| As an emerging water treatment technology with advantages of simplilicity,environmental friendliness,high efficiency and small footprint,membrane separation technology has found wide applications from advanced water treatment and resource recovery to drinking water purification,producing great economic and environmental benefits.At present,the membrane market has been dominated by inorganic ceramic membranes and organic polymeric membranes.However,they usually suffer some technical limitations regarding,for example,the compromise between permeability and selectivity,inherent fouling,low chlorine resistance,leading to low plant reliability and limiting their wide applications in wastewater treatment.To address these problems,this work utilizes carbon nanomaterials to construct high-performance membranes with high water permeability,antifouling and chemical/thermal stability by increasing porosity,decreasing thickness and constructing vertical pore channels.In consideration of distinctive interfacial properties and excellent electric conductivity of carbon nanomaterials,this work endows the membranes new functions under electrochemical assistance to further improve their ability for the removal of pollutants.The main research contents and results are shown as follows:(1)A novel hollow fiber membrane(HFM)composed only of carbon nanotubes(CNTs)was prepared based on electrophoretic deposition.Their water permeability,adsorption capacity and in-situ electrochemically regenerative capability were invesitigated.Experimental results showed that,the CNT HFMs possessed a permeance of approximately 1150 L m-2 h-1 bar-1,which was 1.8 times higher than that of commercial polyvinylidene fluoride(PVDF)membranes.Additionally,they had a dynamic adsorption capacity two orders of magnitude higher than that of PVDF membranes towards Rhodamine B.Benefiting from their excellent physicochemical properties,the CNT HFMs could function as an electrode on which Rhodamine B molecules could be electrochemically degraded,thus featuring an electrochemical regeneration capacity after adsorption saturation.An electrochemically controllable membrane filtration system was subsequently constructed based on the CNT HFMs,and the gated transport of gold nanoparticles(GNPs)across CNT HFMs was investigated.It was found that electrochemistry-induced electrostatic attraction could promote formation of non-convalent interactions between pore interfaces and nanoparticles,resulting in the rejection of GNPs by CNT HFMs;electrostatic repulsion could prevent formation of the non-convalent interactions,which allowed GNPs to penentarte the CNT HFMs.The dynamic switch between "rejection" and "penetration" can be achievd within 10-60 s.In accordance with this principle,the CNT HFMs could achieve both removal of methylene blue molecules from water and their high-concentration recovery.(2)A wet-spinning technology for high-throughput fabrication of length-unlimited,neat CNT HFMs was developed,and the effects of various experimental parameters on structure and morphology of prepared CNT HFMs were investigated.It was found that if the mass ratio of CNTs to poly(vinyl butyral)to N,N-dimethyl formamide was 1:0.5:10,the asymmetric CNT HFMs with a separation layer of only 1.6 μm could be obtained.They possessed a porosity of up to 95±3%and an average size of 100 nm.Experimental results showed that,their water permeance was up to 12000 ± 1500 L m-2 h-1 bar-1,which was 5.6 times higher than that of CNT HFMs prepared with electrophoretic deposition method,10 times higher than that of PVDF HFMs with the similar pore size and 20 times higher than that of Al2O3 membranes with an average pore size of 1000 nm.Additionally,compared with electrophoretic deposition method,the wet-spinning technology needed no templates,which could greatly reduce cost and improve preparation efficiency.(3)A noval CNT HFM with a sandwich-like structure in its cross section was designed and prepared based on layer-by-layer assembly method.They could remove micropollutants from water through adsortption and electrochemical oxidation,which could greatly reduce the energy consumption during a continuous electrochemical degradation of micropollutants by common CNT HFMs.The noval CNT HFMs could construct a complete electrochemistry system by themselves with their outer CNT layer,inner CNT layer and the middle PVDF layer as cathode,anode and insulating layer,respectively.It was found that,through facile switches between adsorption on outer CNT layer in absence of a voltage and electrochemical oxidation on inner CNT layer in presence of a voltage,microcystin-LR could be continuously and energy-efficiently removed by the CNT HFMs.(4)An ultrathin porous graphene membrane much thinner than CNT HFM was prepared by carbothermic-reaction-based punching method,and the effects of experimental parameters on pore size and water flux were investigated.Results revealed that the flux of four-layered graphene membranes with an average pore size of 50 nm and pore density of 1.0×107 cm-2,was measured to be 4600 L m-2 h-1 at a pressure difference of 0.2 bar(calculated permeance of 23000 L m-2 h-1 bar-1),which was 40-400 times higher than those of Al2O3 membranes and polycarbonate membranes with the similar pore size,and 1.9 times higher than that of CNT HFMs with an average pore size of 100 nm.Compared with CNT HFMs,the graphene membranes possessed an infinitesimal hydrodynamic resistance as a result of their atomic-thin architecture and perpendicular pore channels,which accounted for the ultrahigh permeability of graphene membranes.(5)A facile method for one-step growth of ultrathin porous graphene membranes on copper foil was developed by using Cu(NO3)2 as etchant and polymethyl methacrylate as carbon source.It was found that when their pore size was 42 nm,the prepared graphene membranes had a permeance of up to 182000 L m-2 h-1 bar-1,which was 2 orders of magnitude higher than those of conventional polymeric and ceramic membranes and 7.9 times higher than that of graphene membranes prepared by punching method.It was also found that,when the size of polystyrene particles for filtration was 190 nm,the flux recovery after four"filtration-washing" cycles was 80%,which was significantly higher than that(44%)of PVDF membranes,evidencing the high resisitance to irreversible fouling of ultrathin graphene membranes. |
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