Characterization of the thermal decomposition products of δ-FeOOH by Fourier-transform infrared spectroscopy and N2 adsorption

Abstract

The surface and pore structures of the materials resulting on outgassing the colloidal δ-FeOOH particles at different temperatures in the range 50–300 °C have been investigated by a variety of techniques. The FTIR spectrum of the particles outgassed at 100 °C has a weak broad band at 3650 cm^–1 and a strong band at 3150 cm^–1 which are assigned to the surface and bulk OH groups of δ-FeOOH, respectively. When outgassed above 150 °C three bands appear at 3665, 3635 and 3400 cm^–1. The former two bands and the latter one can be assigned to the surface OH groups and the H₂O molecules adsorbed in the micropores, respectively. Increasing the outgassing temperature develops the microporosity of the products. The t-plots of the samples treated above 150 °C indicate the formation of micropores with a 0.8 nm width as confirmed by transmission electron microscopy (TEM).