Chiral separation of phenylalanine in ultrafiltration through DNA-immobilized chitosan membranes

Ultrafiltration experiments for the chiral separation of racemic phenylalanine were performed with DNA-immobilized chitosan membranes having various pore sizes. Atomic analysis on the membranes showed that the chitosan membranes covalently bound six times more DNA than the cellulose membranes used in our previous study [A. Higuchi, Y. Higuchi, K. Furuta, B.O. Yoon, M. Hara, S. Maniwa, M. Saitoh, K. Sanui, Chiral separation of phenylalanine by ultrafiltration through immobilized DNA membranes, J. Membr. Sci. 221 (2003) 207–218]. d-Phenylalanine preferentially permeated through DNA-immobilized chitosan membranes with a pore size <6.4 nm [molecular weight cut-off (MWCO) <67,000]. The binding affinity of a specific enantiomer due to the pore size of the DNA-immobilized membranes regulated the preferential permeation of the enantiomer through the membranes. l-Phenylalanine was adsorbed on the DNA-immobilized chitosan membranes with a pore size <6.4 nm (MWCO < 67,000), while there was little difference between the adsorption of d-phenylalanine and l-phenylalanine on the membranes with a pore size >6.4 nm (MWCO > 67,000). The DNA-immobilized chitosan membranes were categorized as channel type membranes.     

Potentiometric ion- and bio-selective electrodes based on asymmetric cellulose acetate membranes

The potentiometric response properties of ammonium-, carbonate-, and proton-selective electrodes prepared by incorporating appropriate neutral carriers within novel asymmetric cellulose acetate membranes are reported. The membranes are formed by first casting a thin layer of cellulose triacetate without carrier, hydrolyzing one side of this film with base, and then on the other side casting a second layer of cellulose triacetate containing the membrane active components. The resulting asymmetric ion-selective membranes function equivalently, in terms of selectivity and response slopes, to non-asymmetric cellulose triacetate membranes and conventional poly(vinyl chloride)-based membranes. The hydrolyzed surface of the asymmetric membranes can be activated in aqueous solution with carbonyldiimidazole for the direct immobilization of proteins on the surface of the membranes, without loss in potentiometric ion-response. As an example, the immobilization of urease on the surfaces of ammonium- and carbonate-selective membranes yields potentiometric bio-selective urea-probes with desirable dynamic response properties.     

SELECTIVE SEPARATION OF WATER-ETHANOL MIXTURES THROUGH COPOLYMERIC MEMBRANES: Ⅰ. ACRYLIC ACID AND ACRYLONITRILE COPOLYMER AND ITS IONIZED MEMBRANES

The copolymer of acrylic acid and acrylonitrile has been synthesized and pervaporation properties of the copolymeric membranes have been investigated. In order to elucidate the influence of membrane-permeate interaction on the pervaporation of water-ethanol mixtures and to prepare much improved membranes, the membranes have been treated with alkali metal, alkali earth metal and transition metal salt aqueous solutions. The treated membranes (ionized membranes) exhibited higher separation factors than the untreated membranes. The separation factors of various alkali metal cation membranes decreased in the following order : Li~+>Na~+>K~+, and the permeation rates showed an opposite tendency. The dependence of pervaporation behavior on the copolymer composition ,feed concentration and operating temperature have been studied with both ionized and non-ionized membranes. The apparent activation energies of water and ethanol permeation were calculated.     

A review on the latest development of carbon membranes for gas separation

Inorganic membranes have been developed before 1945. The earlier application of inorganic membranes was primarily concentrate on military purpose. Carbon membrane is one type of porous inorganic membrane. Although the concept of carbon membrane for gas separation has been found in the early 1970, the interest to develop carbon membrane only increased, since Koresh and Soffer successfully prepared apparently crack-free molecular sieving hollow fiber carbon membranes. Nowadays, plenty of researchers have used different polymeric materials; including polyimides, to prepare carbon membranes by using pyrolysis. In general, carbon membranes can be divided into four major configurations: flat sheet, membrane supported on tube, capillary, and hollow fiber. Permeation properties of carbon membranes have been improved greatly in these 20 years. Carbon membranes offer advantages over polymeric membranes especially in terms of selectivity as well as thermal and chemical stability. More attention will be paid to carbon membranes in this century. This paper will review the development of carbon membranes in the last 30 years and give a clear future direction in research for carbon membrane.     

Transport properties of highly ordered heterogeneous ion-exchange membranes

Model "ordered" heterogeneous ion exchange membranes are made with ion exchange particles heaving ion exchange capacity in the range 3 to 2.5 meq/gr (dry basis) and diameters ranging from 37 to 7 microm and 2 component room-temperature vulcanizing silicon rubber as a polymeric matrix, by applying an electric field normal to the membrane surface during preparation. These membranes were shown to have an improved ionic conductivity compared with "nonordered" membranes based on the same ion exchange content (for instance, at 10% resin content "nonordered" membranes show <10(-5) mS/cm while "ordered" membranes have conductivity of 1 mS/cm). The transport properties of ordered membranes were compared with those of nonordered membranes, through the current-voltage characteristics. Limiting currents measured for the ordered membranes were significantly higher than those of the nonordered membranes with the same resin concentration. In addition, higher limiting currents were observed in ordered membranes as the resin particles became smaller. Energy dispersion spectrometry analyses revealed that the concentration of cation exchange groups on the membrane surface was higher for ordered membrane as compared to that of nonordered membranes. This implies that the local current density for the conducting domains at the surface of the nonordered membranes is higher, leading to higher concentration polarization and, eventually, to lower average limiting current densities. The effect of ordering the particles on the membrane conductivity and transport properties was studied, and the advantages of the ordered membranes are discussed.     

可调制润湿性和力学性能的电纺纤维膜的制备与性能研究

采用静电纺丝技术分别制备了无规排列和高度取向排列的聚对苯二甲酸乙二醇酯(PET)和PET/CA(柠檬酸)4种纤维膜,对它们的润湿性能和力学性能进行了研究,同时研究了纤维膜厚度对膜的力学性能的影响.研究结果表明,与无规排列的PET纤维膜相比,取向排列的PET纤维膜沿纤维取向方向的力学性能有了很大的提高,而断裂伸长率略有下降;加入柠檬酸(CA)后,PET/CA复合纤维膜的表面水接触角从132.3!减少到0!,且取向排列的纤维膜比无规排列的纤维膜更易润湿;无规排列的复合纤维膜的力学性能因加入CA而大幅下降,取向排列的PET/CA纤维膜沿纤维取向方向的力学性能下降较小,而无规排列的PET/CA纤维膜的断裂伸长率从284.1%增加到444.5%.无规排列纤维膜的力学性能随膜厚度的增加先提高,后来又下降,而取向排列的纤维膜沿纤维取向方向的力学性能随膜厚度增加而单调增加.     

甲壳胺─聚氨酯复合膜的界面粘合研究

测定了甲壳胺─聚氨酯复合膜的静态和动态力学性能，并根据两单组分膜和复合膜的应力－应变行为判断复合膜界面粘合的牢固性。讨论了聚氨酯多孔膜与甲壳胺膜，以及聚氨酯预聚体与甲壳胺膜的粘合机理，并从动态力学性能的测试结果得以证实。     

Covalent attachment of phospholipid analogous polymers to modify a polymeric membrane surface: a novel approach

A novel method for the surface modification of a microporous polypropylene membrane by tethering phospholipid analogous polymers (PAPs) is given, which includes the photoinduced graft polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) and the ring-opening reaction of grafted poly-(DMAEMA) with 2-alkyloxy-2-oxo-1,3,2-dioxaphospholanes. Five 2-alkyloxy-2-oxo-1,3,2-dioxaphospholanes, containing octyloxy, dodecyloxy, tetradecyloxy, hexadecyloxy, and octadecyloxy groups in the molecular structure, were used to fabricate the PAP-modified polypropylene membranes. The attenuated total reflectance FT-IR spectra of the original, poly(DMAEMA)-grafted, and PAP-modified membranes confirmed the chemical changes on the membrane surface. Scanning electron microscope pictures showed that, compared with the original membrane, the surface porosities ofpoly(DMAEMA)-grafted and PAP-modified membranes were somewhat reduced. Water contact angles measured by the sessile drop method on PAP-modified membranes were slightly lower than that on the original polypropylene membrane, but higher than those on poly(DMAEMA)-grafted membranes with the exception of octyloxy-containing PAP-modified membranes. However, BSA adsorption experiments indicated that the five PAP-modified membranes had a much better protein-resistant property than the original polypropylene membrane and the poly(DMAEMA)-grafted membranes. For hexadecyloxy- and octadecyloxy-containing PAP-modified membranes, almost no protein adsorption was observed when the grafting degree was above 6 wt %. It was also found that the platelet adhesion was remarkably suppressed on the PAP-modified membranes. All these results demonstrate that the described approach is an effective way to improve the surface biocompatibility for polymeric membranes.     

Spray-coated and solution-cast ethylcellulose pseudolatex membranes

Membranes of dibutyl sebacate (DBS) plasticized ethylcellulose pseudolatex were prepared by spray-coating and solution-casting methods for the studies of their transport and mechanical properties. The structure of sprayed membranes was more porous than that of cast membranes, so the sprayed membranes were more permeable than the cast membranes. The permeabilities of drug or water vapor through sprayed membranes decreased with increasing plasticizer concentration; on the contrary, those through cast membranes increased with increasing plasticizer concentration. The diffusion through pores accounts for the transport through sprayed membranes, while the solution–diffusion through plasticized polymer phase may become an important role for that through the cast membranes. Mechanically, the sprayed membranes were harder and more brittle than the cast membranes of similar formulation, but membranes prepared from both methods possessed similar breaking tensile strength. The tensile strength and Young's modulus were reduced and the elongation was improved with increasing plasticizer concentration for both kinds of membranes. The sprayed membranes would become less permeable and tougher after the post thermal treatment as the degree of coalescence between the latex particles in the membranes was enhanced.     

Heterogeneous ion-exchange membranes

The field of heterogeneous ion exchange membranes is reviewed briefly. Specific advantages and disadvantages of heterogeneous ion exchange membranes are discussed compared with those of homogeneous ion exchange membranes. p]The development of heterogeneous ion exchange membranes is presented in historical perspective. The electrochemistry of ion-selective membranes began with Ostwald in 1890. After the classical work of Michaelis (1925) with collodion membranes, the first fully synthetic ion exchange membranes were prepared by Zhukov (1933) and Wassenegger (1940), based on sulfonated phenol—formaldehyde resins. These initial membranes, which were of the homogeneous type found no practical uses. The era of commercially useful ion exchange membranes began with the work of Wyllie (1948), Juda (1950), Bodamer (1953) and their collaborators who prepared heterogeneous ion exchange membranes by embedding ion exchange particles into polymer matrices. p]Methods for making heterogeneous ion exchange membranes include compression-molding of polymer powders, compounding on hot rolls, latex or solvent blending in situ generation of either the matrix or the ion exchange material. Microheterogeneous ion exchange membranes can be made from block and graft copolymers, interpolymers snake-cage resins, similar techniques and materials. p]Even though the first commercial ion exchange membranes were heterogeneous, the interest in this type of membranes subsided later. As polymer science progressed, speciality monomers and polymers were being made which opened the way to the preparation of quite sophisticated homogeneous ion exchange membranes of satisfactory mechanical strength. However, the possibilities of heterogeneous ion exchange membranes are by no means exhausted and this field may warrant further exploration, applying modern methods and materials and thus progressing beyond the relatively crude heterogeneous ion exchange membranes of the pioneer times.     

Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

Chitosan membrane: tool for chromium (III) recovery from aqueous solutions

In this study four kinds of Chitosan membranes were prepared. The permeability of the membranes was then investigated by permeation of K+ in these membranes. The performances of the prepared membranes for recovery of chromium (III) from aqueous solution were evaluated. The effects of operation conditions on permeation characteristics were determined, and permeation mechanism was discussed. The stability of the membranes was also studied.     

有机-无机杂化分离膜研究进展

有机-无机杂化膜材料结合了有机膜材料和无机膜材料的优良性能,已成为分离膜材料研究的一个热点。本文以有机、无机组分间相互作用类型对其进行分类,着重介绍组分间以化学键相结合的有机-无机杂化膜的优良特性,总结了影响此类杂化膜结构和性能的主要因素,概括了它在膜分离中的应用,提出了目前研究工作中存在的不足,并做出了简要的述评。     

Preparation and characterization of cross-linked Matrimid membranes for CO2/CH4 separation

For preventing plasticization phenomenon, cross-linked Matrimid membranes were prepared. Matrimid membranes were immersed in a solution of 10% (w/v) ethylenediamine or hexamethylenediamine in methanol for preparation of cross-linked membranes. Using a gas separation membrane unit, permeability properties of pristine and modified membranes for pure gases (CO₂ and CH₄) were investigated. CO₂ plasticization effect on permeability properties of the membranes is discussed. Modified membranes indicated smaller values of tensile strength than pristine membranes. Thermal gravimetric analysis showed that thermal resistance of modified membranes increased in a limited temperature range. In general, modified membranes were thermally stable for separation applications. Formation of amide groups in modified membranes was investigated by Fourier transform infrared spectroscopy analysis.     

MICROPOROUS INORGANIC MEMBRANES

Recent development in microporous inorganic membranes represents a significant advance in materials for separation and chemical reaction applications. This paper provides an in-depth review of synthesis and properties of two groups (amorphous and crystalline) of microporous inorganic membranes. Amorphous microporous silica membranes can be prepared by the sol-gel and phase separation methods. Flat sheet, tubular and hollow fiber amorphous carbon membranes have been fabricated by various pyrolysis methods from polymer precursors. A large number of synthesis methods have been developed to prepare good quality polycrystalline zeolite membranes. Several techniques, including vapor and liquid approaches, are reviewed for pore structure modification to prepare microporous inorganic membranes from mesoporous inorganic membranes. Chemical, microstructural and permeation properties of these microporous membranes are summarized and compared among the several microporous membranes discussed in this paper. Theory for gas permeation through microporous membranes is also reviewed, with emphasis on comparison of theoretical with the experimental data. These inorganic microporous membranes offer excellent separation properties by the mechanisms of preferential adsorption, selective configurational diffusion or molecular sieving.     

Polypyrrole modified solvent resistant nanofiltration membranes

New solvent resistant nanofiltration (SRNF) membranes with polypyrrole (PPy) modified toplayer were prepared on different types support by in situ pyrrole polymerization. The morphology of the membranes was studied by SEM. The PPy modified membranes were applied in the filtration of organic solvents. All the PPy modified membranes showed a very high retention of the negatively charged RB in different solvent systems, comparable to those of the MPF-50 and STARMEM 122 commercial membranes, but at much higher flux. The extended filtration experiment in strong aprotic DMF of PPy modified membranes showed a clearly stable permeability and retention over 30 h. In addition, the PPy modified membranes showed a much higher flux in THF systems than for earlier reported crosslinked poly(imide) membranes.     

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.     

Multiplexed quantification of proteins adsorbed to surface-modified and non-modified microdialysis membranes

A simple and straightforward method for discovery and quantification of proteins adsorbed onto delicate and sensitive membrane surfaces is presented. The adsorbed proteins were enzymatically cleaved while still adsorbed onto the membranes using an on-surface enzymatic digestion (oSED). This was followed by isobaric tagging, nanoliquid chromatography, and tandem mass spectrometry. Protein adsorption on tri-block copolymer Poloxamer 407 surface-modified microdialysis (MD) membranes were compared with protein adsorption on unmodified MD membranes. Ventricular cerebrospinal fluid (vCSF) kept at 37 °C was used as sample matrix. In total, 19 proteins were quantified in two biological replicates. The surface-modified membranes adsorbed 33% less proteins than control membranes and the most abundant proteins were subunits of hemoglobin and clusterin. The adsorption of clusterin on the modified membranes was on average 36% compared to control membranes. The most common protein in vCSF, Albumin, was not identified adsorbed to the surface at all. It was also experimentally verified that oSED, in conjunction with tandem mass spectrometry can be used to quantify femtomole amounts of proteins adsorbed on limited and delicate surfaces, such as MD membranes. The method has great potential and can be used to study much more complex protein adsorption systems than previously reported.     

Applied potential and radiotracer studies on poly(vinyl chloride) matrix ion-selective electrode membranes

This paper reports the effect of applied potentials on PVC matrix membranes containing (i) the barium ion-sensitive barium-Antarox C0880 complex and 2-nitrophenyl phenyl ether solvent mediator, and (ii) the calcium ion-sensitive Orion 92-20-02 phosphate-based calcium liquid ion-exchanger. Platinum electrodes were placed in solutions on each side of the membranes. The barium ion-sensitive membranes are unable to maintain stable current flows but the calcium ion-sensitive membranes are characterized by stable current flows over prolonged periods even after successive polarity reversals. Results are presented, from radiotracer experiments for permeation of ions through the membranes with and without an applied potential. No evidence was found for significant permeation of barium-133 ions through the barium ion-sensing membranes into an initially inactive solution, but it was found that barium-133 ions were incorporated into the membranes after removal of the applied potential. Permeation of sodium-22 ions through the calcium ion-sensing membranes occurred only to a limited extent in the presence of an applied potential and not at all in its absence, confirming electrode selectivity trends for calcium and sodium. Calcium-45 ions did not permeate the calcium ion-sensing membranes into an inactive counter-solution against the potential gradient, but on reversal of the polarity, permeation occurred to a far greater extent than in the absence of an applied potential. These differences in behaviour are compatible with the more complicated membrane pathways of the barium ion-sensing membranes, imposed by the complexing of barium ions by the ethyleneoxy units of Antarox C0880 in a tight helical conformation. The calcium ion-sensing membranes are much less constrained, thus permitting more facile replacement of the calcium ions in the membrane by ions from solution.     

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。