Heterogeneous photocatalysis for water purification

Deterioration of water quality comprises a global environmental issue with detrimental effects on human health and the ecosystem. Among several technologies for water treatment, photocatalytic oxidation has arisen as an emerging field of scientific research due to its efficiency in mineralizing persistent and xenobiotic contaminants. The key advantage of photocatalytic treatment is its capability to destroy contaminants to mineral end-products, without transferring contamination from one phase to another, which is the typical mechanism for conventional treatment technologies. In this chapter the mechanisms, main aspects, and recent advances in heterogeneous photocatalysis for water purification applications are presented. Furthermore, a discussion on the main factors affecting the process efficiency, namely temperature, the physical and chemical characteristics of the water matrix, concentration of the photocatalyst, light wavelength and intensity, initial concentration of the substrate, and pH are discussed. Environmental sustainability aspects of the technology were also considered and pathways to render the technology environmentally sustainable are presented, since this is crucial to enable large-scale photocatalytic applications. Finally, a short discussion on the directions for future research is provided, exploring the application of the technology for the effective treatment of microplastics from natural water matrices. The ubiquitous distribution of microplastics, coupled with their long lifetime and uncontrolled release, has rendered them a major environmental issue of emerging concern, and heterogeneous photocatalysis appears to be a promising technology for their removal from water matrices.