Search results for "porous material"
showing 10 items of 361 documents
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…
Structural Changes in Nanoporous MFI Zeolites Induced by Tetrachloroethene Adsorption: A Joint Experimental and Simulation Study
2011
A joint experimental and molecular simulation study was performed to investigate the adsorption of tetrachloroethene on two MFI zeolites, ZSM-5 with a Si/Al ratio of 26.5, and silicalite-1, which is the pure silica form of ZSM-5. Adsorption isotherms and isosteric heats of adsorption of tetrachloroethene were measured and compared to molecular simulation results. Experimental curves for both MFI zeolites show a step at loading of 4 molecules·uc−1 that was interpreted in terms of a structural change of the host framework. A thermodynamic analysis based on the osmotic ensemble scheme allowed attributing this step to a symmetry change from ORTHO (orthorhombic form with Pnma symmetry) to PARA (…
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…
Bases for the synthesis of nanoparticulated silicas with bimodal hierarchical porosity
2006
Porous silicas with pore sizes at two length scales (meso and large meso/macroporous) have been prepared through a one-pot surfactant assisted procedure by using a simple template agent and starting from silicon atrane complexes as hydrolytic inorganic precursors. The special organization of these bimodal porous silicas can be related to the nanometric character of their constituent mesoporous particles. Whereas the small intra-particle mesopore system is generated by the templating effect of the surfactant, the large pore system is defined by inter-particle voids. We have studied the effect of different procedural parameters on the small pore system and also on the nucleation and growth of…
Enhanced H2O2 production over Au-rich bimetallic Au-Pd nanoparticles on ordered mesoporous carbons
2015
1 figures, 3 tables.-- © 2014. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/