Efficient Charge Carrier Separation in l-Alanine Acids Derived N-TiO(2) Nanospheres: The Role of Oxygen Vacancies in Tetrahedral Ti(4+) Sites

N-doped TiO(2) with oxygen vacancies exhibits many advantages for photocatalysis, such as enhanced visible light absorbency, inhibition of the photogenerated charge carrier recombination, etc. However, preparation of N-doped TiO(2) with oxygen vacancies under mild conditions is still a challenge. Herein, N-doped TiO(2) nanospheres with tetrahedral Ti(4+) sites were synthesized by using dodecylamine as template and assisted by l-alanine acids. The obtained samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis diffuse reflectance spectra (UV–Vis DRS). It was found that the dodecylamine as a neutral surfactant controlled the structure of TiO(2) spherical, while l-alanine acids provided a nitrogen source. The existence of tetrahedral Ti(4+) sites in N-doped TiO(2) was also confirmed. The N-doped TiO(2) sample with tetrahedral Ti(4+) sites exhibited significantly improved photocatalytic performance for degradation of methylene blue solution under UV light or visible light irradiation. A combined time-resolved infrared (IR) spectroscopy study reveals that the enhanced photocatalytic performance could be attributed to a large amount of photogenerated charge carriers and efficient charge separation. It is demonstrated that the shallow donor state produced by oxygen vacancies of tetrahedral Ti(4+) sites can effectively promote separation of charge carriers besides capturing electrons.