Surface modification of activated carbon fabric with ozone. Part 3: Thermochemical aspects and electron spin resonance

It is shown that the differential scanning calorimetry (DSC) analysis of water desorption from activated carbon fabric (ACF) surfaces having different degrees of oxidation, is a valid alternative to immersion calorimetry in determining the desorption/adsorption energy of an adsorbate on the oxidized ACF surfaces. Processing the DSC endotherm relative to water desorption through the Clausius-Clapeyron equation it is possible to calculate either the water desorption energy from the oxidized ACF surfaces and also the hydrogen bond energy through which the water molecules are bound to the oxidized ACF surface. The DSC analysis of the ozonized ACF has revealed that secondary ozonides and peroxides are formed together with other oxygenated groups on the ACF surface, and were detected through an exothermal transition with two peaks at 118°C and 142°C with the measured decomposition enthalpy directly proportional to the degree of oxidation of the ACF surface. The ESR analysis on pristine ACF has revealed the presence of clustered paramagnetic centers. The reaction of the ACF with ozone greatly enhances the ESR signal since more free radicals are formed on the surface mainly in the form of oxygen-centered peroxide-type.