Quantification of surface oxides on carbonaceous materials

X-ray photoelectron spectroscopy (XPS) in conjunction with chemical derivatization has been developed to quantify the concentrations of hydroxyl, carboxylic acid, and carbonyl groups on carbonaceous surfaces, specifically black carbons (BCs). Control studies on polymers and graphite were performed to establish the selectivity and stoichiometry of each derivatization reaction toward the targeted oxide. Hydroxyl groups were successfully derivatized with trifluoroacetic anhydride. Derivatization strategies using trifluoroethanol, however, had to be modified from protocols used in polymer studies in order to effectively derivatize carboxylic acid groups on BCs. Derivatizing agents previously used to target carbonyl groups on polymers were found unsuitable for BC materials because of nonspecific adsorption interactions between the phenyl ring of the derivatizing agent and the extended graphene sheets of the BCs. These complications were overcome by employing trifluoroethyl hydrazine as a new derivatizing agent for the quantification of carbonyl groups. These three derivatization reactions were used in combination with XPS to quantify the surface concentrations of hydroxyl, carboxylic acid, and carbonyl groups on several BC materials including natural chars, soots, and an activated carbon. Experiments using these derivatization reactions in conjunction with energy dispersive spectroscopy were also evaluated as a means to probe the oxide concentrations within the bulk of these materials.