Abstract
Energetic properties of γ-Fe2O3 surface were investigated by means of adsorption calorimetry. The heat of adsorption and isotherm of water vapor on γ-Fe2O3 surfaces were measured directly and simultaneously by use of an adsorption calorimeter. The surface of γ-Fe2O3 was found to be less active and relatively uniform in energy for water adsorption. It was suggested that there exist at least two types of cation sites, i. e., five-coordinated Fe3+ ions and three-coordinated Fe3+ ions, for water adsorption. The former sites can interact with water molecules to produce surface hydroxyl groups on which further water molecules are physisorbed, while the latter ones act only as physisorption sites for water under usual conditions. The heat treatment at a temperature higher than 250°C or the oxygen treatment at 200°C reduces the energetic homogeneity of the adsorption sites on γ-Fe2O3.
