Confirmation of the assignment of vibrations of goethite: an ATR and IES study of goethite structure.

ABSTRACT

Transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM/EDS) and X-ray diffraction (XRD) were used to characterize the morphology of synthetic goethite. The behavior of the hydroxyl/water molecular units of goethite and its thermally treated products were characterized using Fourier transform-infrared emission spectroscopy (FT-IES) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The results showed that all the expected vibrational bands between 4000 and 650 cm(-1) including the resolved bands (3800-2200 cm(-1)) were confirmed. A band attributed to a new type of hydroxyl unit was found at 3708 cm(-1) and assigned to the FeO-H stretching vibration without hydrogen bonding. This hydroxyl unit was retained up to the thermal treatment temperature of 500 °C. On the whole, seven kinds of hydroxyl units, involving three surface hydroxyls, a bulk hydroxyl, a FeO-H without hydrogen bonding, a nonstoichiometric hydroxyl and a reversed hydroxyl were observed, and three kinds of adsorbed water were found in/on goethite.