| The design and preparation of reverse osmosis/nanofiltration membranes with high flux is of great significance for improving membrane separation efficiency and reducing process costs.PIM-1(Polymer of Intrinsic Microporosity-1)is a typical intrinsic microporous polymer;its non-planar and twisted structure causes the molecular chains to pack ineffectively,form large number of micropores and high free volume,so PIM-1 has excellent permeability to small molecules.Up to now,membranes prepared by PIM-1 as the key material have been mainly used in the fields of gas separation and organic solvent separation,it was rarely reported in the field of water treatment.Based on the good permeability of PIM-1 with non-planar and twisted structures,the thesis proposed the idea of introducing non-planar and twisted structures into reverse osmosis/nanofiltration membranes to increase their flux.In order to introduce the non-planar and twisted structures to reverse osmosis/nanofiltration membranes by interfacial polymerization,water-soluble PIM-1 of low molecular weight with non-planar and twisted structure was added to aqueous phase to prepare reverse osmosis membranes.And then the polyester nanofiltration membrane was prepared by the reaction TTSBI(5,5'6,6'-Tetrahydroxy-3,3,3'3,-tetramethyl-1,1'-spirobisindane)with spiro-ring structure and glutaryl chloride,the influence of the acid chloride species on the membrane separation performance was investigated.The main contents were as follows:(1)The preparation of water-soluble a-LPIM-1 with non-planar and twisted structure:In order to introduce the non-planar and twisted structure of PIM-1 into the reverse osmosis membrane by interfacial polymerization,the selected ratio of synthetic monomers and the hydrolysis modification were designed to obtain water-soluble a-LPIM-1(PIM-1 of low molecular weight with amide groups).Chemical structure of a-LPIM-1 was characterized by infrared spectroscopy,and its molecular weight was estimated by gel permeation chromatography and theoretical calculations.The feasibility of incorporating a-LPIM-1 into the separation layer was verified by water solubility experiment,solubility parameter calculation and freestanding interfacial polymerization with acyl chloride.(2)The preparation and characterization of reverse osmosis membrane containing a-LPIM-1:Different ratios of a-LPIM-1 and 2wt%meta-phenylenediamine(MPD)were dissolved in aqueous solution and trimesoyl chloride(TMC)was dissolved in organic phase,they reacted to prepare reverse osmosis membranes with non-planar and twisted structures by interfacial polymerization.The chemical structure,hydrophilicity,and surface structure of the separation layer was characterized by infrared spectroscopy,contact angles,scanning electron microscopy and atomic force microscopy;the separation performance of reverse osmosis membranes was tested for desalination of 2000 ppm NaCl aqueous solution,and results showed that the flux of reverse osmosis membranes with addition of a-LPIM-1 was two times higher than pristine reverse osmosis membranes under optimal condition,and the rejection of both membranes decreased slightly.(3)The preparation of nanofiltration membrane with non-planar and twisted structures by TTSBI as a monomer:GC-TTSBI polyester nanofiltration membrane was obtained by interfacial polymerization of TTSBI in aqueous phase and glutaryl chloride(GC)in organic phase.The effect of reaction conditions such as monomer concentration,ratio of TTSBI and NaOH,interfacial polymerization time and post-treatment temperature on the membranes formation was investigated,and then the optimized interfacial polymerization conditions were obtained.The chemical structure,surface morphology and properties of the separation layer were characterized by infrared spectroscopy,scanning electron microscopy and zeta potential.The separation performance of membranes under optimal conditions on 50ppm Congo red-2000 ppm NaCl solution was tested.The results showed that the flux of the membrane was much higher than that of the traditional nanofiltration membranes,and the flux reached 400.0 L/m2.h,the rejection of Congo Red was 95.4%,and the rejection of NaCl was 8.3%.(4)The preparation of membranes with non-planar and twisted structures from different chloride monomers:In order to investigate the influence of acyl chloride monomer structures on membranes with non-planar and twisted structures,TMC with benzene ring,GC with short-chain and SDC(sebacic acid dichloride)with long-chain were used,three separation membranes of TTSBI-TMC,TTSBI-GC and TTSBI-SDC were prepared and tested for 50ppm Congo red-2000ppm NaCl mixed solution,Congo red,sunset yellow and methyl orange aqueous solution.The flux order of the three membranes was F(TMC-TTSBI)>F(GC-TTSBI)>F(SDC-TTSBI),and the order of solute rejection was R(SDC-TTSBI)>R(GC-TTSB I)>R(TMC-TTSBI),this is because as the flexibility of the acyl chloride increases,the packing density between the molecular chains in the separation layer increases,the selectivity increases,and the permeability decreases.In summary,by introducing non-planar twisted folded structure molecules into the skin layer of the reverse osmosis/nanofiltration membrane,the number of pores and free volume in the separation layer increased,and the flux of the membrane significantly improved.In addition,increasing the flexibility of the molecular chains of skin layer could reduce the free volume and pore size,leading to decreased permeability and increased selectivity.Therefore,the performance of the reverse osmosis/nanofiltration membranes can be adjusted by changing the stacking and flexibility of the polymer molecular chains of the skin layer,it provided a new approach for improving reverse osmosis/nanofiltration membranes. |
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