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. 2021 Aug 30;3(20):5841-5852.
doi: 10.1039/d1na00335f. eCollection 2021 Oct 12.

Covalent organic functionalization of graphene nanosheets and reduced graphene oxide via 1,3-dipolar cycloaddition of azomethine ylide

Luca Basta  1 , Aldo Moscardini  1 , Filippo Fabbri  1 , Luca Bellucci  1 , Valentina Tozzini  1 , Silvia Rubini  2 , Andrea Griesi  3   4 , Mauro Gemmi  4 , Stefan Heun  1 , Stefano Veronesi  1
Affiliations

Covalent organic functionalization of graphene nanosheets and reduced graphene oxide via 1,3-dipolar cycloaddition of azomethine ylide

Luca Basta et al. Nanoscale Adv. .

Erratum in

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.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Schematic representation of the 1,3-DC of azomethine ylide on GNS and rGO.
Fig. 2
Fig. 2. (a) STEM image of a functionalized GNS. (b) EDX map of a functionalized GNS, showing the uniform distribution of the N atoms (green pixels). (c–e) Optical microscopy images of functionalized GNS in (c) NMP and (d) in DMF, and (e) functionalized rGO in DMF dropcasted onto silica substrates for Raman measurements.
Fig. 3
Fig. 3. Raman spectra of (a) pristine GNS in NMP and (b) functionalized GNS in NMP and (c) in DMF. The fit of each spectrum is shown and all peaks are labeled (the peaks that appear only after the functionalization of GNS by 1,3-DC of azomethine ylide are in bold).
Fig. 4
Fig. 4. Raman spectra of pristine rGO taken in the (a) lower, (b) intermediate, and (c) higher region of Raman shifts. Raman spectra of functionalized rGO taken in the (d) lower, (e) intermediate (zoom is shown in the inset), and (f) higher region (zoom, where a smoothing of the signal was performed, is shown in the inset) of Raman shifts. The fit of each spectrum is shown and all peaks are labeled (the peaks that appear only after the functionalization of rGO by 1,3-DC of azomethine ylide are in bold).
Fig. 5
Fig. 5. Distribution of the RESP-derived partial atomic charges reported as a color gradient for the atoms in (a) pristine rGO and (b) functionalized rGO (blue = positive, red = negative). The highest positive/negative charge values are close to the epoxy groups (that present O atoms outside the graphene plane). The amplification of the charge gradient due to the presence of the azomethine ylide is visible.
Fig. 6
Fig. 6. (a) Model of the azomethine ylide attached to rGO, where the red atoms are the oxygens of the epoxy groups. The functional groups of interest are highlighted: carboxyl group = yellow, nitrogen and the connected atoms = orange, methyl group = violet, cathecol group = green. (b) Power spectrum (PS) of the velocity autocorrelation function (black). Projections on the PS for the functional groups of interest are highlighted in the same colors of panel (a). The regions of interest are labeled. The inset shows the zoom of the region where the stretching of the CN bonds are visible. It is worth to recall that the intensities of the peaks in the simulated PS do not directly correspond to the ones from the experimental Raman spectra, where additional selection rules are involved.
Fig. 7
Fig. 7. XPS spectrum of the C 1s core level of functionalized GNS in DMF, and the fit showing the individual components (Shirley-type background in brown).
Fig. 8
Fig. 8. Normalized XPS spectra of N 1s core levels of functionalized GNS in NMP, GNS in DMF, and rGO in DMF (shifted in height). The different positions of the peak related to the solvent are labeled (dashed black line for NMP, dashed blue line for DMF), together with the constant position of the peak from the ylide (dashed green line). Each fit is shown by a dashed line, with a Shirley-type background in brown (the spectrum of functionalized GNS in NMP shows an additional signal arising from NaNO2, and its fit is shown as dashed violet line).
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