Catalytic and photocatalytic reduction/degradation of methyl red dye by metal nanoparticles, metal oxides, and their composites: a critical review

-assisted reduction of MR, while semiconductor photocatalysts and hybrid nanocomposites are examined for photocatalytic and oxidative degradation applications. The fundamental mechanisms governing electron transfer, hydrogen atom transfer, reactive oxygen species generation, and azo bond cleavage are critically analyzed. Moreover, the influence of operational parameters like catalyst composition, light intensity, pH, catalyst loading, particle size, dye concentration, temperature, and oxidant dosage on reaction efficiency is systematically discussed. Particular attention is given to catalyst stability, recyclability, thermodynamic aspects, and the role of support materials in enhancing catalytic performance. Current challenges like incomplete mineralization, metal leaching, nanoparticle aggregation, and limitations associated with real wastewater treatment which are also highlighted. Finally, future perspectives focusing on multifunctional nanomaterials, solar-driven processes, green synthesis approaches, and scalable treatment technologies are presented. This review provides a comprehensive framework for the rational design of highly efficient and sustainable catalysts for MR remediation in wastewater treatment systems.