Infrared absorption on hydrogen in anatase TiO2

IR absorption study of natural single-crystalline anatase TiO2 has been performed. It was found that as-received material reveals absorption lines at 3357.8, 3359.3, 3372.5, and 3389.3 cm(-1), whose intensity grows if the sample is hydrogenated from the H-2 ambient at 450 degrees C. In addition, hydrogenation results in the appearance of two lines at 3412.4 and 3416.9 cm(-1). Isotope substitution experiments have shown that all six lines are due to the stretch local vibrational modes (LVMs) of O-H bonds, which are preferentially aligned parallel to the c-axis of TiO2 . The group of LVMs at 3357.8, 3359.3, 3372.5, and 3389.3 cm(-1) retains the same relative intensities and is stable against thermal treatments up to 450 degrees C, whereas the hydrogen-related complex(es) responsible for the 3412.4 and 3416.9 cm(-1) lines disappear(s) after annealing at 250 degrees C. The nature of the defects resulting in these vibrational modes is discussed. (C) 2015 WILEY - VCH Verlag GmbH & Co. KGaA, Weinheim