Versatile approach to synthesis of 2-D hexagonal ultra-large-pore periodic mesoporous organosilicas (original) (raw)
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Large-Pore Ethylene-Bridged Periodic Mesoporous Organosilicas with Face-Centered Cubic Structure
2010
Low-temperature (∼15°C) Pluronic-F127-templated synthesis of periodic mesoporous organosilicas (PMOs) with ethylene (-CH 2 -CH 2 -) framework groups and a face-centered cubic structure of spherical mesopores (Fm3m symmetry) was greatly enhanced through the use of judiciously chosen swelling agents and the optimization of synthesis conditions. The resulting materials were characterized by using small-angle X-ray scattering (SAXS), nitrogen adsorption, transmission electron microscopy (TEM), and thermogravimetry. While it was confirmed that 1,3,5-trimethylbenzene is a facile swelling agent for F127-templated ethylene-bridged PMOs with cubic Fm3m structure and our optimization of the synthesis afforded hitherto unreported unit-cell size and pore size, it was also shown that swelling agents predicted to have a higher extent of solubilization in Pluronics provide vast new opportunities. In particular, xylene was found to afford highly ordered PMOs with large unit-cell size and pore diameter, and a wide range of moderately or weakly ordered organosilicas with very large unit-cell parameters (up to ∼50 nm) and pore diameters (up to ∼18 nm). In the case of xylene, the pore size and unit-cell size were tunable by adjusting the amount of inorganic salt (KCl) in the synthesis mixture. The use of toluene allowed us to obtain unprecedented well-ordered PMOs with large unit-cell size (∼42 nm), very large mesopores (nominal diameter 16-17 nm; capillary condensation pressure up to ∼0.87 p/p 0 ), and enhanced primary mesopore volume, and also afforded large-pore (nominal diameter ∼15 nm) PMO in the absence of an inorganic salt. The use of benzene also afforded large-pore PMO under salt-free conditions. Ethylene-bridged PMO was successfully converted to closed-pore ordered mesoporous silica at a temperature as low as 400°C. The identification of new swelling agents for large-pore ethylenebridged PMO with spherical mesopores is likely to be extendable on PMOs of other framework compositions and on other related materials.
Zeitschrift für anorganische und allgemeine Chemie, 2014
The applicability of a recently identified potent micelle swelling agent, ethylbenzene, was verified for periodic mesoporous organosilicas (PMOs) and its performance was found to be comparable to that of xylene, which was previously shown to be an excellent swelling agent for surfactant-templated ordered mesoporous silica and organosilica synthesis. Large-pore ethylene-bridged PMOs with facecentered cubic structures of spherical mesopores were synthesized using Pluronic F127 (EO 106 PO 70 EO 106 ) surfactant and ethylbenzene or xylene swelling agents at temperatures from 15 down to 7°C. In the case of ethylbenzene, PMOs were synthesized at 15°C using two different amounts of the inorganic salt (KCl) and under salt-free conditions. It was found that ethylbenzene and xylene perform comparably well, allowing one to synthesize highly ordered face-centered cubic ethylene-bridged PMOs with unit-cell parameters ca. 40 nm and nom-* Prof. Dr. M. Kruk Fax: +1-718-982-3910 E-Mail: Michal.Kruk@csi.cuny.edu [a]
Langmuir, 2012
Large-pore ethenylene-bridged (−CHCH−) and phenylene-bridged (−C 6 H 4 −) periodic mesoporous organosilicas (PMOs) with face-centered-cubic structure (Fm3m symmetry) of spherical mesopores were synthesized at 7°C at low acid concentration (0.1 M HCl) using Pluronic F127 triblock copolymer surfactant in the presence of aromatic swelling agents (1,3,5trimethylbenzene, xylenes−isomer mixture, and toluene). In particular, this work reports an unprecedented block-copolymertemplated well-ordered ethenylene-bridged PMO with cubic structure of spherical mesopores and an unprecedented block-copolymer-templated face-centered cubic phenylene-bridged PMO, which also has an exceptionally large unit-cell size and pore diameter. The unit-cell parameters of 30 and 25 nm and the mesopore diameters of 14 and 11 nm (nominal BJH-KJS pore diameters of 12−13 and 9 nm) were obtained for ethenylenebridged and phenylene-bridged PMOs, respectively. Under the considered reaction conditions, the unit-cell parameters and pore diameters were found to be similar when the three different methyl-substituted benzene swelling agents were employed, although the degree of structural ordering appeared to improve for phenylene-bridged PMOs in the sequence of decreased number of methyl groups on the benzene ring.
Ethenylene-bridged periodic mesoporous organosilicas with ultra-large mesopores
Chemical Communications, 2009
A novel class of periodic mesoporous organosilicas with E-and/or Z-configured ethenylene bridges was prepared under acidic conditions using the triblock copolymer Pluronic P123 as a structure directing agent. The isomeric configuration of the precursor has a drastic effect on the properties of the resulting PMO materials. The diastereoisomerically pure E-configured ethenylene bridged PMOs reveal higher structural ordering, narrower pore size distributions, and enhanced hydrothermal stability than their diastereoisomerically impure counterparts. These properties have been correlated with the molecular level structure of pore walls probed by solid-state NMR spectroscopy.
Synthesis of pore-enlarged mesoporous organosilicas under basic conditions
Microporous and Mesoporous Materials, 2004
A series of mesoporous organosilicas (MOs) in the ½3:2; 11:1 nm pore diameter range has been obtained in basic media by using 1,2-bis(triethoxysilyl)ethane (BTEE) or 1,2-bis(trimethoxysilyl)ethane (BTME) as a silica source, binary surfactant mixtures [CH 3 (CH 2 ) 17 NMe 2 (CH 2 ) 3 NMe 3 ] 2þ 2Br À (C 18-3-1 ) and [CH 3 (CH 2 ) 15 NMe 3 ] þ Br À (C 16 TABr) as structure-directing agents (SDAs), and TMB (mesitylene) or TPB (1,3,5-triisopropylbenzene) as swelling agents. Pore size control has been achieved via variation of (i) the binary surfactant ratio, (ii) base (sodium hydroxide) concentration, (iii) reaction time and temperature, and (iv) type of expander molecule. The surface morphology and silanol population of the dehydrated MOs was examined by TMDS (tetramethyldisilazane) silylation. The parent and functionalized MOs were characterized by powder X-ray diffraction, N 2 physisorption, elemental analysis, FTIR, and solid-state ( 1 H, 13 C, 29 Si) NMR spectroscopy. According to their PXRD patterns, the pore-enlarged MO materials do not display any long-range order, however, pore volumes >2 cm 3 /g. The type of hysteresis loop exhibited by the N 2 adsorption and desorption isotherm changed remarkably for MOs synthesized at low concentrations of divalent surfactant as well as base, which can be attributed to a change of pore topology. 29 Si MAS NMR spectroscopy revealed the prominent T 2 and T 3 peaks at )58and)58 and )58and)64 ppm, respectively, indicative of an intact wall and surface structure. The silyl group coverage was determined as 0.8-1.3 SiHMe 2 groups per nm 2 corresponding to approximately half of that found on purely siliceous periodic mesoporous silicas such as MCM-41 or MCM-48.
Journal of Colloid and Interface Science, 2010
Large-pore phenyl-bridged periodic mesoporous organosilicas (PMOs) were facilely synthesized by evaporation-induced self-assembly of 1,4-bis(triethoxysily)benzene and triblock copolymer Pluronic F127 as a template under acid conditions combined with a mixed-solvothermal treatment. The ordered PMOs exhibit large uniform mesopores of $9.9 nm in diameter after calcination at 350°C in a nitrogen atmosphere. The mesoporous phenyl-bridged organosilica products have an ordered hexagonal mesostructure with space group p6mm. N 2 adsorption/desorption isotherms reveal imperfect mesopore channels with high surface areas (up to 1150 m 2 /g) and thick pore walls (up to 7.7 nm). The mesopores can be expanded with the decrease of acidity, as well as the increase of Pluronic F127 content. A mixed-solvothermal treatment in N,N-dimethylformamide (DMF) and water at 100°C was first used to improve the periodicity of the mesopore walls, as well as increase the wall thickness. The composites exhibit efficient adsorption capacities (2.06 mmol g À1 ) for benzene, suggesting a potential adsorbent for removal of volatile organic compounds. The EISA approach combined with the mixed-solvothermal treatment provides important insights into the development of large-pore PMOs by using long-chain organosilanes, and further demonstrates the ability to fabricate materials with thick walls.
Materials Chemistry and Physics, 2009
Porous organosilicas with 1.5-100 mol.% of bridging 1,5-bis-(2 -ethyl)-xylene (BDEX) groups were synthesized by a template-directed procedure and characterized using FTIR spectroscopy, temperature programmed desorption mass-spectrometry, X-ray diffraction and methanol adsorption. The formation of dually porous structure, consisted in small low-ordered mesoporous (2-3 nm) MCM-41 type particles united in aggregates with wide interparticle pores (8-20 nm), was found. If the concentration of the BDEX groups is smaller than 10 mol.%, the BDEX groups can be thermally oxidized without dually porous structure damage. The aggregation of the primary particles by chemical cross-linking is an alternative way to form a network of large so-called "transport" pores in the mesoporous material.
Periodic Mesoporous Organosilicas Consisting of 3D Hexagonally Ordered Interconnected Globular Pores
The Journal of Physical Chemistry C, 2009
A new family of periodic mesoporous organosilicas with 100% E-configured ethenylene-bridges and controllable pore systems is presented. 2D hexagonally ordered hybrid nanocomposites consisting of cylindrical pores are obtained, of which some are filled with solid material. The architectural composition of these hybrid materials can be accurately controlled by fine-tuning the reaction conditions; that is, there is a unique correlation between the reaction mixture acidity and the amount of confined mesopores. This correlation is related to the filling of the pores with solid material whereby the length of the pore channels can be tailored. Hereby the mesophase either shifts toward long-ranged 2D hexagonally ordered open cylinders or toward 3D hexagonally ordered interconnected spheres. The synthesis of these organic-inorganic hybrid composites is straightforward via the direct condensation of E-1,2-bis(triethoxysilyl)ethene, in the presence of pluronic P123. The true nature of these periodic mesoporous organosilicas is disclosed by means of nitrogen gas physisorption, nonlocal density functional theory, SAXS, TEM, and electron-tomography.