Visible-light sensitization of TiO₂ photocatalysts via wet chemical N-doping for the degradation of dissolved organic compounds in wastewater treatment: a review

Increased pollution of ground and surface water and emerging new micropollutants from a wide variety of industrial, municipal, and agricultural sources has increased demand on the development of innovative new technologies and materials whereby challenges associated with the provision of safe potable water can be addressed. Heterogeneous photocatalysis using visible-light sensitized TiO₂ photocatalysts has attracted a lot of attention as it can effectively remove dissolved organic compound in water without generating harmful by-products. On this note, recent progress on visible-light sensitive TiO₂ synthesis via wet chemical N-doping method is reviewed. In a typical visible-light sensitive TiO₂ preparation via wet chemical methods, the chemical (e.g., N-doping content and states) and morphological properties (e.g., particle size, surface area, and crystal phase) of TiO₂ in as-prepared resultants are sensitively dependent on many experimental variables during the synthesis. This has also made it very difficult to provide a universal guidance at this stage with a certainty for each variable of N-doping preparation. Instead of one-factor-at-a-time style investigation, a statistically valid parameter optimization investigation for general optima of photocatalytic activity will be certainly useful. Optimization of the preparation technique is envisaged to be beneficial to many environmental applications, i.e., dissolved organic compounds removal in wastewater treatment.