Effect of wet chemical treatments on the distribution of surface oxides on carbonaceous materials

The properties of carbonaceous materials are often modified using wet chemical treatments; however, the detailed changes in the oxide distribution that accompany different chemical treatments have not been clearly elucidated. To illustrate how this information can be obtained, we have employed chemical derivatization in conjunction with X-ray photoelectron spectroscopy (XPS) to quantify changes in the concentration of hydroxyl, carbonyl, and carboxylic acid groups on the surface of a modified wood char following several different wet chemical treatments (H2O2, HNO3, ammonium persulfate, O3, and NaBH4). Results from the present investigation highlight the fact that changes in surface oxide distributions are sensitive to the chemical treatment. For example, ammonium persulfate selectively increases the carboxylic acid group concentration. In contrast, O3 increases the concentrations of hydroxyl, carbonyl, and carboxylic acid groups with roughly equal propensity. These oxide distributions were further modified by reduction with NaBH4, which generally converts carbonyl and carboxylic acid groups to hydroxyl groups. A comparison of results obtained from XPS and chemical analysis reveal that the oxidative effects of wet chemical treatments are restricted to the char’s surface.