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 H2 ambient at 450 °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 °C, whereas the hydrogen-related complex(es) responsible for the 3412.4 and 3416.9 cm−1 lines disappear(s) after annealing at 250 °C. The nature of the defects resulting in these vibrational modes is discussed. [ABSTRACT FROM AUTHOR]