DETERMINATION OF HYDROGEN-BONDING ACID SITES ON SILICA USING THE CAL-AD METHOD

Silica gel, under various hydration conditions, was investigated using a novel calorimetric adsorption (Cal-Ad) method. This method combines data from calorimetric and adsorption titrations of a solid surface using a small Probe molecule in a noninteractive solvent. The Cal-Ad method proved to be more sensitive than other characterization techniques (e.g. temperature-programmed desorption) and calorimetric techniques. Previously, it was believed that the silica surface consisted of one type of hydrogen-bonding site. The Cal-Ad method has elucidated three hydrogen-bonding sites of different strengths using pyridine as the basic probe molecule. The equilibrium constant of binding, enthalpy of binding, and number of each of these sites have been determined.