Low-k periodic mesoporous organosilica with air walls: POSS-PMO

Periodic mesoporous organosilica (PMO) with polyhedral oligomeric silsesquioxane (POSS) air pockets integrated into the pore walls has been prepared by a template-directed, evaporation-induced self-assembly spin-coating procedure to create a hybrid POSS-PMO thin film. A 10-fold increase in the porosity of the POSS-PMO film compared to a reference POSS film is achieved by incorporating ～1.5 nm pores. The increased porosity results in a decrease in the dielectric constant, k, which goes from 2.03 in a reference POSS film to 1.73 in the POSS-PMO film.     

Templated synthesis of electroactive periodic mesoporous organosilica bridged with oligoaniline

The synthesis and characterization of novel electroactive periodic mesoporous organosilica (PMO) are reported. The silsesquioxane precursor, N,N'-bis(4'-(3-triethoxysilylpropylureido)phenyl)-1,4-quinonene-diimine (TSUPQD), was prepared from the emeraldine base of amino-capped aniline trimer (EBAT) using a one-step coupling reaction and was used as an organic silicon source in the co-condensation with tetraethyl orthosilicate (TEOS) in proper ratios. By means of a hydrothermal sol-gel approach with the cationic surfactant cetyltrimethyl-ammonium bromide (CTAB) as the structure-directing template and acetone as the co-solvent for the dissolution of TSUPQD, a series of novel MCM-41 type siliceous materials (TSU-PMOs) were successfully prepared under mild alkaline conditions. The resultant mesoporous organosilica were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry, X-ray diffraction, nitrogen sorption, and transmission electron microscopy (TEM) and showed that this series of TSU-PMOs exhibited hexagonally patterned mesostructures with pore diameters of 2.1-2.8 nm. Although the structural regularity and pore parameters gradually deteriorated with increasing loading of organic bridges, the electrochemical behavior of TSU-PMOs monitored by cyclic voltammetry demonstrated greater electroactivities for samples with higher concentration of the incorporated TSU units.     

Synthesis of porphyrin-bridged periodic mesoporous organosilica and their catalytic applications

Periodic mesoporous organosilicas (PMOs) were prepared by cooperative assembly with corresponding organosilane precursors in the presence of surfactants. Recently, approaches for the preparation of a new class of porphrin-bridged PMOs have been developed. Porphyrin-bridged PMOs were synthesized by direct co-condensation using a thermal sol–gel method or a rapid microwave-assisted method with tetrakis(carboxyphenyl)porphyrin(TCPP)-silsesquioxane (TCPPS) and various silica sources in the presence of templates. These porphyrin PMO exhibited high catalytic activities and selectivity and could be used repeatedly in many kinds of applications owing to easy accessibility, rapid diffusion, and favorable mass transfer for substrates into and out of the mesopores. In addition, the TCPPS incorporated into the PMO walls could effectively defend damage of the ordered structure and also inhibit the leaching of active sites. The current review deals with recent development in the synthesis, characterization, and applications such as hydrogenation, photocatalysis, chiral catalysis, and Baeyer–Villiger oxidation of each of these types of porphyrin-bridged periodic mesoporous silica materials.     

Synthesis and lysozyme adsorption of rod-like large-pore periodic mesoporous organosilica

Highly ordered rod-like large-pore periodic mesoporous organosilica (PMO) was successfully synthesized at low acid concentration with the assistance of inorganic salt using triblock copolymer P123 as a template. The roles of inorganic salt and acidity in the production of highly ordered mesostructure and the morphology control of PMOs were investigated. It was found that the inorganic salt can significantly widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rod-like PMOs can only be synthesized in a narrow range of acid and salt concentrations, which were sensitive to induction time. The adsorption of lysozyme on PMO was studied at different pH values in comparison with adsorption on pure silica material under controlled morphology and pore structure. It was found that the adsorption capacity of lysozyme on the PMO was lower than that on pure SBA-15 silica material and the adsorption amounts are larger at pH 9.6 than at 7.0 for both materials. The results show that the electrostatic interaction between lysozyme and PMO/SBA-15 surface is more dominant than the hydrophobic forces and the interaction of neighboring lysozyme molecules also plays an important role.     

Highly ordered three-dimensional large-pore periodic mesoporous organosilica with Im3m symmetry

Highly ordered three-dimensional Im3m-type periodic mesoporous organosilica with a cavity size of 9.8 nm has been synthesized under strongly acidic media in the presence of inorganic salts using triblock copolymer F127 as the template and 1,2-bis(trimethoxysilyl)ethane as the organically bridged silica source.     

新型苯基桥键色谱固定相的热力学性质

将制备的球形苯基桥键型杂化介孔色谱固定相与商品化的C18和苯基键合硅胶固定相对比,研究其热力学性质。以稠环芳烃为例,探讨了溶质在固定相和流动相之间的迁移焓变、迁移熵变等热力学参数的变化。结果表明,与两种商品化的固定相不同,实验制备的苯基桥键固定相不存在明显的焓-熵补偿效应,证实新型桥键固定相分离机理是疏水作用、π-π作用、包结作用等协同作用的结果。     

Self-assembled highly ordered ethane-bridged periodic mesoporous organosilica and its application in HPLC

Monodisperse spherical periodic mesoporous organosilicas (PMOs) with ethane integrated in the framework were synthesized and their application as stationary phase for chromatographic separation is demonstrated. The ethane-PMOs were prepared by condensation of 1,2-bis(triethoxysilyl)ethane (BTSE) in basic condition using octadecyltrimethylammonium chloride (C(18)TMACl) as template and ethanol as co-solvent. The morphology and mesoporous structure of ethane-PMOs were controlled under different concentrations of sodium hydroxide (NaOH) and EtOH. The results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), nitrogen sorption measurement, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis showed that ethane-PMOs have spherical morphology, uniform particle distribution, highly ordered pore structure, high surface area and narrow pore-size distribution. The column packed with these materials exhibits good permeability, high chemical stability and good selectivity of mixtures of aromatic hydrocarbons in normal phase high-performance liquid chromatography (HPLC).     

Novel and efficient multifunctional periodic mesoporous organosilica supported benzotriazolium ionic liquids for reusable synthesis of 2,4,5-trisubstituted imidazoles

A series of periodic mesoporous organosilica supported benzotriazolium ionic liquids were synthesized and tested as effective and practical heterogeneous catalysts in the condensation reaction of diphenylethanedione, aromatic aldehydes and ammonium acetate. The catalyst PMO@ILBF4(1.0) showed brilliant catalytic activity for the synthesis of 2,4,5-trisubstituted imidazoles with good to high yields. We also found that the catalytic activity could be significantly influenced by the loading levels and functional anions of the benzotriazolium-cation ionic liquid, probably due to an intensification of intramolecular synergistic effect. Furthermore, the multifunctional catalyst PMO@ILBF4(1.0) could be easily recovered by filtration and recycled for six times with no significant loss in activity, indicating its excellent stability and reusability. This method provides an efficient and environmentally-friendly procedure for the production of 2,4,5-trisubstituted imidazoles.     

Synthesis and catalytic activity of a chiral periodic mesoporous organosilica (ChiMO)

A chiral vanadyl salen complex having two peripheral trimethoxysilyl groups has been used to obtain a chiral periodic mesoporous organosilica having MCM-41 periodicity and the two Si-CH2 groups anchored on the framework; this solid induces 30% enantioselectivity in the cyanosilylation of benzaldehyde.     

Aminopropyl-functionalized ethane-bridged periodic mesoporous organosilica spheres: preparation and application in liquid chromatography

A synthetic approach for synthesizing spherical aminopropyl-functionalized ethane-bridged periodic mesoporous organosilicas (APEPMOs) is reported. The mesoporous material was prepared by a one-step co-condensation of 1,2-bis(triethoxysilyl)ethane (BTSE) and 3-aminopropyltriethoxysilane (APTES) using cetyltrimethylammonium chlorine (C(18)TACl) as a template with the aid of a co-solvent (methanol) in basic medium. The APEPMOs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), nitrogen sorption measurement, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. It was shown that this material exhibited spherical morphology, ordered cubic mesostructure and good mechanical strength. The APEPMOs were tested as a potential stationary phase for liquid chromatography (LC) because the column exhibited reduced back pressure. Moreover, they exhibited good chemical stability in basic mobile phase, which can be ascribed to the ethane groups in the mesoporous framework.     

Preparation and characterization of periodic mesoporous organosilica terminally functionalized with fluorocarbon groups by a direct synthesis

Fluorocarbon groups were used to modify the pore channels of ethane-bridged periodic mesoporous organosilica by the co-condensation of 1,2-Bis(triethoxysilyl)ethane (BTESE) and trifluoropropyltrimethoxysilane (TFPTMS) in the presence of Poly(ethylene glycol)-B-Poly(propylene glycol)-B-Poly(ethylene glycol) (P123) surfactants under acidic conditions. The functionalized materials were investigated in detail by means of XRD, TEM, FT-IR, solid-state NMR, and N₂ adsorption. The effect of fluorocarbon groups concentration on the mesoscopic order and pore structure of the functionalized materials was also studied. The results show that bridging groups in the framework do not cleave and fluorocarbon groups are attached covalently to the pore wall of periodic mesoporous organosilica after functionalization. The samples functionalized with 20% TFPTMS remain desired mesoporous architecture, with a narrow pore size distribution centered at 4.1 nm, a large surface of 834 m²/g and a pore volume of 0.91 cm³g⁻¹, without pronounced change compared to the pure periodic mesoporous organosilica. Unfortunately the functionalized materials become structurally disordered with increasing amount of fluorocarbon groups.     

Heterogeneous organocatalysis at work: functionalization of hollow periodic mesoporous organosilica spheres with MacMillan catalyst

We report a new method for the synthesis of hollow-structured phenylene-bridged periodic mesoporous organosilica (PMO) spheres with a uniform particle size of 100-200 nm using α-Fe(2)O(3) as a hard template. Based on this method, the hollow-structured phenylene PMO could be easily functionalized with MacMillan catalyst (H-PhPMO-Mac) by a co-condensation process and a "click chemistry" post-modification. The synthesized H-PhPMO-Mac catalyst has been found to exhibit high catalytic activity (98% yield, 81% enantiomeric excess (ee) for endo and 81% ee for exo) in asymmetric Diels-Alder reactions with water as solvent. The catalyst could be reused for at least seven runs without a significant loss of catalytic activity. Our results have also indicated that hollow-structured PMO spheres exhibit higher catalytic efficiency than solid (non-hollow) PMO spheres, and that catalysts prepared by the co-condensation process and "click chemistry" post-modification exhibit higher catalytic efficiency than those prepared by a grafting method.     

Surfactant mediated control of pore size and morphology for molecularly ordered ethylene-bridged periodic mesoporous organosilica

A series of ethylene-containing mesoporous organosilica materials were fabricated via surfactant-mediated assembly of 1,2-bis(triethoxysilyl)ethylene (BTEE) organosilica precursor using alkyltrimethylammonium bromide (CnTAB) surfactants with different alkyl chain length (n=12, 14, 16, 18) as supramolecular templates. The presence of molecularly ordered ethylene groups in the resulting periodic mesoporous organosilica (PMO) materials was confirmed by XRD data along with 29Si and 13C MAS NMR analysis. Additional characterization techniques, namely nitrogen sorption, TEM, and TGA, confirmed the structural ordering and thermal stability of the molecularly ordered ethylene-bridged PMOs. The PMOs exhibit molecular-scale ordering (with a periodicity of 5.6 A) within the organosilica framework and tunable pore size, which depending on the alkyl chain length of the surfactant templates, varied in the range 23-41 A. Furthermore, depending on the alkyl chain length of the templates, the particle morphology of the PMOs gradually changed from monodisperse spheres (for C12TAB) to rod or cakelike particles (for C14TAB) and elongated ropelike particles for longer chain surfactants. Variations in the surfactant chain length therefore allowed control of both the pore size and particle morphology without compromising molecular-scale or structural ordering. The reactivity of ethylene groups was probed by bromination, which demonstrated the potential for further functionalization of the PMOs.     

Ferroelectric metal-organic framework with a high dielectric constant

Hydrothermal reaction of (l)-N-(4'-cyanobenzy)-(S)-proline with CdCl2 as a Lewis acid catalyst and NaN3 gives colorless block compound 1, in which 1 displays a complicated 3D framework. Ferroelectric and dielectric property measurements reveal that 1 exhibits physical properties comparable to that of a typical ferroelectric compound with a dipole relaxation process and a dielectric constant of ca. 38.6 that makes it, by definition, a high dielectric material.     

Synthesis of coesite nanocrystals from ethane bridged periodic mesoporous organosilica at low temperature and extreme pressure

Coesite nanocrystals have been synthesized from periodic mesoporous organosilica (PMO) with (CH(2))(2) bridges heated at 300 °C for 150 min and 12 GPa. The crystals are not sintered, single crystalline, and have diameters of ca. 100-300 nm. Below 300 °C, an amorphous non-porous organosilica glass was obtained. Heating above 300 °C at 12 GPa results in the rapid crystal growth and micron size coesite crystals were formed.     

Highly efficient three-component coupling reaction catalyzed by gold nanoparticles supported on periodic mesoporous organosilica with ionic liquid framework

A novel gold nanoparticle supported periodic mesoporous organosilica with alkylimidazolium framework, Au@PMO-IL, was shown to be a highly active and recyclable catalyst for three-component coupling reaction of aldehyde, alkyne and amine to give the corresponding propargylamine.     

Effects of trace metals and organic additives on porosity and dielectric constant of high purity mesoporous silica films

The beneficial effects that alkali metal and alkylammonium salt additions to molecularly templated silica sols have on the resulting mesoporous silica films formed from evaporative-coating methods with respect to porosity, elastic modulus, dielectric constant, and film surface uniformity were investigated and identified.     

Ferroelectric metal-organic coordination polymer with a high dielectric constant

Two homochiral MOFs, (CBQ)CuI3(CN)3Br (1) and (CBC)CuI2.5(CN)2Br1.5 (2), were prepared by the solvothermal reaction of CuCN with N-4-cyanobenzyl quinidinium bromide (CBQ-Br) and N-4-cyanobenzylcinchonidinium bromide (CBC-Br). 1 and 2 are typical ferroelectric compounds while may have dipolar relaxation ferroelectrics and a high dielectric constant (epsilon o = 119.3).     

High-quality free-standing and oriented periodic mesoporous organosilica films grown without a solid substrate at the air-water interface

In this communication, we report the first synthesis of high-quality free-standing and oriented periodic mesoporous organosilica (PMO) films grown without a solid substrate, by surfactant templating at the air-water interface.     

The formation of percolative composites with a high dielectric constant and high conductivity

The dielectric constant and electrical conductivity of a composite of two insulators, poly(1,1-difluoroethylene) (yellow) and K(2) CO(3) (white), increased dramatically near the percolation threshold?f(c) (f=concentration of K(2) CO(3) ). This intriguing phenomenon can be interpreted in terms of interface percolation caused by the formation of chemically activated interfaces.