Preparation Of Metal-biochar Catalysts And Their Activation Mechanisms To Persulfate

Advanced oxidation technology has been used for the degradation of refractory organics?i.e.aromatic pollutants?,using the high oxidation-reduction of·OH and SO₄^·-can degrade most of the refractory organics,and even mineralize it to CO₂ and H₂O.In recent years,advanced oxidation technology has developed rapidly which is based on persulfate,it has been applied in soil and groundwater remediation,and the degradation mechanism could be divided into radical pathway and nonradical pathway.Four metal-biochar were prepared in this study,to investigate the key factors of nanocomposites in activation of PS for the degradation of benzene ring pollutants.?1?Preparation of nZVI/BC by liquid phase reduction method,and using it activated PS to generate free radical for textile dyeing wastewater degradation?TDWW?.The results showed that the system could reduce the pH of the wastewater?11.45 to 9.77?,UV₂₅₄ was reduced from 17.84 to 9.26,and greatly improved the biodegradability of the wastewater?B/C increased from 0.14 to 0.48?.After loading nZVI,the functional groups would be transferred to form the new active species(BC_surface-O-FeO)which could as the electron transfer mediator to adsorbed pollutant's electrons through?-?and?-?-metal bonds.Resulting that the aromatic pollutants would as the electron donor,the BC_surface-O-FeO would as the electron transfer mediator,and the PS would as the electron acceptor.In this reaction,the BC_surface-OFeO would be converted into persistent free radicals?PFRs?,other PFRs were come from the reaction between the functional gourps and nZVI.Those reactions would heterogenous activate S₂O₈^2-to rapidly generate·OH and SO₄^·-for aromatic pollutants degradation.Thus,it would form an adsoption-degrdation-adsoption synergistic degradation cycle on the nZVI/BC₅ surface.Unlike traditional Fenton reaction,this reaction would generate a large number of·OH even after 240 min,and the nanocomposites still had high activity and stability after the conversion of active species.?2?The nonradical pathway was verified by preparing three typical materials by hydrothermal method:CuO/BC,Fe₃O₄/BC and ZnO/BC.Using those composites activated PS to degrade Bisphenol A?BPA?.Meanwihile,the growth mechanism of nanocomposites and the reason for the functional groups transition was explored,and the key factors in nonradical pathway were also considered.The results showed that BPA in the CuO/BC-PS system was degraded by the nonradical pathway which was based on electron transfer complexes,and this process only consumed a small amount of PS?0.17 mM?for all BPA degradation?100?M?.In addition,quenching experiments showed that the nonradical pathway was not inhibited by the alcohol quenchers in the CuO/BC-PS system,and the system could still maintain high k_obs(⁰.0607 min^-1).In the Fe₃O₄/BC-PS system,the radical pathway was obviously inhibited by alcohol quenchers.Only a small quantity of·OH and SO₄^·-was generated by heterogeneous activation of PS,so a weakly BPA degradation efficiency was obtained in this system(without quenchers k_obs=0.0037 min^-1).The nonradical pathway and the radical pathway were both presence in ZnO/BC-PS system,but their activities were both weak.The dominant pathway in system was based on free-moving electron that destroyed the intermediates to activate PS,which could generate·OH for BPA degradation(without quenchers k_obs=0.0046 min^-1).The results showed that CuO/BC with the high specific surface area,the abundant of unsaturated bonds?C=O,lactone group?and the benzene ring structures could effectively react with PS to form the intermediates.In addition,the reuse experiments verify that the nonradical pathway in CuO/BC-PS system was more stable,and CuO/BC still has high catalytic activity even after five reuse times.Finally,the activity of nonradical pathway was determined by the stability of the intermediates,the electron transfer capacity and the electrical resistance of nanocomposites themselves.