Charged ultrafiltration membranes of polyacrylonitrile covalently binding amphiphilic quaternary ammonium group: effect of aliphatic hydrophobic groups on the filtration properties

Amphiphilic monomers of chloromethylstyrene derivative were synthesized and then copolymerized with acrylonitrile for the preparation of positively charged ultrafiltration membranes. Four types of the polyacrylonitrile charged membranes having quaternary ammonium group with trimethyl, dimethylbutyl, dimethyloctyl and dimethylstearyl groups were prepared by the phase-inversion method. The ultrafiltration properties of the charged membranes were measured by using dextran molecular probes at various NaCl concentrations. Then, the filtration behavior was compared in these charged membranes. For membranes with trimethyl and dimethylbutyl groups on the quaternary ammonium salt, the values of the molecular weight cutoff and the permeation rate of the solute solution increased when the salt concentration increased. However, for membranes having amphiphilic quaternary ammonium groups with octyl and stearyl aliphatic chains, the filtration properties did not change with the salt concentration. We concluded that a compact conformation of the amphiphilic polyionic segments in the membrane causes stable filtration properties.     

Highly hydrophobic microporous low‐density polyethylene hollow fiber membranes by melt‐extrusion coupled with salt‐leaching technique

Microporous and highly hydrophobic low‐density polyethylene (LDPE) hollow fiber membranes were successfully prepared via a solvent‐free method, combining melt‐extrusion, and salt‐leaching techniques. NaCl particles with particle size of 5–10 µm were mixed with LDPE pellets to produce a blend of 35, 40, 50, 60, 65 and 68 wt% of salt. A microporous structure was produced by leaching the salt particles from the hollow fiber matrix via immersion in water at 60°C. The fabricated membranes were then characterized in terms of morphology, porosity and pore size distribution, surface roughness, and hydrophobicity, as well as mechanical properties. The remarkable increase in the water contact angles from 98° for LDPE hollow fibers fabricated without the addition of salt (blank sample) to 130° for membranes fabricated with initial salt content of 68 wt% is mainly attributed to the rough surface structure, comprising a large number of micropapillas produced by removing the imbedded salt crystals. The increase in surface roughness and porosity of hollow fiber membranes with increasing initial salt content was confirmed by scanning electron microscope and atomic force microscopy. Copyright © 2013 John Wiley & Sons, Ltd.     

苯基修饰的疏水微孔二氧化硅膜的制备与表征

采用苯基三乙氧基硅烷(PTES)和正硅酸乙酯(TEOS)作为前驱体,通过溶胶-凝胶法制备了苯基修饰的SiO2膜材料。利用扫描电镜、N2吸附、视频光学接触角测量仪、热重分析、红外光谱等测试手段对膜的孔结构以及疏水性能进行了表征,最后还研究了修饰后膜材料在室温条件下的单组份气体渗透和分离性能。结果表明,随着PTES加入量的增大,膜材料的疏水性逐渐增强,当PTES/TEOS和H2O/TEOS的化学计量比分别达到0.6和9.6时,膜材料对水的接触角达到115±0.5°,仍保持良好的微孔结构,其孔体积为0.17cm3/g,孔径为0.4-0.5nm。室温下氢气在修饰后SiO2膜的输运既遵循发生在微孔孔道的表面扩散机理也遵循发生在较大孔道或者微缺陷的努森扩散机理,膜材料的H2渗透率达到1.49×10-6mol?m-2?Pa-1?s-1,H2/CO2 和H2/SF6的理想分离系数分别达到4.64和365.59     

PVA/PVP共混交联膜的渗透蒸发分离性质(Ⅰ)

研究了4,4'-双叠氮芪-2,2'-二磺酸钠和戊二醛对聚乙烯吡咯烷酮(PVP)、聚乙烯醇(PVA)共混膜的交联及交联对共混膜分离恒沸点附近的乙醇/水混合物的影响.结果表明,膜的分离性质随着膜中PVP含量的增加而改变;采用混合型交联剂对PVA/PVP共混膜交联能明显改善膜的选择性.     

Isolation of lysozyme from hen egg albumen using glass fiber-based cation-exchange membranes

In this study, porous glass fiber membranes were coated with monophenyl trimethoxysilane (MPh) and then sulphonated by chlorosulphonic acid to prepare the cation-exchange membranes with sulphonic acid groups. Different MPh-coating times were tested and the properties of the resulting membranes such as contact angle, FTIR spectrum, conductivity, and ion-exchange capacity were measured. It was found that the optimal MPh-coating time was 60 min and the related ion-exchange capacity was 49.5 μequiv./disc. The modified membrane under the optimal MPh-coating condition was adopted for lysozyme isolation. The results were compared with those for the commercial cation-exchange membrane with sulphonic acid groups (ICE 450 unsupported membrane). Although the prepared membrane exhibited less adsorption capacity than ICE 450 unsupported membrane in the batch lysozyme adsorption experiment, it showed lower non-specific binding ratio under higher salt concentration. In the flow process isolating lysozyme from hen egg albumen, the purification effectiveness obtained using the prepared cation-exchange membrane was superior to the ICE 450 unsupported membrane.     

直径大于2nm的(15, 15)碳纳米管的仿生生物改性及其脱盐行为的分子模拟

模仿水通道蛋白结构在直径大于2 nm的(15, 15)的碳纳米管内壁添加不同数量的―NH₃⁺和―COO^-,并结合端口改性建立连续的碳纳米管膜模型,利用分子动力学模拟方法研究了水以及Na⁺和Cl^-在碳纳米管中的通量、密度分布和离子进入碳纳米管的平均力势。结果表明,在200 MPa压力下,对碳纳米管进行内壁和端口改性可以在保持较高水通量基础上显著提高碳纳米管的截盐作用。当在(15, 15)碳纳米管内壁添加5对―COO^-和―NH₃⁺基团或内壁添加4对―COO^-和―NH₃⁺且端口添加1对时, Cl^-截盐率可达到100%, Na⁺的截盐率达到88%。改性(15, 15)碳纳米管的最小水通量仍是未改性(8, 8)碳纳米管的4.6倍。     

Modified cellulose acetate flat membranes for desalination

In this article, the radiation grafting of acrylamide on to cellulose acetate flat membranes using UV-irradiation on the initiator is described. The modified membranes thus obtained have been characterized by IR, DSC, and TGA. Their transport properties have been studied. The modified membranes exhibit higher salt rejection with slightly reduced water flux as compared with cellulose acetate membrane. The work is further extended to study the thermal stability of these modified membranes in a dry state. These modified membranes up to 330°C are stable.     

Effect of silane coupling agents on the performance of RO membranes

This study investigates the effect of silane coupling agents on the performance of reverse osmosis (RO) membranes on the basis of sol–gel coating method. The surfaces of the RO membranes were chemically modified with four different alkoxysilanes in order to reduce their hydrophilicity. The objective of this study is to superpose hydrophobic polysiloxane layer on the surface of a polyamide TFC RO membrane and to increase the extent of salt rejection by the modified membranes. A commercial composite RO membrane (SWC1) was treated with silane coupling agents in ethanol at three different concentrations: 1.0, 1.5, and 2.0% (w/v). The silane coupling agents contain one alkyl or phenyl and three alkoxy groups (e.g., methyltriethoxysilane, octyltriethoxysilane, octadecyltrimethoxysilane and phenyltriethoxysilane). In addition, the effect of alkyl or phenyl group hydrophobicity on the permeability and salt rejection of the modified membrane was examined. The surfaces of the modified membranes were characterized by SEM, AFM, contact angle analyzer, and XPS in order to confirm successful sol–gel methods. The modified membranes showed significantly enhanced salt rejection without a decrease in flux. From the surface analysis results, we can observe the changes in the surface roughness, elemental composition, electron energy, and hydrophilicity.     

Structure and properties of charge-mosaic membranes from modified polyethylene. I. Preparation and characterization

Charge-mosaic membranes (CMMs) were prepared by modification of polyethylene (PE) with poly(styrene-co-divinylbenzene) or poly(vinylpyridine-co-divinylbenzene) and by selective insertion of cation and anion exchange groups in these copolymers. Changes of divinylbenzene content in the monomer mixture gave rise to differences in transport properties mainly through the change in water content. The CMMs were characterized by physico-chemical properties of control membranes, i.e., they contained only one type of modified PE. Values were similar to those obtained from measurements carried out for CMMs. Diffusion coefficients determined in 0.1/0.02N NaCl solutions were in the range (1.5-–5.7) × 10^?7 cm²s^?1. These values indicate that transport of salt through these CMM's occurs by a typical mechanism for such membranes.     

Development of polyelectrolyte multilayer-coated electrospun cellulose acetate fiber mat as composite membranes

Electrostatic multilayers of chitosan (CHI)/sodium alginate (SA) and CHI/poly(styrene sulfonate) sodium salt (PSS) were alternatively coated on electrospun cellulose acetate (CA) fiber mat. Morphologies of the composite membranes were characterized by scanning electron microscopy. The morphology of the CHI/SA-coated membrane was denser than the CHI/PSS-coated one. The top layers consisted of carboxyl and sulfonic functional groups for SA and PSS layers, respectively. Amino groups of CHI were only presented in slight quantity. X-ray photoelectron spectroscopy (XPS) confirmed the deposition of the amino groups of CHI on the multilayer membrane surface. These composite membranes were characterized for its water permeability where the water flux decreased with an increase in the number of the bilayers. The water flux was in the range of 60 and 40 L m⁻² h⁻¹ for 15 and 25 bilayered membranes, respectively. The sodium chloride (NaCl) solution flux was lower than the pure water flux due to the effect of osmotic pressure, and it decreased with an increase in the NaCl concentration. The rejection of NaCl increased substantially with the number of the bilayers of the polyelectrolytes multilayers. The level of NaCl rejection from this work was in the range of 6% and 15% for 15 and 25 bilayered membranes, respectively.     

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.     

Polymeric membranes based on cellulose acetate loaded with candle soot nanoparticles for water desalination

This study is concerned with modifying cellulose acetate (CA)/polyethylene glycol (PEG) membranes prepared via phase inversion technique in the presence of carbon nanoparticles; candle soot (CS) resulting from combusted candle. CS nanoparticles were analyzed via Fourier transform infrared spectroscopy and transmission electron microscopy. The developed membranes were characterized for their surface morphology, mechanical properties as well as thermal stability. CS nanoparticles contributed in improving the salt rejection % with a slight reduction in the water flux behavior. Employing the annealed cellulose acetate/polyethylene glycol membranes loaded with candle soot nanoparticles provides an adequate approach towards water desalination implementations.     

Transport properties of Nafion membranes modified with tetrapropylammonium ions for direct methanol fuel cell application

This work presents a study of transport properties (proton conductivity, methanol permeability, and water uptake) and acid-base properties of commercial Nafion-112, -115, and -117 membranes modified with tetrapropylammonium (TPA) cations. In the interaction between TPA hydroxide and protons of sulfonate groups in the Nafion matrix, some of the protons are shown to be bound to sulfonate groups and do not participate in transport processes. These findings are confirmed by IR spectroscopy, acid-base titration, and data on proton conductivity of the modified membranes. Proton conductivity of the modified membranes is shown to be effectively described by a percolation model with parameters that agree with published data for commercial Nafion membranes. Based on these results, a model is proposed for the interaction of TPA cations with the sulfonate groups in Nafion membranes. According to this model, TPA cations form hydrophobic clusters in hydrophilic regions of the polymer matrix, thus preventing some of the protonated sulfonate groups from participating in transport processes.     

Novel thin film nanocomposite membranes incorporated with polyoxovanadate nanocluster for high water flux and antibacterial properties

Using interfacial polymerization (IP) of m-phenylenediamine aqueous solution containing polyoxovanadate nanoclusters (POV) and trimesoyl chloride (TMC) in organic solution, we fabricated a novel polyamide (PA)- polyoxovanadate nanocluster (POV) nanocomposite membranes (PA-POV TFN). The chemical structures and morphologies of the synthesized membranes were characterized by Fourier transform infrared (FTIR) spectroscopy, atomic force microscope (AFM), scanning electron microscopy (SEM) and water contact angle measurements. Experimental results showed that the performances of PA-POV TFN membranes are remarkably dependent on POV incorporation in the membranes, which could be controlled by using different amounts of POV particles. Moreover, the PA-POV TFN membranes illustrated outstanding antibacterial properties against Gram-negative E. coli. On the other hand, the incorporation of various amounts of POV in the membranes improved the membrane separation performances (water flux and salt rejection) as well as the antibacterial activity in FO process as compared to the original thin-film composite (TFC) polyamide membrane.     

Performance enhancement of thin‐film composite membranes in water desalination process by wood sawdust

In this study, polysulfone/wood sawdust (PSf/WSD) mixed matrix membrane (MMM) was prepared as a novel substrate layer of thin‐film composite (TFC) membrane in water desalination. The main aim was to evaluate how different amounts of WSD (0‐5 wt%) and PSf concentrations (12‐16 wt%) in the porous substrate affect the properties of the final TFC membranes in the separation of organic and inorganic compounds. Morphological and wettability studies demonstrated that the addition of small amount of WSD (less than or equal to 1 wt%) in the casting solution resulted in more porous but similar hydrophobic substrates, while high loading (greater than or equal to 2 wt%) of WSD not only changed the substrate wettability and morphology but also increased and decreased the swelling and mechanical properties of substrate layer. Therefore, PA layer formed thereon displayed extensively varying film morphology, interfacial properties, and separation performance. Based on approximately stable permeate flux (ASPF) and apparent salt rejection efficiency (ASRE), the best TFC membrane was prepared over the substrate with 12 to 14 wt% of PSf and around 0.5 to 1 wt% of WSD. Although notable improvements in permeate flux were obtained by adding a small amount of sawdust, the results clearly indicate that the salt rejection mechanism of TFC membrane was different from the glycerin rejection mechanism. Furthermore, durability results of TFC membranes showed that in continuous operation for 30 days, TFC‐14/0.5 and TFC‐14/01 have the maximum plateau levels of stable permeate flux and salt rejection among the all TFC membranes.     

Preparation of Hydrophilic UHMWPE Hollow Fiber Membranes by Chemically Bounding Silica Nanoparticles

In this work, ultra-high molecular weight polyethylene (UHMWPE) microfiltration hollow fiber membranes prepared via the thermally induced phase separation (TIPS) method were modified by chemically bounding hydrophilic silica (SiO_2) nanoparticles onto the surface to improve anti-fouling performance. A range of testing techniques including attenuated total reflection Flourier transformed infrared spectroscopy(ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), water contact angle, mechanical test,filtration and anti-fouling performance were carried out to discuss the influence of different modification conditions on the properties of the membranes. The prepared hollow fiber membranes display the significantly excellent performance when the vinyl trimethoxy silane (VTMS) concentration was 13%, the pH value of the hydrolyzate was 4 and the hydrolysis reaction time was 6 h. In particular, the hydrophilicity of modified membranes was improved effectively, resulting in the enhancement of membrane anti-fouling properties. The results of this work can be consulted for improving the anti-fouling performance of the UHMWPE microfiltration hollow fiber membrane applied in the field of water purification.     

Pervaporation separation of ethanol/water mixtures with chlorosilane modified silicalite-1/PDMS hybrid membranes

<正>Ultra-fine silicalite-1 particles were modified with four kinds of chlorosilanes(dodecyltrichlorosilane, octyltrichlorosilane,hexadecyltrichlorosilane and octadecyltrichlorosilane) and characterized by FI-IR,TGA,contact angle measurements and BET analysis.It was found that the surface hydrophobicity of silicalite-1 particles was improved significantly as the alkyl group was strongly bonded to the particle surface.Modified silicalite-1 particles were incorporated into PDMS(poly(dimethylsiloxanediol)) membranes,which were applied for the pervaporation separation of ethanol/water mixtures.The effect of surface properties,zeolite loading and operation conditions on pervaporation performance of the membranes was investigated.The separation factor of PDMS membranes filled with modified silicalite-1 increased considerably compared with that filled with unmodified ones,and the total flux decreased with increasing zeolite loading. The solution and diffusion selectivity of hybrid membranes were also measured to explain the pervaporation properties of silicalite-1 filled PDMS membranes.It was found that modification of silicalite-1 with dodecyltrichlorosilane effectively improved the solution and diffusion selectivity of silicalite-1 filled PDMS membranes with high zeolite loading.This may be attributed to the high surface hydrophobicity of modified silicalite-1 and its good integration with PDMS membranes.Both the high separation factor and solution selectivity indicated that modification of silicalite-1 with chlorosilanes was an effective method to improve the selectivity of silicalite-1/PDMS hybrid membranes for ethanol.     

Surface modification of polyethersulfone membranes by blending triblock copolymers of methoxyl poly(ethylene glycol)-polyurethane-methoxyl poly(ethylene glycol)

The surface of polyethersulfone (PES) membrane was modified by blending triblock copolymers of methoxyl poly(ethylene glycol)-polyurethane-methoxyl poly(ethylene glycol) (mPEG-PU-mPEG), which were synthesized through solution polymerization with mPEG Mns of 500 and 2000, respectively. The PES and PES/mPEG-PU-mPEG blended membranes were prepared through spin coating coupled with liquid-liquid phase separation. FTIR and (1)H NMR analysis confirmed that the triblock copolymers were successfully synthesized. The functional groups and morphologies of the membranes were studied by ATR-FTIR and SEM, respectively. It was found that the triblock copolymers were blended into PES membranes successfully, and the morphologies of the blended membranes were somewhat different from PES membrane. The water contact angles and platelet adhesion were decreased after blending mPEG-PU-mPEG into PES membranes. Meanwhile, the activated partial thromboplastin time (APTT) for the blended membranes increased. The anti-protein-fouling property and permeation property of the blended membranes improved obviously. SEM observation and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay proved the surfaces of the blended membranes promoted human hepatocytes adhesion and proliferation better than PES membrane.     

聚多巴胺/聚乙烯亚胺共沉积中间层增强薄膜复合正渗透膜性能

以聚多巴胺/聚乙烯亚胺(PDA/PEI)共沉积于三醋酸纤维素(CTA)多孔支撑膜表面形成中间层,再结合界面聚合法获得聚酰胺薄膜,构建了PDA/PEI共沉积中间层改性薄膜复合(TFC)正渗透(FO)膜.通过傅里叶变换衰减全反射红外光谱法、扫描电子显微镜、原子力显微镜、溶质截留法、水接触角仪等研究了PDA/PEI共沉积中间层对CTA膜和TFC膜的表面结构和性质的影响.研究结果表明,PDA/PEI共沉积使得CTA膜表面变得更为平滑,表面孔径减小至(30.0±4.1) nm,且表面孔径分布趋于均一.同时,在PDA/PEI共沉积改性CTA膜表面界面聚合得到的聚酰胺层呈现出更均匀的叶片状结构和优异的亲水性.基于此,具有PDA/PEI共沉积中间层的TFC正渗透膜显著提高了水通量(FO模式:(7.1±2.3) L/(m^2·h)),较空白TFC膜提升了57.6%.同时,中间层改性TFC膜具有更低的反向盐通量(FO模式:1.4±0.1 g/(m^2·h))和"净盐通量"(FO模式:(0.2±0.06) g/L),与空白TFC膜相比分别下降了83.9%和90.6%.说明PDA/PEI共沉积中间层不仅能有效提升TFC正渗透膜的水渗透性,而且大幅提升了膜的截盐性和渗透选择性.     

Surface modification of microporous polypropylene membranes by the grafting of poly(γ-stearyl-l-glutamate)

A polypeptide, poly(γ-stearyl-l-glutamate) (PSLG), was grafted on the surface of hydrophobic polypropylene hollow fiber membranes through the ring opening polymerization of N-carboxyanhydride (NCA) of γ-stearyl-l-glutamate initiated by amino groups which was generated by ammonia plasma. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), together with water contact angle and bovium serum albumin adsorption measurements were used to characterize the modified membrane surface. The XPS and FT-IR spectra demonstrated that polypeptide was actually grafted on the membrane surface despite of the low degree of graft polymerization due to the hydroxyl groups on the membrane surface. To subject the ammonia plasma-treated membrane with γ-(aminopropyl)triethanoxysilane (γ-APS) which can react with hydroxyl groups and leave amino groups, the degree of graft polymerization could be improved. The bovium serum albumin adsorption measurement was conducted to further examine the surface properties of modified and original membranes. Potential applications of the PSLG grafted membranes are expected for enantiomer separation and/or enzyme immobilization.