Alternating chiral selectivity of aldol reactions under the confined space of mesoporous silica.

The chiral selectivities were altered and high diastereo- and enantio-selectivities of the products were obtained in water medium without adding acid co-catalysts when a primary-tertiary diamine catalyst was immobilized on mesoporous SBA-15 to form a recyclable catalyst for the direct asymmetric aldol reaction of cyclohexanone with p-nitrobenzaldehyde.

A new era of catalysis: efficiency, value, and sustainability.

Value proposition: Global warming and climate change urge the chemical industry to develop new processes, in which sustainability is a necessity and requirement. Catalysis is recognized to be one of the key technologies in enabling sustainability. This special issue, assembled by guest editors Soofing Chen and Shawn D. Lin, highlights some of the best work presented at "The 6th Asia-Pacific Congress on Catalysis (APCAT-6)", with as major theme "New Era of Catalysis: Efficiency, Value, and Sustainability".

Anion-exchange induced phase transformation of mesostructured silica.

Mesostructured silica synthesized using cetyltriethylammonium (CTEA) ion as the pore-directing agent in acidic environments was ready to have interfacial anions exchanged at ambient temperature. In situ techniques including small-angle X-ray scattering (SAXS) and optical microscopy were used to examine the structural and morphological changes of the as-made mesostructured materials, and pyrene fluorescence quenching experiment was used to probe the variation in interfacial environment during the anion-exchange processes. About one-half of the interfacial anions between the silica framework and micelle were exchanged based on the fluorescence quenching experiments of pyrene, which was dissolved in the hydrophobic core of the micelle. Altering in the pore structure and the architecture of the silica framework was observed when the interfacial anions were exchanged by anions of higher salting-in power. The resultant phase transformation and morphological change were always toward pore structures of lower curvature. The influence of anion follows the Hofmeister series commonly encountered in macromolecular and biological systems. The mesophase transformation induced by the interfacial anion exchange provides a unique technique to study anions which are not yet included in the Hofmeister series.

Liquid crystal cells with built-in CdSe nanotubes for chromogenic smart emission devices.

A simple and general approach for controlling optical anisotropy of nanostructured semiconductors is reported. Our design involves the fabrication of liquid crystal devices with built-in semiconductor nanotubes. Quite interestingly, it is found that semiconductor nanotubes can be well aligned along the orientation of liquid crystals molecules automatically, resulting in a very large emission anisotropy with the degree of polarization up to 72%. This intriguing result manifests a way to obtain well aligned semiconductor nanotubes and the emission anisotropy can be easily manipulated by an external bias. The ability to well control the emission anisotropy should open up new opportunities for nanostructured semiconductors, including optical filters, polarized light emitting diodes, flat panel displays, and many other chromogenic smart devices.

Synthesis of thermally stable zirconia-based mesoporous materials via a facile post-treatment.

A novel method of preparing thermally stable zirconia-based mesoporous materials was developed. The zirconia-based mesoporous materials of 2D-hexagonal structure were prepared using zirconium sulfate as the zirconium precursor and cetyltrimethylammonium (CTMA) as the pore-directing agent with the aid of salt in the synthesis solution to reduce the sulfate content in the final product and significantly improve the crystallographic ordering. Post-treatment of the mesoporous material with NaCl solution and lowering the ramping rate to less than 0.2 degrees C/min during the calcination process, however, were the key steps to hinder the growth of the dense zirconia phase and to retain the ordered mesostructure up to 600 degrees C. It was found that a portion of the surfactant (8.9-17.4 wt %) and sulfate ions (0.5-1.2 wt %) were removed during the post-treatment, which prevented the remaining sulfate groups from being reduced by the hydrogen-rich surfactant during the calcination process as confirmed by sulfur K-edge X-ray absorption near edge structure (XANES) and infrared spectroscopy. The maintenance of sulfur in the sulfate state seemed to be important in stabilizing the mesoporous structure of zirconia materials. The mesoporous zirconia materials after extraction with NaCl solution three times and calcination at 550-600 degrees C had the composition ZrO(2-x)(SO4)x with x = 0.10-0.27. The material possesses high surface area (approximately 200 m2/g), large pore volume (approximately 0.10 cm3/g), and wormlike mesopores. In comparison with the mesoporous zirconia materials stabilized by chemical treatment, the present route was simpler and more environmentally friendly and resulted in mesoporous zirconia materials of better thermal stability.

Formation of porous carbon materials with in situ generated NaF nanotemplate.

Porous carbon materials with pore sizes from 3 to 200 nm were synthesized by reacting hexafluorobenzene with Na liquid at 623 K. NaF crystals, a byproduct formed in the reaction, acted as nanotemplate to assist the pore formation. By employing hexafluorobenzene to react with Na incorporated within the channels (diameter 200 nm) of anodized aluminum oxide (AAO) membranes at 323-623 K, the carbon material can be fabricated into aligned porous nanotube arrays (ca. 250 nm in diameter, ca. 20 nm in wall thickness, ca. 0.06 mm in length, and ca. 3-90 nm in pore diameter). These materials were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray energy dispersive spectroscopy, electron diffraction, thermal gravimetric analysis, and nitrogen physical adsorption experiments.

Direct synthesis and catalytic applications of ordered large pore aminopropyl-functionalized SBA-15 mesoporous materials.

SBA-15 mesoporous silica has been functionalized with aminopropyl groups through a simple co-condensation approach of tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) using amphiphilic block copolymers under acidic conditions. The organic-modified SBA-15 materials have hexagonal crystallographic order, pore diameter up to 60 A, and the content of aminopropyl groups up to 2.3 mmol g(-1). The influences of TEOS prehydrolysis period and APTES concentration on the crystallographic order, pore size, surface area, and pore volume were examined. TEOS prehydrolysis prior to the addition of APTES was found essential to obtain well-ordered mesoporous materials with amino functionality. The amount of APTES incorporated in the silica framework increased with the APTES concentration in the synthesis gel, while the ordering of the mesoporous structure gradually decreased. Analysis with TG, IR, and solid state NMR spectra demonstrated that the aminopropyl groups incorporated in SBA-15 were not decomposed during the preparation procedure and the surfactant P123 was fully removed through ethanol extraction. The modified SBA-15 was an excellent base catalyst in Knoevenagel and Michael addition reactions.

Preparation of ordered large pore SBA-15 silica functionalized with aminopropyl groups through one-pot synthesis.

Highly ordered large pore SBA-15 silica functionalized with up to 16% aminopropyl groups, which gave high catalytic activity and selectivity toward flavanone synthesis through aldol condensation and subsequent intramolecular Michael addition of benzaldehyde and 2'-hydroxyacetophenone, was synthesized for the first time via co-condensation of tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) using an amphiphilic block copolymer as the structure-directing agent.

Drying induced phase transformation of mesoporous silica.

Solvent evaporation upon drying the precipitate was found to be the key factor for the phase transformation of cubic mesoporous silica SBA-1 to hexagonal SBA-3 studied by in-situ X-ray diffraction and 29Si solid state NMR on the precipitates formed various crystallisation conditions.