Structural Complexity of Graphene Oxide: The Kirigami Model

Investigation of highly oxidized graphene oxide (GO) by solid-state nuclear magnetic resonance (NMR) spectroscopy has revealed an exceptional level of hitherto undiscovered structural complexity. A number of chemical moieties were observed for the first time, such as terminal esters, furanic carbons, phenolic carbons, and three distinct aromatic and two distinct alkoxy carbon moieties. Quantitative on-edimensional (1D) and two-dimensional (2D) C-13{H-1} NMR spectroscopy established the relative populations and connectivity of these different moieties to provide a consistent local chemical structure model. An inferred 2 nm GO sheet size from a very large (similar to 20%) edge carbon fraction by NMR analysis is at odds with the >20 nm sheet size determined from microscopy and dynamic light scattering. A proposed kirigami model where extensive internal cuts/tears in the basal plane provide the necessary edge sites is presented as a resolution to these divergent results. We expect this work to expand the fundamental understanding of this complex material and enable greater control of the GO structure.

Automated summary

Investigation of highly oxidized graphene oxide using solid-state nuclear magnetic resonance spectroscopy revealed previously undiscovered structural complexity, including new chemical moieties. Discrepancies between NMR analysis and microscopy/dynamic light scattering results led to the proposal of a kirigami model as a resolution. This work is expected to advance fundamental understanding and control of graphene oxide structure.