Fabrication Of Functional Adsorbents Based On Boronate Affinity And Their Application In The Separation Of Shikimic Acid

The drug resources in natural environment are very rich,especially the natural products in environmental plants are important raw materials of many drugs or health products.As a key raw material for the synthesis of oseltamivir phosphate,a specific drug against influenza virus,shikimic acid（SA）is in great demand.Currently,SA is mainly extracted from environmental plants.However,the extracted SA is often accompanied by a lot of impurities.The traditional separation and purification methods have some common problems,such as complicated operation steps,long time,low separation efficiency and poor selectivity,which makes it difficult to achieve rapid and efficient separation of SA.Therefore,it is urgent to establish and perfect a new method for selective identification,separation and purification of shikimic acid.Owing to their unique affinity recognition and separation ability,boronate affinity functional materials show attractive application prospects in the selective separation of complex samples containing cis-dihydroxyl structures.However,for actual samples with complex compositions,the practical application of single boronate affinity materials will be limited by the lack of specific recognition sites,the high p K_avalue of boric acid ligand,the slow mass transfer rate,and the insufficient p H response ability to capture and release cis dihydroxyl compounds.Therefore,in this work,based on the unique cis-dihydroxyl structure of shikimic acid molecules,boronate affinity technology was combined with surface chemical modification,molecularly imprinting,electrospinning and self-driven motor technology to prepare boronate affinity specific composites with high specific surface area,high porosity,abundant specific recognition sites and strong mass transfer efficiency to effectively improve the separation efficiency of shikimic acid.The main research contents are as follows:1.Preparation of boronate affinity functionalized natural polymer composites and study on the separation performance of shikimic acid（1）Considering the effect of material microstructure on separation performance,the magnetic core Fe₃O₄ nanoparticles prepared by solvothermal reaction was coated with chitosan to form a magnetic chitosan matrix.Carboxylate chitosan was prepared by crosslinking magnetic chitosan with epiclorohydrin under alkaline conditions.Then 3-aminobenzenoborate（APBA）was used as boric acid ligand and modified on the surface of carboxyl modified chitosan by chemical bonding to synthesize boronate affinity functionalized magnetic chitosan adsorbent（FCT-COOH-BA）.The static adsorption experiment results showed that the maximum adsorption capacity of FCT-COOH-BA was 23.8 mg g^-1 at p H=8 and 25°C.Adsorption kinetic fitting results showed that the specific adsorption process of FCT-COOH-BA for SA was dominated by chemisorption.The competitive adsorption behavior of FCT-COOH-BA towards SA and its structurally similar compounds such as p-nitrophenol（P-NP）,hydroquinone（HDQ）,Resorcinol and p-hydroxybenzoic acid（PHB）was studied.The results showed that FCT-COOH-BA has excellent specific selective recognition ability.And FCT-COOH-BA still had high activity after multiple adsorption-desorption cycles,the microstructure of the material was intact,and the recycling rate was high.（2）Naturalβ-cyclodextrin polymer with abundant functional groups was used as the main adsorption material,and boric acid modified magneticβ-cyclodextrin polymer（FPCD-COOH-BA）with porous structure,rapid magnetic response and p H response was designed and prepared by surface chemical modification.Firstly,dopamine-modified Fe₃O₄ nanoparticles（Fe₃O₄@PDA）were synthesized,and thenβ-cyclodextrin was introduced to obtain magneticβ-cyclodextrin composites（Fe₃O₄@PDA@β-CD）.Boronate affinity functionalized magneticβ-cyclodextrin adsorbent was prepared by surface grafting of carboxyl group,boronate affinity and surface modification.The maximum adsorption capacity of FPCD-COOH-BA reached 31.6 mg g^-1 at p H=8.5 and 25°C.Moreover,FPCD-COOH-BA showed good adsorption selectivity and regeneration performance.The adsorption capacity remained above 83%after 5 regeneration cycles.2.Preparation of boronate affinity molecularly imprinted polymers and study on the separation performance of shikimic acid（1）From the perspective of boronate affinity/molecularly imprinted double recognition sites and the effect of porous structure on the separation performance of adsorbent,double bonds were introduced on the surface of dendritic fibrous porous silica nanoparticles（DFSP）prepared by hydrothermal method.On this basis,the boronate affinity molecularly imprinted layer was constructed via one step to obtain materials with boronate affinity/molecularly imprinted double recognition sites（DFSP@MIPs）.The introduction of DFSP provided excellent specific surface area and mesoporous structure.The results of static adsorption experiments showed that DFSP@MIPs had a maximum adsorption capacity of 43.71 mg g^-1 for SA at p H=8and 35°C,which is 3.75 times than that of non-imprinted materials.The construction of boronate affinity/molecularly imprinted double recognition sites significantly improved the adsorption specificity of DFSP@MIPs.Compared with other adsorption competitors,DFSP@MIPs showed higher imprinting factors and selectivity factors for SA.The results of five successive regeneration experiments showed that DFSP@MIPs has good adsorption and regeneration ability for the target SA.（2）In order to further improve the operability during the separation process,boronate affinity molecularly imprinted membrane materials with high selectivity and stability were constructed in situ on the commercially available porous PVDF membrane matrix combined with membrane separation technology.The surface of PVDF membrane was functionalized with dopamine and used as the secondary platform for vinyl modification.Then boronate affinity molecularly imprinted membrane material（SA-imprinted-BAMIMs）was prepared by surface imprinting.The microstructure,chemical composition,surface wettability and stability of SA-imprinted-BAMIMs were studied in detail by means of various characterization methods.The results of the water contact angle experiment showed that the hydrophilic imprinted layer was successfully constructed on the surface of hydrophobic PVDF membrane,which was conducive to the selective separation of SA.Static adsorption experiment results showed that the maximum adsorption capacity of SA-imprint-BAMIMs was 51.99 mg g^-1,nearly 7 times higher than that of SA-BANIMs(7.42 mg g^-1)under p H=8 and 35°C.The competitive adsorption behavior of SA-imprinted-BAMIMs towards SA and its structurally similar compounds PHB,HDQ and Quercetin was studied.The results showed that the selectivity factors of SA-imprinted-BAMIMs for SA/PHB,SA/HDQ and SA/Quercetin were 5.759,4.415 and 3.360,respectively,indicating that the material has good adsorption selectivity.Compared with non-covalent imprinting,boronate affinity covalent imprinting has great advantages in improving adsorption capacity and specificity.In addition,the adsorption capacity loss of SA-imprinted-BAMIMs was 6.98%after 8 cycles,and continuous ultrasonic processing caused little damage on the adsorption performance of SA-imprinted-BAMIMs,demonstrating that the SA-imprinted-BAMIMs has excellent stability and reproducibility.3.Preparation of electrospinning fiber based teamed boronate affinity functionalized molecularly imprinted composites and study on the separation performance of shikimic acid（1）Teamed boronate affinity（TBA）strategy was adopted to achieve the goal of reducing the binding p H to neutral or acidic conditions.Firstly,the polyacrylonitrile（PAN）substrate membrane was prepared by electrospinning,then the multi-functional intermediate layer of polyethylenimine（PEI）-PAN was constructed by electrospinning technology and abundant amino groups were introduced.Subsequently,the"sandwich-like"electrospun nanofiber-based TBA molecularly imprinted membrane（S-MIPM）were prepared by surface imprinting techniques.The introduction of PEI enhanced the adhesion between PAN substrate and subsequent molecularly imprinted layer,additionally,offered abundant reaction sites for more boric acid moieties to decrease the p K_a value of boric acid.Compared with S-MIP_gPM prepared by conventional chemical grafting,S-MIPM was superior to S-MIP_gPM in surface wettability,tensile resistance and selective permeability.The static adsorption results showed that the optimal binding p H of S-MIPM decreased to neutral,and the maximum adsorption capacity was 50.4 mg g^-1.The maximum adsorption capacity of S-MIPM obtained by Langmuir isotherm model was 2.45 times higher than that of S-MIP_gPM.The adsorption selectivity and permeability tests showed that S-MIPM possessed excellent ability of specific recognition and capture.It can be inferred from the selective permeation results that the specific recognition sites for SA on the surface of S-MIPM effectively intercepted the SA in the solution in the permeation process driven by concentration gradient.Such specific recognition and capture property significantly inhibited the permeation of SA and played a leading role in the selective separation of SA.（2）ZIF-8 cubes synthesized with zinc nitrate hexahydrate and 2-methylimidazole as raw materials were blended with PAN to form a spinning precursor solution to prepare ZIF-8/PAN nanofibers by electrospinning.Hollow electrospun nanofibers（HCESNFs）with highly porous structure were obtained by high temperature anaerobic calcination of ZIF-8/PAN nanofibers,which was used as the reaction platform for epoxy modification.Then PEI was modified on the surface of HCESNFs by epoxy ring-opening reaction.TBA molecular group was formed by self-assembly of 1,6-hexamethylenediamine and APBA.The molecularly imprinted hollow electrospinning nanofibers（MI-HCESNFs）derived from ZIF-8/PAN nanofibers were obtained by TBA strategy.The specific surface area of MI-HCESNFs was 764.52 m²g^-1 and the material possessed excellent mesoporous structure.The highly porous hollow fiber substrate was conducive to surface modification and construction of abundant active sites,leading to the enhancement of recognition ability and mass transfer efficiency.Additionally,the surface imprinting process by TBA strategy minimized the diffusion path of the target molecule and endowed the material with excellent adsorption performance.The results of static adsorption experiments showed that the maximum adsorption capacity of MI-HCESNFs for SA reached 127.8mg g^-1 at p H=7.Moreover,the competitive adsorption behavior of MI-HCESNFs towards SA and its structurally similar compounds HDQ,PHB,Quercetin and 2,4-DHBA was studied.The results showed that MI-HCESNFs presented good adsorption selectivity with selectivity factors of 9.642,7.916,3.605 and 13.84 for SA/HDQ,SA/PHB,SA/Quercetin and SA/2,4-DHBA,respectively.4.Preparation of biomass-based boronate affinity functionalized molecularly imprinted micro/nanomotors and study on the separation performance of shikimic acid（1）Boronate affinity molecularly imprinted materials were combined with self-driven motors to prepare adsorbent materials with both motion characteristics and specific adsorption ability for the separation and purification of SA.Waste rape pollen was used as biological template to prepare hollow biomass carbon particles.The bimetallic oxide micromotors（C/Al₂O₃/Mn O₂/Mg-Al LDH）were prepared by hydrothermal method and immersion-hydrothermal method successively.The molecularly imprinted layer was constructed on the surface of the micromotors combined with the TBA strategy to prepare boronate affinity functionalized molecularlyimprintedMg-Albimetallicoxidemicromotors（C/Al₂O₃/Mn O₂/LDH/MIPs）.The static adsorption experiment results showed that the maximum adsorption capacity of C/Al₂O₃/Mn O₂/LDH/MIPs could reach 129.51 mg g^-1 at p H=7 with 7 wt%H₂O₂.The presence of H₂O₂ significantly improved the adsorption kinetic properties and adsorption capacity of C/Al₂O₃/Mn O₂/LDH/MIPs.In the absence of H₂O₂,C/Al₂O₃/Mn O₂/LDH/MIPs achieved adsorption saturation within 240 min,and the maximum adsorption capacity was 113.2 mg g^-1.When 7 wt%H₂O₂ was added to the solution,the material could move rapidly driven by bubbles and reach adsorption equilibrium in about 180 min,shortening the time to reach adsorption equilibrium.In addition,the C/Al₂O₃/Mn O₂/LDH/MIPs also exhibited high adsorption selectivity and regeneration ability.（2）Natural Kapok was used as biological template to prepare hollow biomass carbon fibers,the surface of the template was loaded with Mn O₂ and Ni（OH）₂nanosheets by hydrothermal in-situ growth technique.On this basis,APBA and 3-Triethoxysilylpropylamine（APTES）were adopted as bi-functional monomers with SA as template molecule,TEOS as crosslinking agent and ammonia as initiator to prepare boronate affinity multilayer tubular covalent/non-covalent molecularly imprinted micromotor（CF@Mn O₂@Ni（OH）₂-MIPs）.Ni（OH）₂ nanosheets provided large surface area and outstanding mesoporous structure,which was conducive to the construction of bi-functional monomer imprinting sites.The results of static adsorption experiments showed that the synergistic effect of bi-functional monomers improved the utilization of imprinting sites on the surface of materials.The maximum adsorption capacity of CF@Mn O₂@Ni（OH）₂-MIPs reached 127.1 mg g^-1 at p H=7.5with 10 wt%H₂O₂.Compared with non-motion state,the adsorption capacity was increased by 20%.Besides,CF@Mn O₂@Ni（OH）₂-MIPs also possessed competitive adsorption selectivity and reusability,with the adsorption capacity remaining above95%after 5 cycles.The separation ability of eight boronate affinity adsorbents including FCT-COOH-BA,FPCD-COOH-BA,DFSP@MIPs,SA-imprinted-BAMIMs,S-MIPM,MI-HCESNFs,C/Al₂O₃/Mn O₂/LDH/MIPs and CF@Mn O₂@Ni（OH）₂-MIPs from environmental waste star anise were studied.The results showed that the eight materials could separate shikimic acid specifically from the actual extract of star anise,and the separation efficiency was 16.44%,32.26%,55.84%,70.00%,53.76%,88.53%,97.01%and 90.02%.This work provides theoretical and technical support for expanding the separation of natural products in the environment by boronate affinity adsorbents.