Surface modification of a TiO2 photocatalyst with Ba species was investigated in photoassisted nitrogen oxide (NOx) storage under UV-light irradiation. The NOx storage capacity in the Ba-modified TiO2 photocatalyst was 1.4 times higher than that of the non-modified TiO2 photocatalyst. Structure and role of the surface Ba species on a TiO2 surface were characterized using temperature programmed reaction (TPR), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). The characterization results suggested that Ba-Ti mixed oxides with a two-dimensional layer and amorphous structure on a TiO2 surface were generated via decomposition of Ba(NO3)(2) precursors by O-2 pretreatment at 773 K. Based on the results of the characterizations and the reactions, the generated Ba-Ti mixed oxides on a TiO2 surface stored NOx more densely than the TiO2 surface; therefore, the generation improved the activity in the photoassisted NOx storage under UV-light irradiation. (C) 2015 Elsevier B.V. All rights reserved.