| Nanofiltratrtion (NF) is an emerging pressure-driven liquid separation technology,its separation characteristics boundary between reverse osmosis (RO) and ultrafiltration(UF). NF membrane has not only nanoscale pore, but also a surface electric charge.Nanofiltration can intercept types of nanoparticles with a molecular weight of between200-1000Da (e.g. small organic molecules, bacteria and viruses), and retain saltseffectively. Nanofiltration separation processes and mass transfer are controlled bydifferent mechanisms, including convection, diffusion (screening), adsorption andcharge effects (e.g. Donnan Effect) and so on. Therefore NF process has manyadvantages compared to conventional technology. Nanofiltration technology in recentyears gained significant attention and rapid development, and has been widely used infood, pharmaceutical and chemical fields. Currently, the nanofiltration membranes onthe market are mainly spiral wound membranes, most commercialization nanofiltrationmembrane material is polyamide (aramid and polyethylene piperazine amide).nanofiltration hollow fiber membrane have many advantages,such as high packingdensity, high membrane area in unit membrane volume, no need of feed and permeatebreaking net, lower requirements of pretreatment and maintenance than spiral woundmembrane. Therefore, in recent years, many researchers shifted their focus on researchand development of nanofiltration hollow fiber membrane.Chitosan not only has good biodegradability, permeability, film-forming ability,but also has some antibacterial properties. O-carboxymethyl chitosan (O-CMC) is awater-soluble derivatives of chitosan, its solution is an amphoteric electrolyte havingan anticancer action, has been used to prepare various separation membranes.In this study, amphoteric chitosan derivative (O-CMC) with good film-formingproperties was synthesized with chitosan. It was characterized by infrared spectrometer and carboxylation detection. It proved the successful synthesis of O-CMC with thegrafting reaction, which carboxylation degree D.D. was0.82. With O-CMC as theactive material, epichlorohydrin as a crosslinking agent, by coating-cross-linkingmethod, the active material is cross-linked on polysulfone hollow fiber ultrafiltrationmembrane surfaces. Preparing an amphoteric O-carboxymethyl chitosan/polysulfonehollow fiber composite nanofiltration membrane using this method. The influence ofthe preparation process and operating conditions on separation performance of thecomposite NF membranes were studied. Scanning electron microscopy (SEM), atomicforce microscopy (AFM), Fourier transform infrared spectroscopy and other equipmentwere used to study the structural characteristics of the composite nanofiltrationmembrane. Finally, the characteristics of the composite membrane, such as themolecular weight cutoff, Zeta potential, contact angles and stability was analyzed.The experimental results showed that: O-carboxymethyl chitosan was coated onpolysulfone ultrafiltration membrane surface successfully by cross-linking reaction;Dipping time, the concentration of the crosslinking agent, the concentration of thecasting solution, the reaction temperature and reaction time influence the performanceof the composite membrane; membrane preparation conditions was: dipping time20min, casting solution concentration of3.0wt%, crosslinking agent concentration2.0vol%, crosslinking temperature50℃, crosslinking time8h; the prepared compositenanofiltration membrane the order of retention rate of different salts was as follows:Na2SO4> NaCl> MgSO4> MgCl2, while inorganic salt solution flux varies littledifference; composite nanofiltration membrane surface roughness dropped from34.6nm to4.6nm; composite nanofiltration membrane MWCO was727Da, Zetapotential was-10.03mV, negatively charged composite film, the contact angledecreased (down from72.35°to46.03°), stable performance of the compositenanofiltration was not very good. |
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