TiO 2 -Based Composites for Water Decolorization

Photocatalysis, being a sustainable and environmentally friendly technology with potential for low-cost applications, is one of the most researched methods for dye decolourization. Among the various photocatalysts available, TiO2 is a highly efficient and stable photocatalyst. Even though reports of scientific studies on the use of TiO2 dates to 1930s, wider attention and numerous studies on its application as a photocatalyst for environmental remediation started after the study by Fujishima and Honda in 1972. The use of pure TiO2 as photocatalyst is limited due to its high band gap energy and recombination rate. Also, the photo excitation of TiO2 is in the ultraviolet (UV) range and consequently, only 5% of the total solar energy could be utilized for photocatalysis with pure TiO2. Another limiting factor affecting the efficiency of degradation is mass transport limitation and agglomeration of the photocatalyst. This chapter reviews composites with metals, non-metals, semiconductors, carbon derivatives and other support structure, which are developed to tackle the limitations of photocatalysis with pure TiO2. Metal-doped photocatalysts aid in reduced recombination and visible light photocatalysis. Non-metal doping leads to band gap modification and redshift. Heterojunctions with semiconductors as photosensitizer or electron sinks are possible. Carbon derivative-based composites and support structure-based composites also are studied extensively. Of late, co-modified composites are gaining importance. Overall, this book chapter intends to take the readers through the journey of development and application of TiO2-based photocatalysts for dye degradation with emphasis on composites.