纳滤膜新型材料研究

纳滤是一种介于超滤与反渗透之间的重要膜分离过程,具有工作压力低、无相转变及分离效率高等独特优势。膜污染及渗透性/选择性之间的平衡是纳滤膜在使用和研发过程中面临的亟待解决的两个主要问题。膜材料是膜与膜分离技术的核心,开发新型的纳滤膜材料是解决上述问题的重要手段。本文从新型纳滤膜材料的设计与选择的角度出发,总结归纳了近年来新型材料在纳滤膜的制备与应用研究现状,包括新型有机纳滤膜材料、新型无机纳滤膜材料和新型有机-无机杂化纳滤膜材料三个方面,拓展了对纳滤膜材料的认知,探讨了新型纳滤膜材料的共性及其存在的主要问题,并对未来高性能纳滤膜材料的研制方向进行了展望。     

用流动电位法表征纳滤膜的结构及性能

利用测量流动电位的方法考察了纳滤膜的表面电学性能对纳滤膜的截留性能的影响.首先,采用不同功能层材料制备了复合纳滤(NF)膜,考察功能层的交联时间、单体结构等对表面电性能的影响,研究纳滤膜对不同无机盐的选择截留性能与表面电性能的关系.通过流动电位法测定纳滤膜的表面电学参数,如流动电位(ΔE)、zeta电位(ζ)和表面电荷密度(σd).实验表明,这些电学参数的变化与功能层交联时间和纳滤膜截留率的变化一致,在交联时间为45 s时,3种电学参数的绝对值均最大,而纳滤膜对无机盐的截留率也最大.复合纳滤膜zeta电位的绝对值(|ζ|)按照Na2SO4>MgSO4>MgCl2变化,同截留率的变化相同.带侧基单体交联后得到的纳滤膜的表面电性能参数的绝对值小于不带侧基单体的.因此,流动电位法可用于研究复合纳滤膜的截留机理和功能层结构.     

相转化纳滤膜的膜材料结构设计及调控策略

非溶剂致相分离技术由于其制膜工艺简便且对膜结构调控手段多样化,在制备高通量、具有选择性筛分特性的纳滤膜上具有显著优势。然而如何进一步提升相转化纳滤膜的分离精度及渗透系数,仍受国内外学者广泛关注。本文首先系统阐述了相转化过程中,铸膜液热力学性质及成膜动力学对膜结构及性能的影响机理。其次总结了传统膜材料,如聚砜、聚醚砜等材料在纳滤膜制备中的研究进展。然后重点分析了两亲性嵌段共聚物材料的特点及在相转化纳滤膜制备中的突出优势。最后,本文展望未来制备高性能相转化纳滤膜的发展方向。     

高分子纳滤膜的制备技术

纳滤膜是介入于反渗透膜和超滤膜之间的一种压力驱动的新型分离膜,已成为近年来研究的热点,由于其载留分子量范围相对较窄（200－1000）且孔径处于纳米级（10^-9m),因此膜材质的选择及制备技术成为制备出高性能纳滤膜的关键。本文介绍了高分子纳滤膜的几种主要的制备工艺,并概述了近年来国内外在高分子纳滤膜材质、制备方法以及所制膜性能及应用方面的研究进展。     

荷电高聚物纳滤膜

本文对荷电聚合物纳纳滤膜的制备、性能及应用进行了全面的介和评述，反映了近年来荷电聚合笺纳滤膜研究的最新进展和动向。     

聚电解质层层自组装纳滤膜*

层层自组装技术能够方便地对膜的微观结构和组成进行调控,已在制备复合型纳滤膜方面取得了迅速的发展。本文综述了近年来用于聚电解质层层自组装纳滤膜的制备方法,种类以及影响因素。介绍了静态层层交替沉积、压力驱动自组装和电场强化自组装等三种制备方法;归纳了均聚型、共聚型和有机/无机杂化型等三类用于层层自组装纳滤膜的聚电解质的特点;讨论了聚电解质的荷电性、电荷密度和电离程度等因素对其自组装膜分离性能的影响。总结了聚电解质自组装纳滤膜在水处理和有机溶剂中物质的分离等方面的应用。同时,对提高聚电解质自组装纳滤膜的组装效率,分离性能和发展方向提出了设想和建议。     

解读纳滤:一种具有纳米尺度效应的分子分离操作

纳滤膜是20世纪80年代末期发展起来的一种广泛用于液体分离的新型分离膜。早期研究中,先后提出的基于筛分效应的细孔模型,基于静电效应的电荷模型,以及同时考虑上述两种效应的静电位阻模型和道南位阻模型等为人们更好地理解纳滤膜分离机理和指导纳滤膜过程应用发挥了十分重要的作用。然而由于这些具有“疏松型反渗透膜”特点的纳滤膜没有相应的膜性能预测评价软件,使得针对具体应用过程的纳滤膜的大规模标准化应用受到了一定的制约。为此,结合上述模型,根据一些特定实验拟合确定混合盐体系同号离子间的竞争作用和异号离子间的调节作用,提出了一个适于混合盐体系的纳滤膜分离性能评价模型,促进了纳滤膜技术在水处理过程的大规模推广。最近,根据纳滤膜对离子选择性分离性能及其伴随的动电性质的细致而深入的实验研究,发现仅考虑筛分效应和静电效应并不能完全合理地解释纳滤膜的分离性能,且在动电性质的解析上也存在一定缺陷,进而对纳滤膜纳米级孔径引起的特殊效应和溶液体系中复杂相互作用引起的荷电性质变化有了更为深刻的认识和理解,提出并定量分析了离子透过纳滤膜时存在的介电排斥效应。     

具有图灵结构的聚苯并咪唑耐溶剂纳滤膜的制备及性能

以聚苯并咪唑(PBI)为原料,采用配位诱导相转化法制备具有图灵结构的纳滤膜.通过改变聚合物的含量调控图灵膜的形貌,探究图灵膜的纳滤性能,并对图灵膜在有机溶剂中的稳定性进行测试.使用光学显微镜(OM)、扫描电子显微镜(SEM)及傅里叶变换红外光谱仪(FTIR)等对制备的图灵膜的表面形貌及结构进行表征.首次将配位诱导相转化法制备的图灵膜应用于耐溶剂纳滤中.研究结果表明:制备的图灵膜具有优异的纳滤性能和溶剂稳定性,该膜对玫瑰红(RB)、溴百里香酚蓝(BTB)及亚甲基蓝(MB)的截留率均可达到99%以上,在强极性溶剂N,N-二甲基甲酰胺(DMF)中过滤时间长达40 h时,对RB的截留率仍达到86.66%以上,在耐溶剂纳滤(SRNF)中具有良好的应用前景.     

耐溶剂纳滤膜*

纳膜分离过程是一种选择性高、操作简单、能耗低的分离技术,已在各工业领域和科学研究中得到广泛的应用。纳滤过程的诸多优点,使其在石油化工、医药、食品等领域的非水溶液体系中具有极大的潜在应用价值,而传统的纳滤膜难以拓宽到非水溶液体系中使用,为此进一步研究和发展耐溶剂纳滤膜,对于拓宽纳滤过程的应用极其重要。目前,耐溶剂纳滤膜已成为膜分离科学领域的研究热点,在现有报道的文献基础上,本文综述了有关在非水溶液体系中使用的耐溶剂纳滤膜制备的研究进展,并对将来的发展方向提出了建议。     

低聚壳聚糖制备液纳滤纯化的可行性研究

通过对筛选的3种纳滤膜结构及对低聚壳聚糖、氨基葡萄糖和NaAc溶液的截留性能和纯化过程研究发现,3种纳滤膜的膜面粗糙度大小依次为:DL>DK>NTR-7450,均能对低聚壳聚糖100%截留,但只能部分截留氨基葡萄糖和NaAc,其截留率大小为:DK>DL>NTR-7450。从低聚壳聚糖的纯化工艺要求和抗污染能力方面考虑,NTR-7450纳滤膜更具有工业应用价值。此外,纳滤膜对溶质的分离效果主要由空间位阻和静电效应决定,综合作用结果导致了低聚壳聚糖体系中的各种主要阳离子在纳滤过程中存在竞争透过,截留次序依次为:高分子低聚壳聚糖>氨基葡萄糖>Na+>H+。在Donnan效应和电离平衡的影响下,体系中Ac-在纳滤过程中也被脱出。纳滤纯化低聚壳聚糖制备液在技术上可行。     

Influence of diazonium-induced surface grafting on PES NF membrane fouling reduction in algal-rich water treatment

The algae bloom phenomenon incurs a major challenge to conventional drinking water treatment processes due to the discharges of a large amount of intracellular pollutant and odor compounds in the water sources. Membrane processes have been considered as promising technologies to treatment of algal-rich water due to complete algal cell rejection however, its application has been limited by membrane fouling. In this work, the high-performance loose antifouling PES NF membranes were fabricated using diazonium-induced grafting and applied for treating real algal effluent. The modified membranes exhibited complete algal dye removal and turbidity removal throughout the long-term filtration. Also, the coupling and radically modified membranes can be able to removed COD by up to 90% and 88%, respectively, while a removal efficiency of 24% was observed for bare membrane. It is worth noting that, a relative smooth behavior in permeate flux by loose modified membranes during prolonged algal dye filtration, demonstrating exceptional anti-fouling property of membranes. In addition, the fouled modified membranes were effectively recovered by water flushing. Both loose modified membranes exhibited excellent resistance in the strongly acidic environment. These high performance antifouling NF membranes affords an innovative methodology toward the treatment of algal-rich water.     

紫外接枝聚合聚乙二醇甲基丙烯酸甲酯制备抗污染聚砜超滤膜

以二苯甲酮(BP)为紫外引发剂,将聚乙二醇甲基丙烯酸甲酯(PEGMA)接枝在聚砜超滤膜表面以提高膜的抗污染性能.在二苯甲酮存在的条件下,波长较长(λ300nm)的紫外光(UV)辐射下发生提氢反应,可以有效防止聚砜分子主链的剪切,保持改性膜的分离性能.考察了PEGMA浓度、UV辐射时间和BP浓度对改性超滤膜接枝度、亲水性和抗污染性能的影响.用表面全反射红外光谱(ATR/FTIR)表征改性前后膜表面化学组成的变化.表面改性膜的纯水通量略有降低而牛血清白蛋白(BSA)截留率有所提高.随着接枝度的提高,PEGMA接枝改性膜的抗污染性能增加.     

Enhancing the antifouling property of polyethersulfone ultrafiltration membranes through surface adsorption-crosslinking of poly(vinyl alcohol)

An adsorption-crosslinking process of poly(vinyl alcohol) (PVA) was introduced to modify the surface of polyethersulfone (PES) ultrafiltration membranes for enhancement of their antifouling property. XPS and water contact angle measurement confirmed the obvious enhancement of surface hydrophilicity. Ultrafiltration results showed that the spreading of PVA chains over the hydrophobic membrane surface caused substantial but acceptable decrease on membrane flux. The fouling type analysis indicated that PVA adsorption effectively improved the antifouling property of PES membranes. With a PVA concentration of 0.5 wt% and three cycles of alternative adsorption-crosslinking, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than those of control PES membrane (0.61 and 0.47), and the flux recovery ratio was increased accordingly. The long-term ultrafiltration experiment demonstrated the improvement of recycling property and the reliability of adsorption-crosslinking process.     

Colloidal interactions and fouling of NF and RO membranes: a review

Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of colloidal fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling colloidal fouling of both RO and NF membranes. Major colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for colloidal fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter?100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF colloidal fouling are also identified in the current paper.     

Alteration of the morphology of polyvinylidene fluoride membrane by incorporating MOF-199 nanomaterials for improving water permeation with antifouling and antibacterial property

MOF-199@PVDF composite membranes are prepared by blending with different amounts of ultrasonic synthesized MOF-199 nanomaterials for improving the pure water flux (PWF) and achieving better antifouling and antibacterial performance. The membrane morphology, elemental composition, and surface properties are analyzed by various means of characterizations, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and water contact angle measurements. The performance of the modified membranes is also determined from the perspective of the PWF, bovine serum albumin rejection, as well as antifouling and antibacterial properties. Due to the variation in the viscosity of dope solution, the composite membranes possess remarkably different morphology, and the M5 membrane, which exhibited a sponge-like structure, the largest surface pore size, and the highest porosity, shows the highest PWF, reaching up to 185.05 L/m²h. Moreover, with the incorporation of MOF-199 nanocrystals, the antifouling property, together with the antibacterial property, toward both gram-negative bacteria and gram-positive bacteria, based on M5 and M7 membranes, increases dramatically compared with the pristine polyvinylidene fluoride membrane. In addition, the long-term permeation performance and copper leakage of the membrane are investigated. As a result, the composite membrane, M5, shows great potential in real water treatment.     

Enhanced antifouling performance of ZnS/GO/PVDF hybrid membrane by improving hydrophilicity and photocatalysis

In order to improve the antifouling performance of PVDF membrane, a novel zinc sulfide/graphene oxide/polyvinylidene fluoride (ZnS/GO/PVDF) composite membrane was prepared by immersed phase inversion method. The surface morphology, crystal structure, photocatalytic activity, and antifouling property of the as‐prepared membranes were systematically studied. Results showed that the ZnS/GO/PVDF hybrid membranes were successfully fabricated with uniform surface. The hybrid membrane surface possessed higher hydrophilicity with water contact angle decreasing from 77.1° to 62.2°. The permeability of the hybrid membrane was therefore enhanced from 222.9 to 326.1 L/(m² hour). Moreover, bovine serum albumin (BSA) retention experiment showed that the hybrid membrane separation was also promoted by 7.2%. The blending of ZnS and GO enhanced the hydrophilic and photocatalytic performances of PVDF membrane, which mitigated the membrane fouling effectively. This novel hybrid membrane could accelerate the practical application of photocatalytic technology in membrane separation process.     

Blood compatibility and permeability of heparin-modified polysulfone as potential membrane for simultaneous hemodialysis and LDL removal

Heparin was covalently immobilized on PSf membranes to obtain a dialysis membrane with high affinity for LDL. WCA and streaming potential measurements were performed to investigate wettability and surface charge of the membranes. The morphology of the membranes was investigated by SEM. An ELISA was used to measure the adsorption and desorption of LDL on plain and modified PSf. Blood compatibility was studied by measurement of thrombin time, partial thromboplastin time, kallikrein activity and platelet adhesion. It was found that the blood compatibility of the membrane was improved by covalent immobilization of heparin at its surface. However, PSf-Hep membrane showed higher flux recovery after BSA solution filtration, which revealed antifouling property of PSf-Hep membranes.     

The electrostatic and steric-hindrance model for the transport of charged solutes through nanofiltration membranes

Nanofiltration (NF) membranes possess the intermediate molecular weight cut-off between reverse osmosis membranes and ultrafiltration membranes, and also have rejection to inorganic salts. So one can assume that NF membranes have charged pore structure. We have developed the electrostatic and steric-hindrance (ES) model from the steric-hindrance pore (SHP) model and the Teorell-Meyer-Sievers (TMS) model (Wang et al., J. Chem. Eng. Japan, 28 (1995) 372) to predict the transport performance of charged solutes through NF membranes based on their charged pore structure. In this article, by doing the permeation experiments of aqueous solutions of neutral solutes and sodium chloride, the structural parameters (the pore radius and the ratio of membrane porosity to membrane thickness) and the charge density of NF membranes (Desal-S, NF-40, NTR7450 and G-20) were estimated on the basis of SHP model and the TMS model, respectively. Then, we selected an aqueous solution of different tracer charged solutes (sodium benzenesulfonate, sodium naphthalenesulfonate and sodium tetraphenyl-borate) and a supporting salt (sodium chloride) to verify the ES model. The prediction based on the ES model was in good agreement with the experimental results.     

纳滤膜盐水溶液软化过程中膜面动态结垢机理研究进展

膜面结垢是纳滤(NF)膜盐水溶液软化过程中遇到的最主要问题之一。尽管已有大量的研究者对NF膜面结垢趋势预测和膜面污染物形貌的先进科学表征进行了深入广泛的研究,但对NF膜面动态结垢机制和过程还没有系统的报道。本文详细描述了包括膜阻力、浓差极化阻力、滤饼层阻力和膜孔堵塞阻力在内的NF膜结垢阻力理论模型;综述了包括膜面浓差极化、构晶离子成核和膜面结晶沉淀的NF膜面动态结垢过程的研究进展,重点阐述了表面结晶和主体结晶两种NF膜面结晶生长机制的研究概况,并展望了NF膜面结垢机理的研究前景。