Mechanisms Of Accelerated Degradation Of 2,4-DCP In Sr/Fe Co-Doped Biochar-Enriched Water Driven By Natural Light Conditions

At present,domestic and foreign methods for treating chlorophenol wastewater,typified by 2,4-dichlorophenol（2,4-DCP）,are usually based on physical adsorption and chemical degradation.Although the adsorption technology alone is simple and can enrich the pollutants in the water but cannot completely degrade the pollutants to make them harmless;the chemical degradation technology mainly by advanced oxidation has shown the ability to efficiently degrade chlorophenols in water,but for the time being,it r emains in the laboratory stage due to the complex process equipment,energy-consuming reaction conditions,difficult to control the degradation process,poor catalyst stability and secondary pollution of disinfection by-products.However,due to the complex process equipment,energy-consuming reaction conditions,difficult to control the degradation process,poor stability of the catalyst and secondary pollution of disinfection by-products,it is still at the laboratory stage for the time being.Therefore,this experiment seeks a combined adsorption and degradation technology to endow the general adsorbent with chemical degradation ability,so that it can spontaneously and rapidly enrich the pollutants in the water body under natural conditions and efficient ly drive their degradation,and finally achieve the purpose of pollutant harmlessness.In this experiment,a Sr/Fe co-doped biochar catalyst with the ability of rapid enrichment of 2,4-DCP in water and spontaneous degradation of pollutants in multiple ways（reductive dechlorination and Fenton-like advanced oxidation）under natural light conditions without external light source was optimized by choosing strontium nitrate and ferrous nitrate nonahydrate and walnut shell biochar.It provides a new solution for low energy consumption,stable function and efficient degradation of chlorophenolic pollutants in water.The Sr/Fe loaded biochar catalysts for the efficient removal of 2,4-DCP were successfully synthesized.The Fe/Sr loaded biochar was characterized using X-ray diffraction analysis（XRD）,SEM-EDS,specific surface area analysis（BET）,X-ray photoelectron spectroscopy（XPS）and quantitative Fourier infrared spectroscopy（FI-TR）.The results showed that the one-pot method successfully loaded the permanent magnet Sr Fe₁₂O₁₉ on the surface of the biochar,which imparted magnetic properties to the biochar;after the reduction by Na BH₄,Sr,Fe,O and C were uniformly distributed on the surface of the raw biochar（BC）.（2）Response surface methodology was used to study the effects of ambient temperature,p H,material dosing dose,contact time and initial concentration of contaminants in the reaction system on the removal of 2,4-DCP from water by BSFBC5%.The results showed that when the pollutant concentration of 2,4-DCP was 20 mg·L^-1,p H=5～9,T=45℃,and the dose of BSFBC5%was 0.15g·L^-1,BSFBC5%adsorbed and removed 98.7%of 2,4-DCP in water within 60minutes,which was 1.24 and 2.07 times of the removal rate of SFBC5%an d BC.（3）To investigate the adsorption behavior and degradation pathways of BSFBC 5%for the removal of 2,4-DCP.In the continuous adsorption co-degradation experiments,based on the instantaneous 2,4-DCP concentration and the dynamic changes of TOC and Cl^-in the reaction system,it was shown that the catalyst rapidly enriched 2,4-DCP in water within 5～10 min while rapidly driving the degradation process in the system.The reaction products analysis,radical trapping and bursting experiments,light avoidance and single-factor control experiments showed that the Fe⁰-based multiple reduction dechlorination pathway and the natural light Sr-excited catalyst generated superoxide radicals（·O₂^-）,singlet oxygen（¹O₂）and h⁺,and formed a Fenton-like oxidative mineralization pathway with Fe²⁺in the system,both of which synergistically promoted the degradation of the enriched 2,4-DCP.The combined pathway of 2,4-DCP removal was determined as rapid enrichment,multiple dechlorination processes and oxidative mineralization to finally achieve harmless 2,4-DCP degradation products in water.（4）The application stability study of strontium iron modified biochar showed that BSFBC5%has low metal leaching and good recyclability,and the degradation rate of 2,4-DCP was over 80%after repeated magnetic recycling for 5 times,and the adsorption capacity was over 120 mg·g^-1.BSFBC5%has strong resistance to anion interference,and in actual water samples,BSFBC5%can still achieve 80.1%adsorption capacity and 60%degradation capacity of 2,4-DCP in actual water samples,which has good potential for practical application.In summary,a two-step synthesis method of"one-pot method+one-step reduction method"was proposed to synthesize Sr/Fe loaded biochar（BSFBC5%）with high metal effective loading rate,uniform loading,low metal ion leakage rate and stable magnetic recovery effect.The walnut shell biochar was endowed with the ability to adsorb and simultaneously spontaneously drive the degradation of 2,4-DCP in water under natural light conditions.The multi-pathway（adsorption enrichment,stepwise reduction dechlorination,Fenton-like advanced oxidation）mechanism of BSFBC5%adsorption co-degradation was investigated in depth.The feasibility of BSFBC5%with good adsorption and degradation capacity of 2,4-DCP in real water bodies was verified.This experiment provides a new synthetic method for the problems of low metal effective loading rate,easy agglomeration of nanoparticles and difficult recovery during the preparation and use of metal-modified biochar.It provides a new solution for low energy consumption,functional stability and efficient degradation of chlorophenolic pollutants in water.