Optimization And Construction Of Functional Porous PVDF Based Imprinted Composite Membrane And Their High Selective Recognition And Separation Performance For Tetrabromobisphenol A

Tetrabromobisphenol A（TBBPA）as the most consumable flame retardant in the world,is widely used in the electronic and electrical industry.However,it is easy to cause TBBPA leakage during the preparation or abandonment of electronic devices,which will cause cytotoxicity,neurotoxicity,immunotoxicity and endocrine disruption to organisms,and seriously threaten environmental safety and human health.At present,the commonly used treatment methods include biodegradation,chemical removal,physical adsorption and membrane separation,but the common defects of these methods are poor selectivity and low removal efficiency.Molecularly imprinted membranes（MIMs）are new type of separation materials which can recognize target molecules and thus achieve selective separation.However,the application of MIMs for selective separation of TBBPA is still limited by the following aspects:the structure-activity relationship between membrane microstructure and selective adsorption/separation of TBBPA is not clear;It is also urgent to study the influence of various factors（ion effect,p H,microorganism,etc.）on the selective separation of TBBPA by MIMs in the actual separation environment.Therefore,in this paper,polyvinylidene difluoride（PVDF）membrane was used as the base membrane,taking membrane microstructure regulation as the focus,MIMs recognition site construction as the main line.Multi-type TBBPA molecularly imprinted membranes（TB-MIMs）were designed to investigate the effect of membrane microstructure on the selective adsorption/separation of TBBPA.The synergistic relationship between selective separation and rapid penetration of TBBPA was studied by constructing high density recognition site MIMs.According to the particularity of actual separation environment,a new integrated separation method of TBBPA/typical associated metal ions by Janus imprinted membrane（JIM）was proposed.The main research contents were as follows:1.Preparation of surface imprinted MIMs based on adjustable ordered porous PVDF membranes and study on the selective separation performance of TBBPA（1）The influence of different membrane structures on the adsorption/separation performance of TBBPA was investigated through the regulation of membrane microstructure.Firstly,different proportions of polyvinylpyrrolidone（PVP）were mixed into the membrane substrate to modify functional groups on the membrane surface while adjusting the pore size.After introducing covalent bonds,TBBPA recognition sites were constructed on the membrane surface based on click chemistry（CC）imprinting strategy.It was found that the pore structure of the membrane had a great influence on the adsorption and permeability towards TBBPA.The PVDF/PVP membrane containing 7 wt%PVP showed the best surface properties,adsorption capacity of TBBPA(21.61 mg g^-1)and permeability(5.10 mg cm^-2 min^-1).After imprinting,the adsorption capacity of TB-MIMs increased to 118.27 mg g^-1.The relative separation factors of BPA,BP and DDBP(α’_TBBPA/BPA=3.82,α’_TBBPA/BP=3.81,α’_TBBPA/BBPA=3.11)and the permeability selectivity coefficient(γ_TBBPA/BPA=3.72,γ_TBBPA/BP=3.86,γ_TBBPA/BBPA=3.92)were much better than TB-NIMs.At the same time,TB-MIMs showed excellent stability in complex application environment and long-term use process,showing great practical application prospect.（2）In view of the membrane contamination phenomenon in the actual water treatment process,the influences of different synthesis methods on the microstructure,surface properties and TBBPA adsorption/separation efficiency were explored.It was found that TB-MIMs prepared by delayed phase inversion method（DPIM）had dense and uniform Si O₂ layer on the surface,which showed better infiltrative properties（42.3°）,water flux(405 L m^-2 h^-1)and significantly increased adsorption capacity(83.476 mg g^-1)compared with the MIMs synthesized by blending method and grafting method.The use of sol-gel imprinting strategy could improve the anti-fouling property of the membrane,the relative separation factor(α’_TBBPA/BPA=3.76,α’_TBBPA/BP=3.71,α’_TBBPA/BBPA=3.27)and the permeability selectivity coefficient(γ_TBBPA/BPA=3.66,γ_TBBPA/BP=3.68,γ_TBBPA/BBPA=3.72)of TB-MIMs were improved,demonstrating its ability to selectively separate TBBPA.These excellent properties highlighted the advantages of DPIM in the preparation of nanomaterials composite membranes.2.Preparation of high-throughput/multi-site MIMs by in-situ imprinting based on mesoporous silicon/PVDF and study on the selective separation performance of TBBPA（1）Aiming at the insufficient specific surface area of membrane materials and the embedding and embedding of nanoparticles in the blending process,functional mesoporous silicon nanoparticles（FMSNs）was adopted as the additive to prepare TB-MIMs with high specific surface area by DPIM for selective adsorption/separation of TBBPA.The effect of the polarity of coagulation bath on the segregation process of nanoparticles and the structure-activity relationship between the distribution state of nanoparticles on the membrane surface and the properties of the membrane were investigated in detail.It was found that when the volume of ethanol and water in the solidification bath was 4:1,the membrane performance was the best.After sol-gel imprinting,the water flux,adsorption capacity and retention rate of TB-MIMs increased to 1016.5 L m^-2 h^-1,295.59 mg g^-1 and 85%,respectively.In addition,the performance test of TB-MIMs was carried out through anti-fouling experiments,selective adsorption and penetration experiments,and the results showed that TB-MIMs not only had anti-fouling performance,but also showed excellent selectivity to TBBPA.The relative separation factors wereα’_TBBPA/BPA=4.16,α’_TBBPA/BP=4.16,α’_TBBPA/BBPA=4.02,respectively.The permeability selectivity coefficients wereγ_TBBPA/BPA=4.07,γ_TBBPA/BP=4.91,γ_TBBPA/BBPA=5.75,respectively.In addition,the permeation flux of TB-MIMs to competitors was 4-5 times higher than that of TBBPA,proving that the proposed method could effectively solve the difficult tradeoff between permeation and selectivity during membrane separation.（2）In order to further explore the influence of different binding modes between membranes and additives on the adsorption/separation efficiency of TBBPA,FMSNs were introduced into coagulation bath and mixed matrix membrane was prepared based on DPIM,then TB-MIMs was obtained by surface sol-gel imprinting technology.The results showed that FMSNs could be assembled on the membrane surface simply by adjusting the polarity of the solidification bath.When the polarity of the solidification bath reached a certain level,the FMSNs on the membrane surface presented a dense,uniform and continuous distribution.This excellent structure was conducive to the formation of a hydration layer on the membrane surface,effectively blocking the adsorption of BSA on the membrane surface,thus the flux could recover to the original level after multiple cycles,indicating the membrane had excellent anti-fouling performance and stability.In addition,the uniform distribution of FMSNs on the membrane surface played a synergistic effect on the adsorption and reaction kinetics of TB-MIMs,and the adsorption amount of TBBPA reached 415.00 mg g^-1 within 10 min.The selectivity results showed that TB-MIMs had high separation factor(α’_TBBPA/BPA=4.99,α’_TBBPA/BP=4.90,α’_TBBPA/BBPA=5.02)and permeation selectivity(γ_TBBPA/BPA=9.60,γ_TBBPA/BP=9.07,γ_TBBPA/BBPA=8.17).The permeation flux of its competitor was almost 8.5 times higher than that of TBBPA,and the selective separation of TBBPA was achieved while maintaining high flux.3.Preparation of directionally imprinted MIMs based on Janus surface structure and study on the integrated selective separation performance of TBBPA/heavy metal ions（1）The existence of high concentration of heavy metal ions in the osmotic solution of electronic device waste will form combination with TBBPA,leading to co-pollution,therefore,a new type of JIM was proposed for the selective separation and classification of TBBPA and cadmium ions(Cd²⁺).The identification sites suitable for TBBPA and Cd²⁺were separately constructed on both sides of the membrane by DPIM and coating methods.The adsorption capacities of JIM for TBBPA and Cd²⁺were 58.279 mg g^-1and 83.159 mg g^-1,respectively.Compared with JNM,the separation factors of Pb²⁺,Cu²⁺,Zn²⁺,Sn²⁺,Hg²⁺,Co²⁺and Cr³⁺were 2.56,2.87,3.07,2.52,3.53,3.66 and 4.05,respectively.The separation factors for BP,BPA and DDBP were 2.44,2.56 and 2.67,respectively,which demonstrated excellent selectivity for the two targets.At the same time,the adsorption capacity of TBBPA and Cd²⁺by JIM remained at 96%and 97%of the original adsorption capacity after ten cycles.The effectiveness of the identification sites on both sides of the membrane for the selective capture of pollutants and the practicability of preventing the secondary pollution caused by the contact of two pollutants in the elution process were proved by the classification and recovery experiment.（2）In order to further simplify the preparation process of Janus membrane and improve the selectivity of the membrane separation process,JIM was constructed by DPIM and interfacial polymerization,and its anti-interference ability to the selective adsorption and separation of TBBPA and chromium ions(Cr⁶⁺)was investigated.Through one-step DPIM,the Janus structure with one hydroxyl and one covalent bond was formed on both sides of the membrane.Finally,the interaction between JIM and TBBPA and Cr⁶⁺was enhanced based on chemisorption and coordination.The results showed that JIM had good adsorption selectivity for TBBPA and Cr⁶⁺,and the selectivity coefficients for BP,BPA,BBPA,Ni²⁺,Cu²⁺and Cd²⁺are 5.412,4.787,5.092,5.597,5.806 and 5.950,respectively.JIM remained highly selective to Cr⁶⁺even in binary systems containing high concentrations of TBBPA,and vice versa.At the same time,JIM could capture pollutants specifically in the complex actual wastewater,realizing the selective separation of different pollutants.