Deposition of nanoporous BiVO4 thin-film photocatalyst by reactive magnetron sputtering: Effect of total pressure and substrate

International audienceNanoporous BiVO4 thin films were deposited using reactive magnetronsputtering in Ar and O2 atmosphere, on various substrates,employing pulsed direct-current (DC) power supplies applied tometallic Bi and V targets for rapid deposition. The procedure wasfollowed by a post-annealing treatment in air to crystallize thephotoactive monoclinic scheelite structure. The influence of totalpressure and substrate on the crystal structure, morphology,microstructure, optical and photocatalytic properties of the filmswas investigated. The crystallization of monoclinic scheelitestructure deposited on fused silica substrate starts at 250 °C andthe films are stable up to 600 °C. The morphology of the films israther dense, despite at the high sputtering pressure (>2 Pa),with embedded nanopores. Among the thin films deposited on fusedsilica, the one deposited at 4.5 Pa exhibits the highest porosity(52%), with the lowest bandgap (2.44 eV) and it shows the highestphotocatalytic activity in the degradation of Rhodamine-B (26%after 7 h) under visible light irradiation. The film deposited onthe silicon substrate exhibits the highest photoactivity (53% after7 h). Lack of hypsochromic shift in the UV−Vis temporal absorptionspectra shows the dominance of the chromophore cleavage pathway inthe photodecomposition

Reactive magnetron sputtered BiVO4 thin film as an efficient visible light photocatalyst

International audience

Nanoporous BiVO4 thin film deposition by reactive magnetron sputtering

International audience

Reactive magnetron sputtered BiVO4 thin film as an efficient visible light photocatalyst

International audienceHaving strong photoactivity under visible light, BiVO4 thin film is considered a great candidate to replace low efficient UV-active photocatalysts e.g. TiO2, and to reduce recyclability and reusability problems of powder photocatalysts. In this research, BiVO4 thin films were deposited on fused silica substrate using reactive magnetron sputtering employing metallic Bi and V targets, followed by a post-annealing treatment for 2 h at 450 ̊C, which is relatively high compared to Bi melting point (271 ̊C), to obtain nanoporous morphology based on Kirkendall effect. The thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and ultraviolet-visible-infrared spectroscopy (UV- Vis-IR). The XRD data showed that the as-deposited films were amorphous, and after the post-annealing treatment, the monoclinic scheelite BiVO4 crystal structure was obtained. FESEM observations exhibited nanopores with an average diameter of 20-40 nm. UV-Vis spectrophotometry results proved light absorption in the visible region with a bandgap value of 2.45 eV. The thin film managed to photodegrade 80 % of Rhodamine-B solution after 7 h, showing the great photoactivity of BiVO4 thin films. These results established that the combination of reactive magnetron sputtering and post-annealing treatment is an effective technique to produce nanoporous BiVO4 thin films with great potential in photocatalysis for water treatment applications using solar energy

Ag-Doped BiVO4 Thin Films Deposited by Reactive Magnetron Sputtering as Visible Light Photocatalysts

International audienceIn this study, the Ag-doped monoclinic BiVO4 thin films weresynthesized with a reactive magnetron sputtering technique and apost-annealing treatment. The X-ray diffraction and scanningelectron microscopic analysis exhibited the formation of silvervanadate and metallic silver phase with various quantitiesdepending on Ag loading. The photocatalytic experiments establishedthe importance of Ag distribution in photoactivity enhancementsince the heterojunctions between the phases are responsible forthe charge separation. It was also proved that Ag-doping improvesthe photoactivity of monoclinic BiVO4 at neutral pH by favoring thechromophore cleavage pathway in the photodegradation mechanism,which is a significant advantage over the pristine BiVO4 beingoptimal at acidic pH

Enhanced photocatalytic activity of sputter-deposited nanoporous BiVO4 thin films by controlling film thickness

International audienceIn this study, nanoporous BiVO4 thin films were deposited using reactive direct-current (DC) magnetron sputtering. The effects of thickness on the film morphology, crystal structure, microstructure, composition, optical and photocatalytic properties under visible light were investigated. The film porosity and refractive index were also determined via the UV-Vis spectrophotometric technique using transmittance and reflectance spectra and Cauchy dispersion law as the fitting model. The nanoporous morphology was observed using field-emission scanning electron microscopy (FESEM) with average pore sizes in the 20–40 nm range. The X-ray diffraction (XRD) results showed different texture grades corresponding to the (040) crystallographic plane, establishing the film thickness influence on the preferential orientation. The X-ray photoelectron spectroscopy (XPS) was also implemented to investigate the chemical state of the film surface, as well as to determine the valence band position. The film 715 nm in thickness showed the highest porosity (52%), narrowest bandgap (2.44 eV), highest exposed (040) crystallographic plane and highest visible-light-driven photodegradation towards Rhodamine-B (RhB) solution. The pH of the solution also impacted the RhB photodegradation which was optimum at pH 3 with chromophore cleavage pathway dominance, whereas at neutral pH it had distinctively slow kinetics probably due to poor electrostatic interactions and the N-deethylation kinetics bottleneck. The photocatalytic cycle experiments exhibited high stability and recyclability of BiVO4 thin-film photocatalysts after four cycles (4 ×7 h) of exploitation. The photocatalytic mechanism was determined using scavengers and the significance of hydroxyl radicals and photogenerated holes were established. The photocatalytic activity reached 97% after 7 h of illumination with a 400 W light source

Preparation of sputter-deposited Cu-doped BiVO4 nanoporous thin films comprised of amorphous/crystalline heterostructure as enhanced visible-light photocatalyst

International audienceThe synthesis of Cu-doped BiVO4 nanoporous thin films with various Cu contents was performed using reactive magnetron sputtering to prepare a stable and inexpensive photocatalyst with high photoactivity under visible light for wastewater treatment applications. The X-ray diffraction (XRD) analysis showed exclusively the formation of the photoactive monoclinic BiVO4 phase up to 17 at.% Cu. Beyond, a Cu-based compound crystallizes in addition to the BiVO4 monoclinic phase. The field-emission scanning electron microscopy (FESEM) and elemental mappings results revealed the formation of shard-like nodules composed of V, O and Cu in the films having less than 6 at. % Cu. From 6 at. % Cu, the morphology appears more homogeneous. X-ray photoelectron spectroscopy (XPS) showed the presence of Cu2+ and Cu+, as well as the rise of V4+/V5+ ions. Transmission electron microscopy (TEM) verified the amorphous structure of the Cu-O-V phase, as well as demonstrated the crystallographic interplanar spacings of BiVO4. The thin film with a 2 at. % Cu exhibited superior photoactivity (100, 99 and 63 %) over pristine BiVO4 in photocatalytic dye degradation (Rhodamine-B, Methylene Blue and Methyl Orange). The thin films’ stability, recyclability and reusability were demonstrated in the recycling experiment, and the crucial role of photogenerated charge carriers and hydroxyl radicals was identified in the experiment involving scavengers. The photocatalytic performance towards various dye pollutions at acidic, basic and neutral pH conditions is also discussed in detail