Construction Of Chitosan-Based Molecularly Imprinted Membranes And The Mechanism Of Selective Identification And Separation Of Phenolic Compounds

In olive oil processing and production,a large amount of olive mill wastewater（OMW）will be generated.It is urgent to develop effective treatment of OMW that meets the national conditions.This leads to a series of environmental pollution problems,which directly affect human health.However,PCs have been shown to have various pharmacological and biological activities.The conventional wastewater treatment technology is difficult to achieve the effective separation and resource utilization of high-concentration PCs in OMW,which causes significant environmental pollution and resource waste.Therefore,it is essential to study and develop a selective separation method to selectively separate the single PCs in OMW.In recent years,molecularly imprinted membranes（MIMs）have shown unique advantages in selective separation,extraction,enrichment,and purification.However,traditional MIMs cannot meet the effective separation of high-concentration PCs due to bottlenecks such as few specific recognition sites and poor selectivity.Therefore,it is of great significance and research value to develop MIMs with high selectivity,high permeability,excellent aqueous phase recognition ability,and high density of recognition sites for the efficient separation of single PCs in OMW.This thesis addressed the serious scientific problem of selective recognition and separation of high-concentration PCs in OMW.We used the preparation concepts of covalent/non-covalent assembly strategy,tannic acid modulation strategy,and light/heat-driven environmental response strategy to successfully obtain chitosan-based molecularly imprinted membranes and achieve the system construction for selective separation of three representative PCs（lignocaine,kaempferol,and quercetin）in OMW.The prepared chitosan-based molecularly imprinted membranes can effectively solve the problems of difficult identification/separation of single PCs in complex environments,enhance the selectivity,permeability,fouling resistance,and stability of MIMs,and deeply investigate the specific recognition mechanism of MIMs,which provides research ideas and experimental basis for the study and development of functional MIMs with high selectivity for selective separation of PCs.The main research contents of this thesis are as follows:（1）Construction of high performance MIMs based on covalent/non-covalent assembly strategy and the mechanism of selective separation of luteolina.With the starting point of enhancing the adsorption capacity and selectivity,manganese particles（Mn NPs）extracted from green tea were homogeneously blended in polyacrylonitrile（PAN）solution by the blending method and nanofiber membranes were prepared by the electrostatic spinning method.The chitosan（CS）was wrapped on the surface of the nanofiber membrane to form a hydrated layer to improve its fouling resistance and tensile strength.Subsequently,lignocaine（LTL）nanofiber imprinted membranes（E-LMIMs）were prepared using LTL as a template molecule,4-aminophenylboronic acid（4-APBA）and phenyltriethoxysilane（PTEOS）as bifunctional monomers,and tetramethoxysilane（TMOS）as a crosslinker.The adsorption and separation properties of E-LMIMs were investigated by isothermal adsorption,kinetic adsorption,selective permeation,and dynamic separation.And excellent selectivity coefficients（3.55 and 4.20）,separation factors（4.04）,and permeation selectivity coefficients（4.41 and 5.41）were obtained,resulting in E-LMIMs with both high selectivity and high adsorption capacity.Meanwhile,the selective separation mechanism was deeply investigated by in-situ diffuse reflection infrared Fourier transform spectroscopy（in-situ FTIR）and molecular dynamics simulation.The spatial effect of the specific recognition sites and the covalent/non-covalent interaction with LTL further improved the selectivity of E-LMIMs.The chitosan-based nanofiber imprinted membrane constructed by the Mn NPs induction strategy is expected to deal effectively with OMW.b.With the starting point of constructing high-matching imprinted sites and further enhancing selectivity,LTL composite imprinted membranes（MPL@CSMIMs）were successfully constructed by a bilayer surface imprinted strategy for the selective separation of LTL.Firstly,polydopamine（PDA）was used as a functional monomer and molecular linker to construct the first layer of imprinted sites on the CS membrane surface.Secondly,the second layer of recognition sites was successfully constructed by introducing covalent/non-covalent functional monomers（phenylboronic acid and amino functional groups）on the surface of the first PDA layer via atom transfer radical polymerization（ATRP）.The isothermal and kinetic adsorption,permeation selectivity,and stability of MPL@CSMIMs were investigated.The results showed that MPL@CSMIMs had excellent adsorption capacity(49.63 mg g^-1)and selective permeation performance(β_AGN/LTL=5.80,β_CTC/LTL=12.82)and achieved selective discrimination and separation of LTL in the mixed system.Meanwhile,the selective separation mechanism was deeply investigated by in-situ FTIR,molecular dynamics simulation,and X-ray photoelectron spectroscopy（XPS）.The MPL@CSMIMs constructed by the bilayer surface imprinting strategy have more stable and precise imprinted sites to improve selective recognition and separation performance,providing a feasible strategy for developing and designing high-performance MIMs.（2）Construction of high-density imprinting site MIMs based on tannic acid regulation strategy and study on the mechanism of selective separation of kaempferola.Taking the effect of constructing high-density sites in the membrane pore structure on selectivity as the starting point,we successfully prepared porous CS membranes with interpenetrating network structure.Deep eutectic solvent（DES）and CS molecular chains effectively regulated the membrane pore structure using non-covalent interactions（hydrogen bonding）.Subsequently,the tannic acid（TA）and3-aminopropylethoxysilane（ATPES）were used to construct specific recognition sites on the porous CS membrane surface and in the micropore channels by in-situ growth strategy to successfully prepare kaempferol（KMF）monolithic imprinted membranes（E-KMIMs）.MIMs with only TA/APTES imprinted sites on the membrane surface（S-KMIMs）were also prepared as a comparison term to investigate their isothermal adsorption,kinetic adsorption,and permeation properties.Compared with S-KMIMs(α_KMF/AGN=2.38 andα_KMF/QRE=2.47),E-KMIMs combined higher selective adsorption(α_KMF/AGN=3.48 andα_KMF/QRE=3.51)and selective permeation performance(β_AGN/KMF=4.14 andβ_QRE/KMF=2.78).The selective identification and separation of KMF in the mixed system were achieved.In addition,molecular dynamics simulations and in-situ FTIR were used to demonstrate the non-covalent interactions between KMF and specific recognition sites.This work provides a feasible strategy for designing and developing simple and efficient molecularly imprinted separation membranes.b.The influence of membrane pore structure on permeate flux and permeate selectivity was used as the starting point to design and prepare two-dimensional（2D）layered nanosheet assembly separation membranes.The TA-functionalized nanosheets（f-BN）were successfully obtained by inserting green surfactant in the middle of hexagonal boron nitride nanosheets（h-BN）with chemical inertness and antifouling properties through exfoliation technique to weaken the interlayer interactions.Subsequently,f-BN was immobilized on the CS membrane surface by vacuum filtration to obtain a high-density hydrophilic layer.The lamellar separation channel provided an excellent hydrophilic chemical environment to provide sufficient growth space for the subsequent synthesis of imprinted sites.KMF mixed matrix imprinted membranes（KMIMs）were successfully prepared by free radical polymerization using KMF as the template molecule and two different ionic liquids as functional monomer and crosslinker.The selective separation performance of KMIMs was investigated by isothermal adsorption,kinetic adsorption,dynamic filtration,and selective permeation experiments.The results showed that the KMIMs exhibited high selective separation factors(α_KMF/AGN=3.99 andα_KMF/QRE=3.32)and selective permeation factors(β_AGN/KMF=6.65 andβ_QRE/KMF=4.63)for the selective discrimination and separation of KMFs.The selective separation mechanism of KMIMs was demonstrated using UV absorption spectroscopy and in-situ FTIR.This work provides a new idea for constructing specific selective sites in 2D separation membranes,optimizing the chemical microenvironment,and achieving specific separation.（3）Construction of environmentally-responsive MIMs based on co-imprinting strategy driven by light/heat and study on the mechanism of selective quercetin separationa.Based on a simple,efficient,and fast method to promote the capture/release performance of target molecules,light-driven MIMs with fast response were prepared.Firstly,tetraethyl orthosilicate（TEOS）as a silane precursor was hydrolyzed to silane hydroxyl groups under acidic conditions to obtain an organic-inorganic hybrid membrane with large pore structure.Light-driven responsive quercetin（QRE）organic-inorganic hybrid imprinted membranes（P-QMIMs）were synthesized using QRE as the template molecule,4-methylacryloxyazobenzene（MAA）as the photo-responsive functional monomer,acrylamide（AM）as the co-monomer,ethylene dimethacrylate（EGDMA）as the crosslinker,and azobisisobutyronitrile（AIBN）as the initiator.The photo-responsive performance of P-QMIMs was investigated by visible light/ultraviolet light alternating irradiation.The results showed that the P-QMIMs undergo trans-cis-isomerization reversible reaction under the alternating irradiation of visible light（440 nm）and ultraviolet light（365 nm）to rapidly capture and release the QRE.The selective separation performance of P-QMIMs was investigated by isothermal adsorption,kinetic adsorption,and permeation experiments.The results showed that P-QMIMs have both high adsorption selectivity(α_QRE/AGN=3.18 andα_QRE/KMF=3.32)and permeability selectivity(β_AGN/QRE=3.68 andβ_KMF/QRE=2.52),achieving the selective identification and separation of QRE.XPS and in-situ FTIR were used to explain the specific recognition mechanism and obtain the selective mass transfer mechanism.This work opens new ideas for designing and developing"intelligent"MIMs.b.To further simplify the regeneration process and synergistically enhance the fouling resistance as the starting point,N-isopropylacrylamide（PNIPAM）was used as a thermal-responsive skeleton monomer and antifouling polymer chain to prepare thermal-driven responsive MIMs.Firstly,organic-inorganic hybrid membranes（CS@TEOS）were prepared by optimizing and regulating the polycondensation time of TEOS and the molecular weight of the pore-producing agent to obtain more suitable pore size and structure,to effectively balance the influence of membrane permeability flux on selectivity.Subsequently,thermal-driven responsive QRE self-cleaning imprinted membrane（T-QMIMs）was prepared by ATRP using QRE as template molecule,NIPAM as thermal-responsive monomer,3-AAPBA as covalent functional monomer and N,N’-methylene diacrylamide as a hydrophilic crosslinker.The thermal-responsive pattern of T-QMIMs was investigated by adsorption experiments at different temperatures.The experimental results showed that the PNIPAM chain could produce a conformational transformation when the temperature was below or above the critical temperature（32 ^oC）,which effectively adsorbed and desorbed QRE.And the PNIPAM chain would collaboratively produce hydrophilic/hydrophobic surface performance to regulate the regeneration performance of T-QMIMs to achieve the self-cleaning performance.The selective separation performance of T-QMIMs was investigated by adsorption and permeation experiments.The results showed that T-QMIMs exhibited excellent selective separation factors(α_QRE/AGN=4.45 andα_QRE/KMF=3.95)and high permeability selectivity(β_AGN/QRE=3.62 andβ_KMF/QRE=3.04),which realized the selective identification and separation of QRE.XPS and in-situ FTIR investigated the specific recognition/separation mechanism of T-QMIMs.The successful preparation of this experiment provides a solid theoretical and practical basis for the design and development of collaborative antifouling and highly selective environmentally responsive MIMs.