Preparation Of Zero Valent Iron-cyclodextrin Composite Material To Remove P-Nitrophenol In Groundwater

The organic pollution of groundwater in the heavy industrial areas along the northeast coast of China is serious,and the concentration of sulfide exceeds the standard.Moreover,it is easy for seawater intrusion to lead to high salinity in groundwater.These situations have brought great difficulties to the remediation of groundwater pollution.Zero-valent iron（ZVI）has high reactivity and can treat various pollutants,which is commonly used in groundwater pollution remediation.However,ZVI is prone to agglomeration and passivation,and it is easy to react with groundwater components,resulting in low utilization efficiency.Cyclodextrin polymer（CDP）can form inclusion complexes by host-guest interaction and molecular recognition,accounting for high selectivity for organic pollutants.CDP also has porous network structure.Therefore,zero-valent iron-cyclodextrin composite（ZVI-CDP）was prepared to immobilize ZVI in the CDP network to slow down agglomeration and passivation,and the synergistic effect of selective adsorption of CDP and high activity of ZVI was used to remove organic pollutants in groundwater.In this study,CDP was prepared by cross-linking polymerization and ZVI-CDP was prepared by impregnation-in-situ liquid phase reduction.The material is about 100μm spherical black particles,which are composed of ZVI and CDP.ZVI and its oxidized product-iron oxides are distributed in the CDP structure.XPS spectra show that the composite material with the mass ratio of total iron to CDP of 1:10 has high ZVI content（13.1%）in the surface structure.Compared with CDP,the composite has smaller specific surface area,larger pore size and pore volume.The composite material synergistically removes p-nitrophenol（PNP）through CDP adsorption and ZVI degradation.Taking p H 7.0 as an example,CDP adsorption contributes33.3%for the removal of PNP by ZVI-CDP,and ZVI contributes 66.7%by reducing PNP to p-aminophenol and oxidizing it to hydroquinone.The effects of p H,dissolved oxygen（DO）and groundwater composition on the PNP removal performance of ZVI-CDP were investigated.The removal efficiency of PNP by ZVI-CDP decreased by 64.2%when p H value increased from 3 to 12.With the increase of solution p H,the degradation activity of ZVI decreased and the dissociation of PNP into anion form which was difficult to be adsorbed by ZVI-CDP was promoted,thereby reducing the removal effect of PNP by ZVI-CDP.When DO concentration in the reaction system increased from zero to 9.00 mg/L,the removal efficiency of PNP decreased by only 5.7%.Column experiments were carried out using ZVI-CDP filled columns to treat PNP solution aeration with nitrogen and air respectively.When 60 column volumes（CV）were running,the removal efficiency of PNP by the two treated columns both could reach 100%.The presence of DO had little effect on the removal of PNP by ZVI-CDP.In the groundwater components(NO₃^-,NH₄⁺,S^2-and NOM),when the concentration of NO₃^-was greater than 50 mg/L,the removal of PNP by ZVI-CDP was inhibited.When the concentration of NO₃^-was 50 mg/L and 100 mg/L,the removal efficiency of PNP by ZVI-CDP were reduced by 10.7%and 12.6%,respectively.Other ions and NOM had no inhibitory effect on the removal of PNP by ZVI-CDP at the set maximum concentration.In the cyclic degradation experiments,when the sulfur ion concentration was 50mg/L,the removal of PNP by ZVI-CDP was not inhibited at the first reaction time.At the beginning of the second cycle,the removal of PNP was inhibited due to the decrease of the specific surface area of ZVI-CDP.Other ions（except NO₃^-）and NOM had no inhibitory effect on the removal of PNP.According to GB/T 14848-2017 groundwater quality standard V,the simulated PNP（10mg/L）contaminated groundwater was prepared.The removal efficiency of PNP in groundwater by ZVI-CDP filled column was evaluated.It was found that the removal efficiency of PNP by ZVI-CDP was maintained at 100%in 70 CV,and the effective treatment load was 58.3 mg PNP/g ZVI-CDP,which was 7 times higher than that of CDP and ZVI physical mixture.