Removal of nitrogenous heterocycles by a CoMoS3/NH2-MIL-53(Fe)-catalyzed photo-Fenton-like process: effect, mechanism and toxicity evaluation

A novel flower-like visible light catalyst CoMoS3/NH2-MIL-53(Fe) (expressed as CMS@NMF) was synthesized through a convenient hydrothermal method. The CMS@NMF composite possessed excellent photocatalytic performance for the photo-Fenton-like degradation of nitrogenous heterocycles. The degradation efficiency of 50 mg L-1 indole and 50 mg L-1 quinoline by CMS@NMF with potassium persulfate as the oxidant reached 100% after 30 and 80 min, respectively. Simultaneously, the degradation kinetics results indicated that the rate constants of indole and quinoline by the CMS@NMF composite were 8.64 times (0.121 min(-1)) and 7.5 times (0.03 min(-1)) higher than that of pristine CoMoS3, respectively. The reactive species capture and electron spin resonance analysis illustrated that O-2(-) and SO4- play dominant roles in nitrogenous heterocycle degradation. This benefited from the suitable interfacial contact and electron band structure between NH2-MIL-53(Fe) and CoMoS3, as well as the synergistic effects between CMS@NMF and potassium persulfate, which were conducive to charge separation and promoted photocatalytic degradation. In addition, the toxicities of the indole and quinoline solutions before and after treatment with CMS@NMF were evaluated by plant seed germination. The cycling experiment demonstrated that the CMS@NMF composite exhibited considerable stability and reusability. The possible photo-Fenton-like degradation pathways and the mechanism of nitrogenous heterocycles by CMS@NMF were proposed.