Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

Nanoscale Research Letters, Dec 2013

Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.

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Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

Min Zhang 0 Xinluan Yu 0 Dandan Lu 0 Jianjun Yang 0 0 Key Laboratory for Special Functional Materials of Ministry of Education, Henan University , Kaifeng 475004, People's Republic of China Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail. - Background Recently, nanoscale TiO2 materials have attracted extensive interest as promising materials for its applications in environmental pollution control and energy storage [1]. However, TiO2 is only responsive to UV light ( < 380 nm, 3% to 5% solar energy) due to its large bandgap energy (typically 3.2 eV for anatase). It hinders the practical application of TiO2 for efficient utilization of solar energy [2]. Many studies have been performed to extend the spectral response of TiO2 to visible light and improve visible light photocatalytic activity by doping and co-doping with metals of V, Fe, Cu, and Mo or nonmetals of N, B, S, and C [3,4]. Among the efforts of mono-doping, nitrogen-doped TiO2 was considered to be a promising visible light active photocatalyst. Asahi et al. reported that the effect of N doping into TiO2 achieved enhanced photocatalytic activity in visible region than 400 nm [5]. Theoretical works revealed that the result of the narrowed bandgap is due to N dopinginduced localized 2p states above the valence band [6]. However, these states also act as traps for photogenerated carriers and, thus, reduce the photogenerated current and limit the photocatalytic efficiency. In order to reduce the recombination rate of photogenerated carriers in the nitrogen-doped TiO2, co-doping transition metal and N have been explored [7]. Recently, theoretical calculations have reported that visible light activity of TiO2 can be even further enhanced by a suitable combination of Zr and N co-doping [8]. The Zr/N co-doping of anatase TiO2 could narrow bandgap by about 0.28 eV and enhance the lifetimes of photoexcited carriers. Previously, we had fabricated N-doped TiO2 with visible light absorption and photocatalytic activity using precursor of nanotubular titanic acid (NTA, H2Ti2O4 (OH)2) [9]. The visible light sensitization of N-doped NTA sample was due to the formation of single-electron-trapped oxygen vacancies (SETOV) and N doping-induced bandgap narrowing. It was also found that the N-doped TiO2 prepared by NTA showed the highest visible light photocatalytic activity compared with the TiO2 prepared by different other precursors such as P25 [10]. To obtain further enhanced photocatalytic performance, in this work, we prepared Zr and N co-doped TiO2 nanostructures using nanotubular titanic acid (NTA) and P25 as precursors by a facile wet chemical route and subsequent calcination. A systemic investigation was employed to reveal the effects of Zr and N doping/codoping in the enhancement of visible light absorption and photoactivity of the codoped TiO2 made by NTA and P25. The results showed that Zr/N-doped TiO2 nanostructures made by nanotubular NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. This work provided a strategy for the further enhancement of visible light photoactivity for the TiO2 photocatalysts in practical applications. Methods Synthesis of NTA precursors The precursor of nanotubular titanic acid was prepared and used as a co-doped precursor according to the procedures described in our previous reports [11-13]. Briefly, the Degussa P25 TiO2, a commercial standard TiO2 photocatalyst, reacted with concentrated NaOH solution to obtain Na2Ti2O5 H2O nanotubes, and then, NTA was synthesized by an ion exchange reaction of Na2Ti2O5 H2O nanotubes with an aqueous solution of HCl. Preparation of N and Zr co-doped TiO2 The as-prepared NTA was mixed with urea (mass ratio of 1:2) and dissolved in a 2% aqueous solution of hydrogen peroxide, followed by the addition of pre-calculated amount of Zr(NO3)4 5H2O (Zr/Ti atomic ratio, 0%, 0.1%, 0.3%, 0.6%, 1.0%, 5.0%, and 10%). The resultant mixed solution was refluxed for 4 h at 40C and followed by a vacuum distillation at 50C to obtain the product of x% Zr/N-NTA. Final Zr/N co-doped TiO2 were prepared by the calcination of x% Zr/N-NTA at a temperature range of 300C to 600C for 4 h. The target nanosized TiO2 powder was obtained, denoted as x% Zr/N-TiO2 (temperature), for example 0.6% Zr/N-TiO2(500). For reference, Degussa P25 TiO2 powders were used a (...truncated)


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Min Zhang, Xinluan Yu, Dandan Lu, Jianjun Yang. Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors, Nanoscale Research Letters, 2013, pp. 543, Volume 8, Issue 1, DOI: 10.1186/1556-276X-8-543