Synthesis and characterization of acidic properties of Al-HMS materials of varying Si/Al ratios

HMS and Al-HMS materials with Si/Al ratio in the range 5-45 were synthesized by neutral templating pathway. The as synthesized as well as calcined samples were examined for pore size distribution, surface area and XRD. These investigations confirmed the hexagonal mesoporous structure formation at all Si/Al ratios. The TGA measurements indicated that two types of template species interacting with Si or Al could be distinguished. The acidity and acid strength distribution studies using microcalorimetric NH₃ adsorption indicated that the acidity increases with Al content in the mesoporous structure. The presence of Al in the structure creates a wide variety of acid sites of varying strengths. The heterogeneity of the sites also increases with Al content of the catalysts. The activities for cumene cracking reaction to test acidity of the materials supported the trend obtained from microcalorimetric NH₃ adsorption results.     

介孔二氧化钛的合成及其对甲基橙降解的光催化活性

以十六烷基三甲基溴化铵为模板剂,通过水解钛酸正丁酯合成了介孔二氧化钛分子筛,探讨了合成条件的影响。采用X射线粉末衍射(XRD)、红外光谱(FT-IR)、透射电子显微镜(TEM)和N2吸附-脱附等技术对介孔二氧化钛的晶相、结构、形貌、比表面积和孔径分布进行了表征。实验结果表明:得到的介孔二氧化钛分子筛的孔径为4-4.3nm,用抽提的方法去除模板剂得到的介孔二氧化钛的比表面积比焙烧的要高。以甲基橙为模型污染物,检验了所合成介孔二氧化钛的光催化性质。     

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.     

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.     

Mesoporous aluminum phosphite

High surface area pure mesoporous aluminum-phosphorus oxide-based derivatives have been synthesized through an S⁺I⁻ surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from aluminum atrane complexes and phosphoric and/or phosphorous acids. A soft chemical extraction procedure allows opening the pore system of the parent as-prepared materials by exchanging the surfactant without mesostructure collapse. The nature of the pore wall can be modulated from mesoporous aluminum phosphate (ALPO) up to total incorporation of phosphite entities (mesoporous aluminum phosphite), which results in a gradual evolution of the acidic properties of the final materials. While phosphate groups in ALPO act as network building blocks (bridging Al atoms), the phosphite entities become basically attached to the pore surface, what gives practically empty channels. The mesoporous nature of the final materials is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption–desorption isotherms. The materials present regular unimodal pore systems whose order decreases as the phosphite content increases. NMR spectroscopic results confirm the incorporation of oxo-phosphorus entities to the framework of these materials and also provide us useful information concerning the mechanism through which they are formed.     

Sol–gel synthesis of mesoporous silicas containing albumin and guanidine polymers and its application to the bilirubin adsorption

The organic–inorganic composite materials based on mesoporous silica were synthesized using sol–gel method. The surface area of silicas was modified by bovine serum albumin (BSA) and guanidine polymers: polyacrylate guanidine (PAG) and polymethacrylate guanidine. The mesoporous silicas were characterized by nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, transmission electron microscopy. The obtained materials were used as adsorbents for selective bilirubin removal. It was shown that the structural properties and surface area of modified materials depend on the nature of polymers. Incorporation of polymers in silica gel matrix during sol–gel process leads to the formation of mesoporous structure with high pore diameter and a BET surface area equals to 346 m²/g for SiO₂/BSA and 160 m²/g for SiO₂/PAG. Analysis of adsorption isotherms showed that modification of silica by BSA and guanidine polymers increases its adsorption ability to bilirubin molecules. According to Langmuir model, the maximum bilirubin adsorption capacity was 1.18 mg/g.     

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.     

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.     

In Situ and Post Reaction Cobalt-Incorporation into Periodic Mesoporous Ethanesilica Materials

Cobalt incorporated periodic mesoporous organosilica materials were synthesized in situ by condensation of 1,2-bistrimethoxysilylethane (BTME) in the presence of cetyltrimethylammonium bromide (CTAB) and cobalt nitrate and by incipient wetness addition of Co to BTME mesoporous silica. BET and pore measurements as well as DTA and TGA analysis of the materials revealed that the mesoporous structure is retained under the synthetic conditions used, after solvent extraction and importantly to temperatures of ca. 400°C under N₂. Raman spectroscopy also revealed the presence of the ethane moiety in the Co materials and that the surfactant was removed by solvent extraction. BET and pore measurement studies revealed that the surface area and pore volume of the materials decreased with increasing cobalt loading. The studies indicate that the new Co materials have potential as Fischer-Tropsch catalysts.     

有序介孔二氧化硅对正丁醛的吸附性能

合成了一系列具有不同孔结构与性质的有序介孔二氧化硅材料SBA-15、MCM-41、SBA-16、KIT-6, 同时通过改变水热温度制备了不同孔径大小的SBA-15, 并利用小角X射线散射、透射电镜、扫描电镜和氮气吸附-脱附等手段, 对其介孔结构进行了表征. 以正丁醛为探针分子, 考察了其对有机醛的吸附, 并与Y-沸石的吸附性能做了对比. 结果表明, 材料的介孔比表面积与其对正丁醛的吸附量成正比, 吸附等温线符合Langmuir 模型, 属于单层吸附, 具有最大介孔比表面积的MCM-41对正丁醛的吸附量最大(484 mg·g^-1). 最后将SBA-15添加到卷烟滤嘴中, 实验结果表明, SBA-15能显著降低卷烟烟气中巴豆醛的释放量.     

有序介孔二氧化硅对正丁醛的吸附性能

合成了一系列具有不同孔结构与性质的有序介孔二氧化硅材料SBA-15、MCM-41、SBA-16、KIT-6,同时通过改变水热温度制备了不同孔径大小的SBA-15,并利用小角X射线散射、透射电镜、扫描电镜和氮气吸附-脱附等手段,对其介孔结构进行了表征.以正丁醛为探针分子,考察了其对有机醛的吸附,并与Y-沸石的吸附性能做了对比.结果表明,材料的介孔比表面积与其对正丁醛的吸附量成正比,吸附等温线符合Langmuir模型,属于单层吸附,具有最大介孔比表面积的MCM-41对正丁醛的吸附量最大(484 mg·g-1).最后将SBA-15添加到卷烟滤嘴中,实验结果表明,SBA-15能显著降低卷烟烟气中巴豆醛的释放量.     

Oligomeric polymer surfactant driven self-assembly of phenylene-bridged mesoporous materials and their physicochemical properties

The detailed synthesis of highly hydrophobic average pore benzene-bridged hybrid mesoporous silicas under an acidic medium is described. With the use of a 1,4-bis(triethoxysilane)benzene silsesquioxane precursor and biodegradable alkyl polyoxyethylene (Brij-56 or Brij-76) nonionic surfactant oligomers as supramolecular templates, no molecular scale periodicity was observed. The well-defined mesoporous materials could be synthesized with two-dimensional hexagonal (p6mm) symmetries. The textural and surface properties (adsorption isotherms of water and benzene vapors) were estimated and were compared to the analogous benzene-bridged mesoporous silica with molecular scale periodicity which was prepared using cationic surfactant under basic conditions. Different textural properties resulted for the two kinds of materials and revealed some important insights regarding the structure and nature of the materials.     

Study of the Adsorption Properties of MCM-41 Molecular Sieves Prepared at Different Synthesis Times

The variation of surface properties of SiMCM-41 and AlMCM-41 nanoporous materials as function of synthesis time was examined. The main properties studied were: surface area, pore diameter, pore volume, mesoporous parameter, and wall thickness. Siliceous MCM-41 molecular sieves were synthesized starting from hydrogels with the following molar compositions: 4.58SiO₂:0.435Na₂O:1 CTMABr:200 H₂O for SiMCM-41, and 4.58SiO₂:0.485 Na₂O:1 CTMABr:0.038 Al₂O₃:200 H₂O, for AlMCM-41. Cetyltrimethylammonium bromide (CTMABr) was used as the structural template. The crystallographic parameters were obtained from XRD data and by nitrogen adsorption using the BET and BJH methods. The results obtained showed a significant variation of the surface properties of the MCM-41 materials as a function of the synthesis time reaching silica wall thickness of ca. 2 nm on the fourth day.     

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.     

Crystalline-like molecularly ordered mesoporous aluminosilicates derived from aluminosilica-surfactant mesophases via benign template removal

We report the preparation of mesoporous aluminosilicate materials that exhibit molecular-scale ordering in their pore wall framework. The materials were derived from mesoporous aluminosilica-surfactant mesophases via benign template removal methods, which allowed the retention of molecular ordering in surfactant-free materials. The molecularly ordered aluminosilica-surfactant mesophases were obtained from hydrothermal crystallization of cetyltrimethylammonium hydroxide/Al,Si/H2O systems at 135 degrees C for 12 days. Benign template removal via H2O2-mediated oxidation of the surfactant at room temperature was found to be the most effective method in generating surfactant-free materials with molecular ordering, high textural properties (depending on Al content), and high acidity. The Al in the resulting aluminosilicates was entirely incorporated in framework (tetrahedrally coordinated) sites. Template extraction in acidified ethanol also generated molecularly ordered materials but compromised the Al content and acidity. Template removal via conventional calcination generated porous materials with high textural properties but which exhibited only limited molecular ordering and had relatively low acidity and significant amounts of nonframework Al. This work demonstrates that molecular ordering in mesoporous silicate-surfactant mesophases is due to crystallographic ordering within inorganic frameworks rather than the arrangement/packing of surfactant molecules.     

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.     

Modification of Surface and Structural Properties of Ordered Mesoporous Silicates

Two simple modification methods for ordered mesoporous silicas were examined and compared. MCM-41 molecular sieve was physically coated with 4-cyano-4-biphenyl [4(4-pentenyloxy)]benzoate (CBPB) and chemically modified using trimethylethoxysilane. The structural and surface properties of the obtained materials were characterized using elemental analysis, thermogravimetry and nitrogen adsorption over a wide pressure range.It was shown that the pore size of the MCM-41 material was not decreased significantly after the coating procedure, even for high loadings of CBPB. Moreover, low pressure adsorption measurements indicated that significant fractions of the MCM-41 surface were not covered by CBPB, even for high CBPB loadings, which suggests that the attained coverage may be very nonuniform. The chemical bonding procedure led to a marked decrease in the pore size and change of surface properties.It was demonstrated that nitrogen adsorption measurements provide a means of a thorough characterization of modified MCM-41 materials, allowing to estimate the surface area, pore volume and pore size distribution. Moreover, low pressure adsorption data can be used to qualitatively or semiquantitatively assess the surface coverage of the coated/bonded organic groups, which may be used to estimate the uniformity of the coverage and therefore, the usefulness of the modification procedure.     

Characterization of the hydrophobicity of mesoporous silicas and clays with silica pillars by water adsorption and DRIFT

The hydrophobic-hydrophilic properties of a solid are related to the material chemistry and, often, these properties are relevant to the applications of a particular material. Contrarily to what happens with other properties, such as specific surface areas or pore volumes, the methodologies to ascertain on the hydrophilicity of a porous material are not well defined. In this work, we discuss and relate the information on the hydrophobicity degree obtained from water adsorption isotherms and from diffuse reflectance infrared Fourier transform (DRIFT), in a set of porous materials. The studied materials were mainly mesoporous solids, namely of MCM-41 and SBA-15 types, two xerogels and also different porous clays heterostructures. Both techniques were informative on the hydrophobic-hydrophilic properties of the studied samples, but the correlation between the information obtained by each technique was not straightforward. Water adsorption isotherms are much more sensitive to the differences of the studied materials than the DRIFT spectra. For silica-based mesoporous materials with similar surface chemistry, the water adsorption process and hence, the hydrophobic-hydrophilic properties, is mainly dependent on the pore diameters. However, water adsorption is much more sensitive to changes in the nature of the adsorbent surface than to changes in the pore diameter.     

超临界条件下合成晶型骨架的介孔氧化锆

采用聚氧乙烯型非离子表面活性剂(PEO)为模板剂,超临界乙醇为介质,在不同条件下(各种PEO,不同pH值和络合剂)合成了类似于MSU的介孔氧化锆.XRD,N₂物理脱吸附曲线,TEM及选区电子衍射证明该介孔氧化锆骨架为四方晶型;改变表面活性剂类型、络合剂及pH可调变介孔氧化锆的BET表面积与孔分布.     

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.