Frontiers in Magnetic Resonance

Frontiers in Magnetic Resonance

Electron Paramagnetic Resonance in Modern Carbon-Based Nanomaterials

This volume presents information about several topics in the field of electron paramagnetic resonance (EPR) study of carbon-containing nanomaterials. It introduces the reader to an array of ...
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Resolution of EPR Signals in Graphene-based Materials from Few Layers to Nanographites

Pp. 36-66 (31)

Francesco Tampieri and Antonio Barbon

Abstract

The focus of this chapter is set on the application of EPR methods to carbon-based materials, from nanographites to graphene-based materials, for the resolution and characterization of the different signals, related to the presence of specific species, or structures. Because of the intrinsic heterogeneity of the samples, this goal is not simple: most of the signals coming from different types of structures have similar spectroscopic features and are overlapping in the cw-EPR spectra with very different relative intensities. It is then necessary to use all possibilities that EPR offers, from the cw-EPR techniques to pulse EPR methods, to disentangle ideally all contributions. Our analysis of the EPR spectra considers the presence of three types of paramagnetic contributions: conduction electrons, edge states and molecular states. This interpretation framework has been shown to be effective for the considered materials, characterized by the presence of finite-dimension graphene layers, eventually stacked one above the other. In our analysis, we investigated different experimental parameters, like the variation in the temperature of the EPR intensity, the values of the g-tensors and the homogeneous lineshapes of the spectra to obtain further structural information. Pulse EPR methods were used to study and characterize species with long relaxation times (molecular states). Echo-detected EPR enabled to obtain their spectral lineshapes. Hyperfine spectroscopies, ESEEM, ENDOR and HYSCORE, determined the electron hyperfine couplings of unpaired electrons with magnetic nuclei, thus allowing the evaluation of the extent of the π-system and the presence of different types of nuclei.

Keywords:

Conduction electrons, Dysonian lineshape, Edge states, Echodetected EPR (ED-EPR), ENDOR, EPR, ESEEM, Expanded graphite, FT EPR, Graphene defects, Graphite, Hyperfine interaction, HYSCORE, Lorentzian lineshape, Molecular states, Nanographite, Natural graphite, π-systems, Reduced graphene oxide (RGO), Synthetic graphite.

Affiliation:

Department of Chemical Sciences, University of Padova, Padova, Italy.