- Email: [email protected]
Composite TiO2–SnO2 nanostructured films prepared by spin-coating with high photocatalytic performance
Catalysis Communications 9 (2008) 2357–2360
Contents lists available at ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Composite TiO2–SnO2 nanostructured films prepared by spin-coating with high photocatalytic performance E.M. El-Maghraby a,*, Y. Nakamura b, S. Rengakuji c,1 a
Physics Department, Faculty of Science, Assiut University, Assiut 71516, Egypt Center for Instrumental Analysis, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan c Graduate School of Science and Technology, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan b
a r t i c l e
i n f o
Article history: Received 11 April 2008 Received in revised form 13 May 2008 Accepted 26 May 2008 Available online 5 June 2008 PACS: 81.20.Fw 82.80.Ej 83.10.Tv
a b s t r a c t We have prepared nanoscale composite TiO2–SnO2 thin films with different Sn ratios. Sol–gel TiO2–SnO2 solutions with different ratios were deposited on quartz substrates by the spin-coating. XRD and AFM experiments showed that smooth and uniform anatase, anatase-rutile as well as rutile structural thin films were formed at 500 °C depending on Sn ratio. The nanocomposite films with Ti:Sn ratio of 3:1 proved an excellent photocatalytic activity in the UV–Vis region. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Sol–gel Spin-coating Nanocomposite TiO2–SnO2 thin films Structural analysis Photocatalytic activity
1. Introduction Titanium dioxide (TiO2) is widely used in wide range of technological applications. Examples are, dye sensitized solar cells [1,2], photo-catalysts [3,4], optical coating [5] and capacitors for largescale integrated devices [6]. The tetrahedral TiO2 structure crystallizes in three forms, namely, rutile, anatase and brookite [7,8]. Among which anatase type is believed to be the most efficient for photo-induced technological applications. Anatase crystallizes in a metastable state at temperatures below 600 °C and at high temperatures transforms to the rutile phase, which has better thermal stability [9]. The transition temperature depends on different physical and chemical parameters; pressure [10], stress [11], oxygen deficiency [12], contaminants [13], etc. The choice of the doping type may play a crucial rule in the crystalline structure and then the stable phase of TiO2 thin films. In our previous work
* Corresponding author. Tel.: +20 88 2412195; fax: +20 88 2342708. E-mail address: [email protected] (E.M. El-Maghraby). 1 Present address: Hokuriku Polytechnic College, 1289-1 Kawafuchi Uozu, Toyama 937-0856, Japan. 1566-7367/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2008.05.037
[14], high surface area nanometer anatase TiO2 thin films have been prepared with crystallization temperature at 300 °C by advanced sol–gel, ASG, spin-coating method [15,16]. The films showed good photocatalytic activity. Details about this technique can be found elsewhere [14–17]. The anatase and the rutile phases of TiO2 have band gaps of 3.2 eV and 3.0 eV, respectively. The semiconductor SnO2 has the tetrahedral structure with wide band gap (Eg = 3.6 eV) and crystallizes only in the TiO2 rutile (1 1 0) structure. Both titanium oxide and tin oxide [13] are widely reported materials for many technological applications. The thermal stability of both TiO2 and SnO2 as a rutile-type TiO2, the almost closed values of both Ti and Sn ionic radii (0.68 Å and 0.71 Å, respectively), equivalency and their advantages for environmental improvements and industrial technology promoted us to carry out the present study. The aim of this paper is to study the effect of Sn doping on the structural stability of TiO2 thin films and then its effect on the photocatalytic activity. Developing the more stable rutile-type TiO2 thin films at low temperatures therefore is promised and has a great importance. However, single-phase Sn-doped TiO2 nanostructured films of the rutile-type (1 1 0) at 500 °C have not been reported yet.
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2. Experiment Precursor solutions of TiO2, SnO2 were prepared according to the ASG method. Pure as well as TiO2–SnO2 composite (with different ratios of Ti:Sn) nanometer thin films were prepared in one cycle by sol–gel spin-coating method, SGSC, on quartz (fused silica) substrates in the clean room. The substrates were subjected to ultrasonic cleaning in ethanol for 5 min. and then dried on the spin coater. Washing with butanol and then acetone followed this process. After thermal stability of the precursor solution for 24 h at room temperature, a spin-coating process at 5000 rpm for 10 s was used for thin films deposition. Then, the deposited films were subjected to heat treatment by IR radiation. To search the phase structure, the films were annealed at different temperatures for 1 h using a Super-Burn oven (Motoyama-SL, Japan) with annealing schemes allowing precise slow rate for both the heating and cooling cycles. The thickness of the films was detected by the XRF (PW 2404 R, Philips Japan Co. Ltd.). For structural analysis of the films, a thin film X-ray diffractometer (XRD-6000, Shimadzu Corporation) using Cu Ka irradiation (k = 0.15408 nm) was used. The surface morphology of the films was observed by AFM (SPM 9500 J2-Scanning Probe Microscope, Schimadzu). The absorption spectra were recorded with a UV–Vis spectrophotometer (Shimadzu 2101, UV–Vis). Also the photocatalytic activity of 3–1 mol ratio of Ti:Sn and anatase TiO2 thin films of our previous work [14] was measured by recording the transmittance of soot ink (bokujyu) coated films on the same apparatus.
peak at (1 1 0) direction for Ti:Sn molar ratio of 10:1, i.e., when SnO2 P10%. This is the lowest temperature at which TiO2 rutiletype (1 1 0) thin films have been obtained so far. The (1 1 0) highest peak at 2h 27.4° suggests the rutile TiO2 structure in the nanoscale. In the literature, we have found the only study on Sn-doped TiO2 (1 1 0) rutile-type structure [18] showed the XRD diffraction pattern of the calcined gel powder not that of the thin film. Also, they show SEM image of a non-doped sample with non-uniform and non-homogeneous surface. The (1 1 0) surface, which is often used as a system model for metal oxides, has been the focus of several surface science theoretical studies [19,20]. Sn doping may modify the Fermi levels; energy gaps as well as the localization and composition of both valance and conduction band main components. This may referred to the inclusion of Sn ions in the TiO2 lattice and decreasing the energy gap due to the quantum size confinement. The average grain size of the annealed films in this experiment (500 °C) is around 4.2 nm, which is approximately half that of the rutile-type TiO2 thin film annealed at 800 °C. This result is promise to expect that our samples will give high photocatalytic activity. As we reported before [14], the advanced SGSC method gives homogeneous, nanosize anatase TiO2 structure, which is responsible for this result.
3. Results and discussion Typical XRD patterns of the TiO2–SnO2 composite thin films (the mol ratio of Ti:Sn = 3:1) annealed at different temperatures are shown in Fig. 1. As seen from Fig. 1, the rutile phase appeared at 500 °C. Fig. 2 shows the XRD patterns of SnO2–TiO2 films composed of various mol ratios of Ti:Sn heat treated at 500 °C. We have also shown the diffraction patterns of both rutile phase of SnO2 (500 °C), and TiO2 (800 °C), thin films. It can be seen that the XRD patterns show obvious peaks of pure rutile TiO2 with highest
Fig. 1. XRD patterns of TiO2–SnO2 thin films (the mole ratio of Ti:Sn = 3:1) deposited on quartz substrates annealed at various temperatures.
Fig. 2. XRD patterns of films composed of various mole ratios of compound of TiO2– SnO2 heat treated at 500 °C: (s) TiO2 anatase phase, (d) TiO2 rutile phase. Diffraction patterns of both pure TiO2 and SnO2 thin films (rutile phases) annealed at 800 °C and 500 °C, respectively, are also shown.
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65 TiO2-SnO2 Ti:Sn 3:1 TiO2 Anatase
Transmittance %
60
55
50
45 0
50
100
150
Time/ hour Fig. 4. Transmittance of TiO2–SnO2 (the mole ratio of Ti:Sn = 3:1) and anatase TiO2 thin films coated with ink (bokujyu) and irradiated with fluorescence lamb against time.
Fig. 3. AFM images of Ti:Sn thin films (3:1): (a) 2-D image, (b) 3-D image.
Improvement of the photocatalytic of TiO2 is possible either by nanosize surface fabrication or by doping with metal oxides like Sn. We have found that the Ti:Sn ratio has a pronounce effect on the stable structure of the obtained films. As shown in Fig. 2, anatase phase is the stable structure for Ti:Sn molar ratio of 50:1 (SnO2 P2%). Mixed anatase-rutile TiO2 phase is formed when Ti:Sn ratio of 20:1 (SnO2 P5%), i.e., with increasing the Sn ratio. However, mixed-phase Sn-doped TiO2 thin films worthy to be studied in details. Since no Sn phase in the XRD and based on the valence state of both Sn and Ti (4+), it could be concluded that Sn should be uniformly dispersed in the TiO2 crystallites. The 2-D and 3-D AFM images of the surface of TiO2–SnO2 (3:1) film annealed at 500 °C are shown in Fig. 3. The transparent surface was homogenous and uniform without any particles on the surface of the film. From Fig. 3, the surface shows very small roughness of about 5.32 nm (the height of the RMS) and particle size of about 3.7 nm as determined also from the FWHM (by Scherer formula) of the (1 1 0) peak of the XRD pattern. This ratio shows the smallest particle size as compared to other compositions. This is clear from the difference in the sharpness of the (1 1 0) peaks in the XRD pattern of Fig. 2. The thickness of the films was determined by XRF (X-ray fluorescence) and measures about 70 nm.The absorption spectra of the TiO2–SnO2 composite thin films were measured (not shown here). The films with Ti:Sn ratios of 50:1, 15:1, 10:1 and 3:1 show absorption edges around 220–380 nm with considerable shift towards the red region. This shift may refer to the charge transfer transition between Sn electrons and TiO2 conduction band. Also, it is noticed that films with Ti to Sn ratio of 3:1 are the best
absorber in the visible region. The reason may refer to the small grain size. This extended absorbance in the visible region enhances the photocatalytic activity of the film. Then, this makes it good candidate for photocatalytic applications under UV–Vis irradiation. The photocatalytic activity of Ti:Sn ratio of 3:1, as an example from the present study, and also anatase TiO2 thin films are shown in Fig. 4. Light of fluorescent lamp (27 W, 1000 Lux) filtered by DFC and DF-M was shone on the quartz substrate. Soot of ink (bokujyu), as a good example of hydrocarbon contaminants, was attached to the films. The considerable change of which was evaluated by measuring the transmittance at 550 nm. From Fig. 4, it is clear that the photo-decomposition activity of the 3:1 ratio of Ti:Sn film is around 50% greater than that of anatase TiO2, which is five times of other films as reported before [14]. The small grain size of the films, as indicated by AFM and XRD measurements, in addition to the smooth surface are responsible for the decomposition process. The high photocatalytic performance of our samples needs further studies to shed more light on this issue. This work is under progress. 4. Conclusions Rutile-type Sn-doped TiO2 (1 1 0) thin films were fabricated from the precursor solution prepared by the sol–gel spin-coating method. XRD patterns of the annealed films showed that the crystalline rutile phase appeared at 500 °C. We were able to control the desired phase by the appropriate Sn ratio. AFM surface image of Sn-doped TiO2 thin films were smooth and uniform. The samples show high absorbance and high photocatalytic performance in the UV–Vis region and films with Ti to Sn ratio of 3:1 are the best. Acknowledgements E.M. El-Maghraby is greatly indebted to Professor Rengakuji for his kind hospitality at the Venture Business Laboratory, Graduate School of Materials Science and Technology, Toyama University, Japan. References [1] B. O’Regan, M. Gratzle, Nature 353 (1991) 737. [2] A. Hagfelt, M. Gratzel, Chem. Rev. 95 (1995) 49. [3] A. Fujishima, K. Honda, Nature 238 (1972) 371.
2360 [4] [5] [6] [7] [8] [9] [10]
E.M. El-Maghraby et al. / Catalysis Communications 9 (2008) 2357–2360
A. Fujishima, K. Honda, Bull. Chem. Soc. Jpn. 44 (1971) 1148. G.S. Brady, Materials Handbook, 10th ed., McGraw-Hill, New York, 1971. Y.H. Lee, Vacuum 51 (1998) 503. I. Beattie, T. Gilson, Proc. R. Soc. A 307 (1968) 407. U. Balachandran, N. Elror, J. Solid State Chem. 42 (1982) 276. K.J. Hubbard, D.G. Schlom, J. Mater. Res. 11 (1996) 2757. National Institute of Standards and Technology, Phase Equilibrium Diagrams, Version 2.2, The American Ceramic Society, Westerville, 1998, Fig. 4258. [11] J.M. Criado, C. Real, J. Soria, Solid State Ionics 32/33 (1989) 461. [12] R.D. Shanon, J.A. Pask, J. Am. Ceram. Soc. 48 (1965) 391. [13] Y. Hideaki, Chem. Senses 14 (1998) 41.
[14] E.M. El-Maghraby, Y. Fujii, Y. Nakamura, S. Rengakuji, Electrochemistry 72 (2004) 4557. [15] S. Rengakuji, Y. Hara, Patent No. 2000-273647 A, Japan, 2000. [16] Y. Hara, S. Rengakuji, Y. Nakamura, A. Shinagawa, Electrochemistry 70 (2002) 13. [17] S. Rengakuji, Y. Hara, Y. Nakamura, C. Shimasaki, S. Ikeno, T. Kato, K. Kubota, Electrochemistry 67 (1999) 243. [18] S. Mahanty, S. Roy, S. Sen, J. Cryst. Growth 261 (2004) 77. [19] M. Menetrey, A. Markovits, C. Minot, Surf. Sci. 524 (2003) 49. [20] J.R. Samrano, G.F. Nóberga, C.A. Taft, J. Andrés, A. Beltrán, Surf. Sci. 580 (2005) 71.
Contents lists available at ScienceDirect
Catalysis Communications journal homepage: www.elsevier.com/locate/catcom
Composite TiO2–SnO2 nanostructured films prepared by spin-coating with high photocatalytic performance E.M. El-Maghraby a,*, Y. Nakamura b, S. Rengakuji c,1 a
Physics Department, Faculty of Science, Assiut University, Assiut 71516, Egypt Center for Instrumental Analysis, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan c Graduate School of Science and Technology, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan b
a r t i c l e
i n f o
Article history: Received 11 April 2008 Received in revised form 13 May 2008 Accepted 26 May 2008 Available online 5 June 2008 PACS: 81.20.Fw 82.80.Ej 83.10.Tv
a b s t r a c t We have prepared nanoscale composite TiO2–SnO2 thin films with different Sn ratios. Sol–gel TiO2–SnO2 solutions with different ratios were deposited on quartz substrates by the spin-coating. XRD and AFM experiments showed that smooth and uniform anatase, anatase-rutile as well as rutile structural thin films were formed at 500 °C depending on Sn ratio. The nanocomposite films with Ti:Sn ratio of 3:1 proved an excellent photocatalytic activity in the UV–Vis region. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Sol–gel Spin-coating Nanocomposite TiO2–SnO2 thin films Structural analysis Photocatalytic activity
1. Introduction Titanium dioxide (TiO2) is widely used in wide range of technological applications. Examples are, dye sensitized solar cells [1,2], photo-catalysts [3,4], optical coating [5] and capacitors for largescale integrated devices [6]. The tetrahedral TiO2 structure crystallizes in three forms, namely, rutile, anatase and brookite [7,8]. Among which anatase type is believed to be the most efficient for photo-induced technological applications. Anatase crystallizes in a metastable state at temperatures below 600 °C and at high temperatures transforms to the rutile phase, which has better thermal stability [9]. The transition temperature depends on different physical and chemical parameters; pressure [10], stress [11], oxygen deficiency [12], contaminants [13], etc. The choice of the doping type may play a crucial rule in the crystalline structure and then the stable phase of TiO2 thin films. In our previous work
* Corresponding author. Tel.: +20 88 2412195; fax: +20 88 2342708. E-mail address: [email protected] (E.M. El-Maghraby). 1 Present address: Hokuriku Polytechnic College, 1289-1 Kawafuchi Uozu, Toyama 937-0856, Japan. 1566-7367/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2008.05.037
[14], high surface area nanometer anatase TiO2 thin films have been prepared with crystallization temperature at 300 °C by advanced sol–gel, ASG, spin-coating method [15,16]. The films showed good photocatalytic activity. Details about this technique can be found elsewhere [14–17]. The anatase and the rutile phases of TiO2 have band gaps of 3.2 eV and 3.0 eV, respectively. The semiconductor SnO2 has the tetrahedral structure with wide band gap (Eg = 3.6 eV) and crystallizes only in the TiO2 rutile (1 1 0) structure. Both titanium oxide and tin oxide [13] are widely reported materials for many technological applications. The thermal stability of both TiO2 and SnO2 as a rutile-type TiO2, the almost closed values of both Ti and Sn ionic radii (0.68 Å and 0.71 Å, respectively), equivalency and their advantages for environmental improvements and industrial technology promoted us to carry out the present study. The aim of this paper is to study the effect of Sn doping on the structural stability of TiO2 thin films and then its effect on the photocatalytic activity. Developing the more stable rutile-type TiO2 thin films at low temperatures therefore is promised and has a great importance. However, single-phase Sn-doped TiO2 nanostructured films of the rutile-type (1 1 0) at 500 °C have not been reported yet.
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2. Experiment Precursor solutions of TiO2, SnO2 were prepared according to the ASG method. Pure as well as TiO2–SnO2 composite (with different ratios of Ti:Sn) nanometer thin films were prepared in one cycle by sol–gel spin-coating method, SGSC, on quartz (fused silica) substrates in the clean room. The substrates were subjected to ultrasonic cleaning in ethanol for 5 min. and then dried on the spin coater. Washing with butanol and then acetone followed this process. After thermal stability of the precursor solution for 24 h at room temperature, a spin-coating process at 5000 rpm for 10 s was used for thin films deposition. Then, the deposited films were subjected to heat treatment by IR radiation. To search the phase structure, the films were annealed at different temperatures for 1 h using a Super-Burn oven (Motoyama-SL, Japan) with annealing schemes allowing precise slow rate for both the heating and cooling cycles. The thickness of the films was detected by the XRF (PW 2404 R, Philips Japan Co. Ltd.). For structural analysis of the films, a thin film X-ray diffractometer (XRD-6000, Shimadzu Corporation) using Cu Ka irradiation (k = 0.15408 nm) was used. The surface morphology of the films was observed by AFM (SPM 9500 J2-Scanning Probe Microscope, Schimadzu). The absorption spectra were recorded with a UV–Vis spectrophotometer (Shimadzu 2101, UV–Vis). Also the photocatalytic activity of 3–1 mol ratio of Ti:Sn and anatase TiO2 thin films of our previous work [14] was measured by recording the transmittance of soot ink (bokujyu) coated films on the same apparatus.
peak at (1 1 0) direction for Ti:Sn molar ratio of 10:1, i.e., when SnO2 P10%. This is the lowest temperature at which TiO2 rutiletype (1 1 0) thin films have been obtained so far. The (1 1 0) highest peak at 2h 27.4° suggests the rutile TiO2 structure in the nanoscale. In the literature, we have found the only study on Sn-doped TiO2 (1 1 0) rutile-type structure [18] showed the XRD diffraction pattern of the calcined gel powder not that of the thin film. Also, they show SEM image of a non-doped sample with non-uniform and non-homogeneous surface. The (1 1 0) surface, which is often used as a system model for metal oxides, has been the focus of several surface science theoretical studies [19,20]. Sn doping may modify the Fermi levels; energy gaps as well as the localization and composition of both valance and conduction band main components. This may referred to the inclusion of Sn ions in the TiO2 lattice and decreasing the energy gap due to the quantum size confinement. The average grain size of the annealed films in this experiment (500 °C) is around 4.2 nm, which is approximately half that of the rutile-type TiO2 thin film annealed at 800 °C. This result is promise to expect that our samples will give high photocatalytic activity. As we reported before [14], the advanced SGSC method gives homogeneous, nanosize anatase TiO2 structure, which is responsible for this result.
3. Results and discussion Typical XRD patterns of the TiO2–SnO2 composite thin films (the mol ratio of Ti:Sn = 3:1) annealed at different temperatures are shown in Fig. 1. As seen from Fig. 1, the rutile phase appeared at 500 °C. Fig. 2 shows the XRD patterns of SnO2–TiO2 films composed of various mol ratios of Ti:Sn heat treated at 500 °C. We have also shown the diffraction patterns of both rutile phase of SnO2 (500 °C), and TiO2 (800 °C), thin films. It can be seen that the XRD patterns show obvious peaks of pure rutile TiO2 with highest
Fig. 1. XRD patterns of TiO2–SnO2 thin films (the mole ratio of Ti:Sn = 3:1) deposited on quartz substrates annealed at various temperatures.
Fig. 2. XRD patterns of films composed of various mole ratios of compound of TiO2– SnO2 heat treated at 500 °C: (s) TiO2 anatase phase, (d) TiO2 rutile phase. Diffraction patterns of both pure TiO2 and SnO2 thin films (rutile phases) annealed at 800 °C and 500 °C, respectively, are also shown.
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65 TiO2-SnO2 Ti:Sn 3:1 TiO2 Anatase
Transmittance %
60
55
50
45 0
50
100
150
Time/ hour Fig. 4. Transmittance of TiO2–SnO2 (the mole ratio of Ti:Sn = 3:1) and anatase TiO2 thin films coated with ink (bokujyu) and irradiated with fluorescence lamb against time.
Fig. 3. AFM images of Ti:Sn thin films (3:1): (a) 2-D image, (b) 3-D image.
Improvement of the photocatalytic of TiO2 is possible either by nanosize surface fabrication or by doping with metal oxides like Sn. We have found that the Ti:Sn ratio has a pronounce effect on the stable structure of the obtained films. As shown in Fig. 2, anatase phase is the stable structure for Ti:Sn molar ratio of 50:1 (SnO2 P2%). Mixed anatase-rutile TiO2 phase is formed when Ti:Sn ratio of 20:1 (SnO2 P5%), i.e., with increasing the Sn ratio. However, mixed-phase Sn-doped TiO2 thin films worthy to be studied in details. Since no Sn phase in the XRD and based on the valence state of both Sn and Ti (4+), it could be concluded that Sn should be uniformly dispersed in the TiO2 crystallites. The 2-D and 3-D AFM images of the surface of TiO2–SnO2 (3:1) film annealed at 500 °C are shown in Fig. 3. The transparent surface was homogenous and uniform without any particles on the surface of the film. From Fig. 3, the surface shows very small roughness of about 5.32 nm (the height of the RMS) and particle size of about 3.7 nm as determined also from the FWHM (by Scherer formula) of the (1 1 0) peak of the XRD pattern. This ratio shows the smallest particle size as compared to other compositions. This is clear from the difference in the sharpness of the (1 1 0) peaks in the XRD pattern of Fig. 2. The thickness of the films was determined by XRF (X-ray fluorescence) and measures about 70 nm.The absorption spectra of the TiO2–SnO2 composite thin films were measured (not shown here). The films with Ti:Sn ratios of 50:1, 15:1, 10:1 and 3:1 show absorption edges around 220–380 nm with considerable shift towards the red region. This shift may refer to the charge transfer transition between Sn electrons and TiO2 conduction band. Also, it is noticed that films with Ti to Sn ratio of 3:1 are the best
absorber in the visible region. The reason may refer to the small grain size. This extended absorbance in the visible region enhances the photocatalytic activity of the film. Then, this makes it good candidate for photocatalytic applications under UV–Vis irradiation. The photocatalytic activity of Ti:Sn ratio of 3:1, as an example from the present study, and also anatase TiO2 thin films are shown in Fig. 4. Light of fluorescent lamp (27 W, 1000 Lux) filtered by DFC and DF-M was shone on the quartz substrate. Soot of ink (bokujyu), as a good example of hydrocarbon contaminants, was attached to the films. The considerable change of which was evaluated by measuring the transmittance at 550 nm. From Fig. 4, it is clear that the photo-decomposition activity of the 3:1 ratio of Ti:Sn film is around 50% greater than that of anatase TiO2, which is five times of other films as reported before [14]. The small grain size of the films, as indicated by AFM and XRD measurements, in addition to the smooth surface are responsible for the decomposition process. The high photocatalytic performance of our samples needs further studies to shed more light on this issue. This work is under progress. 4. Conclusions Rutile-type Sn-doped TiO2 (1 1 0) thin films were fabricated from the precursor solution prepared by the sol–gel spin-coating method. XRD patterns of the annealed films showed that the crystalline rutile phase appeared at 500 °C. We were able to control the desired phase by the appropriate Sn ratio. AFM surface image of Sn-doped TiO2 thin films were smooth and uniform. The samples show high absorbance and high photocatalytic performance in the UV–Vis region and films with Ti to Sn ratio of 3:1 are the best. Acknowledgements E.M. El-Maghraby is greatly indebted to Professor Rengakuji for his kind hospitality at the Venture Business Laboratory, Graduate School of Materials Science and Technology, Toyama University, Japan. References [1] B. O’Regan, M. Gratzle, Nature 353 (1991) 737. [2] A. Hagfelt, M. Gratzel, Chem. Rev. 95 (1995) 49. [3] A. Fujishima, K. Honda, Nature 238 (1972) 371.
2360 [4] [5] [6] [7] [8] [9] [10]
E.M. El-Maghraby et al. / Catalysis Communications 9 (2008) 2357–2360
A. Fujishima, K. Honda, Bull. Chem. Soc. Jpn. 44 (1971) 1148. G.S. Brady, Materials Handbook, 10th ed., McGraw-Hill, New York, 1971. Y.H. Lee, Vacuum 51 (1998) 503. I. Beattie, T. Gilson, Proc. R. Soc. A 307 (1968) 407. U. Balachandran, N. Elror, J. Solid State Chem. 42 (1982) 276. K.J. Hubbard, D.G. Schlom, J. Mater. Res. 11 (1996) 2757. National Institute of Standards and Technology, Phase Equilibrium Diagrams, Version 2.2, The American Ceramic Society, Westerville, 1998, Fig. 4258. [11] J.M. Criado, C. Real, J. Soria, Solid State Ionics 32/33 (1989) 461. [12] R.D. Shanon, J.A. Pask, J. Am. Ceram. Soc. 48 (1965) 391. [13] Y. Hideaki, Chem. Senses 14 (1998) 41.
[14] E.M. El-Maghraby, Y. Fujii, Y. Nakamura, S. Rengakuji, Electrochemistry 72 (2004) 4557. [15] S. Rengakuji, Y. Hara, Patent No. 2000-273647 A, Japan, 2000. [16] Y. Hara, S. Rengakuji, Y. Nakamura, A. Shinagawa, Electrochemistry 70 (2002) 13. [17] S. Rengakuji, Y. Hara, Y. Nakamura, C. Shimasaki, S. Ikeno, T. Kato, K. Kubota, Electrochemistry 67 (1999) 243. [18] S. Mahanty, S. Roy, S. Sen, J. Cryst. Growth 261 (2004) 77. [19] M. Menetrey, A. Markovits, C. Minot, Surf. Sci. 524 (2003) 49. [20] J.R. Samrano, G.F. Nóberga, C.A. Taft, J. Andrés, A. Beltrán, Surf. Sci. 580 (2005) 71.