Search results for "mesoporous material"
showing 10 items of 262 documents
Flow-through pore characteristics of monolithic silicas and their impact on column performance in high-performance liquid chromatography
2008
Abstract In order to elucidate the role of the flow-through characteristics with regard to the column performance in high-performance liquid chromatography (HPLC) native and n -octadecyl bonded monolithic silica rods and columns, respectively of 100 mm length and 4.6 mm ID with mesopores in the range between 10 and 25 nm and macropores in the range between 0.7 and 6.0 μm were examined by mercury intrusion/extrusion, scanning electron microscopy, image analysis and permeability. The obtained data of the flow-through pore sizes and porosity values as well as surface-to-volume ratio of the stationary phase skeleton enabled to predict their influence to the chromatographic separation efficiency…
Comprehensive pore structure characterization of silica monoliths with controlled mesopore size and macropore size by nitrogen sorption, mercury poro…
2005
The porosity of monolithic silica columns is measured by using different analytical methods. Two sets of monoliths were prepared with a given mesopore diameter of 10 and 25 nm, respectively and with gradated macropore diameters between 1.8 and 7.5 microm. After preparing the two sets of monolithic silica columns with different macro- and mesopores the internal, external and total porosity of these columns are determined by inverse size-exclusion chromatography (ISEC) using polystyrene samples of narrow molecular size distribution and known average molecular weight. The ISEC data from the 4.6 mm analytical monolithic silica columns are used to determine the structural properties of monolithi…
Textural characterization of native and n-alky-bonded silica monoliths by mercury intrusion/extrusion, inverse size exclusion chromatography and nitr…
2008
Native and n-alkyl-bonded (n-octadecyl) monolithic silica rods with mesopores in the range between 10 and 25 nm and macropores in the range between 1.8 and 6.0 microm were examined by mercury intrusion/extrusion, inverse size exclusion chromatography (ISEC) and nitrogen sorption. Our results reveal very good agreement for the mesopore size distribution obtained from nitrogen adsorption (in combination with an advanced NLDFT analysis) and ISEC. Our studies highlight the importance of mercury porosimetry for the assessment of the macropore size distribution and show that mercury porosimetry is the only method which allows obtaining a combined and comprehensive structural characterization of m…
Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatography
2006
Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (approximately 1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the microme…
Synthesis and Structure Determination of the Hierarchical Meso-Microporous Zeolite ITQ-43
2011
[EN] The formation of mesopores in microporous zeolites is generally performed by postsynthesis acid, basic, and steam treatments. The hierarchical pore systems thus formed allow better adsorption, diffusion, and reactivity of these materials. By combining organic and inorganic structure-directing agents and high-throughput methodologies, we were able to synthesize a zeolite with a hierarchical system of micropores and mesopores, with channel openings delimited by 28 tetrahedral atoms. Its complex crystalline structure was solved with the use of automated diffraction tomography.
Mn 12 single-molecule magnets incorporated into mesoporous MCM-41 silica
2003
Abstract The incorporation of four Mn12 derivatives, namely [Mn12O12(O2CR)16(H2O)4] (R=CH3 (1), CH3CH2 (2), C6H5 (3), C6F5 (4)), into the hexagonal channels of the MCM-41 mesoporous silica have been studied. Only the smallest clusters 1 and 2 that are those with compatible size with the pores of MCM-41 could be incorporated into the mesoporous silica. Powder X-ray diffraction (XRD) analysis and N2 adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn12 clusters are inside the pores. The magnetic properties of the MCM-41/1 nanocomposite material indicate that the structure of the cluster is maintained after incorporat…
One‐Pot Synthesis of Superparamagnetic CoO‐MCM‐41 Nanocomposites with Uniform and Highly Dispersed Magnetic Nanoclusters
2004
Superparamagnetic CoO-MCM-41 mesoporous nanocomposites, with variable cobalt amounts, in the form of well-dispersed CoO-like clusters, were prepared in a large compositional range by a one-step reproducible procedure employing co-hydrolysis and co-condensation of the inorganic precursors in a water/triethanolamine medium. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Ordered mesoporous silicas as host for the incorporation and aggregation of octanuclear nickel(ii) single-molecule magnets: a bottom-up approach to n…
2006
Silica-based mesoporous materials have been employed as the support host for a suitably designed small octanuclear nickel(II) guest complex with a moderately anisotropic S = 4 ground spin state (D = −0.23 cm−1), which behaves as a single-molecule magnet at low temperature (TB = 3.0 K). Both unimodal MCM-41 and bimodal UVM-7 porous silica provide appropriate template conditions for the incorporation and aggregation of the Ni8 complex precursor into larger complex aggregates, showing slow relaxation of the magnetization at higher blocking temperatures than the crystalline material. By playing with the initial complex vs. silica concentration, two series of samples with varying complex loading…
Drug delivery devices based on mesoporous silicate.
2004
A mesoporous material based on aluminosilicate mixture was studied to investigate its ability to include drugs and then release them. Nonsteroidal anti-inflammatory agents such as diflunisal, naproxen, ibuprofen and its sodium salt have been used in this study. The preparation of the mesoporous material and its characterization by X-ray, N2 absorption-desorption isotherm, and thermogravimetry analysis have been described. Drug loading was performed by a soaking procedure. Drug-loaded matrices were characterized for entrapped drug amount, water absorption ability, and thermogravimetric behavior. Drug release studies also were performed at pH 1.1 and 6.8 mimicking gastrointestinal fluids. Exp…
Characterization of Nd-MCM41 obtained by impregnation
2008
Abstract Silica mesoporous molecular sieves (MCM-41), prepared by using micelles as template, were functionalized by means of incipient wetness method. Evidence for the neodymium presence in the silica matrix was obtained by means of EDX. SEM micrographs showed that impregnation does not change significantly MCM-41 morphology. The maintenance of the hexagonal structure was confirmed by XRD pattern analysis. However, the observed loss of long-range ordering, the cell parameter increase and the surface area decrease, observed by gas adsorption technique, were attributed to the introduction of neodymium oxide inside the MCM-41 mesochannels. By FT-IR and Raman spectra it was found that the main…