Optimization Studies of Photocatalytic Tungsten-Doped Titania Coatings Deposited by Reactive Magnetron Co-Sputtering

In this article we investigate the structural and photocatalytic properties of W-doped titanium dioxide coatings. TiO2-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

Optimisation of HiPIMS photocatalytic titania coatings for low temperature deposition

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 °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

Micro-patterning of magnetron sputtered titanium dioxide coatings and their efficiency for photocatalytic applications

© 2020 by the authors. Titanium dioxide thin films were deposited onto sola-lime glass substrates by reactive magnetron sputtering. Fine stainless steel mesh sheets with different aperture sizes were applied as masks over glass substrates to allow the deposition of the coatings with micro-patterned structures and, therefore, enhanced surface area. Non-patterned titania films were deposited for comparison purposes. The titanium dioxide films were post-deposition annealed at 873 K for crystallinity development and then extensively analysed by a number of analytical techniques, including scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), optical and stylus profilometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy. The photocatalytic activity of non-patterned and micro-patterned titania films was assessed under UV light irradiation by three different methods; namely methylene blue, stearic acid, and oleic acid degradation. The results revealed that the micro-patterned coatings significantly outperformed non-patterned titania in all types of photocatalytic tests, due to their higher values of surface area. Increasing the aperture of the stainless steel mesh resulted in lower photocatalytic activity and lower surface area values, compared to the coatings deposited through a smaller aperture mesh

Photocatalytic visible-light active bismuth tungstate coatings deposited by reactive magnetron sputtering

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

HiPIMS deposition of tungsten-doped titania coatings for photocatalytic applications

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

Superhydrophobic photocatalytic PTFE – titania coatings deposited by reactive pDC magnetron sputtering from a blended powder target

The production of photocatalytic coatings with superhydrophobic properties, as opposed to the conventional hydrophilic properties, is desirable for the prevention of adhesion of contaminants to photocatalytic surfaces with subsequent deterioration of photocatalytic properties. In this work polytetrafluoroethylene (PTFE) – TiO2 composite thin films were deposited using a novel method of reactive pulsed direct current (pDC) magnetron sputtering of a blended PTFE – titanium oxide powder target. The surface characteristics and photocatalytic properties of the deposited composite coatings were studied. The as-deposited coatings were annealed at 523 K in air and analysed with Raman spectroscopy, optical profilometry and scanning electron microscopy. Hydrophobicity was assessed though measurements of water contact angles, and photocatalytic properties were studied via methylene blue dye degradation under UV irradiation. It was found that variations of gas flow and, hence, process pressures allowed deposition of samples combining superhydrophobicity with stable photocatalytic efficiency under UV light irradiation. Reversible wettability behaviour was observed with the alternation of light-dark cycles

A Novel Technique for the Deposition of Bismuth Tungstate onto Titania Nanoparticulates for Enhancing the Visible Light Photocatalytic Activity

A novel powder handling technique was used to allow the deposition of bismuth tungstate coatings onto commercial titanium dioxide photocatalytic nanoparticles. The coatings were deposited by reactive pulsed DC magnetron sputtering in an argon/oxygen atmosphere. The use of an oscillating bowl with rotary particle propagation, positioned beneath two closed-field planar magnetrons, provided uniform coverage of the titania particle surfaces. The bismuth/tungsten atomic ratio of the coatings was controlled by varying the power applied to each target. The resulting materials were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) surface area measurements, transmission electron microscopy (TEM), and UV-visible diffuse reflectance spectroscopy. Photocatalytic properties under visible light irradiation were assessed using an acetone degradation test. It was found that deposition of bismuth tungstate onto titania nanoparticles resulted in significant increases in visible light photocatalytic activity, compared to uncoated titania. Of the coatings studied, the highest photocatalytic activity was measured for the sample with a Bi/W atomic ratio of 2/1

Crystalline TiO₂ supported on stainless steel mesh deposited in a one step process via pulsed DC magnetron sputtering for wastewater treatment applications

© 2020 The Author(s). TiO2 thin films were deposited on woven stainless-steel mesh by pulsed DC magnetron sputtering, at room temperature without substrate bias or annealing. Woven stainless-steel mesh is inexpensive, flexible, semi-transparent and has a high surface area. This coating/substrate combination was selected for future photocatalytic reactor integration. The effect of operating pressure and magnetron power on coating crystallinity and photocatalytic activity were investigated. Results indicate that magnetron power is a key factor, as it affects the crystallinity and morphology of the thin films. A combination of low pressure and high-power lead to a one-step synthesis of TiO2 coatings with a mixed anatase and rutile phase. An optimised sample was produced and tested for methylene blue, methyl orange and rhodamine B decomposition under UV-A. Using various trapping agents, OH and O2- radicals were identified as the main photogenerated species responsible for the model pollutant degradation. Finally, durability tests revealed little to no photocatalytic performance deterioration after ten repeated cycles. This confirmed the suitability of this coating/substrate combination for future photocatalytic reactor integration

Visible light active photocatalytic C-doped titanium dioxide films deposited via reactive pulsed DC magnetron co-sputtering: Properties and photocatalytic activity

Doping of TiO2 with carbon is known to be an efficient method of enhancing visible light photocatalytic activity. The present work describes the deposition of carbon-doped titania coatings deposited by reactive magnetron co-sputtering of Ti and C targets. Undoped titania coatings were produced under similar deposition conditions for comparison purposes. Following deposition, all coatings were annealed in air at 873 K for 30 min to develop the required crystalline structure; and then analysed with EDS, XRD, AFM, XPS and UVevisible spectrophotometry. A number of tests, including methylene blue and stearic acid decomposition tests, and photo-induced hydrophilicity measurements, were employed for the assessment of the photocatalytic properties of the C-doped and un-doped titanium dioxide coatings under UV and visible light irradiation. It was found that carbon-doped titania coatings significantly outperformed undoped titania when using both visible and UV irradiation. Similar trends were observed for other properties. While excessive carbon doping has been shown to have a negative effect on the photocatalytic properties of the titanium dioxide, overall, carbon doping via reactive co-sputtering has been confirmed as an efficient method of photocatalytic property enhancement. This is due to a narrowing of the bandgap and to extended lifetimes of the photo-generated charge carriers