Introduction of acidic groups at the surface of activated carbon by microwave-induced oxygen plasma at low pressure

Functional groups at the surface of a commercial granulated activated carbon were modified at low temperature in an oxygen plasma. Changes in the chemistry of the surface were monitored by thermal desorption, titration of acidic groups, and XPS. A comparison of untreated and plasma-treated carbons, both before and after acid-washing and crushing, showed that reactions in oxygen plasma yield a low surface acidity with minimal modification of the initial sample porosity. Carboxylic groups, which are largely responsible for the surface acidity, appear to be unstable in the presence of the most reactive oxygen species of the plasma. (C) 2000 Elsevier Science Ltd. All rights reserved.