Platinized WO3 as an Environmental Photocatalyst that Generates OH Radicals under Visible Light

Abstract

This study aims to understand the visible light photocatalytic activities of platinized WO₃ (Pt/WO₃) on the degradation of aquatic pollutants and the role of main photooxidants. The presence of Pt on WO₃ is known to facilitate the multielectron reduction of O₂, which enables O₂ to serve as an electron acceptor despite the insufficient reduction potential of the conduction band electrons (in WO₃) for the one-electron reduction of O₂. The concurrent oxidative reactions occurring on WO₃ were markedly enhanced in the presence of Pt and accompanied the production of OH radicals under visible light, which was confirmed by both a fluorescence method (using a chemical trap) and a spin trap method. The generation of OH radicals mainly comes from the reductive decomposition of H₂O₂ that is produced in situ from the reduction of O₂ on Pt/WO₃. The rate of in situ production of H₂O₂ under visible light was significantly faster with Pt/WO₃ than WO₃. Six substrates that were tested for the visible light (λ > 420 nm) induced degradation on Pt/WO₃ included dichloroacetate (DCA), 4-chlorophenol (4-CP), tetramethylammonium (TMA), arsenite (As(III)), methylene blue (MB), and acid orange 7 (AO7). The degradation (or conversion) of all six substrates was successfully achieved with Pt/WO₃ and the role of OH radicals in Pt/WO₃ photocatalysis seemed to be different depending on the kind of substrate. In the presence of tert-butyl alcohol (TBA: OH radical scavenger), the photocatalytic degradation was markedly reduced for 4-CP or completely inhibited for DCA and TMA whereas that of As(III), MB, and AO7 was little affected. Pt/WO₃ photocatalyst that oxidizes various substrates under visible light with a sufficient photostability can be applied for solar water treatment.