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Now showing items 1 - 12 of 12

  • HiPIMS deposition of tungsten-doped titania coatings for photocatalytic applications

    Ratova, M.   West, G.T.   Kelly, P.J.  

    Tungsten-doped titania coatings have been deposited from a Ti-5 at.% W alloy target in HiPIMS mode. The coatings were weakly crystalline and showed mixed anatase/rutile structures in the as-deposited condition. Their photocatalytic activity was assessed in terms of the degradation rate of methylene blue dye. The W-doped coatings showed no improvement in activity, compared to pure titania coatings under UV irradiation, however under fluorescent and visible light sources, the activity was significantly enhanced. This was attributed to a red-shift in the band gap energy of the doped coatings. [All rights reserved Elsevier].
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  • Optimisation of HiPIMS photocatalytic titania coatings for low temperature deposition

    Ratova, M.   West, G.T.   Kelly, P.J.  

    Titanium dioxide in its anatase form is widely used in photocatalytic applications due to its high photocatalytic activity, stability and low cost. Titania coatings directly deposited by conventional magnetron sputtering tend to have an amorphous microstructure. For the anatase structure to develop, substrate heating or post-deposition thermal treatment is usually required, with the anatase crystal phase generally forming at temperatures in excess of 400 degrees C. This precludes the choice of thermally sensitive substrate materials for the photoactive coating. Depending on the nature of the driving voltage waveform, high power impulse magnetron sputtering (HiPIMS) has been shown to deliver a relatively low thermal flux to the substrate, whilst still allowing the direct deposition of crystalline titania coatings. Consequently, this technique offers the potential to deposit photocatalytically active titania coatings directly onto polymeric substrates and, therefore, opens up a range of new applications. In the present work a range of titanium dioxide thin films were deposited by HiPIMS onto glass substrates in order to study the influence of various process parameters, such as pressure, pulse frequency and pulse duration on coating structure and photocatalytic properties. The photocatalytic properties of the coatings were assessed by their ability to degrade the organic dye methylene blue under UV and fluorescent light irradiation. The degradation rate of methylene blue was calculated by measuring its absorption peak height at 665 nm in continuous mode under UV/fluorescent light source. The hydrophilic properties of the coatings were also investigated by measuring the contact angle of water droplets on the coating surfaces. Experimentally, the optimum conditions to maximise the photocatalytic performance of the coatings were found. The influence of various deposition parameters on the photocatalytic properties and crystal structure of the coatings is discussed. Optimised coatings then were deposited onto polymeric substrates, such as polyethylene terephthalate (PET) and polycarbonate, to assess the suitability of using this method for high-energy, low-temperature deposition of photoactive titania coatings and the relevance of the optimised condition was tested for other types of substrates other than glass. It was found that titania coatings deposited by HiPIMS directly onto polymeric substrates showed relatively high levels of activity in their as-deposited state. The ability to deposit crystalline titania with photocatalytic functionality at temperatures low enough to enable the use of polymer substrates is a significant advancement in the field. It could potentially allow the production of high volumes of photocatalytic material on substrates, such as polymer web, which is not possible with current deposition techniques. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.
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  • Enhanced properties of magnetron sputtered photocatalytic coatings via transition metal doping

    Ratova, M.   Kelly, P.J.   West, G.T.   Iordanova, I.  

    To investigate the effect of transition metal doping on photocatalytic activity, thin films of titania doped with W, Mo, Nb or Ta were deposited onto soda-lime glass by pulsed DC reactive magnetron sputtering. As-deposited coatings and coatings annealed at both 400 degrees C and 600 degrees C were characterised by X-ray diffraction (XRD), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). The band gap values were determined from optical data for all samples. The photocatalytic properties of the coatings were studied by the degradation of methylene blue dye under both ultra-violet and fluorescent light sources. The results of the study showed that annealed TiO2 coatings doped with Mo and Nb had high photocatalytic activity in terms of methylene blue degradation, due to the presence of the anatase crystalline phase, whereas W and Ta-doped samples were predominantly of the rutile phase, and exhibited a lower photocatalytic activity. Doping of the titania coatings with Mo and W caused a band gap shift towards the visible range and improved the photocatalytic activity under visible light, compared to undoped titania. Excessive doping in all cases reduced the photocatalytic activity. (C) 2012 Elsevier B.V. All rights reserved.
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  • Antibacterial titania-based photocatalytic extruded plastic films

    Ratova, M.   Mills, A.  

    Photocatalytic antibacterial low density polyethylene (LDPE)-TiO2 films are produced by an extrusion method and tested for photocatalytic oxidation activity, via the degradation of methylene blue (MB) and photocatalytic antibacterial activity, via the destruction of Escherichia Coll. The MB test showed that extruded LDPE films with a TiO2 loading 30 wt.% were of optimum activity with no obvious decrease in film strength, although the activity was less than that exhibited by the commercial self-cleaning glass, Active (R). UVC pre-treatment (9.4 mW cm(-2)) of the latter film improved its activity, with the level of surface sites available for MB adsorption increasing linearly with UVC dose. Although the MB test revealed an optimum exposure time of ca. 60 min photocatalytic oxidation activity, only 30 min was used in the photocatalytic antibacterial tests in order to combine minimal reduction in film integrity with maximum film photocatalytic activity. The photocatalytic antibacterial activity of the latter film was over 10 times that of a non-UVC treated 30 wt.% TiO2 film, which, in turn was over 100 times more active than Active. (C) 2014 Elsevier B.V. All rights reserved.
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  • Photocatalytic visible-light active bismuth tungstate coatings deposited by reactive magnetron sputtering

    Ratova, M.   West, G.T.   Kelly, P.J.  

    Photocatalytic bismuth tungstate thin films with visible-light activity were deposited via reactive pulsed DC magnetron sputtering onto soda-lime glass substrates. Varying the power delivered to the bismuth and tungsten targets allowed control over the Bi/W ratio in the coatings, and therefore the structural and optical properties of the coatings. As-deposited coatings were characterised with amorphous microstructures and were annealed at 673 K to develop crystallinity. The visible light photocatalytic activity of the coatings, which was analysed using the methylene blue degradation test, was found to be superior to that of a commercial titania-based photocatalytic product. (C) 2015 Elsevier Ltd. All rights reserved.
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  • Synergistic effect of doping with nitrogen and molybdenum on the photocatalytic properties of thin titania films

    Ratova, M.   West, G.T.   Kelly, P.J.   Xia, X.   Gao, Y.  

    Doping of titania with metal and non-metal elements provides a simple and efficient pathway to significant enhancement of photocatalytic properties. In this work titania thin films co-doped with molybdenum and nitrogen were prepared by reactive magnetron sputtering. Additionally, coatings doped only with nitrogen were prepared under identical deposition conditions for comparison purposes. Coatings were annealed at 873 K in air and analysed by Raman spectroscopy, XRD and XPS. Photocatalytic properties of the coatings were evaluated on the basis of the photodegradation rate of methylene blue dye under UV, fluorescent and visible light. It was found that the photocatalytic activity of co-doped samples was significantly higher than that of N-doped coatings. Unlike N-doped titania films, co-doped coatings exhibited high photocatalytic activity under the fluorescent light source and noticeable activity under visible light. The possible mechanism for the enhancement of the photocatalytic activity of Mo-N co-doped titania coatings is discussed. (C) 2014 Elsevier Ltd. All rights reserved.
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  • Photocatalytic visible-light active bismuth tungstate coatings deposited by reactive magnetron sputtering

    Ratova, M.   West, G. T.   Kelly, P. J.  

    Photocatalytic bismuth tungstate thin films with visible-light activity were deposited via reactive pulsed DC magnetron sputtering onto soda-lime glass substrates. Varying the power delivered to the bismuth and tungsten targets allowed control over the Bi/W ratio in the coatings, and therefore the structural and optical properties of the coatings. As-deposited coatings were characterised with amorphous microstructures and were annealed at 673 K to develop crystallinity. The visible light photocatalytic activity of the coatings, which was analysed using the methylene blue degradation test, was found to be superior to that of a commercial titania-based photocatalytic product. (C) 2015 Elsevier Ltd. All rights reserved.
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  • Deposition of photocatalytic titania coatings on polymeric substrates by HiPIMS

    Kelly, P. J.   Barker, P. M.   Ostovarpour, S.   Ratova, M.   West, G. T.   Iordanova, I.   Bradley, J. W.  

    Titania coatings have been deposited onto PET substrates by reactive magnetron sputtering in the HiPIMS (high power impulse magnetron sputtering) mode and for comparison, pulsed DC mode. In the latter case, the substrate showed evidence of melting, but the HiPIMS results were dependent on the characteristics of the power supply when operating under nominally identical conditions. A coating deposited by one of the HiPIMS supplies was found to have a mixed phase structure and to demonstrate a level of photocatalytic activity comparable to conventional coatings which had been post-deposition annealed. (C) 2012 Elsevier Ltd. All rights reserved.
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  • Tuning the composition of porous resin-templated TiO2 macrobeads for optimized photocatalytic performance

    Naqvi, Q. A.   Ratova, M.   Klaysri, R.   Kelly, P. J.   Edge, M.   Potgieter-Vermaak, S.   Tosheva, L.  

    TiO2 in the form of macroscopic beads was prepared by resin templating. Anion-exchange macroporous resin beads were treated with a synthesis gel containing titanium isopropoxide, iso-propanol and diluted (0-5 wt.%) tetrapropylammonium hydroxide (TPAOH) aqueous solutions. The Ti-resin composite obtained was calcined at 600 degrees C to remove the resin. The presence of TPAOH in the precursor solution was essential for producing intact TiO2 beads. The use of 1-1.5 wt.% TPAOH resulted in anatase beads, whereas further increase in the TPAOH content promoted the anatase to rutile phase transformations. Decreasing the heating rate used during calcination also resulted in changes in the TiO2 composition from pure anatase (16 degrees C min(-1) heating rate) to anatase with rutile impurities (0.5 degrees C min(-1) heating rate). The photocatalytic activity of the TiO2 beads was evaluated for the degradation of acetone under ultraviolet irradiation. A high activity was displayed by the TiO2 samples composed of anatase with rutile impurities, whereas the activity was lower for pure anatase samples or samples containing mainly rutile. The TiO2 beads showed higher rates of charge carrier generation and slower charge trapping/recombination rates compared to a reference Cristal ACTiV (TM) PC500. In addition, the TiO2 beads could be used in at least five consecutive catalytic cycles without any in-between cycle treatment, without significant changes in their activity. The TiO2 beads prepared in this work are beneficial for photocatalytic applications in the gas-phase compared to powders due to easy handling, reduced pressure drop and attrition resistance.
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  • Optimization Studies of Photocatalytic Tungsten-Doped Titania Coatings Deposited by Reactive Magnetron Co-Sputtering

    Ratova, M.   West, G.T.   Kelly, P.J.  

    In this article we investigate the structural and photocatalytic properties of W-doped titanium dioxide coatings. TiO 2-W thin films were deposited onto glass slides by reactive magnetron co-sputtering. The properties of the films were analyzed using such techniques as XRD, Raman spectroscopy, EDX, TEM, and surface profilometry. The photocatalytic properties of the coatings were assessed using the methylene blue (MB) degradation test under UV and fluorescent light sources. The methylene blue decomposition experiments showed that, at the optimum dopant concentration of tungsten, the photocatalytic activity can be improved by a factor of 6, compared to undoped titania. For the coatings discussed within this work, the optimum dopant concentration was determined to be 5.89 at.% of W. The results indicated that tungsten doping at this level extends the lifetime of the photogenerated charge carriers and significantly increases the photocatalyst surface area.
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  • Enhanced properties of magnetron sputtered photocatalytic coatings via transition metal doping

    Ratova, M.   Kelly, P. J.   West, G. T.   Iordanova, I.  

    To investigate the effect of transition metal doping on photocatalytic activity, thin films of titania doped with W, Mo, Nb or Ta were deposited onto soda-lime glass by pulsed DC reactive magnetron sputtering. As-deposited coatings and coatings annealed at both 400 degrees C and 600 degrees C were characterised by X-ray diffraction (XRD), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). The band gap values were determined from optical data for all samples. The photocatalytic properties of the coatings were studied by the degradation of methylene blue dye under both ultra-violet and fluorescent light sources. The results of the study showed that annealed TiO2 coatings doped with Mo and Nb had high photocatalytic activity in terms of methylene blue degradation, due to the presence of the anatase crystalline phase, whereas W and Ta-doped samples were predominantly of the rutile phase, and exhibited a lower photocatalytic activity. Doping of the titania coatings with Mo and W caused a band gap shift towards the visible range and improved the photocatalytic activity under visible light, compared to undoped titania. Excessive doping in all cases reduced the photocatalytic activity. (C) 2012 Elsevier B.V. All rights reserved.
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  • Photocatalytic activity of reactively sputtered and directly sputtered titania coatings

    Farahani, N.   Kelly, P. J.   West, G.   Ratova, M.   Hill, C.   Vishnyakov, V.  

    It is well known that, depending on deposition conditions, the structure of titania coatings may be amorphous, anatase or rutile, or a mixture of phases, and that the anatase phase is the most promising photocatalyst for the degradation of organic pollutants. The formation of anatase depends on the energy delivered to the growing film, which in turn depends on the operating parameters chosen. In this study, titania coatings have been deposited onto glass substrates by pulsed magnetron sputtering both from metallic targets in reactive mode and directly from oxide powder targets. The as-deposited coatings were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400-700 degrees C and re-analysed. The photocatalytic activity of the coatings has been investigated through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. Further sets of coatings have been produced both from metallic and powder targets in which the titania is doped with tungsten. These coatings have also been analysed and the influence of the dopant element on photocatalytic activity has been investigated. It has been found that, after annealing, both sputtering processes produced photo-active surfaces and that activity increased with increasing tungsten content over the range tested. Furthermore, the activity of these coatings under exposure to fluorescent lamps was some 50-60% of that observed under exposure to UV lamps. (C) 2011 Elsevier B.V. All rights reserved.
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