The use of TiO2/clay heterostructures in the photocatalytic remediation of water containing organic pollutants: A review

The increasing demand for water in the manufacturing sector in a quest to meet the needs of the ever-growing population is inherently associated with a corresponding increase in the number and quantity of toxic and refractory wastes and dyes released into the environment. In most cases, polluted water from industries is discharged into surface water sources without the thorough treatment required to meet the lawfully set effluent control standards. Of the available water treatment technologies, TiO2 photocatalysis has greater potential but its large-scale use is impeded by several technical factors associated with TiO2 such as its high bandgap, particle agglomeration, fast electron-hole recombination, poor adsorption capacity towards organics, and difficulties in recovery after water treatment. Immobilizing TiO2 nanoparticles (NPs) onto clays (phyllosilicates) eliminates these issues through the formation of the Ti-O-Si and Al-O-Ti bonds between TiO2 NPs and the aluminosilicate layers of the clay supports. Recent interest is on the fabrication of porous ternary or quaternary TiO2/Clay nanocomposites with improved physicochemical and optoelectronic properties such as improved surface area, surface acidity, narrowed bandgap, extended electron-hole separation, and recombination time among others. Our review focuses on the different synthetic methods to fabricate binary, ternary, and quaternary TiO2/clay-based nanocomposites and drawing a correlation between their properties and their ability to photodegrade multifarious organic water pollutants. The application of TiO2/clay nanocomposites and their engineered products such as photoresponsive thin films and membranes in the remediation of real-life wastewater matrices and full-scale real-life wastewater treatment systems is also discussed.