Enhanced photo-Fenton activity and stability for sulfamethoxazole degradation by FeS2@TiO2 heterojunction derived from MIL-125

FT-x composites with core-shell structure (FT = FeS2@TiO2, x represents the mass ratio of the used FeCl3·6H2O to MIL-125) were fabricated by a hydrothermal method using MIL-125(Ti) as a self-sacrificing template. Both the photo-Fenton activity and stability of the FT-1 were improved greatly in comparison with its counterparts due to the unique core-shell structure and synergistic effect between FeS2 and TiO2. Especially, the Fe leaching concentration of FT-1 was approximately 1/10 of the individual FeS2, benefiting from the protection effect of TiO2 shell. Under dark condition, the formed FeOOH occupied active sites and inhibited iron cycle as well as H2O2 decomposition, leading to the inactivation of FT-1. UV light irradiation not only boosted the catalytic activity but also prevented the FT-1 from reactivity decline owning to the regeneration of Fe2+ by photogenerated electrons and continuous generation of ·OH. Experimental and DFT calculation results indicated that a type-II heterojunction was formed, in which photogenerated electrons were transferred from FeS2 core to TiO2 shell, accelerating charge separation and further boosting sulfamethoxazole (SMX) degradation. FT-1 displayed outstanding photo-Fenton activity in wide pH ranged from 2 to 6 and good anti-interfering ability toward impurities in water matrix. Besides, the reusability of FT-1 was good, in which 90% SMX degradation was maintained even after 5 runs. Noteworthy, the photo-Fenton activity was recovered via a revulcanization process, in which FeOOH was completely transformed into FeS2. This founding provided insights for the design and construction of heterojunction with both excellent photo-Fenton activity and stability.