Core-shell catalysts for the elimination of organic contaminants in aqueous solution: A review

Since a large number of harmful chemical substances in industrial, agricultural and domestic effluent are discharged into natural water, there is an urgent need to mitigate the threat to human health and the ecological environment posed by those toxic contaminants. Advanced oxidation processes (AOPs) are particularly useful for the treatment of a wide range of bio-refractory organics in the water thanks to the in-situ generation of strong oxidants. Therefore, there is a boom in research on the development of heterogeneous AOP catalysts that facilitate the production of such oxidizing radical species in the presence of primary oxidants (O-3, persulfate (PS), H2O2 and/or external irradiation (ultraviolet (UV) light or visible light). Catalyst with a core-shell structure is a relatively new emerging class of materials that achieves functional complimentary of distinct particles and optimization of morphology simultaneously. This review provides typical synthetic procedures for core-shell materials, especially some magnetite-and-silica-composed ones, and presents an in-depth assessment of core-shell catalysts designed for the improvement of one or more aspects of recycling, catalytic activity and stability, for clean-up organic-contaminated water in different AOP systems. We lay special stress on analyzing the influence of the composition and structural characteristics of the core-shell catalysts on the catalytic degradation efficiency of organic compounds. Nonetheless, massive challenges remain in the exploration of cost-effective, efficient, robust and sustainable core-shell catalysts.