Preparation And Properties Of Solvent-resistant Composite Nanofiltration Membrane Constructed From UiO-66 And Carbon Nanotubes

With the development of modern industry in China,the application of organic solvent system is more and more extensive,which makes people put forward higher requirements for the nanofiltration membrane of solvent resistant nanofiltration（SRNF）.SRNF is an emerging membrane separation technology,which can be used for the efficient separation of small organic molecules with molecular weight of 200～1000 in organic solvents.It is a green,efficient and energy-saving new membrane technology for the treatment of organic solvents.Aiming at the problems of poor solvent resistance,small solvent flux and poor separation performance of traditional nanofiltration membranes in the process of organic solvent separation,this paper used dopamine（PDA）to co-deposit with UiO-66 and UiO-66@CNT composite materials on polyetherimide（PEI）cross-linked by 1,6-hexanediamine to prepare nanocomposite interlayers,and excellent solvent-resistant composite nanofiltration membranes were obtained.The main conclusions were as follows:（1）Preparation and performance of PDA-UiO-66 solvent-resistant composite nanofiltration membrane.In this work,PEI ultrafiltration membrane was prepared by phase inversion method using PEI as membrane material.After successfully preparing PEI ultrafiltration membrane,it was chemically crosslinked with hexamethylenediamine（HDA）to improve solvent resistance.Subsequently,UiO-66nanoparticles were deposited on the surface of the ultrafiltration membrane by self-polymerization of dopamine,and then a dense skin layer was formed on the surface by interfacial polymerization to prepare a solvent-resistant composite nanofiltration membrane with PDA-UiO-66 interlayer（TFN-U）.The performance differences between TFN-U membranes prepared with different UiO-66 loadings were investigated,and their pollution resistance,solvent resistance and operational stability were studied.It was found that the introduction of PDA-UiO-66nano-composite interlayer can improve the permeation flux of the membrane.Compared with the thin film composite（TFC）membrane without interlayer,when the mass concentration of UiO-66 nanoparticles was 0.2 g/L,the pure water flux of TFN-U₂ membrane increased from 27.91 L/（m²·h）to 63.83 L/（m²·h）,and the pure water flux was more than twice that of TFC membrane.At the same time,the methanol flux of the membrane was 28.50 L/（m²·h）.The retention rate of Congo red aqueous solution and Congo red methanol solution can still maintain 98.2%and93.2%.At the same time,it was also found that the membrane retained more than 94%of Congo red after being soaked in anhydrous ethanol,acetone,ethyl acetate,n-hexane and N,N-dimethylformamide（DMF）organic solvents for 48 h.The flux recovery rate reached 78.1%during the pollution resistance test.After continuous filtration of Congo red methanol solution for 24 h,the methanol flux of the membrane was 14.13 L/（m²·h）,and the rejection rate was 98.3%.（2）Preparation and properties of PDA-UiO-66@CNT interlayer solvent-resistant composite nanofiltration membrane.In this work,functionalized carbon nanotubes were selected to hybridize with UiO-66 to improve the defects of particle aggregation caused by excessive metal-organic framework（MOF）during membrane preparation.UiO-66@CNT composite nanoparticles were successfully synthesized by solvothermal method and co-deposited with dopamine on PEI-based membrane to prepare solvent-resistant composite nanofiltration membrane（TFN-UC）with PDA-UiO-66@CNT nanocomposite interlayer.The effects of carbon nanotube loading in UiO-66@CNT composites on the separation performance,pollution resistance,solvent resistance and running stability of TFN-UC membrane were investigated.It was found that the unique hollow tubular structure of CNT can provide a special transport channel for water molecules,thereby increasing the flux of the membrane.When the CNT loading in the UiO-66@CNT composite nanoparticles was 2 wt%,the pure water flux of the TFN-U₂C₂ membrane was126.32 L/（m²·h）,and the methanol flux was 45.45 L/（m²·h）.The rejection rates of Congo red aqueous solution and Congo red methanol solution can still be maintained at 96.9%and 92.1%,and the membrane flux recovery rate was 83.3%during the antifouling performance test.At the same time,the membrane still has a complete membrane morphology after soaking in acetone,DMF,n-hexane,absolute ethanol,ethyl acetate and other organic solvents for 48 h,and the rejection rate of Congo red is greater than 94%.