Passivated n-p co-doping of niobium and nitrogen into self-organized TiO₂ nanotube arrays for enhanced visible light photocatalytic performance

Passivated n-p co-doping of niobium and nitrogen was successfully incorporated into self-organized TiO₂ nanotube arrays by anodizing Ti-Nb alloys, followed with the heat treatment in a flow of ammonia gas. Nb was doped into TiO₂ nanotube arrays during the anodization by substituting Ti⁴⁺ with Nb⁵⁺, while N was doped into TiO₂ nanotube arrays during the heat treatment by substituting O^2- with N^3-. Since Nb in TiO₂ enhanced the adsorption of NH₃ molecules onto the nanotube arrays, Nb doping was found to promote the subsequent N doping into the anatase lattice. As predicted by first-principles band structure calculations, Nb/N co-doped titanium oxide nanotube arrays demonstrated a largely enhanced visible light response and visible light photocatalytic performance on the degradation of methylene blue, compared to TiO₂ nanotube arrays or TiO₂ nanotube arrays with either dopant. The passivated n-p co-doping approach may also be applied to other material systems and promise a wide range of technical applications.