Preparation And Characterization Of Novel Organic-inorganic Hybrid Charged Nanofiltration Membranes

The dyeing industry developed rapidly in pasted years,accompanied with lots of dye wastewater containing inorganic salts and dyes produced.Traditional wastewater treatment methods,such as chemical/physical adsorption and biodegradation,cannot recycle dyes and inorganic salts in waste water.Nanofiltration technology,due to the unique microporous structure of nanofiltration membrane,has been applied to recover valuable materials in waste water.However,the traditional nanofiltration membranes usually intercept both dyes and inorganic salts simultaneously in the treatment process,resulting in mixture of dyes and inorganic salts,which is an additional environmental pollution.In order to solve this problem,the nanofiltration membrane was modified by blending charged nano-materials to prepare the organic-inorganic hybrid charged nanofiltration membrane,which is expected to recycled dyes and inorganic salts respectively.Different dimensions inorganic nano-materials such as silicon dioxide（SiO₂）,halloysite nanotubes（HNTs）and molybdenum disulfide（MoS₂）were modified by silane coupling agents.Then graft polymerization of zwitterionic monomers on the surface of nanomaterials was introduced to obtain charged nanomaterials by reverse atom transfer radical polymerization.Zwitterionic monomers and ionic liquid were derivedfrom2-methacryloyloxyethylphosphorylcholine（MPC）,3-[dimethyl-[2-（2-methyl prop-2-enoyloxy）ethyl]azaniumyl]propane-1-sulfonate（SBMA）,1-allyl-3-methylimidazoliumchloride（AMImCl）and1-allyl-3-methylimidazolium bistrifluoromethane sulfonimide salt（AMBA）.Finally,after blending with polyethersulfone（PES）materials,the organic-inorganic hybrid nanofiltration charged membranes were prepared by phase inversion method.Measuring and test instruments including X-ray diffraction（XRD）,high resolution transmission electron microscopy（HR-TEM）,X-ray photoelectron spectroscopy（XPS）,thermogravimetric analysis（TGA）,fourier transform infrared（FT-IR）,field emission scanning electron microscopy（FESEM）,atomic force microscope（AFM）,water contact angle meter（WCA）and membrane performance testing instrument,were used to investigate the structure and the effect of separation performance of the charged nanomaterials.Some experimental rules of preparation of organic-inorganic hybrid membranes are recognized,which provides some basic theoretical direction for the application of organic-inorganic hybrid charged nanofiltration membrane in dyeing industry.The main research contents are as follows:Preparation and performance testing of SiO₂-PMPC/PES and SiO₂-PSBMA/PES hybridized charged nanofiltration membranes.The nano-silica with primary particle size around 100-300 nm was synthesized via the Stober method.After being modified by silane coupling agent,polyphosphoric choline（PMPC）and polysulphonate betaine（PSBMA）were successfully grafted on the surface of the nano-silica.Charged nanomaterials SiO₂-PMPC and SiO₂-PSBMA were blended with PES to prepare organic-inorganic hybrid charged nanofiltration membranes SiO₂-PMPC/PES and SiO₂-PSBMA/PES by phase inversion method.At the pressure of 0.4 MPa,when the doping amount of SiO₂-PMPC was 1.5%,the rejection rate of SiO₂-PMPC/PES hybrid membrane to Reactive black 5 and Reactive green 19 was 82.6%and 92.4%respectively,and the retention rate of monovalent and divalent salts was less than10%,whereas the water flux decreased to 79.3 L/（m².h）.When the doping amount of SiO₂-PSBMA was 0.5%,the rejection rate of SiO₂-PSBMA/PES hybrid membrane to Reactive black 5 and Reactive green 19 was 97.9%and 99.0%respectively.At the same time the retention rate of Na₂SO₄ was less than 13%and the retention rate of other salts was less than 3%.The pure water flux was 147.3 L/（m².h）.Compared with the blank membrane,the hydrophilicity of the hybridized nanofiltration membrane was improved due to the introduction of charged materials.SiO₂-PSBMA/PES hybrid membrane showed excellent separation performance and pure water permeability.PSBMA was suitable for the preparation of hybrid membrane by grafing nano-silica.Preparation and performance of HNTs-PSBMA/PES and HNTs-PAMImCl/PES hybrid nanofiltration charged membranes.Silane coupling agent was used as modifier for the surface-modification of the natural halloysite nanotubes（HNTs）.After modification,PSBMA and poly（1-allyl-3-methylimidazolium chloride）（PAMImCl）graftedHNTsthroughRATRP.Hybridiznanofiltrationmembranes HNTs-PSBMA/PES and HNTs-PAMImCl/PES were prepared by phase inversion method.At 0.4 MPa,when the content of HNTs-PSBMA was 1.0%,the rejection of Reactive black 5 and Reactive green 19 was 89.2%and 98.9%respectively.The rejection of monovalent and divalent inorganic salts was less than 10%and the pure water flux was 142.7 L/（m².h）;when the HNTs-PAMImCl amount was 1.5%,the rejection of the hybrid membrane to Reactive black 5 and Reactive green 19 was 92.4%and 99.1%,respectively.The rejection rate for Na₂SO₄ was 26.7%and other inorganic salts were less than 2.0%,and the pure water flux was 401.7 L/（m².h）.The hydrophilicity of hybrid membranes increased by the addition of two one-dimensional nano-charged materials,and the hydrophilicity of hybrid membranes increased with the increase of nano-charged materials.In general,the addition of appropriate amount of HNTs-PSBMA can improve the separation performance of hybrid membranes,which maintain a higher water flux and has best performance;Though HNTs-PAMImCl does not improve the permeability of inorganic salts,it makes the water flux of hybrid membranes increase more than three times,and still maintains a higher retention rate of dyes.Preparation and properties of MoS₂-PSBMA/PES and MoS₂-PAMBA/PES hybrid charged nanofiltration membranes.Commercial layered molybdenum disulfide was successfully exfoliated into mutillayer or few layers by solvent ultrasonication in a mixed solution of NMP and NaOH.The surface modification was followed by the RATRPmethodtograftPSBMAand1-Allyl-3-methylimidazolium bistrifluoromethanesulfonimide salt（PAMBA）on the surface of MoS₂.The two charged nanosheet materials of MoS₂-PSBMA and MoS₂-PABMA blended with polyethersulfone（PES）.The MoS₂-PSBMA/PES and MoS₂-PAMBA/PES hybrid charged nanofiltration membranes were prepared by phase inversion method.At the press of 0.4 MPa,when the content of MoS₂-PSBMA was 1.0%,the rejection of the hybrid membrane to Reactive black 5 and Reactive green 19 was as high as 98.2%and 99.3%,and the interception rate of inorganic salt was less than 2%.The pure water flux of the MoS₂-PSBMA/PES hybrid membrane was 65.8 L/（m².h）.When the MoS₂-PAMBA content was 1.5%,the rejection of the hybrid membrane to RB5 and RG19 was as high as 93.6%and 99.8%respectively,and the rejection for inorganic salts was less than 13%.The pure water flux of the MoS₂-PAMBA/PES hybrid membrane was 144.3 L/（m².h）.Compared with the blank membrane,the hydrophilicity of the two hybrid charged nanofiltration membranes was improved and the hybrid membrane had high dye retention and inorganic salt permeability.A large-sized organic-inorganic hybrid nanofiltration membrane with 24 cm×35cm was prepared by phase inversion method.The hybrid membrane prepared by the method has the advantages of uniform thickness and easy repetition.The surface hydrophilicity and cortex thickness of hybrid membranes were improved by modification of different dimension nanomaterials with phosphatidylcholine,sulfobetaine and ionic liquid.The pure water flux,dye retention and selectivity of hybrid membranes were different.Compare with the hybrid charged membranes,MoS₂-PSBMA/PES had the best separation performance.The rejection rate of reactive dyes remained above 98%,while the rejection rate of inorganic salts was only 2%.The water flux of the hybrid charged membranes was significantly increased by adding ionic liquids.