Photoelectrochemical Activation Of Sulfite For Degradation Of Ammonia Nitrogen By Nanometer Molybdenum Disulfide Electrode

At present,the treatment of ammonia nitrogen is mainly carried out by the traditional technologies such as biological treatment,membrane separation,ion exchange,chemical oxidation and breakpoint chlorination,in the aspect of new repair technology,electrochemical oxidation methods of ammonia nitrogen removal have problems such as excessive energy consumption and the need for additional chemicals.And photocatalytic removal of ammonia nitrogen was found that·OH as the main oxidant is not suitable for removing ammonia species.Therefore,effective,low-cost and environment-friendly methods for removing NH₃-N from wastewater have not been reported.In recent years,advanced oxidation processes?AOPs?based on oxysulfur radicals(SO₃^·-,SO₄^·-and SO₅^·-)have attracted more and more attention in wastewater treatment.In this paper,we report the in situ photoelectrochemical activation of sulfite to produce oxysulfur radicals with MoS₂ nanosheets as a photoanode.The efficient conversion of ammonia was achieved under visible light irradiation.And ammonia nitrogen is mainly converted into nitrogen and other gases to discharge from water.MoS₂,as a typical transition metal sulfide,has semiconductor properties.Nanomaterials with adjustable band gap can be prepared by adjusting their thickness.At present,liquid-phase exfoliation method has become a common method for preparing MoS₂ nanomaterials because of its simple preparation process,less investment and less pollution.In this paper,MoS₂ nanosheets were prepared by liquid-phase exfoliation method.MoS₂/TiO₂/ITO electrode was further prepared by dropping coating method.The effects of ultrasonic power and time,solvent system and centrifugal speed on the preparation of MoS₂ nanosheets were investigated.The results showed that MoS₂ nanosheets with higher concentration and thinner thickness could be obtained by ultrasonic power of 400W for 4 h and centrifugal speed of 4000 r/min.The photoelectric performance of the electrode is best when the load of MoS₂ is 3 mg/cm².The prepared MoS₂ electrode was used for PEC activation of sulfite to remove ammonia nitrogen under visible light irradiation.The effects of initial pH,bias potential,oxygen concentration,sulfite concentration and ammonia nitrogen concentration on the ammonia nitrogen degradation were investigated,and the degradation pathway and mechanism of ammonia nitrogen were further studied.The results showed that the degradation rate of ammonia nitrogen solution of 10mg/L could reach 84.8%when 0.6 V was applied and 0.1 M sodium sulfite was used as electrolyte under the condition of slowly air pumping for 6 h,and the main conversion product of ammonia nitrogen is nitrogen and other gases.The impact test of free radical scavengers,dissolved oxygen and electrolytes on the conversion of ammonia also confirmed that oxysulfur radicals are more powerful than hydroxyl radicals in ammonia conversion.WS₂/MoS₂ heterojunction was formed by coupling nanometer WS₂ with MoS₂,and WS₂/MoS₂ composite electrode was prepared to further enhance the photocharge transfer efficiency,thereby improving the photocatalytic performance of the electrode and further improving the degradation efficiency of ammonia nitrogen by about 15%.The system is suitable for in-situ treatment of wastewater containing ammonia and sulfite pollutants.In addition,this work provides a design of AOPs,where oxysulfur radicals can work together with hydroxyl radicals for simultaneous pollutants degradation.