Computationally Supported Neutron Scattering Study of Natural and Synthetic Amorphous Carbons

Neutron powder diffraction and inelastic neutron scattering (INS) were used to determine the structure and hydrogen content of basic structure units (BSUs) of sp2 amorphous carbons at the atomic level. A comparative study of two natural (shungite carbon and antraxolite) and two synthetic (carbon blacks) species of the highest-rank carbonization revealed nanosize stack structure of all samples. The stacks are formed by BSUs representing framed graphene molecules (graphene oxyhydrides) of ∼2.5 nm lateral dimension. The INS study showed the presence of hydrogen atoms in the BSU framing area as well as of adsorbed water in the sample pores configured by BSU stacks. Simulated INS spectra of adsorbed water showed its monolayer disposition within the pores. BSU INS spectra were simulated for a set of particular models simulating H-standard features of the INS spectra of graphene-based species, in general, and BSU hydrogen component of the studied samples, in particular. Simulations were performed in the framework of both spin-independent (density functional theory) and spin-dependent (unrestricted Hartree-Fock) molecular vibrational dynamics. The obtained results allowed a reliable presentation of the hydrogeneous component of the BSU atomic structure and proposing a specific INS classification of sp2 amorphous carbons with respect to their hydrogeneousness. © 2019 American Chemical Society.