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 into TiO2 nanotube arrays.
• Anodization of Ti–Nb alloys for Nb dopant incorporation and uniform distribution.
• Nb doping was found to promote the subsequent N doping into the anatase lattice.
• Largely enhanced visible light response from Nb/N co-doping.
• Largely enhanced visible light photocatalytic degradation of MB from Nb/N co-doping.

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 O2− with N3−. 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.

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