Article pubs.acs.org/JPCC
Thermodynamic Properties of α‑Fe2O3 and Fe3O4 Nanoparticles Elinor C. Spencer,† Nancy L. Ross,*,† Rebecca E. Olsen,‡ Baiyu Huang,‡ Alexander I. Kolesnikov,§ and Brian F. Woodfield‡ †
Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, United States Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States § Chemical and Engineering Materials Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, United States ‡
S Supporting Information *
ABSTRACT: The thermodynamic properties of hydrated αFe2O3 (hematite) and Fe3O4 (magnetite) nanoparticles have been comprehensively assessed. In addition to 9 nm Fe3O4, three α-Fe2O3 nanoparticles samples of different sizes (11, 14, and 25 nm) and bulk α-Fe2O3 have been evaluated by inelastic neutron scattering methods. The contribution of the two-level magnetic spin flip transition to the heat capacity of the αFe2O3 particles has been determined. The isochoric heat capacity of the water confined on the surface of these two types of iron oxide particles have been calculated from their INS spectra, and is affected by the chemical composition of the underlying particle. Furthermore, the heat capacity and dynamics of the particle hydration layers appear to be influenced by a complex array of factors including particle size, water coverage, and possibly the magnetic state of the particle itself. ∼6000 m2 mol−1. However, α-Fe2O3 has a strong affinity for water, and the sorption of water onto the particle relaxes the surface thus reducing its energy, and consequently hydrated αFe2O3 particles are more thermodynamically stable at the nanoscale than akaganeite, lepidocrocite (at surface areas
