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

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 (FF-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 degrees 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. (C) 2013 Elsevier B.V. All rights reserved.