Soft X-ray Absorption Spectroscopy Studies of the Electronic Structure Recovery of Graphene Oxide upon Chemical Defunctionalization

A comparative evaluation of the efficacy of different reducing agents in defunctionalizing graphene oxide is performed using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at carbon and oxygen K-edges. The relative intensities of pi* and sigma* resonances in carbon K-edge NEXAFS spectra suggest relatively high extents of recoveries of pi-conjugation upon reduction using vapor-phase phenylhydrazine or hydrazine as well as neat phenylhydrazine. The use of these reducing agents in combination with modest thermal annealing appears to be particularly effective for deepoxidation and decarboxylation of graphene oxide. Polarized carbon K-edge NEXAFS spectroscopy measurements allow evaluation of the extent of warping or planarity induced upon chemical reduction. Treatment with vapor phenylhydrazine and subsequent thermal annealing entirely disrupts the alignment of reduced graphene oxide while facilitating substantial recovery of pi conjugation. In contrast, annealing subsequent to treatment with vapor-phase hydrazine yields high dichroic ratio values that are substantially increased as compared to unreduced graphene oxide, indicating a greater extent of substrate alignment. Restoration of excitonic confinement of the sigma* resonance is seen to be most pronounced for reduction of graphene oxide by NaBH4 and vapor-phase phenylhydrazine after annealing, suggesting relatively large conjugated domains in these materials after chemical reduction.