| Nowadays,along with the population growth and development of social economy,there gradually appear the problem of water pollution and water resource shortage. As a promising method to solve water resource shortage, water treatment technology has been widely concerned. With the advantages of low energy consumption, high efficiency, work under ambient condition and simple technics, as one of water treatment method, membrane base separation technology can concentrate and recycle useful substances in wastewater, for the purpose of resource fully utilized. In order to solve the shortcoming of commercial nanofiltration membrane, such as low flux and poor selectivity, a composite nanofiltration membrane with high flux and high selectivity was prepared on polysulfone ultrafiltration membrane by using layer by layer assembly method.With the advantage of versatility, simplicity and easy operation of the composite film, Layer by Layer（Lb L）assembly method has become one of important methods for creating ultrathin functional film layers, owning the structure and the films were controllable. Due to the unique charge characteristics, polyelectrolyte multilayers are very suitable as the active skin layer of the nanofiltration membrane.In this study, three kinds of polyelectrolytes, polyethyleneimine（PEI） as polycations, polyacrylic acid（PAA） and sodium polystyrene sulfonate（PSS） as polyanions, was selected to modify polysulfone ultrafiltration membrane（Alfa Laval UFX-10） to prepare polyelectrolytes multilayer nanofiltration membranes. The influences of assembling condition, such as the number of bilayers, deposition time, p H value of deposition solutions et al., on the performance of polyelectrolyte nanofiltration membrane were investigated. It was found that the number of bilayers, deposition time, p H value of deposition solution and polyelectrolyte species of outmost layer et al. have great effect on the performance of modified membranes. With the bilayer number increased, salt rejection（R） increased but flux（F） decreased. The ion was mainly rejected by the out-layer of the PEMs. Considering the influence of various parameters on membrane performance, the optimum conditions of PEMMs forming was found. The rejection of（PEI/PSS）5、（PEI/PSS）5.5、（PEI/PAA）5、（PEI/PAA）5.5 films to Mg SO4 solution（2000mg/L） were 71.15%,719.5%,4.29%,23.57% and the permeating flux were 22.86 L/（m2·h）, 17.14 L/（m2·h）, 4.29 L/（m2·h）, 23.57 L/（m2·h）, respectively. We also investigated the stability of modified membranes. The flux and rejection of modified membranes had changed little during the 18 hours running time.The modified nanofiltration membranes were characterized by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy（ATR-FTIR）.The ATR-IR spectrum of PEI/PSS multilayer basically overlapped with the IR spectrum of substrate membrane. Both the 1015cm-1 absorption peak of the sulfonic base on the ATR-FTIR spectrum of（PEI/PSS）n membranes and the 1738cm-1 absorption peak of carboxyl base on the ATR-IR spectrum of（PEI/PAA）n membranes increases gradually with the increase of the bilayer number,which is a demonstration of the Lb L assembly process. The SEM images showed that the surface of modified membranes were smooth and compact. The contact angle of modified PEMs films were measured by contact angle meter, and the result indicated that the modification of membrane enhanced the hydrophilic performance of membrane.The effect factors influencing separation performance of the polyelectrolyte nanofiltration membrane were investigated including feed temperature, p H value of feed solution, kind and concentration of feed solution. The results of researching on the performance of polyelectrolyte nanofiltration membrane indicated that those multilayer polyelectrolyte membranes are excellently suited for ion rejection and ion selective. |
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