Enhanced esterification of carboxylic acids with ethanol using propylsulfonic acid-functionalized natural rubber/hexagonal mesoporous silica nanocomposites

Propylsulfonic acid-functionalized natural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites (NR/HMS-SO₃H) with different acid contents were prepared via an in situ sol–gel process, and then applied as heterogeneous acid catalysts in the esterification of model carboxylic acids and palm fatty acid distillate (PFAD) with ethanol. The NR/HMS-SO₃H composites exhibited a wormhole-like framework with enhanced wall thickness, high mesoporosity, and enhanced hydrophobicity. The NR/HMS-SO₃H composites exhibited a superior catalytic performance compared to a commercial Nafion/silica composite solid acid catalyst (SAC-13) and conventional propylsulfonic acid-functionalized HMS (HMS-SO₃H). The NR/HMS-SO₃H catalyst can be regenerated and reused in the esterification.     

Preparation of bicontinuous mesoporous silica and organosilica materials containing gold nanoparticles by co-synthesis method

Catalytic activities of gold strongly depend on its particle size. It is necessary to have homogeneous distributions of small gold nanoparticles with diameters between 2 and 5 nm for excellent catalytic activities. In this study, gold-containing mesoporous silica materials were prepared by a co-synthesis method. The essence of this sol–gel co-synthesis method is to combine together neutral surfactant template synthesis of mesoporous silica materials with the introduction of metal ions via bifunctional silane ligands, so that the formation of mesostructures and metal–ion doping occur simultaneously. The formation of gold nanoparticles with size less than 5 nm inside mesoporous materials (HMS, MSU, and PMO) has been achieved by this co-synthesis sol–gel process. In addition, the effects of post-treatments, such as calcination and reduction, on pore structures and nanoparticle size distributions were also investigated.     

六方介孔氧化硅负载磷钨酸的催化性能

采用浸渍法将磷钨酸(HPW)负载于六方介孔氧化硅(HMS)上,制备HPW改性HMS介孔材料HPW/HMS,对其进行了表征;以HPW/HMS为催化剂,催化2-萘甲醚(2-MN)与乙酸酐(AA)的酰化反应,考察了各因素对催化反应的影响. 结果表明,HPW高度分散在HMS上,HPW/HMS的酸量和酸强度随HPW负载量增加而增加. 在温度120℃、时间4 h、催化剂用量0.3 g及2-萘甲醚/乙酸酐摩尔比1:2条件下,2-萘甲醚转化率为75.3%(mol),目标产物2-甲氧基-1-萘乙酮的选择性达83.0%(mol). 催化剂可回收再利用,催化活性略有降低.     

Preparation of mesoporous silica fiber matrix for VOC removal

A novel method for the preparation of the mesoporous silica fiber matrix was introduced for a removal of volatile organic compounds (VOCs). Paper making technology was applied to make a sheet of mesoporous silica fiber matrix. Reinforcing the mesoporous silica fiber with the ceramic fibers (50 wt.%) increased the mechanical strength of the matrix. Mesoporous silica fibers using TMOS (tetramethoxysilane) as a silica source and CTAC (cetyltrimethyl-ammoniumchloride) as a surfactant were drawn by the spinning method. The spinning process increased both the crystallinity and the fraction of mesopores (1.9 nm) of the fiber. As the spinning rate was increased both the crystallinity and the specific area of the mesoporous silica fiber increased, but the diameter of fiber decreased. We could control the size and morphology of mesoporous silica fiber matrix by changing the shape of substrates. This leads to easy fabrication of honeycomb-structured adsorbent which can be used for the VOC removal.     

Simple Design of Hydrophobic Zeolite Material by Modification Using TEFS and its Application as a Support of TiO2 Photocatalyst

Through the simple process using alkoxide reagent containing fluorine, triethoxyfluorosilane (TEFS), hydrophobic mesoporous silica material (HMS) was prepared. The surface modified HMS have still maintained its mesoporous structure and large surface area and showed considerable hydrophobic property compared with non-modified HMS. Moreover the surface modified HMS was applied as a support of TiO₂ photocatalyst with the aim of the efficient degradation of organic pollutant in water. Due to the hydrophobic property, the fine TiO₂ photocatalyst particles were generated on the modified HMS and both the adsorption properties and photocatalytic activities for the degradation of 2-propanol diluted in water were dramatically increased.     

Efficient adsorption and photocatalytic degradation of organic pollutants diluted in water using the fluoride-modified hydrophobic titanium oxide photocatalysts: Ti-containing Beta zeolite and TiO2 loaded on HMS mesoporous silica

Using the F⁻ media, the hydrophobic zeolite and mesoporous silica can be synthesized. These hydrophobic porous materials exhibit the high ability for the adsorption of organic compounds diluted in water and become the useful supports of photocatalyst. The hydrophobic Ti-Beta(F) zeolite prepared in the F⁻ media exhibited high efficiency than the hydrophilic Ti-Beta(OH) zeolite prepared in OH⁻ media for the liquid-phase photocatalytic degradation of 2-propanol diluted in water to produce CO₂ and H₂O. The TiO₂ loaded on the hydrophobic mesoporous silica HMS(F) (TiO₂/HMS(F)), which was synthesized using tetraethyl orthosilicate, tetraethylammonium fluoride as the source of the fluoride and dodecylamine as templates, also exhibited the efficient photocatalytic performance for the degradation. The amount of adsorption of 2-propanol and the photocatalytic reactivity for the degradation increased with increasing the content of fluoride ions on these photocatalysts. The efficient photocatalytic degradation of 2-propanol diluted in water on Ti-Beta(F) zeolite and TiO₂/HMS(F) mesoporous silica can be attributed to the larger affinity for the adsorption of propanol molecules on the titanium oxide species depending on the hydrophobic surface properties of these photocatalysts.     

Zeolite beta monoliths with hierarchical porosity by the transformation of bimodal pore silica gel

Zeolite beta monoliths with hierarchical porosity were prepared by the steam-assisted conversion of pre-seeded bimodal pore silica gel using the Layer-by-Layer process. The bimodal pore silica gel acts as both macrotemplates and silica source. The zeolite beta monoliths were characterized by X-ray diffraction, scanning electron microscopy, IR absorption spectra and nitrogen adsorption measurements. This zeolite beta monolith had hierarchical porosity: the unique micropores within the zeolite, the small macropores generated by aggregation of crystallites and three dimensionally interconnected macropores formed by template of silica gel. It is believed that the hierarchical structured zeolite monoliths will show good properties and potential applications the fields of catalyst, ion exchange, and adsorption.     

胺功能化介孔二氧化硅捕集CO2的研究进展

胺功能化介孔二氧化硅因其高选择性、高吸附容量、快速的吸附动力学、良好的再生性能和循环稳定性受到广泛关注,在二氧化碳捕集技术中具有优良的应用前景。本文比较了胺改性的M41S、SBA-n、KIT-n、介孔二氧化硅泡沫、介孔二氧化硅纳米球和六方介孔二氧化硅的吸附性能,总结了MCM-41和SBA-15的结构特点。介绍了胺化合物的负载方式——湿法浸渍、化学接枝和原位聚合的胺负载原理。分析了硅源、载体内部性质、气体选择性和不同添加剂对胺功能化介孔二氧化硅材料吸附二氧化碳能力的影响。最后,点明了吸附剂未来的发展目标,对胺功能化介孔二氧化硅材料的研究方向进行了展望。指出未来可关注介孔二氧化硅微观结构和温度对胺与二氧化碳相互作用的影响,增强胺功能化介孔二氧化硅的稳定性,推进其在实际环境下的应用。     

One-pot synthesis of silica monoliths with hierarchically porous structure

Poly(furfuryl alcohol) (PFA) and block copolymer Pluronic F127 were used as pore templates to create mechanically robust silica monoliths with a hierarchical and interconnected macro-mesoporous network in an easy, reproducible bimodal scale templating process. Control over the morphology was obtained by varying the reactant ratios. Phase separation on the submicrometer scale occurred when furfuryl alcohol was cationically polymerized and therefore became immiscible with the solvent and the silica precursor. Upon a subsequent sol-gel reaction, a silica-F127 matrix formed around the PFA spheres, leading to macropore structures with mesoporous walls. Surface areas of the final structures ranged from 500 to 989 m² g⁻¹ and a maximum pore volume of 4.5 mL g⁻¹ was achieved. Under mildly acidic conditions, micelle-templated mesopores resulted. Interconnected macropores could be obtained by increasing the pH or the block copolymer concentration. The formation mechanism and the relationship between PFA, Pluronic F127 and acidity are discussed in detail.     

Removal of DDT from aqueous solutions using mesoporous silica materials

BACKGROUND: There are few reports about adsorbents for the effective removal of large‐molecule pesticides such as DDT (1,1,1‐trichloro‐2,2′ bis(p‐chlorophenyl)ethane). Some mesoporous silica materials and their modified derivatives might serve as good adsorbents for these large organic molecules because of their large pore diameter and special pore structures. In this work, the adsorption processes of DDT in aqueous solutions were investigated using different mesoporous silica materials, including HMS, MCM‐41, SBA‐15 and MCM‐48. RESULTS: All these materials exhibit efficient DDT removal, and the adsorption is a rapid process with over 50% of DDT removed within approximately 2 h. The efficiency of DDT removal is influenced by the adsorbent characteristics, such as pore volume, pore diameter, connectivity between pore channels and surface OH groups. The influences of water/acetone ratio and initial DDT concentration in solution were also explored. It was found that with enhancing DDT solubility, the addition of acetone in the reaction solution had no evident impact on DDT adsorption efficiency. Increasing the initial concentration of DDT resulted in a decrease of DDT adsorption efficiency. The adsorption kinetics of DDT on mesoporous silica material is shown to be pseudo‐second‐order. After thermal treatment at a relatively low temperature of 450 °C, the adsorbed DDT was completely decomposed and the adsorbents, except MCM‐41, were regenerated well. CONCLUSION: The results demonstrate the potential of a simple and efficient new approach for the removal of OCPs (organochlorine pesticides), especially large OCP molecules from surface water or groundwater. Copyright © 2008 Society of Chemical Industry     

介孔材料的形貌控制及其应用

综述了近期介孔材料研究在形貌控制方面取得的成果,着重介绍了在酸性条件下具有孔结构的氧化硅薄膜,薄片,空心球,硬球和纤维的合成。这些特定形貌的介孔材料在催化,纳米材料合成,光学器件和色谱载体等领域具有广泛的应用前景。     

Mesoporous silica fibers prepared by electroblowing of a poly(methyl methacrylate)/tetraethoxysilane mixture in N,N-dimethylformamide

Electroblowing and sol–gel reaction were combined to prepare mesoporous silica fibers. Poly(methyl methacrylate) (PMMA), a simple commercial polymer with weak hydrogen bonding to silica, was demonstrated to be valuable in improving the electrospinnability and as a porogenic agent. Compared with that in electrospinning, the jet stream in electroblowing was more stable and the resultant fibers were more uniform. The electroblown fibers were characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption and desorption isotherms. The phase separation behavior and mechanism for the formation of the amorphous mesoporous structure were discussed. Although there was no covalent bonding between PMMA and silica, macrophase separation was completely prevented in the electroblown fibers and the pore size in the calcined silica fibers ranged from 10 to 20 nm. However, the previously reported electrospun silica fibers, in which surfactants or polymers with strong hydrogen or covalent bonding to silanol groups were used as structure directing agents, had average pore sizes below 10 nm. The present study offers a facile method for the preparation of highly mesoporous silica fibers with large mesopores.     

Spherical silica micro/nanomaterials with hierarchical structures: synthesis and applications

This paper reviews the progress made recently in synthesis and applications of spherical silica micro/nanomaterials with multilevel (hierarchical) structures. The spherical silica micro/nanomaterials with hierarchical structures are classified into four main structural categories that include (1) hollow mesoporous spheres, (2) core-in-(hollow porous shell) spheres, (3) hollow spheres with multiple porous shells and (4) hierarchically porous spheres. Due to the complex structures and being focused on spherical silica micro/nanomaterials, some novel methods based on the combination of two routine methods or two surfactants, and some special synthetic strategies are proposed to produce the spherical silica micro/nanomaterials with hierarchical structures. Compared with the same-sized solid, porous or hollow silica spheres, these fantastic spherical silica micro/nanomaterials with hierarchical structures exhibit enhanced properties which may enable them to be used in broad and promising applications as ideal scaffolds (carriers) for biological, medical, and catalytic applications.     

Improvement of uncooled infrared imaging detector by using mesoporous silica as a thermal isolation layer

Thermal-insulation properties of ordered mesoporous silica could possibly improve the efficiency of uncooled infrared imaging detector by introducing a mesoporous silica layer between TiN absorber and Si₃N₄ passivation layer. IR absorption rate of 50% porosity mesoporous silica was simulated and the results showed that above 90% infrared absorptance could be achieved in 8–12 μm wavelength region. Thermal conductivity of mesoporous silica was measured by 3ω method. Finite element modeling was used to simulate thermal isolation effect of mesoporous silica inserted structure. The result shows that an effective thermal-insulation effect could be obtained with 150 nm thick mesoporous silica layer. Also according to the simulation result of time transient temperature variation, it was found that mesoporous silica layer for thermal isolation induced an increase of 30% of residual temperature on TiN absorber. The mesoporous silica film was found to be a good thermal isolation layer for microbolometer.     

Preparation of Spherical Hexagonal Mesoporous Silica

A series of hexagonal mesoporous silica (HMS) have been synthesized by the neutral assemble pathway in water-alcohol cosolvent systems, using dodecylamine (DDA) and tetraethyl orthosilicate (TEOS) as the starting materials. These materials were characterized with powder X-ray diffraction, nitrogen sorption measurement, differential thermal analysis, and transmission electron microscopy. The XRD patterns of these samples exhibited a strong intense reflection at low angle, suggesting the excellent mesostructures of the samples. The particle size of HMS decreased and the morphology of HMS exhibited high textural porosity as the HMS was prepared with high addition rate of TEOS. The particle size of HMS prepared without aging was smaller than that aged for 18 h, due to the reaction time of TEOS was not enough to form complete particles. Addition of NaCl and HCl hindered the formation of HMS mesoporous structure. In contrast, addition of 1-butanol did not affect the formation of HMS mesoporous structure. The sphereical HMS silica with uniform size has been synthesized by adjusting DDA and TEOS concentrations. The shape of HMS became larger and more spherical as the concentrate on of DDA decreased. The stirring rate of the reaction mixture had no effect on either the shape or the size of the spheroid HMS silicas. However, the particles started to crack at higher stirring rates.     

Unprecedented oxidative properties of mesoporous silica materials: Towards microwave-assisted oxidation of lignin model compounds

The unusual oxidative ability of mesoporous silicas towards oxidation of an important lignin model molecule, 1,2-(4-hydroxy-3methoxy-phenoxy) ethanol, apocynol under microwave irradiation is presented in this work. Mesoporous MCM-41, HMS, SBA-15 and amorphous silica were employed as catalysts in the present study. Different reactivities were obtained for the various silica materials. It was assumed that the substrate conversion and product selectivity were highly influenced by the nature of mesoporous silica materials. Based on the nature of the catalysts and reaction product profile, a plausible mechanism has been proposed.     

Syntheses and application of silica monolith with bimodal meso/macroscopic pore structure

A route to synthesize porous materials with a bimodal macro/mesoscopic pore system has been investigated in this work. Polystyrene with sub-micrometer size was used as a template in the synthesis. The resulting mesoporous silica wall replicated inversely the morphology of polystyrene template and had highly ordered three-dimensional arrays of macro pores. Large and moldable meso/macro porous silica monoliths could be obtained in centimeter scale by using monodispersed polystyrene beads and PEO-PPO-PEO/SBA-15 sol solutions. These bimodal structured porous silicates have been used as supports for asymmetric kinetic resolution of racemic epoxides to synthesize optically pure epoxide.     

Syntheses and application of silica monolith with bimodal meso/macroscopic pore structure

A route to synthesize porous materials with a bimodal macro/mesoscopic pore system has been investigated in this work. Polystyrene with sub-micrometer size was used as a template in the synthesis. The resulting mesoporous silica wall replicated inversely the morphology of polystyrene template and had highly ordered three-dimensional arrays of macro pores. Large and moldable meso/macro porous silica monoliths could be obtained in centimeter scale by using monodispersed polystyrene beads and PEO-PPO-PEO/SBA-15 sol solutions. These bimodal structured porous silicates have been used as supports for asymmetric kinetic resolution of racemic epoxides to synthesize optically pure epoxide.     

A comparative study on the synthesis mechanism and microstructural development of hierarchical porous mullite monoliths obtained by the sol–gel process with three different silicon sources

Hierarchical porous mullite monoliths have been prepared via a sol–gel process accompanied by phase separation. Propylene oxide (PO) acted as an acid scavenger to mediate the gelation, poly(ethylene oxide) (PEO) as the phase-separation inducer and network former, aluminum chloride hexahydrate (AlCl₃·6H₂O) as the aluminum source. The route was improved by using hypotoxic tetraethylorthosilicate (TEOS) and nontoxic aqueous colloidal silica (Aq) instead of tetramethoxysilane (TMOS). The synthesis mechanism and microstructural development were comparatively investigated by scanning electron microscopy (SEM), thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption–desorption. It was found that the mixing degree of precursors and concurrent process of gelation and phase separation are key elements to get well-defined hierarchical porous mullite monoliths. In addition, the monoliths with high relative crystallinity are more likely to be obtained under low transformation temperature in organic silicon sources system.     

A novel [Bmim]PW/HMS catalyst with high catalytic performance for the oxidative desulfurization process

To effectively reduce the sulfur content in model fuel, [Bmim]PW/HMS catalyst was synthesized through impregnating the hexagonal mesoporous silica (HMS) support by phosphotungstic acid (HPW) and ionic liquid [Bmim] HSO₄. Physical structure characterizations of the catalysts showed that HMS retained mesoporous structure, and [Bmim] PW was well dispersed on the support of HMS. The catalytic activity of the [Bmim]PW/HMS was evaluated in the oxidative desulfurization process, and the optimal reaction conditions including loading of the catalysts, reaction temperature, catalyst amount, O/S (H₂O₂/sulfur) molar ratio and agitation speed were investigated. Under the optimal reaction conditions, the conversion of benzothiophene (BT), dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) could reach 79%, 98%, 88%, respectively.