Preparation Of The Nanoscale Iron-based Composite Adsorbent And Its Application In Wastewater Treatment

With the rapid development of China’s economy,the pollution of heavy metal wastewater and dye wastewater caused by industrial production is becoming serious,and the accumulated pollutants will eventually damage the human body while destroying the environment.As a new environmental remediation material,nanoscale zero-valent iron(nZVI)is widely used because of its high reactivity and large specific surface area.However,nZVI is easy to aggregate and oxidize,which greatly limits reactivity and hinders its application in practical wastewater treatment.Therefore,nZVI needs to be improved by chemical modification.In this study,we prepared carboxylated cellulose nanocrystal(CCNC)through an efficient one-step hydrolytic oxidation of biomass material microcrystalline cellulose(MCC).The as-obtained CCNC was used for the immobilization of nZVI and provided composites,termed CCNC supporting nZVI(CCNC-nZVI).In addition,to improve the reactivity of nZVI,we also prepared composite adsorbent named CCNC supporting iron/copper bimetallic nanoparticles(CCNC-nZVI/Cu)in this research.The experiments conducted a series of characterization analyses on these materials,and the adsorption effect of CCNC-nZVI on Pb2+ and Cu2+and the adsorption effect of CCNCnZVI/Cu on methyl orange were studied.Moreover,the adsorption mechanism was also discussed.The main results obtained are as follows:(1)The prepared CCNC were mainly in the form of nanorods with lengths ranging from 80 to 250 nm,and the successful transformation of surface hydroxyl groups to carboxyl groups greatly improved the dispersion of CCNC in aqueous solution.The agglomeration of nZVI in CCNC-nZVI was effectively inhibited,and the iron nanoparticles were well dispersed on the CCNC surface with a size of～10 nm.The specific surface area of CCNC-nZVI increased to 23.43 m2·g-1,three times that of nZVI.The saturation magnetization of CCNC-nZVI reached 72.52 emu·g-1,exhibiting strong paramagnetism.Furthermore,the addition of CCNC also made CCNC-nZVI feature a corrosion inhibition performance.(2)The adsorption of Pb2+ and Cu2+on CCNC-nZVI was investigated respectively.The results showed that the optimal mass ratio of CCNC and nZVI in the adsorbent was 1:1,and the adsorption property gradually weakened with the increase of temperature.The most suitable adsorption pH was determined to be 4.The adsorption behavior of CCNC-nZVI for both Pb2+ and Cu2+was consistent with the pseudo-second-order kinetic model,and the maximum adsorption capacity was 653.59 mg·g-1 and 116.28 mg·g-1,respectively.The adsorption mechanism analysis demonstrated that CCNCnZVI exerted both reduction and co-precipitation effect on metal ions.(3)In the prepared bimetallic composite adsorbent CCNC-nZVI/Cu,the nanoscale iron spheres were uniformly dispersed on the surface of CCNC,while the doped copper particles also covered the surface of nano-iron,which provided conditions for improving the reactivity of nZVI.Meanwhile,CCNC-nZVI/Cu formed a mutuallysupporting porous structure with a specific surface area of 27.73 m2·g-1.(4)The adsorption effect of CCNC-nZVI/Cu for methyl orange was studied.The results showed that CCNC-nZVI/Cu was very efficient in methyl orange removal,reaching the adsorption equilibrium within 4 h,and the maximum adsorption capacity was 813.01 mg·g-1.The results of model fitting indicated that the intraparticle diffusion of methyl orange and the reaction with active sites were the control steps of adsorption,and the adsorption changed from monolayer adsorption to multilayer non-uniform adsorption with increasing temperature.In this study,the composite adsorbents of biomass materials supporting magnetic nano-iron and bimetal were successfully prepared,which effectively solved the problems of easy agglomeration and oxidation of nZVI.And the adsorbents exhibited excellent removal effect on Pb2+,Cu2+and methyl orange,providing an effective method for the treatment of heavy metal and dye wastewater.