Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored.

The electronic structure and spin magnetism for few-layer-graphene nanoribbons synthesized by chemical vapor deposition have been investigated using near-edge x-ray absorption fine structure ͑NEXAFS͒ and electron-spin resonance ͑ESR͒. For the pristine sample, a prepeak was observed below the ‫ء‬ peak close to the Fermi level in NEXAFS, indicating the presence of additional electronic states close to the Fermi level. The intensity of this prepeak decreased with increasing annealing temperature and disappeared after annealing above 1500°C. The ESR spectra, which proved the presence of localized spins, tracked the annealingtemperature-dependent behavior of the prepeak with fidelity. The NEXAFS and ESR results jointly confirm the existence of a magnetic edge state that originates from open nanographene edges. The disappearance of the edge state after annealing at higher temperatures is explained by the decrease in the population of open edges owing to loop formation of adjacent graphene edges.

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