Mesoporous silica helical ribbon and nanotube-within-a-nanotube synthesized by sol-gel self-assembly

Using N-miristoyl-l-alanine sodium salt (C₁₄-l-AlaS) and 3-aminopropyltriethoxysilane (APES) as structure and co-structure-directing agents (CSDA), mesoporous silicas with the morphologies of helical ribbon and nanotube-within-a-nanotube have been fabricated just by increasing the APES/C₁₄-l-AlaS molar ratio from 1.0 to 1.15 and 1.25. The microstructures of the mesoporous silicas have been studied by electron microscopy and it was found that: 1) The mesostructure of the helical-ribbon silica materials was double-layer and the mesopores in the wall were disordered; 2) The nanotube-within-a-nanotube silica was multilayer and the mesopores in the wall were also disordered; 3) The silica materials obtained by increasing the APES/C₁₄-l-AlaS molar ratio to 1.25 maintained the nanotube-within-a-nanotube morphology, but with the existence of larger mesopores in the wall.     

缓冲溶液中制备掺杂高度隔离铁物种的介孔氧化硅(英文)

使用P123作为模板剂,采用不同的硅源(正硅酸甲酯,正硅酸乙酯,硅酸钠)在弱酸性的条件下(pH=4.4,乙酸-乙酸钠缓冲溶液)合成掺杂铁的介孔氧化硅材料.正硅酸甲酯和硅酸钠形成有序的二维六方相的介孔结构,而正硅酸乙酯形成了囊泡结构.紫外可见漫反射光谱和紫外共振拉曼光谱表明,在环境友好的条件下,采用硝酸铁和硅酸钠可以合成出高度隔离的铁物种.缓冲溶液提供了一条便捷的途径,通过简单改变硅源来控制介孔结构.掺杂铁的介孔氧化硅材料在苯酚的羟化反应中表现出优异的催化性能,主要由于铁物种高度分散在氧化硅载体上,介孔结构使铁活性位更易于接近反应物分子.     

Rational Synthesis of Metal Nanotubes and Nanowires from Lamellar Structures

A generic method has been developed for the synthesis of crystalline metal nanowires or nanotubes (such as bismuth nanotubes, tungsten nanowires) from lamellar structures. In a typical process, lamellar surfactant/inorganic composite precursors are first prepared by reacting cationic or anionic surfactants with inorganic species under appropriate conditions. After treating these precursors by hydrothermal pyrolysis, or other processes, crystalline metallic nanotubes or nanowires are obtained.     

介孔材料的制备及表征

以正硅酸乙酯(TEOS)为硅源、十六烷基三甲基溴化铵(CTAB)为模板剂,在酸性溶液的条件下,利用模板剂与硅源水解后生成的聚集体之间相互作用,通过分子自组装,萃取除去模板剂而形成蠕虫状的介孔SiO2材料。采用TEM、XRD、N2吸附/脱附和FT—R等测试手段对产物进行了表征。结果表明,合成的介孔固体材料为无定型氧化硅,与煅烧法相比,该介孔固体的孔径较大(7nm以上)、孔壁较厚、孔径分布较窄、BET表面积较大(可达1200m2/g)。     

Ordered nanoporous polymer-carbon composites

Nanostructured organic materials, particularly those constructed with uniform nanopores, have been sought for a long time in materials science. There have been many successful reports on the synthesis of nanostructured organic materials using the so-called, 'supramolecular liquid crystal templating' route. Ordered nanoporous polymeric materials can also be synthesized through a polymerization route using colloidal or mesoporous silica templates. The organic pore structures constructed by these approaches, however, are lower in mechanical strength and resistance to chemical treatments than nanoporous inorganic, silica and carbon materials. Moreover, the synthesis of the organic materials is yet of limited success in the variation of pore sizes and structures, whereas a rich variety of hexagonal and cubic structures is available with tunable pore diameters in the case of the inorganic materials. Here we describe a synthesis strategy towards ordered nanoporous organic polymers, using mesoporous carbon as the retaining framework. The polymer-carbon composite nanoporous materials exhibit the same chemical properties of the organic polymers, whereas the stability of the pores against mechanical compression, thermal and chemical treatments is greatly enhanced. The synthesis strategy can be extended to various compositions of hydrophilic and hydrophobic organic polymers, with various pore diameters, connectivity and shapes. The resultant materials exhibiting surface properties of the polymers, as well as the electric conductivity of the carbon framework, could provide new possibilities for advanced applications. Furthermore, the synthesis strategy can be extended to other inorganic supports such as mesoporous silicas.     

Synthesis of 3-dimensional mesoporous silica using a di-block copolymer template

Exploring polymeric surfactants as templates for synthesizing ordered mesoporous silicas has become increasingly important for both academic interests and industrial applications. In this work, we employed C₁₆EO₄₀, a di-block copolymer polyethylene-poly(ethylene oxide), as template in an attempt to synthesize a modified 3-dimensional wormhole mesoporous silicas (WMS-39). In addition, various synthesizing conditions were investigated, including pre-hydrolysis time of TEOS, reaction temperatures and the ratios of TEOS to template. The products were characterized using powder XRD, TEM, ²⁹Si MAS NMR and nitrogen adsorption measurements. The characteristics of as-synthesized mesoporous silica were compared with SBA-15, a highly ordered mesoporous silica, prepared using non-ionic tri-block copolymers of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) as templates. The WMS-39 materials have a BET surface area of 600–970 m²/g and narrowly distributed pore diameter around 3.9 nm. The morphology of WMS-39 was found to be wormhole framework as indicated in TEM diagrams. Thermal transformation of the as-synthesized mesoporous materials were carefully analyzed with TGA/DTA. Findings obtained from this work enable us to propose a modified assembly mechanism of mesoporous silicas.     

Adsorption of duplex DNA on mesoporous silicas: possibility of inclusion of DNA into their mesopores

It is well known that a silica surface cannot adsorb duplex DNA in common aqueous solution (not chaotropic solution) because of the electrostatic repulsion of the silica surface and polyanionic DNA. However, we recently found that when duplex DNA in phosphoric acid form (or in acidic solution) was used, DNA was successfully adsorbed into mesoporous silicas even in low-salt aqueous solution. The adsorption behaviors of DNA into mesoporous silicas were influenced by the pore diameter sizes. Mesoporous silicas with 2.80- or 3.82-nm peak pore diameters adsorbed DNA the best in diluted NaCl solution. Formation of the hydrogen bond between P(O)OH groups in DNA and adsorbed water, SiOH groups, or both on silica surfaces is regarded as a main factor in this adsorption. The coincidence of the pore sizes and DNA diameter realizes this unique adsorption promoted by the effect of encompassing DNA with the inner surface of mesoporous silica. Although there is no clear direct evidence for including duplex DNA in the mesopores yet, this adsorption technique is expected to provide a new tool for DNA science, because DNA in the pore size 2-5 nm in diameter has to be in unusual disentangled thread form.     

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20–30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous–macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.     

Control of pore size distribution of silica gel through sol-gel process using inorganic salts and surfactants as additives

For control of the pore size distribution of silica gel, the gel was prepared using the sol-gel process modified by adding several kinds of inorganic salts and surfactants. The addition of any inorganic salt decreased the gel surface area and depressed the formation of mesopores. The surface area and the volume occupied by mesopores changed with the valency of the cation of the salt used. When surfactants were employed as additives, the surface area and the pore size distribution were greatly dependent on the kind of head group of the surfactant: non-ionic surfactant addition monotonously increased the surface area owing to the formation of larger mesopores; anionic surfactant addition significantly decreased the surface area because of the decrease in the volume of mesopores; cationic surfactants caused the surface area to decrease with small additions as anionic surfactants did, while further addition raised the surface area. The rise in the surface area was due to a marked formation of smaller mesopores. These results are discussed on the basis of the interfacial properties of the additives.     

2-Mercaptothiazoline modified mesoporous silica for mercury removal from aqueous media

Mesoporous silicas (SBA-15 and MCM-41) have been functionalized by two different methods. Using the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the mesoporous silica surface to give the chlorinated mesoporous silica Cl-SBA-15 or Cl-MCM-41. In a second step a multifunctionalized N, S donor compound (2-mercaptothiazoline, MTZ) was incorporated to obtain the functionalized silicas denoted as MTZ-SBA-15-Het or MTZ-MCM-41-Het. Using the homogeneous route, the functionalization was achieved via the one step reaction of the mesoporous silica with an organic ligand containing the chelating functions, to give the modified mesoporous silicas denoted as MTZ-SBA-15-Hom or MTZ-MCM-41-Hom. The functionalized mesoporous silicas were employed as adsorbents for the regeneration of aqueous solutions contaminated with Hg (II) at room temperature. SBA-15 and MCM-41 functionalized with MTZ by the homogeneous method present good mercury adsorption values (1.10 and 0.7mmolHg (II)/g of silica, respectively). This fact suggests a better applicability of such mesoporous silica supports to extract Hg (II) from aqueous solutions. In addition, it was observed the existence of a correlation between mercury adsorption with pore size and volume since, SBA-15 with lower areas and higher pore sizes functionalized with sterically demanding ligands, show better adsorption capacities than functionalized MCM-41.     

Grafting fluorescence molecules into the pore surface of bimodal mesoporous silicas with different routes

Novel luminescent hybrid silicas have been synthesized through one-step and two-step methods and their different luminescent properties have been investigated. The results showed that the samples synthesized with two-step procedure exhibited a more evident blue shift of photoluminescence performance resulting from the high efficiency of surface amine than that by one-step route. The structure characteristic and texture properties of resultant hybrid silicas were characterized by XRD, TEM, FT-IR and N₂ adsorption-desorption techniques, indicating that inorganic/organic nanocomposites could maintain the bimodal mesoporous structure. Finally, a possible involved mechanism has been put forward.     

The effect of ormosil nano-particles on the toughness of a polyester resin

Organic–inorganic hybrid nano-particles have been synthesized via a modified Stöber method. Nano-particles have been prepared from silica precursors with different organic functionalities. Methyl, ethyl, vinyl and phenyl modified silicas have been synthesized with a view to using these particles as modifiers for polymers and polymer matrix composites. Nano-composites have been produced using polyester as a matrix. The effect of the nano-particles on the toughness of the polyester has been investigated and it is shown that the incorporation of nano-particles leads to an improvement in toughness. For the methyl, ethyl and vinyl ormosils (organically modified silicas) the improvement is minor. The phenyl ormosil gives a greater improvement. This is attributed to different toughening mechanisms.     

Mesoporous silica with controlled porous structure and regular morphology

A new procedure for the synthesis of mesoporous silica with controlled porous structure and regular morphology was developed. It is based on the precipitation from a homogeneous environment using cetyltrimethylammonium bromide as a structure directing agent. The decrease in pH, which causes the formation of solid particles, is achieved by the hydrolysis of ethyl acetate. The procedure enables to obtain not only the MCM-41 mesoporous molecular sieve with a very high degree of pore ordering and phase purity, but also materials of a new type, viz. bimodal silicas containing both the MCM-41 mesopore system with a pore size of about 3 nm and a system of larger mesopores with sizes ranging from 10 to 30 nm. Owing to their structural properties and regular worm-like morphology, bimodal silicas are promising materials for applications in separation processes or as supports for bulky molecules or nanoparticles.     

Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.     

Microstructural studies of the interactions in SB rubber and mesoporous silica mixtures

Precipitated silicas have been utilized successfully as rubber reinforcing fillers instead of carbon black. The development of new mesoporous silicas with properties different than the precipitated silicas, specially their high BET surface areas and their organized pore structures with pore sizes between 1.5–10 nm, make them potential materials in rubber reinforcing. The knowledge of the interactions between rubber and its filler at a fundamental level is important to understand the physical and mechanical properties of a filled rubber system. This paper presents a comparative microstructural analysis of the interactions of the styrene butadiene rubber (SBR) with mesoporous silica and with Ultrasil VN3 silica, made on mixtures prepared in a rheometer at 150 °C and their toluene extracted residues. Solid state nuclear magnetic resonance, Fourier transform infrared (FTIR), thermogravimetry (TGA), scanning electron microscopy (SEM) and nitrogen adsorption isotherms, show a relation between the strength of the interaction and the particle size and pore structure characteristics of the mesoporous materials. Such a material prepared under certain specific conditions shows better interaction with the rubber than Ultrasil VN3 silica. Electronic Publication     

Recent progress in the synthesis and selected applications of MCM-41: a short review

Recent progress in the synthesis and applications of MCM-41 based mesoporous materials is reviewed. Since the independent discovery in the early 1990s by groups in the Japan and USA of the formation of mesostructured silica using surfactants as structure directing agents, a variety of alternative synthesis routes have been proposed. These include the use of ionic (both cationic and anionic) surfactants, neutral surfactants based on block and star diblock copolymers, non-surfactant organic compounds and the Stöber process for synthesizing silica spheres. The unique properties of MCM-41 based silica materials make them attractive candidates for applications in catalysis, production of novel materials by encapsulating metals, semiconductors and biofluids. Particular attention is given to the use of these composites in biotechnology including biosensors, biocatalysis and drug delivery.     

周期性介孔有机官能化氧化硅材料(PMOs)表面修饰的研究现状

综述了周期性介孔有机官能化氧化硅材料(PMOs)及其表面修饰的研究现状.PMOs的结构与性能取决于有机硅前驱体中有机桥联基团的种类.分布在骨架和孔道内的有机官能基团由于所处的环境以及基团种类的不同,将表现出不同的化学特性,从而赋予材料不同的化学和物理性能.所以近年来,国际上很多研究人员采用不同的官能团对PMOs的孔结构进行修饰,以期获得性能更为优异的新型介孔材料.     

以STAB和手性阴离子胶体制备介孔二氧化硅

以十八烷基三甲基溴化铵（STAB）为模板,手性阴离子小分子胶体为结构助剂,采用溶胶一凝胶法制备介孔二氧化硅纳米材料,通过改变胶体与STAB的摩尔比和搅拌速度控制介孔二氧化硅的形貌和孔结构,随着二者的摩尔比从0增加到0．032,其结构从具有螺旋孔道的纳米棒状变为具有同心环形孔道的纳米棒,同时表面逐渐出现层状孔道。另外,搅拌速度的增加有利于纳米棒的形成。     

Preparation of lamellar hybrid inorganic–organic films of layered titanate and cationic or anionic surfactants

Hybrid inorganic–organic films were fabricated from aqueous colloidal solutions of a layered titanate salt and cationic and anionic surfactants. Cetyltrimethylammonium bromide and dodecyl phosphate were used as cationic and anionic surfactants, respectively. When the substrates dip-coated with mixtures of the titanate salt colloids and the surfactants were treated with steam in a closed vessel, hybrid inorganic–organic films with a lamellar structure were fabricated. Although the titanate layers have a negative charge, the hybrid inorganic–organic films consisting of the titanate layer and the anionic surfactant could be obtained, as well as the ones including the cationic surfactants.     

Multiscale Phase Separations for Hierarchically Ordered Macro/Mesostructured Metal Oxides

Porous architectures play an important role in various applications of inorganic materials. Several attempts to develop mesoporous materials with controlled macrostructures have been reported, but they usually require complicated multiple‐step procedures, which limits their versatility and suitability for mass production. Here, a simple approach for controlling the macrostructures of mesoporous materials, without templates for the macropores, is reported. The controlled solvent evaporation induces both macrophase separation via spinodal decomposition and mesophase separation via block copolymer self‐assembly, leading to the formation of hierarchically porous metal oxides with periodic macro/mesostructures. In addition, using this method, macrostructures of mesoporous metal oxides are controlled into spheres and mesoporous powders containing isolated macropores. Nanocomputed tomography, focused ion beam milling, and electron microscopy confirm well‐defined macrostructures containing mesopores. Among the various porous structures, hierarchically macro/mesoporous metal oxide is employed as an anode material in lithium‐ion batteries. The present approach could provide a broad and easily accessible platform for the manufacturing of mesoporous inorganic materials with different macrostructures.