A method for determining the maeropore-size distribution in a porous solid, as well as the derived distributions for some typical porous materials, is presented. A glass dilatometer placed in a thermostated high-pressure bomb is used to measure the small changes in volume of a mass of mercury, in which the porous material under investigation is immersed, when the mercury is subjected to varying external pressure.

The effect of water on the reaction of 3-aminopropyltriethoxysilane (APTES) with mesoporous silica is investigated on two model systems. A MCM-41type material with a well-defined pore size is used to investigate changes in the pore size distribution upon reaction with APTES in toluene containing various amounts of water. It is found that, with increasing amount of water, clustering of APTES occurs, leading to a nonuniform distribution of the grafted amino groups and a scarcely functionalized pore body. A second model system with defined particle morphology and one-dimensional channels is employed to visualize the distribution of the grafted amino groups by fluorescent labeling and confocal laser scanning microscopy. The combination of nitrogen sorption and confocal laser scanning microscopy provides valuable insights concerning the role of trace water in the functionalization of mesoporous silica with alkoxysilanes. SECTION Nanoparticles and Nanostructures

The accessibility of amino groups in postsynthetically functionalized mesoporous silica MCM-41, MCM-48, and SBA-15 is investigated by reaction with fluorescein isothiocyanate (FITC). The quantitative analysis of the surface-grafted amino groups in relation to the amount of coupled FITC over a wide range of loadings affords information about potential pore blocking. In the pore diameter domain of 3−4 nm, the actual pore size of materials with a one-dimensional channel system (MCM-41) strongly affects the FITC coupling yield and the distribution of the anchored fluorescein moieties. In the case of SBA-15 (7.6 nm pore diameter), the accessibility of the grafted amino groups is similar to what is expected for a material with a completely open surface. However, grafting in the intrawall micropores of SBA-15 leads to a substantial fraction of inaccessible amino groups. As a direct consequence of short channel lengths and large external surface area, excellent accessibility is also observed for nanometer-sized MCM-41 (3.2 nm pore diameter).

A comparative study of the functionalization of mesoporous silica MCM-41 by deposition of 3-aminopropyltrimethoxysilane from toluene and from the vapor phase

Macropore-size distributions in typical porous substances have been measured, using the pressure porosimeter described in the previous paper. Substances investigated include Fuller's earth, diatomaceous earths, silica-alumina gels, flint quartz, porous iron, activated clay pellets and porous desiccants. POROUS materials are characterized by two related quantities: a particle density which is appreciably lower than the real or true density of the material, and a surface area which is greater than the observable geometric surface area.Porous materials differ widely in each of these characteristics; for example, the particle density of some diatomaceous earths is only 20% of the true density, and some activated carbons have surface areas 500,000 times the external geometric area, while the particle ^Second part of paper on "Pore-Size Distribution in Porous Materials." First part is found on page 782.