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efficiency of the ZnO/TiO2 composites was improved 2.17 times Hubei Province Science and Technology Support Project (no.
more than that of the pure ZnO, and 5.29 times more than that 2013BHE012), and the Fundamental Research Funds for the
of the pure TiO2 lm. Cycle degradation of methyl blue with the Central Universities.
ZnO/TiO2 composite was conducted, as shown in Fig. 11(b).
Obviously, there was no decrease aer recycling the composite 6
times, which proved there was a good stability of contact at the
Notes and references
interface between the ZnO and the TiO2. Similarly, the degra-
dation of methylene blue also greatly improved with the data k
(ZnO) ¼ 0.05868 hꢂ1, k (TiO2) ¼ 0.03194 hꢂ1, k (ZnO/TiO2) ¼
0.07132 hꢂ1, as shown in Fig. 12.
1 A. Fujishima, X. T. Zhang and D. A. Tryk, Surf. Sci. Rep., 2008,
63, 515–582.
2 G. Liu, L. Z. Wang, H. G. Yang, H. M. Cheng and G. Q. Lu,
J. Mater. Chem., 2010, 20, 831–843.
We believe that the above results were due to the synergistic
effect of TiO2 and ZnO, which increased the separation effi-
ciency of the photo-generated carriers, and thus improved the
photocatalytic efficiency.30 That is to say, the higher photo-
catalytic activity of the TiO2/ZnO composite was related to the
role of the ZnO nanoneedles grown upon the TiO2 layer.
According to our previous work, during high-temperature
thermal oxidation, the Zn lm was oxidized into ZnO nano-
needles, and there was good lattice matching between the TiO2
and the ZnO through the short atom diffusion at the inter-
face.12,20,21 Different to the relatively “loose” heterojunction
prepared from regular chemical methods, this kind of tight
contact heterojunction exhibited a great effect on the photo-
generated carriers' movement.
3 S. H. Nam, H. S. Shim, Y. S. Kim, M. A. Dar, J. G. Kim and
W. B. Kim, ACS Appl. Mater. Interfaces, 2010, 2, 2046–2052.
4 P. S. Archana, R. Jose, T. M. Jin, C. Vijila, M. M. Yusoff and
S. Ramakrishna, J. Am. Ceram. Soc., 2010, 93, 4096–4102.
5 Y. P. Zhang, C. Z. Li and C. X. Pan, J. Am. Ceram. Soc., 2012,
95, 2951–2956.
6 R. Ostermann, D. Li, Y. D. Yin, J. T. McCann and Y. N. Xia,
Nano Lett., 2006, 6, 1297–1302.
7 Z. Y. Liu, D. Sun, P. Guo and J. O. Leckie, Nano Lett., 2007, 7,
1081–1085.
8 M. A. Kanjwal, N. Barakat, F. A. Sheikh and H. Y. Kim,
J. Mater. Sci., 2010, 45, 1272–1279.
9 D. L. Li and C. X. Pan, Prog. Nat. Sci., 2012, 22, 59–63.
10 Y. P. Zhang, L. F. Fei, X. D. Jiang, C. X. Pan and Y. Wang,
J. Am. Ceram. Soc., 2011, 94, 4157–4161.
According to the photocatalytic mechanism, under light
irradiation, due to the energy band differences between the ZnO 11 H. Y. Wang, Y. Yang, X. A. Li, L. J. Li and C. Wang, Chin.
and the TiO2, the photo-induced electrons will transfer from the
Chem. Lett., 2010, 21, 1119–1123.
ZnO conduction band to the TiO2 conduction band, while the 12 D. L. Li, X. D. Jiang, Y. P. Zhang, B. Zhang and C. X. Pan,
photo-induced holes move from the TiO2 valence band to the
J. Mater. Res., 2013, 28, 507–512.
ZnO valence band.12,30,36 During these transforming processes, 13 N. X. Wang, C. H. Sun, Y. Zhao, S. Y. Zhou, P. Chen and
we believe that the tight and compact heterojunction interface L. Jiang, J. Mater. Chem., 2008, 18, 3909–3911.
between the ZnO nanoneedles and the TiO2 layer played a key 14 R. L. Liu, H. Y. Ye, X. P. Xiong and H. Q. Liu, Mater. Chem.
role as a charge transport bridge, which signicantly increased Phys., 2010, 121, 432–439.
the separation efficiency of the photo-generated carriers, and 15 Y. X. Liu, Y. Z. Xie, J. T. Chen, J. Liu, C. T. Gao, C. Yun,
enhanced the photocatalytic efficiency of the ZnO/TiO2
composite.
B. G. Lu and E. Q. Xie, J. Am. Ceram. Soc., 2011, 94, 4387–
4390.
16 M. A. Kanjwal, N. Barakat, F. A. Sheikh, S. J. Park and
H. Y. Kim, Macromol. Res., 2010, 18, 233–240.
17 M. E. Fragala, I. Cacciotti, Y. Aleeva, R. Lo Nigro, A. Bianco,
G. Malandrino, C. Spinella, G. Pezzotti and G. Gusmano,
CrystEngComm, 2010, 12, 3858–3865.
4. Conclusions
A novel ZnO/TiO2 heterojunction composite with a nanoneedle-
on-lm structure was prepared via three steps of MAO, plating
and thermal oxidation. By using a high temperature treatment 18 Y. Z. Li, W. Xie, X. L. Hu, G. F. Shen, X. Zhou, Y. Xiang,
in air, metal Zn was directly transformed into ZnO nanoneedles X. J. Zhao and P. F. Fang, Langmuir, 2010, 26, 591–597.
upon the MAO TiO2 layer, which formed a tight contact het- 19 A. B. Djurisic, X. Y. Chen, Y. H. Leung and A. Ng, J. Mater.
erojunction between the ZnO and the TiO2. This greatly
Chem., 2012, 22, 6526–6535.
increased the separation efficiency of the photo-induced 20 D. L. Li, W. H. Wu, Y. P. Zhang, L. L. Liu and C. X. Pan,
carriers for improving the photocatalytic properties. This J. Mater. Sci., 2014, 49, 1854–1860.
physical process provided an effective method for preparing 21 C. Z. Luo, D. L. Li, W. H. Wu, Y. P. Zhang and C. X. Pan, RSC
high-performance thin-lm photocatalysts. It exhibited several Adv., 2014, 4, 3090–3095.
advantages, such as simplicity, economy, suitability for mass 22 Y. Q. Wang, X. D. Jiang and C. X. Pan, J. Alloys Compd., 2012,
production, and potential applicability in the elds of photo-
catalysis, solar cells and supercapacitors, etc.
538, 16–20.
23 Y. Han, D. H. Chen and L. Zhang, Nanotechnology, 2008, 19,
335705.
24 K. Y. Jung and S. B. Park, Appl. Catal., B, 2000, 25, 249–256.
25 B. S. Liu, L. P. Wen and X. J. Zhao, Sol. Energy Mater. Sol.
Cells, 2008, 92, 1–10.
Acknowledgements
This research was supported by the National Natural Science
Foundation of China (nos 11174227, 51209023, J1210061), the 26 H. Yang and C. X. Pan, J. Alloys Compd., 2010, 492, L33–L35.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 18186–18192 | 18191