Nature of Adsorption Hysteresis in Cylindrical Pores: Effect of Pore Corrugation

To examine the effect of pore corrugation on the nature of adsorption and desorption branches due to capillary condensation in cylindrical pores, we measured the adsorption subloops and temperature dependence of the adsorption desorption isotherms for oxygen on ordered mesoporous silicas COK-11 and MCM-41. Although the two samples give very sharp steps due to capillary condensation in the isotherms, the pores of COK-11 are corrugated, whereas the amplitude of the pore corrugation in MCM-41 synthesized with the pH adjustment is negligibly small. The pore corrugation affects significantly the nature of adsorption hysteresis. The temperature dependence of capillary condensation/evaporation pressure of oxygen on the MCM-41 synthesized very carefully is perfectly consistent with the theoretical prediction for a pore of cylindrical shape open at both ends. On the other hand, the hysteresis temperature, above which the adsorption hysteresis disappears, is not appreciably affected by the pore corrugation.