Ternary FeS/γ-Fe2O3@N/S-doped carbon nanohybrids dispersed in an ordered mesoporous silica for efficient peroxymonosulfate activation

Abstract

Heterogeneous activation of peroxymonosulfate (PMS) has gained much attention for wastewater treatment. It is important to develop efficient catalysts and understand the reaction mechanism. In this work, a novel ordered mesoporous composite catalyst, in which an intimate ternary nanohybrid containing γ-Fe2O3, FeS and N/S-doped carbon (C-N-S) highly dispersed in the mesoporous silica (SBA-15), is presented. Using the facile solvent-free nanocasting method, the composite is synthesized by directly heating a solid mixture of methionine (Met), Fe(NO3)3·9H2O and SBA-15. Under optimal conditions, the melting infiltration and confined pyrolysis enable the formation of γ-Fe2O3 nanoparticles, FeS nanoclusters and C-N-S with intimate contacts but no severe embedment and no pore blockage. The optimized composite exhibits outstanding performance in PMS activation for degradation of carbamazepine (CBZ) with rapid and complete removal and high mineralization. The high performance relies on the cooperative roles of FeS with interfacial ≡Fe(II) sites for activation of PMS, C-N-S for adsorption of CBZ and facilitation of electron transfer to circulate ≡Fe(II)/Fe(III), SBA-15 for easy aqueous dispersion and mass transportation and γ-Fe2O3 for easy magnetic separation. The concentration evolutions of ≡Fe(II) sites and PMS over the reaction process are tracked and correlated with the catalyst structure and performance. The radical pathway dominates the degradation and the PMS activation mechanism is discussed. This work could provide a facile route for the synthesis of ordered mesoporous composites and improve the understanding of metal/carbon composites for PMS activation.