HYDROPHOBIC AND HYDROPHILIC BEHAVIOR OF MICELLE-TEMPLATED MESOPOROUS SILICA

Adsorption of water on M41s systems has been studied by means of micro calorimetry and IR spectroscopy. After thermal treatment at only 423 K , the samples show two types of surface patches, one hydrophobic (char acterized by isolated silanols not interacting with water) and the oth er highly hydrophilic (showing the highest heat of reversible adsorpti on observed so far for the H2O/SiO2 system). Thermal treatment at 1023 K causes an extensive dehydration, partially recovered by dissociativ e adsorption. Both the propensity for silanol condensation (and the op posite reaction of hydrolysis of siloxane bridges) and the very high h eat of reversible adsorption are related to the structural properties of M41s.