MCM-41 Porosity: Are Surface Corrugations Micropores?

摘要

Since the discovery of MCM-41, the interpretation of its structureand porous texture has evolved from a simple model of straight parallel mesoporesto a much more complex model with a rough surface. The physisorption ofnitrogen at 77.3 K and 87.5 K and of carbon dioxide at 273 K was carried out onboth MCM-41 and a precipitated silica (PSIL). This silica was prepared forcomparison purposes under identical conditions to those for MCM-41 but withoutthe use of the surfactant. The adsorption characteristics of both materials for bothadsorptives were indistinguishable at low adsorption pressures independent of theadsorption temperature employed, suggesting similarities in parts of their porosity(i.e. excluding mesoporosity). We propose that, in addition to its well-acknowledged mesoporosity, MCM-41 includes considerable surface roughnessand/or heterogeneities similar to that shown by microporous silica. This surfacestructure appears to have adsorption characteristics indistinguishable fromclassical microporosity, and may also be an important feature of this materialwhich is very often not taken into consideration in most of its applications.