Filmes com heterojunção de Fe2O3 e WO3: efeito relativo das posições das bordas das bandas de condução na fotocorrente e degradação de RhB sob irradiação policromática

Abstract

In the search for efficient and low cost processes for wastewater treatment many methods have been investigated in the literature. Among them, the Advanced Oxidative Processes (AOPs) using semiconductor oxides in suspension or immobilized in the form of films has been receiving great attention due to efficiency in the degradation of several pollutants.In this work dissertation, photoanodes were fabricated with the heterojuntion of Fe2O3 films by hydrothermal method, heat-treated in an autoclave at 120 ºC for 1 h, modified with WO3 by the drop-casting method and taken to thermal treatment (500 ° C for 2 h) in each deposition. The photoanodes were prepared on conducting substrate in two different configurations (FTO|Fe2O3|WO3 and FTO|WO3|Fe2O3) were used with photo catalysts for removal of Rhodamine B (RhB) dye. X-ray diffraction (XRD) analyzes associated with the Rietveld refinement shown that the heterojunction films have a trigonal structure corresponding to α-Fe2O3 (hematite) and a monoclinic structure to γ-WO3, also presented Fe:SnO2 phase. The morphological study by FEG-SEM revealed that the films are formed by structure of nanorods and thickness ranging from 670 to 1250 nm. The optical characterization of the films showed a band gap energy (EBG) estimated by the TAUC method corresponding to the region of the visible. Photoelectrochemical properties were investigated in aqueous solution 0.1 mol L-1 of Na2SO4 in the absence of light and under polychromatic irradiation. Linear sweep voltammograms data were used with Bultler-Gärtner equation to estimated the conduction band (CB) edge position of the films. The photoanodes exhibited photoeletrochemical behavior of n-type semiconductors when irradiated. The modified films obtained an anodic photocurrent density values about 3.0 to 5.0 times higher than the Fe2O3 film (~3.0 μA cm-2) in 0.7 V (vs. Ag / AgCl). In comparison to the Fe2O3 film an increase of the photocurrent was observed in the heterostructured films. This increase was attributed to the synergistic effect of WO3 on heterojunction. From this study, films were used as photocatalysts in the degradation of 5.0 μmol L-1 Rhodamine B (RhB) dye aqueous solution in the configuration of heterogeneous photocatalysis (HP) and heterogeneous photocatalysis electrochemically assisted photocatalysis (EHP). After 3h of irradiation, FTO|WO3|Fe2O3 film in the EHP configuration showed better photocatalytic activity in the degradation of the RhB (~29%). The results demonstrated that the application of the potential bias in electrodes FTO|WO3|Fe2O3 heterojuntion minimizes recombination of the photogenerated charge carriers and increase the photocatalytic activity. However, FTO|WO3|Fe2O3 heterojuntion films show great configuration and can be used in photocatalysis and another solar energy conversion process.