title: Validity of the t-plot method to assess microporosity in hierarchical micro/mesoporous materials.
abstract: The t-plot method is a well-known technique which allows determining the micro- and/or mesoporous volumes and the specific surface area of a sample by comparison with a reference adsorption isotherm of a nonporous material having the same surface chemistry. In this paper, the validity of the t-plot method is discussed in the case of hierarchical porous materials exhibiting both micro- and mesoporosities. Different hierarchical zeolites with MCM-41 type ordered mesoporosity are prepared using pseudomorphic transformation. For comparison, we also consider simple mechanical mixtures of microporous and mesoporous materials. We first show an intrinsic failure of the t-plot method; this method does not describe the fact that, for a given surface chemistry and pressure, the thickness of the film adsorbed in micropores or small mesopores (< 10σ, σ being the diameter of the adsorbate) increases with decreasing the pore size (curvature effect). We further show that such an effect, which arises from the fact that the surface area and, hence, the free energy of the curved gas/liquid interface decreases with increasing the film thickness, is captured using the simple thermodynamical model by Derjaguin. The effect of such a drawback on the ability of the t-plot method to estimate the micro- and mesoporous volumes of hierarchical samples is then discussed, and an abacus is given to correct the underestimated microporous volume by the t-plot method.
authors.affiliation: Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, ENSCM, 8 rue de l'Ecole Normale, 34296 Montpellier Cedex 05, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Galarneau
authors.forename: François
authors.initials: F
authors.lastname: Villemot
authors.forename: Jeremy
authors.initials: J
authors.lastname: Rodriguez
authors.forename: François
authors.initials: F
authors.lastname: Fajula
authors.forename: Benoit
authors.initials: B
authors.lastname: Coasne