DOI: 10.1002/chem.201302286

Gray TiO2 Nanowires Synthesized by Aluminum-Mediated Reduction andTheir Excellent Photocatalytic Activity for Water Cleaning

Hao Yin,[a] Tianquan Lin,[a, b] Chongyin Yang,[a, b] Zhou Wang,[a, b] Guilian Zhu,[a, b]

Tao Xu,[c] Xiaoming Xie,*[d] Fuqiang Huang,*[a, b] and Mianheng Jiang[d]

Solar photocatalysts have been attracting interest as a po-tential cost-effective approach to tackling various environ-ment and energy-related challenges.[1] Good photocatalystsrequire excellent light-harvesting efficiency over the fullsolar spectrum, efficient charge transport to surface-reactivesites, and high chemical stability. As a wide-band-gap semi-conductor with decent electron mobility in its conductionband and chemical inertness, TiO2 has received intense ex-ploration for its photocatalytic properties. In particular, itsone-dimensional morphology, including nanowires andnanotubes, exhibits superior transport properties over nano-particles owing to fewer grain boundaries and defective sitesin one-dimensional TiO2 structures.[2] However, the utiliza-tion of one-dimensional TiO2 nanowires as photocatalystshas been largely limited owing to their poor absorption overthe full range of the solar spectrum. The wide band gapACHTUNGTRENNUNG(~3.2 eV) of TiO2 only enables it to absorb in the UV regionof the solar spectrum (less than 6 % of the available solarenergy). Although doping TiO2 nanowires with nitrogen ormetals can engineer band gaps suitable for enhanced ab-sorption in the visible region,[3] the introduced dopants canalso act as charge-carrier-recombination centers, a majorissue affecting the photocatalytic efficiency.[4]

Recently, a dopant-free high-pressure hydrogenationmethod was successfully demonstrated to enable efficientvisible-light absorption, a method that resulted in the forma-tion of black TiO2.

[5] Ambient-pressure approaches werealso successfully created by involving hydrogen as a reduc-ing agent.[6] This method was quite versatile and applicableto other oxides such as ZnO[7] and WO3.

[8] Because hydro-gen is a flammable dangerous gas, it is thus highly desirableto explore a safer and simpler way to obtain dopant-freeTiO2 with enhanced absorption in the visible and infraredregions.

Here, we report a facile and safer approach to synthesizegray TiO2 nanowires through a reduction process. Instead ofusing hydrogen as the reducing agent, we have used moltenaluminum as the reducing agent. The mixture of metallicaluminum and oxides are well known as thermites. Our alu-minum reduction is conducted in a two-zone tube furnace,the schematic drawing of which is shown in Figure S1 (seethe Supporting Information). We show that the Al-reducedTiO2 nanowires (TiO2-R), which possess a core (TiO2�x)/shell (TiO2) structure, exhibit visible-light and even infrared-light absorption with high photocatalytic activity. The sam-ples are very stable at room temperature and in open air;they display no noticeable color change over a period ofmonths. The photocatalytic efficiency in dye photodegrada-tion is four times higher than Degussa P25 after six cycles,demonstrating the high potential of such TiO2 nanowires.

Figure 1 a shows the diffusive reflectance and absorbancespectra of TiO2-R and TiO2 nanowires annealed at the sametemperature in air (TiO2-air) as a reference. Compared withthe stoichiometric TiO2-air, the partially reduced sampleshows highly enhanced visible- and infrared-light absorption.

[a] Dr. H. Yin, T. Lin, C. Yang, Z. Wang, G. Zhu, Prof. Dr. F. HuangDepartment CAS Key Laboratory of Materials forEnergy Conversion, Shanghai Institute of CeramicsChinese Academy of Sciences, Shanghai 200050 (P.R. China)Fax: (+86) 21-54216360E-mail : huangfq@mail.sic.ac.cn

[b] T. Lin, C. Yang, Z. Wang, G. Zhu, Prof. Dr. F. HuangBeijing National Laboratory for Molecular Sciences andState Key Laboratory of Rare Earth Materials Chemistry andApplications, College of Chemistry and Molecular EngineeringPeking University, Beijing 100871 (P.R. China)

[c] Prof. Dr. T. XuDepartment of Chemistry and BiochemistryNorthern Illinois University, DeKalb, Illinois 60115 (USA)

[d] Prof. Dr. X. Xie, Prof. Dr. M. JiangDepartment State Key Laboratory of Functional Materials forInformatics, Shanghai Institute of Microsystem and InformationTechnology, Chinese Academy of SciencesShanghai 200050 (P.R. China)Fax: (+86) 21-54219909E-mail : xmxie@mail.sim.ac.cn

Supporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/chem.201302286.

Figure 1. a) UV/Vis absorption spectra of TiO2-R and TiO2-air nanowiresformed at 700 8C, b) XRD patterns of TiO2-R and TiO2-air nanowiresformed at 700 8C. R denotes peaks from rutile phase.

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In good agreement with these measurements, TiO2-R is grayin color. A photo of the gray TiO2-R nanowires, as well asthe white TiO2-air sample, is shown in the inset of Figure 1 a.The absorption of visible light increases with increasingtreatment temperature (see the Supporting Information,Figure S2), and the samples get darker in color.

Powder X-ray diffraction analysis (Figure 1 b) shows that,compared with pure anatase TiO2-air (JCPDS No.21-1272),TiO2-R presents intense anatase peaks as the main crystal-line phase and a set of rutile peaks with weak intensities.The transition temperature of the nanowires from anataseto rutile exceeds 800 8C in the oxygen-rich regime,[9] whereaswith our Al-mediated reduction conditions it drops to700 8C. This is because annealing in a reducing environmentcreates oxygen vacancies in the TiO2 crystal structure, a factthat facilitates lattice rearrangement and accelerates phasetransformation.[6c] Melted aluminum can decrease theoxygen partial pressure by forming aluminum oxide accord-ing to the Ellingham diagram, similar to annealing in a re-ducing environment, such as H2.

The SEM and TEM images in Figure 2 (a and b) show thetypical morphology of TiO2-R, that is, nanowires 50–150 nmin diameter and several micrometers in length. Figure 2 c

presents a typical high-resolution transmission electron mi-croscopy (HRTEM) image of TiO2-R nanowires. Two sets oflattice fringes with spacing of 0.35 and 0.47 nm were clearlyobserved, corresponding to {101} and {002} atomic planes ofthe anatase TiO2, respectively. The corresponding selected-area electron diffraction (SAED) pattern (Figure 2 d) showsthat the sample is well-crystallized with atomic planes. It isworthwhile to note that the specific surface area of TiO2-Ris larger than that of TiO2-air (see the Supporting Informa-tion, Table S1), a fact that is advantageous for photocatalyticapplications.

Raman scattering measurements were employed to exam-ine the structural properties of TiO2-R and TiO2-air nano-wires (Figure 3 a). The six Raman-active modes of the ana-tase phase were detected in both of the investigated sam-

ples, with the corresponding peaks at 141 cm�1 (Eg, v6),197 cm�1 (Eg, v5), 399 cm�1 (B1g, v3), 514 cm�1 (A1g +B1g,v1+v2), and 639 cm�1 (Eg, v4) (Figure 3 a).[10] Obviously, theEg peak located at 141 cm�1 broadened and displayed ablueshift for the gray TiO2-R sample compared with theTiO2-air sample. As is well known, the blueshift and broad-ening of the Eg peak are due to either nano-sized grainACHTUNGTRENNUNG(<10 nm) or shortening of the correlation length because ofthe presence of defects.[6c,11] In the present case, it indicatesthat defects (Ti3+ and oxygen vacancy, VO) are formed byAl-mediated reduction.

Considering the fact that there are unpaired electrons inboth Ti3+ and VO, the samples were further measured byEPR spectroscopy to determine the presence of unpairedelectrons after Al-mediated reduction. TiO2-R gave rise to astrong EPR signal, whereas no signal was seen for the TiO2-air sample, as shown in Figure 3 b. The g tensor of TiO2-Rhas three values (g1 = 2.005, g2 =2.004, g3 =2.003) very simi-lar to that of a single-electron-trapped oxygen vacancy, andalso similar to the nitrogen doped TiO2 previously report-ed.[12] Thus, it is clear that VO were induced by Al-mediatedreduction.

The EPR spectra of TiO2-R synthesized at different tem-peratures are shown in Figure S3 (see the Supporting Infor-mation). The signal at g=2.003 increased as the temperaturewas increased to 400 8C, and decreases thereafter, indicatingthat the density of single-electron-trapped oxygen vacancieson the surface reached a maximum at 400 8C, and diminishesthereafter. Interestingly, the samples made at increasingtreatment temperatures appeared continuously darker. Athigh temperature, VO may transfer from the surface to thebulk.[6c] Thus, VO in the surface decreased, although thetotal VO density increased. Ti3+ sites, always paired with VO,may penetrate deep into the crystal lattice in TiO2-R, sothat they cannot be oxidized. This is evident from the factthat the gray color from Ti3+ can remain for months underambient conditions.

Figure 2. a) SEM, b), c) TEM images, and d) SAED pattern of TiO2-R.

Figure 3. a) Raman spectra, b) EPR spectra, c) normalized Ti 2p XPSspectra, and d) FTIR of TiO2-R and TiO2-air.

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X-ray photoelectron spectroscopy (XPS) measurementswere performed on the gray TiO2-R and white TiO2-air sam-ples. Figure 3 c shows the Ti 2p core level XPS spectra ofTiO2-R and TiO2-air. The peak of TiO2-R unambiguouslyshows a downshift in binding energy, indicating that Tiatoms in TiO2-R and TiO2-air have different chemical envi-ronments. However, there is no obvious Ti3+ peak evidentin TiO2-R. We think that the density of Ti3+ in the surface islower than the XPS detection limit. In many previous re-ports, Ti3+ is not detected by XPS in the case of H2-basedreduction because of the absence of Ti3+ at the surface.[5,6c]

What should be emphasized is that no aluminum impuritieshave been detected by XPS in the TiO2-R sample during thepresent research, as shown in Figure S4 (see the SupportingInformation). This fact indicates that melted aluminum, as athermite, only provides a reducing atmosphere for TiO2

nanowires and does not dope or coat them. Hence, we pro-pose that TiO2-R has a core (TiO2�x)/shell (TiO2) structure,which makes it able to absorb visible light and stable in airand water.

FTIR spectra of TiO2-R and TiO2-air in the region 400–4000 cm�1 are shown in Figure 3 d. The wide band centeredaround 510 cm�1 for both samples can be assigned to Ti-O-Ti stretching vibration of the interconnected octahedral[TiO6].[13] However, the absorption we found at 763 cm�1 forTiO2-air, undergoes a blueshift to 810 cm�1 for TiO2-R. The763 and 810 cm�1 peaks are attributed to middle and strongstretching vibrations of Ti-O-Ti, respectively.[14] FTIR peaksare determined by the frequency of chemical bond vibra-tions, a value that is closely related to the bond characteris-tics: the shorter the bond, the higher the bond energy. Ablueshift indicates that the bond energy increases and theaverage length of Ti�O is shortened. We attribute the blue-shift to VO formation. Both samples show strong absorptionaround 3400 cm�1 and 1630 cm�1, peaks that were assignedto O-H stretching vibrations of surface hydroxyl groups andH-O-H bending vibrations of physically adsorbed water, re-spectively.[15]

The solar-driven photocatalytic performances of the sam-ples were evaluated by using the degradation of methyleneorange (MO). Commercially available Degussa P25 TiO2

was used as a reference for comparison. As shown in Fig-ure 4 a, the photocatalytic efficiency of TiO2-R is muchhigher than that of TiO2-air and P25. For instance, TiO2-Rdecomposed over 95 % of MO within 10 min of irradiation,whereas only about 45 % of MO was decomposed by TiO2-air under the same reaction conditions. The pseudo-first-order kinetics of the photodegradations are illustrated inFigure 4 b. The observed kinetic constants were calculated,and are listed in Table S1 (see the Supporting Information).In the presence of TiO2-R, the MO-removal rate was greatlyenhanced, with a rate constant of 0.33 min�1, three timeslarger than that of TiO2-air and 1.3 times that of P25.

Recycling tests revealed that the gray TiO2-R sample wasvery stable in six photocatalytic cycles, as shown in Fig-ure 3 c. It was found that the photocatalytic rate of TiO2-Ris four times higher than that of P25 after six cycles, as

TiO2-R remains stable but P25 exhibits a gradually decreas-ing degradation rate (see the Supporting Information, Fig-ure S5).[16]

To throw further light on their photocatalytic efficiency,we have measured the formation of active hydroxyl radicals(·OH) upon irradiation, which are considered the most im-portant oxidative species in photocatalytic reactions.[17] Thelinear relationship between fluorescence intensity and irradi-ation time confirms the stability of all samples (see the Sup-porting Information, inset of Figure S6). TiO2-R and TiO2-air show larger gradients than P25 because their one-dimen-sional structures suppress charge-carrier recombination. Asshown in Figure S6, TiO2-R exhibits the best activity amongthe samples. The results clearly reveal the enhanced photo-reactivity of TiO2-R, an observation that can be attributedto its enhanced visible- and infrared-light absorption. Ab-sorption of solar energy (phonon) generates highly reactiveelectrons and holes for catalytic reactions. The measurementof photoluminescence (PL) emission was performed to un-derstand the fate of these photogenerated electrons andholes in the photocatalysts, as PL emission results from therecombination of free charge carriers.[18] As shown in Fig-ure S7 (see the Supporting Information), the order of PLemission intensity is TiO2-R<TiO2-air<P25, a fact that in-dicates that the recombination rate of photogenerated elec-trons and holes is suppressed in TiO2-R owing to its in-creased oxygen vacancy. VO actually serve as electron traps,thus to prevent recombination.[18]

Figure 4. a) The photocatalytic degradation of MO, b) first-order kineticsof photocatalytic degradation in the presence of TiO2-air, TiO2-R, andP25 under solar-light irradiation, c) recycling tests of photocatalytic activ-ity of gray TiO2-R nanowires.

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COMMUNICATIONGray TiO2 Nanowires

In summary, gray TiO2 nanowires with high photocatalyticactivity have been successfully synthesized by aluminum-mediated reduction in a two-zone furnace. The Al-reducedTiO2 nanowires show high stability in air and water under ir-radiation. They exhibit excellent photocatalytic efficiencythat far exceeds that of commercial Degussa P25. The suc-cess of the present work lies in the clear understanding ofthe aluminum-mediated-reduction effects. The present studyfurther motivates us to treat other metallic oxides with alu-minum-mediated reduction, which has promising applica-tions for photocatalysts, solar cells, and photonic and opto-ACHTUNGTRENNUNGelectronic devices.

Experimental Section

Synthesis : Protonated titanate nanowires were prepared by using an alka-line hydrothermal method. Anatase powder was dispersed in 70 mL 10m

NaOH solution in a Teflon-lined autoclave, which was sealed and placedin an oven at 200 8C for 18 h. The products were washed, first with 0.1m

HCl, and then repeatedly with deionized water and ethanol, and thendried in air. The protonated titanate nanowires were used as precursorsfor gray TiO2. The powder (0.5 g) was treated under vacuum at 200–900 8C for 4 h in a two-zone furnace, where aluminum powder was put inthe zone set at 800 8C. A schematic drawing of the furnace is shown inFigure S1 (see the Supporting Information). The optimized temperaturefor photocatalytic applications was 700 8C. The sample reduced by Al at700 8C was noted as TiO2-R. As a comparison, the protonated titanatenanowires were dehydrated at 700 8C for 4 h at atmospheric pressure;this sample was noted as TiO2-air.

Photocatalysis : The photocatalytic activities of the samples were evaluat-ed by monitoring the decomposition of methyl orange (MO) in an aque-ous solution under solar-light irradiation with a 400W iodine–galliumlamp. Before solar-light irradiation, a suspension containing 100 mL of10 mg L�1 MO solution and 100 mg of solid catalyst was sonicated for5 min and stirred for 30 min in the dark to allow sorption equilibrium.Then, the mixture was irradiated and, at given time intervals, approxi-mately 5 mL of the suspension was withdrawn for analysis after centrifu-gation. The residual concentration of MO was detected by using a Hita-chi U-4100 UV/Vis spectrophotometer at 464 nm. Terephthalic acid (TA)was used as a fluorescence probe. TA can react with ·OH in basic solu-tion to generate 2-hydroxy terephthalic acid (TAOH). TAOH emits aunique fluorescence signal with the spectrum peak around 426 nm. Typi-cally, the photocatalyst was suspended in 100 mL of aqueous solutioncontaining 0.01 m NaOH and 3.0 mm terephthalic acid. The suspensionwas stirred in the dark for 0.5 h to ensure the adsorption/desorption equi-librium before the solar-light irradiation. Then, 5.0 mL of solution wastaken out every 30 min for fluorescence measurements. Excitation light:320 nm, emission range: 350–600 nm.

Sample characterizations : The samples� morphology and SAED werecharacterized by FE-SEM (Philips XL30FEG) and TEM (JEOL JEM-2100). UV/Vis diffuse reflectance spectra were obtained by using a UV/Vis spectrometer (Hitachi U-4100) by using BaSO4 as a reference andwere converted from reflection to absorbance by the Kubelka–Munkmethod. Raman spectra were collected on a Thermal Dispersive Spec-trometer using a laser with an excitation wavelength of 532 nm at laserpower of 10 mW. Solid-state XRD patterns were obtained with a BrukerD8 advance diffractometer operating with CuKa radiation. XPS experi-ments were carried out on a RBD upgraded PHI-5000C ESCA system(Perkin–Elmer) with MgKa radiation (hn=1253.6 eV). FTIR spectra wererecorded on a Perkin–Elmer Spectrum 100 using KBr disks. EPR spectrawere collected by using a Bruker EMX-8 spectrometer at 9.44 GHz andat 300 K. PL spectra were measured at 300 K on a fluorescence spectro-photometer (F-4600, Hitachi, Japan) with an excitation wavelength of320 nm.

Acknowledgements

This work is financially supported by NSF of China (Grant Nos.51125006, 91122034, 51121064), 973/863 Programs of China (Grant Nos.2011AA050505, 2009CB939900), and CAS program (KGZD-EW-303).TX acknowledges the support from the US National Science Foundation(CBET�1150617).

Keywords: nanowires · photocatalysis · titanium dioxide ·visible-light absorption · water cleaning

[1] a) H. Tong, S. X. Ouyang, Y. P. Bi, N. Umezawa, M. Oshikiri, J. H.Ye, Adv. Mater. 2012, 24, 229 –251; b) Z. K. Zheng, B. B. Huang,J. B. Lu, X. Y. Qin, X. Y. Zhang, Y. Dai, Chem. Eur. J. 2011, 17,15032 – 15038.

[2] a) N. Q. Wu, J. Wang, D. Tafen, H. Wang, J. G. Zheng, J. P. Lewis,X. G. Liu, S. S. Leonard, A. Manivannan, J. Am. Chem. Soc. 2010,132, 6679 –6685; b) J. Y. Liao, B. X. Lei, H. Y. Chen, D. B. Kuang,C. Y. Su, Energy Environ. Sci. 2012, 5, 5750 – 5757.

[3] a) J. Wang, D. N. Tafen, J. P. Lewis, Z. L. Hong, A. Manivannan,M. J. Zhi, M. Li, N. Q. Wu, J. Am. Chem. Soc. 2009, 131, 12290 –12297; b) D. Dvoranov�, V. Brezova, M. Mazur, M. A. Malati, Appl.Entomol. Zool. Appl. Catal. B-Environ 2002, 37, 91– 105.

[4] a) W. Choi, A. Termin, M. R. Hoffmann, J. Phys.Chem. 1994, 98,13669 – 13679; b) S. T. Martin, C. L. Morrison, M. R. Hoffmann, J.Phys. Chem. 1994, 98, 13695 – 13704.

[5] X. B. Chen, L. Liu, P. Y. Yu, S. S. Mao, Science 2011, 331, 746 –750.[6] a) Z. K. Zheng, B. B. Huang, J. B. Lu, Z. Y. Wang, X. Y. Qin, X. Y.

Zhang, Y. Dai, M. H. Whangbo, Chem. Commun. 2012, 48, 5733 –5735; b) W. Wang, Y. R. Ni, C. H. Lu, Z. Z. Xu, RSC Adv. 2012, 2,8286 – 8288; c) A. Naldoni, M. Allieta, S. Santangelo, M. Marelli, F.Fabbri, S. Cappelli, C. L. Bianchi, R. Psaro, V. Dal Santo, J. Am.Chem. Soc. 2012, 134, 7600 – 7603; d) G. M. Wang, H. Y. Wang, Y. C.Ling, Y. C. Tang, X. Y. Yang, R. C. Fitzmorris, C. C. Wang, J. Z.Zhang, Y. Li, Nano Lett. 2011, 11, 3026 –3033.

[7] X. H. Lu, G. Wang, S. Xie, J. Shi, W. Li, Y.-X. Tong, Y. Li, Chem.Commun. 2012, 48, 7717 –7719.

[8] G. Wang, Y. Ling, H. Wang, X. Yang, C. Wang, J. Z. Zhang, Y. Li,Energy Environ. Sci. 2012, 5, 6180 – 6187.

[9] a) H. Yin, G. Ding, B. Gao, F. Huang, X. Xie, M. Jiang, Mater. Res.Bull. 2012, 47, 3124 – 3128; b) S. Pavasupree, Y. Suzuki, S. Yoshika-wa, R. Kawahata, J. Solid State Chem. 2005, 178, 3110 – 3116.

[10] H. Yin, H. Liu, W. Z. Shen, Nanotechnology 2010, 21, 035601.[11] W. D. Zhu, C. W. Wang, J. B. Chen, D. S. Li, F. Zhou, H. L. Zhang,

Nanotechnology 2012, 23, 455204.[12] S. Livraghi, A. Votta, M. C. Paganini, E. Giamello, Chem. Commun.

2005, 4, 498 –500.[13] A. J. Manhique, W. W. Focke, C. Madivate, Hydrometallurgy 2011,

109, 230 –236.[14] a) V. A. Zeitler, C. A. Brown, J. Phys. Chem. 1957, 61, 1174 –1177;

b) S. Benmokhtar, A. El Jazouli, S. Krimi, J.-P. Chaminade, P. Grave-reau, M. M�n�trier, D. De Waal, Mater. Res. Bull. 2007, 42, 892 –903.

[15] a) S. Papp, L. Korosi, V. Meynen, P. Cool, E. F. Vansant, I. Dekany,J. Solid State Chem. 2005, 178, 1614 – 1619; b) U. Sulaeman, S. Yin,T. Sato, J. Nanomater. 2010, 2010, 629727.

[16] X. G. Han, Q. Kuang, M. S. Jin, Z. X. Xie, L. S. Zheng, J. Am.Chem. Soc. 2009, 131, 3152 –3153.

[17] H. G. Yang, G. Liu, S. Z. Qiao, C. H. Sun, Y. G. Jin, S. C. Smith, J.Zou, H. M. Cheng, G. Q. Lu, J. Am. Chem. Soc. 2009, 131, 4078 –4083.

[18] X. Jiang, Y. Zhang, J. Jiang, Y. Rong, Y. Wang, Y. Wu, C. Pan, J.Phys. Chem. C 2012, 116, 22619 –22624.

Received: June 17, 2013Published online: September 6, 2013

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X. Xie, F. Huang et al.

Supporting Information� Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2013

Gray TiO2 Nanowires Synthesized by Aluminum-Mediated Reduction andTheir Excellent Photocatalytic Activity for Water Cleaning

Hao Yin,[a] Tianquan Lin,[a, b] Chongyin Yang,[a, b] Zhou Wang,[a, b] Guilian Zhu,[a, b]

Tao Xu,[c] Xiaoming Xie,*[d] Fuqiang Huang,*[a, b] and Mianheng Jiang[d]

chem_201302286_sm_miscellaneous_information.pdf

Figure S1 Schematic drawing of the two-zone furnace.

Figure S2 Absorption of the samples Al-reduced at different temperature

and TiO2-air.

Figure S3 EPR spectra of the samples Al-reduced at different temperature

and TiO2-air.

Figure S4 Survey XPS of TiO2-air and TiO2-R. (a): wide spectrum; (b): in

the range of 50-100 eV. There is no aluminium observed. It indicated that

no aluminium doped in or coated on TiO2 nanowires.

Figure S5 Cycling tests of photocatalytic activity of P25.

Figure S6 Fluorescence spectra of solar light irradiated samples in

terephthalic acid (3 mM) after irradiation for 90 min; inset: the time

dependences of fluorescence intensity at 426 nm.

Figure S7 PL spectra of P25, TiO2-air and TiO2-R.

Table S1 Specific surface area, pore structure parameters, and the

photocatalytic rate of the P25, TiO2-air and TiO2-R.

Catalyst SBETddd

(m2/g)

Pore

volume (m3/g)

Pore

diameter (nm)

Kdddd

(min-1)

k/SBET

P25 48.2 26.4 31.6 0.25 0.0052(1)

TiO2-air 15.6 15.1 13.7 0.11 0.0071(1.37)

TiO2-R 20.9 19.4 17.1 0.33 0.0158(3.04)