Study On Loading And Adsorption Properties Of AOPAN/Cyclodextrin Nanofiber Membrane

With the rapid development of nuclear energy,the problem of uranium-containing wastewater has become increasingly prominent.Uranium-containing wastewater poses a great threat to the ecological environment and human health,and its treatment has become an urgent problem for people to solve.In recent years,adsorption technology has been very active in uranium extraction and uranium-containing wastewater treatment.The key to adsorption lies in high-adsorption property materials and processes.Amidoxime-based chelating fibers have the advantages of high adsorption capacity,high selectivity and high degree of functionalization,so it is regarded as an ideal material for uranium-containing wastewater treatment.AOPAN/?-CD nanofiber membranes were synthesized in one step using polyacrylonitrile(PAN)and beta-cyclodextrin(?-CD)as raw materials by in-situ amidoxime modification with hydroxylamine hydrochloride and then electrospinning technology with high fiber quality,good adsorption performance and high selectivity.A large amount of Saccharomyces cerevisiae was loaded on fiber to prepare nanofiber membrane with high content of active groups and excellent adsorption performance by in-situ loading technology.A series of characterization of membrane materials were carried out to research the loading characteristics of fiber membranes on microorganisms and adsorption characteristics,and to study the adsorption mechanism of materials.The main contents are as follows:(1)AOPAN/?-CD nanofiber membranes were synthesized in one step using polyacrylonitrile(PAN)and beta-cyclodextrin(?-CD)as raw materials by in-situ amidoxime modification with hydroxylamine hydrochloride and then electrospinning technology.This paper explored the effect of different modification conditions on the adsorption performance of AOPAN/?-CD nanofiber membranes,and use SEM,FT-IR,XPS and other analysis techniques to explore the fiber surface morphology,performance and modification mechanism.The results showed that when the molar ratio of cyanohydroxylamine was 1:1 and the modification time was 2 h,the morphology distribution of the AOPAN/?-CD nanofiber membrane was more uniform,and the fiber diameter was about 230 nm.The tensile strength of AOPAN/?-CD is 3.006 MPa,which can maintain thermal stability at 200�C.The adsorption capacity is the highest,reaching78.62 mg�g^-1.(2)Use batch adsorption experiments to study the adsorption performance of AOPAN/?-CD to U(VI),The results show that the adsorption capacity of AOPAN/?-CD adsorbent for U(VI)at p H=5.0,T=328.15 K,t=1440 min,C₀=260 mg�L^-1,and the dosage is 0.02 g,the maximum adsorption capacity is 315.71 mg�g^-1.the fitting analysis of isothermal adsorption model and kinetic model shows that the adsorption of uranium by AOPAN/?-CD is mainly a monolayer chemical adsorption process,which is a endothermic and spontaneous.The coexisting ions Cu²⁺,Ni²⁺,Pb²⁺,Mg²⁺,Sr²⁺and Zn²⁺have little effect on the adsorption of U(VI)by AOPAN/?-CD,and the AOPAN/?-CD nanofiber membrane has a good selectivity for uranium,because its distribution coefficient K_d is about 10000 m L�g^-1.The main adsorption mechanism of AOPAN/?-CD for U(VI)is Chelation:the oxime group and amino group in the amidoxime on the surface of the fiber membrane coordinate and chelate with the uranyl ion to form a stable chelate,the hydroxyl O of inside the cyclodextrin is coordinated and complexed with uranyl ions.(3)AOPAN/?-CD immobilization saccharomyces nanofiber membranes(AOPAN/?-CD@SC)were synthesized using saccharomyces as the functional monomer by in-situ crosslinking method.To study the influence of electrospinning process and conditions of immobilization on yeast load and the U(VI)adsorption performance of AOPAN/?-CD@SC nanofiber membrane.The results confirm that the optimal conditions for prepare AOPAN/?-CD@SC are as follows:the addition amount of cyclodextrin is 70%,the applied voltage is 12 Kv and receiving distance is 16 cm.The optimal loading conditions for AOPAN/?-CD@SC are as follows:the culture temperature is 30�C,the culture time is 32 h,and crosslinking agent concentration is 0.4%.(4)Use batch adsorption experiments to study the adsorption performance of AOPAN/?-CD@SC to U(VI),The results show that the adsorption capacity of AOPAN/?-CD@SC adsorbent for U(VI)at p H=5.0,T=328.15 K,t=1440 min,C₀=270 mg�L^-1,and the dosage is0.01 g,the maximum adsorption capacity is 637.23 mg�g^-1.the fitting analysis of isothermal adsorption model and kinetic model shows that the adsorption of uranium by AOPAN/?-CD@SC is mainly a monolayer chemical adsorption process,which is a endothermic and spontaneous.The coexisting ions Ni²⁺,Mg²⁺,Sr²⁺and Zn²⁺have little effect on the adsorption of U(VI)by AOPAN/?-CD@SC,while Cu²⁺and Pb²⁺has a greater competitive relationship with the adsorption of U(VI)by AOPAN/?-CD@SC.The main adsorption mechanism of AOPAN/?-CD@SC to U(VI)is coordination and ion exchange:The oxime group and amino group in the amidoxime on the surface of the fiber membrane coordinate and chelate with the uranyl ion to form a stable chelate.The hydroxyl O in the cyclodextrin is coordinated and complexed with the uranyl ion,and the amino group on the yeast surface,Carboxyl group,phosphoric acid group coordinate with uranyl ion,The K and Mg ions undergo an ion exchange reaction with uranyl ions.