Ultralow temperature synthesis of ordered hexagonal smaller supermicroporous silica using semifluorinated surfactants as template

Synthesis and Shape-Selective Catalytic Application of Ordered Cubic Ia3̅d Supermicroporous Materials Templated by Rosin-Derived Quaternary Ammonium Salt with a Hydroxyl Radical in the Headgroup

We described the comprehensive synthesis, characterization, and catalytic performance of a novel type of the ordered cubic Ia3̅d supermicroporous silicas by using tetraethyl orthosilicate as a silicon source and a hydroxyl-functionalized quaternary ammonium salt as a template under alkali conditions. The effects of various reaction conditions on the pore structure and morphology of the silica materials were thoroughly investigated. Our results showed that under a wide range of reaction conditions, supermicroporous silicas with a highly ordered cubic Ia3̅d structure can be produced with a large BET specific surface area of 1741 m²/g, high pore volume of 0.91 cm³/g, concentrated pore size at 19.1 Å, and crystalline morphology. After Al doping, the obtained aluminosilicates preserved a highly ordered cubic supermicroporous structure. By using the H-form aluminosilicates as catalysts, we selectively dimerized β-pinene. The catalysts exhibited an excellent catalytic activity for β-pinene dimerization with a conversion yield up to 100%. Compared with conventional mesoporous H-form Al-MCM-48 catalysts, the prepared supermicroporous catalysts exhibited superior catalytic performance due to their excellent shape-selective properties, producing the β-pinene dimer in a yield up to 72.4% with dimer/oligomer ratios in the range of 7.5-10.1. This study featured a detailed preparation and characterization of supermicroporous silica with novel microstructures and showed its utility in catalytic dimerization.

Ordered lamellar supermicroporous titania templating by rosin-derived quaternary ammonium salt

By using dehydroabietyltrimethyl ammonium bromine (DTAB), a novel rosin-derived quaternary ammonium salt, as template and peroxotitanium acid as precursor, ordered lamellar supermicroporous titania has been synthesized via a hydrothermal process. The template agent:titanium source molar ratio in the synthesis system and the hydrothermal temperature have great impact on the microstructure characteristics of the samples. The increase of DTAB:TiO₂ molar ratio from 0.04:1 to 0.10:1 is favorable to the increase of regularity of pore structures, but has no significant effects on the crystalline structures. The increase of the hydrothermal temperature from 343 to 393 K can induce an increase in crystallinity of the samples. However, the exorbitant hydrothermal temperature will reduce the regularity of pore structures. When the mole ratio of DTAB:TiO₂ is 0.10:1 and the hydrothermal temperature is 373 K, the as-synthesized sample possesses pore structure with the highest level of long-range order, as well as pore wall with semicrystallized anatase phase. The pore size and the pore wall thickness are about 2.0 nm and 1.0 nm, respectively.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

A comprehensive review of the recent progress in the applications of hierarchically structured porous materials is given.

Synthesis of ordered porous SiO2 with pores on the border between the micropore and mesopore regions using rosin-based quaternary ammonium salt

Ordered hexagonal supermicroporous silica with nanosheet morphology has been synthesized with a type of rosin-based quaternary ammonium salt.

An economic method for synthesis of highly ordered porous silica

We report an economic method for synthesis of highly ordered silica with a mixing surfactant system containing short-chain cationic surfactant (decyltrimethyl ammonium bromide, denoted C10TMAB) and short-chain anionic surfactant (sodium octyl sulfate, denoted SOS) as the templating agents. Highly ordered supermicroporous silica was synthesized by judiciously chosen mixing ratio of surfactants. The samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The results showed that the pore structure of the resulting silica belongs to the two-dimensional hexagonal structure (space group 2D-p6mm) with a pore size of ca. 2.2nm. Moreover, the method proposed herein is expected to facilitate the synthesis of not only porous silicas but also materials with other framework compositions.

Microstructure investigation on micropore formation in microporous silica materials prepared via a catalytic sol-gel process by small angle X-ray scattering

The so-called sol-gel technique has been shown to be a template-free, efficient way to create functional porous silica materials having uniform micropores. This appears to be closely linked with a postulation that the formation of weakly branched polymer-like aggregates in a precursor solution is a key to the uniform micropore generation. However, how such a polymer-like structure can precisely be controlled, and further, how the generated low-fractal dimension solution structure is imprinted on the solid silica materials still remain elusive. Here we present fabrication of microporous silica from tetramethyl orthosilicate (TMOS) using a recently developed catalytic sol-gel process based on a nonionic hydroxyacetone (HA) catalyst. Small angle X-ray scattering (SAXS), nitrogen adsorption porosimetry, and transmission electron microscope (TEM) allowed us to observe the whole structural evolution, ranging from polymer-like aggregates in the precursor solution to agglomeration with heat treatment and microporous morphology of silica powders after drying and hydrolysis. Using the HA catalyst with short chain monohydric alcohols (methanol or ethanol) in the precursor solution, polymer-like aggregates having microscopic correlation length (or mesh-size) < 2 nm and low fractal dimensions ∼2, which is identical to that of an ideal coil polymer, can selectively be synthesized, yielding the uniform micropores with diameters <2 nm in the solid materials. In contrast, the absence of HA or substitution of 1-propanol led to considerably different scattering behavior reflecting the particle-like aggregate formation in the precursor solution, which resulted in the formation of mesopores (diameter >2 nm) in the solid product due to apertures between the particle-like aggregates. The data demonstrate that the extremely fine porous silica architecture comes essentially from a gaussian polymer-like nature of the silica aggregates in the precursor having the microscopic mesh-size and their successful imprint on the solid product. The result offers a general but significantly efficient route to creating precisely designed fine porous silica materials under mild condition that serve as low refractive index and efficient thermal insulation materials in their practical applications.

Microporous silica thin films with low refractive indices and high Young's modulus

A microporous silica thin film with low refractive index (low-n) of 1.27 and high Young's modulus of 19.5 GPa was obtained by sol-gel synthesis using hydroxyacetone catalyst with tetramethyl orthosilicate and water in ethanol. Transmission electron microscope images and nitrogen adsorption-desorption measurements showed that the pores in the synthesized silica were <1 nm in diameter. Unlike many other microporous synthesis methods, our method did not require sacrificial reagents as templates. This allowed low-temperature fabrication of high-strength low-n silica.

Ordered cubic mesoporous silicas with large pore sizes synthesized via high-temperature route

Ordered cubic mesoporous silicas with large pore sizes (LP-SBA-16) have been successfully synthesized at high temperatures (180-220 degrees C) using polymer surfactant of F127 as a template. Compared with conventional SBA-16 with entrance size at 3.6 nm, LP-SBA-16 samples synthesized at high temperatures show large entrance sizes at 11.8-24.7 nm, confirmed by the pore size distribution and TEM images. The formation of these large pore sizes in the samples is attributed to the increase of surfactant hydrophobicity and the merging of mesopores at high temperatures. The results obtained from NMR and XRD techniques show that ordered mesostructure in LP-SBA-16 samples basically remained even if the surfactant (F127) is fully decomposed at high temperatures, indicating that F127 surfactant becomes unimportant when the mesoporous walls of silica have been condensed. Furthermore, we have compared the adsorption capacity of myoglobin over conventional SBA-16 and LP-SBA-16 samples, and it is found that LP-SBA-16 samples exhibit much higher adsorption capacity than conventional SBA-16, which is potentially important for immobilization of enzymes on ordered mesoporous materials.

Hydrothermal synthesis of mesoporous InVO4 hierarchical microspheres and their photoluminescence properties

In this work, uniform InVO4 hierarchical microspheres with the assistance of sodium dodecyl benzene sulfonate (SDBS) have been successfully synthesized by a facile hydrothermal method. X-ray diffraction, X-ray photoelectron spectra, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction were used to characterize the as-synthesized samples. The results indicate that such 3D hierarchical architecture InVO4 microspheres are polycrystalline and assembled by numerous nanocrystals. Nitrogen adsorption-desorption measurement and the pore size distribution curve suggest that mesopores exist in these hierarchical microarchitectures. The formation mechanism has been proposed based on Oswald ripening and nonoriented attachment. It is further found that SDBS plays a key role in the formation process, and when the amount of SDBS is adjusted, the average diameter of such InVO4 microspheres could be controlled from 5 to 1 microm. UV-vis diffuse reflectance and PL spectra are employed to estimate the photoluminescence property of as-prepared InVO4 samples.