STM 9

Selective Covalent Organic Functionalization of Graphene via 1,3-Dipolar Cycloaddition

Notwithstanding graphene’s great application potential, its outstanding properties come also with some limitations. The absence of a band-gap makes graphene’s use as an active element in electronic devices and sensors challenging and, therefore, an engineering of graphene’s properties is required. Surface functionalization of graphene with suitable molecules offers the possibility to finely tune the system’s physical and chemical properties, resulting in a synergistic combination of the individual features of each component. However, while the high specific surface area of graphene provides numerous possible binding sites, its chemical inertness makes it difficult to functionalize the surface.

We have successfully performed organic functionalization of graphene 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 presence of the pyrrolidine ring of the azomethine ylide on the surface of functionalized graphene, while micro-Raman spectroscopy has allowed detecting new spectral features arising from the functionalization, which are described in agreement with the power spectrum obtained from ab initio molecular dynamics simulation. Moreover, X-ray photoelectron spectroscopy of functionalized graphene allows a quantitative elemental analysis and the estimation of the surface coverage, showing a higher degree of functionalization for reduced graphene oxide. This higher reactivity 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.

In a next step, we performed the selective surface functionalization of exfoliated graphene flakes via electron irradiation, which allows both a controlled enhancement of the chemical reactivity of the high quality graphene flakes and the precise design and engineering of the functionalized area. Pristine exfoliated monolayer graphene flakes are characterized by AFM and Raman spectroscopy, and then exposed to electron beam irradiation with energy of 30 kV and dose of 40.000 μC/cm2 (as previously reported). Subsequent AFM images clearly resolve the pattern designed by the electron beam, with 0.1 μm step size (Fig. 1a). Raman maps show a homogeneous defect coverage in the exposed area, with the emergence of the characteristic D peak only in the patterned region. Graphene is functionalized via 1,3-dipolar cycloaddition of azomethine ylides. This reaction in-situ involves the localization of a C=C bond, which is favorable in presence of the defects, hence introducing a selective control of the chemical modification of graphene. The Raman analysis on the functionalized flakes exhibits new features in the region 1050 – 1750 cm-1, observed only in the patterned area. Ab initio DFT simulations of the power spectrum of functionalized graphene (model in Fig. 1b) allow to identify the vibrational contribution both of the functional groups of the azomethine ylides grafted on the graphene surface and of the modified vibrational modes of the graphene sheet (Fig. 1c). Finally, under laser irradiation (up to 1.6 mW) the recovering towards the Raman spectrum of non-functionalized defected graphene indicates the desorption of the ylide and the reversibility of the functionalization. Functionalization of patterned graphene using 1,3-dipolar cycloaddition is thus shown to be a significant step towards the controlled synthesis of graphene-based complex structures and devices at the nanoscale.


Figure 1: (a) AFM image showing the defect pattern after electron irradiation; (b) DFT model of the azomethine ylide attached to graphene (the functional groups of interest are highlighted with different colors); (c) Raman spectrum of functionalized patterned graphene, showing the fit of the new features.

Publications:

  1. Luca Basta, Aldo Moscardini, Filippo Fabbri, Luca Bellucci, Valentina Tozzini, Silvia Rubini, Andrea Griesi, Mauro Gemmi, Stefan Heun, Stefano Veronesi: Covalent Organic Functionalization of Graphene Nanosheets and Reduced Graphene Oxide via 1,3-Dipolar Cycloaddition of Azomethine Ylide, arXiv:2112.12505 [cond-mat.mtrl-sci].
  2. Luca Basta, Aldo Moscardini, Filippo Fabbri, Luca Bellucci, Valentina Tozzini, Silvia Rubini, Andrea Griesi, Mauro Gemmi, Stefan Heun and Stefano Veronesi: Covalent organic functionalization of graphene nanosheets and reduced graphene oxide via 1,3-dipolar cycloaddition of azomethine ylide, Nanoscale Adv., 2021, 3, 5841.
  3. Luca Basta, A. Moscardini, S. Veronesi, F. Bianco: Substrate surface effects on electron-irradiated graphene, arXiv:2103.15725 [cond-mat.mtrl-sci].
  4. Luca Basta, Aldo Moscardini, Stefano Veronesi, Federica Bianco: Substrate surface effects on electron-irradiated graphene, Surfaces and Interfaces 28 (2022) 101694.
  5. Luca Basta, Federica Bianco, Aldo Moscardini, Filippo Fabbri, Luca Bellucci, Valentina Tozzini, Stefan Heun, Stefano Veronesi: Deterministic Covalent Organic Functionalization of Monolayer Graphene with 1,3-Dipolar Cycloaddition Via High Resolution Surface Engineering, arXiv:2202.06609 [cond-mat.mtrl-sci].
  6. Deterministic Graphene organic functionalization: a controlled functionalization for energy storage and sensing, Cnr Nano Activity Report 2022. [Pages 84-85]
  7. Luca Basta: Defect-engineered graphene functionalization via cycloaddition reaction – towards a versatile platform for nanoscale devices and 3D heterostructures, PhD Thesis, Scuola Normale Superiore, Pisa, Italy, 2022.
  8. L. Basta, F. Bianco, A. Moscardini, F. Fabbri, L. Bellucci, V. Tozzini, S. Heun, and S. Veronesi: Deterministic organic functionalization of monolayer graphene via high resolution surface engineering, J. Mater. Chem. C 11 (2023) 2630 – 2639.

Presented at:

  1. L. Basta, F. Bianco, A. Moscardini, F. Fabbri, L. Bellucci, V. Tozzini, S. Heun, S. Veronesi: Selective Covalent Organic Functionalization Of Patterned Graphene Via 1,3-Dipolar Cycloaddition, chem2Dmat, Virtual Online Conference, 31 August – 03 September 2021 (oral). [Abstract] [Talk]
  2. L. Basta, A. Moscardini, F. Fabbri, L. Bellucci, V. Tozzini, S. Rubini, A. Griesi, M. Gemmi, S. Heun, S. Veronesi: Covalent Organic Functionalization of Graphene Nanosheets and Reduced Graphene Oxide via 1,3-Dipolar Cycloaddition of Azomethine Ylide, 31st International Conference on Diamond and Carbon Materials, Virtual Online Conference, 6 – 9 September 2021 (oral). [Abstract] [Talk]
  3. L. Basta: Defect-engineered graphene functionalization via cycloaddition reaction: towards a versatile platform for nanoscale devices and 3D heterostructures, PhD thesis defense, Scuola Normale Superiore, Pisa, Italy, 13 December 2022. [Talk]
  4. Stefano Veronesi, Luca Basta, Federica Bianco, Aldo Moscardini, Filippo Fabbri, Luca Bellucci, Valentina Tozzini, Stefan Heun: Deterministic organic functionalization of exfoliated monolayer graphene via high-resolution surface engineering, CMD 30 Fismat 2023, Milan, Italy, September 4 – 8, 2023. [Abstract] [Talk]