| With the development of industrialization,the problem of heavy metal pollution in water is becoming more and more serious.As a common heavy metal pollutant,hexavalent chromium（Cr（Ⅵ））will pose a serious threat to groundwater quality once it enters the groundwater due to its high toxicity,easy migration,strong oxidation and other characteristics.Therefore,it is urgent to deal with chromium pollution in groundwater.Nanometer zero-valent iron（nZVI）,as a common groundwater heavy metal remediation material in recent years,has a good ability to remove hexavalent chromium.However,due to its easy oxidation and agglomeration characteristics,its treatment efficiency in practical application is limited.In order to overcome the defects of zero-valent nano-iron materials,N-isopropylacrylamide（NIPAM）was selected as the modified material for modification in this study,which could reduce agglomeration oxidation and provide more functional groups at the same time,which was conducive to the removal of chromium.Surface modified nZVI（P@nZVI）and supported nZVI hydrogels（PA-nZVI）were successfully prepared and applied to Cr（Ⅵ）removal.The materials were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Zeta potential before and after the reaction.The effects of different environmental conditions,such as p H,temperature,initial Cr（Ⅵ）concentration and material dosage,on the Cr（Ⅵ）removal ability of the two materials were also discussed.The main conclusions are as follows:The successful synthesis of P@nZVI was confirmed by XRD,XPS and other characterization.P@nZVI is a core-shell structure consisting of an internal nZVI core and an external PNIPAM polymer shell.The structure can effectively prevent chain-like agglomeration and oxidation of the material.Under acidic conditions（pH=2）and anaerobic conditions,the maximum unit removal capacity is increased by 34.93%and 9.49%,respectively.The unit removal capacity of Cr（Ⅵ）reached 86.25mg/g after 120 min reaction at pH 5 and 25℃.The material has better removal effect under anaerobic conditions.The mechanism study shows that P@nZVI reduction of hexavalent chromium is a process of chemisorption,reduction and co-precipitation.PA-nZVI hydrogels have an interpenetrating network structure with pore sizes ranging from1 to 5μm.nZVI particles are mainly distributed in the internal network structure of the material,which can effectively inhibit the agglomeration of nZVI.PA hydrogel carrier can be reused.The unit removal capacity of Cr（Ⅵ）reached 94.25mg/g at pH 5 and 25℃.Under the low critical solution temperature（LCST）of PA material,the removal ability of Cr（Ⅵ）increases with the increase of temperature.Coexisting anions in groundwater,such as SO42-,NO3-and high concentration of humic acid,will inhibit the removal effect of Cr（Ⅵ）by PA-nZVI,and the removal of Cr（Ⅵ）by PA-nZVI is a process of adsorption,reduction and co-precipitation.This study effectively alleviates the problems of easy agglomeration and easy oxidation of nZVI,and provides certain theoretical and technical support for the practical application of nZVI. |
