Molybdenum and nitrogen co-doped $TiO_2$ nanotube arrays (TNAs) were preparedby anodizing in association with hydrothermal treatment. As-prepared Mo and Nco-doped TNAs were characterized by field emission scanning electronmicroscopy, X-ray diffraction, X-ray photoelectron spectroscopy andultraviolet-visible light diffuse reflection spectroscopy. Besides, thephotocatalytic activity of Mo and N co-doped TNAs for the degradation ofmethylene blue (denoted as MB) under visible light irradiation was evaluated.It was found that N in co-doped TNAs coexists in the forms of N-Ti-O andN-O-Ti, while Mo exists as $Mo^{6+}$ by substituting Ti in the lattice of$TiO_2$. In the meantime, Mo and N co-doping extends the absorption of TNAsinto the whole visible light region and results in remarkably enhancedphotocatalytic activity for the degradation of MB under visible lightirradiation. This could be attributed to the synergetic effect betweenMo-doping and N-doping. Namely, Mo and N passivated co-doping produces newstates in TNAs, thereby narrowing the bandgap and decreasing the recombinationrate of electrons and holes. As a result, the visible light absorption andphotocatalytic activity of TNAs is greatly increased. Furthermore, Mo ions withmultiple valences in all co-doped samples could act as trapping sites toeffectively decrease the recombination rate of electrons and holes, which alsocontribute to improved photocatalytic activity of Mo and N co-doped TNAs.Keywords: TiO2 Nanotube Arrays, Mo, N, Co-Doping, Photocatalytic Activity.
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