Preparation of a colloidal array of NaTaO3 nanoparticles via a confined space synthesis route and its photocatalytic application

The confined space synthesis method has been applied to the preparation of sodium tantalate (NaTaO(3)); hydrothermal reaction of NaOH and Ta(2)O(5) was carried out in the pores of a three-dimensional mesoporous carbon, which was replicated by the colloidal array of silica nanospheres (SNSs) 20 nm in size. This approach led to the formation of a colloidal array of NaTaO(3) nanoparticles 20 nm in size with a surface area of 34 m(2) g(-1). The photocatalytic performance of the colloidal array of NaTaO(3) nanoparticles for overall water splitting under UV irradiation (λ > 200 nm) was evaluated after loading a NiO cocatalyst onto NaTaO(3) samples. The NiO-loaded NaTaO(3) nanoparticles showed photocatalytic activity for overall water splitting more than three times as high as non-structured bulk NaTaO(3) particles.     

Chemical modification of colloidal masks for nanolithography

A method is presented to tune the holes in colloidal masks used for nanolithography. Using a simple wet-chemical method, a thin layer of silica is grown on masks of silica particles. The size of the holes is controlled by the amount of tetraethoxysilane (TEOS) added. More accurate tuning of the hole size is possible in the presence of a calibrated seed dispersion of silica colloids. We demonstrate modified masks that were used to create arrays of metal nanoparticles with a size ranging from 400 nm, for unmodified masks, down to tens of nanometers. The method is easy-to-use, fast, and inexpensive.     

Tailored core-shell-shell nanostructures: sandwiching gold nanoparticles between silica cores and tunable silica shells

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.     

Effects of pH on mechanical and morphological studies of silica filled polyvinyl chloride-50% epoxidized natural rubber (PVC-ENR50) nanocomposite

Effects of pH on mechanical properties as well as morphological studies of sol–gel derived in situ silica in polyvinyl chloride-50% epoxidized natural rubber (PVC-ENR50) nanocomposites are reported. In particular, a range of acid concentrations was investigated. These nanocomposites were prepared by solution casting technique and tetraethoxysilane (TEOS) was used as the silica precursor. The prepared nanocomposites were characterized using tensile test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tensile test indicated that the highest mechanical strength was at 30% TEOS added for the nanocomposite prepared at pH 2.0. At pH 1.0 and 1.5 the maximum tensile strength reading was at 20% TEOS added with value of 24.3 and 24.5 MPa, respectively. SEM and TEM revealed the dispersion of silica particles in the polymer matrix. For nanocomposites prepared at pH 1.0 and 1.5, the silica particles were finely dispersed with the average size of 60 nm until 20% TEOS added. Meanwhile for nanocomposite prepared at pH 2.0, silica particles were homogenously distributed in the polymer matrix with average diameter of 30 nm until 30% TEOS and agglomerated after 30% TEOS loading.     

Management of both toughness and stiffness of polypropylene nanocomposites using poly(5‐hexen‐1‐ol‐co‐propylene) and silica nanospheres

We developed novel polypropylene (PP)/silica nanocomposites using PP and silica nanospheres (SNSs) combined with poly(5‐hexen‐1‐ol‐co‐propylene) (PPOH), which is a functionalized PP containing hydroxyl groups that was assumed to play a role as not only an elastomer but also an interface modifier. Since the affinity between the PP matrix and silica filler was expected to be improved by blending with PPOH, its influence on the mechanical properties, structure, and toughness of the ternary composites was examined in detail to provide a better understanding of the role of the matrix‐filler affinity on the mechanical properties. The dispersity of the SNSs in the fabricated PP/PPOH/SNS nanocomposite was improved by increasing the hydroxyl group content of PPOH due to the enhanced affinity between PPOH and the SNSs. The SNSs in the composite with PPOH containing 6.4 mol% hydroxyl groups (PPOH6.4) were almost dispersed in the microscale domain, while the SNSs in the composite with 1.3 mol% hydroxy groups (PPOH1.3) were considerably aggregated. The toughness of the nanocomposite was noticeably improved by blending PPOH6.4 without a significant loss of stiffness. In contrast, the toughness was hardly improved using PPOH1.3. Therefore, both the fine dispersion of the SNSs and the excellent affinity between PPOH6.4 and the SNSs contributed to the good balance of toughness and stiffness of the PP/PPOH/SNS nanocomposite.     

Double function of tris(hydroxymethyl)aminomethane (THAM) for the preparation of colloidal silica nanospheres and the conversion to ordered mesoporous carbon

Tris(hydroxymethyl)aminomethane (THAM) has been found to be an excellent catalyst for the preparation of colloidal silica nanospheres around 10 to 20 nm in size, and THAM on the surfaces of nanospheres is an efficient carbon source for the synthesis of highly ordered mesoporous carbon with controlled pore size by using closely packed nanospheres as a porogen.     

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.     

Effect of synthesis conditions on the mesoscopical order of mesoporous silica SBA-15 functionalized by amino groups

Mesoporous amine-functionalized SBA-15 silica has been synthesized directly by the co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyl-trimethoxysilane (APTMS) under acidic conditions with an APTMS/(APTMS + TEOS) molar ratio of 10%. The effect of synthesis conditions, including TEOS pre-hydrolysis, as well as the heating temperature and time, on the mesoscopical order and pore structure of the functionalized SBA-15 have been studied in detail by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, infrared spectra and solid state ²⁹Si nuclear magnetic resonance. A functionalized SBA-15 silica with a highly ordered two-dimensional P6 mm hexagonal symmetry and a narrow pore size distribution centered at 6 nm can be obtained if TEOS is allowed to pre-hydrolyze for 2 h. For the sample with TEOS pre-hydrolysis time of 4 h, aging at 50°C or 150°C leads to a more ordered pore arrangement compared to 100°C and also a narrower pore size distribution with larger pore volume. Increasing aging time is in favor of the formation of mesoscopically ordered structure, but fails to obtain a superior pore structure.     

A novel method for synthesis of silica nanoparticles

A sequential method has been used, for the first time, to prepare monodisperse and uniform-size silica nanoparticles using ultrasonication by sol-gel process. The silica particles were obtained by hydrolysis of tetraethyl orthosilicate (TEOS) in ethanol medium and a detailed study was carried out on the effect of different reagents on particle sizes. Various-sized particles in the range 20-460 nm were synthesized. The reagents ammonia (2.8-28 mol L(-1)), ethanol (1-8 mol L(-1)), water (3-14 mol L(-1)), and TEOS (0.012-0.12 mol L(-1)) were used and particle size was examined under scanning electron microscopy and transmission electron microscopy. In addition to the above observations, the effect of temperature on particle size was studied. The results obtained in the present study are in agreement with the results observed for the electronic absorption behavior of silica particles, which was measured by UV-vis spectrophotometry.     

Synthesis of spherical submicron-sized magnetite/silica nanocomposite particles

This paper describes a method for fabricating spherical submicron-sized silica particles that contained magnetite nanoparticles (magnetite/silica composite particles). The magnetite nanoparticles with a size of ca. 10 nm were prepared according to the Massart method, and were surface-modified with carboxyethylsilanetriol. The fabrication of magnetite/silica composite particles was performed in water/ethanol solution of tetraethoxyorthosilicate with ammonia catalyst in the presence of the surface-modified magnetite nanoparticles. The magnetite/silica composite particles with a size of ca. 100 nm were successfully prepared at 0.05 M TEOS, 15 M water, and 0.8 M ammonia with injection of the magnetite nanoparticle colloid at 2 min after the initiation of hydrolysis reaction of TEOS. Magnetite concentration in the composite particles could be raised to 17.3 wt.% by adjustment of the injected amount of the magnetite colloid, which brought about the saturation magnetization of 7.5 emu/g for the magnetite/silica composite particles.     

Facile synthesis of mesoporous silica nanoparticles with controlled morphologies using water–acetone media

Mesoporous silica nanoparticles with controlled morphologies including nanococoons, nanorods and nanospheres have been synthesized in water–acetone media at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained nanoparticles generally show hexagonal-like mesoporous structures with average pore size ranging from 2.7 to 3.3 nm and surface area from 806 to 1055 m²/g, respectively. It was found that the changes in water-to-acetone molar ratios have a dramatic impact on the morphologies of the mesoporous silica with different surface roughness, probably due to the solvent influence on the rate of the hydrolysis of tetraethoxy silane (TEOS) and the polymerization of inorganic species. Interestingly, the morphology of the mesoporous silica products can be controlled in shape from nanococoons to nanorods to nanospheres just by decreasing the water-to-acetone molar ratio from 75 to 30 to 15, respectively. From transmission electron microscopy (TEM) images, it was observed that mesoporous parallel channels run along the short axis in some areas in the nanorods, whereas the radially arranged mesopore channels are present in the nanospheres. Additionally, hydrothermal treatment leads to rougher surfaces while retaining the morphologies and nanostructures of these mesoporous silicas.     

Ultrafast enzyme immobilization over large-pore nanoscale mesoporous silica particles

By finely tuning the TEOS/P123 molar ratio of the octane/water/P123/TEOS quadruple emulsion system and by controlling the synthesis conditions, an ultrafine emulsion system was isolated, under the confinement of which, nanoscale silica particles with ordered large mesopores (approximately 13 nm) have been successfully constructed; the obtained mesoporous silica particles have an unusual ultrafast enzyme adsorption speed and the amount of enzyme that can be immobilized is larger than that of conventional mesoporous silica, which has potential applications in the fast separation of biomolecules.     

Preparation and characterization of composites built of poly(N-benzophenoyl methacrylamide-co-N-hydroxyethyl acrylamide) cores and silica raspberry-like shells with dual orthogonal functionality

The design and fabrication of novel poly(N-benzophenoyl methacrylamide-co-N-hydroxyethyl acrylamide)@SiO(2) composites are reported herein. These core-shell composites demonstrate orthogonal functionality, composed of photoreactive cores, containing a benzophenone (BPh) moiety and silica (SiO(2)) shells, enabling the utilization of the free hydroxyl groups via silane-based chemistry. The co-polymer cores, which are 1.28μm in diameter, are first obtained by dispersion polymerization of photoreactive (N-benzophenoyl methacrylamide) (polyBPMA) and N-Hydroxyethyl acrylamide (HEAA). Next, silica seeds with a 42nm diameter are deposited onto the surfaces as a result of the hydrolysis and the condensation of tetraethyl orthosilicate (TEOS) in a basic condition. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), UV-spectrophotometry, X-ray photoelectron spectroscopy (XPS), and ζ-potential measurements were used to characterize the composites. The morphology and surface smoothness of the deposited silica nanoparticles (NPs) were found to strongly depend on a number of parameters such as the pH value of the medium, TEOS concentration, and the temperature.     

Facile preparation of highly monodisperse small silica spheres (15 to >200 nm) suitable for colloidal templating and formation of ordered arrays

Highly monodisperse spherical silica nanoparticles with diameters ranging from ca. 15 to 200 nm were prepared using an environmentally friendly water-based synthesis. The size of the spheres can be precisely controlled by using a facile regrowth procedure in the same reaction media. Furthermore, these monodisperse silica spheres can be successfully used as seeds in the well-established St?ber silica preparation. The regrowth approach allows for easy incorporation of functional additives. High monodispersity and charge stabilization renders these nanoparticles highly suitable for close-packed array formation and colloidal templating.     

Synthesis of nanoporous graphite-derived carbon-silica composites by a mechanochemical intercalation approach

A mechanochemical intercalation approach which applies a simple mechanical milling to induce intercalation reaction was applied to introduce controlled amount of tetraethoxylsilane (TEOS) into surfactant-preexpanded graphite oxide, and the relationships between the intercalation structure, the porosities of the calcined products, and the Si addition were examined. It was found that a small added amount of TEOS produced a more expanded ordered layer structure with the interlayer distance and silicon content increasing with the amount of TEOS added, although a large amount of added TEOS easily induces layer delamination, resulting in a less ordered structure. The silica structure in the composite is changed from a disordered structure having enhanced bond strain to a condensed silica network when the amount of TEOS added increases. The porosities of the final calcined samples increase with the increase of silicon content but then decrease slightly after reaching a maximum where silicon content starts to become constant, indicating that both silicon content and the composition state of silica particles and carbon layers play important roles in porosity formation.     

CdSe/CdS/SiO2复合纳米球的制备及发光性能

采用两相法合成了CdSe/CdS核-壳结构的量子点, 用氨水催化水解正硅酸乙酯制得复合结构的CdSe/CdS/SiO₂发光纳米球. 通过对量子点用量、氨水用量、反应时间及溶剂比例等实验条件的调节, 得到了单分散性较好, 尺寸在23~145 nm的复合发光纳米球. 利用紫外-可见吸收光谱和荧光发射光谱对其发光性能进行了研究, 同时利用透射电镜(TEM)观察复合纳米球的形貌. 结果表明, 复合发光纳米球样品的最高荧光量子产率可达8%.     

A "teardown" method to create large mesotunnels on the pore walls of ordered mesoporous silica

A "teardown" method to create large mesotunnels (approximately 9 nm) on the pore walls of ordered mesoporous silicas is demonstrated by digesting the organic constituents from polymer-silicate nanocomposites. The ordered mesostructured polymer-silicate composites were first obtained via the evaporation-induced triconstituent co-assembly method by using a low-molecular-weight phenolic resin (resols) as an organic precursor; prehydrolyzed TEOS as an inorganic precursor, and triblock copolymer F127 as a template. All of organic components including F127 and phenolic resins are removed by the microwave digestion (MWD) method from mesostructured polymer-silica composites. While the removal of triblock copolymer F127 generates main pore channels, the phenolic resins can also be torn down from the pore walls, yielding mesotunnels between the channels. The resulting silica products exhibit ordered 2-D hexagonal mesostructure, large pore volume (up to 1.92 cm(3)/g), and very large pore size (up to 22.9 nm), which is even larger than their mesostructural cell parameter (14.2 nm). TEM images confirm the existence of mesotunnels on the silica pore walls. FT-IR and (29)Si solid-state NMR results reveal that these silica products have a large number of silanol groups.     

Preparation of “Green” Composites by the Sol-Gel Process: In Situ Silica Filled Natural Rubber

“Green” composites with different amounts of in situ silica nano-particles were prepared by a sol-gel reaction of tetraethoxysilane (TEOS) in natural rubber (NR). The control of swelling degree of TEOS in NR and concentration of n-butylamine in water was useful to change the amount of generated in situ silica in the uncured NR matrix. In situ silica up to 42 parts per hundred rubber by weight (phr) was successfully filled in the NR matrix. The particle size of in situ silica became larger with the increase of silica content from ca. 10 nm to ca. 40 nm for 10 phr--40 phr loadings in the NR matrix, respectively. Even when the amount of in situ silica content was high, the dispersion of in situ silica particles was more homogeneous than that of commercial silica (VN-3). The reinforcement effect of the in situ silica for NR vulcanizates increased with increasing the in situ silica content.     

一种可精确控制粒径的SiO2微球合成方法

用改进的种子法合成SiO2微球. 微球生长过程中连续缓慢添加正硅酸乙酯,使用动态光散射法实时监控微球粒径的增长过程,调节正硅酸乙酯的添加,实现对粒径的精确控制. 为制备禁带位置位于1000 nm 的光子晶体,合成粒径为446 nm的SiO2微球,微球粒径在4 h内从193 nm 增长到446 nm,远远快于传统种子法,微球粒径与目标粒径偏差为±5 nm. 制得的SiO2微球被组装为光子晶体,其禁带位置恰好位于1000 nm.     

Seed polymerization of tetraethyl orthosilicate in the presence of colloidal silica spheres

Kinetic analyses were made for the seed polymerization of tetraethyl orthosilicate (TEOS) in the presence of colloidal silica sphere seeds by turbidity and dynamic light scattering (DLS) measurements. Transmission electron microscopy (TEM) of the spheres formed was also used. TEOS is polymerized exclusively on the surfaces of the seed spheres, their sizes ranging from 29 to 184 nm in diameter. The sphere size versus time and the cube root of the absorbance versus time from DLS and turbidity measurements agree well, especially in the beginning of the reaction. The seed polymerization starts immediately on the addition of seed spheres, though the polymerization in the absence of the seeds proceeds after a certain induction time ranging several tens of seconds to several minutes. The polymerization rates of the reaction increase when the size and/or the concentration of the seed spheres increases. The thickness of the TEOS layers formed on the seed surfaces increases as the seed size increases; this is confirmed by the TEM pictures. These results are consistent with the polymerization mechanism of the formation of small preliminary particles followed by their coalescence on the surfaces of seeds to the final large spheres coated with silica layers. Received: 25 January 2001 Accepted: 30 May 2001