| Reverse osmosis has become one of the most economical techniques in the desalination of seawater and brackish water. For the desalination by reverse osmosis composite membrane, the current main problem is the high water pressure and low flux, thus resulting in much of higher energy consumption and cost in water desalination. Therefore, the further research and development in high flux membrane materials and membrane technology need to reinforce, in order to develop reverse osmosis technology in the sea water and brackish water desalination application. A new composite membrane based on electrospinning nanofibers showed 10 times higher than that commercial composite membranes in water flux, and now is expected to further optimize for water desalination. Polyamide reverse osmosis composite membrane based on poly(vinyl chloride) nanofibrous substrate was prepared in order to improve the performance of aromatic polyamide membrane in this work. Furthermore, the membrane structure and its performance under relevant experimental conditions were studied in detail.PVC nanofiber membrane was prepared through the optimization of spinning process. The fiber diameter was between 500 to 800 nm. The surface hydrophilicity of hydrophobic electrospun PVC nanofibrous membrane were improved by coating dopamine via the dopamine self-polymerizing and adherring firmly to the membrane surface in mild aqueous environments. The membrane surface hydrophilicity was investigated by water contact angle measurement. Experimental results showed that the optimum conditions were dopamine solution of pH 8.0, the concentration of 1.0g / L, modified time of 12 hours. Chemical and morphological changes of the membrane surfaces before and after hydrophilic modification were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and atomic force microscope (AFM). It was found that the hydrophilic polymer coating layers containing carboxyl, hydroxyl and amino groups were substantially attached onto the hydrophobic PVC electrospun membrane surfaces.A polyamide reverse osmosis composite membrane was prepared by interfacial polymerization of m-phenylenediamine and trimesoyl chloride on the PVC nanofibrous membrane. In order to gain the optimal conditions of membrane-forming, a series of experiments were conducted to investigate the influences of interfacial polymerization conditions on membrane performance, including concentration of reactants, pH, reacting time, curing temperature and time. The optimal preparation conditions of polyamide reverse osmosis membrane were given as follows: 2wt% m-phenylenediamine solution in water, pH range from 9 to 11, 0.2wt% trimesoyl chloride in hexane, reacting time 60 seconds at room temperature, curing temperature range from 70 to 90℃and curing time range from 8 to 12 min. The surface composition and structure of membrane were characterized by Fourier transform infrared spectroscopy, scanning electronic microscopy and atomic force microscopy. Infrared spectrum suggested acyl amide existed in the surface of polyamide membrane. Scanning electronic microscopy showed an active layer formed on the PVC nanofibrous membrane. Atomic force microscopy displayed that the surfaces of reverse osmosis membranes appeared the apparent structure of peaks and valleys.Additionally, the membrane performances such as salt rejection and flux were also studied. The effects of operating conditions on the performance of polyester-amide reverse osmosis composite membrane were investigated, including operating pressure, operating temperature and electrolyte concentration. For 1000mg/L of sodium chloride solution, at a lower pressure, with the operating pressure increases, the water flux of polyamide membrane is almost linear rise; at a certain pressure, the membrane flux decreased with the concentration of sodium chloride increased at the same time membrane salt rejection of NaCl decreased slightly. As the temperature increases, membrane flux and salt rejection increase simultaneously.
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