Enhanced Photodegradation of Synthetic Dyes Mediated by Ag3PO4-Based Semiconductors under Visible Light Irradiation

Abstract

Four silver phosphate-based materials were successfully synthesized, characterized, and evaluated, together with TiO2, in the photodegradation of synthetic dyes (tartrazine, Orange II, rhodamine, and Brilliant Blue FCF) under two irradiation sources centered at 420 and 450 nm. Scanning Electron Microscopy (SEM) images showed different topologies of the synthesized materials, whereas diffuse reflectance spectra demonstrated that they display absorption up to 500 nm. Degradation experiments were performed in parallel with the silver materials and TiO2. Upon irradiation centered at 420 nm, the abatement of the dyes was slightly more efficient in the case of TiO2—except for Orange II. Nevertheless, upon irradiation centered at 450 nm, TiO2 demonstrated complete inefficiency and silver phosphates accomplished the complete abatement of the dyes—except for Brilliant Blue FCF. A careful analysis of the achieved degradation of dyes revealed that the main reaction mechanism involves electron transfer to the photogenerated holes in the valence band of silver photocatalysts, together with the direct excitation of dyes and the subsequent formation of reactive species. The performance of TiO2 was only comparable at the shorter wavelength when hydroxyl radicals could be formed; however, it could not compete under irradiation at 450 nm since the formed superoxide anion is not as reactive as hydroxyl radicals.