Abstract
Nanocomposites of α-Fe2O3 (hematite) and (N-doped) graphene oxide (GO) were investigated using first-principles calculations with focus on structure, chemical bonding, electronic structure and H2O adsorption. The nanocomposites were modeled as the interface between the α-Fe2O3 (0 0 0 1) surface and the basal plane of reduced graphene oxide, comprising epoxy groups (C:O ratio of 8) as well as graphitic and pyridinic nitrogen doping. The composite structures exhibited strong chemical bonding by the formation of a bridging Fe–O–C bond. The calculated binding energy between the materials was −0.56 eV per Fe–O–C bond for GO and up to −1.14 eV for N-doped GO, and the binding energies were found to correlate with the charge of the bridging oxide ion. The composites exhibited partly occupied carbon states close to or above the α-Fe2O3 valence band maximum. Dissociative adsorption of H2O was found to be more exothermic for the composites compared to the individual materials, ranging from about −0.9 to −1.7 eV for the most stable configurations with hydroxide species adsorbed to GO and protons forming NH groups or adsorbed to the α-Fe2O3 surface.
Highlights
Synergistic combinations of the functional properties of metal oxides and graphitic materials have shown great promise for a range of applications including photocatalysts, supercapacitors, batteries and gas sensors [1e4]
The improved performance of photocatalysts comprising an oxide semiconductor and graphene oxide (GO) has been ascribed to longer charge carrier lifetime as photogenerated electrons are injected into GO
Graphene oxide has been used as a conductive network in quantum dot sensitized solar cells [7]
Summary
Synergistic combinations of the functional properties of metal oxides and graphitic materials have shown great promise for a range of applications including photocatalysts, supercapacitors, batteries and gas sensors [1e4]. The functional properties of the nanocomposites can be expected to depend on the interface between the materials, which is inherently challenging to accurately characterize in terms of chemical bonding, electronic structure and electrochemical properties. We focus on two of the most common substitutions: quaternary N which substitutes C in the graphene lattice, denoted graphitic N, and pyridinic N which can form on graphene edges or within the basal plane as a cluster comprising a C vacancy surrounded by three quaternary N In both cases, sp hybridization is retained for pristine graphene, while the hybridization depends on the local structural configuration of the functional groups in the case of GO. Chemisorption of H2O on the (N-doped) GO and a-Fe2O3 surface region was investigated
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