Mechanism Of Molybdenum Disulfide Activating Hydrogen Peroxide To Produce Reactive Oxygen Species And Its Degradation Performance For Methyl Orange

Organic wastewater possesses many hazardous characteristics,such as poor biodegradability and high toxicity,which directly affects human health and environmental safety.Advanced oxidation process（AOPs）produces reactive oxygen species（ROS）with high oxidation activity and non-selective oxidation for organic pollutants,thereby producing environmentally friendly CO₂,H₂O and inorganic ions.Therefore,it is often used to treat organic compounds that are not easily destroyed by conventional treatment methods for repairing the wastewater environment.Molybdenum disulfide（MoS₂）nanosheets（or quantum dots）can produce ROS in the presence of hydrogen peroxide（H₂O₂）.However,the mechanism of the interaction between multi-layered MoS₂ and H₂O₂ and the generation of ROS is not clear.Moreover,there have been no reports on using ROS generated by the MoS₂/H₂O₂system to degrade organics in the dark.Therefore,to elucidate the mechanism on MoS₂/H₂O₂ system for producing ROS is of great significance to the environmental advanced oxidation process.Based on the research advance,multi-layered 2H-MoS₂nanosheets were synthesized via a simple hydrothermal reaction,and its catalytic capability in the presence of H₂O₂ was investigated with degradation of methyl orange（MO）as probe for the oxidizing ability of ROS.The evolution of morphology and composition of both 2H-MoS₂ and liquid phase were systematically monitored to figure out its interaction with H₂O₂,and the possible mechanism of the reaction process was discussed.The specific research results are as follows:First,MoS₂ was successfully synthesized by a simple hydrothermal reaction.The results have shown that molybdenum source,sulfur source,hydrothermal reaction time,synthesis temperature,high temperature calcination,p H of precursor solution,etc.affect the structure and morphology of MoS₂.Using sodium molybdate and L-cysteine as molybdenum source and sulfur source,respectively,the multi-layered flowerlike MoS₂nanosheets were successfully prepared by reacting at 210℃ for 36 h.XPS and other series of characterization proved that the MoS₂ prepared under this condition was 2H phase with high crystallinity.Second,in the MO/H₂O₂/MoS₂ system,the multi-layered 2H-MoS₂ catalyst exhibits high adsorption and degradation activity for methyl orange in the dark.When the reaction temperature is 35℃ and the concentration of H₂O₂ is 21 m M,the degradation of methyl orange follows pseudo-first-order reaction kinetics.The decolorization rate of methyl orange reaches up to 89.0%after 60 minutes,and the rate constant is 0.05974 min^-1.Thirdly,the interaction between multi-layered 2H-MoS₂ and H₂O₂ in MO/H₂O₂/MoS₂ or H₂O₂/MoS₂ system was explored,and the principle of multi-layered2H-MoS₂ activating H₂O₂ to generate ROS was clarified.The prepared multi-layered2H-MoS₂ is exfoliated or tailored into smaller nanosheets accompanied by the formation of electron-rich 1T phase in the presence of H₂O₂,and the exfoliated MoS₂nanosheets are more easily oxidized and dissolved by H₂O₂,thereby generating Mo O₄^2-,SO₄^2-and H⁺,while causing the p H of the solution to decrease.Therefore,under the acidic conditions created by itself,the hydroxyl radicals（·OH）are generated by the incompletely reduction of H₂O₂ in the molybdenum（Mo）centers of resulting nanosheets,especially at the Mo center of the exfoliated electron-rich 1T-MoS₂,thus successively producing superoxide radicals(O₂^·-)and singlet oxygen（¹O₂）.The generated ROS will oxidize the MoS₂ nanosheets,further promoting the dissolution of MoS₂.Fluorescence,ESR characterization and free radical scavenging experiments confirmed the production of·OH,O₂^·-and ¹O₂ and their effects on the degradation performance of MO.In this paper,the principle of multi-layered 2H-MoS₂ activating H₂O₂ to generate ROS,the evolution mechanism of the reaction system during the interaction between2H-MoS₂ and H₂O₂,and its oxidative degradation performance for methyl orange have been systematically studied.Therefore,this study provides data support for the direct generation of ROS by transition metal dichalcogenides such as MoS₂ and its application research in advanced oxidation technologies such as degradation of organic pollutants.