Metal coordinated PAN hollow fiber membranes with triaxial cross-linked structure and its self-cleaning performance
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摘要:
目的 中空纤维膜经过多次膜分离过程后容易堵塞，从而影响其使用寿命，而自清洁功能改性是改善其重复使用性能的方式之一。光、电催化剂可有效恢复膜通量等指标，但对光、电等能源依赖性大，负载工艺复杂。本文拟通过制备一种金属螯合三维交联结构的聚丙烯腈基中空纤维膜，借助于Fe与HO间的芬顿反应(Fenton)达到温和自清洁膜材料的目的。此外，立足于金属螯合物形成的交联网络，达到提高中空纤维膜物理截留效率的目的。 方法 以聚丙烯腈为溶质，N，N-二甲基甲酰胺为溶剂配制铸膜液，采用湿法纺丝技术制备聚丙烯腈中空纤维膜(PAN-HFM)。在不同反应条件下对其进行偕胺肟改性，以探讨肟化程度与改性条件间的关系。将肟化聚丙烯腈中空纤维膜(AOPAN-HFM)与金属Fe离子进行配位制备金属螯合三维交联结构中空纤维膜(FePAN-HFM)。红外光谱、X射线衍射光谱、电子显微镜、静态接触角分析仪等技术被用于对比分析PAN-HFM、AOPAN-HFM、FePAN-HFM的分子结构、表面形貌、亲疏水性能；通量、截留率等性能测试用于分析膜材料自清洁性能。 结果 从PAN-HFM的偕胺肟化改性实验可以看出，中空纤维膜氰基转化率和增重率会随着反应时间、反应温度、盐酸羟胺浓度的增加而增加；红外光谱和X射线衍射光谱结果显示，AOPAN-HFM在3650-3000，1650，913 cm等波数处出现归属于偕胺肟基团的特征峰，其中913 cm附近归属于N—O键的特征吸收在FePAN-HFM中发生偏移，证实了配位键的形成，而PAN-HFM在改性和配位反应后特征衍射峰发生宽化现象，说明其蕴晶结构受偕胺肟支链影响向非晶结构转化；SEM形貌分析显示，PAN-HFM结晶结构的坍塌促进了孔道形成；静态接触角测试结果表明，FePAN-HFM疏水性优于PAN-HFM，该结果有利于膜表面的自清洁。文章对比测试了PAN-HFM、AOPAN-HFM、FePAN-HFM通量、截留率等指标，发现Fe离子与HO组成的Fenton催化体系赋予了FePAN-HFM中空纤维膜较好的自清洁性能，膜通量恢复率达84.6%，明显高于其他样品。为进一步探讨Fenton反应对FePAN-HFM中空纤维膜自清洁性能的影响，将不同Fe离子负载量FePAN-HFM用于亚甲基蓝降解测试，结果显示Fe离子负载量为3.6 mg/g时催化降解活性最高，该结果通过假一级反应动力学计算得到证实。 结论 自清洁功能改性是改善中空纤维膜材料重复使用性能的重要方式之一，常见的光、电催化法因过于依赖外部条件而受到使用限制，而基于Fe离子与HO间的芬顿反应具有反应速率快，对光、电等条件依赖度低等优点。本文主要通过构建基于偕胺肟聚丙烯腈基中空纤维膜的金属螯合交联结构，来实现中空纤维膜自清洁性能改性的目的。本文报道的偕胺肟基金属螯合中空纤维膜，不仅通过引入Fenton反应体系而获得较好的自清洁性能，而且因其三维交联分子结构实现了截留效率的提升。当FePAN-HFM中Fe(III)负载量为3.6 mg/g时自清洁性能最佳。 Abstract: To explore a kind of triaxial cross-linked hollow fiber membrane (HFM) with self-cleaning performance, polyacrylonitrile based HFM which was prepared by wet processing was chemically modified into amidoximated PAN hollow fiber membranes. Then the active groups were coordinated with metal ions (Fe3+) randomly to achieve metal coordinated amidoximation PAN hollow fiber membranes with triaxial cross-linked structure. Preparation process, structural composition, surface morphology, hydrophilic and hydrophobic properties, membrane flux and retention, self-cleaning performance of the hollow fiber membranes were studied. Results show that the amidoximation rate of the membranes increases with the rise of time, temperature and hydroxylamine hydrochloride concentration during the modification process, and the modification levels would affect the crystallinity of the hollow fiber membranes so as to enhance the adsorption of small molecules into the fiber material. Although the Fe ions on the membranes would impact their crystal structure, hydrophilic property and membrane flux, but the triaxial cross-linked structure would promote the retention performance for bovine serum albumin to 88%. Besides, Fenton catalytic system coupled by Fe(III) and H2O2 endows FePAN-HFM with antifouling and self-cleaning properties and the flux recovery rate reaches to 84.6% significantly.-
Key words:
- polyacrylonitrile /
- hollow fiber membrane /
- self-cleaning /
- metal coordination /
- membrane flux
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图 1 反应条件对AOPAN中空纤维膜改性情况的影响
Figure 1. Effect of modification conditions on AOPAN-HFMs’ anmidoximation
图 2 聚丙烯腈(PAN)中空纤维膜在肟化改性和配位反应前后的FTIR(a)、XRD(b)图谱
Figure 2. FTIR(a) and XRD(b) spectra for Polyacrylonitrile (PAN)-HFM, AOPAN-HFM and FePAN-HFM
图 3 聚丙烯腈基铁配合物中空纤维膜(FePAN-HFM)(a, b)、AOPAN-HFM(c,d)和FePAN-HFM(e,f)的SEM及EDS能谱(g)分析
Figure 3. SEM analysis for Polyacrylonitrile-based iron complex Hollow fiber membrane (FePAN-HFM) (a,b), AOPAN-HFM(c,d), FePAN-HFM(e,f) and EDS for FePAN-HFM(g)
图 4 PAN-HFM、AOPAN-HFM、FePAN-HFM静态接触角测试
Figure 4. Static contact angle test for PAN-HFM, AOPAN-HFM and FePAN-HFM
图 5 FePAN-HFM自清洁性能在膜分离过程中的表现：中空纤维膜样品在纯水、牛血清白蛋白中的通量变化(a, b)及其截留率(c)
Figure 5. Self-cleaning performance of FePAN-HFM in membrane separation process: membrane flux variation in pure water, bovine serum albumin (a, b) and its retention ratio (c)
图 6 Fe离子负载量对FePAN-HFM自清洁性能的影响(a)及其动力学分析(b)
Figure 6. Effect of different Fe ions loading desage on FePAN-HFM self-cleaning performance (a) and its kinetic study (b)
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