Modification of TiO₂ by Er³⁺ and rGO enhancing visible photocatalytic degradation of arsanilic acid

As a typical wide band gap photocatalyst, titania (TiO₂) cannot use the visible light and has fast recombination rate of photogenerated electron-hole pairs. Simultaneous introduction of erbium ion (Er³⁺) and graphene oxide (rGO) into TiO₂ might overcome these two drawbacks. In this study, Er³⁺ and rGO were co-doped on TiO₂ to synthesize Er³⁺-rGO/TiO₂ photocatalyst through a two-step sol-gel method. Based on the UV-visible diffuse reflectance spectra and photoluminescence spectrum, the introduction of Er³⁺ and rGO increased the visible light absorption efficiency and enhanced the migration of photogenerated electron. Pure TiO₂ has almost no photocatalytic activity for arsanilic acid (p-ASA) degradation under visible light irradiation. However, while doping with 2.0 mol% Er³⁺ and 10.0 mol% rGO, the p-ASA could be completely degraded within 50 min by the Er³⁺-rGO/TiO₂ photocatalyst under visible light irradiation, and most of produced inorganic arsenic was in situ removed by adsorption from the solution. The reactive oxygen species (ROS) reacting with p-ASA was determined and superoxide radical (O₂^•-) and singlet oxygen (¹O₂) were the dominant ROS for the oxidation of p-ASA and arsenite. This work provides an approach of introducing Er³⁺ and rGO to enhance the visible light photocatalytic efficiency of TiO₂.