Dual heterojunction-based Au@TiO2 photoelectrode exhibiting efficient charge separation for enhanced removal of organic dye under visible light

Abstract

An inventive strategy that involves photo-deposition of Au nanoparticles (NPs) on the flower-like TiO₂ nanomicrospheres with co-exposed {001} and {101} facets was reported to construct an advanced visible-light responsive Au@A-FH TiO₂/Ti photoelectrode. The plasmonic Au NPs lead to the effective utilization of visible light. The plasmonic Au NPs generate hot e⁻ under visible light and then ransferred to TiO₂ through the Au/TiO₂ Schottky junction, which finally reach the Ti substrate along the {001}/{101} facet heterojunction (FH). The in situ Kelvin probe force microscopy (KPFM) technology measured the high-resolution contact potential difference (CPD) images between the single Au NP region and the surrounding TiO₂ under the visible light, indirectly visualizing the different electron transfer directions between single Au NP and TiO₂. Quantitative calculations revealed improved light absorption, charge separation, and surface charge injection efficiency due to the presence of dual heterojunctions (Au/TiO₂ Schottky junction and {001}/{101} FH), which together account for high PEC efficiency. The obtained Au@A-FH TiO₂/Ti shows high PEC performance under visible light, achieving almost 100% removal of methyl orange (MO) within 2 h. This study provides a set of reliable experimental evidence to verify the electron transfer direction and photoelectrocatalytic mechanism and also offers a new avenue for the design of an efficient TiO₂-based visible-light responsive photoelectrode.