Enhanced visible light activity and mechanism of TiO2 codoped with molybdenum and nitrogen

Mo-N-codoped TiO2 was synthesized by using ammonium molybdate tetrahydrate and ammonia water as the sources of Mo and N, respectively. The resulting materials were characterized by X-ray diffraction (XRD), X-photoelectron spectroscopy (XPS) and UV–vis light diffuse reflection spectroscopy (DRS). Furthermore, the activity enhanced-mechanism was proposed. XRD results indicated that codoping favored the formation of anatase and improved the anatase crystallinity. XPS analysis revealed that N was incorporated into the lattice of TiO2 through substituting lattice O and coexisted in the substitutional forms. Meanwhile, Mo was incorporated into the lattice of TiO2 through substituting Ti and coexisted in the forms of Mo6+ and Mo5+. DRS showed that the light absorption in visible region was improved by co-doping, leading to a narrower band gap and higher visible activity for the degradation of phenol than that of others. The enhanced activity was attributed to the high anatase crystallinity, large amount of surface oxygen vacancies, intense light absorption and narrow band gap.