Synthesis conditions for hexagonal mesoporous silica layers

Abstract

Hexagonal mesoporous silica layers were prepared by the sol±gel route using silicon alkoxides as silica precursors and alkyltrimethylammonium bromides to form the templating liquid crystal mesophase. The synthesis conditions required to obtain well-ordered crack-free layers were investigated. Thin layers exhibiting these properties were deposited from diluted sols. X-Ray diffraction enabled characterisation of the thermal evolution of their ordered structure and crystalline texture. Their porosity was experimentally measured from nitrogen adsorption±desorption analyses carried out directly on the thin layers. Two main synthesis parameters were identi®ed. The ®rst is the ageing time of the sol before deposition: 29 Si NMR showed that the disappearance of the ordered structure in the layers is related to the appearance of the Q 3 species in the sol. The second important synthesis parameter is the surfactant volume fraction in the medium after the removal of the volatile components. Using hexadecyltrimethylammonium bromide, well-ordered hexagonal layers were obtained for surfactant volume fractions ranging from 0.5 to 0.65, as expected from the corresponding water± surfactant binary diagram. For surfactants with shorter alkyl chains, the domain of existence of the hexagonal layers shifts to higher surfactant volume fractions in agreement with the evolution previously observed on the water±surfactant binary diagrams.

Adsorption and Desorption Isotherms at Ambient Temperature Obtained by Ellipsometric Porosimetry to Probe Micropores in Ordered Mesoporous Silica Films

“…3(b)) is designated as a Type IVc (mesopores) in the IUPAC classification (Sing et al, 1985), the four others are composite isotherms of Type I (micropores) and Type IVc (mesopores). Similar composite isotherms have been already obtained on ordered hexagonal silica powders (Albouy and Ayral, 2002) and layers (Klotz et al, 2000) in the case of nitrogen adsorption at 77.4 K.…”

“…Usually composite isotherms are obtained with N 2 as adsorptive on micro/mesoporous silica materials, from which the microporosity can be evaluated with different methods (Albouy and Ayral, 2002;Klotz et al, 2000;Colomer and Anderson, 2001;Poladi and Landry, 2002). In the case of microporous materials as those used in gas separation and methane storage, Lozano-Castello et al (2002) have suggested that the most important parameter is the micropore size distribution They have estimated it in microporous carbon materials from high-pressure CO 2 and CH 4 adsorption isotherms around ambient temperature by application of the General Adsorption Isotherm model (McEnaney et al, 1987).…”

Dynamics of pH-sensitive nitroxide radicals in water adsorbed in ordered mesoporous molecular sieves by EPR Spectroscopy

“…The ordered structure of MCM-41 and SBA-15 is a honeycomb type hexagonal array of regular non-crossing pores-channels with a narrow pore size distribution. The walls of the channels have a definite thickness and are constituted of amorphous SiO 2 [1,2]. The channel diameter can be tuned from 3 to 50 nm depending on the synthesis conditions [3].…”

Biomimetic and Bioinspired Hybrid Membrane Nanomaterials

“…These membranes have been tested in selective Na þ /K þ transport. Periodic mesoporous materials have attracted considerable attention during the last decade because of their promising applications as membranes or as hosts for functional membrane materials [55,56]. Many of these applications benefit from arrangements of preferentially aligned, ordered arrays of certain mesostructures.…”