Preparation Of Nitrogen-doped Core-shell Carbon-zero-valent Iron Composites And Study On Remediation Of Groundwater Phenol

Phenol containing wastewater has a wide range of pollution and great harm,especially the elimination of phenol pollution in groundwater environment is becoming a thorny environmental problem.Carbon-coated nano-zero-valent iron（n ZVI）activated persulfate is a promising technology for groundwater remediation.At present,the low yield and easy oxidation of zero-valent ferri-based biochar prepared with ferritic salt as iron source limit its large-scale application.Studies have shown that nano-Fe₃O₄ as iron source is not only easier to generate n ZVI,but also reduce the consumption of carbon in the process of thermal reduction,which is beneficial to the use of carbon shell to protect n ZVI from oxidation.To solve the above problems,an N-doped core-shell zero-valent iron composite（Fe⁰@NC-0.8-0.6-800）was prepared by using glucose as carbon source,Fe₃O₄ as iron source and urea as nitrogen dopant through the strategy of"hydrothermal coating-pyrolytic reduction",which improved the defects of zero-valent iron oxidation and agglomeration.The phenol was effectively degraded in persulfate system.In this experiment,the preparation conditions and experimental parameters of the catalyst were optimized.Through a series of characterization and experiments,the structure,catalytic performance,stability,adaptability to degradation of different pollutants and differences in the active species of the system were compared between the two catalysts with or without nitrogen doping.The results showed that Fe⁰@NC-0.8-0.6-800 has the highest catalytic activity.The preparation of Fe⁰@NC-0.8-0.6-800 under the optimal conditions was able to completely remove phenol within 20 min,and the reaction rate constant(k_obs)was0.204 min^-1,which was 2.4 times higher than that of Fe⁰@C-0.8-0-800(0.0866 min^-1)without doped N.Fe⁰@NC-0.8-0.6-800 exhibited excellent reusability,strong mineralization ability,and adaptability to degradation of various pollutants.In addition,Fe⁰@NC-0.8-0.6-800 could effectively deal with real phenol contaminated groundwater,which was beneficial for practical applications.EPR and quenching experiments confirmed that the major active species in the Fe⁰@NC-0.8-0.6-800/PS system were SO₄^·-and ¹O₂,while the major active species in Fe⁰@C-0.8-0-800/PS was only SO₄^·-.N-doping played an important role in biochar structure and catalytic performance as follows:（i）N doping increased the thickness and specific surface area of biochar,which not only inhibited the oxidation of n ZVI,but also promoted the adsorption of phenol;（ii）N doped biochar matrix was a good electron transfer carrier,which could accelerate the Fe（III）/Fe（II）cycle;（iii）N defects in biochar after N doping promoted PS activation via a non-radical pathway.In this study,the synthesis strategy of carbon coated Fe⁰ nanocomposites was optimized,which provided a promising strategy for the remediation of groundwater organic pollution.