The interaction of O2, NO, and N2O with surface defects of dispersed titanium dioxide

A combined study of intrinsic structural defects in reduced TiO2 was performed using mass spectrometry, optical diffuse-reflectance spectroscopy, and UV photoelectron spectroscopy (UPS). It was found that the reduction of TiO2 resulted in the appearance of absorption in the region 0.50 less than or equal to hv less than or equal to 3.50 eV (400 less than or equal to lambda less than or equal to 2500 nm), which is formed by absorption due to free electrons (a continuum at hv less than or equal to 1.50 eV), local centers - Ti3+ ions (a band at 2.00 eV), and oxygen vacancies (bands at 1.17, 2.81, and 2.55 eV). The spectrum of induced occupied electronic states in the forbidden gap and the position of oxygen vacancy levels with respect to the Fermi level were determined by UPS. The absorption of reduced TiO2 was stable on the sample to T = 800 K in a vacuum; however, it weakened in contact with O-2, NO, and N2O molecules beginning at T = 300 K (surface sites) and T greater than or equal to 400 K (subsurface sites) as a result of filling oxygen vacancies with atomic oxygen in the course of dissociative adsorption. The adsorption complexes formed by the interaction of O-2, NO, and N2O With defects were analyzed by temperature-programmed desorption. The distribution of sites over the energies of oxygen binding was found with the use of a nonuniform surface model, and specific oxygen adsorption species were revealed. It was found that the irradiation of TiO2 activates the formation and decay of sites and results in the formation of specific O-2 and N2O adsorption species.