Preparation Of Anti-fouling Ciprofloxacin Molecularly Imprinted Membranes Based On Molecular Recognition And Research On Selective Separation Behavior And Mechanisms

Extensive employment of ciprofloxacin（CFX）in medical treatment,animal husbandry and breeding has led to generation of abundant CFX-containing sewage.CFX will still show the biological activity after entering water body directly or indirectly by sewage,which has great harm to ecological environment and human health.Furthermore,the toxic effect of CFX in sewage on microorganisms will weaken the biological treatment effect of other pollutants.Therefore,development of highly efficient and selective removal technology that directly acting on CFX before treatment of other pollutants is necessary.In recent years,molecularly imprinted membranes（MIMs）have shown great superiority in selective separation,removal,extraction,enrichment and purification.However,most MIMs still exhibit shortcomings such as low rebinding capacity,limited selectivity and poor anti-fouling performance.Therefore,development of highly selective and anti-fouling MIMs is of great research value and social significance to selective removal of CFX from sewage.In this context,highly selective and anti-fouling MIMs were developed in this thesis based on membrane preparation technology,anti-fouling modification technology and molecular imprinting technology for selective separation and removal of CFX.The anti-fouling substrate membranes were constructed based on the coupling of polyvinylidene fluoride（PVDF）and β-cyclodextrin（βCD）.A synergistic improvement of anti-fouling performance,rebinding capacity,selectivity and stability was achieved by combination of polydopamine（PDA）and βCD.The self-cleaning performance was achieved on MIMs by introducing the composite photocatalytic system.In this thesis,interactions between template and functional monomers were systematically studied.Specific recognition mechanism of molecularly imprinted sites was deeply explored.Mechanisms of synergistic improvement of performance on MIMs is fully illustrated.Main results are as follows:1.Preparation of anti-fouling MIMs induced by PCD as well as study on performance and mechanisms of selective separation of CFX（1）Preparation of PVDF membranes was optimized.The anti-fouling modification of PVDF membrane was achieved by βCD based on surface modification strategy.βCD surfacely modified PVDF-based CFX molecularly imprinted membranes（P@β-CMIMs）were prepared by thiol-ene click reaction.Results showed that the introduction of βCD effectively improved the anti-fouling properties of PVDF-based MIMs,as well as resulted in high relative separation factors(α’CFX/NFx=1.99,α’_CFX/EFX=2.16,α’_CFX/OFx=3.29)and permselectivity coefficients(β_NFX/CFX=1.28,β_EFX/CFX=1.30,β_OFX/CFX=1.43)of as-obtained P@β-CMIMs.It confirmed the selective separation mechanism of of P@β-CMIMs by retarding permeation of CFX.Meanwhile,the P@β-CMIMs also exhibited superior regeneration stability.（2）In view of the complicated surface anti-fouling modification of PVDF byβCD,a simple hybrid modification strategy was employed to constructβCD/PVDF-based anti-fouling composite membranes.Suitable functional monomers for CFX-imprinting were investigated and screened based on affinity adsorption of non-imprinted polymers.Then,the βCD blending-modified PVDF-based CFX molecularly imprinted membranes（P/β-CMIMs）were synthesized based on click reaction.The results showed that 2-（trifluoromethyl）acrylic acid exhibited well affinity with CFX.Compared with P@β-CMIMs,the as-prepared P/β-CMIMS showed better anti-fouling performance,rebinding capacity(32.49 mg g^-1)and selectivity(a’_CFX/NFX=2.33,a’_CFX/EFX=2.53,a’_CFx/OFx=4.30,β_NFX/CFX=1.35,β_EFX/CFX=1.41 and β_OFX/CFX=1.46),which confirmed the superiority of MIMs based onβCD blending strategy.2.Preparation of high-selective and anti-fouling MIMs synergistic improved by PCD/PDA as well as study on the performance and mechanism of selective separation of CFX（1）In order to further improve the rebinding capacity and selectivity of MIMs,PDA was introduced based on the surface biomimetic modification and employed as a secondary reaction platform to prepare PVDF/βCD@PDA-based CFX molecularly imprinted membranes（P/β@D-CMIMs）.The optimal ratio（1:4）was obtained based on template-monomer interactions.According to the results,rebinding capacity of P/β@D-CMIMs(45.27 mg g^-1)and selectivity(α’_CFX/NFX=3.02,α’_CFX/EFX=3.41,α’_CFX/OFX=5.23,β_NFX/CFX=1.39,β_EFX/CFX=1.44 and β_OFX/CFX=1.48)were significantly improved with the employment of PDA.It proved the positive effect of PDA on improving the distribution and amount of molecularly imprinted recognition sites.Additionally,P/β@D-CMIMs still maintained superior selectivity and stability after repeated applications.（2）In order to improve the weakened anti-fouling performance caused by surface modification of PDA,a phase transformation fixation strategy was adopted to avoid the formation of dense PDA layer on the membrane surface.Then,the PVDF/βCD/PDA-based CFX molecularly imprinted membranes（P/β/D-CMIMs）were synthesized by thiol-ene click polymerization.The results indicated that the combination of βCD-blending modification and PDA-embedding modification showed a synergistic effect on anti-fouling performance of as-obtained MIMs,together with syperior relative separation factors(α’_CFX/NFX=3.69,α’_CFX/EFX=4.07 and α’_CFX/OFX=5.26)and permselectivity coefficients(β_NFX/CFX=1.57,β_EFX/CFX=1.68 andβ_OFX/CFX=1.83).It verified the synergistic effect of this strategy on anti-fouling and selectivity.Moreover,the specific recognition and rebinding mechanism of molecularly imprinted sites on membranes were explored by molecular dynamics simulations.Based on these simulations,the mass transfer mechanism of selective separation onto P/β/D-CMIMs was obtained.3.Preparation of self-cleaning MIMs assisted by PDA as well as study on the performance and mechanism of selective separation of CFXTo eliminate the adverse effects of the unavoidable fouling on selectivity and rebinding capacity during employment of MIMs,PVDF/βCD spinning fiber membrane was combined with Z-Scheme heterojunction photocatalytic system based on multiple mechanisms of PDA for construction of C₃N₄/Ag₃PO₄/PDA-based anti-fouling and self-cleaning CFX molecularly imprinted membranes（C/A/P-CMIMs）.CFX specific recognition sites were efficiently formed by bionic self-polymerization of PDA.Z-Scheme heterojunction photocatalytic system with superior performance was constructed based on strong electron transport and light absorption properties of PDA.The stable binding of photocatalyst and substrate membrane was achieved by strong interface adhesion of PDA.Results suggests that the membrane flux of foul C/A/P-CMIMs rapidly recovered to 84.4%of the original flux after being irradiated by visible light.The superior relative separation factors(α’_CFX/NFX=1.43,α’_CFX/EFX=1.73 and α’_CFX/NFX=2.36)and permselectivity coefficients(β_NFX/CFX=1.65,β_EFX/CFX=1.90 and β_OFX/CFX=2.08)indicated that the C/A/P-CMIMs owns superior selectivity towards CFX with well stability.