Adsorption Performance And Mechanism Of Electrospun Nanofiber Membranes For Heavy Metals In Groundwater

Heavy metal pollution in groundwater is a serious problem,which has attracted scholars’ extensive attention all around the word in recent years.How to effectively remove toxic heavy metals from groundwater has always been a research hotspot in the field of groundwater and environment.Adsorption has become a common method to remove heavy metals in contaminated groundwater,due to its advantages such as a wide variety of adsorbents,high efficiency,easy operation,good reversibility and low cost.Nanofibrous membranes prepared by electrospinning technique have some advantages,such as large specific surface area,high porosity,good flexibility,easy separation and recycling.In addition,the electrospun nanofibrous membranes(ENFMs)could be transformed into adsorption materials with special through a variety of material blending,surface modification and other method.Thus,ENFMs have aroused considerable interests in the field of adsorption of heavy metals in water.In this paper,a variety of organic/inorganic composite CENFMs were prepared using polyvinyl alcohol(PVA),chitosan(CS)/PVA(CS/PVA),polystyrene(PS)organic polymer as the substrate,and mixing activated carbon(AC),graphene oxide(GO)and multi-walled carbon nanotubes(MWCNTs)as inorganic material,respectively.After preliminary screening,the PS/AC CENFMs showed the best performance.When the doping amount of AC is 3 wt%,the PS/AC CENFMs showed the best adsorption performance,and their maximum adsorption capacities for Cu(II)and Cr(VI)in water could reach 231.05 and 215.90 mg/g,respectively.On this basis,the adsorption kinetics and isotherm of heavy metals in water by PS/AC CENFMs were studied,and the effects of initial concentration,AC doping amount,solution p H value,and reaction temperature on the adsorption performance of the CENFMs were investigated.The results showed that the adsorption processes of Cu(II)and Cr(VI)on the PS/AC-3% CENFMs conformed to the pseudo-first-order kinetic model and Langmuir isotherm adsorption model,indicating that they are monolayer adsorption on the membrane surface.The adsorption of heavy metals on CENFMs mainly depended on the electrostatic interaction between the active site on the surface of activated carbon and metal ions,and were spontaneous endothermic processes.Finally,dynamic adsorption experiments were carried out using actual polluted groundwater to investigate the dynamic adsorption capacity of PS/AC-3% CENFMs for various heavy metals in water under different flow rates,membrane thicknesses and different initial concentrations of Cu(II).The experimental results showed that the PS/AC-3% CENFMs have a good adsorption and removal efficiency for various heavy metals in actual groundwater.The low flow rate could improve the adsorption capacity and utilization efficiency of the CENFMs in the dynamic adsorption process.The increase of initial Cu(II)concentration increased the adsorption capacity of the CENFMs when reaching penetration and saturation adsorption,but could not significantly improve their utilization efficiency.With the increase of membrane thickness,the penetration time was prolonged,but the saturated adsorption capacity and utilization efficiency of the CENFMs were not significantly affected.