Characterization of the surface carbonyl and hydroxyl coverage on glassy carbon electrodes using Raman spectroscopy

Abstract

A fluorescein derivative was synthesized and covalently bonded to hydroxyl groups on glassy carbon surfaces. Since the fluorescein fluorescence was quenched by the carbon surface, its resonance Raman spectrum could be observed at surface coverages of approximately 1%. The fluorescein/GC bond was stable to repeated sonication in ethanol, but was rapidly hydrolyzed by mild base. This new label for surface hydroxyl groups was combined with a similar label for carbonyl groups to assess changes in the coverage of surface C–OH and CO with GC pretreatment. The relative densities of these species varied with both the initial GC heat treatment and with subsequent chemical treatment in hot HNO3 or hot KOH solutions. HNO3 increased the CO coverage on vacuum heat treated (VHT) GC, while KOH increased the C–OH coverage. Chemical treatments of GC following polishing or heat treatment were less selective, due to the significant initial coverage of CO and C–OH. In all cases, significant surface oxygen on GC was present in forms other than CO and C–OH.