Synthesis and characterization of uniform alumina-mesoporous silica hybrid membranes

The synthesis and characterization of alumina-mesoporous silica (alumina-MS) hybrid membranes are reported. The hybrids are formed using a variation of the evaporative-induced self-assembly (EISA) process reported by Hayward et al. (Langmuir 2004, 20, 5998) based on dip coating of an Anopore 200 nm membrane with a Brij-56/TEOS/HCl/H2O solution. Numerous analytical methods are used to probe both the hybrid material and the silica phase after dissolution of the Anopore substrate. Most importantly, He/N2 permeation measurements show that the effective pore size of the membrane can be tuned from 20 to 5 nm based on the number of dip-coating cycles used. The observed He/N2 permselectivity of 2.7 +/- 0.11 is nearly identical to the theoretical value obtained (2.65) assuming Knudsen diffusion dominates. The selectivity of these membranes is higher than that of most commercial "5 nm" membranes (2.29), which is ascribed to the lack of pinhole defects in the materials reported here. The hybrid membranes as well as the silica obtained after dissolution of the Anopore substrate have been characterized using scanning and transmission electron microscopy and X-ray diffraction. Those results indicate that the silica deposited in the Anopore membrane possesses uniform pores approximately 5 nm in size, consistent with the permeation studies. The current work presents an alternative approach to materials that possess many of the properties of mesoporous silica thin films (i.e., pores of controlled size and topology) without the difficulty of growing mesoporous silica thin films on porous supports.     

Synthesis of ordered mesoporous silica membrane on inorganic hollow fiber

This paper reports on a new method for the preparation of mesoporous silica membranes on alumina hollow fibers. A surfactant-silica sol is filled in the lumen of an alpha-alumina hollow fiber. The filtration technique combined with an evaporation-induced self-assembly (EISA) process results in the formation of a continuous ordered mesoporous silica layer on the outer side of alpha-alumina hollow fibers. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen isothermal adsorption measurements reveal that these membranes possess hexagonal (P6mm) mesostructures with pore diameters of 4.48 nm and BET surfaces of 492.3 m(2) g(-1). Scanning electron microscopy (SEM) studies show that the layers are defect free and energy-dispersive spectroscopy (EDS) mapping images further confirm the formation of continuous mesoporous silica layer on the outer side of alpha-alumina hollow fibers. Nitrogen and hydrogen permeance tests show that the membranes are defect free.     

Anodic alumina supported dual-layer microporous silica membranes

We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk™) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 Å). Subsequently, the microporous gas separation membrane layer is deposited by spin-coating, resulting in a defect-free dual-layer micro-/mesoporous silica membrane exhibiting high permeance and high selectivity for size selective gas separations. For example, in the case of CO₂:N₂ separation, the CO₂ permeance reached 3.0 MPU (1 MPU = 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹) coupled with a CO₂:N₂ separation factor in excess of 80 at 25 °C. This processing scheme can be utilized for laboratory-scale development of other types of microporous or dense inorganic membranes, taking advantage of the availability, low cost and low permeation resistance of anodic alumina (or other metal oxide) meso- and macroporous supports.     

Fabrication and analytical applications of hybrid mesoporous membranes.

Recently, a hybrid mesoporous membrane composed of surfactant-templated mesoporous silica inside a porous anodic alumina membrane has been developed. Since this membrane allows the use of columnar silica-mesopores (silica-nanochannels) as nanofluidic channels, separation of molecules can be realized by mass transport through the silica-nanochannel with molecular dimensions. Here, we review the methods to fabricate the hybrid mesoporous membranes, their structural features, and the analytical applications of hybrid mesoporous membranes.     

Evolution of pore size distribution and average pore size of porous ceramic membranes during modification by counter-diffusion chemical vapor deposition

The modification of porous ceramic membranes by counter-diffusion chemical vapor deposition (CVD) is studied theoretically and experimentally. Numerical simulations of the evolution of the membrane permeance, average pore size and pore size distribution as a function of extent of modification are presented and compared with experimetal data. It is found that the change of the average pore size of the membranes after modification strongly depends on the initial pore size distribution of the membrane, CVD reaction kinetics and characterization method. Experimental data suggest that CVD of zirconia (and yttria) inside porous ceramic membranes by reaction of zirconium (and yttrium) chlorides with steam/air at elevated temperatures proceeds by quasi-zero reaction kinetics with respect to the oxidant, typical of non-stoichiometric supply of the reactants from opposite sides of the membrane. Under such conditions, CVD modification may result in a modest increase of the average pore size of coarse-pore ceramic membranes as suggested by numerical calculations and experimental data.     

NPE在有序介孔炭上的吸附行为研究

采用有序介孔硅为硬模板制备了具有不同孔径的有序介孔炭(OMCs). 氮气吸附测试表明, 有序介孔炭具有丰富的介孔表面和集中的介孔分布. 以壬基酚聚氧乙烯醚(NPE)为探针分子, 研究了大分子酚类在有序介孔炭上的吸附行为. 吸附研究表明, NPE在有序介孔炭上的吸附满足Langmuir吸附模型. 孔结构分析表明, 大于1.5 nm的孔的表面积是决定NPE吸附量的关键因素, 而有序介孔炭的最可几孔径决定吸附速率的大小. 与吸附量相比, 吸附速率更容易受环境温度的影响. 动力学研究表明, NPE在有序介孔炭上的吸附满足准二级动力学方程.     

Preparation of silica–alumina composite membranes for hydrogen separation by multi-step pore modifications

In the present paper, a silica–alumina composite membrane for hydrogen separation was prepared within an α-alumina support by the multi-step pore modification. The α-alumina support has an asymmetric structure composed of a thin dense skin layer and a thick coarse layer and the average pore size of its skin layer is 80 nm. The composite membrane layer was formed in the vicinity of the interphase between the two layers of the support by two consecutive steps; namely, in situ silica sol–gel reaction and soaking and vapor deposition. In order to enhance the hydrogen selectivity, palladium (Pd) particles were impregnated in the final step utilizing Pd-acetate as a Pd precursor. Although both silica and Pd induced the surface diffusion, Pd was more effective for selective hydrogen adsorption than silica. This multi-step method produced a porous membrane with moderate hydrogen selectivity and satisfactory hydrogen permeance at high temperature and at high transmembrane pressure. The separation factor of hydrogen relative to nitrogen was maintained at about 10 even when the transmembrane pressure was as high as 110 kPa, and the hydrogen permeance was still much higher than that of non-porous polymeric membranes. In addition, the microstructural distributions of Si and Pd within the intermediate membrane layer were examined by a scanning electron microscopy (SEM) and an energy dispersive X-ray analysis (EDX)     

Highly permeable mesoporous silica membranes synthesized by vapor infiltration of tetraethoxysilane into non-ionic alkyl poly(oxyethylene) surfactant films

Mesoporous silica membranes were prepared on porous alumina substrates by a vapor infiltration of tetraethoxysilane (TEOS) into a non-ionic poly(oxyethylene) (Brij56) surfactant film. Periodic mesostructured silica membranes were formed on both α- and γ-alumina substrates pre-treated with polystyrene. The polystyrene polymer plugged the pores of the alumina substrates and inhibited the deposition of silica in the alumina pores, resulting in the formation of a very thin silica membrane without a silica/alumina composite layer at the interface between mesoporous silica and the alumina substrates. The calcined mesoporous silica membrane showed very high nitrogen permeance (>10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹). The single gas permeation was governed by the Knudsen diffusion mechanism. The durability of the mesoporous silica membrane against moisture in air was improved by a silylation with trimethylethoxysiliane.     

Preparation of alpha-alumina-supported mesoporous bentonite membranes for reverse osmosis desalination of aqueous solutions

In this study, mesoporous bentonite clay membranes approximately 2 microm thick were prepared on porous alpha-alumina substrates by a sol-gel method. Nanosized clay particles were obtained from commercial Na-bentonite powders (Wyoming) by a process of sedimentation, washing, and freeze-drying. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption were employed for membrane characterization. It was found that the content of solids, concentration of polymer binder, and pH value of the clay colloidal suspension had critical influences on membrane formation during the dip-coating process. The membranes were tested for reverse osmosis separation of a 0.1 M NaCl solution. Both water permeability and Na(+) rejection rate of the supported membranes were comparable to those of the compacted thick membranes reported in the literature. However, due to the drastically reduced membrane thickness, water permeance and flux of the supported membranes were significantly higher than those of the compacted thick membranes. It was also observed that the calcination temperature played a critical role in determining structural stability in water and desalination performance of the clay membrane.     

基于裂结技术的单分子尺度化学反应研究进展

分子电子学是研究单分子器件的构筑、性质以及功能调控的一门新兴学科。其中,金属/分子/金属结的构筑和表征是现阶段分子电子学的主要研究内容。裂结技术是当前分子电子学研究的主要实验方法,主要包括机械可控裂结技术和扫描隧道显微镜裂结技术。本文对裂结技术进行了介绍,并对近年来利用这些技术,在单分子尺度化学反应的检测和动力学研究,以及将这些技术与溶液环境、静电场、电化学门控等方法相结合,调控单分子器件的电输运性质等方面所取得的进展进行了概述。     

苯及苯磺酸基官能化的中孔分子筛的合成及催化应用

近年来 ,通过对介孔分子筛 (如 MCM,HMS,MSU-X)结构及组成的化学“裁剪”,制备具有特定结构和表面性质的催化材料成为该领域的研究热点之一 [1～ 5] .许多文献报道了 MCM-4 1的有机官能化中孔材料的制备技术 [5～ 8] ,并将其应用于有机合成反应 ,取得了较好的结果 [7,8] .其中 MSU-X介孔分子筛结构具有三维排列“Worm-like”孔道特征 ,有利于物料传输 ;相对于 MCM-4 1分子筛在合成方面具有以中性表面活性剂作模板剂且模板剂容易去除等诸多优点[9] .本文采用非离子表面活性剂 C11— 15H2 3— 31(CH2 CH2 O) 9H(AEO9)为模板剂 ,…     

NPE在有序介孔炭上的吸附行为研究

采用有序介孔硅为硬模板制备了具有不同孔径的有序介孔炭(OMCs). 氮气吸附测试表明, 有序介孔炭具有丰富的介孔表面和集中的介孔分布. 以壬基酚聚氧乙烯醚(NPE)为探针分子, 研究了大分子酚类在有序介孔炭上的吸附行为. 吸附研究表明, NPE在有序介孔炭上的吸附满足Langmuir吸附模型. 孔结构分析表明, 大于1.5 nm的孔的表面积是决定NPE吸附量的关键因素, 而有序介孔炭的最可几孔径决定吸附速率的大小. 与吸附量相比, 吸附速率更容易受环境温度的影响. 动力学研究表明, NPE在有序介孔炭上的吸附满足准二级动力学方程.     

以手性两亲小分子自组装体为模板制备介孔二氧化硅空心球

合成了手性阳离子型两亲性小分子化合物,利用圆二色谱分析了其在水中形成的自组装体的结构;以该化合物的自组装体为模板,在正丙醇和氨水的混合溶剂中制备得到了介孔二氧化硅空心球;利用扫描电镜、透射电镜、X射线衍射仪以及氮气吸附-脱附试验装置分析了二氧化硅空心球的形貌及孔结构.结果表明,两亲性小分子在水中形成的自组装体呈现手性堆积;合成的介孔二氧化硅空心球的直径约为600~800nm,壁厚约为100~150nm,其孔道垂直于球的表面,孔径约为3.0nm,比表面积约为306m2·g-1.正丙醇作为模板控制二氧化硅空心球的空腔尺寸和形貌,而两亲性小分子的自组装体作为模板控制放射状孔道的形貌和尺寸.     

Facile synthesis of mesoporous silica sublayer with hierarchical pore structure on ceramic membrane using anionic polyelectrolyte

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.     

Mesoporous silica hybrid membranes for precise size-exclusive separation of silver nanoparticles

One-dimensional (1D) nanomaterials have unique applications due to their inherent physical properties. In this study, hexagonally ordered mesoporous silica hybrid anodic alumina membranes (AAM) were synthesized using template-guided synthesis with a number of nonionic n-alkyl-oligo(ethylene oxide), Brij-type (C(x)EO(y)), which are surfactants that have different molecular sizes and characteristics. The hexagonal mesoporous silicas are vertically aligned in the AAM channels with a predominantly columnar orientation. The hollow mesostructured silicas had tunable pore diameters varying from 3.7 to 5.1 nm. In this synthesis protocol, the surfactant molecular natures (corona/core features) are important for the controlled generation of ordered structures throughout AAM channels. The development of ultrafiltration membranes composed of silica mesostructures could be used effectively in separating silver nanoparticles (Ag NPs) in both aqueous and organic solution phases. This would be relevant to the production of well-defined Ag NPs with unique properties. To create a size-exclusive separation system of Ag NPs, we grafted hydrophobic trimethylsilyl (TMS) groups onto the inner pores of the mesoporous silica hybrid AAM. The immobilization of the TMS groups allowed the columnar mesoporous silica inside AAM to retain this inner pore order without distortion during the separation of solution-phase Ag NPs in organic solvents that may cause tortuous-pore membranes. Mesoporous TMS-silicas inside 1D AAM channels were applicable as a size-exclusive separation system to isolate organic solution-phase Ag NPs of uniform morphology and size.     

Preparation and characteristics of electrospun activated carbon materials having meso- and macropores

Mesoporous activated carbon samples were prepared from electrospun PAN-based carbon fibers using physical activation with silica. Textural characterization was performed using nitrogen adsorption at 77 K. The BET specific surface area and pore size distribution of silica activated carbon materials were investigated. According to the increment of silica, BET specific surface area was increased about thirty times and it was found that silica activated carbon materials were highly mesoporous by studying pore surface distribution and pore volume distribution. Surface morphology of silica activated carbon materials were observed by SEM images. The spherical typed carbon materials were investigated. The diameter of spherical typed carbon materials was increased in proportional of the increment of silica.     

ZSM-5分子筛膜的研究进展

本文分析了ZSM-5分子筛膜的主要合成方法和研究现状,总结了ZSM-5分子筛膜的缺陷与修饰方法,指出了ZSM-5分子筛膜的表征手段是以XRD、SEM、TEM和单组分气体渗透等为主,对ZSM-5分子筛膜的应用和前景进行了展望。     

Mesoporous Silica Layer: Preparation and Opportunity

Periodic mesoporous silicas, which were prepared from silica‐surfactant mesostructured materials, have been investigated for a wide range of application due to their very large surface area, high porosity, pore size uniformity and variation, periodic pore arrangement and possible pore surface modification, after the pioneering papers on the formation of mesoporous silicas (MCM‐41 and FSM‐16). Morphosyntheses from such macroscopic morphologies as bulk monolith and film to nanoscopic ones, nanoparticles and their stable suspension, make mesoporous materials more attractive for applications and detailed characterization. Mesoporous silicas have been studied initially for such applications as adsorbent and catalyst, and more recently, optical, electronic, and bio‐related applications have been investigated. This review summarizes the studies on mesoporous silica film to highlight the present status and future of the preparation, characterization and application of the mesoporous silica film.     

具有不对称孔道结构的小介孔二氧化硅粒子的合成及其高分子杂化膜的构建

利用手性阴离子酸表面活性剂, 采用软模板法制备了具有不对称孔道结构的小介孔二氧化硅(SiO₂)粒子. 将小介孔SiO₂粒子引入聚偏四氟乙烯(PVDF)和聚酰亚胺(PI)中构建了两种有机/无机杂化膜. 利用傅里叶变换红外光谱(FTIR)、 透射电子显微镜(TEM)、 扫描电子显微镜(SEM)和比表面积分析等表征了小介孔SiO₂粒子和有机/无机杂化膜的微结构, 并通过超滤实验和气体渗透实验分别考察两种杂化膜的性能. 研究结果表明, 表面含有大量亲水基团的小介孔SiO₂粒子具有规则有序排列的孔道结构, 该孔道结构呈现螺旋扭曲和不对称性. 构建的两种有机/无机杂化膜的极性显著提升, 进而有效增强了PVDF杂化膜的膜通量和抗污染性能及PI杂化膜对CO₂气体的分离性能, 克服了高分子膜的博弈效应(Trade-off效应). 另外, SiO₂的小介孔孔道还可以在PI杂化膜中引入优先通过CO₂分子的限域传质通道, 加速了CO₂气体在杂化膜中扩散. 但过多小介孔SiO₂粒子的加入导致其在高分子基质中团聚, 削弱杂化膜的极性和亲水性, 从而降低了两种杂化膜的分离性能.     

A controlled release of ibuprofen by systematically tailoring the morphology of mesoporous silica materials

A series of mesoporous silica materials with similar pore sizes, different morphologies and variable pore geometries were prepared systematically. In order to control drug release, ibuprofen was employed as a model drug and the influence of morphology and pore geometry of mesoporous silica on drug release profiles was extensively studied. The mesoporous silica and drug-loaded samples were characterized by X-ray diffraction, Fourier transform IR spectroscopy, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. It was found that the drug-loading amount was directly correlated to the Brunauer-Emmett-Teller surface area, pore geometry, and pore volume; while the drug release profiles could be controlled by tailoring the morphologies of mesoporous silica carriers.