Preparation Of Antifouling Molecularly Imprinted Composite Membranes And The Selective Separation Performance And Mechanism For Tetracycline

Tetracycline（TC）,as a broad-spectrum antibiotic,is widely used for the inhibition of most Gram-positive or Gram-negative bacteria or bacterial infections.Due to its extensive use in persons and animal treatment,and its own characteristics of biological accumulation and toxicity,this poses a huge threat to the ecosystem.Hence,it is of great significance and value to study the efficient separation and removal of TC from wastewater.At present,the removal methods of TC in water mainly include photodegradation,adsorption and membrane separation.Among them,photodegradation method and adsorption method are difficult to recover due to the disadvantages of catalyst and adsorbent,and the membrane separation method is not enough to achieve the specific separation of a single molecule.Therefore,it is very important to achieve efficient and selective removal of TC from wastewater.As a new separation material,molecularly imprinted membranes（MIMs）have been widely used in selective recognition and separation of specific molecules,because the separation process has its advantages of low energy consumption,continuous use and good permeability.However,the imprinting process is a key step in the preparation of imprinted membranes,hence,the efficient and rapid realization of the imprinting process has been the focus of research in the preparation process.Among many membrane materials,PVDF is widely used because of its excellent stable performance and mechanical properties.However,due to the hydrophobicity and complex environment of PVDF material,it is very easy to cause the membrane surface pollution,the decrease of infiltration flux and the reduction of recycling times,and so on,which leads to the shortened service life of MIMs.Therefore,improving the fouling resistance,flux and reusability of membrane materials has become the focus of MIMs research.In this paper,combined with MIT,MST,membrane preparation technology,surface modification technology and click chemistry polymerization,with TC as the target object,an anti-fouling MIMs were constructed for selective separation and removal of TC in water environment.Specific research contents are as follows:1.Preparation of PMMA-PEG-PVDF blending-crosslinked molecularly imprinted composite membrane as well as study on the performance and mechanism of selective separation of TCHydrophilic PVDF membranes were prepared by blending PMMA and PEG hydrophilic materials.Hydrophilic tetracycline molecularimprinted membranes（TCMIMs）were successfully prepared by surface polymerization method for selective separation and removal of TC in water environment.It has been proved by various characterizations that TCMIMs has more microporous structure,at the same time,the surface hydrophilicity and anti-fouling performance of the membrane material were significantly improved.And the results of adsorption test showed that the maximum adsorption capacity of TCMIMs reached 42.51 mg g^-1 compared with TCNIMs.Relative selectivity coefficientα＇（TC/OTC=2.98,TC/CTC=2.65）,selective permeability factorβ（TC/OTC=2.58,TC/CTC=2.75）,the results showed that the prepared TCMIMs showed stronger specific adsorption ability to the target.2.Preparation of PEI-PDA-PVDF click-polymerization molecularly imprinted composite membrane as well as study on the performance and mechanism of selective separation of TCA hydrophilic layer was formed on the surface of hydrophobic PVDF membrane by surface grafting of PEI and DA.Tetracycline was selected as the template molecule,and the template was molecularly imprinted on the surface of the membrane material by click chemistry polymerization under mild reaction conditions.The tetracycline molecularly imprinted composite membranes（TCMIMs）were successfully prepared.In addition,the chemical structure,elemental composition and surface morphology of TCMIMs were studied in detail by SEM,FTIR and XPS techniques.The anti-fouling performance,adsorption performance and selective separation ability of TCMIMs and non-imprinted membrane（TCNIMs）were also discussed.The experimental results showed that the equilibrium adsorption capacity of TCMIMs is much higher than that of TCNIMs,the relative selectivity coefficientα＇（TC/OTC=2.89,TC/CTC=2.91）,selective permeability factorβ（TC/OTC=2.58,TC/CTC=2.75）,this indicated the successful construction of imprinted sites on TCMIMs with specific adsorption ability to TC.After 10 cycles of experiments,the adsorption amount decreased by less than10%and it has the ability to be reused in the water environment.3.Preparation of three-dimensional macroporous PEI-PDA-PVDF click-polymerization molecularly imprinted composite membrane as well as study on the performance and mechanism of selective separation of TCThe three-dimensional macroporous membrane was prepared by uniformly mixing PVDF powder and NaCl particles and then washing the NaCl particles after melting at 200℃.After alkali treatment,the surface grafting of PEI and DA not only improved the hydrophilicity of the membrane,but also provided a secondary reaction platform because of the existence of polydopamine（PDA）layer.The tetracycline molecularly imprinted membrane（TCMIMs）with high flux;high anti-fouling and high selectivity was obtained by click chemistry polymerization.The prepared TCMIMs were systematically evaluated by flux test,anti-fouling performance,regeneration performance and selection performance.The experimental results showed that the maximum adsorption capacity of TCMIMs reached 65.61 mg g^-1,the adsorption capacity of TCNIMs for TC is far less than this value,which indicates that the successfully constructed TCMIMS has the ability to select and recognize the target molecule TC while the membrane flux is significantly increased.