Sorption with activated carbon material has been proven as a reliable technology in water treatment due to fast sorption kinetics and high sorption capacity. Enhancing sorption reactions, particularly on novel nanofibrous forms of carbon, requires functionalizing the surface with specific chemical groups while maintaining overall physical structure. Here we focus on generating carboxylic acid groups on an activated carbon nanofiber material (ACNF) as the first step in functionalization. We assessed both the traditional wet chemical oxidants of HNO3, HNO3/H2SO4, KMnO4 and more novel oxidants of OsO4 and RuO4 in order to optimize the formation of carboxylic acids while limiting material degradation. OsO4 requires a secondary oxidation, for which we examined oxone and KMnO4. The strong HNO3 or mixture with H2SO4 destroyed the macrostructure of ACNF, and resulted in yields of less than 83%. Apart from the low yield of &lt;50% after RuO4 oxidation, other treatments resulted in at least 96% mass recovery. Among these oxidants, OsO4+KMnO4 resulted in both high yield and significant oxidation, with the largest percent as carboxylic acids (85%) as opposed to lactone or phenol groups based on boehm titrations. The quantity of carboxylic acids on the surface increased from about 1.5 mmol/g on ACNF to at least 5 mmol/g with OsO4 and RuO4 oxidations. Given the same initial reactant concentrations in the KMnO4 and OsO4 treatments, and the fact that OsO4 treatment resulted in additional carboxylic acid groups, the data suggests that OsO4 promotes the formation of dicarboxylic acid groups as suggested by the literature. To understand the position and density of carboxylic acid groups, further characterization is needed. The formation of either single or adjacent carboxylic acid groups on the surface are good building blocks for further functionalization with specific ligands or groups that have the potential to enhance sorption of micropollutants.

Comparison of chemical oxidation pathways on nanofibrous activated carbon materials

251st National Meeting (2016)

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