Atomistic Model of Micelle-TemplatedMesoporous Silicas:Structural, Morphological, and Adsorption Properties.

The structural, morphological, and adsorption propertiesof MCM-41porous silicas are investigated using a realistic numerical modelobtained by means of ab initiocalculations [Ugliengo,P.; et al. Adv. Mater.2008, 20, 1]. Simulated X-ray diffraction, small angle neutronscattering, and electronic microscopy for the atomistic model arein good agreement with experimental data. The morphological featuresare also assessed from chord length distributions and porous volumeand specific geometrical surface calculations, etc. The N2, CO2, and H2O adsorption isotherms in theatomistic model of MCM-41 are also in reasonable agreement with theirexperimental counterpart. An important finding of the present workis that water forms a film adsorbed on specific hydrophilic regionsof the surface while the rest of the surface is depleted in watermolecules. This result suggests that the surface of MCM-41 materialsis heterogeneous, as it is made up of both hydrophilic and hydrophobicpatches. While adsorption and irreversible capillary condensationcan be described using the thermodynamical approach by Derjaguin (alsoknown as the Derjaguin–Broekhoff–De Boer model), theFreundlich equation fits nicely the data for reversible and continuousfilling in small pores. [ABSTRACT FROM AUTHOR]