High efficient PMS activation by synergistic effects of bimetallic sulfide FeS2@MoS2 for rapid OFX degradation

Antibiotics have been widely used to treat bacterial diseases. Their wide spread in ecological environment will induce generation of antibiotic-resistant bacteria Therefore, it is critical to create an eco-friendly and effective approach for their removal. Herein, a bimetallic sulfide FeS2@MoS2 with rich sulfur vacancies (SVs) and high percentage of metallic 1T phase MoS2 was prepared by one-step solvothermal method to degrade ofloxacin (OFX) by activated peroxymonosulfate (PMS). FeS2@MoS2-1 (the mass ratio of Fe/Mo is 1) exhibited excellent performance for PMS activation, with 99.26% OFX removed in 20 min (0.2 g/L FeS2@MoS2-1, 0.2 mM PMS, initial pH). The degradation rate constant of kobs was 0.21 min−1 with FeS2@MoS2-1 system, which was about 4.88 and 22.91 times of FeS2/PMS and MoS2/PMS systems under the same experimental conditions respectively. In FeS2@MoS2-1, besides S2−, SVs would also accelerate Fe(III)/Fe(II) circulation through increasing the exposure of Mo(IV) active sites. Additionally, MoS2 transferred from the semi-conductive 2H phase to the metallic 1T phase, which could speed up electron transfer rate significantly. Quenching experiment and EPR test showed that SO4− and O2− were the main active oxygen species. Degradation pathway was proposed through the active sites identification by DFT calculations and intermediates detection by HPLC-MS analyzation. The results showed that OFX were vulnerable to be attacked and broke to form small molecular compounds through hydrogen loss, oxidative cracking, decarboxylation and demethylation four ways. In addition, their bio-toxicity was investigated and results showed that the toxic was diminished. This work indicated that the satisfactory universality, recyclability and stability enabled FeS2@MoS2-1 could be used as an efficient catalyst to activate PMS to degrade refractory organic pollutants in water.