Better bioactive ceramics through sol-gel process

Bioactive glasses and glass ceramics need to be capable of growing a calcium phosphate layer at their surfaces in physiological environment in order to bond with living bone. Sol-gel prepared silica (silica gel) and titania (titania gel) are efficient calcium phosphate absorbents. Both gels extract calcium and phosphate from surrounding physiological and other calcium phosphate solutions and form a calcium phosphate at their surfaces in return. Thus, they can integrate with bone. Under the same condition, however, silica and titania, as both prepared through a conventional high temperature process, are unable to transfer calcium and phosphate from the solutions to obtain a calcium phosphate at their surfaces. Therefore, it is concluded that using inorganic or metal organic precursors, sol-gel process can yield bioactive materials with a high bioactivity.     

Synthesis and characterization of UV‐curable phosphorus containing hybrid materials prepared by sol–gel technique

In this study, a series of ultraviolet (UV)‐curable organic–inorganic hybrid coating materials containing phosphorus were prepared by sol–gel approach from acrylate end‐capped urethane resin, acrylated phenyl phosphine oxide oligomer (APPO), and inorganic precursors. TEOS and MAPTMS were used to obtain the silica network and Ti:acac complex was employed for the formation of the titania network in the hybrid coating systems. Coating performance of the hybrid coating materials applied on aluminum substrates was determined by the analysis techniques, such as hardness, gloss, impact strength, cross‐cut adhesion, taber abrasion resistance, which were accepted by international organization. Also, stress–strain test of the hybrids was carried out on the free films. These measurements showed that all the properties of the hybrids were enhanced effectively by gradual increase in sol–gel precursors and APPO oligomer content. The thermal behavior of the hybrid coatings was investigated by thermogravimetric analysis (TGA) analysis. The flame retardancy of the hybrid materials was examined by the limiting oxygen index (LOI); the LOI values of pure organic coating (BF) increased from 31 to 44 for the hybrid materials containing phosphorus (BF‐P:40/Si:10). The data from thermal analysis and LOI showed that the hybrid coating materials containing phosphorus have higher thermal stability and flame resistance properties than the organic polymer. Besides that, it was found that the double bond conversion values for the hybrid mixtures were adequate in order to form an organic matrix. The polycondensation reactions of TEOS and MAPTMS compounds were also investigated by ²⁹Si‐NMR spectroscopy. SEM studies of the hybrid coatings showed that silica/titania particles were homogenously dispersed through the organic matrix. In addition, it was determined that the hybrid material containing phosphorus and silica showed fibrillar structure. Copyright © 2009 John Wiley & Sons, Ltd.     

A general method for the synthesis of monodisperse hollow inorganic-organic hybrid microspheres with interior functionalized poly(methacrylic acid) shells

Hollow inorganic-organic hybrid microspheres, such as silica, titania, and zirconia, with interior poly(methacrylic acid) (PMAA) functionalized shell were synthesized by a general method containing a two-stage reaction. The hollow inorganic shell-layer with interior polymeric component was formed over the PMAA template during the second-stage controlled hydrolysis of inorganic precursors together with disintegration of PMAA cores and adhering to the interior wall of the silica during the drying process due to the capillary force as well as the competitive hydrogen bond interaction. In this process, PMAA microspheres were prepared by distillation precipitation polymerization of methacrylic acid (MAA) in acetonitrile as the first-stage reaction. The present work elaborately investigated the effects of the reaction conditions, including the amount of the tetraethyl orthosilicate (TEOS) precursors and the amount of ammonium hydroxide catalyst on the morphology and structure of the resultant hollow composite microspheres, which were characterized by transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption.     

Synthesis and characterization of new silica–titania mixed oxide in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide by sol–gel technique

Silica–titania mixed oxide were prepared by sol–gel method from tetraethylorthosilicate and titanium (IV) isopropoxide as precursors in the presence of room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [C₄MIm][NTf₂]. The effects of [C₄MIm][NTf₂] on the structural and textural characteristics of silica–titania matrix are investigated in this paper. The materials obtained were well characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis X-ray powder diffraction (XRPD), field emission scanning electron microscope (FESEM) and N₂ adsorption–desorption analysis. It is believed that the [C₄MIm][NTf₂] plays an important role as a template and the high surface area of the samples is thought to mainly attribute to the formation of microporous in the reaction. The synthesized materials showed the presence of C–N groups in the FTIR spectrum which indicates the presence of RTIL in the silica–titania matrix. XRPD, FESEM and N₂ adsorption–desorption analysis results indicated that the composite materials possessed good microporous character. The subsequent material displayed average pore diameter of 1.70–2.12 nm, pore volume of 0.08–0.19 cm³/g and BET surface area of 191–386 m²/g. Increasing the content of RTIL resulted in an increase of the average pore diameter of the silica–titania gel.     

Gelatine thin films as biomimetic surfaces for silica particles formation

The formation of silica nanostructures by several living organisms, such as diatoms or sponges, involves specific macromolecules that control the growth and the organization of silica nanoparticles. In order to investigate if a single molecular system could perform both particle size control and morphological template, gelatine thin films of various concentration and strength were prepared as biomimetic models and their reactivity towards sodium silicate aqueous solutions was studied. Simultaneous formation of silica particles in the nanometric and micrometric size range was observed. The former corresponds to colloids grown at the surface of the gelatine films and the latter to particles induced by gelatine chain brushes formed at the film/water interface. These results are in good agreement with well-known principles of biomineralization and suggest that multi-molecular systems, rather than single components, are responsible for biogenic silica nanostructure formation.     

Templated Synthesis of Nitrogen‐Enriched Nanoporous Carbon Materials from Porogenic Organic Precursors Prepared by ATRP

A facile templated synthesis of functional nanocarbon materials with well‐defined spherical mesopores is developed using all‐organic porogenic precursors comprised of hairy nanoparticles with nitrogen‐rich polyacrylonitrile shells grafted from sacrificial cross‐linked poly(methyl methacrylate) cores (xPMMA‐g‐PAN). Such shape‐persistent all‐organic nanostructured precursors, prepared using atom transfer radical polymerization (ATRP), assure robust formation of template nanostructures with continuous PAN precursor matrix over wide range of compositions, and allow for removal of the sacrificial template through simple thermal decomposition. Carbon materials prepared using this method combine nitrogen enrichment with hierarchical nanostructure comprised of microporous carbon matrix interspersed with mesopores originating from sacrificial xPMMA cores, and thus perform well as CO₂ adsorbents and as supercapacitor electrodes.     

General and Facile Syntheses of Metal Silicate Porous Hollow Nanostructures

Porous hollow nanostructures have attracted intensive interest owing to their unique structure and promising applications in various fields. A facile hydrothermal synthesis has been developed to prepare porous hollow nanostructures of silicate materials through a sacrificial‐templating process. The key factors, such as the concentration of the free metal cation and the alkalinity of the solution, are discussed. Porous hollow nanostructures of magnesium silicate, nickel silicate, and iron silicate have been successfully prepared by using SiO₂ spheres as the template, as well as a silicon source. Several yolk–shell structures have also been fabricated by a similar process that uses silica‐coated composite particles as a template. As‐prepared mesoporous magnesium silicate hollow spheres showed an excellent ability to remove Pb²⁺ ions in water treatment owing to their large specific surface and unique structures.     

柔软的球状和长方体状氧化硅中空结构的制备研究

采用自组装形成的芘纳米结构作为模板,成功地制备了柔软的球状和长方体状氧化硅中空结构.当不同量的芘在十六烷基三甲基溴化铵(CTAB)溶液中自组装时,产生的自组装结构展现出明显的从球状到长方体状的形貌变化.这些结构被用作氧化硅前驱体溶胶-凝胶反应的模板,获得了球状和长方体状氧化硅/芘复合结构.通过乙醇除去模板后,生成了柔软的球状(直径约为400nm)和长方体状(长为0.5—2.5μm)的氧化硅中空结构.这些结果展现了采用有机纳米结构作为模板来合成无机中空结构的优势:合成简便、结构多样以及结构形貌的灵活可控.     

硫和银共掺杂介孔TiO2的制备表征及光催化活性

以P123为模板,以钛酸四正丁酯、硝酸银和硫脲为原料采用模板法制备了一系列硫和银共掺杂介孔TiO2光催化材料。利用扫描电子显微镜（SEM）、X射线衍射（XRD）、BET和紫外-可见光谱（UV-Vis）等技术对其形貌、晶体结构及表面结构、光吸收特性等进行了表征。以甲基橙溶液的光催化降解为模型反应, 考察了不同掺杂量的样品在紫外和可见光下的光催化性能。结果表明：用模板法制备的共掺杂介孔TiO2光催化材料在紫外和可见光条件下较纯介孔TiO2和单掺杂介孔TiO2对甲基橙溶液具有更好的光催化降解效果, 且硫和银的掺杂量及样品焙烧温度显著影响该材料的催化性能。当硫掺杂量为2%（mol）和银掺杂量为1%（mol）,在500℃焙烧2 h所得光催化材料的催化性能最佳, 4 h即可使甲基橙的降解率达98.8%,重复使用4次仍可使甲基橙的降解率保持在87.5%以上。因此, 以该模板合成法, 通过硫和银的共掺杂有望使TiO2成为一种低或无能耗、高活性的绿色环保型催化材料。     

A New Synthetic Route to Microporous Silica with Well‐Defined Pores by Replication of a Metal–Organic Framework

Microporous amorphous hydrophobic silica materials with well‐defined pores were synthesized by replication of the metal–organic framework (MOF) [Cu₃(1,3,5‐benzenetricarboxylate)₂] (HKUST‐1). The silica replicas were obtained by using tetramethoxysilane or tetraethoxysilane as silica precursors and have a micro–meso binary pore system. The BET surface area, the micropore volume, and the mesopore volume of the silica replica, obtained by means of hydrothermal treatment at 423 K with tetraethoxysilane, are 620 m²g^?1, 0.18 mL g^?1, and 0.55 mL g^?1, respectively. Interestingly, the silica has micropores with a pore size of 0.55 nm that corresponds to the pore‐wall thickness of the template MOF. The silica replica is hydrophobic, as confirmed by adsorption analyses, although the replica has a certain amount of silanol groups. This hydrophobicity is due to the unique condensation environment of the silica precursors in the template MOF.     

Silica-based mesoporous organic-inorganic hybrid materials

Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.     

Syntheses of spherical silica and titania from alkoxides on a laboratory scale

Summary A process to synthesize silica and titania as spherical packing materials has been investigated on the laboratory scale by the sol-gel method. The silica and titania obtained were tested under normal-phase separation conditions for comparison of their retention characteristics silica witha a commercial. The silica was found to be similar in its retention behaviour to the commercial silica. The titania showed basic properties and strongly retained acidic compounds.     

原位自组装形成二氧化硅/十六烷基三甲基溴化铵纳米网络粒子

提出了以具有纳米尺寸孔径及孔壁厚度的MCM 48作为无机基体、以无机 有机原位自组装的方法形成纳米网络粒子 .研究结果表明 ,在一定实验条件下 ,有机相可进入无机相的三维孔道自组装形成立方有序结构的纳米网络复合粒子 .通过研究纳米网络粒子在极性介质和非极性介质中的分散发现 ,有机相的存在有利于纳米网络粒子的分散     

无机材料的仿生合成

生物矿化重要的特征之一是细胞分泌的有机基质调制无机矿物的成核和生长, 形成具有特殊组装方式和多级结构特点的生物矿化材料(如骨、牙和贝壳)。仿生合成就是将生物矿化的机理引入无机材料合成, 以有机物的组装体为模板, 去控制无机物的形成,制备具有独特显微结构特点的无机材料, 使材料具有优异的物理和化学性能。仿生合成已成为无机材料化学的研究前沿。本文综述了无机材料仿生合成的发展现状。     

Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts

In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer. The resulting materials are active oxidation and hydrogenation catalysts. The effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.     

Controlled synthesis of nanostructured silica-based materials from designed alkoxysilanes

Recent progress in the synthesis of nanostructured silica-based materials through the self-assembly process using well-designed alkoxysilane precursors is presented. Alkoxysilanes with covalently attached hydrophobic organic tails become amphiphilic when hydrolyzed to form silanol groups, leading to the formation of various mesostructures upon evaporation of solvents. The precursors having large oligosiloxane heads are particularly important because of their ability to form cylindrical assemblies, providing a direct pathway to ordered porous silica by removal of the organic groups. Our recent research includes (i) templated-synthesis of hierarchically ordered structures and (ii) design of molecules having chemically cleavable bonds to generate pores without calcination.     

Coated gas bubbles for the continuous synthesis of hollow inorganic particles

We present a microfluidic approach for the controlled encapsulation of individual gas bubbles in micrometer-diameter aqueous droplets with high gas volume fractions and demonstrate this approach to making a liquid shell, which serves as a template for the synthesis of hollow inorganic particles. In particular, we find that an increase in the viscosity of the aqueous phase facilitates the encapsulation of individual gas bubbles in an aqueous droplet and allows control of the thickness of a thin aqueous shell. Furthermore, because such droplets contain a finite amount of water, uncontrolled hydrolysis reactions between reactive inorganic precursors and bulk water can be avoided. We demonstrate this approach by introducing reactive inorganic precursors, such as silane and titanium butoxide, for sol-gel reactions downstream from the formation of the bubble in a droplet and consequently fabricate hollow particles of silica or titania in one continuous flow process. These approaches provide a route to controlling double-emulsion-type gas-liquid microstructures and offer a new fabrication method for thin-shell-covered microbubbles and hollow microparticles.     

Surfactant-mediated self-assembly of Au nanoparticles and their related conversion to complex mesoporous structures

In this work, we report a hydrothermal method for self-assembly and organization of as-synthesized gold nanoparticles into various aggregative morphologies. Using the assembled gold nanoparticles as structural precursors, furthermore, mesoporous gold spheres in either discrete or interconnected form can be prepared at higher process temperatures through removal of bidentate organic linker molecules. Excellent product controllability and high morphological yield have been achieved via tuning preparative parameters. Our preliminary investigations also show that the assembled gold nanoparticles and nanostructures can be used as building blocks for construction of three-dimensional networks as well as for fabrication of two-dimensional porous thin films. The present work confirms our earlier prediction that Ostwald ripening may also be operative for pre-organized organic capped nanocrystallites in producing hollow structures.     

Morphology and dispersion control of titania–silica monolith with macro–meso pore system

Macroporous gels with bicontinuous morphology in micrometer range were prepared in a titania?Csilica system containing 5 and 7.6 mass?% titania using tetraethoxysilane and four kinds of Ti precursors, two titanium alkoxides, titanium chloride and titanium sulfate, under coexistence of poly(ethylene glycol) (PEG) with an average molecular weight of 20,000. In all the systems with different Ti precursors, the addition of PEG induced phase separation, and the macroporous morphology was formed when the transitional structure of phase separation was frozen-in by sol?Cgel transition of inorganic components. However, we can see large differences in phase separation tendency and Ti dispersion in silica network depending on the Ti precursors used. When titanium alkoxides were added into pure silica sol?Cgel system, phase separation tendency largely decreased, so that low temperature reaction was necessary for macropore formation. When we used titanium salts, on the other hand, phase separation tendency does not change much from pure silica system. The difference has been tentatively attributed to the difference in the mixing level of Ti in silica network. Although titania tended to aggregate when titanium alkoxides were used as precursors, Ti could be well dispersed in silica gel matrix when acetylacetone was added in the alkoxide system or when titanium salts were used as Ti precursors.     

模板法制备复合中空微球

本文报道以一种商品化的聚苯乙烯中空球为模板, 采用溶胀聚合技术合成了具有IPN(Inter-Penetrating Network)结构的复合中空球; 对其中的一种高分子网络进行化学改性引入所需官能团, 制得带有羧基的聚合物凝胶中空球; 利用凝胶诱导生长特性, 成功制得聚合物复合中空球. 此方法无需去除模板就可批量制备各种复合功能中空球.