Abstract
Self-organized W/WO3 nanoporous electrodes can be obtained by simple electrochemical anodization of W foil in 0.15 mol L-1 NaF solution as the supporting electrolyte, applying a ramp potential of 0.2 V s-1 until it reached 60 V, which was maintained for 2 h. The monoclinic form is majority in the highly ordered WO3 annealed at 450 °C, obtaining a higher photoactivity when irradiated by visible light than by UV light. The electrode promotes complete discoloration of the investigated basic red 51 dye after 60 min of photoelectrocatalytic oxidation, on current density of 1.25 mA cm-2 and irradiation on wavelength of 420-630 nm. In this condition it was obtained 63% of mineralization. Lower efficiency is obtained for the system irradiated by wavelength (280-400 nm) when only 40% of total organic carbon removal is obtained and 120 min is required for complete discoloration.
Highlights
The aim of the present study is to investigate the capability of W/WO3 semiconductor systems to degrade a basic red 51 dye, used as a model pollutant of hair dye bearing azo groups as chromophore in photoeletrocatalytic system irradiated by both ultraviolet (280-400 nm) and visible (420-630 nm) light
In order to diagnose possible contamination in the synthesis process of the film W/WO3, the prepared electrode was analyzed by energy dispersive X-ray spectroscopy (EDX), revealing the relative intensity of characteristic peaks of oxygen and tungsten identified on the surface
Our findings indicate that W/WO3 thin films can be grown by electrochemical anodization on W foil and it is the base to form photoanodes with uniform nanoparticles of 100 nm
Summary
The use of TiO2 as photoanode in photoelectrocatalytic degradation of pollutants is well known in literature.[1,2,3,4,5,6,7,8,9,10] this material presents band gap energy around 3.2 eV, which is photoexcited only in the ultraviolet region (l ≤ 380 nm).[11,12,13,14] Tungsten trioxide has been an excellent alternative material, since it presents smaller band gap energy (2.4-2.8 eV) and can be photoexcited in the visible region close to the UV region.[15,16,17,18] most of the studies found in literature explore tungsten trioxide only as electrochromic applications and solar energy conversion.[1]. Several techniques for improving photoresponse of thin film electrodes W/WO3 have already been proposed. The electrodeposited Pt/WO3 catalysts have improved the oxidation of methanol and formic acid.[35,36,37,38] The WOx films with Pt, Sn, and Ru dopands were used for electrooxidation of acetaldehyde. Some authors have described the photoelectrocatalytic degradation of Remazol Black B dye, methylene blue and 4-chlorophenol in aqueous solutions by using n-WO3 photoelectrode activated by ultraviolet irradiation.[39,40,41,42] In general, the systems exhibited
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