Activation Efficiency And Mechanism Of Iron And Nitrogen Co-doped Biochar On Sodium Persulfate

In recent years,peroxydisulfate（PDS）-based advanced oxidation processes have emerged in the field of environmental catalysis due to their advantages of high reactivity,promising mineralization efficiency,and superior environmental adaptability.Although ironbased catalysts as PDS activators have advantages of fast reaction speed and less environmental toxicity,the leaching of iron ions during the reaction process,poor catalyst stability and environmental tolerance have become the main reason for limiting the application of iron-based catalysts.In order to design a catalytic system with high catalytic activity and low metal loss,this study combined iron and nitrogen with carbon-based materials to prepare two different iron,nitrogen co-doped biochar by one-step calcination method and calcination combined with redox method.The effect of nitrogen-doping on iron-based catalysts was investigated,the activation mechanism of iron,nitrogen co-doped catalysts on PDS was studied,and the action mechanism of different species on the catalyst surface in the PDS activation were analyzed.The main contents and results are as follows:（1）Iron and nitrogen co-doped biochar（Fe-NBC）was prepared by a one-step calcination method using potassium ferrate as iron source and dicyandiamide as nitrogen source combined with lignin.Taking bisphenol A（BPA）as the target pollutant,the catalytic degradation performance of Fe-NBC with different doping ratios was investigated and compared with the performance of iron-doped biochar（Fe-BC）.Electron microcopy results revealed that the incorporation of N caused dramatic changes in the catalyst surface,resulting in a distinct stacking and wrinkling structure,which played a protective role for the iron species.The FeNBC prepared by 1.0 g lignin combined with 9.0 m M potassium ferrate and 12.0 m M dicyandiamide exhibited high-efficiency catalytic performance while ensuring stability of the catalyst.Compared with Fe-BC,the Fe leaching of Fe-NBC had a significantly lower Fe leaching rate during the reaction.The removal rate of BPA by Fe-NBC/PDS remained at 90.5%after four cycles of use.The main reactive oxygen species in Fe-NBC/PDS system and the pathway of BPA degradation were explored by quenching experiments and electron paramagnetic resonance spectroscopy.The Fe-NBC/PDS system achieves efficient removal and mineralization of BPA through the synergy of free-radical and non-radical processes.Nitrogen doping played a key role in the nonradical activation of PDS to generate singlet oxygen.（2）Nitrogen-doped biochar loaded with nano-zero-valent iron（n ZVI@NBC）were prepared by calcination combined with the redox method.Compared with pristine biochar loaded with nano-zero-valent iron（n ZVI@BC）,nano-zero-valent iron（n ZVI）,and nitrogendoped biochar（NBC）,n ZVI@NBC exhibited the best catalytic performance.The results showed that NBC provided suitable sites for the anchoring and dispersion of n ZVI,and the synergistic effect between NBC and n ZVI improved the activation efficiency of n ZVI@NBC for PDS.The results of quenching experiments,electron paramagnetic resonance spectroscopy,and PDS concentration determination demonstrated that the activation of PDS by n ZVI@NBC includes the free radical pathway dominated by nano-zero valent iron and the nonradical pathway driven by the active site introduced by nitrogen-doping.The n ZVI@NBC/PDS system degraded BPA through dehydrogenation,hydroxylation,isopropylidene bridge cleavage,β-scission and nonradical pathways.