Removal Of Typical Refractory Organic Compounds By Persulfate Activated By Mn-N Co-Doped Biochar(MnN@BC) Particle Electrode

Various Persistent organic pollutants（POPs）,such as drugs,antibiotics,pesticides,industrial chemicals,etc.,were widely present in natural water,soil,landfill leachate,and other environmental media,posing a great threat to drinking water safety,human health,and ecological environment.The existing technology was difficult to remove it efficiently,and there were also problems of high energy consumption,secondary pollution,and poor practical application.In view of the good oxidation efficiency and environmental friendliness of the three-dimensional electrode system,the high degradation of peroxynitrate advanced oxidation technology for the treatment of POPs,and the practical application prospect of the special non-radical pathway in the electro-activated peroxydisulfate（PDS）system,we conducted a study in the system of three-dimensional electro-activated PDS using carbamazepine（CBZ）as the target pollutant.In this study,firstly,manganese-nitrogen co-doped biochar（MnN@BC）was prepared,and then the role of MnN@BC in the removal of CBZ in electrochemical activation of PDS（E/MnN@BC/PDS）system was studied.Besides this,the efficacy,optimal working conditions,and mechanism of the system were investigated.And the potential applications of system were evaluated,including its efficacy in real water bodies,the effect of anions and natural organic matter,and the removal performance of other POPs.It was hoped that this study could provide new ideas for the design of particle electrodes in the three-dimensional electrical activation of PDS,and could also provide some theoretical basis for subsequent studies.The conclusions were as follows:（1）The MnN@BC was prepared by hydrothermal method.The properties and structures were characterized by SEM,EDS,XPS,XRD,FTIR and Raman.The results showed that the Mn-N nanoclusters with a particle size of 200 nm were not only successfully deposited on the porous laminar structure of BC,but also deeply embedded in the carbon network structure of BC.There were Mn₄N and Mn O on the surface of MnN@BC.In addition,the material appeared graphitized structure and more defects after Mn-N doping,which favored the activation of PDS.（2）The degradation efficiency and reaction rate of the E/MnN@BC/PDS system were significantly higher than those of the MnN@BC/PDS and the E/PDS system,indicating that significant synergy between electric and catalytic activations of PDS.Under the conditions that the initial concentration of CBZ was 10 mg L^-1,the dosage of PDS was 4 m M,the current density was 20 m A cm^-2,and the dosage of MnN@BC composite was 0.1 g L^-1,the E/MnN@BC/PDS system had the optimal degradation efficiency,the removal rate of CBZ and TOC were 96.84%and 31.12%after 60 min,respectively.And the removal rate of TOC reached 46.73%after 120 min.Besides this,this system achieved excellent degradation under wide p H range of 3-11.The MnN@BC composites still had good catalytic performance after 10 cycles（E/MnN@BC/PDS）.This may be ascribed to the electric field,which maintained the activity of the MnN@BC composites in terms of reducing the active site loss and by-product deposition.In addition,Mn-N site may be the key active site in the E/MnN@BC/PDS system,and the surface oxygen-containing functional groups,the graphitized structure,and the defect structure may also provided active sites for electro-activation of PDS.（3）The reactive oxygen species（ROSs）produced in the E/MnN@BC/PDS system were identified by quenching experiments,free radical probe experiments,and electron paramagnetic resonance spectroscopy（EPR）.In E/MnN@BC/PDS system,the removal of CBZ can be achieved by DET,electro-adsorption,PDS oxidation alone,ROS oxidation(·OH,SO₄^·-,and ¹O₂),and non-radical oxidation.The relative contributions of DET,electro-adsorption,PDS oxidation alone,ROS oxidation(·OH,SO₄^·-,and ¹O₂),and non-radical oxidation were 17.00%,11.70%,3.09%,60.48%,and 7.73%,respectively.The results demonstrated that MnN@BC was favorable for adsorption,electron transfer,and ROSs formation.Among them,·OH and ¹O₂were the main active species with the relative contributions of 33.96%and 22.29%,respectively.In general,the non-radical pathways contributed more in the system compared to the free radical pathways.This suggested that electroactivation and manganese-nitrogen co-doped biochar composites may indeed be beneficial to the non-radical pathway activation of PDS.This maybe ascribed to more active sites,the graphitized structure,the defective structure,the excellence electrical conductivity,and electron transfer capability of the MnN@BC composites.（4）In E/MnN@BC/PDS system,the removal efficiency of CBZ in ultrapure water,tap water,and surface water were 96.84%,88.98%,and 63.69%,respectively.This may be attributed to the presence of HA and some inorganic ions in surface water.Competing reactions were generated,scavenging part of SO₄^·-and·OH,thus limiting its oxidation efficiency.Among them,Cl^-significantly promoted the degradation of CBZ,while HCO₃^-,PO₄^3-,NO₃^-and HA inhibited the degradation of CBZ.Besides,the system also remained efficient in the removal of ATZ,CIP and SMX.The results confirmed that the system had good anti-interference capacity for coexisting substances and can be used for the efficient removal of POPs in different water bodies.