Study on Degradation of Sulfamethoxazole in Water by Activated Persulfate of Molybdenite Supported on Biochar

TL;DR

This study explores using a biochar-supported molybdenite composite to activate persulfate for efficiently degrading sulfamethoxazole in water.

Contribution

A novel composite material (Molybdenite@BC) is developed and shown to effectively activate persulfate for sulfamethoxazole degradation.

Findings

The Molybdenite@BC/PMS system achieved 97.87% sulfamethoxazole degradation in 60 min under optimal conditions.

Singlet oxygen (1O2) was identified as the main reactive species driving sulfamethoxazole degradation.

Degradation led to reduced toxicity and mineralization into harmless byproducts like CO2 and H2O.

Abstract

In this study, the advanced oxidation system of peroxymonosulfate (PMS) was activated by molybdenite supported on biochar (Molybdenite@BC), and the degradation efficiency, influencing factors and degradation mechanism of sulfamethoxazole (SMX) were explored through experiments. Molybdenite@BC, a composite material used in the study, was prepared by pyrolysis at high temperature. The optimum pyrolysis temperature was 700 °C, and the mass ratio of molybdenite to biochar (BC) was 1:3. By changing dosage of Molybdenite@BC, pH value, initial concentration of PMS, and the types and concentration of inorganic anions, the effects of various factors on SMX degradation were systematically studied. The optimum reaction conditions of the Molybdenite@BC/PMS process were as follows: Molybdenite@BC dosage was 100 mg/L, PMS concentration was 0.2 mM, pH value was 6.9 ± 0.2, and initial SMX concentration was 6 mg/L. Under these conditions, the degradation rate of SMX was 97.87% after 60 min and 99.06% after 120 min. The material characterization analysis showed that Molybdenite@BC had a porous structure and rich active sites, which was beneficial to the degradation of pollutants. After the composite material was used, the peaks of MoO2 and MoS2 became weaker, which indicated that there was some loss of molybdenum from the material structure. Electron paramagnetic resonance (EPR) and radical quenching experiments revealed that Molybdenite@BC effectively catalyzed PMS to generate various reactive oxygen radicals and non-free radicals, including singlet oxygen (1O2), hydroxyl radical (•OH), sulfate radical (SO4•−) and superoxide radical (•O2−). 1O2 played a leading role in the degradation of SMX, while •OH and SO4•− had little influence. The intermediate products of the degradation of SMX in Molybdenite@BC/PMS system were analyzed by liquid chromatography–tandem mass spectrometry (LC–MS). The results showed that there were nine main intermediate products in the process of degradation, and the overall toxicity tended to decrease during the degradation of SMX. The degradation path analysis showed that with the gradual ring opening and bond breaking of SMX, small molecular compounds were generated, which were finally mineralized into H2O, CO2, CO32−, H2SO4 and other substances. The research results confirmed that the Molybdenite@BC/PMS process provided a feasible new method for the degradation of SMX in water.

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