Covalent Organic Functionalization of Graphene Nanosheets and Reduced Graphene Oxide via 1,3-Dipolar Cycloaddition of Azomethine Ylide

TL;DR

This study demonstrates a successful method for organic functionalization of graphene nanosheets and reduced graphene oxide using 1,3-dipolar cycloaddition of azomethine ylide, with optimized solvents and techniques, confirmed by multiple characterization methods.

Contribution

It introduces an effective functionalization process for graphene using 1,3-dipolar cycloaddition, highlighting the role of solvent choice, dispersion technique, and surface reactivity differences.

Findings

N,N-dimethylformamide and homogenization are most effective for functionalization.

Functionalization is confirmed by EDX, Raman, and XPS techniques.

Reduced graphene oxide shows higher degree of functionalization due to surface charge localization.

Abstract

Organic functionalization of graphene is successfully performed via 1,3-dipolar cycloaddition of azomethine ylide in the liquid phase. The comparison between 1-methyl-2-pyrrolidinone and N,N-dimethylformamide as dispersant solvents, and between sonication and homogenization as dispersion techniques, proves N,N-dimethylformamide and homogenization as the most effective choice. The functionalization of graphene nanosheets and reduced graphene oxide is confirmed using different techniques. Among them, energy-dispersive X-ray spectroscopy allows to map the pyrrolidine ring of the azomethine ylide on the surface of functionalized graphene, while micro-Raman spectroscopy detects new features arising from the functionalization, which are described in agreement with the power spectrum obtained from ab initio molecular dynamics simulation. Moreover, X-ray photoemission spectroscopy of functionalized graphene allows the quantitative elemental analysis and the estimation of the surface coverage, showing a higher degree of functionalization for reduced graphene oxide. This more reactive behavior originates from the localization of partial charges on its surface due to the presence of oxygen defects, as shown by the simulation of the electrostatic features. Functionalization of graphene using 1,3-dipolar cycloaddition is shown to be a significant step towards the controlled synthesis of graphene-based complex structures and devices at the nanoscale.