Electronic and magnetic properties of acid-adsorbed nanoporous activated carbon fibers

Nanoporous activated carbon fibers (ACFs) feature 3D disordered networks of nanographite domains that consist of stacks of 3–4 nanographene sheets each. At the peripheries of the nanographene sheets, the localized spins of a nonbonding edge state are created. The magnetic properties of the edge-state spins in ACFs are investigated in relation to the interaction with acid molecules adsorbed in the nanopores. HCl molecules condensed physisorptively in the nanopores mechanically compress the nanographite domains, resulting in the reduction of the magnetic moments of the edge-state spin in the form of a magnetic switching effect. HNO3 molecules, which have significant oxidation ability, are subjected to charge transfer from the nanographite domains. This induces a two-step reduction in the edge-state spin concentration, wherein the first and second steps are related to the charge transfer with the nanographene sheets that directly face the nanopores and that with the nanographene sheets in the interior of the nanographite domains, respectively. In diluted HNO3, the blockade by water molecules prevents the interaction of the HNO3 molecules with the interior nanographene sheets, allowing for charge transfer only with the graphene sheets that directly face the nanopores; this results in a single-step change in the spin concentration.