Synthesis of CaWO 4  as a photocatalyst for degradation of methylene blue and carmine under ultraviolet light irradiation

Abstract

Due to its advantages of high efficiency, simplicity of operation, and no secondary pollution, photocatalysis is considered as a promising method for wastewater treatment. Most synthesized photocatalysts are structure complex and costly. Thus, in this study, a novel CaWO4 sample was synthesized by a co-precipitation method in one step and proved as a preferable photocatalytic material by a series of characterization methods. The synthesized CaWO4 can be used as a catalyst to degrade dyes as methylene blue (MB) and carmine (CR), under UV light without the addition of oxidants. The effects of water matrix, including pH value, solid-liquid ratio, light intensity, and initial concentration of pollutants on photocatalytic degradation were studied. According to the results of scavengers experiments, holes and hydroxyl radicals dominate the degradation of MB while hydroxyl radical and superoxide anion are mainly responsible for the degradation of CR. Furthermore, i-t curves demonstrate the CaWO4 has good photoelectric response capability. It means that photogenerated electrons generated on the surface of the CaWO4 can form electron hole pairs, thereby forming hydroxyl radical and superoxide anion to degrade dyes. In addition, the CaWO4 has good cycling performance in the process of degrading MB. Results indicate that minerals-based photocatalyst can be synthesized in one step by simple coprecipitation and exhibit good photocatalytic effect. It provides a new idea for the study of photocatalytic degradation of dyes by mineral-like materials.