Preparation of WO3-modified TiO2 thin film by peroxo sol–gel method and its photocatalytic activity in degradation of methylene blue

Abstract

A series of WO₃-modified TiO₂ sols with various WO₃ contents were synthesized by peroxo sol–gel method using H₂O₂ as the agent. The as-synthesized WO₃-TiO₂ sols were light yellow in color. The maximum amount of WO₃ which could be incorporated into the TiO₂ sol was 4?wt.%. The pH values of the as-prepared sols were near neutral. These sols were very stable even after 2?years in stock. The sols were used to coat on glass substrate. The XRD patterns and the SAED patterns indicated that the phase of TiO₂ was anatase. There were no characteristic XRD peaks of WO₃ in the WO₃-modified TiO₂ sol, possibly due to low WO₃ loading. The particles were rhombus shaped with the major axis and minor axis of 30–77?nm and 15–31?nm, respectively. WO₃ was incorporated into the surface structure of TiO₂ and modified the electronic state of Ti. The film coated onto glass substrate was very uniform, and the film thickness was?~?160?nm. The XPS results exhibited that W existed as 5?+?and 6?+?oxidation states and Ti existed in Ti³⁺ and Ti⁴⁺. These four chemical states play a role of gathering the photogenerated holes and capturing the photogenerated electrons in the lower conduction band of WO₃, respectively. This can effectively enhance the separation rate of photogenerated electron–hole pairs and increase the photoactivity. WO₃/TiO₂ samples had high photocatalytic activity under UV light illumination to degrade methylene blue, because it had high OH and O^2? group contents.