L. Borello

The benzene molecule as a probe for steric hindrance at proton sites in zeolites: an IR study

When a molecule, like benzene, is engaged in H-bonding with an acidic proton in zeolites, secondary interactions with the surrounding walls may occur, orienting the molecule and effecting the spectroscopic measure of the acidity. Information is gained on the geometry of the site from an otherwise disturbing phenomenon.

Accessibility to gases of dye molecules in hybrid surfactant-silica mesophases

Abstract Two types of CTABr-silica mesophases have been prepared, one of them a powder with hexagonal structure containing Congo Red, another one a film with cubic structure containing Disperse Red 1. In the former case the dye has been occluded via co-entrapping, whereas in the latter it has been covalently anchored to the silica matrix via a co-condensation route. In both systems, the dye molecules proved to be accessible to NH 3 , HC1 and (CH 3 ) 3 N in the gas phase, notwithstanding the presence of micelles in the mesophase, which results to be fully permeable to such molecules.

Differences between isolated silanols in all-silica ITQ-2 and MCM-41

Abstract The isolated SiOH species at the surface of all-silica ITQ-2 and MCM-41 have been compared as it concerns their IR features and the equilibrium constant of the interaction with some bases. The O-H stretching frequency is strictly the same and the same acidity has been observed with NH 3 and CO. Acetone shows instead with MCM-41 a marginally higher O-H shift, and a definitely larger equilibrium constant. These differences are ascribed to secondary interactions between H-bonded acetone and the surrounding of the SiOH group, favoured by the curved nature of the mesoporous wall of MCM-41, interactions absent in ITQ-2 because of the peculiar crystalline nature of the surface.

Accessibility of dye-molecules embedded in the micellar phase of hybrid mesostructured MCM41-type materials.

Abstract Silica-based hybrid mesostructured materials (MCM-41 type) containing surfactant- embedded Methylene Blue have been prepared and characterized by several techniques, including UV-Vis spectroscopy and cyclic voltammetry, and compared to other systems containing the same dye molecule. The micellar phase of the hybrid material was found to be permeable to protons, which may be of interest for potential applications in chemical and biological sensing devices.

Covalent bonding of Disperse Red 1 in HMS silica: synthesis and characterisation

Abstract Optical properties of the dye Disperse Red 1 covalently bonded to HMS surface via a one- step procedure are strongly affected by the polarity at the silica surface, which is modulated by the amount of residual template molecules and ethoxy groups formed during extraction in refluxing hot ethanol.

Acidity of ITQ-2 zeolite as studied by FT-IR spectroscopy of adsorbed molecules in comparison with that of MCM-22

Publisher Summary This chapter presents the acidity of ITQ-2 zeolite as studied by the Fourier transform infrared (FT-IR) spectroscopy of adsorbed molecules in comparison with that of MCM-22. ITQ-2, a novel zeolitic structure prepared by swelling and delaminating a MWW precursor, has been studied by IR spectroscopy. The same precursor yields, when calcined, the zeolite MCM-22. BrOnsted acidity has been measured as the propensity either to engage in H-bonds or to transfer the proton to unsaturated hydrocarbons. Comparison with MCM-22 shows that dealumination accompanies the process of delamination, but no appreciable change in residual BrOnsted acidity takes place. Reaction of propene with BrOnsted sites to branched oligomers occurs mainly on the external surface. Oligomers show no tendency to evolve to allylic cationic species, in contrast with MCM-22.