Mesoporous Silica Xerogel Research Articles

Transport properties of fast proton conducting mesoporous silica xerogels

Abstract Mesoporous acid-free silica xerogels exhibiting a proton conductivity of 2.0×10 −2 Scm −1 at 80 ◦ C and 81% RH is reported for the first time.The proton conductivity values, lower cost and higher hydrophilicity of mesoporous silica xerogels make them potential substitutes for Nafionmembranes in proton exchange membranes fuel cells (PEMFCs).© 2007 Elsevier B.V. All rights reserved. Keywords: Fuel cells; Proton exchange membranes; Silica xerogels; Mesoporosity 1. Introduction Proton conducting materials have attracted much attentionbecause of their potential use in clean-energy fields such as fuelcells [1], capacitors [2], proton sensors [3], and ion-exchange-membranes [1]. The series of perfluorosulfonate ionomers suchas Nafion are the most well-known proton conductive mate-rials and serve as ion-exchange membranes due to their highproton conductivity [1]. However, their conductivity decreasesat temperatures higher than 80 ◦ C because of their inabilityto retain water, instability at high temperature (above 100

Synthesis of sol-gel mesoporous silica materials providing a slow release of doxorubicin

Samples of mesoporous base-catalysed silica xerogel materials made by the sol-gel process were impregnated with an anticancer drug—doxorubicin, followed by different times of ageing at room temperature. The effect of ageing time on the physical and structural properties as well as sorption–desorption of the drug was investigated. The obtained results suggest an inverse relationship with a solid density and surface area increasing as the pore size and volume decrease during ageing time. These results also revealed the effect of ageing time on the efficiency of sorption–desorption of the drug. An increase in ageing time results in an increase of the efficiency of drug sorption and a decrease in the rate of drug release.

Application of Percolation Theory to the Drainage of Liquid Nitrogen from Mesoporous Silica Xerogel Gelsil 50

Previous in situ small-angle neutron scattering studies of nitrogen adsorption and desorption at 78 K on the mesoporous silica xerogels Gelsil 50 and Gelsil 75 revealed the formation of ramified clusters of vapor-filled pores on desorption, which is characteristic for a percolation process. In the present work, we check whether the adsorption/desorption isotherm data for a monolithic sample of Gelsil 50 can be analyzed in terms of a bond-percolation model. Three powder samples were studied too. Percolation probability data are presented and the effects of heterogeneous nucleation, finite size, and surface clusters on drainage from Gelsil 50 are addressed. The mean coordination number was derived. The results of the analysis are discussed with respect to recent theoretical work for interactions of fluids with complex pore systems. The monolithic sample and a powder sample were characterized by small-angle neutron scattering data.

Silica Xerogel Supported Cobalt Metal Fischer−Tropsch Catalysts for Syngas to Diesel Range Fuel Conversion

Fischer−Tropsch synthesis of diesel range straight-chain hydrocarbons from CO and H2 over a cobalt nanoparticle catalyst supported by a mesoporous silica xerogel is reported. A possible advantage of sol−gel-derived catalyst supports is the tunability of their porosity to favor synthesis of diesel range hydrocarbons. The preparation of the xerogel supports, optimal loading of the supports with cobalt, the percent conversion of syngas to Fischer−Tropsch hydrocarbons, a gas chromatography−mass spectrometry analysis of the diesel range product distribution, and characterization of the catalysts are reported.

Proton conductivity in nanopore silica xerogels

The lower cost and higher hydrophilicity of silica xerogels could make them potential substitutes for perfluorosulfonic polymeric membranes in Proton Exchange Membrane Fuel Cells (PEMFCs). For that purpose, we need to obtain micro or micro plus mesoporous silica xerogels with a high porosity.

High porosity silica xerogels prepared by a particulate sol–gel route: pore structure and proton conductivity

The lower cost and higher hydrophilicity of silica xerogels could make them potential substitutes for perfluorosulfonic polymeric membranes in proton exchange membrane fuel cells (PEMFCs). For that purpose, we need to obtain micro or micro and mesoporous silica xerogels with a high porosity. The preparation of micro (<2 nm) and micro and mesoporous silica xerogels (2<d pore size ⩽10 nm) from particulate as oppossed to polymeric suspensions of silica using tetraethyl orthosilicate (TEOS) as precursor is used. Two techniques of varying packing density have been performed in this work: (1) Control of the aggregation degree in the sol by adjusting its pH before gelation (pH 5, 6 and 8) and (2) Mixture of sols with a different average particle size (particles formed under acid and base catalyzed reactions). Proton conductivity of the obtained xerogels was studied as a function of temperature and relative humidity (RH). High pore volume, high porosity and small pore size SiO 2 xerogels have been achieved in the calcination temperature range from 250 to 550 °C. The calcined xerogels showed microporosity or micro and mesoporosity in the whole range of calcination temperatures. By mixing sols (molar ratio: acid/base=4.8) porosities up to 54.7±0.1% are achieved, at 250 °C of firing temperature. According to EMF measurements, electrical transport is due to protons in this kind of materials. The proton conductivity of the studied xerogels increased linear with measured temperature. A S-shaped dependence of the conductivity with the RH was observed with the greatest increase noted between 58% and 81% RH. Xerogels with a low porosity (40.8±0.1%) and an average pore size less than 2.0 nm showed lower values of proton conductivity than that of xerogels with a higher porosity and a higher average pore size in the whole range of temperature and RH. When silica xerogels, with the highest conductivity, are treated at pH 1.5, that property increased from 2.84×10 −3±5.11×10 −5 S/cm to 4.0×10 −3±7.2×10 −5 S/cm, at 81% RH and 80 °C. It indicates that the surface site density of these materials has a strong effect on conductivity. Proton conductivity values achieved are less than one order of magnitude lower than that of Nafion, under the same conditions of temperature and RH.

Metallic nanoparticles from heterometallic Co–Ru carbonyl clusters in mesoporous silica xerogels and MCM-41-type materials

Download options Please wait... Article information DOI https://doi.org/10.1039/B002682O Article type Communication Submitted 04 Apr 2000 Accepted 31 May 2000 First published 26 Jun 2000 Download Citation Chem. Commun., 2000, 1271-1272 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Metallic nanoparticles from heterometallic Co–Ru carbonyl clusters in mesoporous silica xerogels and MCM-41-type materials F. Schweyer, P. Braunstein, C. Estournès, J. Guille, H. Kessler, J. Paillaud and J. Rosé, Chem. Commun., 2000, 1271 DOI: 10.1039/B002682O To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Fanny Schweyer Pierre Braunstein Claude Estournès Jean Guille Henri Kessler Jean-Louis Paillaud Jacky Rosé