Construction Of Functional Ion-imprinted Nanocomposite Membranes For The Selective Separation And Mechanism Research

Membrane separation technique（MST）is a new type of separation technique.It has been widely applied in various areas including pollution control,resource recycling and wastewater treatment owing to low energy consumption,wide range of application and easy operation.However,due to the defects and deficiencies of existing commercial membranes,there are often unfavorable factors such as poor hydrophilicity and easy contamination in practical applications,which limits the application of membranes.Moreover,commercial membranes still have difficulties in efficiently selective separation of target ions from analogues with similar radii and properties.In this context,ion-imprinted nanocomposite membranes（IINMs）are presented by combining MST with nanocomposite technique（NT）and ion-imprinting technique（IIT）.NT is used to load functional nanomaterials on membranes,thereby providing different functional properties（such as hydrophilicity and anti-fouling property）for membranes,effectively improving its comprehensive performance and expanding the range of applications.IIT is used to build“selective recognition sites”on surface and in pores of membranes,which makes them feasible to effectively separate,concentrate and purify target ions.In this research,novel ion-imprinted nanocomposite membranes have been investigated.Li⁺-imprinted nanocomposite membranes（Li-IIMs）were prepared based on polyethersulfone membranes.The surface adhesion of the materials was improved by dopamine biomimetic modification techniques.Pd²⁺-imprinted nanocompsite membranes（Pd-IIMs）were prepared based on polydimethylsiloxane membranes.Secondary reaction platform was established by the surface modification of silane coupling agent.Eu³⁺-imprinted nanocomposite membranes（Eu-IIMs）were prepared with regenerated cellulose membranes as substrates.Silver nanoparticles were grafted on membranes to enhance the anti-fouling performance.Fourier Transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and atomic force microscopy（AFM）were used to reveal chemical compositions and surface morphologies of membranes.The surface hydrophilicity of membranes was investigated using water contact angle（CA）tester.The selectivities of the as-prepared membranes for ions separation were systematically revealed by isothermal adsorption and kinetic adsorption.The separation mechanism of ion-imprinted nanocomposite membranes towards target ions was explored based on isothermal adsorption model and kinetic adsorption model.The details are as follows:（1）Preparation of Li⁺-imprinted nanocomposite membranes based on multilayer functionalization modification and study of selective separation performance towards Li⁺Polydopamine/silicon dioxide/12-crown-4 multilayer Li⁺-imprinted nanocomposite membranes（Li-IIMs）were developed based on polyethersulfone membranes using Li⁺as templates,12-crown-4 as ligands andα-methacrylic acid as functional monomers.Surface adhesion and hydrophilicity were improved by biomimetic modification of dopamine and surface nanocomposite modification process.The better fitting results of Li-IIMs isothermal adsorption data to the Langmuir model showed that the adsorption process of Li-IIMs towards Li⁺is single-layer adsorption,and the adsorption sites were evenly distributed on the surface of the membranes.The better fitting results of Li-IIMs kinetic adsorption data to the pseudo-second-order model showed that Li-IIMs adsorption towards Li⁺included both physical diffusion and chemical adsorption,demonstrating the successful construction of Li⁺-imprinted sites.Restlus of adsorption and penetration in simulated salt lake environment showed that Li-IIMs have superior adsorptive selectivity（Li⁺/Na⁺=1.85,Li⁺/K⁺=2.07）and permeation selectivity（Na⁺/Li⁺=7.39,K⁺/Li⁺=9.86）towards Li⁺.Rebinding capacity of Li-IIMs was still higher than 88.1%of the original after ten regeneration cycles.Above results proved that the as-prepared Li-IIMs possessed superior regeneration and stability performance with high selectivity towards Li⁺in aqueous solutions.（2）PreparationofPd²⁺-imprintednanocompositemembranesbasedon three-dimensional macroporous materials and study of selective separation performance towards Pd²⁺Polydimethyl siloxane（PDMS）with good chemical stability,wide heat resistance range,high mechanical strength and good flexibility was used as the membrane material.Three-dimensional macroporous PDMS basilar membranes with high flux and mechanical strength were developed based on sacrificial template method using sugar cubes as hard templates.The secondary reaction platform for subsequent processes was established by the surface modification of KH570.Three-dimensional macroporousPd²⁺-imprinted nanocomposite membranes（Pd-IIMs）with high flux were prepared using Pd²⁺as templates,8-aminoquinoline and 4-vinylpyridine as ligands,as well as hydroxyethyl methacrylate as functional monomers.The better fitting results of Pd-IIMs isothermal adsorption data to the Langmuir model showed that the adsorption process of Pd-IIMs towards Pd²⁺is single-layer adsorption,and the adsorption sites were evenly distributed on the surface of the membranes.The better fitting results of Pd-IIMs kinetic adsorption data to the pseudo-second-order model showed that Pd-IIMs adsorption towards Pd²⁺included both physical diffusion and chemical adsorption,demonstrating the successful construction of Pd²⁺-imprinted sites.Restlus of adsorption and penetration in simulated electroplating wastewater environment showed that Pd-IIMs have superior adsorptive selectivity(Pd²⁺/Co²⁺=2.72,Pd²⁺/Cu²⁺=2.95,Pd²⁺/Cd²⁺=2.53,Pd²⁺/Ni²⁺=3.29)and permeation selectivity(Co²⁺/Pd²⁺=4.48,Cu²⁺/Pd²⁺=3.86,Cd²⁺/Pd²⁺=4.27,Ni²⁺/Pd²⁺=4.33)towards Pd²⁺.Rebinding capacity of Pd-IIMs was still higher than 90.6%of the original after ten regeneration cycles.Above results proved that the as-prepared Pd-IIMs possessed superior regeneration and stability performance with high selectivity towards Pd²⁺in aqueous solutions.（3）Preparation of thermosensitive Eu³⁺-imprinted composite membranes based on intercalation and study of selective separation performance towards Eu³⁺The graphene oxide/silicon dioxide basilar membranes were prepared by an intercalation method.Silver nanoparticles were grafted on basilar membranes to enhance the anti-fouling performance.The thermosensitive Eu³⁺-imprinted nanocomposite membranes（Eu-IIMs）for selective separation of Eu³⁺from mixed rare earth ions were prepared using Eu³⁺as templates,N-isopropyl acrylamide and acrylamide as functional monomers.The better fitting results of Eu-IIMs isothermal adsorption data to the Langmuir model showed that the adsorption process of Eu-IIMs towards Eu³⁺is single-layer adsorption,and the adsorption sites were evenly distributed on the surface of the membranes.The better fitting results of Eu-IIMs kinetic adsorption data to the pseudo-second-order model showed that Eu-IIMs adsorption towards Eu³⁺included both physical diffusion and chemical adsorption,demonstrating the successful construction of Eu³⁺-imprinted sites.Restlus of adsorption and penetration in simulated mixture of rare earth ions showed that Eu-IIMs have superior adsorptive selectivity(Eu³⁺/La³⁺=1.82,Eu³⁺/Gd³⁺=1.57,Eu³⁺/Sm³⁺=1.45)and permeation selectivity(La³⁺/Eu³⁺=3.82,Gd³⁺/Eu³⁺=3.47,Sm³⁺/Eu³⁺=3.34)towards Eu³⁺.Rebinding capacity of Eu-IIMs was still higher than 91.9%of the original after ten regeneration cycles.Above results proved that the as-prepared Eu-IIMs possessed superior regeneration and stability performance with high selectivity towards Eu³⁺in aqueous solutions.The results showed that functional ion-imprinted nanocomposite membranes based on membrane separation technique,nanocomposite technique and ion-imprinting technique have the advantages of high selectivity,high functionality,excellent comprehensive performance and devisable preparation.They have potential applications in salt lake resource extraction,electroplating wastewater treatment and rare earth separation.