【作者】 廖婵娟；

【导师】 罗运柏；

【作者基本信息】 武汉大学 ， 应用化学， 2011， 博士

【摘要】 膜分离技术是解决当代能源、资源和环境污染问题的重要高新技术以及可持续发展的技术基础。在我国,超滤膜的品种和质量跟国际先进水平相比还存在一定的差距,因此,关于超滤膜的研究有着重大的理论意义和实际运用价值。目前,超滤膜的研究方向主要是提高膜的抗污染性能以及降低操作成本。聚偏氟乙烯材料化学稳定性高,耐热性好,强度高,韧性好,是膜制备的优选材料。由于聚偏氟乙烯的强疏水性,在过滤操作时,聚偏氟乙烯超滤膜极易受蛋白质、油类等物质的污染。膜污染直接导致膜使用寿命缩短,操作成本增加,并极大的限制了超滤膜的应用范围。所以,聚偏氟乙烯超滤膜的改性就显得尤为重要。纳米材料被公认为是重点发展的新型材料之一。将纳米无机材料与聚偏氟乙烯相结合,不但能集中无机材料与有机材料的各自优点,弥补它们的缺陷,而且可以发展单一膜材料原先没有的综合性能,满足特定的需求。本课题选择了具有介孔结构的二氧化硅(SBA-15)、纳米粉体二氧化硅(SiO2)、NaY型纳米沸石分子筛、纳米碳酸钙(Nano-CaCO3)以及纳米氧化锌(Nano-ZnO)作为改性材料,通过相转化法分别制备了不同纳米材料的聚偏氟乙烯改性超滤膜。探讨了无机纳米材料的浓度对改性膜结构和性能的影响,并采用现代仪器分析方法和过滤操作对改性膜的表面、横截面形貌结构、热力稳定性、机械性能、亲水性、过滤性能以及抗污染性能进行了研究和分析。自制了新型无机纳米介孔二氧化硅材料SBA-15,通过相转化法制备了含低浓度SBA-15粒子(≤0.72 wt%)的PVDF共混改性膜。通过扫描电镜(SEM), X-射线能谱(EDX),拉伸力测试,热重分析(TGA),接触角测定,水通量和牛血清蛋白(BSA)截留率等方法表征了改性膜的性质。发现,低浓度SBA-15粒子的引入对膜的上表面,横截面形貌以及内部孔径没有明显影响。实验结果表明,添加低含量的SBA-15粒子能够有效地改善PVDF超滤膜的亲水性,提高膜的抗污染性、机械强度和热稳定性,而且在膜通量增大的同时,保持了BSA截留率在87%以上。比较了原始PVDF超滤膜和两种低浓度不同结构二氧化硅(N-SiO2和M-SiO2粒子)的共混聚偏氟乙烯改性膜。通过SEM和原子力显微镜(AFM)分别观察膜的横截面和表面形貌；通过对改性膜表面接触角的测定表征了多孔膜表面的亲水性能；通过测定水通量和BSA截留率比较了改性膜的过滤性能；根据BSA渗透通量得到了膜的平均孔径和孔隙率大小；通过TGA和弹性拉伸力测试,表征了改性膜的热稳定性和机械强度。结果表明,N-SiO2和M-SiO2浓度相同时,N-SiO2/PVDF (P-N)改性膜的平均孔径和孔隙率更大,水通量更高,但是BSA截留率有轻微降低；相对于P-N改性膜,M-SiO2/PVDF (P-M)改性膜表面的亲水性更高、表面粗糙度相对较低,抗污染性能较好,而且P-M改性膜的机械强度相对更高。此外,两种改性膜都具有典型的非对称膜形貌以及优良的热稳定性。通过相转化法制备了一种新型抗菌AgNaY/PVDF (P-AgNaY)共混改性超滤膜。AgNaY共混膜对大肠杆菌具有优异和长效的抗菌活性。结果表明,银离子含量越高抗菌活性越强。P-AgNaY-3的接触角降低到81.6°,膜表面的亲水性得到改善。与PVDF原始膜相比,P-AgNaY改性膜的过滤性能,热力稳定性和机械强度都有所改善,而且BSA截留率在92%以上。通过抑菌圈法测定了改性膜对大肠杆菌的抗菌活性和抗菌长效性。运用SEM,X-射线衍射法(XRD),拉伸力测试,TGA,接触角测试和膜通量的测试表征了P-AgNaY共混膜的各种性能。Nano-CaCO3作为掺杂材料,通过相转化法制备了不同浓度的Nano-CaCO3/PVDF共混超滤膜。讨论了改性膜的膜孔结构、机械性能、热力稳定性、亲水性以及过滤性能。随着Nano-CaCO3含量的增加,改性膜在保持膜的非对称结构的同时,它们的孔隙率和平均孔径逐渐增加,膜表面的接触角整体呈下降趋势,亲水性随之提高,同时增加了改性膜的水通量和抗污染性能,提高了改性膜的热力稳定性。由于Nano-CaCO3的强亲水性,使其在疏水性聚偏氟乙烯铸膜液中存在少量的团聚,从而降低了Nano-CaCO3粒子在膜中的分散程度,当Nano-CaCO3浓度为1.2 wt%时机械强度综合性能较好。自制了Nano-ZnO粒子,通过相转化法制备了不同浓度的Nano-ZnO/PVDF共混超滤膜。随着Nano-ZnO含量的增加,改性膜的接触角逐渐减小,膜表面的亲水性逐渐提高,孔隙率也有所增大,从而提高了PVDF改性膜的水通量,当Nano-ZnO含量为5 wt%时水通量达到最大值。考察了不同Nano-ZnO含量PVDF改性膜的机械强度,发现Nano-ZnO含量为5 wt%时,改性膜的机械性能较好。添加5 wt%的Nano-ZnO颗粒能够有效地调控膜孔结构,改变膜孔分布,改善膜的过滤性能,提高膜的水通量。Nano-ZnO还有效地提高了改性膜的热力稳定性能。更多还原

【Abstract】 Membrane separation technology is an important high-tech to solve energy, resources, and environmental pollution problem of the time. It is a technology foundation of the sustainable development. The quality and category of domestic ultrafiltration (UF) membranes still need improving. Research in UF membrane technology has great significance of theoretical and practical values. The most concentrated research focused on UF membranes is to enhance anti-fouling property and to reduce costs. Poly (vinylidene fluoride) (PVDF) is a preferred material for membrane preparation. It has excellent chemical stability, thermal stability, strength, and toughness. However, these membranes are susceptible to be fouled by oils and proteins because of their high hydrophobicity, which limits their application in filtrating aqueous mixtures. Consequently, modification plays a very important role in PVDF membrane application. Nano-materials are recognized as one of the focus on the development of new materials. The combination of nano-inorganic materials and PVDF plays their respective advantages, makes up their deficiencies, exploits a comprehensive performance, and meets the specific needs.Nano-SiO2, nano-NaY zeolites, nano-CaCO3, and nano-ZnO modified PVDF UF membranes were prepared by phase inversion method in this study, respectively. Meanwhile, the effects of inorganic nano-particles on the morphology, thermal stability, mechanical property, hydrophilicity, membrane flux, and antifouling performance of the membranes were discussed as well.PVDF membranes with low contents of mesopours silica SBA-15 particles (≤0.72wt%, by weight of PVDF) were prepared by a phase inversion process. The thin membranes were then characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), tensile stress tests, thermogravimetric analysis (TGA), contact angle technique, water flux and bovine serum albumin (BSA) retention to investigate the influence on the final properties of the developed membrane. The resulting modified membrane exhibited no particular influence on the structures of the air surface, cross-section and inner pores. The experiment results confirmed that the addition of low contents of SBA-15 particles could effectively improve membrane hydrophilicity, antifouling performance, mechanical property and thermal stability, and increased membrane flux with the resistance of BSA solution above 87%.The comparison of the morphology and performance was carried out between virgin PVDF UF membrane and PVDF composite membranes with low content of two different SiO2 (N-SiO2 and M-SiO2 particles). Cross-sectional area and surface morphology of the membranes were observed using SEM and atomic force microscope (AFM). Surface hydrophilicity of the porous membranes was determined by the measurement of a contact angle. Performance tests were conducted on the composite membranes by water flux and BSA retention. Mean pore size and surface porosity were calculated based on the permeate flux. Thermal stability and mechanical stability were determined with TGA and tensile tests. The results indicated that the N-S1O2/PVDF (P-N) membranes possessed bigger average pore size and porosity, which led to higher water flux and a slight decline of BSA retention. And M-SiO2/PVDF (P-M) membranes had better mechanical stability and antifouling performance with enhanced membrane hydrophilicity and decreased membrane surface roughness. Both of the P-N and P-M membranes displayed typical asymmetric morphology and improved thermal stability.A novel antibacterial UF membrane obtained by blending PVDF with Ag+ exchanged NaY zeolite particles (AgNaY) was prepared using phase inversion methods. The AgNaY hybrid PVDF membranes exhibited excellent and long-lasting antibacterial activity against Escherichia coli (E. coli). Its antibacterial activity was improved with increased Ag+content. The hydrophilicity of P-AgNaY-3 was improved with a low contact angle of 81.6°. Compared with P-0, the permeate performance, thermal stability, and mechanical properties of P-AgNaY was improved with a steady BSA retention above 92%. Antibacterial activity of the membranes against E. coli was measured using the halo zone test. The characterization of AgNaY/PVDF hybrid membranes was investigated by scanning electron microscope, X-ray diffraction (XRD), tensile stress tests, TGA, contact angle tests, pure water flux, and permeation flux.PVDF membranes with different contents of nano-CaCO3 particles were prepared by a phase inversion process. The effect on morphology, mechanical property, thermal stability, hydrophilicity, and filtration performance of the modified membranes were discussed. With the increasing content of nano-CaCO3 particles, the porosity and average pore size of the modified membranes were increased, and the hydrophilicity was improved by decreased contact angle, which increased the membranes water flux and antifouling performance as well. Meanwhile, the modified membranes still maintained asymmetric structures. The attractive hydrophilicity caused partial aggregation of nano-CaCO3 in PVDF casting solution, which affect the dispersion of nano-CaCO3. And a best mechanical stability of modified membranes appeared at nano-CaCO3 concentration of 1.2 wt%.PVDF membranes with different contents of nano-ZnO particles were prepared by a phase inversion process. With the increasing content of nano-ZnO particles, the porosity of the modified membranes was increased; the hydrophilicity was improved by decreased contact angle, which led to the increase of the membranes water flux. The water flux and mechanical stability reached peak when nano-ZnO concentration was at 5 wt%. The results confirmed that the addition of 5wt% nano-ZnO could effectively dominate membrane pore structure and distribution, which improved membrane filtration performance and water flux. Nano-ZnO also improved membrane thermal stability effectively.更多还原