Engineering TiO2 photocatalysts for enhanced visible-light activity in wastewater treatment applications

Wastewater treatment is an environmental imperative due to increasing water stress and ecological crises particularly in view of the inherent limitations of conventional treatment methods, which frequently demonstrate suboptimal efficiency and tend to produce undesirable secondary by-products. In this context, advanced oxidation processes (AOPs), especially heterogeneous photocatalysis, have demonstrated significant potential as ecologically and economically viable solutions for the complete degradation of pollutants into CO 2 and H 2 O under ambient conditions. Titanium dioxide (TiO 2 ) is the most widely used photocatalyst owing to its non-toxicity, photochemical stability, and high reactivity. However, its practical application is hindered by several limitations, including activation restricted to UV light (due to a wide bandgap), rapid recombination of photogenerated electron–hole pairs, and relatively low surface area. To overcome these challenges, this review discusses recent strategies for modifying the properties and structure of TiO 2 to enhance its photocatalytic performance under visible light. These strategies include metal or non-metal doping, the formation of heterostructures, and dye sensitization, all aimed at extending light absorption into the visible range and improving charge separation and transport. Furthermore, the integration of TiO 2 with bismuth-based photocatalysts, such as BiVO 4 , Bi 2 WO 6 , and Bi 2 MoO 6 , is explored. These materials exhibit efficient visible-light absorption and favorable electronic properties, significantly boosting the photocatalytic activity of TiO 2 . By implementing these modifications, TiO 2 -based photocatalysts are expected to play a key role in environmental remediation and contribute to the development of sustainable water treatment technologies.