ChemComm
Communication
From the above experimental evidence, we can speculate that facets by a facile and one-step solution method. This photo-
silicon is mainly doped into the bulk anatase TiO2 crystals. catalyst exhibits excellent stability and a high hydrogen evolu-
The photocatalytic activity of the samples was evaluated by tion rate under visible light. The results clearly demonstrate
detecting the formation of active hydroxyl radicals (ꢀOH), which that it is the unique stepped atomic configuration on the high-
are considered as the most important oxidative species in index {201} facets and incorporation of silicon in the bulk of
photo-oxidation reactions.12 As shown in Fig. S8a–c (ESI†), TiO2 that enhance their photocatalytic activity, which is also
significant fluorescence spectra associated with TAOH were proved by theoretical calculations. We expect that this finding
observed upon visible-light irradiation of the as-prepared will inspire us to design other new and highly reactive photo-
samples. The nearly linear relationship between fluorescence catalysts for hydrogen evolution.
intensity and irradiation time (Fig. S8d, ESI†) verifies the
This work was financially supported by Major Basic
stability of silicon doped anatase TiO2 single crystals. The Research Programme of Science and Technology Commission
ST-201 shows three times higher efficiency than the ST-101. of Shanghai Municipality (10JC1403200), Shuguang Talents
We further studied the photocatalytic H2 evolution rates of the Programme of Education Commission of Shanghai Municipality
Si-doped anatase TiO2 (ST-201 and ST-101) and compared them (09SG27), National Natural Science Foundation of China
to those of the T-101. As shown in Fig. 2b, on the basis of (20973059, 91022023, 21076076), Fundamental Research Funds
the surface area of the samples ST-201 and ST-101 (0.40 and for the Central Universities (WJ0913001), Program for Professor of
0.34 m2 gÀ1, respectively), the amount of hydrogen evolved in Special Appointment (Eastern Scholar) at Shanghai Institutions of
2.5 hours for ST-201 was 2.3 times higher than that for ST-101 Higher Learning and Program for New Century Excellent Talents
under visible light and was also 7.8 times higher than that for in University (NCET-09-0347). CS thanks Queensland Govern-
the reported nitrogen-doped TiO2.2f Although the pure anatase ment for financial support (Smart Future Fellowship) and
TiO2 single crystals exhibit high activity under UV light, there is Australian National Computational Infrastructures and University
no hydrogen evolution under visible light for comparison of Queensland for CPU time.
(inset in Fig. 2b). The capability of water splitting was still
maintained without a noticeable decrease in H2 production
after 20 cycles (Fig. S9, ESI†). The enhanced photocatalytic
activity of Ti0.89Si0.11O2 single crystals bound by {201} facets
Notes and references
1 A. Fujishima and K. Honda, Nature, 1972, 238, 37–38.
2 (a) J. Xing, W. Q. Fang, H. J. Zhao and H. G. Yang, Chem.–Asian J.,
can be explained by the higher active atomic arrangement on
the surface and in situ incorporation of the Si element to extend
the photoresponse of TiO2 from the UV to the visible light
region.
2012, 7, 642–657; (b) L. Wang, L. Zang, J. Zhao and C. Wang, Chem.
Commun., 2012, 48, 11736–11738; (c) S. Ouyang, H. Tong,
N. Umezawa, J. Cao, P. Li, Y. Bi, Y. Zhang and J. Ye, J. Am. Chem.
Soc., 2012, 134, 1974–1977; (d) X. Chen, S. Shen, L. Guo and
S. S. Mao, Chem. Rev., 2010, 110, 6503–6570; (e) X. Chen, L. Liu,
P. Y. Yu and S. S. Mao, Science, 2011, 331, 746–750; ( f ) G. Liu,
H. G. Yang, X. Wang, L. Cheng, J. Pan, G. Q. Lu and H.-M. Cheng,
J. Am. Chem. Soc., 2009, 131, 12868–12869.
3 (a) X. Zong, Z. Xing, H. Yu, Z. Chen, F. Tang, J. Zou, G. Q. Lu and
L. Wang, Chem. Commun., 2011, 47, 11742–11744; (b) X. Zhou,
F. Peng, H. Wang, H. Yu and Y. Fang, Chem. Commun., 2012,
48, 600–602; (c) G. Liu, L. Wang, H. G. Yang, H.-M. Cheng and
G. Q. Lu, J. Mater. Chem., 2010, 20, 831–843; (d) R. Asahi,
T. Morikawa, T. Ohwaki, K. Aoki and Y. Taga, Science, 2001, 293,
269–271.
4 W. Shi, Q. Chen, Y. Xu, D. Wu and C.-f. Huo, J. Solid State Chem.,
2011, 184, 1983–1988.
5 D.-N. Bui, S.-Z. Kang, X. Li and J. Mu, Catal. Commun., 2011, 13,
14–17.
6 G. Liu, J. C. Yu, G. Q. Lu and H.-M. Cheng, Chem. Commun., 2011,
47, 6763–6783.
7 H. G. Yang, C. H. Sun, S. Z. Qiao, J. Zou, G. Liu, S. C. Smith,
H. M. Cheng and G. Q. Lu, Nature, 2008, 453, 638–641.
8 N. Tian, Z.-Y. Zhou, S.-G. Sun, Y. Ding and Z. L. Wang, Science, 2007,
316, 732–735.
It is well known that (001) can easily be reconstructed.
In this work, the (201) surface is targeted because it combines
the features of (101) and (001), as shown in Fig. S10 (ESI†). As a
result, the (101) part can stabilize the whole surface and prevent
the reconstruction. Moreover, to improve the absorption of
visible light, Si-doping has been employed. To illustrate its role
in band gap narrowing, density functional theory plus Hubbard
model (DFT + U) calculation13 has been carried out, with U = 4.0 eV.
More computational details are listed in the ESI.† Fig. S11a and b
(ESI†) show the calculated band structures for undoped and
Si-doped anatase TiO2; it is found that the indirect band gap
(Eg = 2.60 eV) has been reduced and changed to the direct gap
(2.34 eV). This calculated data can explain the improvement in
the sunlight absorption observed in the experiment.
To understand the role of (201), water molecules have been
introduced on the (201) surface randomly and further opti-
mized. Interestingly, one water molecule being close to the
(001)-featured part dissociates spontaneously, as shown in
Fig. S11c and d (ESI†). Such spontaneous dissociation has been
observed on perfect (001) before, but different from (001),
9 (a) G. Liu, H. G. Yang, X. Wang, L. Cheng, H. Lu, L. Wang, G. Q. Lu
and H.-M. Cheng, J. Phys. Chem. C, 2009, 113, 21784–21788;
(b) F. Tian, Y. Zhang, J. Zhang and C. Pan, J. Phys. Chem. C, 2012,
116, 7515–7519; (c) X. H. Yang, Z. Li, G. Liu, J. Xing, C. Sun,
H. G. Yang and C. Li, CrystEngComm, 2011, 13, 1378–1383.
10 Y. Su, S. Chen, X. Quan, H. Zhao and Y. Zhang, Appl. Surf. Sci., 2008,
255, 2167–2172.
surface Ti–O bonds are intact on (201), perhaps due to the 11 (a) Q. Chen, W. Shi, Y. Xu, D. Wu and Y. Sun, Mater. Chem. Phys.,
2011, 125, 825–832; (b) K. E. Karakitsou and X. E. Verykios, J. Phys.
Chem., 1993, 97, 1184–1189.
12 H. G. Yang, G. Liu, S. Z. Qiao, C. H. Sun, Y. G. Jin, S. C. Smith,
stabilization of the (101)-featured part. In addition, Si-doping
does not affect such water dissociation. Overall, we can see that
(201) can offer high reactivity for water dissociation, but has
relatively higher stability than (001).
In conclusion, for the first time, we have successfully
synthesized Ti0.89Si0.11O2 single crystals with high-index {201}
J. Zou, H. M. Cheng and G. Q. Lu, J. Am. Chem. Soc., 2009, 131,
4078–4083.
13 (a) V. I. Anisimov, J. Zaanen and O. K. Andersen, Phys. Rev. B, 1991,
44, 943–954; (b) G. Kresse and D. Joubert, Phys. Rev. B, 1999, 59,
¨
1758–1775; (c) P. E. Blochl, Phys. Rev. B, 1994, 50, 17953–17979.
c
2018 Chem. Commun., 2013, 49, 2016--2018
This journal is The Royal Society of Chemistry 2013