(329m) Adsorption of Water Vapor Onto Microporous Carbons Prepared by Various Oxidation Methods

Activated carbon has been used as adsorbent for removing pollutants such as volatile organic compounds (VOC). However, adsorption of VOC on activated carbon is hampered by moisture in air, since oxygen functional groups act as adsorption primary sites for water molecules though hydrogen bond. Therefore, in this study, equilibrium isotherms of water vapor on microporous carbons containing oxygen functional groups have been investigated in order to see correlation between amounts of water adsorbed and site concentrations of surface oxygen functional groups. Different types of activated carbons, one activated carbon fiber and two granular activated carbons were oxidized by nitric acid, hydrogen peroxide and air at different conditions. Surface chemistry and pore structure of those carbons were characterized respectively by temperature programmed desorption (TPD) and nitrogen adsorption at 77K. Adsorption of water vapor on the oxidized carbon samples was measured with volumetrically apparatus at 298K. The data acquisition was focused solely on the effect of surface oxygen functional groups, since adsorption of water vapor was affected by both of carbon pore characteristics and surface nature. It was found that amounts of water adsorbed depend on the amount of CO2 producing groups at low relative pressure, regardless of pore structure of the microporous carbons. The isotherms were also analyzed by Dubinin-Serpinski (DS) equation. The use of this equation showed that primary adsorption center a0 attributes to the oxygen functional groups, especially CO2 producing groups.