Highly efficient photocatalytic bismuth oxide coatings and their antimicrobial properties under visible light irradiation

The aim of the present paper is to assess the antimicrobial activity of novel narrow band gap semiconductor photocatalysts under visible light irradiation, compared to titanium dioxide, which is the conventionally used photocatalytic material. Bismuth oxide, bismuth tungstate and titanium dioxide coatings were prepared using pulsed DC reactive magnetron sputter deposition onto batches of 2 mm spherical glass beads that were agitated during the deposition process to ensure uniform coverage. Additional coatings were deposited onto flat glass substrates for specific analytical techniques. Following deposition, the coatings were annealed in air at 673 K for 30 min to enable crystal structure development. Annealed coatings were analysed with SEM, EDX, XRD, XPS, AFM, UV-visible spectroscopy and water contact angle measurements. The photocatalytic properties of the coatings were initially assessed via a Rhodamine B dye degradation test under visible light irradiation. Antimicrobial efficiency of the coatings was tested via inactivation of E. coli; additionally, bacterial adhesion experiments were performed for all types of the studied coatings. It was found that the performance of bismuth oxide for both dye degradation and bacterial inactivation experiments under visible light was superior to that observed for either bismuth tungstate or titanium dioxide. Moreover, bismuth oxide coatings (and to a lesser extent – bismuth tungstate), due to its hydrophobic nature was able to inhibit bacterial adhesion to the surface

Pulsed DC magnetron sputtering deposition of crystalline photocatalytic titania coatings at elevated process pressures

© 2017 Elsevier Ltd The use of elevated process pressures is described in the magnetron sputter deposition of titanium dioxide photocatalytic coatings to enable the direct low-temperature formation of the most photoactive titania crystal phase; anatase. Most other works on this subject deal with relatively low ‘conventional’ pressures (0.1–0.5 Pa). However, the present work describes pulsed DC reactive magnetron sputtering deposition of titanium dioxide thin films at process pressures in the range 2–5 Pa in a purpose-built sputtering rig. The influence of the other deposition conditions, such as pulse frequency and duty cycle, is also discussed. Additionally, a series of N-doped titania coatings was produced by using air as the reactive gas. The morphological and compositional properties of the coatings were studied using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability of the films was studied through measurement of water contact angles under UV light irradiation. Photocatalytic properties of the samples were assessed through the degradation of two model pollutants, methylene blue and stearic acid, under UV light irradiation. The results showed that elevated process pressures (4 Pa and above) allow the direct deposition of anatase titania films, without additional heat treatment, while amorphous titania tends to form at lower process pressures

Novel and versatile tio2 thin films on pet for photocatalytic removal of contaminants of emerging concern from water

The current work presents new and versatile photocatalytic surfaces designed to remove contaminants of emerging concerns (CECs) from water. Photocatalytic thin films of titanium dioxide (TiO2) were deposited on a polyethylene terephthalate (PET) surface (PET-TiO2) and photosensitized by a natural and non-hazardous curcumin (turmeric). The TiO2 thin film was deposited in a single stage and solvent-free process, without thermal post treatment, using the high power impulse magnetron sputtering (HiPIMS) technique. The photocatalytic film was characterized by different techniques (SEM/EDS, STEM, AFM, UV–Vis spectroscopy, and wettability via water droplet contact angle). The photocatalytic activity was assessed by the degradation of two model CECs: the fungicide carbendazim (CBZ), used in different crops around the world (coffee, rice, fruits, etc.), and the anthropogenic pollution tracer caffeine (CAF). Removal of these model CECs of up to 39% were achieved under combined UV and visible irradiation under 7 h photocatalytic treatments. The degradation process was further studied by dissolved organic carbon analysis, with up to 80% removal, and acute ecotoxicity tests with Aliivibrio fischeri, indicating reduction of toxicity or non-change. The PET-TiO2 surfaces remained stable for 5 consecutive cycles of use, with similar kinetic rates. Finally, the species involved in photocatalytic reactions were investigated by the use of h+, HO and O2− trapping agents, both in the presence and absence of turmeric. The results indicated that the addition of the turmeric led to an increase in photogenerated O2− radicals due to a synergistic effect between the photocatalyst and photosensitizer. The results demonstrate the potential of the PET-TiO2 surfaces as a straightforward solution for the removal of CECs from waters, using a flexible, scalable, reusable and environmental friendly photocatalytic material

Development of a rapid method for assessing the efficacy of antibacterial photocatalytic coatings

Visible-light activated photocatalytic coatings may represent an attractive antimicrobial solution in domains such as food, beverage, pharmaceutical, biomedical and wastewater remediation. However, testing methods to determine the antibacterial effects of photocatalytic coatings are limited and require specialist expertise. This paper describes the development of a method that enables rapid screening of coatings for photocatalytic-antibacterial activity. Relying on the ability of viable microorganisms to reduce the dye resazurin from a blue to a pink colour, the method relates the time taken to detect this colour change with number of viable microorganisms. The antibacterial activity of two photocatalytic materials (bismuth oxide and titanium dioxide) were screened against two pathogenic organisms (Escherichia coli and Klebsiella pneumoniae) that represent potential target microorganisms using traditional testing and enumeration techniques (BS ISO 27447:2009) and the novel rapid method. Bismuth oxide showed excellent antibacterial activity under ambient visible light against E. coli, but was less effective against K. pneumoniae. The rapid method showed excellent agreement with existing tests in terms of number of viable cells recovered. Due to advantages such as low cost, high throughput, and less reliance on microbiological expertise, this method is recommended for researchers seeking an inexpensive first-stage screen for putative photocatalytic-antibacterial coatings

Cu and Pt clusters deposition on TiO2 powders by DC magnetron sputtering for photocatalytic hydrogen production

Titanium dioxide-based photocatalyst powders were obtained by deposition of copper and/or platinum clusters by means of pulsed direct current magnetron sputtering with different deposition times and plasma composition during Cu/Pt sputtering. A top-down configuration was employed with the sputtering source facing the powder holder mounted on a shaker mechanism, which continuously mixed the powder during the sputtering process. HRTEM analyses revealed the presence of well dispersed, subnanometric sized metal clusters, even for long deposition times, while XRPD analysis showed no modification of the TiO2crystal structure upon metal deposition. The so obtained powders were tested as photocatalysts in methanol photo-steam reforming for hydrogen production. The presence of Pt clusters increased the photoactivity with respect to that of bare TiO2. The plasma composition during Cu sputtering was found to strongly affect the photoactivity of the obtained materials, Cu alone deposited as co-catalyst in an Ar-only atmosphere imparting better photoactivity than Cu sputtered in Ar/O2. When the deposition of Cu clusters was coupled with the deposition of Pt clusters, an additive effect of the two metals in increasing TiO2photoactivity was observed if Cu clusters were sputtered in the absence of oxygen

Structural Formation and Photocatalytic Activity of Magnetron Sputtered Titania and Doped-Titania Coatings

Titania and doped-titania coatings can be deposited by a wide range of techniques; this paper will concentrate on magnetron sputtering techniques, including “conventional” reactive co-sputtering from multiple metal targets and the recently introduced high power impulse magnetron sputtering (HiPIMS). The latter has been shown to deliver a relatively low thermal flux to the substrate, whilst still allowing the direct deposition of crystalline titania coatings and, therefore, offers the potential to deposit photocatalytically active titania coatings directly onto thermally sensitive substrates. The deposition of coatings via these techniques will be discussed, as will the characterisation of the coatings by XRD, SEM, EDX, optical spectroscopy, etc. The assessment of photocatalytic activity and photoactivity through the decomposition of an organic dye (methylene blue), the inactivation of E. coli microorganisms and the measurement of water contact angles will be described. The impact of different deposition technologies, doping and co-doping strategies on coating structure and activity will be also considered

Deposition of Visible Light Active Photocatalytic Bismuth Molybdate Thin Films by Reactive Magnetron Sputtering

Bismuth molybdate thin films were deposited by reactive magnetron co-sputtering from two metallic targets in an argon/oxygen atmosphere, reportedly for the first time. Energy dispersive X-ray spectroscopy (EDX) analysis showed that the ratio of bismuth to molybdenum in the coatings can be effectively controlled by varying the power applied to each target. Deposited coatings were annealed in air at 673 K for 30 min. The crystalline structure was assessed by means of Raman spectroscopy and X-ray diffraction (XRD). Oxidation state information was obtained by X-ray photoelectron spectroscopy (XPS). Photodegradation of organic dyes methylene blue and rhodamine B was used for evaluation of the photocatalytic properties of the coatings under a visible light source. The photocatalytic properties of the deposited coatings were then compared to a sample of commercial titanium dioxide-based photocatalytic product. The repeatability of the dye degradation reactions and photocatalytic coating reusability are discussed. It was found that coatings with a Bi:Mo ratio of approximately 2:1 exhibited the highest photocatalytic activity of the coatings studied; its efficacy in dye photodegradation significantly outperformed a sample of commercial photocatalytic coating

Deposition of Pt nanoparticles on TiO2 by pulsed direct current magnetron sputtering for selective hydrogenation of vanillin to vanillyl alcohol

Pulsed direct current magnetron sputtering (PDC-MSD) was employed for the deposition of Pt nanoparticles (ca. 0.1 wt.%) on anatase TiO2 powder. According to the H2-TPR, XPS, and TEM-EDX results, the characteristics and properties of the deposited nanoparticles depended on the deposition time. During the initial deposition stage (45-90 sec), low-coordinated small spherical Pt nanoparticles were formed. Prolonging the deposition time (135-180 sec), led to the formation of larger Pt nanoparticles, which strongly interacted with the TiO2. The catalytic activities of the prepared Pt/TiO2 with different deposition times in the aqueous phase partial hydrogenation of vanillin to vanillyl alcohol ranged as follows: Pt/TiO2 MSD-45 < Pt/TiO2 MSD-90 < Pt/TiO2 MSD-180 < Pt/TiO2 MSD-135, which was in good agreement with the atomic Pt/Ti ratio and coordinated surface Pt atoms on the catalyst surface. The high catalytic activity of Pt/TiO2 MSD-135 was attributed to the presence of well-dispersed small Pt nanoparticles with more highly-coordinated Pt surface atoms deposited on the TiO2 anatase. PDC-MSD has been proven to be a more effective method for the preparation of supported metal catalysts, compared to those obtained by conventional impregnation technique

Deposition of Visible Light Active Photocatalytic Bismuth Molybdate Thin Films by Reactive Magnetron Sputtering

Bismuth molybdate thin films were deposited by reactive magnetron co-sputtering from two metallic targets in an argon/oxygen atmosphere, reportedly for the first time. Energy dispersive X-ray spectroscopy (EDX) analysis showed that the ratio of bismuth to molybdenum in the coatings can be effectively controlled by varying the power applied to each target. Deposited coatings were annealed in air at 673 K for 30 min. The crystalline structure was assessed by means of Raman spectroscopy and X-ray diffraction (XRD). Oxidation state information was obtained by X-ray photoelectron spectroscopy (XPS). Photodegradation of organic dyes methylene blue and rhodamine B was used for evaluation of the photocatalytic properties of the coatings under a visible light source. The photocatalytic properties of the deposited coatings were then compared to a sample of commercial titanium dioxide-based photocatalytic product. The repeatability of the dye degradation reactions and photocatalytic coating reusability are discussed. It was found that coatings with a Bi:Mo ratio of approximately 2:1 exhibited the highest photocatalytic activity of the coatings studied; its efficacy in dye photodegradation significantly outperformed a sample of commercial photocatalytic coating

Enhanced properties of photocatalytic titania thin films via doping during magnetron sputter deposition

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