Organosilica Precursor Research Articles

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.

Periodic mesoporous organosilicas: mesophase control via binary surfactant mixtures

A series of ordered periodic mesoporous organosilicas (PMOs) with cubic and hexagonal symmetry was synthesized from organosilica precursor 1,2-bis(triethoxysilyl)ethane (BTEE) by using cationic surfactants [CH3(CH2)17NMe3]+Br− (C18TABr) or [CH3(CH2)17NMe2(CH2)3NMe3]2+2Br− (C18-3-1) or binary mixtures herefrom as structure-directing agents (SDAs). Under the prevailing basic reaction conditions, the commercially available quaternary alkyltrimethylammonium salt C18TABr selectively gave materials PMO[MCM-41]-n with hexagonal symmetry (space group P6mm). Depending on the surfactant concentration, the materials obtained from divalent C18-3-1 displayed cubic (PMO[SBA-1]-n with space group Pm3n) or disordered hexagonal structure (mixed phase). Fine-tuning of the total amount and molar ratio of surfactant mixtures of C18-3-1 and C18TABr also accomplished an effective mesophase control of ordered organosilicas PMO[MCM-41]-n and PMO[SBA-1]-n. For a given gel composition, such a mesophase transformation occurred also by addition of inorganic salt KF (hexagonal → cubic) and addition of organic expander molecule mesitylene, TMB (cubic → hexagonal). All of the PMOs were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen physisorption, FTIR spectroscopy, and 29Si and 13C CP MAS NMR spectroscopy. The hexagonal PMOs displayed BET surface areas in the range of 500–1030 m2 g−1, pore volumes as large as 1.62 cm3 g−1, and pore diameters ranging from 29 to 52 Å. Materials PMO[SBA-1]-n exhibited BET surface surface areas in the range of 570 to 800 m2 g−1, pore volumes between 0.51 and 1.08 cm3 g−1, and pore sizes ranging from 29 to 40 Å. Representative PMO samples indicated silanol group populations in the range of 0.6–0.9 OH per nm2 by tetramethyldisilazane silylation (carbon analysis).

Organic–inorganic hybrid mesoporous silicas: functionalization, pore size, and morphology control

Topological design of mesoporous silica materials, pore architecture, pore size, and morphology are currently major issues in areas such as catalytic conversion of bulky molecules, adsorption, host-guest chemistry, etc. In this sense, we discuss the pore size-controlled mesostructure, framework functionalization, and morphology control of organic-inorganic hybrid mesoporous silicas by which we can improve the applicability of mesoporous materials. First, we explain that the sizes of hexagonal- and cubic-type pores in organic-inorganic hybrid mesoporous silicas are well controlled from 24.3 to 98.0 A by the direct micelle-control method using an organosilica precursor and surfactants with different alkyl chain lengths or triblock copolymers as templates and swelling agents incorporated in the formed micelles. Second, we describe that organic-inorganic hybrid mesoporous materials with various functional groups form various external morphologies such as rod, cauliflower, film, rope, spheroid, monolith, and fiber shapes. Third, we discuss that transition metals (Ti and Ru) and rare-earth ions (Eu(3+) and Tb(3+)) are used to modify organic-inorganic hybrid mesoporous silica materials. Such hybrid mesoporous silica materials are expected to be applied as excellent catalysts for organic reactions, photocatalysis, optical devices, etc.

Free-Standing and Oriented Periodic Mesoporous Organosilica Films with Variable Pore Size at the Air−Water Interface

Free-standing and oriented periodic mesoporous organosilica (PMO) films with variable pore size have been synthesized at the air−water interface using cationic alkyltrimethylammonium surfactants (alkyl chain length from 12 to 18 carbon atoms) as the structure-directing agents and 1,2-bis(triethoxysilyl)ethane as the organosilica precursor. After hydrothermal reaction at 95 °C for 8 h, C12TA−PMO, C16TA−PMO, and C18TA−PMO films grown at the air−water interface have a uniform thickness of ∼350, ∼670, and ∼400 nm, respectively. From the XRD patterns and TEM images, PMO films with hexagonal symmetry were identified. It was confirmed by 29Si and 13C CP MAS NMR experiments that the organic−inorganic moiety (−Si−CH2−CH2−Si−) is the basic structural unit in the films. The pore diameter and the surface area of the surfactant-extracted PMO films, e.g., C12TA−, C16TA−, and C18TA−PMO films, obtained from the N2 sorption isotherms were to be determined to be 24.3, 26.4, and 32.8 A and 890.3, 917.7, and 811.0 m2 g-1, re...

Single‐Source Precursors For Synthesizing Bifunctional Periodic Mesoporous Organosilicas

AbstractA new class of bifunctional periodic mesoporous organosilicas (PMOs) composed of organosilicate building blocks with two different silicon sites have been synthesized from the single‐source bifunctional organosilica precursors tris(triethoxysilylethyl)ethoxysilane and bis(triethoxysilylethyl)diethoxysilane, respectively denoted MT3‐PMO and DT2‐PMO. The synthesis of these PMOs is achieved by the co‐assembly of a triblock‐copolymer Pluronic P123 template with the bifunctional organosilica precursor under acid‐catalyzed and inorganic‐salt‐assisted conditions. After template removal through solvent extraction, the MT3‐PMO and DT2‐PMO so obtained show well‐ordered mesopores and display large pore diameters (6–7 nm) and pore volumes (0.6–0.8 cm3 g–1) with a narrow pore‐size distribution and high surface areas (700–800 m3 g–1).

Bifunctional Hybrid Mesoporous Organoaluminosilicates with Molecularly Ordered Ethylene Groups

We report the synthesis and characterization of crystal-like structurally well-ordered ethylene-containing hybrid mesoporous organoaluminosilicate materials, which exhibit molecular-level periodicity in the pore walls and enhanced hydrothermal stability. Distilled 1,2-bis(triethoxysilyl)ethylene (BTEE) was used as the organosilica precursor, aluminum isopropoxide as aluminum source, and cetyltrimethylammonium bromide as template. The materials are structurally well-ordered and exhibit high surface area (>1300 m(2)/g) and pore volume (>1.10 cm(3)/g). The presence of molecularly ordered ethylene groups was confirmed by powder X-ray diffraction, (29)Si and (13)C MAS NMR, and Raman spectroscopy. The ethylene groups are thermally stable up to a temperature of 300 degrees C. The presence of ethylene groups enhances the hydrothermal stability in boiling water of both organosilica and organoaluminosilicate materials. The organoaluminosilicate materials possess a bifunctional character arising from the presence of both tetrahedrally coordinated Al and molecularly ordered ethylene groups in their frameworks.

Synthesis and characterisation of spherical periodic mesoporous organosilicas (sph-PMOs) with variable pore diameters

Monodisperse spherical periodic mesoporous organosilicas (sph-PMOs) with high specific surface areas and narrow pore size distributions were synthesised in a modified Stoeber-reaction using long-chain tetraalkylammonium surfactants under alkaline conditions and 1,2-bis(trimethoxysilyl)ethane (BTME) as a bridged organosilica precursor. Variation of the surfactant chain length leads to pore diameters between 2.5 and 3.2 nm. The synthesis yields particles with an average size between 0.4 and 0.5 μm. The sph-PMOs were characterised by powder X-ray diffraction (P-XRD), nitrogen physisorption, IR spectroscopy, Raman spectroscopy, SEM and TEM.

Macromolecular Templating Approach for the Synthesis of Hydrothermally Stable Mesoporous Organosilicas with High Periodicity and Thick Framework Walls

Hydrothermally stable mesoporous ethanesilica with a long-range hexagonal order (p6mm) and a relatively thick and micropore-free framework wall was synthesized by the core−shell approach using a nonionic PEO−PLGA−PEO triblock copolymer template and a 1,2-bis(triethoxysilyl)ethane (BTESE) organosilica precursor. The pore structure and morphology were characterized by SAXS, TEM, BET, and solid-state NMR measurement. The key parameters in the synthesis of mesoporous ethanesilica with a stable thick wall are the strong contrast between the hydrophilic PEO block and the hydrophobic PLGA block and the compatibility of PEO with the BTESE organosilicate precursor at an optimum reaction temperature of 323 K. The enhanced hydrothermal stability (i.e., the structural integrity was maintained for up to 25 days in boiling water of 373 K) is believed to be due to the thick pore wall (4.2 nm), the high degree of condensation and hydrophobicity of organosilica precursor used, and the significant reduction of micropores.