Recent advances in the applications of encapsulated transition-metal nanoparticles in advanced oxidation processes for degradation of organic pollutants: A critical review

Advanced oxidation processes are widely recognized as effective techniques for the removal of organic pollutants from water. In recent years, encapsulated transition-metal nanoparticle catalysts have exhibited excellent performance in inducing AOPs for elimination of organic contaminants due to their unique physicochemical properties. Taking advantage of the synergy between transition-metal nanoparticles and encapsulation materials, the catalytic activity, stability and selectivity of the catalysts can be adjusted and improved. Particularly, the carbon shell might benefit pollutant enrichment, accelerate charge transfer, enable confinement effect, and protect the transition-metal core from aggregation or deterioration. This review presents recent advances in the applications of encapsulated transition-metal nanoparticle catalysts for AOPs to degrade organic pollutants. Firstly, the structure and composition types of encapsulated transition-metal nanoparticle catalysts were introduced and then the synthetic methods of the catalysts were described. Subsequently, the applications of encapsulated transition-metal nanoparticles as heterogeneous catalysts to degrade organic pollutants in AOPs, including Fenton reactions, photocatalysis, persulfate activation, etc., were discussed with the underlying reaction mechanisms revealed. Finally, the article concludes by highlighting the major challenges and opportunities associated with encapsulated transition-metal nanoparticle catalysts in these AOPs, providing valuable insights for future research and development.