Protein adsorption on the mesoporous molecular sieve silicate SBA-15: effects of pH and pore size

A mesoporous molecular sieve silicate, SBA-15, with three pore sizes (38.1 A, 77.3 A, and 240 A) has been synthesized using a non-ionic, tri-block copolymer as a template in a sol-gel method. The effects of synthesis conditions on the pore size and pore-size distribution of this adsorbent have been described. The adsorption of proteins on these crystalline, ordered, materials has been studied. The kinetics of adsorption and equilibrium capacity have been probed with three proteins of different dimensions. The effects of electrostatic interactions and protein size are illustrated. It has been shown that SBA-15 materials can be tailored to show size selectivity for proteins, and very high capacities (450 mg/g) can be obtained. Furthermore, the rates of adsorption are shown to be dependent on the pore size, protein structure and solution pH.     

Nanoporous silica films containing aluminum and titanium

By utilizing surfactant aggregates as supramolecular templates, mesoporous and mesostructured silicas with highly ordered structures became available. The resulting mesoporous silicas are promising candidates to host various photo- and electro-active species along with catalytically active species, due to their large and controllable pore sizes, highly ordered pore arrangements with low dimensional geometries, and reactive surfaces. We have developed the rapid solvent evaporation method, which is a modified sol-gel process, for synthesizing the mesostructured silica-surfactant films as well as the mesoporous silica films. Supported thin films, self-standing films and bubbles of mesoporous silicas have been synthesized by the rapid solvent evaporation method. The microstructures of the films have also been successfully controlled by changing the synthetic conditions. Taking advantage of the ease of synthetic operation and the transparency and homogeneity of the resulting materials, we have been interested in the introduction of functional units into the mesostructured materials. This paper reports the synthesis of transparent films of titanium- and aluminum-containing nanoporous silicas to modify the surface properties (such as adsorptive and catalytic) of nanoporous silicas. The incorporation of Al led to the formation of cation exchange or acidic sites on the mesopore surface, as revealed by the cationic dye adsorption experiments. The photocatalytic reactions of the Ti-containing nanoporous silica films were also examined.     

Effects of surface curvature and surface chemistry on the structure and activity of proteins adsorbed in nanopores

The interactions of proteins with the surface of cylindrical nanopores are systematically investigated to elucidate how surface curvature and surface chemistry affect the conformation and activity of confined proteins in an aqueous, buffered environment. Two globular proteins, lysozyme and myoglobin, with different catalytic functions, were used as model proteins to analyze structural changes in proteins after adsorption on ordered mesoporous silica SBA-15 and propyl-functionalized SBA-15 (C(3)SBA-15) with carefully controlled pore size. Liquid phase ATR-FTIR spectroscopy was used to study the amide I and II bands of the adsorbed proteins. The amide I bands showed that the secondary structures of free and adsorbed protein molecules differ, and that the secondary structure of the adsorbed protein is influenced by the local geometry as well as by the surface chemistry of the nanopores. The conformation of the adsorbed proteins inside the nanopores of SBA-15 and C(3)SBA-15 is strongly correlated with the local geometry and the surface properties of the nanoporous materials, which results in different catalytic activities. Adsorption by electrostatic interaction of proteins in nanopores of an optimal size provides a favorably confining and protecting environment, which may lead to considerably enhanced structural stability and catalytic activity.     

Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study

The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of organic groups via a co-condensation synthetic method from 15% organosilane and by post-grafting organosilanes onto a pre-made mesoporous silica were synthesized. Comparative studies of their adsorption and release properties for various model drug molecules were then conducted. Functional groups including 3-aminopropyl, 3-mercaptopropyl, vinyl, and secondary amine groups were used to functionalize the mesoporous materials while rhodamine 6G and ibuprofen were utilized to investigate the materials’ relative adsorption and release properties. The self-assembly of the mesoporous materials was carried out in the presence of cetyltrimethylammonium bromide (CTAB) surfactant, which produced MCM-41 type materials with pore diameters of ∼2.7-3.3 nm and moderate to high surface areas up to ∼1000 m²/g. The different functional groups introduced into the materials dictated their adsorption capacity and release properties. While mercaptopropyl and vinyl functionalized samples showed high adsorption capacity for rhodamine 6G, amine functionalized samples exhibited higher adsorption capacity for ibuprofen. While the diffusional release of ibuprofen was fitted on the Fickian diffusion model, the release of rhodamine 6G followed Super Case-II transport model.     

Adsorption of bulky molecules of nonylphenol ethoxylate on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore sizes were prepared using ordered mesoporous silica SBA-15 as hard templates. The OMCs possess abundant mesopores with narrow pore size distribution, on which the adsorption behavior of bulky molecules of nonylphenol ethoxylate (NPE) were investigated. The isotherms of NPE on OMCs can be fitted by Langmuir adsorption model, evidenced by the adsorption data. The surface area of the pores larger than 1.5 nm is a crucial factor to the adsorption capacity of NPE, whereas the most probable pore diameter of OMCs is crucial to the adsorption rate of NPE. The adsorption temperature has more significant effects on adsorption rate than the adsorption capacity. Theoretical studies show that the adsorption kinetics of NPE on OMCs can be depicted with the pseudo-second-order kinetic model. In addition, thermodynamic parameters of adsorption were evaluated based on the equilibrium constants related to the equilibrium of adsorption at different temperatures.     

有序介孔炭的合成及液相有机大分子吸附性能研究

分别采用有序介孔氧化硅SBA-15和NaY分子筛为硬模板合成了系列有序介孔炭OMC和微孔炭CFY. N₂静态吸附测试表明, 所合成的介孔炭具有丰富的介孔结构和集中的介孔分布. 以亚甲基蓝为探针分子, 研究其在有序介孔炭OMC和微孔炭CFY上的吸附行为. 研究结果表明, 有序介孔炭中大于3.5 nm的大介孔孔容是决定亚甲基蓝吸附容量和吸附速率的关键因素. 吸附动力学理论研究表明, 准二级动力学方程可以很好地描述亚甲基蓝分子在介孔炭上吸附动力学行为.     

Preparation of ordered mesoporous SiC from preceramic polymer templated by nanoporous silica

Highly ordered mesoporous SiC materials were prepared by infiltrating viscous liquid preceramic polymer, allylhydridopolycarbosilane, into two types of surface modified nanoporous silica templates: mesoporous silica SBA-15 and mesocellular siliceous foam. The silica templates were subsequently etched off after pyrolysis at 1000 degrees C under nitrogen atmosphere with the resultant formation of ordered mesoporous structures. The mesoporous SiC materials, synthesized from both types of templates possessed high Brunauer-Emmett-Teller (BET) surface areas in the range of 250-260 m(2)/g with pore sizes of 3.4-3.6 nm. The ordered structures of mesoporous SiC were exact inverse replicas of their respective silica templates, as characterized by small angle X-ray diffraction (XRD), transmission electron microscope (TEM) images, and the adsorption-desorption isotherm of nitrogen.     

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.     

Three‐Dimensional Ultralarge‐Pore Ia3d Mesoporous Silica with Various Pore Diameters and Their Application in Biomolecule Immobilization

Highly ordered mesoporous three‐dimensional Ia3d silica (KIT‐6) with different pore diameters has been synthesized by using pluronic P123 as surfactant template and n‐butanol as cosolvent at different synthesis temperatures in a highly acidic medium. The materials were characterized by XRD and N₂ adsorption. The synthesis temperature plays a significant role in controlling the pore diameter, surface area, and pore volume of the materials. The material prepared at 150 °C, KIT‐6‐150, has a large pore diameter (11.3 nm) and a high specific pore volume (1.53 cm³ g^?1). We also demonstrate immobilization of lysozyme, which is a stable and hard protein, on KIT‐6 materials with different pore diameters. The amount of lysozyme adsorbed on large‐pore KIT‐6 is extremely large (57.2 μmol g^?1) and is much higher than that observed for mesoporous silicas MCM‐41, SBA‐15, and KIT‐5, mesoporous carbons, and carbon nanocages. The effect of various parameters such as buffer concentration, adsorption temperature, concentration of the lysozyme, and the textural parameter of the adsorbent on the lysozyme adsorption capacity of KIT‐6 was studied. The amount adsorbed mainly depends on solution pH, ionic strength, adsorption temperature, and pore volume and pore diameter of the adsorbent. The mechanism of adsorption on KIT‐6 under different adsorption conditions is discussed. In addition, the structural stability of lysozyme molecules and the KIT‐6 adsorbent before and after adsorption were investigated by XRD, nitrogen adsorption, and FTIR spectroscopy.     

Aqueous dye adsorption on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore size, and microporous carbon, CFY, were synthesized using ordered mesoporous silica SBA-15 and NaY zeolite as hard templates, respectively. N(2) adsorption tests show that the synthesized OMCs possess abundant mesopores and centralized mesopore distribution. Methylene blue (MB) and neutral red (NR) were used as probe molecules to investigate their adsorption behaviors on OMCs and CFY. As evidenced by adsorption tests, the volume of mesopores of which the pore size is larger than 3.5 nm is a crucial factor for the adsorption capacity and adsorption rate of MB on OMCs. However, the most probable pore diameter of OMCs was found to be vital to the adsorption capacity and adsorption rate of NR. Theoretical studies show that the adsorption kinetics of MB and NR on OMCs can be well depicted by using pseudo-second-order kinetic model.     

功能化有序介孔二氧化硅材料在分析样品前处理中的应用

功能化有序介孔二氧化硅材料具有均一可调的介孔孔径、规则的孔道、稳定的骨架结构、易于修饰的内表面和较高的比表面积、高的吸附容量等特性,可用于生物、医药、环境样品等复杂基体中痕量分析物的高选择性分离与富集,因此在样品前处理中的应用特别引人瞩目。文中简要介绍了功能化有序介孔二氧化硅材料的制备方法,综述了功能化有序介孔二氧化硅材料在分离富集金属离子、有机污染物以及生物大分子样品前处理中的应用进展。     

Guest-host encapsulation of microporous zeolites in ordered mesoporous materials by molecular simulations

The present work provides the first study of ordered mesoporous materials SBA-15 coated with microporous zeolites ZSM-5 using molecular simulations. Several model structures with characteristics such as periodic arrangement of mesopores, randomly arranged micropores, surface hydroxyls and bulk deformations of SBA-15 were used. Cartesian coordinates of ZSM-5 unit lattice were obtained from the literature and the 100 face of H-ZSM-5 unit cell was then placed on the surface of SBA-15 and the entire structure was equilibrated to obtain final configuration. The resulting structure was characterized using simulated small angle and wide angle X-ray diffraction, Connolly surface area (to compare BET area), accessible pore volume for nitrogen molecules (to compare with t-plot volume of micro and mesopores) and methane adsorption at 303 K. The orientation of ZSM-5 on the SBA-15 had no effect on the surface area, pore volume or adsorption capacity. In order to find out if the addition of microporous ZSM-5 should increase the total methane adsorption capacity due to addition of micropores, we studied adsorption on bare and coated SBA-15. However, total adsorption capacity was found to decrease, while the number of methane molecules adsorbed per unit cell of the SBA-15 structure increased. An existing experimental method (J. Am. Chem. Soc., 2004, 126, 14324) of the synthesizing hybrid ZSM-5/SBA-15 structure was studied using accessible micropore volume (by t-plot). It was found that the procedure made all the micropores inaccessible. A modification of the method or use of other host materials is suggested to use the benefits of narrow micropore distribution in ZSM-5.     

Controlling adsorption and release of drug and small molecules by organic functionalization of mesoporous materials

A series of mesoporous nanosphere materials that are functionalized with various terminal and bridging organic groups were synthesized. They have improved adsorption capacity and different release properties for drug and small molecules. The materials contained terminal vinyl, 3-mercaptopropyl, 3-aminopropyl, and secondary amine functional groups and bridging ethane, ethene, and benzene groups within their mesopore channel walls. The samples containing mercaptopropyl and vinyl groups showed greater adsorption capacity and better controlled release behavior for rhodamine 6G molecules. On the other hand, mesoporous matrices containing amine functional groups showed higher adsorption capacity and better release properties for ibuprofen molecules. Further studies revealed that the bridging organic groups in the mesopore channel walls also improved the adsorption capacity and release properties of the materials compared to the corresponding samples containing no bridging organic groups. Such improved adsorption and controlled release properties of molecules by simple changes of functional groups on mesoporous materials are important for the development of nanomaterial drug delivery vehicles and for controlled release of drugs over long time periods at specific targeted sites in the body. By judicious choice of organic groups and by systematic design and synthetic approaches, nanoporous materials having different adsorption capacity and release properties for many other drug molecules can also be achieved.     

硬模板法合成磁性石墨化介孔碳及在中药废水吸附处理中的应用

以SBA-15为模板, 蔗糖为碳源, 硝酸铁辅助催化合成磁性石墨化介孔碳复合材料(Fe/GMC). 利用X射线粉末衍射(XRD)、透射电子显微镜(TEM)、N₂吸附-脱附(BET)、拉曼光谱等对反应产物进行了表征. 硝酸铁辅助催化可以在较低碳化温度(900℃)下实现介孔碳的部分石墨化, 并同步生成磁性Fe₃O₄颗粒, 合成的产物比表面积大、孔道有序、磁性强. 运用紫外-可见(UV-Vis)光谱考察了该复合材料对中药红花色素废水的吸附特性,复合材料的吸附速率快、吸附量高, 具有良好的脱色效果并能实现吸附剂的快速固液磁分离.     

Synthesis and lysozyme adsorption of rod-like large-pore periodic mesoporous organosilica

Highly ordered rod-like large-pore periodic mesoporous organosilica (PMO) was successfully synthesized at low acid concentration with the assistance of inorganic salt using triblock copolymer P123 as a template. The roles of inorganic salt and acidity in the production of highly ordered mesostructure and the morphology control of PMOs were investigated. It was found that the inorganic salt can significantly widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rod-like PMOs can only be synthesized in a narrow range of acid and salt concentrations, which were sensitive to induction time. The adsorption of lysozyme on PMO was studied at different pH values in comparison with adsorption on pure silica material under controlled morphology and pore structure. It was found that the adsorption capacity of lysozyme on the PMO was lower than that on pure SBA-15 silica material and the adsorption amounts are larger at pH 9.6 than at 7.0 for both materials. The results show that the electrostatic interaction between lysozyme and PMO/SBA-15 surface is more dominant than the hydrophobic forces and the interaction of neighboring lysozyme molecules also plays an important role.     

In situ SAXS investigation of dibromomethane adsorption in ordered mesoporous silica

A SAXS/WAXS apparatus with the aid of a specially designed sample cell capable for performing both SAXS and WAXS experiments was used for adsorption studies in nanoporous materials. The applicability of the instrument for structural investigations and its ability for adsorption experiments because of the advanced sample environment were demonstrated by carrying out in situ SAXS measurements during gas physisorption. SAXS profiles of ordered mesoporous silica were measured at selected equilibrium points alongside a dibromomethane (CH₂Br₂) adsorption isotherm at 293 K. SBA-15 was the adsorbent of choice because it consists of a regular 2D hexagonal array of cylindrical mesopores that gives rise to Bragg reflections in the small-angle regime. CH₂Br₂ was selected as a contrast-matching fluid because it has almost the same electron density as silica. We obtained high-quality data comparable to those resulting from experiments performed in synchrotron light sources which produce intense beams of x-rays and support advanced instrumentation for high-resolution diffraction and SAXS studies. The Bragg peaks of the pore lattice are clearly visible for the evacuated sample and at the early stages of the adsorption process. The intensity decrease and the elimination of the Bragg peaks for the saturated sample suggest that an almost perfect contrast matching was achieved. A model has been used for monitoring the fluid condensation and evaporation regime in SBA-15 by taking into account both the Bragg scattering and the diffuse scattering for spatially random pore filling. The results show the absence of spatial correlations between filled pores suggesting random pore filling.     

有机胺修饰具有较大孔径介孔材料的二氧化碳吸附性能

以非离子表面活性剂P123为模板剂,正硅酸甲酯为硅源,通过加入不同的扩孔剂制得具有较大孔径的SBA-15类介孔材料,并采用粉末X射线衍射(XRD)、低温氮气吸附-脱附、扫描电镜(SEM)、傅里叶变换红外(FTIR)光谱等手段对所得样品进行了表征.加入扩孔剂可以明显增大介孔材料的孔容和孔径,而异辛烷为扩孔剂的扩孔效果明显优于四氯化碳.经四乙烯五胺(TEPA)镀饰后,这些样品均表现出良好的CO2吸附性能.其中对于除去模板剂后再镀胺的样品,其CO2吸附能力与介孔材料孔道结构关系不大,而对于未除模板剂的原粉镀胺样品,CO2吸附能力则随孔道的变大而增强.此外,通过吸附等温线和CO2-程序升温脱附(TPD)手段比较了温度和压力对CO2吸附的影响,发现在较高温度下吸附时CO2的吸附能力随压力的变化存在显著差别,因而在这类TEPA修饰的介孔材料上可通过变压吸附的途径来实现对环境气流中CO2的吸附和分离.     

有序中孔炭的电化学储氢性能

将蔗糖、聚环氧乙烯-聚环氧丙烯-聚环氧乙烯三嵌段共聚物和硅源构成的复合物进行预炭化、炭化和除硅处理合成出有序中孔炭, 采用XRD、TEM、HRTEM和N2吸脱附等手段对其进行表征, 并将有序中孔炭制成电极开展恒流充放电储氢性能研究. 结果显示, 具有较高比表面积(720 m2·g-1)和孔容(0.86 cm3·g-1)的有序中孔炭材料的电化学储氢容量为70.1 mAh·g-1, 高于具有相对较低比表面积(610 m2·g-1)和孔容(0.66 cm3·g-1)的有序中孔炭储氢容量(64.1 mAh·g-1). 通过与单壁碳纳米管电极(25.9 mAh·g-1)的对比, 表明有序中孔炭具有良好的电化学储氢性能和更高的电化学活性.     

Physical adsorption characterization of nanoporous materials: progress and challenges

Within the last two decades major progress has been achieved in understanding the adsorption and phase behavior of fluids in ordered nanoporous materials and in the development of advanced approaches based on statistical mechanics such as molecular simulation and density functional theory (DFT) of inhomogeneous fluids. This progress, coupled with the availability of high resolution experimental procedures for the adsorption of various subcritical fluids, has led to advances in the structural characterization by physical adsorption. It was demonstrated that the application of DFT based methods on high resolution experimental adsorption isotherms provides a much more accurate and comprehensive pore size analysis compared to classical, macroscopic methods. This article discusses important aspects of major underlying mechanisms associated with adsorption, pore condensation and hysteresis behavior in nanoporous solids. We discuss selected examples of state-of-the-art pore size characterization and also reflect briefly on the existing challenges in physical adsorption characterization.