| Due to the great strength of the support layer and the high efficiency of the separation layer,the composite membrane can obtain excellent separation performance and stability.It has board application prospects in the challenging separation process.At present,one of the main directions on the development of the composite film is to prepare the thin and complete separation layer with high efficient mass transfer channel.Meanwhile,the problem of matching and interface effect between the separation layer and the support layer should be solved.The effect ways are developing a new type of membrane material and a simple method to construct the composite membrane.In this paper,Metal organic frameworks(MOFs)materials and layered double hydroxides(LDH)materials were employed as porous materials to in situ fabricate composite membrane in Polyacrylonitrile(PAN)and ceramic substrate.MOFs and LDH can form a greatly thin separation layer with three-dimensional or two-dimensional mass transfer channels on the surface of the support,which is beneficial to reduce the mass transfer resistance during the separation process and obtain a composite membrane with high sepration performance.These composite membranes with nano composite film mass transfer channel were used to separate liquid mixtures.Firstly,ZIFs/PAN nanoconfined composite(NCC)membranes were fabricated using a fine-tuning contra-diffusion method.Through investigating the membrane-forming condition(level difference,density difference and concentration difference),Metal-organic framework(MOF)nanocrystals were formed in situ in the nano-porous layer of the sheet polyacrylonitrile(PAN)ultrafiltration support membrane.The morphology and structure of the resulting membranes were characterized by powder X-ray diffraction(XRD),scanning electron microscope(SEM),Fourier transform infrared spectrometer(FTIR),which founding that the dispersion of the ZIF particles was improved due to the confinement effect of the substrate.Most importantly,the composite layer of the formed NCC membrane was of nearly zero thickness,which decreased the mass transfer resistance of water.As a result,the formed ZIFs/PAN membranes showed dramatically increased flux when compared to other nanofiltration membranes reported in the literature,without sacrificing rejection.The nanofiltration separation performance of the ZIF-11/PAN NCC membranes were evaluated by removing dye from water.With the optimum conditions(The diffusion conditions,namely,the liquid level interval between the metal ion solution and ligand solution,the concentration of metal ion,the diffusion time and the drying temperature were set at 4 cm,0.022 g/L,2 h and 50°C,respectively.Finally,the membranes were evaluated at 0.2 MPa operating pressure),the separation performance for the ZIF-11/PAN membrane had a flux of 464L/m~2hMPa and a rejection of 98.4%.This membrane can stably run for 60 h without performance degradation.Secondly,tubic ceramic substrate was used as the support,and LDH layer was grown on the surface of ceramic substrate by in-situ method.The formation of LDH on the ceramic was characterized with an XRD,SEM,EDS and so on.The results show that the formed LDH's channel direction was perpendicular to the substrate,so it can shorten the distance of mass transfer components in membranes.Furthermore,through adjusting the membrane-forming conditions(reaction temperature,time and the precursor concentration)and operating conditions(feed temperature and pressure),the optimum conditions was determined as the reaction temperature was 110 ~oC,the reaction time was 24 h,the molar ratio of cobalt nitrate was 18 mmol/L,respectively.The operating conditions were as follows:the feed temperature was 85 ~oC and the water content of the feed is about 10%.With the optimal conditions,the LDH/ceramic nanoconfined composite membrane showed an excellent performance for the separation of water in ethanol solution with a permeate flux of 1222.4 g/m~2h,while the water content in permeate was 99.83%. |
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