Plasma-promoted Au/TiO2 nanocatalysts for photocatalytic formaldehyde oxidation under visible-light irradiation

As a promising plasmonic photocatalyst under visible-light irradiation, Au/TiO2 nanocatalyst commonly suffers from risk of Au nanoparticles aggregation and relatively long activation period by using the conventional calcination activation method. We report here that a short-term O2 plasma treatment enables the Au/TiO2 catalyst to exhibit higher visible-light photocatalytic activity for formaldehyde (HCHO) oxidation compared with the calcination activated sample. X-ray photoelectron spectroscopy characterization suggests that Au/TiO2 catalyst activated by O2 plasma achieves metallic Au content of 72.4% and surface oxygen species content of 29.8%, which not only lead to rapid reduction of cationic Au in HCHO oxidation but also facilitate the preliminary oxidation of HCHO to dioxymethylene and formate on catalyst surface. UV–vis diffuse reflectance spectra, photoluminescence spectra and diffuse reflectance infrared Fourier transform spectra measurements indicate that O2 plasma activated Au/TiO2 catalyst presents an enhanced visible-light absorption and surface charge transfer efficiency in HCHO oxidation, which accelerates the formation of superoxide (O2−) and OH radicals via hot electron transfer mechanism under visible-light irradiation, remarkably promoting formate oxidation to carbonate, carbonate decomposition and thus HCHO oxidation.