Nonmetal-metal-semiconductor-promoted P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst with superior photocatalytic activity and stability

Recently, modifying TiO2 to develop visible-light-driven photocatalysts via doping with nonmetal elements, metals and semiconductors has attracted much attention. In this study, a facile and reproducible sol-gel method was utilized for the first time to codope nonmetal (P), metal (Ag) and narrow band gap semiconductors (Ag2O and Ag3PO4) in TiO2 to prepare a P/Ag/Ag2O/Ag3PO4/TiO2 composite photocatalyst for developing a novel visible-light-driven photocatalyst. The crystal structure, morphology and optical properties of P/Ag/Ag2O/Ag3PO4/TiO2 were systemically characterized, and the photocatalytic abilities were evaluated under simulated solar light, in comparison with pure TiO2 and Ag/Ag2O/TiO2 photocatalysts. The results indicated that the P/Ag/Ag2O/Ag3PO4/TiO2 composite photocatalyst exhibited a strong absorption band in the visible light region, a small band gap (about 2.2 eV) and extremely high separation efficiency of photo-excited electron-hole pairs, which could account for its enhanced photocatalytic performance. The degradation ratio of rhodamine B (Rh B) by P/Ag/Ag2O/Ag3PO4/TiO2 reached 97.1% after 60 min under simulated solar light with only 13 mW cm(-2) light intensity, while just 26.6% and 66.7% of Rh B were degraded by the as-prepared TiO2 and Ag/Ag2O/TiO2 photocatalysts, respectively. Furthermore, the radical trapping experiments implied that photo-generated holes and O-2 is approximately equal to radicals in the P/Ag/Ag2O/Ag3PO4/TiO2 composite photocatalyst were the major active species for Rh B degradation. Metallic Ag could effectively trap the photo-generated electrons from Ag3PO4 and Ag2O to reduce the possibility of decomposing Ag3PO4 and Ag2O, resulting in an improved stability of the P/Ag/Ag2O/Ag3PO4/TiO2 composite with high photocatalytic ability.