Enhanced photocatalytic activity of electrosynthesised tungsten trioxide–titanium dioxide bi-layer coatings under ultraviolet and visible light illumination

Bi-layer WO3–TiO2 coatings have been synthesised on stainless steel (SS) substrates by consecutive cathodic electrodeposition of WO3 (from peroxytungstate solutions) and TiO2 electrosynthesis (from titanium oxosulfate solutions). The resulting TiO2–WO3/SS photoelectrodes have been screened for their photoresponse under ultraviolet (UV) and visible (vis) light illumination by photovoltammetry in supporting electrolyte (sodium sulfate) and malachite green (a typical dye) solutions. They were also evaluated for malachite green photooxidation during constant potential bulk photoelectrolysis. It was found that both photocurrent values and dye removal rates were higher at TiO2–WO3/SS than at plain WO3/SS photoelectrodes, under both UV and vis illumination (up to 85% and 67% malachite green degradation has been achieved respectively from its 10 ppm solutions after 2 h). The enhancement of the UV and, as reported here for the first time, vis photocatalytic activity of WO3 by the inclusion of TiO2 is interpreted by reduced electron-hole recombination rates due to electron transfer from TiO2 to WO3 (during UV activation) and hole transfer from WO3 to TiO2 (during UV and vis light activation).