Publications
104 results found
Ma Y, Kafizas A, Pendlebury SR, et al., 2016, Photoinduced Absorption Spectroscopy of CoPi on BiVO4: The Function of CoPi during Water Oxidation, Advanced Functional Materials, Vol: 26, Pages: 4951-4960, ISSN: 1616-301X
This paper employs photoinduced absorption and electrochemical techniques to analyze the charge carrier dynamics that drive photoelectrochemical water oxidation on bismuth vanadate (BiVO4), both with and without cobalt phosphate (CoPi) co-catalyst. These results are correlated with spectroelectrochemical measurements of CoII oxidation to CoIII in a CoPi/FTO (fluorine doped tin oxide) electrode during dark electrocatalytic water oxidation. Electrocatalytic water oxidation exhibits a non-linear dependence on CoIII density, with a sharp onset at 1 × 1017 CoIII cm−2. These results are compared quantitatively with the degree of CoPi oxidation observed under conditions of photoinduced water oxidation on CoPi–BiVO4 photoanodes. For the CoPi–BiVO4 photoanodes studied herein, ≤5% of water oxidation proceeds from CoPi sites, making the BiVO4 surface the predominant water oxidation site. This study highlights two key factors that limit the ability of CoPi to improve the catalytic performance of BiVO4: 1) the kinetics of hole transfer from the BiVO4 to the CoPi layer are too slow to effectively compete with direct water oxidation from BiVO4; 2) the slow water oxidation kinetics of CoPi result in a large accumulation of CoIII states, causing an increase in recombination. Addressing these factors will be essential for improving the performance of CoPi on photoanodes for solar-driven water oxidation.
Kafizas A, Wang X, Pendlebury SR, et al., 2016, Where Do Photogenerated Holes Go in Anatase:Rutile TiO<sub>2</sub>? A Transient Absorption Spectroscopy Study of Charge Transfer and Lifetime, JOURNAL OF PHYSICAL CHEMISTRY A, Vol: 120, Pages: 715-723, ISSN: 1089-5639
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- Citations: 119
Ma Y, Le Formal F, Kafizas A, et al., 2015, Efficient suppression of back electron/hole recombination in cobalt phosphate surface-modified undoped bismuth vanadate photoanodes, Journal of Materials Chemistry A, Vol: 3, Pages: 20649-20657, ISSN: 2050-7496
In this paper, we compared for the first time the dynamics of photogenerated holes in BiVO4 photoanodes with and without CoPi surface modification, employing transient absorption and photocurrent measurements on microsecond to second timescales. CoPi surface modification is known to cathodically shift the water oxidation onset potential; however, the reason for this improvement has not until now been fully understood. The transient absorption and photocurrent data were analyzed using a simple kinetic model, which allows quantification of the competition between electron/hole recombination and water oxidation. The results of this model are shown to be in excellent agreement with the measured photocurrent data. We demonstrate that the origin of the improvement of photocurrent onset resulting from CoPi treatment is primarily due to retardation of back electron/hole recombination across the space charge layer; no evidence of catalytic water oxidation via CoPi was observed.
Wang X, Kafizas A, Li X, et al., 2015, Transient Absorption Spectroscopy of Anatase and Rutile: The Impact of Morphology and Phase on Photocatalytic Activity, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 10439-10447, ISSN: 1932-7447
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- Citations: 122
Kafizas AG, Durrant JR, 2015, Transient Absorption Spectroscopy of Anatase and Rutile: the Impact of Morphology and Phase on Photocatalytic Activity, The Journal of Physical Chemistry C, ISSN: 1932-7447
Sotelo-Vazquez C, Noor N, Kafizas A, et al., 2015, Multifunctional P-Doped TiO2 films: a new approach to self-cleaning, transparent conducting oxide materials, Chemistry of Materials, Vol: 27, Pages: 3234-3242, ISSN: 1520-5002
Multifunctional P-doped TiO2 thin films were synthesized by atmospheric pressure chemical vapor deposition (APCVD). This is the first example of P-doped TiO2 films with both P5+ and P3– states, with the relative proportion being determined by synthesis conditions. This technique to control the oxidation state of the impurities presents a new approach to achieve films with both self-cleaning and TCO properties. The origin of electrical conductivity in these materials was correlated to the incorporation of P5+ species, as suggested by Hall Effect probe measurements. The photocatalytic performance of the films was investigated using the model organic pollutant, stearic acid, with films containing predominately P3– states found to be vastly inferior photocatalysts compared to undoped TiO2 films. Transient absorption spectroscopy studies also showed that charge carrier concentrations increased by several orders of magnitude in films containing P5+ species only, whereas photogenerated carrier lifetimes—and thus photocatalytic activity—were severely reduced upon incorporation of P3– species. The results presented here provide important insights on the influence of dopant nature and location within a semiconductor structure. These new P-doped TiO2 films are a breakthrough in the development of multifunctional advanced materials with tuned properties for a wide range of applications.
Pendlebury SR, Wang X, Le Formal F, et al., 2014, Ultrafast charge carrier recombination and trapping in hematite photoanodes under applied bias, Journal of the American Chemical Society, Vol: 136, Pages: 9854-9857, ISSN: 0002-7863
Transient absorption spectroscopy on subpicosecond to second time scales is used to investigate photogenerated charge carrier recombination in Si-doped nanostructured hematite (α-Fe2O3) photoanodes as a function of applied bias. For unbiased hematite, this recombination exhibits a 50% decay time of ∼6 ps, ∼103 times faster than that of TiO2 under comparable conditions. Anodic bias significantly retards hematite recombination dynamics, and causes the appearance of electron trapping on ps−μs time scales. These ultrafast recombination dynamics, their retardation by applied bias, and the associated electron trapping are discussed in terms of their implications for efficient water oxidation.
Knapp CE, Manzi JA, Kafizas A, et al., 2014, Aerosol-Assisted Chemical Vapour Deposition of Transparent Zinc Gallate Films, CHEMPLUSCHEM, Vol: 79, Pages: 1024-1029, ISSN: 2192-6506
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- Citations: 13
Chadwick N, Sathasivam S, Kafizas A, et al., 2014, Combinatorial aerosol assisted chemical vapour deposition of a photocatalytic mixed SnO2/TiO2 thin film, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 5108-5116, ISSN: 2050-7488
Kafizas A, Noor N, Carmichael P, et al., 2014, Combinatorial Atmospheric Pressure Chemical Vapor Deposition of F: TiO 2; the Relationship between Photocatalysis and Transparent Conducting Oxide Properties, ADVANCED FUNCTIONAL MATERIALS, Vol: 24, Pages: 1758-1771, ISSN: 1616-301X
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- Citations: 40
Sathasivam S, Kafizas A, Ponja S, et al., 2014, Combinatorial Atmospheric Pressure CVD of a Composite TiO<sub>2</sub>/SnO<sub>2</sub> Thin Film, CHEMICAL VAPOR DEPOSITION, Vol: 20, Pages: 69-79, ISSN: 0948-1907
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- Citations: 10
Kafizas A, Carmalt CJ, Parkin IP, 2013, CVD and precursor chemistry of transition metal nitrides, COORDINATION CHEMISTRY REVIEWS, Vol: 257, Pages: 2073-2119, ISSN: 0010-8545
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- Citations: 89
O'Keeffe C, Gannon P, Gilson P, et al., 2013, Air purification by heterogeneous photocatalytic oxidation with multi-doped thin film titanium dioxide, THIN SOLID FILMS, Vol: 537, Pages: 131-136, ISSN: 0040-6090
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- Citations: 9
Wilkinson M, Kafizas A, Bawaked SM, et al., 2013, Combinatorial Atmospheric Pressure Chemical Vapor Deposition of Graded TiO<sub>2</sub>-VO<sub>2</sub> Mixed-Phase Composites and Their Dual Functional Property as Self-Cleaning and Photochromic Window Coatings, ACS COMBINATORIAL SCIENCE, Vol: 15, Pages: 309-319, ISSN: 2156-8952
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- Citations: 43
Parkin IP, Kafizas A, 2013, Exothermic Metathesis Reactions, Comprehensive Inorganic Chemistry II (Second Edition): From Elements to Applications, Pages: 471-490, ISBN: 9780080965291
The development of solid-state metathesis (SSM) routes over the last two decades has revolutionized the way in which several industrially important refractory ceramics, intermetallics, and semiconductors are made. In this chapter, the development of SSM routes in synthesizing a range of materials including metal borides and aluminides, carbides and silicides, nitrides, phosphides, arsenides and antimonides, oxides and sulfides, selenides and tellurides is covered. In addition, an overview of the new directions in metathesis is presented, including carbon nanotube and nanocrystal formation. © 2013 Elsevier Ltd. All rights reserved.
Kafizas A, Noor N, Carmalt CJ, et al., 2013, TiO<sub>2</sub>-based transparent conducting oxides; the search for optimum electrical conductivity using a combinatorial approach, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 1, Pages: 6335-6346, ISSN: 2050-7526
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- Citations: 30
Kafizas A, Parry SA, Chadwick AV, et al., 2013, An EXAFS study on the photo-assisted growth of silver nanoparticles on titanium dioxide thin-films and the identification of their photochromic states, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 15, Pages: 8254-8263, ISSN: 1463-9076
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- Citations: 15
Uppal MA, Kafizas A, Ewing MB, et al., 2013, The room temperature formation of gold nanoparticles from the reaction of cyclohexanone and auric acid; a transition from dendritic particles to compact shapes and nanoplates, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 1, Pages: 7351-7359, ISSN: 2050-7488
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- Citations: 29
Ponja S, Sathasivam S, Chadwick N, et al., 2013, Aerosol assisted chemical vapour deposition of hydrophobic TiO<sub>2</sub>-SnO<sub>2</sub> composite film with novel microstructure and enhanced photocatalytic activity, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 1, Pages: 6271-6278, ISSN: 2050-7488
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- Citations: 49
Kafizas A, Carmalt CJ, Parkin IP, 2012, Does a Photocatalytic Synergy in an Anatase-Rutile TiO2 Composite Thin-Film Exist?, Chemistry - A European Journal, Vol: 18, Pages: 13048-13048, ISSN: 1521-3765
It has often been suggested that anatase-rutile mixtures/composites synergistically enhance photocatalysis. However, in the case of dense thin-films containing an intimate mix of both anatase and rutile phases, such an effect has not been observed. In synthesising combinatorial films with graded film thickness and phase, and applying established photocatalytic mapping methods, we were able to assess how dense thin-films of intimately mixed anatase-rutile mixtures affect photocatalytic performance. We found that no photocatalytic synergy between anatase-rutile composites (29≤rutile %≤83) within such dense thin-film systems exists. In fact, an increased presence of rutile caused the photocatalytic activity to fall. This was explained by the unfavourable energetics in the multiple electron transfers required between several neighbouring rutile and anatase sites for the photo-generated electron to reach the material’s surface; encouraging the trapping of electrons within the bulk and increasing the likelihood of charge recombination. The decrease in photocatalytic activity was found to vary linearly with rutile component.
Cabrera RQ, Latimer ER, Kafizas A, et al., 2012, Photocatalytic activity of needle-like TiO2/WO3−x thin films prepared by chemical vapour deposition, Journal of Photochemistry and Photobiology A, Vol: 239, Pages: 60-60, ISSN: 1010-6030
The enhanced photocatalyticactivity of needle-like TiO2/WO3−x (0 < x ≤ 0.3) composite thinfilms is demonstrated in the degradation of stearic acid, a model system for the organic pollutants typically present on window surfaces. The films were synthesised by atmospheric pressure chemicalvapourdeposition (APCVD) from reaction of tungsten and titanium chlorides with ethanol and ethyl acetate as oxygen sources, respectively, and characterised by X-ray diffraction, Raman spectroscopy, SEM and AFM. The increase in activity of films is explained in terms of an effective vectorial charge separation at the interface of the two oxide semiconductors. The interaction of water with the surface of the TiO2/WO3−x composite film is also discussed after water droplet contact angle measurements.
Crick CR, Bear JC, Kafizas A, et al., 2012, Superhydrophobic Photocatalytic Surfaces through Direct Incorporation of Titania Nanoparticles into a Polymer Matrix by Aerosol Assisted Chemical Vapor Deposition, Vol: 24, Pages: 3505–3508-3505–3508, ISSN: 1521-4095
Dunnill CW, Kafizas A, Parkin IP, 2012, CVD Production of Doped Titanium Dioxide Thin Films, Chemical Vapor Deposition, Vol: 18, Pages: 89-89, ISSN: 0948-1907
Kafizas A, Parkin IP, 2012, ChemInform Abstract: Inorganic Thin‐Film Combinatorial Studies for Rapidly Optimizing Functional Properties, ChemInform, Vol: 43, ISSN: 0931-7597
<jats:title>Abstract</jats:title><jats:p>Review: 217 refs.</jats:p>
Kafizas A, Parkin IP, 2012, Inorganic thin-film combinatorial studies for rapidly optimising functional properties, Chemical Society Reviews, Vol: 41, Pages: 738-738
Kafizas A, Parkin IP, 2011, Combinatorial atmospheric pressure chemical vapor deposition (cAPCVD); a route to functional property optimization., Journal of the American Chemical Society, ISSN: 1520-5126
ABSTRACT: We demonstrate how combinatorial atmospheric pressure chemical vapor deposition (cAPCVD) can be used as a synthetic tool for rapidly optimizing the functional properties of thin-films; by analyzing the self-cleaning properties of tungsten doped anatase as an example. By introducing reagents at separate points inside the reactor, a tungsten/ titanium compositional gradient was formed and a diverse range of film growth conditions were obtained. By partially mixing the metal sources, a combinatorial film with a compositional profile that varied primarily in the lateral plane was synthesized. A combinatorial thin-film of anatase TiO2 doped with an array of tungsten levels as a solid solution ranging from 0.38 - 13.8 W: Ti atom % was formed on a single glass substrate. The compositional-functional relationships were understood through comprehensively analyzing combinatorial phase space; with 200 positions investigated by high-throughput methods in this study. Physical and functional properties, and their compositional dependencies, were inter-correlated. It was found that increases in photocatalytic activity and conductivity were most highly dependent on film crystallinity within the 0.38 - 13.8 atom % W: Ti doping regime. However, enhancements in photo-induced surface wetting were primarily dependent on increases in preferred growth in the (211) crystal plane.
Kafizas A, Dunnill CW, Parkin IP, 2011, The relationship between photocatalytic activity and photochromic state of nanoparticulate silver surface loaded titanium dioxide thin-films., Physical Chemistry Chemical Physics, Vol: 13, Pages: 13827-13827, ISSN: 1463-9084
Anatase titania thin-films were prepared by a modified spray-pyrolysis method. Glass substrates were coated at room temperature with an aerosol-spray of a titania sol-gel solution and then annealed at 500 °C to form rough, transparent, crystalline thin-films of anatase TiO(2). Silver nanoparticles were deposited on the surface of these films by a photo-assisted deposition method; films were dip-coated in methanolic solutions of silver nitrate salt and then photo-irradiated for 5 h with UVC light. The AgNO(3) concentration was adjusted to create an array of films with varying silver loadings. The films displayed photochromism; changing colour to orange-brown in UV-light to colourless under white light. The rates of photochromic change, when subjected to four different lighting conditions (UVC, UVA, white light and dark), were analysed by UV-visible spectroscopy. By assessing the photocatalytic activity to these light sources it was found that the initial photochromic state of the material had a profound effect on the films photocatalytic ability. This effect was more pronounced in the more concentrated silver loaded films; where significant enhancements in photoactivity occurred when reactions were initiated from the photo-reduced state. The mode of improved photocatalysis was attributed to the photo-generated electron trapping by silver nanoparticles, which stabilised photo-generated holes and drove photo-oxidation processes. We believe this is the first study in which the relationship between the photochromic state of a thin-film and its subsequent photocatalytic activity is reported.
Knapp CE, Kafizas A, Parkin IP, et al., 2011, The use of combinatorial aerosol-assisted chemical vapour deposition for the formation of gallium-indium-oxide thin films, Journal of Materials Chemistry, Vol: 21, Pages: 12644-12644, ISSN: 0959-9428
Dunnill CW, Page K, Aiken ZA, et al., 2011, Nanoparticulate silver coated-titania thin films-Photo-oxidative destruction of stearic acid under different light sources and antimicrobial effects under hospital lighting conditions, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, Vol: 220, Pages: 113-123, ISSN: 1010-6030
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- Citations: 63
Kundu S, Kafizas A, Hyett G, et al., 2011, An investigation into the effect of thickness of titanium dioxide and gold–silver nanoparticle titanium dioxide composite thin-films on photocatalytic activity and photo-induced oxygen production in a sacrificial system, Journal of Materials Chemistry, Vol: 21, Pages: 6854-6854, ISSN: 0959-9428
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