Non-metal doped ZnO and TiO2 photocatalysts for visible light active degradation of pharmaceuticals and hydrogen production: A review

Abstract

The increasing presence of pharmaceuticals in water bodies has become a major environmental concern. In addition, the need of sustainable and renewable energy resources has highlighted the importance of hydrogen production via water splitting as clean, green and an efficient alternative to fossil fuels. Photocatalysis has emerged as an effective technique for environmental remediation and clean and green energy production. Both ZnO and TiO 2 are the promising photocatalysts in this regard. However, due to their wide bandgap and limited visible light absorption capacity, the effectiveness of ZnO and TiO 2 photocatalysts is hindered under visible light irradiation. Non-metal doping to ZnO and TiO 2 is an effective strategy to address these limitations. Hence, this review focused on the degradation of pharmaceuticals and hydrogen evolution using non-metal doped ZnO and TiO 2 -based visible light active photocatalysts. The non-metals doped ZnO and TiO 2 photocatalysts showed improved degradation of pharmaceuticals under visible light irradiation. In addition, these visible light active nanomaterials have also been shown to produce hydrogen at appreciable rates via water splitting. The fundamental principle of photocatalysis including mechanism of electron-hole pair formation, charge separation and various surface reactions have been explored. The role of non-metals doping in increasing the visible light photocatalytic activity of ZnO and TiO 2 has been explored. Furthermore, the various methods of preparation such as sol-gel, hydrothermal, co-precipitation and microwave assisted have been discussed. This review provides a comprehensive understanding of the current state of non-metal doped ZnO and TiO 2 , knowledge gap and future research directions. • The synthesis methods of non-metal doped ZnO and TiO 2 have been reviewed. • The strategies to reduce the bandgaps of ZnO and TiO 2 have been discussed. • The mechanism of organic pollutants degradation by non-metal doped ZnO and TiO 2 was explained. • The applications of non-metal doped ZnO and TiO 2 for degradation of pollutants and hydrogen production have been explained. • This review serves as a guide for researchers to overcome the inherent challenges of metal oxide-based photocatalysts.

Topics & Concepts