Estudos Fotoeletroquímicos de filmes de WO3 e WO3/CuWO4 para aplicação na degradação dos corantes azul de metileno e alaranjado de metila

Abstract

Tungsten trioxide (WO3) and copper tungstate (CuWO4) have been extensively investigated as photocatalysts for application in the degradation of organic pollutants. However, these two semiconductors used individually have properties such as high resistance to charge transport and rapid recombination that provide their potential in photoelectrocatalysis application. Aiming to circumvent the inferiorities of these oxides, studies have been carried out with the supported material in the form of films. Therefore, this work presents an in situ method for the preparation of heterostructured film WO3/CuWO4 for application in photoelectrocatalysis of organic pollutants. Stable films of WO3/CuWO4 have been successfully prepared on transparent conductive glass (FTO-glass) using hydrothermal methods. The X-ray diffraction (XRD) analysis showed that the material presents monoclinic phases for WO3 and triclinic for CuWO4. Scanning electron microscopy (SEM) images revealed that the heterojunction films are formed by the oxides in the form of plates of about 2 μm, grown perpendicularly on FTO-glass. Optical characterizations revealed that WO3/CuWO4 films calcined at 500 oC have band gap energy (EBG) of 2.62 eV, while WO3 films treated at the same temperature have an EBG of 2.76 eV. In photoelectrochemical studies, WO3 showed high photocurrent values, reaching 400 μA cm-2 (vs Ag/AgCl), in the inert electrolyte. WO3 and WO3/CuWO4 films were used for photodegradation of 1x10-6mol.L solutions of methylene blue (AzM) and methyl orange (AM) in Heterogeneous Photocatalysis (FH), Electrochemically Assisted Heterogeneous Photocatalysis (FHE) and Photolysis configurations. Superior results were observed for both films in the FHE configuration, with a degradation of 84.90% and 30.50% with the WO3 film for the AzM and AM dyes, respectively, and in the heterojunction there was 83.30% and 29.90%. In the investigation of the relative stability through chronoamperometry in a time of 4 hours of irradiation, it was observed that the WO3/CuWO4 films had a superior stability, suggesting that this photoanode has application potential for degradation of organic pollutants in aqueous environments.