Unexpected Chemical and Thermal Stability of Surface Oxynitride of Anatase TiO₂ Nanocrystals Prepared in the Afterglow of N₂ Plasma

Abstract

Passivation of surface defects by the formation of chemically inert structure at the surface of TiO 2 nanocrystals can be potentially useful in enhancing their photocatalytic activity. In this regard, we have studied the surface chemical states of TiO 2 surfaces prepared by a treatment in the afterglow of N 2 microwave plasma using Xray photoemission spectroscopy (XPS). We find that nitrogen is incorporated into the surface after the treatment up to a few atomic percent. Interestingly, the surface oxynitride layer is found to be chemically stable when it's in contact with water at room temperature (RT). The surface nitrogen species were also found to be thermally stable upon annealing up to 150 o C in the atmospheric pressure. Thus, we conclude that the treatment of oxide materials such as TiO 2 in the afterglow of N 2 plasma can be effective way to passivate the surface with nitrogen species.