Abstract: N-doped TiO₂ photocatalyst samples were prepared by manual grinding the mixture of nanotube titanic acid and ammonium bicarbonate followed by annealing the mixture at different temperatures in Ar atmosphere for 4 h. The samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometry, transmission electron microscope, and N₂ adsorption-desorption. The XPS results indicated that the N was in the form of interstitial atom, i.e., Ti–O–N bond. The intermediate (NH₄)₂Ti₂O₄(OH)₂ was formed when the mixture was calcined at different temperatures. Subsequently, the N was released due to the decomposition of (NH₄)₂Ti₂O₄(OH)₂, resulting in the formation of interstitial-N and oxygen vacancies. N-TiO₂ samples showed enhanced visible light absorption and visible light photocatalytic activity because of the existence of interstitial N-dopants and oxygen vacancies. The doped N atoms restrained the phase transition from anatase to rutile at higher temperature. Photocatalytic activity was evaluated by degradation of methyl orange in aqueous solution under xenon lamp irradiation, and the N-TiO₂ sample with n(N)/n(Ti) = 4 annealed at 500 °C exhibited the highest photocatalytic activity. After 130 min irradiation, the photocatalytic degradation rate of methyl orange was up to 100%, almost 30% higher than that of un-doped TiO₂.

Key words: nitrogen doping, solid state method, photocatalysis, nanotube titanic acid, nanotube titanate