A review on nano metal oxides and their nanocomposites for photocatalytic degradation of dyes

Water contamination has emerged as a critical global challenge, exacerbated by accelerated industrial growth and urbanization. Organic pollutants, primarily from industrial discharges, and inorganic contaminants such as heavy metals and nitrates severely compromise water quality. Among various remediation approaches, metal oxide semiconductors (e.g., TiO₂, ZnO, CeO₂, ZrO₂, and SnO₂) have gained significant attention for their photocatalytic capability in degrading organic pollutants and their adsorption and redox potential for inorganic pollutant removal. However, factors such as wide band gaps (requiring UV light) and rapid recombination of photogenerated electron-hole pairs often limit their efficiency. To overcome these challenges, recent advancements have focused on innovative strategies such as doping, nanocomposite formation, and the development of core-shell nanostructures. In particular, rare-earth-doped metal oxides exhibit enhanced interactions with pollutants due to their unique electronic configurations and 4 f orbitals, leading to improved catalytic activity. This review highlights state-of-the-art synthesis techniques for rare-earth-modified metal oxides and nanocomposites, evaluating their performance in degrading organic and inorganic contaminants. It aims to provide a roadmap for developing cost-effective, scalable solutions with significant implications for wastewater treatment and sustainable industrial practices.