Analysis of Surface OH Groups on TiO2 Single Crystal with Polarization Modulation Infrared External Reflection Spectroscopy

Abstract

The surface OH groups on rutile TiO2 single-crystal surfaces under atmospheric conditions were investigated with polarization modulation infrared external reflection spectroscopy (PM-IER). The PM technique is effective for selective detection of the oriented surface OH groups on the TiO2 surface due to the cancellation of strong IR signals from three-dimensional isotropic water vapor and bulk water adsorbed on the surface under atmospheric conditions. The PM-IER spectrum on the TiO2 (110) surface gave only a single peak at 3279 cm−1. The absence of coexisting symmetric and asymmetric peaks of water molecules reveals that the peak is not derived from the water molecules adsorbed on the surface but from the OH groups directly binding to the TiO2 surface. A remarkable decrease of the peak frequency reaching ca. 400 cm−1 compared to that observed by high-resolution electron energy loss spectroscopy (HREELS) under a vacuum condition (3690 cm−1) was observed, indicating that the surface OH groups under atmosphe...