Morphology- and Phase-Controlled Synthesis of Visible-Light-Activated S-doped TiO2 with Tunable S4+/S6+ Ratio

Abstract In this work, a facile one-pot hydrothermal method was developed to prepare morphology- and phase-controlled S-doped TiO2 with tunable S4+/S6+ ratio. Cheap and convenient metal sulfates were employed as a sulfur source. The metal ions from the sulfates were not doped into TiO2, while they did promote S4+ generation and S4+/S6+ co-doping during the preparation process. Meanwhile, SO42- ions not only acted as a sulfur source,but also controlled the morphology and crystalline phase. The S4+/S6+ ratios of the sulfur-doped TiO2 prepared with Na2SO4, ZnSO4·7H2O, MnSO4·H2O and Fe2(SO4)3 were 1:4.9, 1:5.1, 1:5.2 and 1:5.5, respectively. The visible light photocatalytic efficiency for ciprofloxacin (CIP) degradation of S4+/S6+ co-doped samples was influenced by S4+/S6+ ratio. All of the S4+/S6+ co-doped samples showed enhanced activity compared with S6+ mono-doped TiO2 and undoped TiO2. It can be due to the synergistic effect of the crystalline phase, morphology and S4+/S6+ ratio, of which the S4+/S6+ratio may play the more important role. The TiO2 photocatalyst with a S4+/S6+ ratio of 1:5.5 exhibited the highest visible light photocatalytic efficiency to degrade ciprofloxacin (CIP), which was 2.3 and 8.0 times that of S6+ mono-doped and undoped TiO2, respectively.