Adsorption of sulfur dioxide by active carbon treated by nitric acid: II. Effect of preheating on the adsorption properties

The adsorption and desorption of sulfur dioxide by active carbon, treated by nitric acid and followed by heating at 200-1000 degrees C, were studied. The HNO3 treated carbon has a higher adsorption capacity for sulfur dioxide, than the untreated carbon, in spite of its lesser basicity. This may be the result of interaction of the SO2 with the oxygenated surface groups of acidic character. Water promotes the adsorption of SO2. Heating results in a decrease of the carbon acidity because of decomposition of the surface oxygenated structures. It also leads to an increase of basicity resulting from the formation of basic sites. These changes of the carbon acid-base properties are particularly pronounced for the HNO3 treated carbon due to higher concentration of the surface oxygenated groups. The increased basicity promotes adsorption of SO2 and inhibits desorption by an acid-base mechanism different from the mechanism of adsorption on the carbon, which has not been preheated. (C) 1997 Elsevier Science Ltd.