Filmes finos de WO3 modificados com nanopartículas metálicas: propriedades ópticas, estruturais e fotoeletrocatalíticas para a degradação de progesterona em meio aquoso sob irradiação visível

Abstract

In this work, WO3 thin films were synthesized by the drop-casting method, calcined (500 °C for 2h) and theirs surfaces were modified with silver (Ag0) and platinum (Pt0) nanoparticles by photoreduction. The X-ray diffraction (XRD) analysis associated with the Rietveld refinement showed that WO3 films indicate a monoclinic structure. The chemical composition analysis by energy dispersive X-ray spectroscopy (EDS) confirmed the presence of silver and platinum metals on the films surface. Scanning electron microscopy (SEM) images revealed that the films consist of spherical nanoparticles and thickness ~ 1 μm. The optical characterization showed that films have transmittance at ca. 85% in the visible region. The band gap energy (EBG) of the films was estimated by the TAUC method, compared to WO3 powder. Photoelectrochemical properties investigated in aqueous solution Na2SO4 0.1 mol L-1 in the absence of light and under polychromatic irradiation revealed photoelectrochemical behavior typical of n-type semiconductor. Films modified with metallic nanoparticles obtained anodic photocurrent density close to 2.5 times compared to unmodified WO3 at 0.8 V vs. Ag / AgCl. This increase in the photocurrent values attributed to plasmonic effect of the metals, which increases charges separation and recombination lifetime. The recombination lifetime was evaluated by transient current. The films were used as photocatalysts in the degradation of the hormone progesterone (0.35 mg L-1) into aqueous solution in the configurations of heterogeneous photocatalysis (HP) and electrochemically assisted heterogeneous photocatalysis (EHP). After 3h of irradiation, in the EHP configuration, WO3 films modified obtained better catalytic activity and a photostability were maintained after 5 cycles of reuse. The results demonstrate that the application of the potential on the modified WO3 electrodes minimizes recombination of the charge carriers and increase the photocatalytic activity. Therefore, WO3 is a promising material for applications in other processes involving solar energy conversion.