Characterization Studies on the Ionic Liquid-Templated Mesoporous Silica with Wormlike Pores

This article reports a novel preparation of wormlike mesoporous silica with 1-hexadecane-3-methylimidazolium bromide (C₁₆MIM)Br, a kind of room-temperature ionic liquids (RTILs), as a template via a sol-gel nanocasting technique. The characterization studies were carried out in contrast with that of the mesoporous silica with cetyltrimethylammonium bromide (CTAB), a usually used template, which has the same alkyl chain length with (C₁₆MIM)Br. The structures of the silica materials have been characterized by Transmission electron microscopy (TEM), High-resolution TEM (HRTEM) and N₂ adsorption-desorption measurements. The results show that both the mesoporous materials prepared with different templates respectively can form regular wormlike mesopores with ca. 2 nm in pore diameter. They also have large BET surface areas with narrow size distribution. Compared to the CTAB-template mesoporous silica, the material with (C₁₆MIM)Br as a template has highly uniform pore size and larger surface area. In addition, the formation mechanism of the wormlike mesopores with RTIL has been proposed by an electrostatic charge matching assembly-pathway and steric factor.     

Metallic nickel supported on mesoporous silica as catalyst for hydrodeoxygenation: effect of pore size and structure

Catalytic hydrodeoxygenation (HDO) of anisole, a methoxy-rich lignin-derived bio-oil model compound, was carried out over a series of Ni-containing (5, 10, 20, and 30 wt%) catalysts with commercial silica and ordered mesoporous silica SBA-15 as support. Both supports and catalysts were characterized by N₂ adsorption–desorption isotherms, X-ray diffraction, CO chemisorption, and transmission electron microscopy (TEM). Catalytic reaction was performed at 250 °C and 10 bar H₂ pressure. Depending on the catalyst support used and the content of active metal, the catalytic activity and product distribution changed drastically. Increase of the nickel loading resulted in increased anisole conversion and C₆ hydrocarbon (benzene and cyclohexane) yield. However, loading more Ni than 20 wt% resulted in a decrease of both conversion and C₆ yield due to agglomeration of Ni particles. In addition, Ni/SBA-15 samples exhibited much stronger catalytic activity and selectivity toward C₆ hydrocarbon products compared with Ni/silica catalysts. The differences in catalytic activity among these catalysts can be attributed to the effect of the pore size and pore structure of mesoporous SBA-15. SBA-15 can accommodate more Ni species inside channels than conventional silica due to its high pore volume with uniform pore structure, leading to high HDO catalytic activity.     

Tuning particle morphology of mesoporous silica nanoparticles for adsorption of dyes from aqueous solution

Spherical and rod mesoporous silica nanoparticles with hexagonal mesostructure were prepared using the modified Stöber method. The morphology, size and internal pore structure can be controlled by simple changing of surfactant concentration and water:ethanol molar ratio. Monodispersed spheroid MCM-41 was obtained at 40 °C under basic conditions using cetyltrimethylammonium bromide (C₁₆TAB) as template. Obtained materials were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET), transmission electron microscopy (TEM) and scanning electronic microscopy (SEM). The results reveal that the pore volume and surface area increase when the amount of C₁₆TAB increases whereas the pore diameter and particle size decrease. However, the use of ethanol as cosolvent led to an increase in the particles’ size. Moreover, the addition of a 3-aminopropyltriethoxysilane greatly influenced the final particle shape. The material was effectively used for the removal of two fluorescent dyes (Hoechst 33342 and rhodamine 6g) from aqueous solution. Adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. The Langmuir model was found to fit the experimental data better than others models.     

Effect of two Kinds of Imidazolium Ionic Liquids on the Microemulsion Polymerization of Methyl methylacrylate

Summary: In this paper, the microemulsion polymerization of methyl methylacrylate (MMA) was carried out with single and gemini ionic liquids as emulsifier including 1-N-tetradecyl-3-methylimidazolium bromide (C₁₄MIM · Br) and 1, 4-Bis (3-tetradecylimidazolium-1-yl) butane bromide (C₁₄MIM-4-C₁₄MIM · 2Br) respectively, and they were all have typical microemulsion polymerization characters of MMA, but the process of polymerization directly depends on the structure of the imidazolium ionic liquids. The structure and concentration of ionic liquids have effects on the resulted latex particle sizes of PMMA, and much smaller size latexes of PMMA could be gotten with C₁₄MIM · Br as emulsifier than C₁₄MIM-4-C₁₄MIM · 2Br in polymerization. On the other hand, the structure of emulsifier has the effects on the molecular weight (MW) and molecular weight distribution (MWD) of PMMA, so the resulting PMMA prepared from microemulsion polymerization with C₁₄MIM · Br as emulsifier has higher MW but narrower MWD than that of PMMA with the same dosage of C₁₄MIM-4-C₁₄MIM · 2Br as emulsifier.     

Preparation and microstructure of sol-gel derived silver-doped silica

Silver-doped silica was prepared by hydrolysis and condensation of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) in the presence of a silver nitrate (AgNO₃) solution by two different synthesis methods. In the first synthesis route, sol-gel mixtures were prepared using an acid catalyst. In the second synthesis route, silver-doped silica gels were formed by two-step acid/base catalysis. For the same concentration of silver dopant [AgNO₃]/[TEOS] = 0.015 acid-catalyzed sol-gel formed a microporous silica with an average pore size of <25 Å whereas the two-step catalyzed silica had an average pore size of 250 Å and exhibited a mesoporous structure when fully dried. The differences in the pore size affected the silver particle formation mechanism and post-calcination silver particle size. After calcination at 800 °C for 2 h the acid-catalyzed silica contained metallic silver particles size with an average particle size of 24 ± 2 nm whereas two-step catalyzed silica with the same concentration of [AgNO₃]/[TEOS] = 0.015 contained silver nanoparticles with an average size of approximately 32 ± 2 nm. Mechanisms for silver particle formation and for silica matrix crystallization with respect to the processing route and calcination temperature are discussed.     

载有量子点的介孔二氧化硅微球的制备与性能研究

采用自组装方法制备了一种磁核/介孔二氧化硅壳的微球, 调节体系中C₁₈TMS的加入量可控制介孔硅球的比表面积; 并通过化学修饰的方法对介孔微球表面进行巯基功能化修饰. 利用巯基与量子点之间的相互作用可将一定尺寸的量子点吸附于介孔二氧化硅球的孔中, 令介孔微球具有荧光效应; 同时可以利用吸附不同粒径的量子点的荧光光谱对介孔二氧化硅微球孔径的大小进行近似考察.     

1-Hexadecyl-3-methylimidazolium Ionic Liquid as a New Cationic Surfactant for Separation of Phenolic Compounds by MEKC

The ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C₁₆MIm]Br) has been used as a novel cationic surfactant for separation of phenolic compounds, including quinol, phloroglucinol, resorcinol, phenol, p-cresol, and m-nitrophenol, by micellar electrokinetic capillary chromatography (MEKC). The effects of buffer concentration and pH, concentration of [C₁₆MIm]Br, and applied potential were studied. Use of the optimized buffer (25 mmol L^?1 NaH₂PO₄), 10 mmol L^?1 [C₁₆MIm]Br, and an applied potential of ?15 kV enables optimum separation with regard to resolution and migration time. The phenolic compounds were detected at 214 nm. The micelle of this long-alkyl-chain imidazolium ionic liquid acts as a pseudo-stationary phase in this MEKC separation.     

Synthesis of SBA-15 from low cost silica precursor obtained from sugarcane leaf ash and its application as a support matrix for lipase in biodiesel production

Ordered mesoporous silica material was synthesized from a low-cost precursor, sugarcane leaf ash, was used as a support matrix for lipase for the production of biodiesel. The mesoporous samples were characterized using Fourier transform infra red spectroscopy. The surface topography and morphology of the mesoporous materials were studied using scanning electron microscope. The pore diameter, pore volume, Brunauer Emmett and Teller surface area of the mesoporous material were determined by N₂ gas adsorption technique. Different pore size Santa Barbara Acid-15 (SBA-15) samples were synthesized and their lipase immobilization capacity and specific enzyme activity of immobilization lipase were determined and compared. Lipase from Candida Antarctica immobilized on SBA-15 (C) had shown maximum percentage immobilization and specific enzyme activity. The immobilized lipase mesoporous matrix was used for biodiesel production from crude non-edible Calophyllum inophyllum oil. The percentage yield of fatty acid methyl ester, 97.6 % was obtained under optimized conditions: 100 mg of lipase immobilized on SBA-15, 6:1 methanol to oil molar ratio, the reaction of 2 g C. inophyllum oil with methanol.     

Comparison of ordered mesoporous materials sorption properties towards amino acids

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.     

Template-free sol–gel synthesis of high surface area mesoporous silica based catalysts for esterification of di-carboxylic acids

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m²/g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH₃-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.     

Temperature Dependence in the Synthesis of SBA-16-Type Mesoporous Silica with Pluronic F68 Block Copolymer

By adjusting the local effective surfactant packing parameter through synthesis temperature, highly ordered SBA-16-type mesoporous silica materials have been synthesized by templating with a nonionic triblock copolymer Pluronic F68 in strongly acidic conditions at temperature 30～40°C with the addition of K₂SO₄. The prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure were proved by the well-defined x-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy indicated that a transformation from faced-sphere to faced-polyhedron shape morphologies could be induced with increasing of the synthesis temperature. The nitrogen adsorption–desorption analysis revealed that the mean pore size (5.50～6.13 nm) of the prepared materials increased with increasing synthesis temperature. However, when the synthesis temperature exceeded 46°C, only disordered mesoporous silca was obtained. Our synthesis strategies by adjusting the local effective surfactant packing parameter through synthesis condition, even in a narrow range, would be used not only to optimize the synthesis conditions of reported mesoporous silca, but also to fabricate new mesoporous silica materials with well-ordered channel and anticipated morphologies.     

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。     

Titanium-rich highly ordered mesoporous silica synthesized by using a mixed surfactant system

A new titanium-rich highly ordered 2-D hexagonal mesoporous titanium silicate has been synthesized using a mixture of cationic (cetyltrimethylammonium bromide, CTAB) and non-ionic (Brij-35, C₁₂H₂₅-(OC₂H₄)₂₃-OH, a polyether and aliphatic hydrocarbon chain surfactant) mixed surfactant system as the supramolecular structure directing agent (SDA) in the presence of tartaric acid (TA) as a mineralizer of Ti(IV). XRD, N₂ adsorption and TEM data suggested the presence of mesophase with hexagonal pore arrangements and the UV-visible, FT IR and XPS studies suggested the incorporation of mostly tetrahedral titanium (IV) species in the highly ordered silica network. This mesoporous titanium silicate material showed excellent catalytic activity and selectivity in the epoxidation of styrene using dilute aqueous H₂O₂ as oxidant.     

Hierarchical porous carbon with designed pore architecture and study of its adsorptive properties

Ordered mesoporous carbon nanoparticles have been synthesized by a nanocasting procedure from furfuryl alcohol impregnation into alumino–silica UVM-7 material. By a proper adjustment of the synthesis parameters, furfuryl alcohol volume vs. template pore volume, it was possible to obtain a carbonaceous templated material which keeps the hierarchical bimodal porosity of the silica together with its high surface area (>1000 m²/g), as it was confirmed by means of electron transmission microscopy and N₂ adsorption isotherms. This carbon material was evaluated by testing it as a sorbent for several pesticides in aqueous solutions. Its absorption efficiency was compared with typical commercial solid phase extraction materials such as silica C₁₈ and graphitized carbon black GCB.     

Influence of cross profile of PE fibers on thermal properties of materials

Molecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO₂:1.00 Na₂O:200.00 H₂O at 100 °C for 120 h with pH correction. The cetyltrimethylammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn–Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA⁺ species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.     

超声波合成介孔分子筛

介孔分子筛MCM鄄41自问世以来一直是材料研究的热门领域之一[1,2],目前报道的主要合成方法有水热合成法[3,4]、微波法[5,6]等。其中水热法反应时间长达3~5d,耗能大,不利于实用化生产。超声波化学又称声化学,是一门新兴的交叉学科。超声波的波长远大于分子尺寸,因而不能对分子直     

仿生光催化剂的优化制备、介孔特性表征及其在催化降解苯酚废水中的应用

以十二胺(DDA)或十八胺(ODA)为模板剂,采用焙烧或萃洗法去除模板剂制备中孔分子筛(HMS).X射线粉末衍射(XRD)及氮吸附表征结果说明,以十二胺为模板剂且采用焙烧法去除模板剂制备的分子筛具有明显的XRD介孔衍射峰,而且其氮吸附曲线具有典型的IV类等温线特征及H1型脱附滞后环,这属于典型的介孔材料特征.以此分子筛为载体,通过F—C反应将磺酸铁酞菁(FePcS)修饰在HMS上,得到新型光催化剂.催化剂的BET比表面积为675.1m2·g-1,平均孔径为5.78nm,孔容为0.587cm3·g-1,且仍保持着鲜明的介孔特征.最后在模拟可见光照射下应用催化剂处理浓度高达1000mg·L-1的模拟苯酚废水,反应400min后,苯酚的转化率达到85%以上,反应溶液pH值也由4.52降到2.65,表明有酸类降解中间产物生成,反应最终苯酚转化率接近100%,总有机碳(TOC)的去除率达81%以上.催化剂表现出了良好的催化降解有机废水的性能.     

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.     

Phase transitions of octamethylcyclotetrasiloxane confined inside aluminosilicate and silicate nanoporous matrices

We report the melting behaviour of a dipolar cyclic siloxane liquid: octamethylcyclotetrasiloxane (OMCTS) confined in three mesoporous silica matrices: Al-SBA-15, SBA-15 and CPG glasses, using differential scanning calorimetry and dielectric spectroscopy. We investigate the influence of acid sites on the adsorptive properties of mesoporous silica materials, which were synthesized by applying Pluronic-type polymers as pore-creating agents. Aluminosilicate matrices have been synthesized by direct synthesis procedure using aluminium chloride. These materials characterized by N₂ sorption measurements, and the small-angle X-ray scattering data exhibit the same hexagonal P6 mm structure with a mean mesopores size of 4.6 nm (Al-SBA-15) and 4.9 nm (SBA-15). The controlled pore glasses used in this experiment have pores of mean diameter of 7.5 nm. For all systems studied, the OMCTS melting point in pores has been found to decrease with decreasing pore diameter. This result is in qualitative agreement with that obtained in molecular simulation where the adsorbate-wall interactions are weak compared to the adsorbate–adsorbate interactions.     

Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 [m²/s] and D _p (90 Å) =5.8?10^?10 [m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.