Photocatalytic reduction of triclosan on Au–Cu2O nanowire arrays as plasmonic photocatalysts under visible light irradiation

Abstract

Triclosan (TCS) is a potential threat to the environment and human health. Photocatalysis can be used to degrade TCS, but the photocatalytic efficiency is usually limited by the photoabsorptivity and photostability of the photocatalyst. In addition, some toxic by-products might also be generated during photocatalytic processes. In this study, we prepared Au-coated Cu₂O nanowire arrays (Au–Cu₂O NWAs) by beam sputtering Au onto Cu₂O nanowires grown from a Cu foil. We found that photocatalytic degradation of TCS under visible light (420 nm < λ < 780 nm) irradiation and Au–Cu₂O NWAs had several advantages. Au–Cu₂O NWAs had good photoabsorptivity, high photostability (negligible activity loss after 16 runs), excellent photocatalytic activity (47.6 times faster than that of Cu₂O), and low yield of dichlorodibenzo-dioxins/dichlorohydroxydibenzofurans. The degradation intermediates were identified as chlorophenoxyphenol, phenoxyphenol, chlorophenol, catechol, phenol, benzoquinone, and lower volatile acids. We developed the degradation pathway of TCS which follows electron reduction and then oxidation by reactive oxygen species. The mechanism was developed and strengthened using the radical trapping and other measurements. The unusual mechanism and photostability of Au–Cu₂O NWAs were attributed to the Au/Cu₂O/Cu “sandwich”-like structure. This structure yields a sustained and steady internal electric field, raises the conduction band of Cu₂O, reinforces the reductive activity of the photo-generated electrons, and eliminates the photo-generated holes that are responsible for the photo-etching of Cu₂O.