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Micromachines (Basel). 2018 Nov 24;9(12). pii: E618. doi: 10.3390/mi9120618.

Enhanced Photocatalytic Performance of Nitrogen-Doped TiO₂ Nanotube Arrays Using a Simple Annealing Process.

Author information

1
Ceramics and Biomaterials Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. lehuuphuoc@tdt.edu.vn.
2
Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. lehuuphuoc@tdt.edu.vn.
3
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30049, Taiwan. letrunghpc@gmail.com.
4
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30049, Taiwan. lamtungoc1310@gmail.com.
5
Faculty of Natural Sciences, Thu Dau Mot University, 6 Tran Van On Street, Thu Dau Mot City 820000, Vietnam. hangntn@tdmu.edu.vn.
6
Faculty of Fundamental Sciences, Thai Nguyen University of Technology, Thai Nguyen 24000, Vietnam. truonglyk3@gmail.com.
7
Ceramics and Biomaterials Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. ltctuyen89@gmail.com.
8
Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. ltctuyen89@gmail.com.
9
Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. phamthanhphong@tdt.edu.vn.
10
Laboratory of Magnetism and Magnetic Materials, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam. phamthanhphong@tdt.edu.vn.
11
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30049, Taiwan. jimleu@mail.nctu.edu.tw.

Abstract

Nitrogen-doped TiO₂ nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N₂ gas at 450 °C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH₄F/ethylene glycol solution. The N-doping concentration (0⁻9.47 at %) can be varied by controlling N₂ gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light (λ ≥ 400 nm) illumination at 120 mW·cm-2. N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h-1, which was a 125% improvement over that of TNAs (0.115 h-1). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electron‒hole recombination rate.

KEYWORDS:

N-doped TNAs; band gap; modified TiO2; photocatalytic activity; thermal annealing; two-step anodization

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