Characterization of mesoporous solids: Pore condensation and sorption hysteresis phenomena in mesoporous molecular sieves

Abstract

We report results of an experimental study of pore condensation and hysteresis phenomena of nitrogen and argon in pristine MCM-48 and MCM-41 silica materials (pore diameter range: 3.5–5 nm). An analysis of nitrogen and argon adsorption/desorption isotherms obtained on a MCM-48 silica sample (pore diameter 4.6 nm) at 77 K and 87 K, respectively, leads to the conclusion, that—although MCM-48 consists of a unique, three-dimensional pore network—the desorption branch of the argon sorption hysteresis loop (type H1) corresponds to the pore diameter. However, the sorption hysteresis behavior for argon sorption at 87 K and 77 K appears to be peculiar in MCM-41 and MCM-48 materials of smaller pore diameters (i.e. in the range between 3.5 and 4.2 nm). A clear correlation between the desorption branch of the observed argon hysteresis loops and the pore diameter is not possible anymore in this pore diameter range. Further, a detailed comparison of the pore condensation and hysteresis behavior in MCM-48 and MCM-41 silica materials of nearly equal pore diameters reveals that sorption hysteresis loops are wider in the pseudo-one-dimensional pores of MCM-41 compared to the three-dimensional pore system of MCM-48 silica.