碳纳米管界面改性超滤膜的抗污机理解析

Anti-fouling mechanism for ultrafiltration membrane of modified surface by carbon nanotubes

以碳纳米管(CNT)为核心改性材料,采用喷涂法对聚醚砜(PES)超滤膜进行界面改性,研究改性膜的抗污染性能.结果表明:改性膜经聚乙烯醇交联稳定后,呈现微弱的通透性降低和明显的亲水性提升,CNT交织网状层提高了界面粗糙度;在牛血清白蛋白(BSA)污染试验中,CNT-10改性膜的抗污性能最好,在20mg/LBSA试验后,其通量恢复率高达95.7%、膜界面可逆污染率接近60%;进一步分析界面电化学阻抗信息发现,污染实验后CNT-10膜的Nyquist曲线右移幅度(实部阻抗增加)明显小于原膜,且曲线半径未见明显扩大,这与改性膜呈现的较小幅度的电导降低和相对稳定的电容一致,表明改性膜具有更少的污染物粘附,与通量变化趋势相符.对频率-电导图进行分频讨论,表明BSA污染了PES-V整个膜表层与膜基层,而并未污染CNT-10整个表层和膜基层;CNT改性层与BSA的界面作用自由能(XDLVO)分析结果显示,改性膜与污染物相吸引作用仅为原膜的一半,从热力学上解释了其优异的抗污染性能.

Carbon nanotubes(CNTs) as the core modification material was spray-coated on polyether sulfone(PES) ultrafiltration membrane towards enhanced anti-fouling property. The permeability of the modified membrane decreased slightly and the hydrophilicity increased obviously, and the layer of woven CNT fibre also increased the membrane roughness. In the presence of bovine serum albumin(BSA) of 20mg/L, the CNT-10membrane exhibited a high flux recovery rate up to 95.7% with the reversible fouling ratio nearly 60%. Then, applying electrical impedance spectroscopy(EIS) to measure membrane fouling extents provided the membrane real-imaginary impedance, conductance and capacitance. The Nyquist curve of CNT-10exhibited less horizontal shift(real impedance increases) towards the right side, and the radius of the curve was not significantly expanded after contamination test,in consistent with the slightly decreased conductance and relatively stable capacitance. It was concluded that the modified membrane has less foulant adhesion, agreeing with the flux variation. The discussion on frequency division of frequency-conductance diagram showed that BSA contaminated the entire surface and membrane of PES-V, but did not pollute the entire surface and membrane of CNT-10. The free energy analysis of the interfacial interaction between CNT modified layer and BSA was only half that for the control, indicating small membrane-foulant attraction, which explained the excellent anti-fouling performance of the CNT modified membrane by thermodynamics.