Well-ordered mesoporous silica prepared by cationic fluorinated surfactant templating

Knutson Chemical and Materials Engineering Department, Department of Occupational and Environmental Health, University of Kentucky, 40506-0046, Lexington, KY, U.S.A
Microporous and Mesoporous Materials (Impact Factor: 3.45). 09/2004; 73(3). DOI: 10.1016/j.micromeso.2004.05.013

ABSTRACT We describe the synthesis and characterization of ordered mesoporous silica using the template 1H,1H,2H,2H-perfluorooctylpyridinium chloride. This surfactant forms several lyotropic mesophases at room temperature, including hexagonal close packed cylinders, an isotropic liquid crystal, and a lamellar phase. Using this surfactant, mesoporous silica is synthesized by room temperature precipitation and surfactant extraction. Both the surfactant and product material are thoroughly characterized. From nitrogen adsorption, the product has a specific surface area of 982 m 2 /g and a pore diameter of 2.6 nm. X-ray diffraction and transmission electron microscopy confirm 2-dimensional close-packed hexagonal long-range ordering. This is the first example of cationic fluorinated surfactant templating of an ordered porous ceramic material.

Download full-text


Available from: Hans-Joachim Lehmler, Sep 28, 2015
10 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: More and more attention has been paid to the synthesis of mesostructured aluminophosphates for many years. A lot of valuable research results, including various synthetic approaches and structural materials, have been obtained. This paper reviews the progress in the synthesis of mesostructured alu- minophosphates over the past few years, with the hope of revealing opportunities for future work.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The use of compressed CO2 processing to alter the pore size, structure and timescale of silica condensation in surfactant templated silica thin films and powders is investigated by systematically varying the template structure and CO2 processing conditions. Tailoring the mesoporous materials increases its potential applications, as demonstrated in catalysis, drug delivery, chromatographic and electrode applications. This work demonstrates for the first time the applicability of fluorinated surfactants as templates for the synthesis of mesoporous silica thin films by dip coating. Well-ordered films with 2D hexagonal close-packed pore structure are synthesized in an acid-catalyzed medium using three cationic fluorinated templates of varied tail length and branching (C6F13C2H4NC5H5Cl, C8F17C2H4NC5H5Cl and (CF3)2CFC5F9C2H4NC5H5Cl). CO2 processing of the fluorinated templated silica results in a significant and controlled increase in pore diameter relative to the unprocessed films. The pore expansion is significantly greater compared to the negligible expansion observed in hydrocarbon (C16H23NC5H5Br) templated silica. The greater swelling of the fluorinated templates is attributed to the favorable penetration of CO2 in the CO2-philic fluorinated tail and the relative solvation of each template is interpreted from their interfacial behavior at the CO2-water interface. The CO2 based pore expansion observed in fluorinated surfactant templated films is extended successfully to base-catalyzed silica powders templated with a fluorinated surfactant (C6F13C2H4NC5H5Cl). Pore expansion in silica powders is significantly less than in acid catalyzed films and demonstrates the effects of pH on surfactant selfassembly in CO2 and increased silica condensation at basic conditions, which inhibits pore expansion. Finally, the use of fluorescence probe molecules is demonstrated for in-situ monitoring of the of CO2 processing of surfactant templated silica films to provide time dependent data on the local environment and dynamics of CO2 penetration. CO2 uptake occurs in surfactant tails even for hydrocarbon templates (C16H23N(CH3)3Br and C16H23NC5H5Br), which display negligible CO2 based swelling of the resulting pores. The timescale of silica condensation increases significantly in the presence of CO2 suggesting opportunities for structure alteration through application of external forces, such as magnetic fields and change in substrate chemistry and system humidity
  • [Show abstract] [Hide abstract]
    ABSTRACT: A cationic partially fluorinated surfactant with four carbons in the chain 1-(3,3,4,4,4-pentafluorobutyl)pyridinium chloride is employed as a structure-directing agent to synthesize nanoporous silica. Samples are prepared in dilute ammonia solutions at room temperature with a range of surfactant:Si ratios. The sample with the largest surfactant:Si ratio forms particles with wormhole-like micropores with an average diameter of 1.6 nm, which corresponds to the anticipated small size of the surfactant aggregates. On the other hand, the sample with the smallest surfactant:Si ratio forms a gel that, upon drying, has uniform 11.1 nm pores. The formation and stabilization of the latter large-mesopore structure is unusual for a sample prepared and dried under ambient conditions, and may reflect favourable roles of the surfactant both in inducing gelation and in stabilizing the pore structure during drying.
    Nanotechnology 07/2005; 16(7):S502-7. DOI:10.1088/0957-4484/16/7/026 · 3.82 Impact Factor
Show more