Recent advancements of wastewater treatment by photocatalysis: A comprehensive review

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.