Modification of TiO 2 by Er 3+ and rGO enhancing visible photocatalytic degradation of arsanilic acid.

As a typical wide band gap photocatalyst, titania (TiO 2 ) cannot use the visible light and has fast recombination rate of photogenerated electron-hole pairs. Simultaneous introduction of erbium ion (Er 3+ ) and graphene oxide (rGO) into TiO 2 might overcome these two drawbacks. In this study, Er 3+ and rGO were co-doped on TiO 2 to synthesize Er 3+ -rGO/TiO 2 photocatalyst through a two-step sol-gel method. Based on the UV-visible diffuse reflectance spectra and photoluminescence spectrum, the introduction of Er 3+ and rGO increased the visible light absorption efficiency and enhanced the migration of photogenerated electron. Pure TiO 2 has almost no photocatalytic activity for arsanilic acid (p-ASA) degradation under visible light irradiation. However, while doping with 2.0 mol% Er 3+ and 10.0 mol% rGO, the p-ASA could be completely degraded within 50 min by the Er 3+ -rGO/TiO 2 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 (O 2 •- ) and singlet oxygen ( 1 O 2 ) were the dominant ROS for the oxidation of p-ASA and arsenite. This work provides an approach of introducing Er 3+ and rGO to enhance the visible light photocatalytic efficiency of TiO 2 .