| The demand for available water resources in modern society is growing,while the population and economic development since the industrial revolution inevitably produce large amounts of waste water and need to be properly disposed of for recycling.Membrane based water treatment technology are widely used in water treatment process for its simple process,low cost and energy efficient and other characteristics.At present,the most widely used filtration membrane materials are polymer membranes,but the polymer membranes are very susceptible to fouling,especially bio-fouling by the adsorption of microorganisms,fungi and algae on the membrane surface.Microorganisms can adhere and proliferate on the membrane surface,making the bio-fouling of the membrane more difficult to eliminate than other types.Therefore,the filtration membrane need modification for improved resistance to bio-fouling,and the commonly used modification methods are blending,coating and grafting.A common strategy for anti-biofouling is to make the membrane surface effective for the rejection or killing of bacterial cells.In this paper,a series of modified filtration membranes were prepared by using coating & cross-linking modification method and organic-inorganic hybrid blending method,hydrophilic polymer polyvinyl alcohol(PVA)was used as substrate or film-forming material,the specific content is as follows:(1)According to the concept of “combining spear and shield”,the super-hydrophilic terpolymer(PDSH)with both bactericidal and bacteriostatic functions was designed and synthesized.Then,the superhydrophilic antimicrobial filtration membrane with tri-layer structure(PDSH-SSMMs)was prepared by successive dip-coating the stainless steel mesh film(SSMM)and cross-linking with DVS.The results show that the PDSH0-SSMM,which does not contain quaternary ammonium monomer,is superior to PDSH5-SSMM in water contact angle,BSA flux attenuation coefficient,rejection rate and xylene content in filtrate,because DMHB molecule with hydrophobic long alkyl chain reduces the hydrophilicity of the copolymer,resulting in PDSH0-SSMM with better filterability,antifouling properties and oil-water separation properties.The antibacterial efficiency of MPDSH0-SSMM and PDSH5-SSMM were as high as 97%,indicating that the bacteriostatic MPDSH0-SSMM also has good antibacterial effect.In addition,after 14 oil-water separation and cleaning cycle,the water flux attenuation coefficient of the filtration membrane is less than 11%,indicating that it has long-term filtration performance and is expected to realize industrialization.(2)The graphene oxide(GO)with multifunctional groups was used as the nanofiller.The GO was modified with KH-892 and loaded with nano silver,and then the obtained Ag@mGO was blended with PVA to prepare the organic-inorganic hybrid microfiltration membrane through NIPS.The results show that the contact angle and water absorption of the hybrid microfiltration membrane decrease with the addition of Ag@mGO,but the water absorption is about 100%,which means that the water resistance is still to be improved.Porosity,average pore size,heat resistance and pure water flux increase with the increase of Ag@mGO,while the flux attenuation coefficient and retention rate are decreasing,but the minimum value of m is 11.7% and the R values were higher than 80%,indicating that the microfiltration membrane has a good anti-fouling and filtration performance.The hybrid membrane could appear with a suitable size of the inhibition zone and good antibacterial effect with the Ag@mGO addition of 0.5%.But the xylene content in the filtrate is too high to exceed 400 mg/L,indicating that the hybrid microfiltration membrane is not suitable for separating mixture of water and oil contaminants with small molecules.(3)The low-cost and easily available halloysite nanotubes(HNTs)were used as nanofillers,and the PVA was firstly modified with GMA to get mPVA.The HNTs were modified with KH-792 and KH-570 and loaded the nano silver to obtain Ag@mHNTs particles,and then blended with mPVA solution to prepare the organic-inorganic hybrid filtration membrane through NIPS and UV curing.The results show that the water absorption of the hybrid membrane is reduced to about 50%,and the water resistance has been remarkably improved.The mPVA and mHNTs containing double bonds made the cross-linked polymer network more hydrophobic and more difficult to infiltrate.When increasing the content of Ag@mHNTs,the thermal stability is also increased,the contact angle,flux attenuation coefficient and retention rate are decreased first and then increased,while the porosity,average pore size and initial water flux increase first and then decreased.The turning point is aroused when the content of Ag@mHNTs reach 5wt.% because the Ag@mHNTs particles have begun to agglomerate.In addition,the inhibition zone test method did not show significant results and the dynamic contact method was use thereafter,the bactericidal efficiency increased with the addition of the Ag@mHNTs and the maximum value reaches 67.06%.(4)The chopped carbon fibers(CFs)with excellent mechanical properties were used as nanofillers.Firstly,CFs were oxidized with concentrated sulfuric acid and concentrated nitric acid to get mCFs containing carboxyl groups,and then blended with PVA solution to prepare the organic-inorganic hybrid membrane through NIPS.The results show that the mCFs have more carboxyl groups after 12 h oxidation,and it is suitable for the preparation of hybrid membrane.When increasing the content of mCFs,the thermal stability increased,the contact angle,flux attenuation coefficient and retention rate are decreased first and then increased,while the porosity,average pore size and initial water flux increase first and then decreased.The peak value is aroused when the content of mCFs reach 0.5 wt.% because the mCFs have begun to apparently be agglomerated.In addition,the tensile strength and Young's modulus of the hybrid membranes increase with the mCFs content while the elongation at break are decreasing,the lowest elongation at break is only 49.1%. |
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