Unusual photo-induced adsorption–desorption behavior of propylene on Ag/TiO2 nanotube under visible light irradiation

Titanium dioxide (TiO2) nanotube with a large amount of single-electron-trapped-oxygen-vacancies (coded as T2) was obtained by annealing nanotube H2Ti2O4(OH)2 (coded as T1) at 400 °C in air. Silver nanoparticles with a diameter of about 30–50 nm were loaded onto the surface of T2 via deposition associated with photochemical reduction under ultraviolet irradiation. The resulting Ag/TiO2 nanotube (coded as T3) was characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet–visible light diffusion reflectance spectrometry. It was found that C3H6 experienced unusual photo-induced adsorption–desorption on T3 under visible light irradiation. Namely, C3H6 was initially desorbed from T3 and then adsorbed on T3 under visible light irradiation. On the contrary, C3H6 was initially adsorbed on T3 in the dark, followed by desorption. The reason might lie in that two kinds of active sites exist on the surface of T3, corresponding to quite different rates of adsorption and desorption. It was found that oxygen vacancies in association with deposited silver particles, were responsible for the alternative adsorption–desorption of C3H6 on T3.