| Atrazine（ATZ）as a widely used herbicide in agricultural production,has contributed to the growth of food production worldwide.Its long-term and large-scale use often enters surface water or groundwater under the action of surface run-off,leaching,etc.,causing pollution of water supply sources.Due to its high residue,relative chemical stability and biological toxicity,ATZ is difficult to be effectively removed by conventional water treatment processes,so it will have a direct impact on human health.In order to ensure the quality of the water supply,the development of efficient feedwater depth treatment technology to achieve the effective removal of ATZ pollution has a wide range of social needs and practical significance.Based on the analysis of the current situation of ATZ water pollution,this study aims at the bottleneck problem of low selective separation performance（adsorption capacity,permeability and selectivity）of MIMs in water treatment applications and failure in long-term continuous separation applications.In response to the bottleneck issues of low selective separation performance（adsorption capacity,permeability,and selectivity）and failure in long-term continuous separation applications of MIMs in water treatment applications,it is proposed to use metal organic frameworks（MOFs）composite membrane structure as the imprinting substrate,MOFs based MIMs with enhanced selective separation performance were prepared through the regulation and optimization of the binding method of MOFs material to the basal membrane,as well as the membrane pore structure.Finally,coupled with the light induced regeneration function,the template molecules that are saturated and adsorbed in the imprinted recognition sites are cleared with the assistance of light,ensuring long-term selective separation performance in the continuous separation process of MIMs and solving the problem of membrane failure in continuous separation applications.The interaction relationship between the imprinted recognition sites and the ATZ molecule as well as the mass transfer behavior and mechanism during the separation process are explored in depth,the mechanism of membrane structure regulation and function design to enhance the selective separation performance of MIMs is also clarified.The specific research contents are as follows:1.Construction of ZIF-8 based MIMs based on biomimetic strategy and study on performance and mechanism of selective separation of ATZ（1）The development of biomimetic materials provides a new approach for the design and preparation of high-performance membrane materials.MOFs based MIMs（PM-MIMs）were prepared based on the in-situ biomimetic modification strategy of polydopamine（PDA）.Firstly,ZIF-8 nanocrystals with a PDA surface biomimetic layer were synthesized in one step through in situ dopamine regulation method.Then,it was used as a filling material and combined with the polyvinylidene fluoride（PVDF）substrate membrane using a blending membrane preparation method.Finally,surface imprinting technology was used to construct imprinting recognition sites on the surface of the composite substrate membrane to prepare PM-MIMs.Compared with the MIMs prepared by ZIF-8 nanoparticles without PDA biomimetic modification（NM-MIMs）,the adsorption capacity of PM-MIMs to ATZ increased by 36.43%,and it has a higher selectivity factors(αATZ/AMT=2.44 andαATZ/TBL=2.22)and permselectivity factors(βATZ/AMT=1.60 andβATZ/TBL=1.53).The advantages of constructing MOFs-based MIMs based on PDA biomimetic modification strategy were proved.（2）Although the blending membrane preparation method can easily and efficiently prepare MOFs based MIMs,there are still problems such as low utilization of MOFs materials and embedding of imprinted sites.Inspired by the unique structure of natural spider webs,electrospinning technology was introduced to prepare polyvinylidene fluoride/polyvinyl alcohol（PVDF/PVA）nanofiber substrate membranes.ZIF-8nanocrystals were loaded onto the surface of the nanofibers using in-situ loading method to form MOFs layers.Finally,a surface imprinting method was used to construct ATZ imprinting recognition sites on the surface of MOFs layers to to prepare spider web biomimetic MOFs based molecular imprinted nanofiber membranes（SM-MINMs）.The nanofiber substrate membrane constructed based on MOFs obtained a relatively higher specific surface area(77.306 m2·g-1),which provides more space for the loading of imprinted polymers.Therefore,the prepared SM-MINMs have higher adsorption capacity(29.13 mg·g-1)in a relatively lower target concentration range compared to PM-MIMs,and have higher permeation flux(JATZ=2.3452×10-4 mg min-1 cm-1)and permeation selectivity(βATZ/AMT=4.30 andβATZ/TBL=4.20).This indicates that the spider web biomimetic structure plays an important role in enhancing the selective separation performance of MIMs.2.Construction of UiO-66-NH2 based MIMs based on pore channel optimization strategy and study on performance and mechanism of selective separation of ATZ（1）In order to improve the utilization efficiency of MOFs material pores in imprinting site construction and obtain excellent separation performance of MOFs based MIMs,based on the idea of optimizing the pore design of membrane materials,a substrate membrane loaded with heterogeneous porous UiO-66-NH2 nanoparticles was prepared in one step by dopamine assisted co-deposition technique.The active controllable reverse atom transfer radical polymerization（RATRP）imprinting polymerization method was used to efficiently utilize the pore structure of heterogeneous porous MOFs to establish imprinting recognition sites.Finally,a hierarchically porous/controllable imprinted thin layer MOFs based molecular imprinted composite membrane（HPM-MIMs）with multiple pore size hierarchical structures of micropores,mesopores,and macropores was prepared for efficient and selective separation of ATZ pollution in water.The results showed that the adsorption capacity of HPM-MIMs reached 36.41 mg·g-1 at a target molecular concentration of 10 mg L-1,and they exhibited excellent permeation flux(JATZ=3.321×10-4 mg min-1 cm-1)and permeation selectivity(βATZ/AMT=3.36 andβATZ/TBL=3.15)in permeation experiments.In addition,the ATZ removal rate of HPM-MIMs reached49.69%in the simulated actual samples continuous separation experiment.（2）In order to further enhance the strengthening effect of hierarchically porous membrane structure on the selective separation performance of the prepared MIMs,a porous nanofiber membrane construction method was introduced.Using heterogeneous porous UiO-66-NH2 nanoparticles as matrix,ATZ imprinting recognition sites were constructed on their pores and surfaces by active controllable reversible addition-fragmentation chain transfer（RAFT）imprinting polymerization method.Finally,the imprinted MOFs nanoparticles were blended in the spinning solution,and a porous/multi-channel MOFs-based molecular imprinted nanofiber membrane（MCM-MINMs）with inter-fiber channels,inner-fiber channels,and inner-outer mixed channels were prepared by blending electrospinning combined with water etching.The research results indicate that the multiple transport channel structure in the membrane increases the contact efficiency between imprinted recognition sites and template molecules and improves mass transfer speed,which promotes synchronous enhancement of selectivity and permeability.Therefore,MCM-MINMs have higher adsorption capacity(48.34 mg·g-1),permeation flux(JATZ=4.014×10-4 mg min-1 cm-1)and permeation selectivity(βATZ/AMT=3.52 andβATZ/TBL=3.22).In addition,MCM-MINMs achieved a removal rate of 59.74%for ATZ in simulated actual samples continuous separation experiments.3.Construction of UiO/ZIF based MIMs based on two-dimension layered membrane preparation strategy and study on performance and mechanism of long-lasting selective separation of ATZIn order to solve the problem that the selective separation performance of MIMs in the continuous separation process decreases with the increase of operating time and ultimately fails,the photocatalytic activity of MOFs material is used to remove the target molecules adsorbed on imprinted recognition sites,and MOFs based MIMs with light-induced regeneration function were prepared.Based on the two-dimension layered membrane preparation strategy,ZIF-L nanosheets were used as the main body of the layered membrane,and the UiO-66-NH2 nanoparticles as interlayer supports were introduced onto the surface of ZIF-L nanosheets,which forming 3D/2D heterostructures composite MOFs materials.ATZ imprinting recognition sites are constructed on the surface of the composite MOFs materials using a one-step polymerization co-deposition method.Finally,the imprinted composite nanosheets were assembled into two-dimensional layered MOFs based MIMs（2DM MIMs）by vacuum filtration method.The results showed that the adsorption capacity of the as-prepared 2DM-MIMs onto the target molecule was 50.17 mg·g-1,and the 2DM-MIMs exhibited excellent permeation flux(JATZ=3.321×10-4 mg min-1 cm-1)and permeation selectivity(βATZ/AMT=3.36和βATZ/TBL=3.15).In addition,due to its photoinduced regeneration function,2DM-MIMs can achieve performance regeneration and maintain long-lasting selective separation performance during the continuous separation process assisted by light.The removal rate of ATZ in the simulated actual sample reached 90.76%. |
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