Energy-level matching of Fe(III) ions grafted at surface and. doped in bulk for efficient visible-light photocatalysts

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1 Energy-level matching of (III) ions grafted at surface and doped in bulk for efficient visible-light photocatalysts Min Liu, Xiaoqing Qiu, Masahiro Miyauchi,*,, and Kazuhito Hashimoto*,, Department of Metallurgy and Ceramics Science, Graduate School of Science and Engineering, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo , Japan. Research Center for Advanced Science and Technology, The University of Tokyo, Komaba, Meguro-ku, Tokyo , Japan. Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo , Japan. Japan Science and Technology Agency (JST), PRESTO, Honcho Kawaguchi, Saitama , Japan. Contents Table S1 Figs. S1 to S2 References S1

2 Table S1. ICP measurement of (III)- x Ti 1-x. sample x Ti 1-x (III)- x Ti 1-x Initial X (wt%) Initial grafting (III) (wt%) Measured (III) (wt%) ICP-AES measurement showed that the amount of surface (III) was nearly equal to the initial concentration used in the preparation, indicates nearly all of the (III) was grafted onto the surface of Ti and x Ti 1-x. The doped (III) was equal to the initial concentration when it was less than.5%. S2

3 S1, Crystal models of pure rutile Ti and x Ti 1-x a b Figure S1, (a) Unit cell of rutile Ti (oxygen and titanium atoms are represented by red and light blue spheres, respectively). (b) Ti doped with atom (the substitutional atom is represented by the brown sphere). S3

4 S2. Photos of pure Ti, x Ti 1-x and (III)-Ti Figure S2. Photos of pure Ti, x Ti 1-x and (III)-Ti. S4

5 S3. XRD patterns of x Ti 1-x. Intensity (a.u.) X=1% X=1% X=.5% X=.1% X=.5% X= θ (degree) Figure S3. XRD patterns of x Ti 1-x. It clearly shows that (III) doped into the lattice of Ti did not affect the structure of Ti, even in the high content of 1 wt%. S5

6 S4. ESR spectra of x Ti 1-x (x=.1 wt%). a 1 b 1 x Ti 1-x 5 5 Ti Ti 3+ Intensity (a.u.) Intensity (a.u.) pure Ti Magnetic field (G) Magnetic field (G) Figure S4. (a) ESR spectra of x Ti 1-x (x=.1 wt%). (b) High-resolution ESR spectrum of x Ti 1-x (x=.1 wt%) at the region of Ti 3+. S6

7 S5. SEM images. Figure S5. SEM images of (a) pure Ti, (b) (III)-Ti, (c) x Ti 1-x, and (d) (III)- x Ti 1-x, x=.1wt%, respectively. As can be seen in Figure S5, all the samples were assemblies of uniformly distributed nanoparticles. The average grain size of the nanoparticles was about 2 nm. Introduction of (III) nanoclusters on the surface of Ti as well as (III) ions into the Ti lattice did not change the morphology or the particle size. Therefore, the effects of morphology and size on the photocatalytic activity 1,2 can be excluded in the present study. S7

8 S6. XPS spectra of samples. Pure Ti Ti x Ti 1-x Intensity (a.u.) O (III)-Ti (III)- x Ti 1-x Binding energy (ev) Figure S6. Full-scale XPS spectra of samples. S8

9 S7. TEM images. Figure S7. TEM images of (a) pure Ti, (b) (III)-Ti, (c) x Ti 1-x, and (d) (III)- x Ti 1-x, x=.1 wt%, respectively. As shown in Figure S7, without surface (III) grafting, the surface of bare Ti and x Ti 1-x are clear. After the grafting of (III), the nanoclusters, with very small particle size, can be clearly seen on the surface of (III)-Ti, (III)- x Ti 1-x. S9

10 S8. Visible light irradiation condition. a b Intensity ( uw/cm 2.nm) Wavelength (nm) Figure S8. a) Picture of the photocatalytic activity measurement under visible light irradiation. b) The light source for the visible light irradiation. S1

11 S9. Typical change of the gas concentration during the process of the decomposition of IPA over the (III)- x Ti 1-x 9 Gas concentration (ppm) 6 3 C Acetone IPA Irradiation time (h) Figure S9. Representative time-dependent gas concentrations during IPA decomposition over (III)- x Ti 1-x (x=.1%) under visible light irradiation. The typical change of the gas concentration during the process of the decomposition of IPA over the (III)- x Ti 1-x at x=.1 wt% is shown in Figure S9. Prior to light irradiation, the vessel was kept in the dark for the absorption/desorption equilibrium of IPA on the surfaces of materials. With the visible-light irradiation, IPA concentration further decreased rapidly. Meanwhile, the amount of acetone increased sharply. Accompanying the decease of acetone, the amount of C started to increase quickly. After ~3 h of irradiation, the concentration of C reached approximately 9 ppm (ca. ~18 µmol), which was nearly 3 times the initially injected IPA, indicating the complete decomposition of IPA (CH 3 CHOHCH 3 +9/2 3C +4H 2 O). S11

12 S1. Details of calculation for quantum efficiency 18 C content (umol) Irradiation time (h) Figure S1. The C generation curve over (III)- x Ti 1-x (x=.1 wt%) sample under visible light irradiation. The C generation rate (R CO2 ) was obtained from the slope of the C generation curve between the irradiation time of ca. to 3 h. The calculation of quantum efficiency (QE) was conducted using the same procedure reported in literature (3). Take (III)- x Ti 1-x at x=.1% sample for example. Under the visible light irradiation, the wavelength of visible light is from 4 to 53 nm, and the light intensity is 1 mw/cm 2. The irradiating area is 5.5 cm 2. Therefore, the absorption rate of incident photons (R a p ) was determined to be quanta sec -1 using the following equation: R a p= 53 S α I (S is the area of the sample, α is the light 4 absorption and I is the light intensity at each wavelength). As for C generation, assuming that the reaction from IPA to C is proceeded: C 3 H 8 O+5H 2 O+18h + 3C +18H +, that is, six photons are required to produce one C molecule. The C generation rate (R CO2 ) was obtained from the slope of the S12

13 C generation curve in Figure S9. As shown in Figure S1, R CO2 was determined to be.69 µmol h -1. Thus the QE for C generations were calculated using the following equation: QE = 6 C generation rate/absorption rate of incident photon =6 ( / )mol sec quanta mol -1 / quanta sec -1 = (47.3%). S13

14 S11. Photocatalytic activities of Ti, Ti-x N x, and (III)- x Ti 1-x (x=.1wt%). 18 C content (µmol) (III)- x Ti 1-x Ti-x N x Ti Irradiation time (h) Figure S11. Comparative studies of C generation over bare Ti, Ti-x N x, and (III)- x Ti 1-x (x=.1wt%) nanocomposites samples under the same visible light conditions. S14

15 S12. Pictures of the photocatalytic activity measurement under UV light irradiation and indoor light irradiation. Figure S12. Pictures of the photocatalytic activity measurement under: a) UV light irradiation and b) white LED light irradiation. S15

16 S13. C generation over (III)- x Ti 1-x (x=.1wt%) nanocomposites and P25 under white LED and UV light irradiation. a 3 UV light b 18 Intensity ( uw/cm 2.nm) Wavelength (nm) white LED C con. (µmol) P25 (UV light) (III)- x Ti 1-x (white LED) Irradiation time (h) Figure S13. (a) The light source for the white LED and UV light irradiation with light intensity of 1 mw/cm 2. (b) C generation over (III)- x Ti 1-x (x=.1wt%) nanocomposites and P25 under white LED and UV light irradiation with the same light intensity of 1 mw/cm 2. S16

17 S14. Photocatalytic activities at different (III) doping concentrations C content (umol) X=.5% X=.1% X=.5% Irradiation time (h) Figure S14. Comparative studies of C generation over (III)- x Ti 1-x at x=.5 wt%,.1 wt% and.5 wt% under visible light irradiation. At the lower (III) content, the visible-light absorption is not abundant. Therefore, its activity is not very high. However, further increasing the content to.5wt%, the activity slightly decreased, due to the negative effects of (III) as the recombination center of photoinduced charge carriers. S17

18 S15. Photocatalytic activities at different amount of surface (III) grafted samples C content (umol) % - x Ti 1-x.1% - x Ti 1-x.5% - x Ti 1-x Irradiation time (h) Figure S15. Comparative studies of C generation over.5 wt% (III)- x Ti 1-x,.1 wt% (III)- x Ti 1-x and.5 wt% (III)- x Ti 1-x at x=.1 wt% under visible light irradiation. At the lower content of (III) grafted x Ti 1-x, the amount of surface (III) nanoclusters may not enough to accept the electrons from VB and doped (III). Thus, some electrons would be recombined, decreasing the photocatalytic activity. However, further increasing the amount of (III) in the grafts, resulted in a decrease of the CO2 generation rates. This might be explained by the quenching of the generated holes and (III), 3 as the recombination possibility of the generated holes and (III) would be increased before holes are encounterd with IPA and oxygen molecules are reduced by (III). S18

19 S16. The decomposition of IPA over samples of the samples partly replaced (III) by another very effective Cu(II), such as Cu(II)- x Ti 1-x and (III)-Cu x Ti 1-x 18 (III)- x Ti 1-x C content (µmol) Cu(II)- x Ti 1-x (III)-Cu x Ti 1-x Irradiation time (h) Figure S16 Comparative studies of C generation over (III)-Cu x Ti 1-x, Cu(II)- x Ti 1-x and (III)- x Ti 1-x (x=.1wt%) samples under the same visible light conditions. S19

20 S17. The activity of Cu(II)-Cu x Ti 1-x. 18 C content (umol) (III)- x Ti 1-x Cu(II)-Cu x Ti 1-x Irradiation time (h) Figure S17. The C generation curve over Cu(II)-Cu x Ti 1-x and (III)- x Ti 1-x at x=.1 wt% samples under the same visible light irradiation. S2

21 S18. Photocatalytic activities of the samples by introducing a thin Ti layer between (III) nanoclusters and x Ti 1-x. Ti doped Ti TTIP annealed grafted Figure S18. Scheme for the preparation of the samples by introducing a Ti thin layer between (III) nanoclusters and x Ti 1-x (x=.1 wt%). 1 g x Ti 1-x was put into 1 ml.1 mol/l Titanium tetraisopropoxide solution. The solution was heated at 9 C, and stirred for 1 h in a vial reactor. The suspension was then filtered twice with a membrane filter (.25 µm, Millipore) and washed with sufficient amounts of distilled water. The resulting residues were dried at 11 o C for 24 h and subsequently heated at 95 o C for 3 h. Then, (III) ions were grafted on the obtained powders by the same impregnation method as (III)- x Ti 1-x. S21

22 S19. Photocatalytic activities of the samples by introducing a thin Ti layer between (III) nanoclusters and x Ti 1-x. 18 C content (umol) Control sample (III)- x Ti 1-x Irradiation time (h) Figure S19. The C generation curve over control sample and (III)- x Ti 1-x (x=.1 wt%) sample under the same visible light irradiation. The important of the good junction between surface (III) and bulk (III) for efficient charge transfer was confirmed by the lower activities of adding Ti thin layer between (III) nanoclusters and x Ti 1-x, as shown in Figure S19. When introducting a Ti thin layer between (III) nanoclusters and x Ti 1-x, the activity decreased drastically because the efficient charge transfer between surface (III) and bulk (III) ions was broke by the thin Ti layer. S22

23 S2. The synergy effect of surface (III) and bulk (III) in other semiconductors. a 1-R (%) c 1-R (%) Pure ZnO (III)-ZnO x Zn 1-x O (III)- x Zn 1-x O R (%) Wavelength (nm) 1-R (%) Wavelength (nm) Pure SrTiO 3 (III)-STiO3 x SrTi 1-x O3 (III)- x SrTi 1-x O3 (III)-SrTiO 3 x SrTi 1-x O 3 (III)- x SrTi 1-x O Wavelength (nm) (III)-ZnO x Zn 1-x O (III)- x Zn 1-x O b C content (µmol) d C content (µmol) (III)- x Zn 1-x O (III)-ZnO x Zn 1-x O (III)- x Sr 1-x TiO 3 (III)-SrTiO 3 x Sr 1-x TiO 3 Irradiation time (h) Wavelength (nm) Irradiation time (h) Figure S2. (a, c) UV-visible reflectance spectra of ZnO samples and SrTiO 3 samples. The inset shows the difference UV-vis spectra of ZnO samples and SrTiO 3 samples with bare ZnO and SrTiO 3 respectively. (b, d) The C generation curve over (III) grafted and (III) doped ZnO and SrTiO 3 in the content of.1 wt% under the same visible light irradiation. Figure S2a and c show that there are also energy level matching of surface (III) and bulk (III) in ZnO and SrTiO 3. With the energy level matching of surface (III) and bulk (III), low photocatalytic active ZnO and SrTiO 3 can be conversed into efficient visible-light photocatalysts (Figure S2b and d). S23

24 References 1. Wang, H. H.; Xie, C. S.; Zhang, W.; Cai, S. Z.; Yang, Z. H.; Gui, Y. H. J. Hazard. Mater. 27, 141, Li, D.; Haneda, H.; Chemosphere 23, 51, Yu, H. G.; Irie, H.; Shimodaira, Y.; Hosogi, Y.; Kuroda, Y.; Miyauchi, M.; Hashimoto, K. J. Phys. Chem. C 21, 114, S24