Trends in Carbon, Oxygen, and Nitrogen Core in the X-ray Absorption Spectroscopy of Carbon Nanomaterials: A Guide for the Perplexed

Abstract

Successful deployment of carbon nanomaterials in many applications, such as sensing, energy storage, and catalysis, relies on the selection, synthesis, and tailoring of the surface properties. Predictive analysis of the behavior is difficult without detailed knowledge of the differences between various carbon nanomaterials and their surface functionalization, thus leaving the selection process to traditional trial-and-error work. The present characterization fills this knowledge gap for carbon nanomaterial surface properties with respect to chemical states and functionalization. We present an overview of the chemical trends that can be extracted from soft X-ray absorption spectroscopy (XAS) spectra on an extended set of nonideal carbon nanomaterials as a function of sp2 bonded carbon and bond ordering. In particular, the surface chemical state, the presence of long-range order in the carbon matrix, and a qualitative estimation of the amount of oxygen and nitrogen and their respective functional group formation on the material surface, together with the detailed material fabrication parameters, are reported. The results expand our understanding of carbon nanomaterial functionalization, which can support material selection in practice, provided that the specifications of the application are known.

X-ray Spectroscopy Fingerprints of Pristine and Functionalized Graphene

“…Copyright 2019 American Chemical Society. Spectra very similar to spectra b and d have also been published in ref ( 30 ), which discusses trends of carbon-based materials in XAS measurements from the experimental point of view.…”

“…Experimental spectra of three samples were analyzed by utilizing computational references. Fabrication methods and the spectra themselves have been previously published in ref ( 30 ) as a part of a more comprehensive data set of carbon materials. These particular experimental samples, which are sp 2 -rich, were chosen because they are suitable to be analyzed with the computational references obtained in this work for graphene-based systems.…”

“…The experimental samples were acquired as follows: highly oriented pyrolytic graphite (HOPG) was obtained from a commercial source (Scanwel, U.K.), the graphene sample was fabricated via thermal annealing, and the graphite oxide sample was made by applying a modified Hummers’ method. 30 , 60 …”

“…For XAS measurements, described in more detail in ref ( 30 ), a bending magnet (beamline 8–2) was used at the Stanford Synchrotron Radiation Lightsource (SSRL), employing a 55° incidence angle (magic angle) of X-ray incidence. This beamline has a spherical grating monochromator with approximately 200 meV resolution (using 40 × 40 μm 2 slits).…”

“…During all the measurements, the incoming flux was recorded using a nickel grid with a gold sputtered film. A more detailed description about the measurements as well as sample fabrication can be found in ref ( 30 ), and ref ( 61 ) provides more experimental data about these types of samples.…”