Large pore volume mesoporous aluminum oxide synthesized via nano-assembly

A new nano-assembly approach has been proposed for the preparation of macropore volume mesoporous aluminum oxide supports. Secondary nano-assembly and a frame structure mechanism for large pore volume mesoporous supports have been proposed. In a primary nano-assembly supersoluble micelle, aluminum hydroxide nanoparticles were precipitated in situ in surfactants with a volume balance (VB) less than 1, followed by secondary nano-assembly in linear and cylindrical shapes. The secondary nano-assembly of cylindrical aluminum hydroxides was calcined to form nano cylindrical aluminum oxides. For the formation of macropore volume mesoporous supports, we utilized a frame structure mechanism of mesoporous support, in which the exterior surface of the carrier may not be continuous. This macropore volume support has been used for the hydrotreatment of a residual oil catalyst, which possesses the following physical characteristics: pore volume 1.8–2.7 mL·g⁻¹, specific surface area 180–429 m²·g⁻¹, average pore diameter 17–57 nm, average pore diameter more than 10 nm (81%–94%), porosity 87%–93%, and crush strength 7.7–25 N·mm⁻¹.     

Critical micelle concentrations of cetyltrimethylammonium chloride and their influence on the periodic structure of mesoporous silica

The influence of micelle morphology transformation on the structure of mesoporous materials is fundamental in designing optimal, well-ordered, mesoporous materials. Firstly, the steady-state fluorescence technique was adopted to determine the first and second critical micelle concentrations of cetyltrimethylammonium chloride (CTAC) as 125 and 210 mmol L⁻¹ in an equimolar mixture of water and ethanol at 25°C. Using tetraethylorthosilicate (TEOS) as the precursor, mesoporous silicas (with a surface area of 545.7–1210.5 m 545.7 ∼ 1210.5 m² g⁻¹ and a pore volume of 0.26 ∼ 0.80 cm³ g⁻¹) were synthesized with the CTAC templates in the equimolar mixture of water and ethanol. Characterization by small-angle X-ray diffraction and N 2 adsorption/desorption techniques revealed that the surface area and pore volume of silica increased with the content of CTAC, whereas there existed a transition point at the CTAC/TEOS ratio of 0.15 corresponding to the fade-away of well-ordered mesoporous structure. The negative effect of the much higher content CTAC on the periodic structure of mesoporous silica is attributed to micelle transformation from spheres to cylinders related to the second critical micelle concentration of CTAC. The text was submitted by the authors in English.     

A simple template-free sol–gel synthesis of spherical nanosilica from agricultural biomass

Mesoporous silica nanoparticles with a spherical morphology have been synthesized from rice husk (agricultural biomass) by a simple, template-free synthetic approach, which was carried out via sol–gel technique at ambient condition. Transmission electron micrographs revealed the formation of spherical silica nanoparticles with an average diameter of 50.9 nm. From the nitrogen adsorption–desorption analysis, the rice husk silica shows a high specific BET surface area of 245 m² g⁻¹. The silica nanoparticles have a narrow pore size distribution of 5.6–9.6 nm.     

介孔SiO2的改性及对诺维信漆酶的交联固定化

采用十六烷基三甲基溴化铵(CTAB)为模板剂,四乙氧基硅烷(正硅酸乙酯,TEOS)为硅源,硝酸为催化剂来制备介孔SiO2,并采用后嫁接法对介孔SiO2进行氨基化改性。利用红外光谱(IR),X射线粉末衍射(XRD),差热-热重分析(DTA-TG),扫描电镜(SEM),元素分析,微电泳法及N2吸附-脱附方法对改性前后的产物进行表征。结果表明氨基已成功嫁接到介孔SiO2孔道中,改性后的介孔SiO2有序度有所下降,但仍为介孔材料;改性之后介孔材料的孔径、比表面积、孔体积均变小。等电点由原来的2.74变为4.75。本文还以氨基修饰的介孔SiO2为载体,通过交联剂戊二醛固定诺维信(Novozymes)工业级漆酶,并采用正交设计法对固定化条件进行了优化。研究表明漆酶经固定化后,其操作稳定性比游离酶高。     

Temperature dependent synthesis of micro- and meso-porous silica employing the thermo-responsive polymer of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) as structure-directing agent

Temperature dependent synthesis of micro- and meso-porous silica employing the thermo-responsive homopolymer poly(N-isopropylacrylamide) or the random copolymer poly(N-isopropylacrylamide-co-acrylic acid) as structure-directing agent (SDA) and Na₂SiO₃ as silica source is proposed. The thermo-responsive character of the SDA provides the advantages including (1) temperature dependent synthesis of microporous silica, hierarchically micro-mesoporous silica, and mesoporous silica just by changing the aging temperature below or above the low critical solution temperature of the thermo-responsive SDA, and (2) elimination of the thermo-responsive SDA from silica matrix by water extraction. The synthesis mechanism is discussed, and the effect of the aging temperature and the weight radio of SDA/Na₂SiO₃ on the synthesis of micro- and meso-porous silica are studied. Microporous silica, hierarchically micro-mesoporous silica and mesoporous silica with the surface area at 3.5−9.0 × 10² m²/g and the pore volume at 0.28−1.13 cm³/g and the average pore size ranging from 1.1 to 9.0 nm are synthesized. The strategy affords a new and environmentally benign way to fabricate porous silica materials, and is believed to bridge the gap between the synthesis of microporous and mesoporous silica materials.     

Non‐surfactant template‐directed synthesis of SiO2‐polyimide hybrid self‐standing films with ordered mesoporous structure

The silica‐PI hybrid self‐standing films with ordered mesoporous structure have been prepared by using dibenzoyl‐L ‐tartaric acid (L ‐DBTA) as non‐surfactant template under mild sol–gel route. Polyimide matrix was obtained from polyamic acid (PAA) via thermal imidization process and the template was removed in this process. The PI‐based hybrid film with 20 wt% SiO₂ obtained from DBTA presented the ordered mesoporous channels with average pore size of about 2.0 nm and BET surface area of 1167 m²/g. FTIR and SEM studies indicated that the hydrogen bond interaction between the carboxylic groups of DBTA and benzamide bonds of PAA made the PAA possibly participate in the assembly process of the aggregates of the non‐surfactant template molecules. The mechanical, thermal and some physical properties of these hybrid films materials were also characterized. Copyright © 2010 John Wiley & Sons, Ltd.     

Immobilization and electrochemistry of cytochrome c on amino-functionalized mesoporous silica thin films

The immobilization and electrochemistry of cytochrome c (cyt c) on amino-functionalized mesoporous silica thin films are described. The functionalized silica films with an Im3m cubic phase structure were deposited on conducting ITO substrate by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Pluronic F127 under acidic conditions. The high specific surface area, large pore size and functional inner surface of mesoporous silica thin films result in a high cyt c loading, and the cyt c immobilization on this silicate framework is stable. After adsorption of cyt c, the ordered cubic structure of mesoporous silica and the redox activity of immobilized cyt c are retained as demonstrated by X-ray diffraction (XRD), Transmission electron microscope (TEM) and cyclic voltammetry. The redox behavior of the cyt c/silica film-modified ITO electrode is a surface-controlled quasi-reversible process for the experimental conditions used in this work and the electron transfer rate constant is calculated is 1.33 s⁻¹. The ITO electrode modified by cyt c/silica film possesses a high stability; even cyt c retains its redox activity following immobilization for several months. Furthermore, the electrocatalytic activities of the modified ITO electrode to hydrogen peroxide and ascorbic acid have been studied. Since these behaviors are quite pronounced, the modified electrode can be used for detection of hydrogen peroxide and ascorbic acid.     

Sol–gel synthesis of Na<Subscript>2</Subscript>CaSiO<Subscript>4</Subscript> and its in vitro biological behaviors

In this work we prepared the hybrid material (SG) by the sol–gel method through the reaction between tetraethylortosilicate (TEOS) and acetylacetonatepropyltrimethoxysilane (ACACSIL). We also immobilized the acetylacetonate on silica surface (GR) by the grafting method through the reaction between a commercial silica and ACACSIL. Infrared thermal analysis showed that these materials were thermally stable until 200 °C. SG is a microporous material and has surface area of 500 m² g⁻¹, average porous volume of 0.09 cm³ g⁻¹ and organic content of 1 mmol g⁻¹. GR is a mesoporous material and has surface area of 300 m² g⁻¹, average porous volume of 0.7 cm³ g⁻¹ and organic content of 0.4 mmol g⁻¹. Iron(III) was coordinated to SG and GR resulting in the SG–Fe and GR–Fe silicas which were tested as catalysts on the aerobic epoxidation of cis-cyclooctene. SG–Fe yielded 100% of conversion and 94% of selectivity in epoxide whereas GR–Fe silica led to a maximum conversion of 50% and 100% of selectivity.     

"一步法"合成多级孔SAPO-34分子筛

以TPOAC和硅溶胶为硅源,合成了多级孔SAPO-34分子筛,总比表面积达到649 m²·g^-1。详细考察了TPOAC和硅溶胶的配比对多级孔SAPO-34外比表面的影响,通过XRD、BET、SEM、NH₃-TPD等对其结构进行表征,结果表明多级孔SAPO-34的外比表面积可调变,晶体外观有较多缺陷位置,弱酸量减少,强酸位有变弱的趋势。在TPOAC与硅溶胶的投料比为3:2,晶化时间为10 d,投料比为n_Al2O3:n_P2O5:n_Si:n_TEAOH:n_H2O=1:0.9:0.5:2:60时,合成的多级孔SAPO-34的外比表面积达到最大,为100 m²·g^-1。     

Tuning the wall thickness and pore orientation in mesoporous titania films prepared with low-temperature aging

Porous titania thin films with well-ordered mesostructures are prepared by using Pluronic surfactant P123 as the pore template and aging the films in a high-humidity environment at −6 °C. These structures are stable enough to undergo calcination at 400 °C to generate nanocrystalline TiO₂ walls with retention of mesoporosity. Under the aging conditions used, the films have well-ordered mesostructures even with a molar ratio of P123 to titanium (R) as small as 0.006. Because the P123 micelle diameter remains constant across a range of compositions, the pore diameter also remains fixed but the wall thickness of the titania thin films increases as the P123 concentration decreases without decreasing the long-range order of the products. Furthermore, mesoporous titania thin films with hexagonal close-packed channels oriented perpendicular to the substrate can be obtained R values of 0.008–0.012 by sandwiching the as-prepared films between glass slides modified with crosslinked P123. Analysis of the mesophases obtained here indicates that a transition from films containing significant 2D hexagonal channels to 3D hexagonal structure occurs below P123/Ti = 0.008. This does not match the expected volume fraction for this transition based on the mesophases behavior of aqueous P123 at room temperature, suggesting that a more detailed model would be needed to predict mesostructure in titania films aged below the freezing point of water.     

Fabrication and characterization of hexagonal mesoporous silica monolith via post-synthesized hydrothermal process

Large-sized, optical transparent mesostructured Brij 56/silica monolith has been fabricated using a lyotropic liquid crystal of Brij 56 (C₁₆EO₁₀) as a template and TMOS as a silica source, combined with a optimizing sol-gel process and a hydrothermal aging process. By programmed temperature drying and calcinations, translucent mesoporous silica monolith with two-dimensional hexagonal structure (P6mm) has bee obtained. The ordered mesoporous silica monoliths have been characterized by small-angle X-ray diffraction, transmission electron microscopy (TEM), and nitrogen adsorption, which shows that the materials have a highly ordered two-dimensional hexagonal mesostructure with the high specific surface area of 837 m² · g⁻¹ and narrow pore distribution with a mean BJH pore diameter of 2.73 nm. Based on calculations and differential scanning calorimetry and thermogravimetric analyses, the action mechanism of the hydrothermal aging process has been proposed: the 100°C hydrothermal conditions and autogenous 2.3 atm pressure promote the condensation and dehydration of silanol groups, with the result that cross-linking degree, the flaws and moisture content in gels are reduced notably. Those processes guarantee the integrity of gels in the following drying process.     

Synthesis of silica nanoparticles by modified sol–gel process: the effect of mixing modes of the reactants and drying techniques

A modified preparation of silica nanoparticles via sol–gel process was described. The ability to control the particle size and distribution was found highly dependent on mixing modes of the reactants and drying techniques. The mixture of tetraethoxysilane and ethanol followed by addition of water (Mode-A) produced monodispersed powder with an average particle size of 10.6 ± 1.40 nm with a narrow size distribution. The freeze drying technique (FD) further improved the quality of powder. In addition, the freeze dried samples have shown unique TGA decomposition steps which might be related to the well-defined structure of silica nanoparticles as compared to the heat dried samples. DSC analysis showed that FD preserved the silica surface with low shrinkage and generated remarkably well-order, narrow and bigger pore size and pore volume and also large endothermic enthalpies (ΔH _FD = −688 J g⁻¹ vs. ΔH _HD = −617 J g⁻¹) that lead to easy escape of physically adsorbed water from the pore at lower temperature.     

Preparation,characterisation and electrochromic property of mesostructured tungsten oxide films via a surfactant templated sol–gel process from tungstic acid

A novel kind of mesoporous tungsten oxide films (TOFs) has been prepared via a non-ionic surfactant templated sol–gel route from cheap and easy handling tungstic acid. Characterisations by means of various techniques, including XRD, TEM, SEM, ATR and DTA, confirm that the obtained mesostructures are composed of fine mesopores (2–3 nm) and thin pore walls. Compared with previously reported surfactant templated mesoporous TOFs, our initial evaluation on the electrochromic properties showed that the derived TOFs show greatly enhanced colouration efficiency of 44 cm² C⁻¹ and faster colouration/bleaching speed of 10/2 s, respectively. Owing to the ordering of mesostructures delivered by our method, the mesostructural changes associated with the electrochemical reaction during the electrochromic cycling of such materials can be directly monitored by low-angle XRD measurements.     

Synthesis of mesoporous Stöber silica nanoparticles: the effect of secondary and tertiary alkanolamines

The effect of secondary (diethanolamine) and tertiary (triethanolamine) alkanolamines as catalysts on the formation of mesoporous Stöber silica nanoparticles by sol–gel method was studied. The particles were characterized by thermogravimetry and differential thermal analysis, Fourier transform infrared spectroscopy, N₂ physisorption measurements, and field emission scanning electron microscopy. By using ammonia and different alkanolamines as catalysts, the Brunauer–Emmet–Teller (BET) surface area and pore volume increased in the order of ammonia < diethanolamine < triethanolamine. A maximum BET surface area of 140.1 m² g^?1 and pore volume of 0.66 cm³ g^?1 were obtained from triethanolamine catalyzed silica particles. The average particle size of silica prepared by ammonia and different alkanolamines as catalysts decreased in the order of ammonia > diethanolamine > triethanolamine. The role of different alkanolamines on the textural properties and particle size of silica is explained in terms of their relative steric hindrance and basicity.     

Preparation and photochromism of Keggin-type molybdphosphoric acid/silica mesoporous composite thin films

Using tetraethoxysilane and 3-aminopropyltriethoxysilane as the silica sources, amino-functionalized organic/inorganic hybrid mesoporous silica thin films with 2-dimensional hexagonal structure have been synthesized by evaporation induced self-assembly process in the presence of cetyltrimethyl ammonium bromide templates under acid conditions. The Keggin-type molybdphosphoric acid (PMo) is incorporated into the mesoporous silica thin films with amino-groups by wetness impregnation, and the PMo/silica mesoporous composite thin films are obtained. The results of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and Fourier transform infrared (FTIR) spectra indicate the PMo molecules maintain Keggin structure and are homogeneously distributed inside mesopores. The composite thin films possess excellent reversible photochromic properties, and change from colorless to blue under ultraviolet irradiation. The photochromic mechanism of the composite thin films is studied by ultraviolet-visible (UV-vis), electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) spectra. It is shown that intervalence charge transfer (IVCT) and ligand-to-metal charge transfer (LMCT) are the main reasons of photochromism. PMo anions interact strongly with amino-groups of the mesoporous suface via hydrogen bond and electrostatic force. After ultraviolet irradiation, the charge transfer occurs by reduction of heteropolyanions accompanying the formation of heteropolyblues with multivalence Mo(VI, V), and the bleaching process of composite thin films is closely related to the presence of oxygen.     

Preparation of Monolithic Ti‐incorporated Mesoporous Silica Materials via Tartaric Acid Templated Sol‐gel Process

Monolithic and transparent Ti‐incorporated mesoporous silica materials of large size (e.g. 2 mm) in dimension have been prepared with tartaric add (TA) as template via sol‐gel reactions of tetraethyl orthosilicate (TEOS) and tetrabutyl titanate (TBT). The materials are characterized by infrared (IR), nitrogen adsorption‐desorption isotherms, powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the monolithic materials exhibit large specific surface areas (ca. 1200 mVg) and pore volumes (ca. 0.900 cm³/g).     

介孔氧化镍的合成、表征和在电化学电容器中的应用

以十二烷基硫酸钠为模板剂, 采用尿素为沉淀剂, 用均匀沉淀法, 适当控制尿素的水解速度, 制备具有介孔结构的氢氧化镍胶体, 在不同温度下焙烧处理得到孔分布集中的氧化镍介孔分子筛. 结果表明, 在523 K下焙烧得到的氧化镍BET比表面达到477.7 m²•g^－1. 结构表征还显示, 介孔氧化镍的孔壁为多晶结构, 其孔结构形成机理应为准反胶束模板机理. 循环伏安法表明用NiO介孔分子筛制备的电极有很好的电容性能. 与浸渍法和阴极沉淀法制得的NiO相比, 这种介孔结构的NiO能够大量用来制作电化学电容器电极, 并且保持较高的比电容量和良好的电容性能.     

The effect of molecular imprinting on the pore size distribution of polymers

Molecular imprinting techniques are becoming an increasingly important domain of porous polymers generally, to achieve molecule specific recognition through morphology or stereochemistry of cavities. Imprinting is sought to increase both selectivity and sensitivity where the polymer may be present as particulate, membrane or thin film forms. Here, we detail mechanisms involved in the formation, stability and adsorption of binding sites, through the influence of polymerisation conditions and templates on the porosity of highly crosslinked molecularly imprinted polymers (MIPs). Environmental control represents an important area for porous polymers, here we focus on two template fungicides, iprodione and pyrimethanil, for ethylene glycol dimethacrylate (EGDMA) based polymers. In general, control of the pre-polymerisation interactions were able to vary the surface areas of polymers from 40–60 m² g⁻¹ to 300–436 m² g⁻¹ while pore sizes fell into distributions (a) close to the micropore region at ∼3.8 nm, (b) in the 10 to 20 nm mesopore region and (c) in the 20 to 50 nm mesopore region. The importance of intermolecular interactions and aggregation in the pre-polymerisation solution to the Brunauer, Emmett, Teller (BET) surface areas and pore size distribution of final polymers has been demonstrated by systematic variation of chemical functionality. These effects confirm recent molecular dynamic simulation studies of MIP formation and cavity stability.     

Efficient maximization of coloration by modification in morphology of electrodeposited NiO thin films prepared with different surfactants

In this paper, we report on the nickel oxide (NiO) thin films potentiostatically electrodeposited onto indium-doped tin oxide-coated glass substrates by using two types of organic surfactants: (1) non-ionic: polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) and (2) anionic: sodium dodecyl sulfate (SDS). An aqueous solution containing nickel sulfate precursor and potassium hydroxide buffer was used to grow the samples. The effect of organic surfactants on its structural, morphological, wettability, optical, electrochromic, and in situ colorimetry were studied using X-ray diffraction, scanning electron microscopy, contact angle, FT-IR spectroscopy, optical transmittance, cyclic voltammetry, and CIE system of colorimetry. X-ray diffraction patterns show that the films are polycrystalline, consisting of NiO cubic phase. A nanoporous structure with pore diameter of about 150–200 nm was observed for pure NiO. The films deposited with the aid of organic surfactants exhibits various surface morphological feature. PVP-mediated NiO thin film shows noodle-like morphology with well-defined surface area whereas, an ordered pore structure composed of channels of uniform diameter of about 60–80 nm was observed for PEG. A compact and smooth surface with nanoporous structure stem from SDS helps for improved electrochromic performance compared with that of NiO deposits from surfactant-free solution. Wetting behavior shows, transformation from hydrophilic to superhydrophilic nature of NiO thin films deposited with organic surfactant, which helps for much more paths for electrolyte access. The surfactant-mediated NiO produce high color/bleach transmittance difference up to 57% at 630 nm. On oxidation of NiO/SDS, the CIELAB 1931 2° color space coordinates show the transition from colorless to the deep brown state (L* = 84.41, a* = −0.33, b* = 4.41, and L* = 43.78, a* = 7.15, b* = 13.69), with steady decrease in relative luminance. The highest coloration efficiency of 54 cm² C⁻¹ with an excellent reversibility of 97% was observed for NiO/SDS thin films.     

Electrochemical Characteristics of Discrete,Uniform, and Monodispersed Hollow Mesoporous Carbon Spheres in Double‐Layered Supercapacitors

Core–shell‐structured mesoporous silica spheres were prepared by using n‐octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core–shell‐structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double‐layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer–Emmett–Teller (BET) area and larger pore size.