Highly efficient photocatalysis toward tetracycline under simulated solar-light by Ag+-CDs-Bi2WO6: Synergistic effects of silver ions and carbon dots

A novel Ag+-carbon dots (CDs)-Bi2WO6 ternary composite with excellent solar-light-driven photocatalytic performance was firstly synthesized using hydrothermal-impregnation method. It was used to degrade tetracycline (TC) in water. 5Ag(+)-CDs2.5-Bi2WO6 (0.5 g/L) displayed superior photocatalytic efficiency with nearly 100% removal of TC (20 mg/L) in 20 min and 64% mineralization in 90 min. The degradation reaction coefficient (k(obs)) was approximately 1.8 times higher than pure Bi2WO6 as a result of the synergistic effects of Ag+ and CDs co-doped on the surface of Bi2WO6. Both CDs and Ag+ could effectively trap the photoexcited electrons generated by Bi2WO6, promoting the charge transfer and separation of electron-hole pairs. In addition, after accepting the electrons, Ag+ was photoreduced to Ag attached to Bi2WO6 nanosheets. The plasmonic-Ag and CDs displayed stronger utilization of visible light capacities. Moreover, Ag+ itself also served as an oxidant to degrade TC in water directly. Electron transfer mainly occurred in the order of Bi2WO6 -> Ag -> CDs. Superoxide radical species and photogenerated holes were predominant reactive species responsible for the photodegradation of TC. The study indicated that novel Ag+-CDs-Bi2WO6 has a great potential for rapid and efficient treatment of organic pollutants in water. (C) 2016 Elsevier B.V. All rights reserved.