K. Rajanikara Swamy, G. Shyamala, Thirumala Rao Gurugubelli, Gobinath Ravindran, Babu Bathula
The global need for clean water has led to the study of novel treatment methods, and nanotechnology is one of them as it has a high reactivity and a large surface area. Nanomaterials including titanium dioxide (TiO 2 ), zinc oxide (ZnO), and carbon nanotubes have shown great efficiency in the removal of heavy metals, dyes, and organic pollutants via photocatalytic reactions as a sustainable water treatment process. This review critically analyzes these nanomaterials, with emphasis on metal oxide-based photocatalysts to degrade recalcitrant contaminants in wastewater. It also discusses synthesis methods, such as top-down and bottom-up methods, their working mechanisms, and applications. Ongoing challenges include large-scale production, cost effectiveness, and optimization of synthesis, which have to be addressed further. The review provides a general overview between the material design, photocatalytic activity, and environmental impact and considers the scalability, industrial viability, and long-term sustainability, thus presenting a balanced evaluation of the studies performed on a large scale.