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 π* and σ* resonances in carbon K-edge NEXAFS spectra suggest relatively high extents of recoveries of π-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 π 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 σ* resonance is seen to be most pronounced for reduction of graphene oxide by NaBH 4 and vapor-phase phenylhydrazine after annealing, suggesting relatively large conjugated domains in these materials after chemical reduction. ■ INTRODUCTIONThe peculiarities in the electronic structure of graphene, a monolayer of sp 2 -hybridized carbon atoms arrayed in a hexagonal periodic lattice, give rise to remarkable electrical transport phenomena including the half-integer quantum Hall effect, massless Dirac Fermion behavior of charge carriers, and ballistic conduction. 1−3 Given the exceptional promise of graphene for device integration as the active component of sensing, high-frequency electronics, interconnect, and actuator architectures, 4−6 much effort has been directed toward developing scalable routes for the fabrication and precise positioning of graphene with high crystal quality and controlled dimensions. Chemical vapor deposition 7,8 and solution-phase exfoliation routes 9−11 have emerged as the mainstays of these nascent nanomanufacturing efforts that have been imperative for spurring the commercialization of graphene-based products at an unprecedentedly rapid rate for a new material.As a structurally related material, graphite oxide has also been enjoying a renaissance in recent years. 12−16 Although the edgeand basal-plane functionalities of graphite oxide serve as scattering sites, limiting the obtained carrier mobilities and conductivities, the functional groups also endow the material with beneficial characteristics such as solution processability, chemical tunability, and matrix compatibility. The latter bears much significance for applications of exfoliated graphene oxide (GO) as a filler material within matrices wherein it provides improved electrical conductivity, thermal conductance, and...
We report the synthesis of a new tunnel-structured polymorph of V2O5 (ζ-V2O5) synthesized by topotactic ion extraction.
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