紫外接枝制备亲水性纳滤膜的研究

【作者】 邱长泉；

【导师】 平郑骅；

【作者基本信息】 复旦大学 ， 高分化学与物理， 2005， 博士

【摘要】 纳滤膜由于其工作压力低、渗透通量大、分离效率高、操作成本低在水处理和低分子量有机分子的分离中得到广泛的应用,是近年来发展迅速的膜分离技术。随着纳滤在生物、医药等领域中的广泛使用,提高膜的亲水抗污性已成为纳滤膜研究的热点。本文通过对超滤膜进行紫外辐照接枝的方法制备亲水性纳滤膜,创建了一种制备亲水性纳滤膜的新方法。实验系统研究了酚酞基聚醚酮（PEK-C）超滤膜表面的紫外辐照接枝反应,研究了反应条件、单体性质、链转移剂及共聚接枝等对膜的纳滤分离性能的影响,在此基础上探讨了PEK-C的光接枝反应的机理和Donnan效应对纳滤膜性能的影响。 论文首先研究了在光敏剂BP存在下,通过紫外辐照在PEK-C超滤膜表面接枝亲水性单体丙烯酸（AA）和甲基丙烯酸β-羟乙酯（HEMA）单体制备纳滤膜的方法。用FTIR、AFM、表面接触角测定仪和改性膜对无机盐电解质的纳滤截留性能等方法系统研究了接枝反应的条件对亲水性纳滤膜结构和性能的影响。研究表明,AA和HEMA能够在光敏剂存在下,通过紫外接枝聚合的方法在PEK-C膜表面形成接枝层。其接枝率随辐照时间的增加而增加,膜的水接触角也同步下降,表明改性后膜表面的亲水性得到明显改善。对这两种单体改性的膜进行纳滤分离实验发现,尽管在相同接枝条件下,二者的接枝率相近,但膜的分离性能,特别是对电解质离子的截留率有很大的差别。如在光强为1.56 mW/cm²时,用质量浓度均为10%的AA和HEMA溶液接枝90 min,改性膜对Na₂SO₄的截留率分别为94%和39.5%。这表明,通过在膜表面引入电负性强的单体对提高膜的纳滤分离性能十分有利。 论文也研究了在单体溶液中不加任何光敏剂,用紫外光对PEK-C超滤膜直接辐照接枝丙烯酸单体的反应。结果发现,AA同样能很好地接枝到PEK-C膜上,表明PEK-C具有良好的光敏性。通过增大光强、延长接枝时间和提高单体的浓度,均有利于提高膜表面的接枝率。同样,随着接枝率的提高,水在膜上的接触角变小,膜表面的亲水性提高。通过表面紫外辐照接枝,改性PEK-C膜显示了优良的纳滤分离性能。如当辐射强度为8.7 mW/cm²时,在10%的AA单体溶液辐照5min后,改性膜对Na₂SO₄的截留率可高达99.6%。根据上述实验结果,论文用扩展的Nernst-Planck方程对接枝改性膜的成膜过程和分离机理进行了讨论,认为在微孔中形成的接枝链与溶液分子的磨擦阻力和静电排斥作用是接枝膜对盐离子呈现截留作用的主要原因。通过控制接枝率和接枝链长,改变膜表面的静电排斥力可有更多还原

【Abstract】 Nanofiltration (NF), a pressure-driven separation process, has various applications in many fields, especially in water treatments and the separation of low molecular weight organic compounds. Because of its advantages such as low operating pressures, high fluxes, high retentions of multivalent salts, low investment and operation costs, this technology has rapidly developed in the last ten years. The new applications of nanofiltration in the fields of biotechnology and pharmacy, where the fluid phases to be treated are generally complex and heavily loaded with colloidal matters, require hydrophilic membranes with better fouling resistances.In this article, a novel method was used to prepare hydrophilic nanofiltration membrane by UV irradiation graft polymerization from Polyetherketone (PEK-C) ultrafiltration membrane. The grafting condition and effect of monomer nature on the membrane performance such as salt rejection and permeate flux have been systematically studied. By introducing chain transfer agent and other polar monomer in the grafting solution, the surface nature and structure of the membrane have been changed. The results showed that the function of Donnan effect on the membrane performance, which are very helpful to understand the mechanism of nanofiltration.We introduced at first the graft polymerization of PEK-C ultrafiltration membrane by hydrophilic monomer such as acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in presence of benzophenone BP as photosensitive agent. Several analytic methods such as FTIR-ATR, AFM, CAs were employed to characterize the chemical and physical properties of modified membranes. FTIR-ATR spectra detected AA and HEMA grafts on the surface of PEK-C, and the relative grafting ratio increased with irradiation time, while the contact angle of water on the modified membrane surface measured by CAs decreased. That means the hydrophilicity can be improved by hydrophilic monomers grafting onto the surface of PEK-C membranes. The modified PEK-C membrane showed a good retention to salt that is a characteristic of nanofiltration. The difference in separation performance of membrane modified by AA or HEMA under the similar grafting condition demonstrated that the membrane negatively charged has a higher salt retention. For example, the retentions to sodium sulfate of the membrane grafted AA and HEMA for 90 min under UV intensity of 1.6 mW/cm~2 was 94.1 % and 39.5 % at 0.4 MPa, respectively.The UV irradiation graft polymesization of PEK-C membrane has been also studied in the absence of photoinitiator. The analysis with FTIR, CAs and AFM detected that the graft polymerization took place as well as in the presence of BP too. It showed that the PEK-C is aphotosensitive polymer. According to its chemical formula, we suggested that the structure of benzophenone in main chain of PEK-C could be the photosensitive center. In presence of hydrogen-donor, under UV irradiation, benzophenone would transfer to pinacol radical, and initiated the graft polymerization.The effect of irradiation condition and monomer nature on the membrane performances of modified membrane was systematically investigated. The results obtained by means of FT1R-ATR, AFM, CAs showed that the irradiation graft polymerization of hydrophilic monomer on the PEK-C UF membrane in the absence of BP followed the similar trend that the grafting degree on the membrane surface and their hydrophilicity increased with increasing in irradiation intensity or irradiation time. The retention of sodium sulfate of the membrane modified with 10% of acrylic acid for 5 min irradiation with a UV intensity of 8.7 mW/cnr was very high, about 99.6 % at 0.8 MPa. This result suggested that part of AA chains grafted on the micro-porous wall and decrease the pore sizes on the nanometer order under suitable irradiation condition within a few minutes. According to the experiment results, we discussed the membrane forming process and the mechanism of nanofiltration separation based on extended Nernst-Planck equation. It suggests that the rejection of a charged solute depends on the steric exclusion from partially occluded by grafted PAA chains in the membrane pores and the static expulsion by Donnan potential of PAA chains. It means that the membranes performance can be controlled with varying the length of grafting chain, the grafting ratio and their electronegative properties.UV direct irradiation grafting and polymerization and the nanofiltration performance of four different hydrophilic grafted monomers [neutral (acrylamide (AM), weak acid (2-hydroxyethyl methacrylate (HEMA), acrylic acid (AA), and strong acid (2-acrylamido-2-l-propanesulfonic acid (AMPS)) on PEK-C membranes were measured. Although all the grafted and polymerized monomers increased the surface hydrophilicity of the PEK-C grafted membrane over that for the unmodified PEK-C membranes, their effect on nanofiltration performance was quite different. Using the PEK-C membranes for grafting, membrane with superior performance (high salt retention, high salt solution flux) was obtained with the AMPS. Grafting of AM resulted in substantial decrease in permeability due to the membrane pores were largely occlude by PAM chains, but their retention to salt were very low, even at high AM graft ratio. Those results also testified that more electronegativity of the monomer is, the better nanofiltration performance of the modified membrane. The use of chain transfer agent, iso-propane alcohol (1PA) was use in producing hydrophilic更多还原