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Template-free synthesis of mesoporous N-doped SrTiO3 perovskite with high visible-light-driven photocatalytic activityw

Downloaded by University of Oxford on 13 August 2012 Published on 05 July 2012 on http://pubs.rsc.org | doi:10.1039/C2CC33797E

Fei Zou,abc Zheng Jiang,*ad Xiaoqin Qin,ae Yongxiang Zhao,e Luyun Jiang,a Jinfang Zhi,b Tiancun Xiaoa and Peter P. Edwards*a Received 26th May 2012, Accepted 2nd July 2012 DOI: 10.1039/c2cc33797e An effective, template-free synthesis methodology has been developed for preparing mesoporous nitrogen-doped SrTiO3 (meso-STON) using glycine as both a nitrogen source and a mesopore creator. The N-doping, large surface area and developed porosity endow meso-STON with excellent activity in visible-light-responsive photodegradation of organic dyes. The exceptional electro-optical properties and physicochemical stability of the perovskite SrTiO3 (STO) give rise to its attractive performance in photocatalytic applications of solar power, including photocatalytic degradation of organic pollutants, water splitting and photoreduction of CO2.1–3 However, the intrinsic large bandgap energy (Eg = 3.2 eV) of SrTiO3 allows only the utilization of UV light, encompassing approximately 5.0% energy of the sunlight.4 A variety of transition metals (TM) have been doped into a STO’s crystal matrix in efforts to tune its electronic bandgap for harvesting visible light.5,6 Unfortunately, TM-doping can also bring about either phase impurity or fast recombination of photogenerated charge carriers. Nonmetal-doping represents another effective strategy to realize visible-light response.7–9 Indeed, it was found that N-doped SrTiO3 (SrTiO3 xNx, STON) exhibited excellent photoreactivity and stability under visible-light irradiation.10 Mesoporous-structured photocatalysts are highly desirable in photocatalysis since their large specific surface area (SSA) and mesoporous channels greatly facilitate adsorption, diffusion and surface reaction of the reactants.11 STO perovskite belongs to the cubic crystal system, and typically has low SSA and poor porosity. Moreover, the porosity of STO could be further a

Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, UK. E-mail: [email protected], [email protected]; Tel: +44 (0)1865 272646 b Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, 29 Zhongguancun East Road, Haidian District, Beijing 100190, China c Graduate School of Chinese Academy of Sciences, Beijing 100864, China d Environment and Sustainability Institute, University of Exeter, Cornwall Campus, Penryn, Cornwall, TR10 9EZ, UK e School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China w Electronic supplementary information (ESI) available: Details of synthesis procedure, characterizations, supplementary figures and brief explanation. See DOI: 10.1039/c2cc33797e

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Chem. Commun., 2012, 48, 8514–8516

destroyed by the known processes of nitriding STO to STON.5,12 Although mesoporous STO has been prepared via templatedirected synthesis using various soft (e.g. surfactant or polymer13) and hard (e.g. inorganic salts14) templates, the synthesis of mesoporous STON has rarely been achieved. Here we report a novel, template-free synthesis methodology to prepare mesoporous STON using glycine as both a nitrogen source and a mesopore creator. Aqueous solution of glycine and Sr(NO3)2 was dropped into ethanol solution of titanium butoxide under stirring, followed by solvent evaporation and subsequent calcinations at 550 1C for 2 hours. The obtained STON was characterized by XRD, TEM, FTIR, UV-vis, and XPS techniques and used for the photodegradation of three refractory organic dyes under visible-light irradiation. Only a strong single peak appears in the small angle XRD pattern (Fig. 1) of the STON sample, suggesting that it possesses disordered wormlike mesopores.15 The TEM image in Fig. 2A nicely confirms such mesoporosity. The HRTEM image inserted in Fig. 2A reveals that the walls of the mesopores are comprised of single crystal perovskite STON. The labelled lattice distances are consistent with those of (100) and (110) diffractions obtained from XRD tests (Fig. S1, ESIw). In contrast, the STO sample presents poor mesoporous features in the small-angle XRD (Fig. 1) and TEM image (Fig. S2A, ESIw). The observed type-IV N2 adsorption–desorption isotherm and the type-H2 hysteresis loop of the meso-STON (Fig. 2B) suggest that it possesses ‘‘ink-bottle-like’’ mesopores.16 The mean pore diameter (Dp) of the meso-STON is approximately 4.0 nm with a narrow pore size distribution as revealed by the BJH plot in Fig. 2B. However, STO has a cylinder-like pore structure with Dp of 12.4 nm as evidenced by its type-III N2

Fig. 1 Small angle XRD patterns of STO and STON samples.

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Fig. 2 (A) TEM and (B) N2-isotherm of STON. The insets in (A) and (B) are its HRTEM image and pore-size distribution, respectively.

adsorption–desorption isotherm and type-H3 hysteresis loop (Fig. S2B, ESIw). It is the developed porosity that leads to higher SSA (52.3 m2 g 1) of meso-STON than STO (19.5 m2 g 1) (Table S1, ESIw). Considering the high calcination temperature, our glycine-based methodology is feasible in synthesising mesoporous N-doped perovskite titanates. In this methodology, glycine is thought to coordinate with Sr2+ and Ti4+ to form a variety of amino complexes (Scheme S1, ESIw) which help to improve the subsequent purity of the perovskite phase.14 During the subsequent calcination, the glycine complexes would be oxidized and decomposed to evolve gaseous products. These exiting gases would thus create nanopores in the newly formed meso-STON.17 Meanwhile, a part of the coordinated amino-groups would ultimately convert to N-dopants trapping in the matrix of the meso-STON. STON exhibits an enhanced absorbance in the broad UV-vis region (Fig. 3A) and its absorption edge (425 nm) red shifts by some 25 nm in comparison with STO. The corresponding Eg of STON and STO are 2.9 and 3.2 eV, respectively. The reduced electronic bandgap and enhanced light absorption of STON appear to be induced by the N-doping and the attenuated light scattering by the mesoporous architecture.18 The N-species in the STON were revealed by its broad N1s XPS peak at 396.4 eV (Fig. 3B), which can be deconvoluted into four peaks. The fitted peaks at 395.3, 397.8 and 396.4 eV can be assigned to substituted N-species in different chemical environments, such as Ti–N, O–Ti–N and Ti–N–O bonds;5,7,12 and the peak at 399.2 eV is due to the N–O bond.19 The shoulder peak at 398 eV was assigned to the shift of Ti–N bonds induced by the formation of oxygen vacancies (Ovac) and the Ti3+ cations adjacent to the vacancies (Fig. S3, ESIw).5 Fig. 4(A) shows the FTIR spectrum of as-synthesised STON which is significantly different from that of STO. The weak vibration bands of STON at 1633 cm 1 indicate the existence of surface N–H bonds,20 while the interstitial N–O species can be identified from the vibration signals of nitrite (1453 cm 1) and hyponitrite (1396 cm 1) species.21,22 The broad band This journal is

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Fig. 3 UV-vis diffuse reflectance spectra of STO and STON samples (A) and the N 1s XPS of STON (B).

Fig. 4 (A) FITR and (B) amplitude-normalized ESR spectra of STO and STON at 77 K. Dashed line is the simulated ESR spectrum of STON.

ranging from 600 to 900 cm 1 is attributed to the metal–O stretching vibration mode. The comparative Electron Spin Resonance (ESR) spectra of STO and STON shown in Fig. 4(B) further display the effects of N-doping. The ESR signal of STO and STON at a similar g tensor of 2.007 may be caused by the single-electron-trapped oxygen vacancies induced by N-dopants.23,24 The intensity of Ovac reveals that the concentration of Ovac in STON is approximately 15 times of that in STO.25 The ESR resonance at g tensors of 1.950, 1.987 and 1.991 is related to Ti3+,23 further demonstrating the existence of Ovac. The fitted ESR signal with a g value of 2.014 may be due to the trapped NO species in the STO matrix.26,27 The ESR resonance of meso-STON is broadened by both NOx species and the electron spin–lattice perturbation of Ovac.28 Chem. Commun., 2012, 48, 8514–8516

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large surface area, developed mesoporous structure and enhanced absorption of visible light. We appreciate the Sir John Houghton Fellowship and Principal’s Major Fund at Jesus College (Oxford), Shell Foundation, UKSHEC(EPSRC) and the Royal Society grants (TG092414 and TG101750). We thank Dr Guoquan Liu at Department of Materials (Oxford) for his help with ESR.


Fig. 5 Schematic electronic band structure of STO and STON (Ti3+ (Ovac), NOx, Nsub denoted oxygen vacancy, trapped NOx species and substituted nitrogen, respectively).

Fig. 6 Photodegradation of MB, RhB and MO on STON under visible light irradiation (wavelength > 420 nm).

On basis of the XPS, FTIR and ESR characterisations, we concluded that the visible-light-response (narrowing of electronic band gap) of the meso-STON results from both N-dopants and the doping-enhanced Ovac. As illustrated in Fig. 5, the conduction band minimum (CBM) is shifted towards the valence band (more positive) due to Ovac, while the valence band maximum moves upwards (more negative) due to N-dopants. According to DFT calculations,29,30 we suppose that the crystal-matrix trapped NOx species affects the VBM greater than those of the substituted N-species. The overall contribution of N-dopants and Ovac is an approximately 0.3 eV narrowing of the bandgap in comparison with STO. As shown in Fig. 6, under visible-light irradiation (>420 nm), the meso-STON exhibited excellent activity in photodegradation of dye (10 ppm) aqueous solutions of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO), respectively. In photodegradation of the three dyes under irradiation of visible light greater than 420 nm, the meso-STON is more active than STO and commercial TiO2 (P25 aerosol) (Fig. S4 and S5, ESIw). Despite a very similar bandgap energy (3.2 eV), the STO is more active than P25, which are induced by dyesensitized photo-decomposition.31 There is no deactivation being observed in the cycling tests of photodegradation of MB on the meso-STON (Fig. S6, ESIw), revealing that it possesses outstanding photocatalytic stability. In summary, we have reported here an effective, templatefree glycine methodology for preparing N-doped SrTiO3 with an attendant wormlike mesoporous structure. In the synthesis process, the glycine appears to function as a coordinating reagent, a N-source and a pore creator. Such meso-STON exhibited excellent visible-light response arising from both N-doping and Ovac. We propose that its high activity in photodegradation of organic dyes under visible-light (wavelength over 420 nm) arises primarily from the synergistic effects of

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Notes and references 1 F. T. Wagner and G. A. Somorjai, Nature, 1980, 285, 559–560. 2 Y. Xu and M. A. A. Schoonen, Am. Mineral., 2000, 85, 543–556. 3 K. Iizuka, T. Wato, Y. Miseki, K. Saito and A. Kudo, J. Am. Chem. Soc., 2011, 133, 20863–20868. 4 Z. Jiang, T. Xiao, V. L. Kuznetsov and P. P. Edwards, Philos. Trans. R. Soc. London, Ser. A, 2010, 368, 3343–3364. 5 Y. Y. Mi, Z. Yu, S. J. Wang, X. Y. Gao, A. T. S. Wee, C. K. Ong and C. H. A. Huan, J. Appl. Phys., 2007, 101, 063708. 6 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. 7 R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki and Y. Taga, Science, 2001, 293, 269–271. 8 J. Liu, L. Wang, J. Liu, T. Wang, W. Qu and Z. Li, Cent. Eur. J. Phys., 2009, 7, 762–767. 9 J. Wang, H. Li, H. Li, S. Yin and T. Sato, Solid State Sci., 2009, 11, 182–188. 10 U. Sulaeman, S. Yin and T. Sato, J. Nanomater., 2010, 2010, 32. 11 P. D. Yang, D. Y. Zhao, D. I. Margolese, B. F. Chmelka and G. D. Stucky, Nature, 1998, 396, 152–155. 12 Z. Jiang, F. Yang, N. Luo, B. T. T. Chu, D. Sun, H. Shi, T. Xiao and P. P. Edwards, Chem. Commun., 2008, 6372–6374. 13 D. Grosso, C. Boissiere, B. Smarsly, T. Brezesinski, N. Pinna, P. A. Albouy, H. Amenitsch, M. Antonietti and C. Sanchez, Nat. Mater., 2004, 3, 787–792. 14 X. X. Fan, Y. Wang, X. Y. Chen, L. Gao, W. J. Luo, Y. P. Yuan, Z. S. Li, T. Yu, J. H. Zhu and Z. G. Zou, Chem. Mater., 2010, 22, 1276–1278. 15 Y. Wang, X. Tang, L. Yin, W. Huang, Y. R. Hacohen and A. Gedanken, Adv. Mater., 2000, 12, 1183–1186. 16 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl. Chem., 1985, 57, 603–619. 17 J. Poth, R. Haberkorn and H. P. Beck, J. Eur. Ceram. Soc., 2000, 20, 715–723. 18 H. Zhou, X. Li, T. Fan, F. E. Osterloh, J. Ding, E. M. Sabio, D. Zhang and Q. Guo, Adv. Mater., 2010, 22, 951–956. 19 S. Sato, Chem. Phys. Lett., 1986, 123, 126–128. 20 J. W. Wang, W. Zhu, Y. Q. Zhang and S. X. Liu, J. Phys. Chem. C, 2007, 111, 1010–1014. 21 S. Sakthivel, M. Janczarek and H. Kisch, J. Phys. Chem. B, 2004, 108, 19384–19387. 22 X. B. Chen, Y. B. Lou, A. C. S. Samia, C. Burda and J. L. Gole, Adv. Funct. Mater., 2005, 15, 41–49. 23 C. P. Kumar, N. O. Gopal, T. C. Wang, M. S. Wong and S. C. Ke, J. Phys. Chem. B, 2006, 110, 5223–5229. 24 Y. Wang, C. X. Feng, M. Zhang, J. J. Yang and Z. J. Zhang, Appl. Catal., B, 2010, 100, 84–90. 25 F. Tessier, C. Zollfrank, N. Travitzky, H. Windsheimer, O. MerdrignacConanec, J. Rocherulle´ and P. Greil, J. Mater. Sci., 2009, 44, 6110–6116. 26 Y. Wang, C. Feng, Z. Jin, J. Zhang, J. Yang and S. Zhang, J. Mol. Catal. A: Chem., 2006, 260, 1–3. 27 S. Livraghi, A. Votta, M. C. Paganini and E. Giamello, Chem. Commun., 2005, 498–500. 28 J. Matta, D. Courcot, E. Abi-Aad and A. Aboukais, Chem. Mater., 2002, 14, 4118–4125. 29 W. Wei, Y. Dai, M. Guo, L. Yu, H. Jin, S. Han and B. Huang, Phys. Chem. Chem. Phys., 2010, 12, 7612–7619. 30 W. Wei, D. Ying, J. Hao and H. Baibiao, J. Phys. D: Appl. Phys., 2009, 42, 055401. 31 G. M. Liu, X. Z. Li, J. C. Zhao, H. Hidaka and N. Serpone, Environ. Sci. Technol., 2000, 34, 3982–3990.

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Electronic Supplementary Material (ESI) for Chemical Communications This journal is © The Royal Society of Chemistry 2012

Template-Free Synthesis of Mesoporous N-doped SrTiO3 with Visible-Light-Driven Photocatalytic Activity Fei Zoua,b,e, Zheng Jianga,c*, Xiaoqin Qina,d, Yongxiang Zhaod, Luyun Jianga, Jinfang Zhib, Tiancun Xiaoa, Peter P. Edwardsa* a

Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR,

UK; b

Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of

Physics and Chemistry, 29 Zhongguancun East Road, Haidian District, Beijing, 100190, China c

Environment and Sustainability Institute, University of Exeter, Cornwall Campus, Penryn, Cornwall,

TR10, 9EZ,UK d e

School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China

Graduate School of Chinese Academy of Sciences,Beijing 100864, China

Corresponding authors: Dr. Zheng Jiang, Tel: +44 (0) 1326 255795, Email: [email protected]; Prof. Peter P. Edwards, Tel: 44(0)1865 272646, Email: [email protected]

Part I. Experimental 1. Synthesis of pure SrTiO3 (STO) and N-doped SrTiO3 (STON)

Scheme S1. The molecular structure of metal-glycine complexes All chemicals involved were purchased from Sigma Aldrich and used as received without further purification. Glycine was chosen as coordinate agent to form complex compound with Sr2+ and Ti4+ (Scheme S1) because most amino acids are able to form stable complexes with alkaline earth and transition metals1, 2. In a typical synthesis, 5 mL aqueous solution containing 10 mmol glycine and 10 mmol Sr(NO3)2 were added drop by drop into 40 mL ethanol solution containing 10 mmol of tetrabutyl titanate (TBT, C16H36O4Ti) and 2 mL glacial acetic acid under rigorous stirring, following with natural

1


evaporation and drying in a fume hood. The obtained dry gel was ground and calcinated at 550 ℃/2h, with a temperature ramp of 10 ℃/min, to obtain the meso-STON. Pure SrTiO3 was prepared via the same procedure mentioned above except for without glycine added.

2. Characterization. X-ray powder diffraction data of the prepared samples were recorded on a PANanalytical X’Pert PRO at 40 KV and 30mA. Transmission electron microscopy (TEM) was performed with a Jeol JEM- 2010 electron microscope operated at 200 kV. Nitrogen adsorption-desorption isotherms were measured on a Micromeritics ASAP 2010 at 77 K with samples degassed at 373 K for 5 h. Pore size distributions were calculated from the adsorption isotherm using the BJH method and the BET surface area from a relative pressure of 0.03-0.2. X-Ray photoelectron spectroscopy (XPS) was performed using a Perkin-Elmer RBD upgraded PHI-5000C ESCA system with monochromatic Mg-Ka excitation and a charge neutralizer was used to investigate the surface electronic states of the N doped samples. All the binding energies were calibrated with contaminant C 1s at binding energy of 284.8 eV. The UV-vis diffuse reflectance spectra (DRS) were measured using a UV-Vis DRS (Cary, UV-5000) withina wavelength range of 200-800nm at room temperature. Fourier transform infra red spectra (FTIR) were carried out using diffused reflectance model on a Varian FTS-7000 Fourier Transform Infrared Spectrometers. The electron spin resonance (ESR) spectra were recorded on a Magnettech Miniscope MS200 EMX spectrometer operating at 100 KHz magnetic field modulation. The amplitude was normalized by I/Imax. Simulation of ESR spectra was performed using the EASYSPIN software package. 3

3. Photocatalytic Degradation of Dyes under Visible Light Irradiation The photocatalytic abilities of the STO and STON were evaluated by measuring the degration of Rhodamine B (RhB), Methylene Blue (MB) and Methyl Orange (MO) aqueous solutions, respectively. A 300W Xenon lamp (PLS-SXE300, Beijing TrustTech) was used as the visible-light source with UV-cutoff filters (UVCUT420, Beijing TrustTech). In the typical photocatalytic experiment, 0.1g catalyst was dispersed into 100mL of dye aqueous solution (10 ppm). Prior to irradiation, the

2


suspensions were stirred in dark for 1.0 hour to ensure the absorption-desorption equilibrium of the dye on the surface of catalysts. During the light irradiation, approximately 3.0 mL of suspension was collected every 20 minutes. After removal the photocatalyst particles from the suspension by centrifuge, the supernatant solutions were analyzed by a Perkin-Elmer Lamda 750S UV-visible spectrophotometer. Lambert-Beer rule was applied at the characteristic absorbance bands of dyes, RhB at 553nm, MB 665 nm and MO 463 nm, to determine their concentration changes.

Part II. Disussion 1. XRD patterns of STO and STON

20

30

40

50

2θ(°)

60

(310)

(220)

*+

(211)

(210)

(200)

(111)

(100)

Intensity (a. u.)

(110)

STON STO * TiO2 (anatase) + SrO

70

80

Fig. S1 (A) Wide-angle XRD patterns of STO and STON samples Fig.S1 shows the wide angle XRD patterns of the STO and STON samples, where the Bragg peaks can be well indexed to the perovskite-structured SrTiO3 (JCPDS: 74-1296). The lattice parameter of STON is slightly smaller than that of STO, while the crystallite size of STON (46.4 nm) is nearly half of that of STO (82.5 nm). STON possessed more pure perovskite phase than the STO sample, which comprised of trace amounts of anatase TiO2 (JCPDS: 71-1169) and SrO (JCPDS: 65-2652)4-6. It is previously reported the addition of chelate agent, such as acetylacetone and ethylene glycol, may greatly reduce the impurities (SrO and/or TiO 2) in the chemical synthesis of 3


STO7.

Volume Adsorption (cm3g-1 STP)

60

(B)

50 40

dV/dlog(D) (cm3g-1 nm-1)

2. TEM and N2-isotherm of STO

0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 0

10

20

30

40

50

Pore diameter (nm)

30 20 10 0 0.0

0.2

0.4

0.6

Relative Pressure (P/P0)

0.8

1.0

Fig. S2 Bright-field TEM and HRTEM (inset) images (A) and N2 adsorption-desorption isotherm (B) of STO. The inset of Fig S2(B) is the pore-size distribution of STO sample. The TEM image in Fig.S2(A) shows the STO sample comprises of poor porosity with irregular pore shape and less uniform sizes. The HRTEM image inserted in Fig.S2 (A) reveals that the walls of the mesopores are also single crystal perovskite STO. The labeled lattice distance is consistent with (110) diffraction obtained from XRD tests (Fig.S1).

The porosity of the STO sample was revealed by the observed Type-II N2 adsorption-desorption isotherm and type-H3 hysteresis loop of the meso-STON (Fig.S2B) suggest it possesses “cylinder-like” mesopores8. The pore size distribution of the mesoporous is quite broad as shown in the inset plot of Fig.S2 (B).

3. Ti 2p XPS of STO and STON

30.0k

457.0

Intensity (a. u.)

462.9

25.0k

NSTO 458.1

20.0k 463.9

15.0k STO 10.0k 466

464

462 460 458 Binding Energy / eV

456

454

Figure S3. Ti 2p XPS of STO and STON

4

452


The detailed XPS spectra of Ti 2p around 460 eV are shown in Fig. S3. The XPS spectrum for Ti exhibits two signals of Ti 2p3/2 and Ti 2p1/2. The binding energy of the Ti 2p3/2 and Ti 2p1/2 for STON (457.9, 463.1 eV) are lower than that for pure STO (459.4, 465.4 eV). It is supposed that the red shift of the binding energy of Ti 2p is induced by the N-doping which can reduce Ti4+ to Ti3+. 8 4. Photodegration of RhB of STO and STON under simulated solar irradiation 0.0

1.0 (A)

(B) 0.8

ln(c/c0)

-0.2

c/c0

0.6

-0.4

Blank P25 STO STON

0.4

Blank P25 STO STON

0.2

-0.6

0.0

-0.8

0

20

40

60

80

100

120

Irradiation Time (minute)

140

160

180

0

20

40

60

80

100

120

140


160

180

Figure S4. photodegration of RhB under visible-light irradiation(A) and their corresponding plot of ln(C/C0) versus irradiation time (B). 1.0 (A)

0.0

0.8

-0.4

ln(c/c0)

c/c0

(B)

-0.8

0.6

-1.2

0.4

blank P25 STO STON

0.2

-1.6

0.0 0

20

40

60

80

-2.0 0

blank P25 STO STON 20


40

60


80

Figure S5. photodegration of MB under visible-light irradiation(A) and their corresponding plot of ln(C/C0) versus irradiation time (B). Fig. S4 show the plot of ln(C/C0) versus irradiation time for the photodegration of RhB over STO and STON under visible-light irradiation. Fig. S5 shows the photodegration of MB over STO and STON under visible-light irradiation (A) and their corresponding plot of ln(C/C0) versus irradiation time (B).The apparent RhB and MB photodegration rates under visible-light irradiation listed in Table S1 are derived from pseudo-first-order model, ln(C/C0), where C and C0 are the concentration of RhB (or MB) at time t and 0, respectively, and k is pseudo-first-order reaction rate constant. 9

5


Table S1. Lattice parameters, crystallite size, pore size, BET surface area, Eg and photoreaction rate constants (kRhB) of STO and STON samples under visible-light irradiation. Photocatalyst

a=b=c

Crystallite

(Å) a

size (nm)b

SSAc

Dp (nm)

Eg(eV) d

k (min-1)e

(m2/g) MB

RhB

STO

3.908

82.5

12.4

19.5

3.2

0.0066

0.0007

STON

3.903

46.4

4.0

52.3

2.9

0.0224

0.0031

TiO2 P25

-

-

-

-

3.2

0.0054

0.0002

Note: a lattice parameters; b calculated from the Debye-Scherrer equation; c SSA refers to BET specific surface area; dEg was derived from Eg= 1239.8/λg, where λg is the absorption edge in the UV-Vis spetra; e

apparent kinetics constants of photocatalytic reactions under full arc and visible-light irradiations.

1.0

1st run

3 rd run

5 th run

0.8

C/C0

0.6

0.4

0.2

0.0 0

40

80 0

40

80 0

40

80

Irridation Time (Minute)

Figure S6. Lifetime of visible-light photo-degration MB over STON under visible-light irradiation. The photodegration of MB was cycled 5 times under the same condition to used to investigate the stability of the meso-STON. In the cycling tests, the used meso-STON were centrifuged after completing the photocatalysis reaction and re-dispersed into 100 mL MB solution for the next round of repeated test.

As shown in Fig. S6, meso-STON exhibited very similar photocatalysis activity in 5

times of repeated tests, revealing it is a highly stable photocatalyst.

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