Step-like adsorption isotherms of molecules on γ-FeOOH and the surface homogeneity of γ-FeOOH

Abstract

The adsorption isotherms of H₂O, CCl₄, n-C₆H₁₄ and CH₃OH on the synthetic γ-FeOOH particles have been measured at different temperatures from –5 to 35 °C. The isotherms of H₂O, CCl₄ and n-C₆H₁₄ exhibited a step below their monolayer adsorption capacity, while no step appeared in the isotherm of CH₃OH. The isosteric heats of adsorption of H₂O, CCl₄ and n-C₆H₁₄ showed a maximum at an adsorption coverage of 0.6, 0.8 and 0.75, respectively. The surface fractal dimension was close to 2, indication that the γ-FeOOH surface is homogeneous. It can be concluded that the step-like isotherms reflect the two-dimensional condensation of these molecules on the chemically and geometrically homogeneous surface of γ-FeOOH.