properties, synthesis methods and mechanism clarification. It has been proposed that both efficient light harvesting and charge carriers’ migration are detrimental for high and stable activity under Vis irradiation. Accordingly, photonic crystals (PCs) with photonic bandgap (PBG) and slow photon effects seem to be highly attractive for efficient use of incident photons. Therefore, the study on PCs-based plasmonic photocatalysts has been conducted, mainly on titania inverse opal (IO) modified with nanoparticles (NPs) of NM. Although, the research is quite new and only several reports have been published, it might be concluded that the matching between LSPR and PBG (especially at red edge) by tuning of NMNPs size and IO-void diameter, respectively, is the most crucial for the photocatalytic activity.
  • Maria Guadalupe Méndez-Medrano, Ewa Kowalska, Bunsho Ohtani, Daniel Bahena Uribe, Christophe Colbeau-Justin, Sven Rau, José Luis Rodríguez-López, Hynd Remita
    The Journal of Chemical Physics 153 (3) 034705 - 034705 0021-9606 2020/07/21 [Refereed][Not invited]
    Heterojunctions of small CuO nanoclusters (synthesized by radiolysis) with TiO2 (commercial P25) induced a photocatalytic activity under visible light irradiation in a wide range of wavelengths due to the narrow bandgap of CuO nanoclusters of around 1.7 eV. The optical, chemical, and electrical properties of these composite nanomaterials were studied. The photocatalytic properties of bare and modified TiO2-P25 were studied for water purification (photooxidation of organic compounds such as phenol and 2-propanol) and for hydrogen generation under visible light irradiation. Time resolved microwave conductivity signals showed activation of TiO2 under visible light, proving the injection of electrons from CuO nanoclusters to the conduction band of TiO2-P25. The modified materials showed high photocatalytic activity under visible light. The important role of charge-carriers was demonstrated for both photoreduction and photooxidation reactions.
  • Ying Chang, Penghao He, Zhishun Wei, Yuan Chen, Huihu Wang, Chonggang Wu, Zhiwen Zhou, Huicheng Huang, Ewa Kowalska, Shijie Dong
    Materials Letters 268 127592 - 127592 0167-577X 2020/06 [Refereed][Not invited]
  • Marta Paszkiewicz-Gawron, Samanta Makurat, Janusz Rak, Magdalena Zdrowowicz, Wojciech Lisowski, Adriana Zaleska-Medynska, Ewa Kowalska, Paweł Mazierski, Justyna Łuczak
    Catalysts 10 (4) 371 - 371 2020/03/30 [Refereed][Not invited]
    Formation of a surface complex between organic molecules and TiO2 is one of the possible strategies for the development of visible light-induced TiO2 photoactivity. Herein, three ionic liquids (ILs) with the same cation and different anions (1-butylpirydynium chloride/bromide/iodide) have been applied for the surface modification of TiO2 and to understand the role of anions in visible light-induced activity of ILs-TiO2 systems. Photocatalytic screening tests (the measurements of phenol photodegradation reaction rate) revealed that anion type affected visible light activity (λ > 420 nm) of TiO2 obtained by the ILs-assisted solvothermal method. Density functional theory (DFT) calculations demonstrated that interactions between halogen anions and oxygen vacancies (OV) on the surface of the TiO2 particles could be responsible for the specific wavelength-induced excitation and finally for the observed photoactivity of titania under visible light. Finally, our theoretical calculations have been proven by experiments using monochromatic light (the apparent quantum efficiency was measured) and the properties of obtained samples were characterized using scanning electron microscopy (SEM), X-ray powder diffraction analysis (XRD), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS).
  • Agata Markowska-Szczupak, Zhishun Wei, Ewa Kowalska
    Catalysts 10 (2) 238 - 238 2020/02/17 [Refereed][Not invited]
    Cosmetics and other daily care products contain titanium(IV) oxide (titania). Since multiple risk factors can increase the chance of developing cancer, an evaluation of titania safety has become a matter of concern in recent times. However, it should be pointed out that titania as an efficient photocatalyst has been also applied for inactivation of various pathogens, environmental purification and energy conversion, which might result in significant improvement of human life. Therefore, it is worth considering titania not only as a possible cancer initiator, but also as an efficient solution against cancer cells. Accordingly, in this study, the effect of commercial titania photocatalyst P25 (Degussa/Evonik) on breast adenocarcinoma MCF7 cells (ATCC® HTB-22™, breast adenocarcinoma cell line from human) has been investigated. The cells were treated with titania at doses of 10, 30, and 50 µg/mL under UVA/vis irradiation and in the dark. The significant morphological alterations in living cells were observed for larger doses of titania, such as changes in the shape and the size of cells, the deviation from the normal structure, and an increase in cells’ mortality. Moreover, the effect was significantly higher under irradiation than in the dark confirming strong photocatalytic activity of titania P25. In contrast, the lowest dose of titania (10 µg/mL) did not exhibit a significant impact on MCF7 cells, similarly to the nontreated cells. Accordingly, it has been proposed that locally applied titania might be considered for a cancer therapy after necessary in vivo tests to estimate any possibilities of side effects.
  • Zhishun Wei, Maya Endo-Kimura, Christophe Colbeau-Justin, Bunsho Ohtani, Ewa Kowalska
    Journal of Nanoscience and Nanotechnology 20 (2) 1278 - 1287 1533-4880 2020/02/01 [Refereed][Invited]
    Octahedral anatase particles (OAPs) belonging to faceted titania photocatalysts exhibit one of the highest photocatalytic activities among various titania photocatalysts, probably due to hindered recombination of charge carriers resulting from low content of defects (recombination centers). In this study, OAPs have been examined for oxidative decomposition of acetic acid, dehydrogenation of methanol and bacteria inactivation. OAPs were prepared from partly protonated potassium nanowires by hydrothermal reaction (HT) at various experimental conditions, i.e., the influences of HT temperature and content of reaction reagents were studied in detail. The morphology, composition and crystal structure of the products were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) diffuse reflectance spectroscopy (DRS) and time-resolved microwave conductivity (TRMC) method. It was found that all parameters during HT influenced simultaneously the morphology of obtained products, and even slight change in one of them could result in significant change in the properties, and thus photocatalytic activities. Moreover, it was shown that titania morphology was a key-factor for photocatalytic activity for decomposition of both organic compounds and microorganisms. Although, an imperfection in octahedral shape (semi-OAPs) did not influence the efficiently for decomposition of organic compounds, it had tremendous negative impact on antimicrobial performance, probably due to hindered adsorption of bacterial cells on the photocatalyst surface (preferential on {101} facets).
  • Maria Guadalupe Méndez-Medrano, Ewa Kowalska, Maya Endo-Kimura, Kunlei Wang, Bunsho Ohtani, Daniel Bahena Uribe, Jose Luis Rodríguez-López, Hynd Remita
    ACS Applied Bio Materials 2 (12) 5626 - 5633 2576-6422 2019/12/16 [Refereed][Not invited]
    The photocatalytic disinfection (PCD) properties of TiO2 have attracted attention in the research communities because the produced reactive oxygen species (ROS) allow destruction of different types of microbes, such as fungi, bacteria, viruses, algae, unicellular organisms, etc. on surfaces, in water, and in air. However, TiO2 requires UV irradiation to produce the ROS, which limits its photoactivity in indoor environments. Surface-modified TiO2 with small Ag and CuO nanoclusters in a core-shell structure exhibits antifungal properties under dark and visible conditions, possibly because of the interaction between Ag-CuO nanoclusters in the fungi membrane and their penetration, and the co-presence of Cu2+ and Ag+ ions. Therefore, a synergetic effect is obtained with co-modification of TiO2 with silver and copper, and the sample Ag@CuO/TiO2 (core-shell structure of Ag-Cu in a ratio of 1:3) exhibits the highest antifungal activity; that is, fungi growth inhibition is observed for Aspergillus melleus and Penicillium chrysogenum. Moreover, significant inhibitions of the sporulation and generation of droplets, possibly containing mycotoxins and sclerotia under dark and visible exposure, are also obtained.
  • Kunlei Wang, Maya Endo-Kimura, Raphaëlle Belchi, Dong Zhang, Aurelie Habert, Johann Bouclé, Bunsho Ohtani, Ewa Kowalska, Nathalie Herlin-Boime
    Materials 12 (24) 4158 - 4158 2019/12/11 [Refereed][Invited]
    Laser synthesis was used for one-step synthesis of titania/graphene composites (G-TiO2 (C)) from a suspension of 0.04 wt% commercial reduced graphene oxide (rGO) dispersed in liquid titanium tetraisopropoxide (TTIP). Reference titania sample (TiO2(C)) was prepared by the same method without graphene addition. Both samples and commercial titania P25 were characterized by various methods and tested under UV/vis irradiation for oxidative decomposition of acetic acid and dehydrogenation of methanol (with and without Pt co-catalyst addition), and under vis irradiation for phenol degradation and inactivation of Escherichia coli. It was found that both samples (TiO2(C) and G-TiO2(C)) contained carbon resulting from TTIP and C2H4 (used as a synthesis sensitizer), which activated titania towards vis activity. The photocatalytic activity under UV/vis irradiation was like that by P25. The highest activity of TiO2(C) sample for acetic acid oxidation was probably caused by its surface enrichment with hydroxyl groups. G-TiO2(C) was the most active for methanol dehydrogenation in the absence of platinum (ca. five times higher activity than that by TiO2(C) and P25), suggesting that graphene works as a co-catalyst for hydrogen evolution. High activity under both UV and vis irradiation for decomposition of organic compounds, hydrogen evolution and inactivation of bacteria suggests that laser synthesis allows preparation of cheap (carbon-modified) and efficient photocatalysts for broad environmental applications.
  • Kunlei Wang, Marcin Janczarek, Zhishun Wei, Tharishinny Raja-Mogan, Maya Endo-Kimura, Tamer M. Khedr, Bunsho Ohtani, Ewa Kowalska
    Catalysts 9 (12) 1054 - 1054 2019/12/11 [Refereed][Invited]
    Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed recently. Therefore, this paper presents novel, attractive, and prospective titania photocatalysts, including zero-, one-, two-, and three-dimensional titania structures. The 1D, 2D, and 3D titania structures have been mainly designed for possible applications, e.g., (i) continuous use without the necessity of particulate titania separation, (ii) efficient light harvesting (e.g., inverse opals), (iii) enhanced activity (fast charge carriers’ separation, e.g., 1D nanoplates and 2D nanotubes). It should be pointed out that these structures might be also useful for mechanism investigation, e.g., (i) 3D titania aerogels with gold either incorporated inside the 3D network or supported in the porosity, and (ii) titania mesocrystals with gold deposited either on basal or lateral surfaces, for the clarification of plasmonic photocatalysis. Moreover, 0D nanostructures of special composition and morphology, e.g., magnetic(core)–titania(shell), mixed-phase titania (anatase/rutile/brookite), and faceted titania NPs have been presented, due to their exceptional properties, including easy separation in the magnetic field, high activity, and mechanism clarification, respectively. Although anatase has been usually thought as the most active phase of titania, the co-existence of other crystalline phases accelerates the photocatalytic activity significantly, and thus mixed-phase titania (e.g., famous P25) exhibits high photocatalytic activity for both oxidation and reduction reactions. It is believed that this review might be useful for the architecture design of novel nanomaterials for broad and diverse applications, including environmental purification, energy conversion, synthesis and preparation of “intelligent” surfaces with self-cleaning, antifogging, and antiseptic properties.
  • Zielińska-Jurek, Wei, Janczarek, Wysocka, Kowalska
    Catalysts 9 (11) 940 - 940 2019/11/08 [Refereed][Not invited]
    Different TiO2 photocatalysts, i.e., commercial samples (ST-01 and P25 with minority of rutile phase), nanotubes, well-crystallized faceted particles of decahedral shape and mesoporous spheres, were used as supports for deposition of Pt nanoparticles (NPs). Size-controlled Pt NPs embedded in TiO2 were successfully prepared by microemulsion and wet-impregnation methods. Obtained photocatalysts were characterized using XRD, TEM, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) specific surface area, DR/UV-vis and action spectrum analysis. The effect of deposition method, amount of Pt precursor and TiO2 properties on size, distribution, and chemical states of deposited Pt NPs were investigated. Finally, the correlations between the physicochemical properties and photocatalytic activities in oxidation and reduction reactions under UV and Vis light of different Pt-TiO2 photocatalysts were discussed. It was found that, regardless of preparation method, the photoactivity mainly depended on platinum and TiO2 morphology. In view of this, we claim that the tight control of NPs’ morphology allows us to design highly active materials with enhanced photocatalytic performance. Action spectrum analysis for the most active Pt-modified TiO2 sample showed that visible light-induced phenol oxidation is initiated by excitation of platinum surface plasmon, and photocatalytic activity analysis revealed that photoactivity depended strongly on morphology of the obtained Pt-modified TiO2 photocatalysts.
  • Izabela Wysocka, Agata Markowska‐Szczupak, Piotr Szweda, Jacek Ryl, Maya Endo‐Kimura, Ewa Kowalska, Grzegorz Nowaczyk, Anna Zielińska‐Jurek
    Indoor Air 29 (6) 979 - 992 0905-6947 2019/11 [Refereed][Not invited]
  • Khedr, El-Sheikh, Abdeldayem, Ismail, Kowalska, Bahnemann
    Catalysts 9 (11) 877 - 877 2019/10/23 [Refereed][Not invited]
    In an endeavor to tackle environmental problems, the photodegradation of microcystin-LR (MC-LR), one of the most common and toxic cyanotoxins, produced by the cyanobacteria blooms, was examined using nanostructured TiO2 photocatalysts (anatase, brookite, anatase–brookite, and C/N/S co-modified anatase–brookite) under UV-A, solar and visible light irradiation. The tailoring of TiO2 properties to hinder the electron–hole recombination and improve MC-LR adsorption on TiO2 surface was achieved by altering the preparation pH value. The highest photocatalytic efficiency was 97% and 99% with degradation rate of 0.002 mmol L−1 min−1 and 0.0007 mmol L−1 min−1 under UV and solar irradiation, respectively, using a bare TiO2 photocatalyst prepared at pH 10 with anatase to brookite ratio of ca. 1:2.5. However, the bare TiO2 samples were hardly active under visible light irradiation (25%) due to a large band gap. Upon UV, solar and vis irradiation, the complete MC-LR degradation (100%) was obtained in the presence of C/N/S co-modified TiO2 with a degradation rate constant of 0.26 min−1, 0.11 min−1 and 0.04 min−1, respectively. It was proposed that the remarkable activity of co-modified TiO2 might originate from its mixed-phase composition, mesoporous structure, and non-metal co-modification.
  • Ewa Kowalska, Agata Markowska-Szczupak, Marcin Janczarek
    Catalysts 9 (10) 855 - 855 2019/10/14 [Refereed][Invited]
    Nanomaterials, engineered structures of which a single unit is sized (in at least one dimension) between 1 to 100 nm, are probably the fastest growing market in the world [...]
  • Wei, Endo-Kimura, Wang, Colbeau-Justin, Kowalska
    Nanomaterials 9 (10) 1447 - 1447 2019/10/11 [Refereed][Not invited]
    Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modified samples. Photocatalytic activities of bare and modified OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed different influence on the activity depending on the semiconductor support, i.e., gold-modified TNW and platinum-modified OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modified samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical effect on the overall photocatalytic performance. TRMC analysis confirmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the efficiency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity).
  • Paweł Mazierski, Pablo Nicolás Arellano Caicedo, Tomasz Grzyb, Alicja Mikolajczyk, Juganta K. Roy, Ewelina Wyrzykowska, Zhishun Wei, Ewa Kowalska, Tomasz Puzyn, Adriana Zaleska-Medynska, Joanna Nadolna
    Applied Catalysis B: Environmental 252 138 - 151 0926-3373 2019/09 [Refereed][Not invited]
  • Izabela Wysocka, Ewa Kowalska, Jacek Ryl, Grzegorz Nowaczyk, Anna Zielińska-Jurek
    Nanomaterials 9 (8) 1129 - 1129 2019/08/06 [Refereed][Not invited]
    Noble metal nanoparticles (NMNPs) enhanced TiO2 response and extended its activity under visible light. Photocatalytic activity of TiO2 modified with noble metal nanoparticles strongly depends on the physicochemical properties of NMNPs. Among others, the differences in the size of NMNPs seems to be one of the most important factors. In this view, the effect of the metal’s nanoparticles size, type and amount on TiO2 photocatalytic and biocidal activity was investigated. TiO2 modified with mono- and bimetallic nanoparticles of Pt, Cu and Ag were prepared using chemical and thermal reduction methods. Obtained nanocomposites were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and diffuse-reflectance spectroscopy (DR/UV-Vis) techniques. The photocatalytic activity was examined in 2-propanol oxidation and hydrogen generation processes. The mechanism of modified TiO2 excitation was evaluated in action spectrum measurements during phenol oxidation. A possibility of using less energy-consuming light sources as a set of light-emitting diodes (LEDs) selected based on action spectrum results was examined. It was found that the differences in NMNPs size were the result of the reduction method. Moreover, coupling with a second metal strongly affected and differentiated the photocatalytic and biocidal activity of the obtained TiO2-based photocatalysts.
  • Patrycja Parnicka, Tomasz Grzyb, Alicja Mikolajczyk, Kunlei Wang, Ewa Kowalska, Norbert Steinfeldt, Marek Klein, Paweł Mazierski, Adriana Zaleska-Medynska, Joanna Nadolna
    Journal of Colloid and Interface Science 549 212 - 224 0021-9797 2019/08 [Refereed][Not invited]
  • Tamer Khedr, Said El-Sheikh, Adel Ismail, Ewa Kowalska, Detlef Bahnemann
    Materials 12 (7) 1027 - 1027 2019/03/28 [Refereed][Not invited]
    Microcystin-LR (MC-LR), a potent hepatotoxin produced by the cyanobacteria, is of increasing concern worldwide because of severe and persistent impacts on humans and animals by inhalation and consumption of contaminated waters and food. In this work, MC-LR was removed completely from aqueous solution using visible-light-active C/N-co-modified mesoporous anatase/brookite TiO2 photocatalyst. The co-modified TiO2 nanoparticles were synthesized by a one-pot hydrothermal process, and then calcined at different temperatures (300, 400, and 500 °C). All the obtained TiO2 powders were analyzed by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), specific surface area (SSA) measurements, ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) analysis. It was found that all samples contained mixed-phase TiO2 (anatase and brookite), and the content of brookite decreased with an increase in calcination temperature, as well as the specific surface area and the content of non-metal elements. The effects of initial pH value, the TiO2 content, and MC-LR concentration on the photocatalytic activity were also studied. It was found that the photocatalytic activity of the obtained TiO2 photocatalysts declined with increasing temperature. The complete degradation (100%) of MC-LR (10 mg L−1) was observed within 3 h, using as-synthesized co-modified TiO2 (0.4 g L−1) at pH 4 under visible light. Based on the obtained results, the mechanism of MC-LR degradation has been proposed.
  • Maya Endo-Kimura, Marcin Janczarek, Zuzanna Bielan, Dong Zhang, Kunlei Wang, Agata Markowska-Szczupak, Ewa Kowalska
    ChemEngineering 3 (1) 3 - 3 2019/01/08 [Refereed][Invited]
    Ag2O/TiO2 heterojunctions were prepared by a simple method, i.e., the grinding of argentous oxide with six different titania photocatalysts. The physicochemical properties of the obtained photocatalysts were characterized by diffuse-reflectance spectroscopy (DRS), X-ray powder diffraction (XRD) and scanning transmission electron microscopy (STEM) with an energy dispersive X-ray spectroscopy (EDS). The photocatalytic activity was investigated for the oxidative decomposition of acetic acid and methanol dehydrogenation under UV/vis irradiation and for the oxidative decomposition of phenol and 2-propanol under vis irradiation. Antimicrobial properties were tested for bacteria (Escherichia coli) and fungi (Candida albicans and Penicillium chrysogenum) under UV and vis irradiation and in the dark. Enhanced activity was observed under UV/vis (with synergism for fine anatase-containing samples) and vis irradiation for almost all samples. This suggests a hindered recombination of charge carriers by p-n heterojunction or Z-scheme mechanisms under UV irradiation and photo-excited electron transfer from Ag2O to TiO2 under vis irradiation. Improved antimicrobial properties were achieved, especially under vis irradiation, probably due to electrostatic attractions between the negative surface of microorganisms and the positively charged Ag2O.
  • Endo Maya, Janczarek Marcin, Wei Zhishun, Wang Kunlei, Markowska-Szczupak Agata, Ohtani Bunsho, Kowalska Ewa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 19 (1) 442 - 452 1533-4880 2019/01 [Refereed][Invited]
    Octahedral anatase particles (OAP) with eight equivalent {101} facets and decahedral anatase particles (DAP) with two additional {001} facets were modified with nanoparticles of noble metals (silver, copper, gold and platinum) by photodeposition, and applied for inactivation of Escherichia coli K12. XRD, DRS, XPS and STEM analyses confirmed the presence of noble metals nanoparticles (NPs) on the surface of faceted titania samples. Both OAP and DAP samples modified with silver and copper exhibited high bactericidal activities under visible light irradiation. It was also found that DAP under UV irradiation showed surprisingly high bactericidal activity, which could be attributed to efficient generation of reactive oxygen species, due to intrinsic properties of DAP, i.e., charge carriers' separation (migration of electrons and holes to {101} and {001} facets, respectively). However, an unexpected decrease in activity after DAP modification with gold and platinum NPs (mainly deposited on {101} facets) suggested that bacteria cells were directly decomposed on DAP surface. SEM images revealed that silver-modified samples caused severe damages of cell walls and membranes, due to antibacterial properties of silver (in the dark) and photocatalytic effect under visible and UV irradiation.
  • Zhishun Wei, Marcin Janczarek, Maya Endo, Kunlei Wang, Armandas Balčytis, Akio Nitta, Maria G. Méndez-Medrano, Christophe Colbeau-Justin, Saulius Juodkazis, Bunsho Ohtani, Ewa Kowalska
    Applied Catalysis B: Environmental 237 574 - 587 0926-3373 2018/12/05 [Refereed][Not invited]
    Octahedral anatase particles (OAP, with eight equivalent {101} facets) and decahedral anatase particles (DAP, with two additional {001} facets) were modified with nanoparticles of noble metals (Au, Ag, Cu). The titania morphology, expressed by the presence of different arrangements of exposed crystal facets, played a key role in the photocatalytic properties of metal-modified faceted titania. In the UV/vis systems, two-faceted configuration of DAP was more favorable for the reaction efficiency than single-faceted OAP because of an efficient charge separation described by the transfer of electrons to {101} facets and holes to {001} facets. Time-resolved microwave conductivity (TRMC) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) confirmed that distribution of electron traps (ET) and mobility of electrons were key-factors of photocatalytic activity. In contrast, metal-modified OAP samples had higher photocatalytic activity than metal-modified DAP and metal-modified commercial titania samples under visible light irradiation. This indicates that the presence of single type of facets ({101}) is favorable for efficient electron transfer via shallow ET, whereas intrinsic properties of DAP result in fast charge carriers’ recombination when gold is deposited on {101} facets (migration of “hot” electrons: Au→{101}→Au).
  • Malankowska Anna, Kobylanski Marek P, Mikolajczyk Alicja, Cavdar Onur, Nowaczyk Grzegorz, Jarek Marcin, Lisowski Wojciech, Michalska Monika, Kowalska Ewa, Ohtani Bunsho, Zaleska-Medynska Adriana
    ACS SUSTAINABLE CHEMISTRY & ENGINEERING 6 (12) 16665 - 16682 2168-0485 2018/12 [Refereed][Not invited]
    Novel triple-layered trimetallic Au/Pd/Pt nanoparticles (NPs) with a porous Pt shell, showing a hedgehog-like structure, were successfully bounded with TiO2 and NaTaO3 surfaces, and used for photocatalytic purpose. To characterize all as-prepared samples, XRD, TEM, EDX, SEM, ISP-OES, DRS, XPS, and photoluminescence (PL) emission spectroscopy were applied. It was found that 25 nm Au/Pd/Pt core-shell NPs were formed, and good interaction between the porous Pt outer shells and the semiconductor surface was obtained. To appraise the effect of the semiconductor's matrix type and the amount of used AuPdPt NPs on the photocatalytic performance, three types of reactions were employed: (i) degradation of phenol (under mono- and polychromatic irradiation), (ii) the efficiency of toluene removal in gas phase under visible light, and (iii) yield of H-2 generation under UV-vis irradiation. Our results proved that the decoration of both TiO2 and NaTaO3 by AuPdPt NPs caused not only an increase in degradation yield of contaminants in the aqueous and gas phases but also significant enhancement in hydrogen generation. Amount of formed hydrogen was raised from 2.19 to 213.8 mu mol/min for pristine rutile and rutile decorated by trimetallic NPs, respectively. In addition, the adsorption energy of water and oxygen molecules on modified TiO2_rutile and TiO2_anatase surface were investigated by the density functional (DFT) calculations. Data obtained by theoretical computation was found to be complementary to experimental results. In summary, the ternary metallic core-shell Au/Pd/Pt nanoparticles were successfully applied for TiO2 and NaTaO3 modification and resulted in providing new promising materials for the environmental purification and for production of alternative energy sources when irradiated under visible and UV-vis light.
  • Bajorowicz Beata, Kowalska Ewa, Nadolna Joanna, Wei Zhishun, Endo Maya, Ohtani Bunsho, Zaleska-Medynska Adriana
    DALTON TRANSACTIONS 47 (42) 15232 - 15245 1477-9226 2018/11/14 [Refereed][Not invited]
    CdS quantum dot-decorated KNbO3 composite photocatalysts co-modified with Bi2S3 QDs were designed and synthesized by a combination of the hydrothermal method with a linker-assisted adsorption route, using starch and thioglycolic acid as capping agents, which facilitated the attachment of modifiers to the surface of potassium niobate. The quantum dots were successfully deposited onto the surface of the perovskite-type KNbO3 with a good dispersion and a stable heterostructure was formed. The as-prepared photocatalysts were subsequently characterized by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) specific surface area, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) emission spectroscopy. The obtained KNbO3-based composites showed greatly improved photocatalytic performance for the degradation of phenol in the aqueous phase under visible light irradiation ( > 420 nm) over pristine KNbO3. The highest photocatalytic performance and enhanced stability were observed for the ternary 30% CdS-5%Bi2S3 quantum dot-decorated KNbO3 composite, which could be related to the enhanced visible-light absorption ability, efficient charge separation in the three-level electron transfer heterojunction, improved stability and appropriate amounts of composite components. The formation of a surface layer of CdO decreased the visible light photoactivity of the CdS QD-decorated KNbO3 photocatalysts. The main phenol oxidation intermediates were benzoquinone, catechol, hydroquinone, and 1,2,4-benzenetriol, which underwent further photooxidation to form non-cyclic organic acids. Action spectral analysis proved the better photocatalytic activity of the ternary CdS/B2S3 QDs co-decorated KNbO3 composite compared to the binary CdS QDs decorated KNbO3 sample and revealed that irradiation ranging from 420 to 520 nm was responsible for the visible light photoactivity.
  • Marcin Janczarek, Maya Endo, Dong Zhang, Kunlei Wang, Ewa Kowalska
    Materials 11 (11) 2069 - 2069 2018/10/23 [Refereed][Invited]
    A simple, low-cost method was applied to prepare hybrid photocatalysts of copper (I) oxide/titania. Five different TiO2 powders were used to perform the study of the effect of titania matrix on the photocatalytic and antimicrobial properties of prepared nanocomposites. The photocatalytic efficiency of such a dual heterojunction system was tested in three reaction systems: ultraviolet-visible (UV-Vis)-induced methanol dehydrogenation and oxidation of acetic acid, and 2-propanol oxidation under visible light irradiation. In all the reaction systems considered, the crucial enhancement of photocatalytic activity in relation to corresponding bare titania was observed. The reaction mechanism for a specific reaction and the influence of titania matrix were discussed. Furthermore, antimicrobial (bactericidal and fungicidal) properties of Cu2O/TiO2 materials were analyzed. The antimicrobial activity was found under UV, visible and solar irradiation, and even for dark conditions. The origin of antimicrobial properties with emphasis on the role of titania matrix was also discussed.
  • Markowska-Szczupak A, Rokicka P, Wang K, Endo M, Morawski A.W, Kowalska E
    Catalysts 8 (8) 316  2018/08 [Refereed][Not invited]
  • Marcin Janczarek, Kunlei Wang, Ewa Kowalska
    Catalysts 8 240  2018/08 [Refereed][Not invited]
  • Z. Wei, M. Janczarek, M. Endo, C. Colbeau-Justin, B. Ohtani, E. Kowalska
    Catalysis Today 310 19 - 25 0920-5861 2018/07/15 [Refereed][Not invited]
    Octahedral anatase particles (OAPs) were modified with silver nanoparticles (NPs) by photodeposition method. The properties of OAPs influenced the properties of silver deposits, and thus the photocatalytic activity of the obtained silver-modified OAPs. Photocatalytic activities were tested under UV and vis irradiation for oxidative decomposition of acetic acid and oxidation of 2-propanol, respectively. The properties of silver-modified OAPs were investigated by XRD, STEM, DRS, XPS and time-resolved microwave conductivity (TRMC) method. It was found that electron traps (ETs) worked as nucleation sites for silver, resulting in formation of smaller silver NPs on smaller OAPs with larger content of ETs. The modification with silver resulted in enhanced photocatalytic activity under both UV and vis irradiation. It was found that larger crystallite size of silver NPs, and thus larger polydispersity of silver deposits resulted in broad and intense plasmon resonance peak causing enhanced visible activity. The correlation between photocatalytic activity and TRMC data, e.g., slower decay of TRMC signal for more active samples, allowed discussion on property-governed photocatalytic activities of silver-modified titania.
  • Kunlei Wang, Zhishun Wei, Bunsho Ohtani, Ewa Kowalska
    Catalysis Today 303 327 - 333 0920-5861 2018/04/01 [Refereed][Not invited]
    Commercial titania sample (P25) was homogenized first (HomoP25), and then crystalline phases (anatase and rutile) were isolated from it by chemical dissolution methods followed by samples’ purification by washing and annealing. The photocatalytic activities were tested for anaerobic methanol dehydrogenation in two reaction systems: (1) under UV/vis polychromatic irradiation with in situ platinum (Pt) deposition, and (2) under UV/vis monochromatic irradiation (action spectra) for ex situ platinum deposition. The properties of bare and modified titania samples were investigated by XRD, DRS, STEM, BET and zeta potential measurements. It was found that platinized rutile was more active than platinized anatase and platinized HomoP25, due to ability of photoabsorption of more photons (narrower band gap). Moreover, in HomoP25 sample, rutile was platinized first, probably due to positively charged surface allowing favorable adsorption of chloroplatinate ions. More than 10 times lower content of Pt (< 0.1 wt%) deposited on annealed samples (forming aggregates with an increased interface between titania NPs) than that on HomoP25 (2 wt%) resulted in similar level of photocatalytic activity, suggesting an interparticle electron transfer (IPET) between titania NPs inside one aggregates (one Pt NP was sufficient for one aggregate).
  • Endo Maya, Wei Zhishun, Wang Kunlei, Karabiyik Baris, Yoshiiri Kenta, Rokicka Paulina, Ohtani Bunsho, Markowska-Szczupak Agata, Kowalska Ewa
    BEILSTEIN JOURNAL OF NANOTECHNOLOGY 9 829 - 841 2190-4286 2018/03/07 [Refereed][Invited]
    Commercial titania photocatalysts were modified with silver and gold by photodeposition, and characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). It was found that silver co-existed in zero valent (core) and oxidized (shell) forms, whereas gold was mainly zero valent. The obtained noble metal-modified samples were examined with regard to antibacterial (Escherichia coli (E. coli)) and antifungal (Aspergillus niger (A. niger), Aspergillus melleus (A. melleus), Penicillium chrysogenum (P. chrysogenum), Candida albicans (C. albicans)) activity under visible-light irradiation and in the dark using disk diffusion, suspension, colony growth ("poisoned food") and sporulation methods. It was found that silver-modified titania, besides remarkably high antibacterial activity (inhibition of bacterial proliferation), could also decompose bacterial cells under visible-light irradiation, possibly due to an enhanced generation of reactive oxygen species and the intrinsic properties of silver. Gold-modified samples were almost inactive against bacteria in the dark, whereas significant bactericidal effect under visible-light irradiation suggested that the mechanism of bacteria inactivation was initiated by plasmonic excitation of titania by localized surface plasmon resonance of gold. The antifungal activity tests showed efficient suppression of mycelium growth by bare titania, and suppression of mycotoxin generation and sporulation by gold-modified titania. Although, the growth of fungi was hardly inhibited through disc diffusion (inhibition zones around discs), it indicates that gold does not penetrate into the media, and thus, a good stability of plasmonic photocatalysts has been confirmed. In summary, it was found that silver-modified titania showed superior antibacterial activity, whereas gold-modified samples were very active against fungi, suggesting that bimetallic photocatalysts containing both gold and silver should exhibit excellent antimicrobial properties.
  • Patrycja Parnicka, Pawel Mazierski, Tomasz Grzyb, Wojciech Lisowski, Ewa Kowalska, Bunsho Ohtani, Adriana Zaleska-Medynska, Joanna Nadolna
    Beilstein Journal of Nanotechnology 9 (1) 447 - 459 2190-4286 2018/02/06 [Refereed][Not invited]
    Nd-modified TiO2 photocatalysts have been obtained via hydrothermal (HT) and sol-hydrothermal (SHT) methods. The as-prepared samples were characterized by X-ray diffraction (XRD), BET surface area measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), luminescence spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the synthesized samples was evaluated by the degradation of phenol in aqueous solution under irradiation with UV-vis (λ > 350 nm) and vis (λ > 420 nm) light, as well as by the degradation of gaseous toluene under irradiation with vis (λmax = 415 nm) light. It was found that Nd-modified TiO2 is an efficient photocatalyst for the degradation of phenol and toluene under visible light. XPS analysis revealed that the photocatalyst prepared via HT method contains a three-times higher amount of hydroxy groups at the surface layer and a two-times higher amount of surface defects than that obtained by the SHT method. The photocatalytic efficiency of phenol and toluene degradation under vis irradiation in the presence of 0.25% Nd-TiO2(HT) reached 0.62 and 3.36 μmol·dm-1·min-1, respectively. Photocatalytic activity tests in the presence of Nd-TiO2 and scavenger confirm that superoxide radicals were responsible for the visible light-induced degradation of the model pollutant in aqueous solution.
  • Izabela Wysocka, Ewa Kowalska, Konrad Trzciński, Marcin Łapiński, Grzegorz Nowaczyk, Anna Zielińska-Jurek
    Nanomaterials 8 (1) 2079-4991 2018/01/01 [Refereed][Not invited]
    The combination of TiO2 photocatalyst and magnetic oxide nanoparticles enhances the separation and recoverable properties of nanosized TiO2 photocatalyst. Metal-modified (Me = Pd, Au, Pt, Cu) TiO2/SiO2@Fe3O4 nanocomposites were prepared by an ultrasonic-assisted sol-gel method. All prepared samples were characterized by X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), Mott-Schottky analysis and photoluminescence spectroscopy (PL). Phenol oxidation pathways of magnetic photocatalysts modified with Pt, Pd, Cu and Au nanoparticles proceeded by generation of reactive oxygen species, which oxidized phenol to benzoquinone, hydroquinone and catechol. Benzoquinone and maleic acid were products, which were determined in the hydroquinone oxidation pathway. The highest mineralization rate was observed for Pd-TiO2/SiO2@Fe3O4 and Cu-TiO2/SiO2@Fe3O4 photocatalysts, which produced the highest concentration of catechol during photocatalytic reaction. For Pt-TiO2/SiO2@Fe3O4 nanocomposite, a lack of catechol after 60 min of irradiation resulted in low mineralization rate (CO2 formation). It is proposed that the enhanced photocatalytic activity of palladium and copper-modified photocatalysts is related to an increase in the amount of adsorption sites and efficient charge carrier separation, whereas the keto-enol tautomeric equilibrium retards the rate of phenol photomineralization on Au-TiO2/SiO2@Fe3O4. The magnetization hysteresis loop indicated that the obtained hybrid photocatalyst showed magnetic properties and therefore could be easily separated after treatment process.
  • Marcin Janczarek, Ewa Kowalska
    CATALYSTS 7 (11) 317  2073-4344 2017/11 [Refereed][Not invited]
    Modification of titania with copper is a promising way to enhance the photocatalytic performance of TiO2. The enhancement means the significant retardation of charge carriers' recombination ratio and the introduction of visible light activity. This review focuses on two main ways of performance enhancement by copper species-i.e., originated from plasmonic properties of zero-valent copper (plasmonic photocatalysis) and heterojunctions between semiconductors (titania and copper oxides). The photocatalytic performance of copper-modified titania is discussed for oxidative reaction systems due to their importance for prospective applications in environmental purification. The review consists of the correlation between copper species and corresponding variants of photocatalytic mechanisms including novel systems of cascade heterojunctions. The problem of stability of copper species on titania, and the methods of its improvement are also discussed as important factors for future applications. As a new trend in the preparation of copper-modified titania photocatalyst, the role of particle morphology (faceted particles, core-shell structures) is also described. Finally, in the conclusion section, perspectives, challenges and recommendations for future research on copper-modified titania are formulated.
  • Patrycja Parnicka, Pawel Mazierski, Tomasz Grzyb, Zhishun Wei, Ewa Kowalska, Bunsho Ohtani, Wojciech Lisowski, Tomasz Klimczuk, Joanna Nadolna
    JOURNAL OF CATALYSIS 353 211 - 222 0021-9517 2017/09 [Refereed][Not invited]
    Titanium dioxide (TiO2) nanoparticles (NPs) modified with neodymium (Nd) in the range between 0.1 and 1.0 mol% were prepared via the hydrothermal method. The samples obtained were characterized by diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), X-ray fluorescence (EDX), Brunauer-Emmett-Teller (BET) method, X-ray powder diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The photocatalytic activity of the obtained samples was evaluated by photodegradation of phenol in aqueous solution under ultraviolet-visible (UV-Vis, lambda > 350 nm) and visible (Vis, lambda > 420 nm) irradiation. Experimental results showed that the photocatalysts exhibited high photocatalytic activity under Vis light. The sample showing the highest photoactivity under Vis irradiation was in the form of anatase; its surface area equalled 124 m(2)/g (1.16 times larger than that of pristine TiO2). The average crystal size was 10.9 nm, and it was modified with 0.1 mol% of Nd3+ (28% of phenol was degraded after 60 min of irradiation). The photocatalytic tests of phenol degradation in the presence of scavengers confirm that e(-) and O-2(center dot-) were responsible for the visible light degradation of organic compounds in the aqueous phase. Action spectra analysis revealed that although Nd-modified TiO2 could be excited under visible light in the range of 400-480 nm, the up-conversion process is not responsible for the degradation of phenol under Vis irradiation. (C) 2017 Elsevier Inc. All rights reserved.
  • Ana L. Luna, Diana Dragoe, Kunlei Wang, Patricia Beaunier, Ewa Kowalska, Bunsho Ohtani, Daniel Bahena Uribe, Miguel A. Valenzuela, Hynd Remita, Christophe Colbeau-Justin
    JOURNAL OF PHYSICAL CHEMISTRY C 121 (26) 14302 - 14311 1932-7447 2017/07 [Refereed][Not invited]
    TiO2 surface modification with bimetallic nano particles (NPs) has demonstrated to be a strategy to enhance the hydrogen generation via photocatalysis and to minimize the use of expensive noble metals. A better understanding of the role of bimetallic NPs is of crucial importance to design efficient photocatalysts. Here, we show a systematic study of surface modification of commercial TiO2 (P25) with mono and bimetallic (Ni, Pd, and Ni-Pd) NPs synthesized by radiolysis. The photocatalysts were characterized by High Resolution Transmission Microscopy (HRTEM), Scanning Transmission Electron Microscope (STEM), X-ray Diffraction (XRD), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and UV-vis Diffuse Reflectance Spectroscopy (DRS). The charge-carrier dynamics was studied by Time Resolved Microwave Conductivity (TRMC). The photocatalytic activity was evaluated for hydrogen generation under UV-vis irradiation using polychromatic and monochromatic lights (action spectra analysis of apparent quantum efficiency). TiO2 modified with Pd-Ni bimetallic NPs exhibits a high activity for H-2 generation, and a synergetic effect of the two metals was obtained. The study of light absorption, charge-carrier dynamics, and photocatalytic activity revealed that the main role of the metal NPs is to act as catalytic sites for recombination of atomic hydrogen.
  • Z. Wei, M. Endo, K. Wang, E. Charbit, A. Markowska-Szczupak, B. Ohtani, E. Kowalska
    CHEMICAL ENGINEERING JOURNAL 318 121 - 134 1385-8947 2017/06 [Refereed][Not invited]
    Octahedral anatase particles (OAPs) were prepared by hydrothermal (HT) reaction of titanate nanowires (TNWs). OAPs were modified with noble metals (Au, Ag, Cu and Pt) by two photodeposition methods: in the absence and in the initial presence of oxygen in the system. Photocatalytic activities for oxidative decomposition of acetic acid and anaerobic dehydrogenation of methanol under UV/vis irradiation and for oxidation of 2-propanol under visible light irradiation were investigated. Antibacterial activities for bacteria (Escherichia coli) and fungi (Candida albicans) were investigated in the dark and under UV irradiation and/or visible light irradiation. It was found that the kind of metal deposition significantly influenced the properties of photocatalysts obtained and thus their photocatalytic and antimicrobial activities. Modification of OAPs with metallic deposits resulted in enhanced photocatalytic activities for all tested systems. Pt-modified OAPs showed the highest activity for dehydrogenation of methanol due to their highest work function and lowest activation overpotential of hydrogen evolution. Cu-modified OAPs exhibited the highest activity for oxidative decomposition of acetic acid under UV/vis irradiation, probably due to the heterojunction between Cu oxides and TiO2. On the other hand, Au-modified OAPs showed the highest photocatalytic activity under visible light irradiation due to their plasmonic properties. Bare OAPs, prepared with various durations of the HT reaction, did not have any antibacterial properties in the dark, while their activity under UV/vis irradiation was correlated with their photocatalytic activities for dehydrogenation of methanol and decomposition of acetic acid. Antimicrobial activity of modified OAPs in the dark and under visible light irradiation was the highest for Ag-modified OAPs. Under UV irradiation, Cu-modified OAPs showed the highest activity for inactivation of both bacteria and fungi. (C) 2016 The Authors. Published by Elsevier B.V.
  • Zhishun Wei, Lorenzo Rosa, Kunlei Wang, Maya Endo, Saulius Juodkazis, Bunsho Ohtani, Ewa Kowalska
    APPLIED CATALYSIS B-ENVIRONMENTAL 206 393 - 405 0926-3373 2017/06 [Refereed][Not invited]
    Octahedral anatase particles (OAPs), prepared by ultrasonication-hydtothermal reaction (US-HT), were modified with 2 wt% of gold by photodeposition. COnditions of US-HT process such as durations of US and durations of HT were varied to obtain OAPs products different by physicochemical and morphological properties. Au/OAPs samples were characterized by X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The photocatalytic activity was tested under UV irradiation for decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H-2 system) under aerobic and anaerobic conditions, respectively, and for oxidation of 2-propanol under visible light irradiation. Photodeposition of gold was very fast for all OAPs samples (0.5-10 min) under Ar atmosphere, and the clear correlation between the content of electron traps (ETs) and the induction period, during which nanopartiCles (NPs) of gold are formed, indicates that ETs in titania samples are a key-factor for rapidity of gold photodeposition on titania surface. It was found that better morphology of titania (larger content of faceted particles) resulted in formation of larger gold NPs, while small gold NPs were deposited on structural defects. Modification of OAPs with gold NPs resulted in significant enhancement of photocatalytic activity, being e.g., 1.5 (CO2 system), 7.7 (H2 system), and even more than 40 under vis irradiation. It was found that both the properties of titania and gold are crucial for resultant photocatalytic activity, but a direct correlation between one structural/physical property and photocatalytic activity could not be obtained since all structural properties changed simultaneously when conditions of photo catalyst preparation (US-HT) were changed. Therefore, gold NPs of controlled sizes were deposited on OAPs product with the best morphology by modified photodeposition method. Clear correlation between photocatalytic activity under visible light and the size of gold NPs indicates that gold properties are decisive for visible light activity rather than titania properties. 3D-FDTD simulations confirm that an increase in the size of gold NPs results in extended surface areas with field enhancement. (C) 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license.
  • Z. Wei, E. Kowalska, K. Wang, C. Colbeau-Justin, B. Ohtani
    CATALYSIS TODAY 280 29 - 36 0920-5861 2017/02 [Refereed][Not invited]
    Octahedral anatase particles (OAPs) were prepared by hydrothermal reaction (HT) with various experimental conditions, including different amounts of titanate nanowires (TNWs), different water volumes and different pH values, to obtain products with high contents of OAPs. The properties of photocatalysts were investigated by XRD, SEM, TEM, XPS and time-resolved microwave conductivity (TRMC). Photocatalytic activities for oxidative decomposition of acetic acid (CO2 system) and anaerobic dehydrogenation of methanol (H-2 system) were tested. It was found that a larger amount and concentration of TNWs, as well as higher pressure during HT, resulted in the formation of smaller crystallites with higher density of mobile electrons. Enhanced photocatalytic activity, achieved for samples with the best morphology (higher content of OAPs), correlated with slower TRMC signal decay, i.e., slower recombination of charge carriers (e(-)/h(+)) probably due to lower content of deep electron traps. It was found that properties of platinum nanoparticles, deposited in-situ in the H-2 system in the absence or presence of pre-sparged oxygen, and their connection with OAPs were decisive factors for photocatalytic activity. (C) 2016 Elsevier B.V. All rights reserved.
  • Marcin Janczarek, Zhishun Wei, Maya Endo, Bunsho Ohtani, Ewa Kowalska
    JOURNAL OF PHOTONICS FOR ENERGY 7 (1) 1 - 16 1947-7988 2017/01 [Refereed][Invited]
    Decahedral anatase particles (DAPs) with eight equivalent (101) facets and two (001) facets were prepared by the gas-phase process. Monometallic and bimetallic photocatalysts were prepared by photodeposition of silver and copper on DAP. It was found that the method of metal deposition (sequential/simultaneous) is crucial for resultant properties and thus for photocatalytic performance. The fastest hydrogen evolution during metal deposition was observed for copper deposited on premodified DAP with silver (DAP/Ag/Cu), probably due to partial coverage of silver with fine clusters of Cu and thus facilitation of proton adsorption and reduction on well-dispersed Cu nanoclusters. Although DAP/Ag/Cu exhibited the fastest rate of hydrogen evolution, single-modified DAP with silver exhibited the best performance for oxidative decomposition of organic compounds under vis irradiation. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
  • Méndez-Medrano M.G, Kowalska E, Lehoux A, Herissan A, Ohtani B, Rau S, Colbeau-Justin C, Rodríguez-López J.L, Remita H
    J. Phys. Chem. C 120 (43) 25010 - 25022 2016/12 [Refereed][Not invited]
  • Paulina Rokicka, Agata Markowska-Szczupak, Lukasz Kowalczyk, Ewa Kowalska, Antoni W. Morawski
    POLISH JOURNAL OF CHEMICAL TECHNOLOGY 18 (4) 56 - 64 1509-8117 2016/12 [Refereed][Not invited]
    Antibacterial properties of 15 titania photocatalysts, mono- and dual-modified with nitrogen and carbon were examined. Amorphous TiO2, supplied by Azoty Group Chemical Factory Police S.A., was used as titania source (Ar-TiO2, C-TiO2, N-TiO2 and N, C-TiO2 calcined at 300 degrees C, 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C). The disinfection ability was examined against Escherichia coli K12 under irradiation with UV and artifi cial sunlight and in dark conditions. It has been found the development of new photocatalysts with enhanced interaction ability with microorganisms might be a useful strategy to improve disinfection method conducted under artifi cial sunlight irradiation. The effi ciency of disinfection process conducted under artifi cial sunlight irradiation with carbon (C-TiO2) and carbon/nitrogen (N, C-TiO2) photocatalysts was similar as obtained under UV irradiation. Furthermore, during dark incubation, any toxicity of the photocatalyst was noted.
  • Michal Nischk, Pawel Mazierski, Zhishun Wei, Katarzyna Siuzdak, Natalie Amoin Kouame, Ewa Kowalska, Hynd Remita, Adriana Zaleska-Medynska
    APPLIED SURFACE SCIENCE 387 89 - 102 0169-4332 2016/11 [Refereed][Not invited]
    TiO2 nanotubes arrays (NTs), obtained via electrochemical anodization of Ti foil, were modified with monometallic (Cu, Bi) and bimetallic (AgCu) nanoparticles. Different amounts of metals' precursors were deposited on the surface of NTs by the spin-coating technique, and the reduction of metals was performed via gamma radiolysis. Surface modification of titania was studied by EDS and XPS analysis. The results show that AgCu nanoparticles exist in a Ag-core-Cu-shell form. Photocatalytic activity was examined under UV irradiation and phenol was used as a model pollutant of water. Over 95% of phenol degradation was achieved after 60 min of irradiation for almost all examined samples, but only slight difference in degradation efficiency (about 3%) between modified and bare NTs was observed. However, the initial phenol degradation rate and TOC removal efficiency was significantly enhanced for the samples modified with 0.31 and 0.63 mol% of Bi as well as for all the samples modified with Cu and AgCu nanoparticles in comparison with bare titania nanotubes. The saturated photocurrent, under the influence of simulated solar light irradiation, for the most active Bi- and AgCu-modified samples, was over two times higher than for pristine NTs. All the examined materials were resistant towards photocorrosion processes that enables their application for long term processes induced by light. (C) 2016 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license.
  • Ana L. Luna, Ekaterina Novoseltceva, Essyllt Louarn, Patricia Beaunier, Ewa Kowalska, Bunsho Ohtani, Miguel A. Valenzuela, Hynd Remita, Christophe Colbeau-Justin
    APPLIED CATALYSIS B-ENVIRONMENTAL 191 18 - 28 0926-3373 2016/08 [Refereed][Not invited]
    Au and/or Ni nanoparticles were synthesized by radiolysis on TiO2 (commercial P25) at various composition (metal content). The modified photocatalysts were characterized by High Resolution Transmission Microscopy (HRTEM), Energy-Dispersive X-ray Spectroscopy (EDS), UV-vis Diffuse Reflectance Spectroscopy (DRS) and X-ray Photoelectron Spectroscopy (XPS). The charge-carrier mobility was studied by Time Resolved Microwave Conductivity (TRMC). The photocatalytic activities were tested under UV-vis irradiation using polychromatic and monochromatic light (action spectrum analysis of apparent quantum efficiency). Surface modified TiO2 with Au and Ni nanoparticles showed high photocatalytic activity for hydrogen evolution from aqueous methanol solution. The enhanced hydrogen evolution rate was obtained for TiO2 co-modified with Au and Ni, where synergetic effect of the two metals was revealed. A very small amount of gold associated to nickel (atomic ratio Ni:Au 5:1 with a total optimized metal loading of 0.5 at%) can induce a significant increase in H-2 formation. (C) 2016 Elsevier B.V. All rights reserved.
  • Shuaizhi Zheng, Kunlei Wang, Zhishun Wei, Kenta Yoshiiri, Markus Braumueller, Sven Rau, Bunsho Ohtani, Ewa Kowalska
    JOURNAL OF ADVANCED OXIDATION TECHNOLOGIES 19 (2) 208 - 217 1203-8407 2016/07 [Refereed][Invited]
    Ruthenium(II) complex with the phosphonate anchoring groups of [Ru(tbbpy) 2(4,4'-(CH2PO3H2)(2)bpy)](2+) (Ru(II)CP2, tbbpy= 4,4'-di-tert-butyl-2,2'-bipyridine) and silver nanoparticles (Ag NPs) were used as single or co-modifiers on titania surface. For the dual modified titania, two deposition sequences were applied to obtain Ag/Ru(II)CP2 and Ru(II)CP2/Ag, in which at first ruthenium(II) or silver was deposited on titania, respectively. Diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the existence of modifiers, and the effect of ruthenium(II) on the properties of Ag NPs regarding their crystallite sizes and oxidation states distributions. Photocatalytic activities of the modified titania were investigated for oxidative decomposition of acetic acid and 2-propanol, and anaerobic dehydrogenation of methanol. Under UV/Vis irradiation for the methanol dehydrogenation, co-modified titania of Ag/Ru(II)CP2 showed the best activity, while for acetic acid degradation, singly modified titania with silver showed the highest activity. In contrary, under visible light irradiation, singly fabricated titania with ruthenium(II) complex possessed the highest photocatalytic performance for 2-propanol oxidation. For all the three tested photocatalytic degradation reactions, Ag/Ru(II)CP2 exhibited better photocatalytic activities than Ru(II)CP2/Ag, indicating the different properties caused by opposite deposition sequences, e.g., DRS indicated the smaller sizes of metal NPs and XPS suggested the binding of ruthenium(II) to Ag NPs for Ru(II)CP2/Ag, which in consequence influenced the overall photocatalytic outcome.
  • Marcin Janczarek, Ewa Kowalska, Bunsho Ohtani
    CHEMICAL ENGINEERING JOURNAL 289 502 - 512 1385-8947 2016/04 [Refereed][Not invited]
    Decahedral-shaped anatase particles (DAPs) were prepared by a gas-phase process consisting of titanium (IV) chloride oxidation. The use of a coaxial-flow gas-phase reactor resulted in high reaction yield (ca. 70%) and good reproducibility of DAPs production. The influence of controlled and resultant preparation parameters on the process course and on DAPs properties (such as specific surface area, particle size and particle morphology) is discussed in detail. Correlations between preparation parameters and product properties indicated the best conditions for obtaining DAPs of high quality and thus with a high level of photocatalytic activity for various reaction systems. (C) 2016 Elsevier B.V. All rights reserved.
  • M. G. Mendez-Medrano, E. Kowalska, A. Lehoux, A. Herissan, B. Ohtani, D. Bahena, V. Briois, C. Colbeau-Justin, J. L. Rodriguez-Lopez, H. Remita
    JOURNAL OF PHYSICAL CHEMISTRY C 120 (9) 5143 - 5154 1932-7447 2016/03 [Refereed][Not invited]
    Ag and CuO nanoparticles (NPs) synthesized on the surface of commercial TiO2 (P25) by radiolytic reduction were characterized by diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). In the case of modification with silver and copper, results from HAADF-STEM, EDS, XPS, and XAS show that Ag@CuO nanoparticles (large silver cores decorated with small clusters of CuO) were obtained on TiO2-P25. The photocatalytic properties of bare and modified TiO2-P25 were studied for phenol photodegradation and for acetic acid oxidation under UV and visible irradiation. The mechanisms involved in photo catalysis were studied by time-resolved microwave conductivity (TRMC) and action spectra (AS). The electronic properties of the surface-modified TiO2-P25 were studied by TRMC to follow the charge-carrier dynamics. The modification with Ag nanoparticles or CuO nanoclusters induces an increase in the photocatalytic activity under both IN and visible light. The photocatalytic activity of Ag@CuO/P25 is higher under-UV light but lower under visible light compared to the activity of CuO/P25 and Ag/P25. TRMC measurements show that surface modification of TiO2-P25 with Ag, CuO, and Ag@CuO nanoparticles plays a role in charge-carrier separation, increasing the activity under UV-light, and that Ag@CuO NPs are more efficient electron scavengers than Ag NPs and CuO nanoclusters. The localized surface plasmon resonance (LSPR) of Ag NPs and the narrow band gap of CuO induce an activity under visible light. The TRMC shows also responses under visible-light irradiation at different fixed wavelengths indicating that electrons are injected from Ag NPs in the conduction band (CB) of TiO2-P25. Moreover, under visible light, the photocatalytic activity of CuO/P25 is higher than that of plasmonic Ag/P25. CuO is able to activate TiO2-P25 in a wider range of wavelengths under visible-light irradiation, compared to the activation achieved by the presence of silver. The action spectra correlate with the-absorption spectra for irradiation wavelengths in the range of 350-470 nm proving that dem-xi-position of acetic acid is carried out by a photocatalytic mechanism.
  • Joanna Reszczynska, Tomasz Grzyb, Zhishun Wei, Marek Klein, Ewa Kowalska, Bunsho Ohtani, Adriana Zaleska-Medynska
    APPLIED CATALYSIS B-ENVIRONMENTAL 181 825 - 837 0926-3373 2016/02 [Refereed][Not invited]
    A series of Y3+, Pr3+, Er3+ and Eu3+ modified TiO2 photocatalysts were obtained via sol-gel (SG) and hydrothermal (HT) methods. Samples prepared this way were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission microscopy (STEM), BET surface area method and luminescence spectroscopy. The photocatalytic activity of the synthesized samples was evaluated by the degradation of phenol in aqueous solution under visible and ultraviolet light irradiations. Phenol in aqueous solutions was successfully decomposed under visible light (lambda > 420 nm) using TiO2 modified with RE ions. Luminescence properties of the samples as well as XRD and XPS analyses, indicate that RE are rather in the form of their oxides than in the form of cations in the crystal structure of TiO2. Photocatalysts prepared by SG method possessed higher amount of RE2O3, fewer of OH- groups and Ti3+ species on the surface layer than powders obtained by HT method. Action spectra analysis showed that Pr3+-modified TiO2 could be excited under visible light in the 420-250 nm range. Furthermore, photocatalysts obtained by HT method showed higher photocatalytic activity and lower intensity of luminescence emission than photocatalyst prepared by SG method. (C) 2015 Elsevier B.V. All rights reserved.
  • Shuaizhi Zheng, Zhishun Wei, Kenta Yoshiiri, Markus Braumueller, Bunsho Ohtani, Sven Rau, Ewa Kowalska
    PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES 15 (1) 69 - 79 1474-905X 2016 [Refereed][Not invited]
    Titania of fine anatase nanoparticles (ST01) was modified successively with two components, i.e., a ruthenium(II) complex with phosphonic anchoring groups [Ru(bpy)(2)(4,4'-(CH2PO3H2)(2)bpy)](2+) bpy = 2,2'-bipyridine ((RuCP)-C-II) and gold nanoparticles (Au). Various compositions of two titania modifiers were investigated, i.e., Au, Au + (RuCP)-C-II, Au + 0.5Ru(II)CP, (RuCP)-C-II, 0.5Ru(II)CP and 0.25Ru(II)CP, where Au and (RuCP)-C-II correspond to 0.81 mol% and 0.34 mol% (with respect to titania), respectively. In the case of hybrid photocatalysts, the sequence of modification (ruthenium(II) complex adsorption or gold deposition) was investigated to check its influence on the resultant properties and thus photocatalytic performance. Diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) were applied to characterize the structural properties of the prepared photocatalysts, which confirmed the successful introduction of modifiers of the ruthenium(II) complex and/or gold NPs. Different distributions of gold particle sizes and chemical compositions were obtained for the hybrid photocatalysts prepared with an opposite sequence. It was found that photocatalytic activities depended on the range of used irradiation (UV/vis or vis) and the kind of modifier in different ways. Gold NPs improved the photocatalytic activities, while (RuCP)-C-II inhibited the reactions under UV/vis irradiation, i.e., methanol dehydrogenation and acetic acid degradation. Oppositely, (RuCP)-C-II greatly enhanced the photocatalytic activities for 2-propanol oxidation under visible light irradiation.
  • Ewa Kowalska, Kenta Yoshiiri, Zhishun Wei, Shuaizhi Zheng, Evelyn Kastl, Hynd Remita, Bunsho Ohtani, Sven Rau
    APPLIED CATALYSIS B-ENVIRONMENTAL 178 133 - 143 0926-3373 2015/11 [Refereed][Not invited]
    Plasmonic photocatalysts were prepared by deposition of 2 wt% of gold or silver nanoparticles (NPs) on commercial titania particles with different structural properties. Ruthenium(II) complexes with phosphonic and carboxylic acid binding groups were synthesized and adsorbed on bare titania and noble metal-modified titania. The structural properties of the samples were characterized by DRS, XPS, XRD, STEM, TLC, H-1 NMR and 2D-COSY. Large surface area, small crystallite sizes, low pH value, nature of the deprotected phosphonate binding groups, and pre-deposited nanoparticles of noble metals enhanced the adsorption yield. Modification caused titania activation toward visible light (>450 nm) for 2-propanol oxidation and for methanol dehydrogenation under UV/vis irradiation. The modified samples exhibited enhanced activity under UV/vis irradiation for acetic acid oxidation depending on the kind of modifiers and properties of titania, i.e., 2-6, 3-9 and 1-3-fold enhancement was observed after modification with NPs of gold, NPs of silver and Ru(II) complex. The time-resolved microwave conductivity (TRMC) method proved that higher photocatalytic activity of modified titania under UV irradiation was caused by scavenging of mobile electrons by NPs of noble metals, and therefore decreasing the recombination between charge carriers. The photocatalytic activity of hybrid photocatalysts under UV/vis was influenced by the nature of the plasmonic metal and structural properties of the metal and titania, e.g., crystallite size and polymorphic form. Different kinds of action were observed for two plasmonic metals in two reaction systems under UV irradiation, e.g., modification with an Ru(II) complex caused 12-times faster dehydrogenation of methanol for silver-modified large anatase titania (ST41) and hardly changed the activity of gold-modified samples, while during acetic acid oxidation, only hybrid photocatalysts composed of gold NPs and Ru(II) complex exhibited a slight increase of photocatalytic activity (1.1-1.3 times). The difference between gold and silver hybrid photocatalysts might have been caused by differences in surface charges of metallic deposits, i.e., the surface of silver NPs was mainly positively charged, while gold was zero-valent. Therefore, it is thought that the Ru(II) complex bound also to the surface of positively charged silver. Under visible light irradiation, fine titania modified with an Ru(II) complex exhibited the highest level of photocatalytic activity. The presence of an Ru(II) complex highly enhanced photocatalytic activity of titania modified with plasmonic NPs. However, NPs of plasmonic metals hindered the photoactivity of Ru(II)-titania. (C) 2014 Elsevier B.V. All rights reserved.
  • Agata Markowska-Szczupak, Kunlei Wang, Paulina Rokicka, Maya Endo, Zhishun Wei, Bunsho Ohtani, Antoni W. Morawski, Ewa Kowalska
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 151 54 - 62 1011-1344 2015/10 [Refereed][Not invited]
    Antifungal properties of anatase and rutile crystallites isolated from commercial titania P25 photocatalyst were investigated by mycelium growth in the dark and under indoor light. Investigated fungi, i.e., Pseudallescheria boydii, Scedosporium apiospermum, Pseudallescheria ellipsoidea, Scedosporium aurantiacum, Aspergillus versicolor, Aspergillus flavus, Stachybotrys chartarum, Penicillium chrysogenum, Aspergillus melleus, were isolated from air and from moisture condensed on walls. Anatase and rutile were isolated from homogenized P25 (homo-P25) by chemical dissolution, and then purified by washing and thermal treatment. For comparison, homo-P25 was also thermally treated at 200 degrees C and 500 degrees C. Titania samples were characterized by X-ray diffractomety (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning transmission electron microscopy (STEM). It was found that properties of titania, i.e., band-gap energy, impurities adsorbed on the surface, nanoparticle aggregation, and kind of fungal structure, highly influenced resultant antifungal activities. It is proposed that some fungi could uptake necessary water and nutrient from titania surface. It was also found that even when differences in mycelium growth were not significant, the sporulation and mycotoxin generation were highly inhibited by light and presence of titania. (C) 2015 Elsevier B.V. All rights reserved.
  • Anna Zielinska-Jureka, Zhishun Wei, Izabela Wysocka, Piotr Szweda, Ewa Kowalska
    APPLIED SURFACE SCIENCE 353 317 - 325 0169-4332 2015/10 [Refereed][Not invited]
    Ag-Pt-modified TiO2 nanocomposites were synthesized using the sol-gel method. Bimetallic modified TiO2 nanoparticles exhibited improved photocatalytic activity under visible-light irradiation, better than monometallic Ag/TiO2 and Pt/TiO2 nanoparticles (NPs). All modified powders showed localized surface plasmon resonance (LSPR) in visible region. The photocatalysts' characteristics by X-ray diffractometry (XRD), scanning transmission electron microscopy (STEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption (BET method for specific surface area) showed that sample with the highest photocatalytic activity had anatase structure, about 93 m(2)/g specific surface area, maximum plasmon absorption at ca. 420 nm and contained small NPs of silver of 6 nm and very fine platinum NPs of 3 nm. The photocatalytic activity was estimated by measuring the decomposition rate of phenol in 0.2 mM aqueous solution under Vis and UV/vis light irradiation. It was found that size of platinum was decisive for the photocatalytic activity under visible light irradiation, i.e., the smaller Pt NPs were, the higher was photocatalytic activity. While, antimicrobial activities, estimated for bacteria Escherichia coli and Staphylococcus aureus, and pathogenic fungi belonging to Candida family, were only observed for photocatalysts containing silver, i.e., Ag/TiO2 and Ag-Pt/TiO2 nanocomposites. (C) 2015 Elsevier B.V. All rights reserved.
  • Agata Markowska-Szczupak, Katarzyna Janda, Kunlei Wang, Antoni Waldemar Morawski, Ewa Kowalska
    CENTRAL EUROPEAN JOURNAL OF PUBLIC HEALTH 23 (3) 267 - 271 1210-7778 2015/09 [Refereed][Not invited]
    Aim: The aim of this study was to determine the antifungal activity of titanium dioxide activated by indoor light on Czapek Yeast Agar (CYA). Methods: The agar plate method was used and titania P25 (Evonik) was added to the medium in the amount of 20 The control experiments without titania were also carried out. The water activity (a(w)) of the basal media was adjusted to 0.999, 0.997, 0.975, 0.950, 0.900 and 0.850 with sodium chloride. The photoactivity of titania was tested for six strains of potentially pathogenic fungi: Aspergillus versicolor (WB130, W11), Stachybotlys chartarum (STA1), Pseudallescheria boydii (AP25), Pseudallescheria ellipsoidea (ZUT12), Scedosporium apiospermum (ZUT11), Scedosporium aurantiacum (ZUT4BIS). After inoculation with fungal spore suspensions, one part of CYA plates was incubated in dark, while another part was daily exposed to indoor light for 12 hours per day. The plates were incubated at 25 degrees C for 10 days. The daily growth rates (mm x day(-1)) were calculated from the linear regression equation. Results: The CYA supplementation with titanium dioxide for different availability of water resulted in the decrease of fungal growth rates in dark and under irradiation. The lowest and the highest rates of daily growth were obtained in the presence and absence of titania for the low and high water activity (0.900 a(w) and 0.999 a(w)), respectively. Conclusions: Fungi did not grow on all examined media with the lowest water activity (a(w) 0.850) which confirmed necessity of water for their growth. The fungi Pseudallescheria-Scedosporium were the most sensitive to titania and water activity, while the strains of Aspergillus versicolor were the most resistant to the presence of titania and lack of water. It has been shown that the lack of accessible water resulted in the strongest action of titanium dioxide both in dark and under irradiation. For the lowest amount of accessible water irradiation of titania resulted in complete inhibition of fungal growth. While, under dark conditions, titania presence enhanced the growth of persistent fungi, i.e., Aspergillus versicolor. It is assumed that these fungi could obtain water from the water-rich titania surface.
  • E. Kowalska, Z. Wei, B. Karabiyik, A. Herissan, M. Janczarek, M. Endo, A. Markowska-Szczupak, H. Remita, B. Ohtani
    CATALYSIS TODAY 252 136 - 142 0920-5861 2015/09 [Refereed][Not invited]
    Commercial titania photocatalysts were modified with 2 wt% of silver by photodeposition. The properties of the samples were characterized by DRS, XPS, XRD, FE-SEM and STEM. The modified samples exhibited activity under visible light and enhanced activity under UV irradiation for 2-propanol and acetic acid oxidation, respectively. The time-resolved microwave conductivity (TRMC) analysis indicated that enhanced activity (2.5-8-fold enhancement depending on titania) under UV irradiation was caused by an electron storage in metallic nanoparticles (NPs), and therefore decreasing the recombination between charge carriers. The action spectrum (AS) analysis proved that localized surface plasmon resonance (LSPR) of silver NPs induced the photocatalytic activity under visible light irradiation. The increase of antimicrobial properties under visible light irradiation indicated that not only intrinsic properties of silver in the dark, but also plasmonic properties of Ag@TiO2 were responsible for overall bacteria killing. The evolution of carbon dioxide under both irradiation ranges indicated mineralization of bacteria cells, and therefore possible application of silver-modified titania for decomposition of chemical and biological pollutants. (C) 2014 Elsevier B.V. All rights reserved.
  • Zhishun Wei, Ewa Kowalska, Jonathan Verrett, Christophe Colbeau-Justin, Hynd Remita, Bunsho Ohtani
    NANOSCALE 7 (29) 12392 - 12404 2040-3364 2015 [Refereed][Not invited]
    Octahedral anatase particles (OAPs) were prepared by an ultrasonication (US) hydrothermal (HT) reaction of partially proton-exchanged potassium titanate nanowires (TNWs). The structural/physical properties of OAP-containing samples, including specific surface area, crystallinity, crystallite size, particle aspect ratio, composition and total OAP content, were analyzed. Photocatalytic activities of samples were measured under irradiation (>290 nm) for oxidative decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H-2 system) under aerobic and deaerated conditions, respectively. Total density of electron traps (ETs) was measured by double-beam photoacoustic spectroscopy (DB-PAS). Mobility and lifetime of charge carriers (electrons) were investigated by the time-resolved microwave conductivity (TRMC) method. The effects of synthesis parameters, i.e., HT duration, HT temperature and US duration, on properties and photocatalytic activities of final products were examined in detail. The sample prepared with 1 h US duration and 6 h HT duration at 433 K using 267 mg of TNWs in 80 mL of Milli-Q water exhibited the highest photocatalytic activity. It was found that change in HT duration or HT temperature while keeping the other conditions the same resulted in changes in all properties and photocatalytic activity. On the other hand, duration of US treatment, before HT reaction, influenced the morphology of both the reagent (by TNWs breaking) and final products (change in total OAP content); samples prepared with various US durations exhibited almost the same structural/physical properties evaluated in this study but were different in morphology and photocatalytic activity. This enabled clarification of the correlation between morphology and photocatalytic activity, i.e., the higher the total OAP content was, the higher was the level of photocatalytic activity, especially in the CO2 system. Although the decay after maximum TRMC signal intensity (I-max) was almost constant for all samples used in this study, photocatalytic activities were roughly proportional to Imax, which tended to be proportional to total OAP content. Assuming that Imax corresponds to the product of density of electrons in mobile shallow ETs and their mobility, the results suggest that OAP particles have beneficial shallow ETs in higher density and thereby the OAP content governs the photocatalytic activities. Thus, morphology-dependent photocatalytic activity of OAP-containing particles was reasonably interpreted by density of ETs presumably located on the exposed {101} facets.
  • Zhishun Wei, Ewa Kowalska, Bunsho Ohtani
    MOLECULES 19 (12) 19573 - 19587 1420-3049 2014/12 [Refereed][Invited]
    The influence of changes in structural and physical properties on the photocatalytic activity of octahedral anatase particles (OAPs), exposing eight equivalent {101} facets, caused by calcination (2 h) in air or grinding (1 h) in an agate mortar was studied with samples prepared by ultrasonication (US; 1 h)-hydrothermal reaction (HT; 24 h, 433 K). Calcination in air at temperatures up to 1173 K induced particle shape changes, evaluated by aspect ratio (AR; d(001)/d(101) = depth vertical to anatase {001} and {101} facets estimated by the Scherrer equation with data obtained from X-ray diffraction (XRD) patterns) and content of OAP and semi-OAP particles, without transformation into rutile. AR and OAP content, as well as specific surface area (SSA), were almost unchanged by calcination at temperatures up to 673 K and were then decreased by elevating the calcination temperature, suggesting that calcination at a higher temperature caused dull-edging and particle sintering, the latter also being supported by the analysis of particle size using XRD patterns and scanning electron microscopic (SEM) images. Time-resolved microwave conductivity (TRMC) showed that the maximum signal intensity (I-max), corresponding to a product of charge-carrier density and mobility, and signal-decay rate, presumably corresponding to reactivity of charge carriers, were increased with increase in AR, suggesting higher photocatalytic activity of OAPs than that of dull-edged particles. Grinding also decreased the AR, indicating the formation of dull-edged particles. The original non-treated samples showed activities in the oxidative decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H-2 system) comparable to and lower than those of a commercial anatase titania (Showa Denko Ceramics FP-6), respectively. The activities of calcined and ground samples for the CO2 system and H-2 system showed almost linear relations with AR and I-max, respectively, suggesting that those activities may depend on different properties.
  • Zhishun Wei, Ewa Kowalska, Bunsho Ohtani
    CHEMISTRY LETTERS 43 (3) 346 - 348 0366-7022 2014/03 [Refereed][Not invited]
    Titania samples containing octahedral anatase particles (OAPs) were prepared by the ultrasonication-hydrothermal process of partially proton-exchanged potassium titanate nanowires. It was found that increase in the ultrasonication time changed the product morphology, with other structural properties such as specific surface area, crystalline size, and crystallinity remaining almost constant. The results of photocatalytic activity tests for those samples suggested higher activity of a sample with higher OAP content, especially for reactions in the presence of oxygen.
  • E. Kowalska, M. Janczarek, L. Rosa, S. Juodkazis, B. Ohtani
    Catalysis Today 230 131 - 137 0920-5861 2014 [Refereed][Not invited]
    Titania powders were surface modified with gold and/or silver nanoparticles (NPs) by photodeposition method. Gold modified titania exhibited much higher photocatalytic activity during methanol dehydrogenation under UV irradiation than titania modified with monometallic silver and bimetallic Au-Ag NPs. Bimetallic photocatalysts exhibited either enhanced or reduced visible light activity, depending on properties of noble metal NPs, sequence of their deposition on titania, and properties of host titania. Though numerical simulation (3D-FDTD) showed strong plasmonic field enhancement at the interface between titania and bimetallic core(Au)-shell(Ag) NP, it is thought that co-deposition caused an enhancement of charge carriers recombination (by electron sinking in nearby second metal) inhibiting photoactivity under visible light irradiation. The highest level of photoactivity showed large rutile NPs with successively deposited metals, mainly in the form of individual monometallic NPs, due to size/shape polydispersity of deposited NPs, and thus with ability of light absorption in a broad wavelength range. © 2013 Elsevier B.V.
  • Development of plasmonic photocatalysts for environmental application
    E. Kowalska, Z. Wei, B. Karabiyik, M. Janczarek, M. Endo, K. Wang, P. Rokicka, A. Markowska-Szczupak, B. Ohtani
    Adv. Sci. Technol. 93 174 - 183 2014 [Refereed][Not invited]
  • Ewa Kowalska, Sven Rau, Bunsho Ohtani
    Journal of Nanotechnology 1687-9503 2012 [Refereed][Invited]
    Plasmonic titania photocatalysts were prepared by titania modification with gold by photodeposition. It was found that for smaller amount of deposited gold (0.1wt%), anatase presence and large surface area were beneficial for efficient hydrogen evolution during methanol dehydrogenation. After testing twelve amounts of deposited gold on large rutile titania, the existence of three optima for 0.5, 2 and 6wt% of gold was found during acetic acid degradation. Under visible light irradiation, in the case of small gold NPs deposited on fine anatase titania, the dependence of photoactivity on gold amount was parabolic, and large gold amount (2wt%), observable as an intensively coloured powder, caused photoactivity decrease. While for large gold NPs deposited on large rutile titania, the dependence represented cascade increase, due to change of size and shape of deposited gold with its amount increase. It has been thought that spherical/hemispherical shape of gold NPs, in comparison with rod-like ones, is beneficial for higher level of photoactivity under visible light irradiation. For all tested systems and regardless of deposited amount of gold, each rutile Au/TiO2 photocatalyst of large gold and titania NPs exhibited much higher photoactivity than anatase Au/TiO2 of small gold and titania NPs. Copyright © 2012 Ewa Kowalska et al.
  • Searching for new photocatalysts for the decomposition of contaminants in water using the multi N/C 2100 TOC analyzer
    Ewa Kowalska, Sven Rau, Christian Koch
    Labo 06 28 - 31 2011/06 [Refereed][Invited]
  • Vygantas Mizeikis, Ewa Kowalska, Saulius Juodkazis
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 11 (4) 2814 - 2822 1533-4880 2011/04 [Refereed][Not invited]
    We report results of theoretical simulations of optical field enhancement in a system consisting of spherical and hemispherical noble metal nanoparticles on a smooth titania surface, which is a model system relevant to applications in photo-catalysis and solar energy harvesting. Simulations conducted using Finite-Difference Time-Domain (FDTD) technique reveal presence of resonant optical extinction bands at visible wavelengths, whose optical scattering is weak, but the associated localization and intensity enhancement of optical near-field are significant. For hemispheres, the field is strongly localized at the metal-substrate interface, where intensity enhancement of up to 10(4) times is reached. Moreover, the field is predominantly polarized along the normal to the substrate. These findings indicate potential of the hemisphere-substrate system for applications relying on optically promoted charge transport through the metal-substrate interface, such as photochemical reactions and light-to-current conversion. The results of theoretical analysis are compared with reported experimental data on photo-catalytic reactions.
  • Anna Zielinska-Jurek, Ewa Kowalska, Janusz W. Sobczak, Wojciech Lisowski, Bunsho Ohtani, Adriana Zaleska
    APPLIED CATALYSIS B-ENVIRONMENTAL 101 (3-4) 504 - 514 0926-3373 2011/01 [Refereed][Not invited]
    The Au-TiO(2) and Ag/Au-TiO(2) nanoparticles have been prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane and water/Triton X-100/cyclohexane. The obtained photocatalysts were subsequently characterized by a BET method, DRS spectroscopy, X-ray photoelectron emission spectroscopy (XPS), scanning transmission electron microscopy (STEM) and X-ray powder diffraction analysis (XRD). For gold-doped titanium (IV) oxide nanoparticles the effect of reducing agent and stabilizer on gold particles size and photocatalytic activity were observed. The effect of crystalline form of TiO(2) and gold nanoparticles size on photocatalytic activity of Au-TiO(2) and Ag/Au-TiO(2) in visible light were also investigated. The photocatalytic activity of noble metals modified-TiO(2) powders under visible light irradiation was estimated by measuring the decomposition rate of phenol in an aqueous solution. The best photocatalytic activity revealed samples with large gold particles (similar to 90 nm) deposited on small titania nanoparticles. It was also found that the bimetallic samples (Ag/Au-TiO(2)) showed a higher photodegradation rate in visible region than monometallic photocatalysts. (C) 2010 Elsevier B.V. All rights reserved.
  • Ewa Kowalska, Sven Rau
    Recent Patents on Engineering 4 242 - 266 1872-2121 2010/12 [Refereed][Invited]
    Photochemical oxidation of organic and inorganic pollutants is rapidly becoming an attractive technique for water purification and wastewater treatment. Since artificial sources of light require much energy delivery, this method is recommended for toxic contaminants in a specific concentration range below the recommended levels for recovery and above the levels for conventional biological treatment. Selection of a light source and an oxidation system and determination of key-parameters play an important role in the treatment efficiency. Sufficient UV penetration into the radiated liquid is of crucial importance; especially for an opaque environment the UV radiation is only available very close to the UV lamp surface. High mass transfer rates for efficient interaction between the pollutant and the photocatalyst and for high oxygen uptake at the gas-liquid interface is another requirement for practical applications. In this regard, reactor design for efficient wastewater treatment has been a challenging problem. Many types of photoreactors have already been studied, reported and patented. This paper presents a revision of some conventional and novel photoreactors equipped with UV/vis lamps or working under solar radiation for wastewater treatment in laboratory and industrial scales. © 2010 Bentham Science Publishers Ltd.
  • Vygantas Mizeikis, Ewa Kowalska, Bunsho Ohtani, Saulius Juodkazis
    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 4 (10) 268 - 270 1862-6254 2010/10 [Refereed][Not invited]
    We report theoretical simulations of plasmonic near-field enhancement and polarization in a system consisting of an asymmetric spheroidal Ag nanoparticle on a smooth dielectric surface. Finite-difference time-domain (FDTD) simulations reveal resonant optical extinction bands whose near-field is concentrated at the metal-substrate contact point with intensity enhancement by a factor of 10(3) and predominant polarization along the normal to the surface. These features may help explain enhanced photo-catalytic activity observed for colloidal Au and Ag nanoparticles on titania substrates. [GRAPHICS] Electron microscopy image of Ag-nanoparticles on titania and the used model for numerical FDTD simulations. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Anna Zielinska, Ewa Kowalska, Janusz W. Sobczak, Izabela Lacka, Maria Gazda, Bunsho Ohtani, Jan Hupka, Adriana Zaleska
    SEPARATION AND PURIFICATION TECHNOLOGY 72 (3) 309 - 318 1383-5866 2010/05 [Refereed][Not invited]
    A series of Ag-TiO2 photocatalysts were obtained in microemulsion system (water/AOT/cyclohexane), using several Ag precursor amounts ranging from 1.5 to 8.5 mol.%. The photocatalysts' characteristics by X-ray diffraction, STEM microscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy, BET methods showed that a sample with the highest photo- and bioactivity had anatase structure, about 90 m(2)/g specific surface area, absorbed light over 400 nm and contained 1.64 at.% of silver (0.30 at.% of Ag and 1.34 at.% of Ag2O) and about 13 at.% of carbon in the surface layer. The photocatalytic activity of the catalysts was estimated by measuring the decomposition rate of phenol in 0.21 mM aqueous solution under visible and ultraviolet light irradiation. The bioactivity of silver-doped titanium dioxide nanocomposites was estimated using bacteria Escherichia coli and Staphylococcus aureus, yeast Saccharomyces cerevisiae and pathogenic fungi belonging to Candida family. All modified powders showed localized surface plasmon resonance (LSPR) in visible region with almost the same position of LSPR peaks indicating that similar sizes of silver, regardless of used amount of Ag, is deposited on titania particles during microemulsion method. STEM microscopy revealed that almost 50% of observed silver nanoparticles deposited at the TiO2 surface are in the range from 5 to 10 nm. (C) 2010 Elsevier B.V. All rights reserved.
  • E. Kowalska, S. Rau, R. Abe, B. Ohtani
  • Ewa Kowalska, Orlando Omar Prieto Mahaney, Ryu Abe, Bunsho Ohtani
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 (10) 2344 - 2355 1463-9076 2010 [Refereed][Not invited]
    Fifteen commercial titania (titanium(IV) oxide; TiO2) powders were modified with gold by photodeposition to prepare photocatalysts that work under irradiation with light in the visible range (vis). The gold-modified titania (Au/TiO2) powders were characterized by diffuse reflectance spectroscopy (DRS), field-emission scanning electron microscopy (FE-SEM), scanning transmission microscopy (STEM) and X-ray powder diffraction (XRD). It was shown that all tested powders could absorb visible light with an absorption maximum at localized surface plasmon resonance (LSPR) wavelengths (530-600 nm) and that the size and shape of gold nanoparticles determined the absorption ranges. The photocatalytic activity of Au/TiO2 powders was examined both under ultraviolet and vis irradiation (mainly > 450 nm) for acetic acid and 2-propanol photooxidation. It was found that the activity depended strongly on gold and titania properties, such as particle size and shape, surface area and crystalline form. Under vis irradiation, large rutile particles loaded with gold particles of a wide range of sizes showed the highest level of photocatalytic activity, possibly due to greater light absorption ability in a wide wavelength range resulting from transverse and longitudinal LSPR of rod-like gold particles. Action spectrum analyses showed that visible-light-induced oxidation of organic compounds by aerated gold-titania suspensions was initiated by excitation of LSPR absorption of gold. Although photocatalytic activity of nanosized gold particles under vis irradiation with a wavelength of ca. 430 nm and catalytic activity of gold-modified titania during dark reactions were also found, it was shown that the activities of Au/TiO2 particles originated from activation of LSPR of gold by light of wavelength of 530-650 nm. Participation of molecular oxygen as an electron acceptor and titania as a conductor of electrons is suggested by comparing with results obtained under deaerated conditions and results obtained using a system containing gold-deposited silica instead of gold-titania, respectively. On the basis of these results, the mechanism of visible-light-induced oxidation of organic compounds on gold-titania is proposed.
  • Ewa Kowalska, Ryu Abe, Bunsho Ohtani
    CHEMICAL COMMUNICATIONS (2) 241 - 243 1359-7345 2009 [Refereed][Not invited]
    Action spectrum analyses showed that visible light-induced oxidation of 2-propanol by aerated gold-modified titanium(IV) oxide (titania) suspensions is initiated by excitation of gold surface plasmon, and polychromatic irradiation experiments revealed that the photocatalytic reaction rate depends strongly on properties of titania, such as particle size, surface area and crystalline form (anatase or rutile) and on properties of gold deposits, such as size and shape.
  • Paulina Gorska, Adriana Zaleska, Ewa Kowalska, Tomasz Klimczuk, Janusz W. Sobczak, Ewa Skwarek, Wladyslaw Janusz, Jan Hupka
    APPLIED CATALYSIS B-ENVIRONMENTAL 84 (3-4) 440 - 447 0926-3373 2008/12 [Refereed][Not invited]
    A series of TiO(2) photocatalysts were obtained using several calcination temperatures ranging from 350 to 750 degrees C. The photocatalysts' characteristics by X-ray diffraction, UV-vis and FTIR diffuse reflectance spectroscopies, X-ray photoelectron spectroscopy, BET and BJH methods showed that sample active in vis region had anatase structure, about 200 m(2)/g specific surface area, absorbed light for lambda > 400 nm and contained 10.1 at.% of C-C species. The photocatalytic activity of the catalysts was estimated by measuring the decomposition rate of phenol in 0.21 mM aqueous solution in visible and ultraviolet light. The experimental data clearly indicate correlation between the absorption intensity of irradiation by obtained powders and their photocatalytic performance in phenol degradation. An increase in absorbance over the entire vis region and the highest photocatalytic activity for phenol degradation in visible light (lambda > 400 nm) occurred for photocatalyst calcinated at 350 degrees C. Photocatalyst processed at 450 degrees C had the best activity in UV light (250 < lambda < 400 nm). (C) 2008 Elsevier B.V. All rights reserved.
  • Model studies on degradation of selected pesticides in samples of process wastewater
    M. Grynkiewicz, G. Dembska, G. Sapota, A. Flasinska, S. Wisniewski, B. Aftanas, E. Kowalska
    Ecology and Technology 3 (94) 106 - 113 2008/03 [Refereed][Not invited]
  • E. Kowalska, H. Remita, C. Colbeau-Justin, J. Hupka, J. Belloni
    JOURNAL OF PHYSICAL CHEMISTRY C 112 (4) 1124 - 1131 1932-7447 2008/01 [Refereed][Not invited]
    TiO2 (commercial-P25 and synthesized by sol-gel method) was surface modified with platinum ions or [Pt-3(CO)(6)](6)(2-) clusters to improve its photocatalytic activity. The physical properties of the synthesized photocatalysts were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauer, Emmett and Teller adsorption (BET) methods. To characterize the absorption ability of visible light, the diffusion reflectance spectra (DRS) were recorded. The charge-carrier lifetimes in TiO2 after UV illumination were determined by microwave absorption experiments using the time-resolved microwave conductivity (TRMC) method. The photocatalyst activity was examined by degradation of exemplary aqueous phase pollutants, such as Rhodamine B and phenol. The impact of the adsorbates on the photocatalytic activity depends strongly on the titania precursor (commercial or synthesized), the irradiation wavelength (UV or visible), and the model compound (dye or phenol). The results show that it is possible to enhance the P25 photocatalytic activity under UV-visible light by doping it with Pt clusters. Also, P25 doping with Pt(II) or Pt clusters results in enhancement of the activity under visible light. Pt(IV)/TiO2 synthesized by sol-gel method exhibits better photoactivity under UV-visible and visible light compared to the unmodified titania. In all mentioned systems, a positive effect of modification with platinum clusters and, in particular, an important enhancement in photocatalytic activity under visible light were obtained. These results are explained by enhancement in visible light absorption and inhibition of charge-carrier recombination.
  • A. Zaleska, P. Gorska, E. Kowalska, J. Hupka
    Polish Journal of Chemical Technology 8 (2) 102 - 105 2006/08 [Refereed][Not invited]
  • Jan Hupka, Adriana Zaleska, Marcin Janczarek, Ewa Kowalska, Paulina Gorska, Robert Aranowski
    SOIL AND WATER POLLUTION MONITORING, PROTECTION AND REMEDIATION 69 351 - 367 1568-1238 2006 [Not refereed][Invited]
    Applied research data on advanced photocatalytic methods aimed at treatment of contaminated aqueous phase is presented. Phenol and chloroorganic pesticides ( as model compounds) besides actual wastewater samples were UV-photodegraded using suspended TiO2 or UV/H2O2/air systems. Titanium dioxide catalysts modified with non-metal elements were used to photodegrade phenols in visible light. Laboratory and pilot scale reactors were used and the effect of process scale-up investigated.
  • Treatment of wastewater from production of wood panels
    J. Hupka, M. Janczarek, R. Aranowski, A. Zaleska, M. Chrzanowska, E. Kowalska
    Selected Aspects of Production of Wood Derivatives Materials, Tleń, November 17-18, 2005, Tlen, Po-land 1 - 7 2005/11 [Not refereed][Not invited]
  • Investigation of biological and photochemical treatment of municipal landfill leachates
    M. Chrzanowska, E. Kowalska, J. Hupka
    IWA Specialized Conference: Nutrient Management in Wastewater Treatment Processes and Recycle Streams, 19-21 September, 2005, Cracow, Poland 1107 - 1111 2005/09 [Not refereed][Not invited]
  • Visible light activity of TiO2 modified with thioacetamide
    P. Gorska, E. Kowalska, A. Zaleska, J. Hupka
    Second European Conference on Oxidation and Reduction Technologies for Ex-situ and In-situ Treatment of Water, Air and Soil (ECOR-2), June 12-15, 2005, Güttingen, Germany 191 - 192 2005/06 [Not refereed][Not invited]
  • The TiO2–assisted photodegradation in gas phase
    Ewa Kowalska, Adriana Zaleska
    Przegląd Komunalny 6 (29) 76 - 77 2005/06 [Refereed][Not invited]
  • Characterization and treatment of industrial pesticide wastewater
    E. Kowalska, M. Chrzanowska, M. Janczarek, A. Blaszke, J. Hupka
    Global Symposium on Recycling, Waste Treatment and Clean Technology (REWAS 2004), September 26-29, 2004, Madrid, Spain 2883 - 2884 2004/09 [Not refereed][Not invited]
  • E Kowalska, M Janczarek, J Hupka, M Grynkiewicz
    WATER SCIENCE AND TECHNOLOGY 49 (4) 261 - 266 0273-1223 2004 [Not refereed][Not invited]
    Photodegradation of organic pesticides in industrial wastewater was examined in a UV/H2O2/air system. An experimentally determined optimal amount of hydrogen peroxide (0.008% v/v) indicates that hydrogen peroxide concentration controlled the efficiency of photodegradation. Pre-treatment operations such as sedimentation, filtration and coagulation were used to obtain better efficiency of pesticide removal and to cut down on irradiation time. Finally, scale-up experiments in the air-sparged hydrocyclone (ASH) reactor were carried out. After 5 min irradiation of 100 dm(3) industrial wastewater almost all pesticides were destroyed. Thus the ASH reactor proved to be an effective contactor for carrying out photochemical reactions.
  • Titania modification for photocatalytic wastewater treatment
    E. Kowalska, H. Remita, J. Hupka, J. Belloni
    8th International Conference on TiO2 Photocatalysis: Fundamentals and Applications (TiO2-8), October 26-29, 2003, Montreal, Quebec, Canada 107 - 108 2003/10 [Not refereed][Not invited]
  • H2O2/UV enhanced degradation of pesticides in wastewaters
    E. Kowalska, M. Janczarek, J. Hupka, M. Grynkiewicz
    3rd International Conference on Oxidation Technologies for Water and Wastewater Treatment (AOP’3), May 18-22, 2003, Goslar, Germany 374 - 379 2003/05 [Not refereed][Not invited]
  • Titania doping for catalytic wastewater treatment
    E. Kowalska, H. Remita, J. Hupka, J. Belloni
    3rd International Conference on Oxidation Technologies for Water and Wastewater Treatment (AOP’3), May, 18-22, 2003, Goslar, Germany 885 - 890 2003/05 [Not refereed][Not invited]
  • Photochemical degradation of xylene
    M. Budzisz, E. Kowalska, M. Pertkiewicz-Piszcz
    3rd International Conference on Oil Pollution „Prevention, Characterization, Clean Technology, Septem-ber 8-11, 2002, Gdansk, Poland II 134 - 138 2002/11 [Not refereed][Not invited]
  • H. Tyszkiewicz, M. Biziuk, J. Hupka, A. Zaleska, E. Kowalska, A
    Ecological Chemistry and Engineering. S 8 (8-9) 941 - 946 2001/08 [Refereed][Not invited]
  • Photodegradation of Phenol in Gas-sparged Reactor
    Ewa Kowalska (Artuna, Jan Hupka
    7th Meeting of the Central and East European Section of SECOTOX, October 24-28, 2000, Bratislava, Slovakia 199 - 201 2000/10 [Not refereed][Not invited]
  • Determination of organochlorines pesticides during degradation in a gas-sparged reactor
    E. Kowalska (Artuna, A. Zaleska, J. Hupka
    Fifth International Symposium on Exhibition on Environmental Contamination in Central and Eastern Europe, September 12-14, 2000, Prague, Czech Republic 83 - 88 2000/09 [Not refereed][Not invited]
  • Ewa Kowalska (Artuna, Jan Hupka
    Central European Journal of Public Health 8 (44) 88 - 89 2000/08 [Refereed][Not invited]
  • Photochemical degradation of organic contaminants in aqueous phase
    Ewa Kowalska (Artuna, Jan Hupka
    2nd Conference on Ecological Achievement in Chemical Industry, October 14-15, 1999, Torun, Poland 174 - 182 1999/10 [Not refereed][Not invited]
  • H2O2/UV/air oxidation of organic contaminants in the gas-sparged cyclone reactor
    Ewa Kowalska (Artuna, Jan Hupka
    6th Meeting of the Central and Eastern European Regional Section, September, 19-23, 1999, Balatonfőldvár, Hungary 103 - 105 1999/09 [Not refereed][Not invited]
  • Photocatalytic Degradation of Almost Non-soluble Organics in Gas-sparged Reactor
    J. Hupka, A. Zaleska, E. Kowalska, R. Bokotko, H. Tyszkiewicz, M. Biziuk
    EF Conference Environmental Technology for Oil Pollution, August 29- September 3, 1999, Jurata, Poland II 37 - 42 1999/08 [Not refereed][Not invited]

Books etc

  • Noble metal nanoparticles
    Kowalska E, Endo M, Wei Z, Wang K, Janczarek M (ContributorNANOSCALE MATERIALS IN WATER PURIFICATION)
    Elsevier 2018/10 (ISBN: 9780128139264)
  • Band-gap engineering of photocatalysts: surface modification versus doping
    Kowalska E, Wei Z, Janczarek M (ContributorVisible-Light-Active Photocatalysis: Nanostructured Catalyst Design, Mechanisms and Applications. ed. S. Ghosh)
    Wiley 2018/05 (ISBN: 9783527342938)
  • Plasmonic photocatalysis
    Ewa Kowalska (ContributorGold nanoparticles for physics, chemistry and biology. eds.: C. Louis & O. Pluchery. 2nd edition)
    World Scientific 2017/03 (ISBN: 9781786341242) 46
  • Influence of post-treatment operations on structural properties and photocatalytic activity of octahedral anatase particles prepared by hydrothermal method
    Wei Z, Kowalska E, Ohtani B (ContributorPhotocatalysis: Fundamentals, Materials and Potential. ed.: P. Pichat.)
    MDPI, Basel 2016/07 (ISBN: 9783038421832) 14
  • Silver-gold nano-composites for photo-catalytic and sensing applications, In: Silver Nanoparticles: Synthesis, Uses and Health Concerns
    E. Kowalska, Y. Nishijima, L. Rosa, S.Juodkazis (Contributor)
    Nova Science Publishers 2013 (ISBN: 9781628084023)
  • Development of application of photocatalysts, In: Latest Trends in Plasmonic Nanomaterials
    B. Ohtani, E. Kowalska (Contributor)
    CMC Publishing 2009 (ISBN: 9784781301327) 9
  • Application of spectroscopic method for characterization of Ag-TiO2 nanocomposites. In: Science and In-dustry - Spectroscopic Methods in Practice (Nauka i przemysł - metody spektroskopowe w praktyce)
    A. Zielisnka, A. Zaleska, I. Lacka, M. Gazda, E. Kowalska, J. Hupka (Contributor)
    UMCS Lublin 2008 4
  • UV/VIS light-enhanced photocatalysis for water treatment and protection. In: Soil and Water Pollution Monitoring, Protection and Remediation
    J. Hupka, A. Zaleska, M. Janczarek, E. Kowalska, P. Górska, R. Aranowski (Contributor)
    Springer 2005 (ISBN: 1402047274) 11
  • Determination and pathways of nitrogen during wastewater treatment. In: Pathways of pollutants and miti-gation strategies of their impact on the ecosystems.
    M. Chrzanowska, E. Kowalska, J. Hupka (Contributor)
    Komit. Inż. Środow. PAN, Lublin 2004 9
  • Pathways and degradation of chloroorganic pesticides. In: Pathways of pollutants and mitigation strategies of their impact on the ecosystems
    A. Zaleska, E. Kowalska, J. Hupka (Contributor)
    Komit. Inż. Środow. PAN, Lublin 2004 15

Conference Activities & Talks

Educational Activities

Teaching Experience

  • Advanced Course in Environmental Catalytic Chemistry I
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 光触媒,光酸化分解,超親水化現象,励起電子─正孔,構造と光触媒活性,高活性化,可視光応答 Photocatalyst, Photoinduced oxidative decomposition, Super hydrophilicity, Excited electron-positive hole, Structure-activity correlation, Higher photocatalytic activity, Visible-light response
  • Advanced Course in Environmental Catalytic Chemistry II
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : Scientific Writing; Literature on Environmental Catalytic Chemistry; Manuscript Preparation, Data Presentation, Manuscript Edition
  • Environment and People
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 触媒、化学物質、環境とエネルギー、持続的な社会発展

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