Transformed construction from type-II WO3/BaTiO3 heterojunction to Z-scheme WO3/Ba0.5Sr0.5TiO3 and WO3/SrTiO3 photocatalytic systems: Enhanced photocatalytic activity and mechanism insight

In this study, type-II heterojunction WO3/BaTiO3 and Z-scheme WO3/SrTiO3 or WO3/Ba0.5Sr0.5TiO3 nanocomposite photocatalysts were constructed for photodegradation of organic pollutants in wastewater under visible light. The photocatalytic performance of three WO3/titanate systems were estimated. Some influencing factors such as molar ratio of WO3 and titanates, light irradiation time, catalyst dose, and initial concentration of organic pollutants on the photocatalytic activity were investigated. The stability and reusability of three WO3/titanates systems were examined. Moreover, the production of some radicals in the three WO3/titanates photocatalytic systems was demonstrated, and the three WO3/titanates photocatalytic reaction mechanisms were compared. The results reveal that the configurations of WO3/titanates photocatalytic systems are transformed from type-II heterojunction WO3/BaTiO3 with lower activity to Z-scheme WO3/SrTiO3 and WO3/Ba0.5Sr0.5TiO3 with higher activity via the change of titanates. The WO3/titanate nanocomposites show higher photocatalytic activity at 3.0:1.0 molar ratio of WO3 and titanates, and WO3/Ba0.5Sr0.5TiO3 nanoparticles have superior photocatalytic activity. The order of photocatalytic activity is as follows: WO3/Ba0.5Sr0.5TiO3 > WO3/SrTiO3 > WO3/BaTiO3. Several organic pollutants, such as rhodamine B, methyl parathion, direct brilliant yellow-4R, and methylene blue, can be efficiently degraded using WO3/Ba0.5Sr0.5TiO3 under visible light, and the RhB has higher degradation rate. After four cycles, WO3/titanate nanocomposites still have relatively high stability and reusability. •OH plays a major role in three WO3/titanates photocatalytic degradation. It is expected that the Z-scheme WO3/Ba0.5Sr0.5TiO3 photocatalytic technology creates a good foreground for disposing of dyes and pesticides in water and wastewater.