Engineered Metal Oxide Nanocomposites and Rare-Earth Doping Strategies for Advanced Photocatalytic Environmental Remediation

Abstract

Water pollution from industrial effluents poses a critical global challenge, with synthetic dyes ranking among the most persistent and hazardous contaminants. Their high chemical stability, toxicity, and resistance to biodegradation necessitate advanced treatment methods beyond conventional physicochemical processes. Semiconductor photocatalysis has emerged as a sustainable strategy, exploiting light energy to generate reactive oxygen species that mineralize pollutants into benign products. Classical photocatalysts such as TiO₂, ZnO, WO₃, and Fe₂O₃ exhibit favorable physicochemical properties but suffer from rapid charge- carrier recombination, limited spectral response, and photocorrosion. Recent advances in material engineering, including band- gap tuning, heterojunction construction, catalyst deposition, and carbon- based hybridization, have addressed these limitations. Additionally, rare- earth doping and nanocomposite architectures have demonstrated the ability to extend visible- light activity, enhance structural stability, and improve photocatalytic efficiency. This review synthesizes recent progress in photocatalytic materials and fabrication techniques, with particular emphasis on dye degradation and wastewater remediation. Challenges related to scalability, energy efficiency, and environmental safety are critically examined, and future perspectives are outlined to guide the development of robust, cost- effective, and eco- friendly photocatalytic systems for sustainable water treatment applications.