Heat of Water Adsorption on Large-Pores Mesoporous Silica

The heat of water adsorption on large-pores mesoporous silica suitable for hemostatic applications has been assessed. The values were determined by means of microcalorimetry (as differential heat of adsorption, Qdiff, at 318 K) and variable temperature IR (VTIR) spectroscopy through the thermodynamic analysis of spectroscopic data based on the van’t Hoff equation (as standard enthalpy of adsorption, ΔH0, in the temperature range 318–360 K). The results obtained by the two different techniques are in satisfactory agreement, leading to a value of the water heat of adsorption between 30 and 37 kJ/mol, ascribed to the interaction of water molecules with terminal silanols via one H-bond. The heat of water adsorption (below 44 kJ/mol) reveals that the surface of the large-pores mesoporous silica herein investigated may be considered mainly hydrophobic. For the first time, VTIR spectroscopy of water adsorption has been applied for the characterization of the surface hydrophilicity/hydrophobicity of a silica material.