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.
Highlights
Since Novoselov and Geim isolated graphene for the rst time in 2004,1 many research efforts have been directed to its study, and remarkable results have been achieved in recent years.[2,3,4,5] Graphene is the rst discovered two-dimensional atomic crystal
Exfoliated graphene nanosheets (GNS) produced by wet-jet milling[92] were dispersed in NMP and DMF in order to obtain a stable dispersion ($0.2 mg mLÀ1), as shown in Fig. S1 in the Electronic supplementary information (ESI).† It is well known that these are well-suited organic solvents for the dispersion of graphene,[93] since they minimize the interfacial tension between solvent and graphene
In order to determine the best dispersant solvent and the most efficient dispersion technique, dynamic light scattering (DLS) measurements were performed on pristine GNS
Summary
Since Novoselov and Geim isolated graphene for the rst time in 2004,1 many research efforts have been directed to its study, and remarkable results have been achieved in recent years.[2,3,4,5] Graphene is the rst discovered two-dimensional atomic crystal. 22) provides numerous possible binding sites, its chemical inertness makes it difficult to modify graphene's structure without disrupting it or introducing excessive disorder.[23] Notably, graphene composites have been tailored to have desired solubility and stability,[24,25] tunable optical, electric, thermal, and mechanical properties,[26,27,28,29,30] enhanced catalytic capability,[31,32] and biological interactions.[31,33,34,35] where the 3-dimensionality of graphene-based materials becomes fundamental, like in gas and energy storage applications,[36,37,38,39] the modi cation of graphene's surface with heteroatoms or functional groups allows enhanced performance.[40,41,42,43,44,45,46] to nely control or intentionally design the. The simulated power spectrum provides a precise idea of the Raman signature of functionalized graphene, in agreement with the experimental data
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