基于多巴胺的聚偏氟乙烯膜表面亲水化改性及性能研究

发布时间：2018-03-31 22:17

本文选题：聚偏氟乙烯膜　切入点：亲水化改性　出处：《哈尔滨工业大学》2017年博士论文

【摘要】：近年来,膜分离技术由于其高分离效率和低能耗在污水处理领域得到了广泛应用。聚偏氟乙烯(PVDF)因具有优异的化学稳定性、耐候性及机械性能成为常用的超滤、微滤分离膜材料,在水处理领域展现出良好的应用前景。然而,PVDF的疏水性导致其分离膜在水处理领域应用面临两个重要问题:一方面,其疏水性会降低膜的水通量;另一方面,疏水的PVDF膜表面易被水中蛋白和油污染,导致水通量的急剧下降,并降低膜的使用寿命。提高PVDF膜表面的亲水性是解决上述问题的有效途径。本论文中,采用了三种基于多巴胺自聚合的表面改性策略来提高PVDF膜的亲水性,系统考察了不同改性策略所形成涂层的结构组成、形成机理、润湿性及稳定性,进一步详细研究了表面改性对膜分离性能及抗污染性能的影响。利用弱碱性条件下多巴胺的自聚合在超滤膜表面形成聚多巴胺涂层,之后在酸性条件下进行氟钛酸铵的水解在聚多巴胺涂层表面形成亲水二氧化钛涂层。通过表面全反射红外光谱以及元素分析确定了膜表面聚多巴胺涂层及二氧化钛涂层的形成;通过扫描电子显微镜及原子力显微镜观察了涂层的微观形貌。研究表明,膜表面二氧化钛涂层可大幅度提高超滤膜的亲水性,并且通过调整氟钛酸铵的水解时间,可实现对涂层亲水性的调控。在优化条件下,改性超滤膜的水通量和对牛血清蛋白(BSA)的截留率分别达到了227.9 L m-2 h-1 bar-1和92%。静态吸附试验及动态吸附试验结果表明改性超滤膜具有更低的蛋白吸附量,循环过滤实验结果表明改性膜的水通量回复率可以达到90%以上。此外,PVDF膜表面的二氧化钛涂层具有良好的稳定性,可以耐受剧烈的冲洗。氧元素拟合分峰结果表明其良好稳定性是由于二氧化钛与聚多巴胺涂层形成了较为稳定的配位键所致。此外,利用该策略改性PVDF微滤膜可使之具备超高的水通量和水下超疏油性质,其水通量达到了7600 L m-2 h-1 bar-1,并且可实现对水包油乳液的高效分离。进一步提出了基于弱碱性条件下多巴胺自聚合与正硅酸乙酯水解过程耦合的共涂覆改性策略。该策略可在PVDF基膜表面形成亲水涂层,其亲水性可通过调整正硅酸乙酯浓度及水解时间来控制。扫面电子显微镜显示该涂层在膜表面分布均匀;涂层表面的全反射红外分析表明该涂层是由二氧化硅和聚多巴胺组成;元素面扫描结果表明二氧化硅及聚多巴胺在膜表面分布均匀;通过改性溶液中形成纳米颗粒刻蚀前后的透射电子显微镜照片确定了不同条件下杂化涂层中聚多巴胺与二氧化硅的分布情况。在以上结果的基础上,结合改性溶液在不同反应时间的紫外光谱结果,提出了杂化涂层的形成机理:在弱碱性条件下多巴胺的自聚合与正硅酸乙酯的水解同时进行,聚多巴胺在膜表面附着的同时,通过氢键作用及物理缠绕方式将正硅酸乙酯水解产物固定在膜表面,当混合溶液中正硅酸乙酯较少或者反应时间过长时,形成涂层表面主要以聚多巴胺为主,反之,则以二氧化硅为主。根据此机理优化改性了PVDF微滤膜,使该改性微滤膜具备了高亲水性及水下超疏油特性。改性微滤膜的水通量达到8606 L m-2h-1 bar-1,为未改性PVDF微滤膜水通量的34倍。亲水的杂化涂层赋予改性膜以优异的抗污染性能,并具备优异的稳定性,可耐受剧烈冲洗及低温反复弯折而保持水下超疏油特性。在此基础上,选择了具有亲水基团的γ-缩水甘油醚氧丙基三甲氧基硅烷(KH-560)作为与多巴胺的共涂覆改性剂。通过弱碱性条件下多巴胺自聚合及KH-560水解的耦合作用,在PVDF超滤膜表面形成了杂化涂层。经该方法改性的PVDF超滤膜具有高亲水性。当KH-560的浓度为9 mg m L-1时,改性PVDF超滤膜的水通量达到了185 L m-2 h-1 bar-1,对BSA的截留率超过90%。此外,改性膜对蛋白的吸附量仅为12μg cm-2,具有优异的抗蛋白吸附性能。与本文中另外两种改性策略相比,该改性策略不但可以赋予PVDF膜以更好的润湿性,还可赋予PVDF超滤膜以干法保存的能力。该改性策略同样可以用来改性PVDF微滤膜,使其获得超亲水及水下超疏油特性。改性的PVDF微滤膜水通量达到6500 L m-2 h-1 bar-1,同时具备良好的抗污染性能。该策略所得杂化涂层同样具有优异的稳定性,可以耐受剧烈冲洗及极端环境下的反复弯折而保持高亲水性。本文中的改性策略为PVDF膜的亲水化改性提供了新思路,所得改性膜对处理含蛋白及污油的废水具有较好的应用前景。此外,本论文提出的改性策略也会促进基于多巴胺的仿生表面改性工程的发展。
[Abstract]:In recent years, membrane separation technology due to its high separation efficiency and low energy consumption has been widely used in the field of wastewater treatment. The polyvinylidene fluoride (PVDF) has excellent chemical stability, mechanical properties and weathering has become a common ultrafiltration, microfiltration membrane material in water treatment field show a good application prospect. However, due to the hydrophobic PVDF membrane faces two important issues in the field of water treatment application: on the one hand, the hydrophobic membrane water flux will decrease; on the other hand, PVDF membrane surface hydrophobic protein and susceptible to water oil pollution, resulting in a sharp decline in water flux, and reduce the service life of the film to improve the hydrophilicity. The surface of the PVDF film is an effective way to solve these problems. In this paper, using three kinds of dopamine self polymerization based on surface modification strategies to improve the hydrophilicity of PVDF membranes, investigated the different modification strategies form A coating composition, formation mechanism, wettability and stability, further detailed study of the influence of surface modification on the membrane separation performance and anti fouling properties. Using alkaline conditions of dopamine self polymerization in ultrafiltration membrane formed on the surface of polydopamine coating after hydrolysis of titanium ammonium fluoride under acidic conditions to form hydrophilic titanium dioxide polydopamine coating on the surface of coating. The formation of polydopamine coating and titanium dioxide coated membrane surface was determined by total reflection infrared spectroscopy and surface analysis of elements; by scanning electron microscopy and atomic force microscopy to observe the micro morphology of the coating. The results show that the film on the surface of TiO2 coating can greatly improve the membrane hydrophilicity, and through hydrolysis time adjustment of ammonium fluorotitanate, can realize the regulation of the hydrophilic coating. Under the optimized conditions, the modified ultrafiltration membrane water flux and Bovine serum albumin (BSA) rejection rate reached 227.9 L m-2 H-1 Bar-1 and 92%. static adsorption test and dynamic adsorption test results show that the adsorption capacity of modified protein ultrafiltration membrane has lower filtration, the experimental results show that the water flux of the modified membrane recovery rate can reach more than 90%. In addition, the titanium dioxide coating PVDF film surface has good stability, can withstand the intense flushing. The oxygen peak fitting results show its good stability due to titanium dioxide and polydopamine coating formed a relatively stable coordination bond caused. In addition, the modified PVDF membrane can be equipped with ultra high water flux and underwater superoleophobic properties by using the strategy, its water flux reached 7600 L m-2 H-1 Bar-1, and can realize the efficient separation of oil in water emulsion. Further put forward the alkalescent condition based on dopamine self polymerization with tetraethyl orthosilicate Coupled hydrolysis of esters Co coating modified strategy. This strategy can form hydrophilic coating on the PVDF membrane surface, the hydrophilicity can be controlled by adjusting the TEOS concentration and hydrolysis time. Scanning electron microscopy showed that the coating is evenly distributed on the membrane surface; the surface of the coating the whole infrared reflection analysis shows that the coating is composed of silica and polydopamine composition; element scanning results showed that silica and polydopamine evenly distributed on the membrane surface; the modified solution formed in transmission electron microscope before and after etching the nanoparticles to determine the distribution of Hybrid Coatings under different conditions of polydopamine and silica. On the basis of the above results, with UV spectroscopy results modified solution at different reaction time, the formation mechanism of hybrid coatings in alkaline conditions: dopamine self polymerization and TEOS The hydrolysis and polymerization of dopamine in membrane attached to the surface at the same time, through hydrogen bonding and physical winding will TEOS hydrolysis product is fixed on the membrane surface, when the reaction time is too long or less ethyl silicate solution, forming the coating surface with polydopamine, on the other hand, is based on silicon dioxide according to this. The mechanism of modification of PVDF micro filtration membrane, the modified microfiltration membrane with high hydrophilicity and underwater superoleophobic properties. The water flux of the modified membrane reaches 8606 L, m-2h-1 Bar-1, was 34 times higher than that of unmodified PVDF membrane water flux. The hybrid coating hydrophilic modified membrane to give excellent the anti pollution performance, and has excellent stability, can withstand severe cold washing and repeated bending while maintaining the underwater superoleophobic properties. On this basis, the hydrophilic groups of gamma glycidyl ether oxygen propyl trimethoxysilane Silane (KH-560) and dopamine were coated as modifier. The alkaline conditions and the hydrolysis of KH-560 dopamine self polymerization coupling effect on PVDF membrane formed on the surface of the hybrid coating. By the method of modified PVDF ultrafiltration membrane has high hydrophilicity. When the concentration of KH-560 is 9 mg m L-1 instead, the water flux of PVDF membrane was 185 L m-2 H-1 Bar-1, the retention of BSA over 90%. in addition, the modified membrane adsorption of protein is only 12 g cm-2, with anti protein adsorption properties. And this paper also compared two kinds of modified strategy, the modified strategy not only can give the PVDF film to better wetting ability, can also give PVDF ultrafiltration membrane by dry preservation. The modified strategy can also be used to modified PVDF micro filtration membrane, the super hydrophilic and underwater superoleophobic properties. Modified PVDF micro filtration membrane water flux up to 6500 L m-2 H-1 Ba R-1 also has good anti pollution performance. The same income strategy hybrid coating has excellent stability, can withstand the intense flushing and extreme environment of repeated bending while maintaining high hydrophilicity. The modified strategy in this paper provides a new way for PVDF to improve the hydrophilicity of the membranes, the modified membrane for wastewater treatment of wastewater containing protein and oil has a good application prospects. In addition, the modified strategy proposed in this paper will promote the development of biomimetic surface modification of dopamine based engineering.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ051.893

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