Construction Of Temperature/CO₂-responsive Porous Membrane And Research On Separation Performance

Stimulus-responsive oil-water separation membrane material is a smart material that changes its physical and chemical properties after being stimulated by specific external stimuli,and then selectively permeates oil or water.Compared with membrane materials with single hydrophilicity or hydrophobicity,stimulus-responsive membranes have stronger design and wider application range,and have received extensive attention and research in the field of oil-water separation.Compared with other stimulus elements,the operation methods of temperature and carbon dioxide（CO₂）gas stimulation are simpler and will not introduce any by-products into the system,they are very ideal stimulus elements.Therefore,this article intends to prepare a stimulus-responsive oil-water separation membrane material by introducing temperature-responsive and CO₂-responsive polymers into the oil-water separation membrane material,the morphology,structure,and stimulus responsive behavior of the membrane were investigated in depth,and the oil-water separation performance of the prepared separation membrane under temperature and gas stimulation was systematically studied,and the the internal connection of membrane structure-stimulus response-separation performance were explored.the main conclusions are as follows:（1）Use surface grafting strategy（"graft to"）to prepare a temperature-responsive oil-water separation membrane.Firstly,temperature-responsive sulfhydryl-terminated poly（N-isopropylacrylamide）（PNIPAM-SH）was prepared by reversible addition-fragmentation chain transfer polymerization（RAFT polymerization）and ammonolysis,the structure and the aminolysis process of PNIPAM before and after aminolysis were characterized by nuclear magnetic and ultraviolet-visible spectrophotometer,and the results showed that the preparation of PNIPAM-SH was successful.Then,PNIPAM-SH was grafted onto the PDA-coated saturated polyester（PET）porous membrane through the Michael addition reaction between the sulfhydryl group and polydopamine（PDA）,through Fourier infrared,it can be found that after PNIPAM-SH is grafted onto the PDA-PET membrane,the vibration peak of N-H and the stretching vibration peak of the C=O bond in the amide appear,indicating the successful preparation of the PNIPAM-PDA-PET membrane.The temperature response performance of the prepared membranes were tested,and the results showed that under the stimulation of temperature,the water contact angles and fluxs of PNIPAM-PDA-PET membranes（M1,M2and M3 membranes）grafted PNIPAM with different molecular weight all changed regularly.Among them,the M2 membrane that the molecular weight of grafted PNIPAM was 8600 g/mol is the most significant,and the water contact angle can be changed from 64.6°at 25℃to 90.9°hydrophobic at 45℃.The M2 membrane has a good separation effect on different types of oil-water mixtures（light oil-water mixture and heavy oil-water mixture）,and the separation efficiency can reach more than 95%.It also has good separation effect and flux for oil-in-water emulsions stabilized by different emulsifiers.The separation efficiency can reach more than96%,and the membrane flux is more than 300 L·m^-2·h^-1.When the temperature rises to 45℃,the separation efficiency can still be maintained above 83%,which has certain application prospects in the field of oil-water separation.（2）In order to further improve the stimulus response performance of the membrane and the separation effect of water-in-oil emulsions,introduce a CO₂-responsive polymer—poly（N,N-diethylamino ethyl methacrylate）（PDEAEMA）,The sulfhydryl-terminated block copolymer PNIPAM-b-PDEAEMA-SH was prepared by RAFT polymerization and ammonolysis,and grafted onto a PDA-coated polyacrylonitrile（PDA-PAN）membrane to produce a dual response of temperature and CO₂ responsive PNIPAM-b-PDEAEMA-PDA-PAN membrane.Studies have found that under the stimulation of temperature and CO₂,the water flux and water contact angle of the membranes will change regularly.And the M1 membrane that the molecular weight of grafted the block copolymer was 12800 g/mol is the most obvious,after the M1 membrane was stimulated by CO₂,the water contact angle changed from 92.9°at 25℃to 34.8°,which was hydrophilic.When the temperature rose to 45℃,the water contact angle became more hydrophobic 117.7°.The separation efficiency of oil-in-water emulsions that are stable to different types of emulsifiers can be maintained above 80%,and the flux can also reach above800 L·m^-2·h^-1·bar^-1,after stimulation with CO₂ and temperature,the separation efficiency of the membrane is further improved,and it has a greater application prospect in the field of oil-water separation.