| Polyacrylonitrile(PAN)has strong hydrophilicity,good stability and the ability to effectively adsorb heavy metal ions after being incorporated the adsorbents,but the ability of adsorbing heavy metal ions in the existing PAN adsorption membranes still cannot completely meet the need of wastewater,therefore,it is particular important to select adsorbent to modify the PAN adsorption membrane.Among adsorbents,Graphene Oxide(GO)and Polyamidoxime(PAO)have the advantages of large specific surface area and stable chemical properties,and they can effectively adsorb heavy metal ions by electrostatic and chelating effects respectively.So,in this paper,GO and PAO were used as adsorbents to prepare GO-PAN adsorption membrane and PAO-GO-PAN adsorption membrane,both of them could effectively adsorb Cu(Ⅱ)ions and operated stably during the adsorption process.Firstly,the effect of GO on the adsorption of Cu(Ⅱ)ions on GO-PAN adsorption membrane and the mechanism of Cu(Ⅱ)ions by GO-PAN adsorption membrane were studied.For this purpose,GO-PAN adsorption membrane was prepared by electrospinning,and the optimum membrane forming ratio and electrospinning process parameters were investigated,then the adsorption capacity of Cu(Ⅱ)ions were measured when different GO additions and environmental conditions.The results showed that the oxygen-containing functional groups(hydroxyl and carboxyl groups)on the GO-PAN membrane were negatively charged in water and could adsorb Cu(Ⅱ)ions in large amounts through electrostatic interaction,the maximum adsorption capacity was 84.02mg/g when GO was 5wt%.The optimum pH of adsorption was 5,and the effective adsorption range was concentrated in the acid pH range.The adsorption process was a non-spontaneous endothermic process conforming the Langmuir adsorption model and the pseudo-second-order kinetics model,and the thermodynamic parameter ΔG>0.Membrane surface was uniform,no beading,and no condensation when the spinning voltage was 20 KV,the receiving distance was 20 cm,the inner diameter of needle was0.5mm.Secondly,the effect of PAO on the adsorption of Cu(Ⅱ)ions on PAO-GO-PAN adsorption membrane,the mechanism of Cu(Ⅱ)ions and reusability by PAO-GO-PAN adsorption membrane were studied,For this purpose,PAO-GO-PAN adsorption membrane was prepared by electrospinning,and the adsorption capacity of Cu(Ⅱ)ions were characterized,and the adsorption capacity of Cu(Ⅱ)ions were tested in different environmental conditions.The results showed that the a large amount of amine groups and thiol groups of PAO could adsorb Cu(Ⅱ)ionthrough complex chelation and common chelation.The maximum adsorption capacity of membrane was 122.96mg/g and fiber structure on the membrane surface was complete and moderate in size when the addition of PAO was 2wt%.The effective adsorption range of pH was4-7 and the adsorption process proceeded spontaneously.After 5 times successive adsorption and desorption experiments,the adsorption capacity of membrane could still reach more than 50% of initial.Finally,the dynamic adsorption laws of PAO-GO-PAN adsorption membrane were analyzed to provide a theoretical basis for the practical application.For this purpose,the effect of flow rate,initial concentrate and other heavy metal ions existing on the dynamic adsorption were discussed.The results showed that the adsorption process took place more fully when the flow rate decreased from 50 m L/min to 10mL/min.Adsorption rate was faster when initial concentrate was higher,and 120mg/L Cu(Ⅱ)ion solution could reach saturation adsorption in 200 min.There was a strong linear relationship between the thickness of membrane and penetration time,which is in accordance with the BDST model.The membrane had no selectivity for dynamic adsorption of heavy metal ions,and the order of adsorption was Cu(Ⅱ)>Hg(II)>Cd(II)>Pb(II).After 5times consecutive adsorption and desorption experiments,the adsorption capacity of membrane could still reach more than 55% of initial value. |
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