Jin-Gui Wang

Hierarchically helical mesostructured silica nanofibers templated by achiral cationic surfactant

Recently, ordered chiral mesoporous silica with a twisted hexagonal rod-like morphology and hexagonally ordered chiral channels has been synthesized by using chiral anionic surfactants as a liquid crystal template (S. Che, Z. Liu, T. Ohsuna, K. Sakamoto, O. Terasaki and T. Tatsumi, Nature, 2004, 429, 281). In this work, we report an observation of hierarchically helical mesoporous silica nanofibers organized by the achiral cationic surfactant cetyltrimethylammonium bromide (CTAB). These nanofibers (diameter ranging around 100–300 nm) grew from a two-phase system (H2O, CTAB, HCl for the aqueous phase and tetraethylsiloxane (TEOS) in hexane for the oil phase). SEM and TEM characterizations were performed and the results indicate that these nanofibers possess rope-like twisted hexagonal morphology and helical (chiral) mesoporous channels running inside winding around the fiber axis. These twisted hexagonal nanofibers could further curve spirally to form a second-level helical morphology (hierarchically helical morphology). As no chiral molecules are used in the synthesis, the hierarchically helical morphology of nanofibers could be explained by the different kinds of topological defects existing in the silicate liquid crystal seeds formed in a diffusion-controlled kinetic process, and these defects could initiate and direct the growth of particular forms of mesostructured silica. Formation of the ordered chiral mesorporous silica would be expected to be a general phenomenon in the cooperative assembly between amphiphilic organic molecules (templates) and inorganic species, no matter whether the templates are chiral or achiral.

Facile preparation of Pd/organoclay catalysts with high performance in solvent-free aerobic selective oxidation of benzyl alcohol

A facile method to prepare Pd/organoclay catalysts was reported. At room temperature, in H2PdCl4 solution the quaternary ammonium surfactant modifiers intercalated in the organoclay adsorbed PdCl42− specifically and quickly. After reduction at room temperature, Pd nanoparticles were formed and well-dispersed in the organoclay matrix. The Pd/organoclay catalysts were used in aerobic oxidation of benzyl alcohol to benzaldehyde and exhibited high and stable activity. Particularly, the 0.2 wt% Pd/organoclay gave a remarkably high turnover frequency (up to 6813 h−1) under base- and solvent-free conditions. Our method can be generally applied for the preparation of Ru, Au and Pt/organoclay catalysts.

Anionic surfactant-templated mesoporous silica (AMS) nano-spheres with radially oriented mesopores.

Mesoporous silica nano-spheres with pore size larger than 3 nm were synthesized using an anionic surfactant as the template. These nano-spheres possess centrosymmetric radial mesopores (emanating from the spherical center to the exterior surface) and form stable suspension. The spherical size and mesostructure can be finely tuned by changing the pH value of the synthetic system in the range of 8.8 to 6.4. In addition, when the pH value was decreased to 5.8, instead of spheres, anisotropic morphologies such as elliptical, peanutlike and trifurcate particles were obtained, exhibiting core/shell structure due to the different orientations of the mesopores in the core and the shell of the particles. It is proposed that the evolution of the morphologies and mesostructures of the products templated by anionic surfactants strongly depend on the pH value of the synthetic system.

Polyelectrolyte–Surfactant Complex as a Template for the Synthesis of Zeolites with Intracrystalline Mesopores

Mesoporous zeolite silicalite-1 and Al-ZSM-5 with intracrystalline mesopores were synthesized with polyelectrolyte-surfactant complex as the template. Complex colloids were first formed by self-assembly of the anionic polymer poly(acrylic acid) (PAA) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in basic solution. During the synthesis procedure, upon the addition of the silica source, microporous template (tetrapropylammonium hydroxide), and NaCl, these PAA/CTA complex colloids underwent dissociation and gave rise to the formation of hollow silica spheres with mesoporous shells templated by CTAB micelles and PAA domains as the core. Under hydrothermal treatment, the hollow silica spheres gradually merged together to form larger particles with the PAA domains embedded as the space occupant, which acted as a template for intracrystalline mesopores during the crystallization of the zeolite framework. Amphiphilic organosilane was used to enhance the connection between the PAA domain and the silica phase during the synthesis. After calcination, single crystal-like zeolite particles with intracrystalline mesopores of about 5-20 nm were obtained, as characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N(2) adsorption measurements. With the addition of an aluminum source in the synthesis, mesoporous zeolite Al-ZSM-5 with intracrystalline mesopores was also synthesized, and enhanced catalytic property was observed with mesoporous Al-ZSM-5 in acetalization of cyclohexanone with methanol.

Facile fabrication of noble metal nanoparticles encapsulated in hollow silica with radially oriented mesopores: multiple roles of the N-lauroylsarcosine sodium surfactant

A facile one-pot method was reported to fabricate noble metal nanoparticles encapsulated in silica hollow nanospheres with radially oriented mesopores, and the anionic amino acid surfactant, N-lauroylsarcosine sodium, played multiple roles: reducing agent, stabilizer, emulsion droplets and mesopore template.

Effect of alcohol on morphology and mesostructure control of anionic-surfactant-templated mesoporous silica (AMS)

In the synthesis of anionic-surfactant-templated mesoporous silica (AMS), the effects of alcohols have been investigated for the first time. Without the addition of extra alcohols, spherical mesoporous silica with radially oriented mesopores could be obtained through the anionic surfactant templating route. By using alcohols with different carbon chain length such as ethanol, n-butanol, hexanol and 1-octanol as the additives, different morphologies and mesostructures of mesoporous silica were obtained. It was found that both the types and concentrations of alcohols in the synthesis solution could tune the morphologies and mesostructures of the AMS, giving rise to the formation of hexagonal mesoporous discs and particles with novel multi-layered inner structure. In general alcohol with appropriate carbon chain length such as n-butanol and hexanol could act as the co-surfactant in the synthesis of mesoporous silica templated by anionic surfactant.

Hierarchically mesoporous silica single-crystalline nanorods with three dimensional cubic Fm-3m mesostructure

Hierarchically mesoporous silica nanorods with well-ordered cubic Fm-3m mesostructure were fabricated for the first time under basic conditions by using cationic surfactant cetyltrimethylammonium bromide (CTAB) as a template with poly(acrylic acid) (PAA) and triblock copolymer Pluronic P123 (PEO20PPO70PEO20) as co-templates. Due to the electrostatic interaction between CTAB and PAA, they would co-assemble to form complex colloids. The nonionic surfactant P123 would also be incorporated into the complex. The CTA/PAA/P123 complex colloids exhibited the morphology of nanorods, and the morphology of the final product inherited from the complex. The ordered mesopores (∼3 nm) of hierarchically mesoporous silica were connected with the secondary mesopores, whose average pore size was about 20 nm. Interestingly, the existence of the secondary mesopores did not disturb the ordered mesostructure of the nanorods and thus all the nanorods remained as single-crystalline mesoporous silica crystals. By varying the average molecular weight of the triblock copolymers, we could obtain hierarchically mesoporous silica with 2-D hexagonal mesostructure, which had a high surface area (∼980 m2 g−1) and large pore volume (∼1.3 cm3 g−1). Au-supported hierarchically mesoporous silica nanorods exhibited much higher reaction rate than that of Au-supported MCM-41 in catalytic reduction of 4-nitrophenol, as a result of its unique hierarchically mesoporous structure.

Multi-amine-functionalized cubic Fdm mesoporous silica by an anionic surfactant templating route

Ordered multi-amine functionalized mesoporous silica with a 3D cubic Fdm mesostructure was synthesized with anionic surfactant N-lauroylsarcosine sodium (Sar-Na) as a template, and [3-(2-aminoethyl)-aminopropyl]trimethoxysilane (DAPS) or 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (TAPS) as co-structure directing agents (CSDAs). To our knowledge, this is the first time the use of DAPS and TAPS as CSDAs in an anionic surfactant templated system have been reported. Using DAPS and TAPS as the CSDA favors the formation of a 3D cubic mesocaged solid with Fdm symmetry, while with 3-aminopropyltriethoxysilane (APS) as the CSDA, only the p6mm mesoporous phase was formed. The geometrical change of the CSDA resulted in a change of the surfactant packing parameter, leading to the change of the silica mesophase from 2D-hexagonal p6mm to 3D cubic Fdm symmetry. After extraction of the templates, multi-amine-functionalized cubic Fdm mesoporous silicas were obtained. The multi-amine functionlized mesoporous silicas exhibit excellent properties in adsorption and removal of heavy metal ions in solution as well as the support of noble metal nanoparticles.

Facile fabrication of hierarchically nanoporous SBA-1 nanoparticles

Mesoporous silica nanoparticles are drawing increasing attention in biomedical applications. In this work, hierarchically nanoporous SBA-1 single-crystal-like nanoparticles, with a size of 50–300 nm, were synthesized using a cationic surfactant and anionic polymer poly(acrylic acid) (PAA) mesomorphous complexes as a template. The obtained mesoporous silica nanoparticles showed a well ordered cubic Pmn mesostructure, large pore volume and high BET surface area. The materials possess biomodal nanopores corresponding to well-ordered mesopores and secondary interstitial nanopores.

Synthesis of cubic Ia-3d mesoporous silica in anionic surfactant templating system with the aid of acetate.

Mesoporous silica with three-dimensional (3D) bicontinuous cubic Ia-3d structure and fascinating caterpillar-like morphology was synthesized by using anionic surfactant N-lauroylsarcosine sodium (Sar-Na) as the template and 3-amionpropyltrimethoxysilane (APS) as the co-structure-directing agent (CSDA) with the aid of acetate. A phase transformation from high interfacial curvature 2D hexagonal to low interfacial curvature 3D cubic Ia-3d occurred in the presence of a proper amount of acetate. Other species of salts (excluding acetate) had the ability to induce the caterpillar-like morphology, but failed to induce the cubic Ia-3d mesostructure. Furthermore, [3-(2-aminoethyl)-aminopropyl]trimethoxysilane (DAPS) was also used as the CSDA to synthesize Ia-3d mesostructured silica under the aid of sodium acetate. After extraction of the anionic surfactants, amino and di-amine functionalized 3D bicontinuous cubic Ia-3d mesoporous silicas were obtained and used as supports to immobilize Pd nanoparticles for supported catalysts. The catalytic activity of the catalysts was tested by catalytic hydrogenation of allyl alcohol.