Preparation Of Walnut Shell Powder Immobilized NAVI For Tetracycline Removal From Aqueous Solutions

Tetracycline(TC)is one of the most worldwidely used antibiotics,due to its high quality,cost effect and desirable antimicrobial activity.TC is often used for therapeutic purpose,and illegally used as feed additives by some farming operations.However,TC is difficult to be biodegraded,and has a long environmental half-life,and it can be widely detected in soils and all kinds of water environment.TC can bring potential risks to human beings and ecosystem when TC wastewater is discharged into environment.To date,the treatment techniques of TC effluents mainly include adsorption,flocculation,membrane processes,advanced oxidation processes(AOPs),chemical degradation.etc.Recently,nanoscale zero-valent iron(NZVI)is found to be effective in the removal of a large amount of environmental contaminants,such as antibiotics,heavy metal ions,chlorinated solvents and organic dyes due to the advantages of NZVI,such as strong reduction capacity,small particle size,high surface energy,inexpensiveness,and nontoxicity.No wonder that NZVI has exhibited great potential in TC effluents remediation.In this research,Walnut shell powder(WS)were prepared by grind,wash and dry as raw materials.We employed WS as support material of NZVI to decrease the agglomeration of NZVI particles.Nanoscale zero valent iron on walnut shell powder(WS-NZVI)were synthesized as functionalized composite via liquid phase reduction method.By comparison,the removal efficiencies of TC follow the order of WS-NZVI > NZVI > WS.96.21% and 49.10% of TC was removed from the solution within 1 h using WS-NZVI and NZVI,respectively.However,just only a few of TC was removed by WS(21.20%)at 70 min.In addition,Batch experiments were carried out to determinate the effect of reactant concentration,pH value,solution temperature,and competitive anions.The results show that TC could be removed by physical adsorption and chemical reduction on WS-NZVI in a short time with high removal rates(more than 96.21%)at the optimal experiment conditions.96.00% and 98.21% of TC was removed when pH was decreased to 7.11 and 6.15,respectively.The pH 6 is most appropriate pH for TC removal.It can be seen that the removal rate of TC by WS-NZVI was increased as the solution temperature was increased,a small amount of cations existed and with reducing the initial concentration of TC.The WS,NZVI and WS-NZVI were characterized by SEM,FTIR and XRD.The difference in materials systematic characterization indicated that NZVI loading on WS were beneficial for improving NZVI and dispersion onto WS,hence enhancing the reactivity of WS-NZVI composites.Kinetics for the removal of TC using these WS-NZVI composites fitted well to a two-parameter pseudo-first-order decay model.The by-products of TC degraded by WS-NZVI were qualitatively determined by LC-MS.Because the removal of TC by NZVI is a surface-mediated process,we can be preliminarily inferred that the degradation pathways of TC with WS-NZVI is also a surface-mediated process,In a word,the degradation of TC using WS-NZVI involved physical adsorption and chemical reduction.The findings suggest that the WS-NZVI composites possess huge potential for TC wastewater treatment.