Review of the sol–gel method in preparing nano TiO2for advanced oxidation process

Application of nano titanium dioxide (TiO2) in various fields such as advanced oxidation process (AOP) has led to the development of its preparation technologies. The sol–gel process is a widely used chemical wet method for preparing nanoscale TiO2gels. This technique offers numerous advantages, such as the potential to produce large quantities of homogeneous materials with high purity, surface area, porosity, and reactivity, as well as being cost-effective, simple to implement, and capable of controlling the size and shape of the resulting particles. This review provides a comprehensive overview of the chemicals, reaction conditions, and procedures required for preparing nano TiO2using the sol–gel method. It covers the selection of necessary compounds, such as TiO2precursors, solvents, hydrolysis agents, and additives, along with their composition and sequences of adding, reaction order, and impact on the final product. Additionally, it provides detailed information on the routes of gel formation and ambient conditions, including temperature, humidity, stirring speed, injection rates of compounds, aging process, and storage conditions. This information serves as a basic reference for understanding the sol–gel process and the relative contribution rates of the influencing factors, which is essential for controlling the size, morphology, crystallinity, and other physicochemical properties of the resulting TiO2gel/powder for targeted applications.