Study On Remove Of 2,4,6-TCP By Nano Fe/Ni Loaded By Crofton Weed Biochar Jointly With K₂S₂O₈

Chlorophenols（CPs）is a kind of typical refractory halogenated organics.As raw materials and intermediates in organic chemicals,it is widely used in sterilization,wood preservation and other industries.But it has"three"hazards to organisms and listed as a priority in the water environment to control pollutants.CPs seriously damage the groundwater environment and detrimental to human health after entering the groundwater.In this paper,2,4,6-trichlorophenol（2,4,6-TCP）was selected as the target pollutant,and biochar prepared by using the biological invasive species Crofton weed,then composite materials synthesized by loading nano-iron/nickel（CW-Fe/Ni）.Besides,the reduction properties and mechanism of composites on 2,4,6-TCP also investigated.Batch experiments combined with persulfate oxidation were conducted to further remove 2,4,6-TCP.The research results provide new ideas to the resource utilization,prevent and control of Crofton weed,and also explore new way in situ remediation of groundwater halogenated organic matter.The main findings obtained are as follows:（1）Synthesis of Crofton weed biochar（CW）and its adsorption property to 2,4,6-TCP.The CW prepared by oxygen-limited pyrolysis at different temperatures（400°C,500°C,600°C）,and its adsorption capacity to 2,4,6-TCP is CW600>CW500>CW400,the best preparation temperature is 600°C.The specific surface area（BET）showed that the CW600 had a specific surface area of 264 m²/g and an average pore diameter of3.48 nm.Scanning electron microscopy（SEM）showed that the surface had abundant pore structure.The adsorption kinetics consistent with the Pseudo-first-order kinetic model;the adsorption isotherm conforms to the Freundlich model,and the adsorption of 2,4,6-TCP by CW600 is more favorable under low temperature conditions.（2）The optimum synthesis conditions and characterization of the CW loaded with nano-iron.By comparing the reduction performance of 2,4,6-TCP with different CW and Fe/Ni loading ratios,the optimum material loading ratio of Fe/Ni:CW is1:2.The X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）showed Ni and Fe were successfully composed of bimetallic structure loaded on Crofton weed.The Fe/Ni agglomeration was weakened obviously after loading,and the nano-iron/nickel pellets on the carbon sheet were within 150 nm.（3）The effect of different conditions to adsorption of 2,4,6-TCP by CW-Fe/Ni.The acidic condition is beneficial to the removal of 2,4,6-TCP by CW-Fe/Ni,while T CW-Fe/Ni is easily passivated and the electrostatic repulsion between CW-Fe/Ni and2,4,6-TCP leads to low removal efficiency under alkaline condition.Besides,Sulfate,bicarbonate and nitrate all inhibited the removal of 2,4,6-TCP,and the degree of influence was:nitrate>bicarbonate>sulfate.（4）The mechanism of 2,4,6-TCP removed by CW-Fe/Ni.The Langmuir-Hinshe-lwood model shows the removal of 2,4,6-TCP by CW-Fe/Ni was attributed to adsorption and reduction,and the reduction played a major role.Meanwhile,the rate of reduction reaction is limitedd by the adsorption rate.The detection results of intermediate products and XRD,XPS characterization indicate Fe⁰ converted to Fe₃O₄ and Fe₂O₃,and Cl^-is attached to the surface of the material after the reaction.The above analysis prove that CW-Fe/Ni remove2,4,6-TCP by catalytic reduction dechlorination.The B3LYP method in density functional theory was used to calculate the reaction progress of CW-Fe/Ni and 2,4,6-TCP,and the reaction process was in agreement with the experimental results.（5）The CW-Fe/Ni combined with K₂S₂O₈ packed reaction column to remove2,4,6-TCP.K₂S₂O₈ oxidize 2,4,6-TCP directly,and the total organic carbon（TOC）removal rate in the solution was 6.4%;the TOC removal rate increased to 50.5%after reduced by packed column and oxidation of K₂S₂O₈.The TOC removal rate was increased by 44.1%,and the Fe²⁺and the dephosphorization product of 2,4,6-TCP produced within the reduction stage,which have a coordination effect on the removal of pollutants by the activated K₂S₂O₈.