Motoyasu Kato1,Tomoyuki Tamura1,Mitsuhiro Honda1
Nagoya Institute of Technology1
Motoyasu Kato1,Tomoyuki Tamura1,Mitsuhiro Honda1
Nagoya Institute of Technology1
TiO<sub>2</sub> is a typical photocatalytic material that is relatively inexpensive and highly safe, and has been actively studied to improve its performance for wider range of applications. One of our group reported that the formation of an amorphous structure on TiO<sub>2</sub> surface increased the reaction rate by about 13 times compared to the anatase surfaces. However, its high catalytic activity was reduced when the amorphous surface was scraped by etching. Therefore, it is considered that the control of the amorphous surface is the key of improving the catalytic activity.<br/>STEM-EELS has been widely used in recent years to observe nanoscale atomic-arrangements and electronic structures with high spatial resolution.In particular, ELNES (electron energy-loss near-edge structures) is able to provide sensitive information on chemical bonding, valence states and coordination. We observed amorphous surfaces of TiO<sub>2</sub> samples with high photocatalytic activity using the atomic-resolution electron microscope (JEOL ARM-200F @Nitech), and found that spectra for the surface region were significantly different from those for bulk region. In this study, we identify amorphous surface structures that contribute to improve the catalytic activity using first-principles calculations, combining with electron-microscopy observations.<br/>Amorphous surface models were generated by quenching from the melt using classical MD method and subsequent relaxation using first-principles method with VASP code [1]. Ti <i>L</i>-edge ELNES were simulated for those models with QMAS code [2]. We found that Ti <i>L</i>-edge ELNES for 4-coordinated Ti in the amorphous surface region are in good agreement with experimental results. In addition, in order to clarify the origin of the high photocatalytic activity of the amorphous surface, we investigated the chemical reaction between 4-coordinated Ti and adsorbed molecules. Our results suggest that oxygen defects in the amorphous surface contribute to the improvement of photocatalytic activity.<br/><br/>References : [1] G. Kresse et al, Phys. Rev. B 54, 11169-11186 (1996), Phys. Rev. B 59, 1758-1775 (1999). [2] T. Tamura et al., Phys. Rev. B 85, 205210 (2012).