Removal Performance And Mechanism Of Oxytetracycline And Pb²⁺ By Coconut Shell Biochar Loaded With Nano-zero-valent Iron

With the continuous development of industry and agriculture,the removal of antibiotic and heavy metal complex pollution in water environment has become one of the hot research problems.Among them,two pollutants,oxytetracycline（OTC）and lead(Pb²⁺),are widely exist in various aquaculture wastewater,and the current traditional removal methods cannot remove the complex pollutants efficiently.Biochar,as a raw material abundant,easy to prepare and economical adsorbent,is used in the removal of environmental pollutants from water bodies,but due to the limited adsorption performance of the original biochar,the researchers enhance biochar’s ability to remove pollutants through modification methods.Among them,nano-zero-valent iron（nZVI）,with its small particle size,high reactivity and strong reduction,has good removal effect for antibiotics and heavy metals in water bodies.Therefore,a novel loading material was prepared by combining biochar and nZVI through carrier loading method to remove complex pollutants from the environment.In this paper,coconut shell was used as a raw material,and the raw biochar（BC）was obtained by pyrolysis at 800℃,which was activated by hydrochloric acid impregnation to prepare biochar（HBC）.On this basis,nZVI supported biochar（nZVI-HBC）was prepared by liquid-phase reduction.The biochar before and after loading was also characterized by various characterization tools,and the performance of biochar on the removal of OTC and Pb²⁺alone was investigated by batch adsorption experiments under different influencing conditions,and the mechanism of pollutant removal by biochar before and after loading was investigated by using adsorption isotherms,adsorption kinetics and adsorption thermodynamics.Meanwhile,the removal mechanism of nZVI-HBC on OTC and Pb²⁺composite pollution was investigated,and the main findings were as follows.（1）A series of characterizations of biochar before and after loading were performed by SEM,BET,XRD,FTIR and XPS,et al.The characterization results show that the basic structures of BC and HBC are similar,both have more obvious pore characteristics,increased specific surface area and average pore size,and and both materials contain characteristic peak peaks of Si O₂ and Ca CO₃.Meanwhile,the characterization results of nZVI-HBC both proved that the experiments successfully loaded nZVI onto HBC by liquid-phase reduction method and the main form of iron ions was Fe⁰.（2）The performance of BC,HBC and nZVI-HBC for OTC and Pb²⁺removal alone was investigated by batch adsorption experiments.The results showed that the removal effects of all three types of biochar before and after loading on OTC and Pb²⁺were nZVI-HBC>HBC>BC.The removal efficiency of pollutants gradually increased with the increasing amount of biochar added,and the maximum removal of OTC and Pb²⁺by nZVI-HBC reached 196.6985 mg·g^-1 and 103.6028 mg·g^-1.The removal of OTC and Pb²⁺by nZVI-HBC was found to be a single-molecule layer chemisorption by fitting various adsorption models,and the removal process was spontaneous,heat-absorbing and entropy-increasing.（3）The removal ability of nZVI-HBC for OTC and Pb²⁺complex contamination and the removal mechanism of the complex contamination were investigated.It was shown that nZVI-HBC had good performance on the removal of OTC and Pb²⁺complex pollution,and the removal efficiency was over 90%for both.the effect of Pb²⁺addition on OTC removal was shown to be promoted by low concentration and inhibited by high concentration,and the effect of OTC addition on Pb²⁺removal was shown to be slightly inhibited.（4）The mechanism of OTC and Pb²⁺removal by nZVI-HBC was analyzed by LC-MS and XPS,and the results showed that the mechanism of OTC removal by nZVI-HBC included electrostatic gravitational force,π-πEDA interaction and degradation,and the mechanism of Pb²⁺removal by nZVI-HBC included electrostatic gravitational force,ion exchange and complexation of functional groups.In summary,nZVI-HBC has good removal effect on OTC and Pb²⁺single and composite pollution,and is an effective and potentially valuable material for water remediation.