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TiO2 nanostructures
Materials Letters 62 (2008) 3688–3690
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
A facile method for synthesis of Ag/TiO2 nanostructures Yuekun Lai, Yicong Chen, Huifang Zhuang, Changjian Lin ⁎ Key Laboratory for Physical Chemistry of Solid Surfaces and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China
A R T I C L E
I N F O
Article history: Received 8 December 2007 Accepted 8 April 2008 Available online 23 April 2008 Keywords: Titanium dioxide nanostructure Ag nanoparticle Sol–gel Hydrothermal process
A B S T R A C T A facile sol–gel and hydrothermal process has been developed to prepare the Ag nanoparticles supported TiO2 nanostructures. The chemical composition and structure of the products have been characterized systematically with XRD, HRTEM and XPS spectrum. The results indicate that Ag species nanoparticles dispersed uniformly on the TiO2 nanostructured surface are of metallic nature. A possible mechanism has been proposed to explain the formation of silver nanoparticles on TiO2 nanostructures with high dispersion. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Titanium dioxide (TiO2) has attracted tremendous interest due to its intriguing optical, electrical and photochemical properties, such as the excellent properties of photoelectrochemistry and photocatalytic activity [1–3]. However, for practical application, the photocatalytic activity and photoresponse behavior of TiO2 are very much needed to be further improved. Compared with regular particles, the TiO2-based solids with nanoscale dimensions and high morphological specificity, e. g. nanosheets or nanotubes may offer a unique reaction vessel for nanoscale photoactive building devices due to its high specific surface area. In recent years, great efforts have been devoted to the design and fabrication of nanostructured systems with tunable physical–chemical properties for advanced photocatalytic applications [4,5]. It is of great interest to encapsulate or adorn the TiO2 nanostructures with highly dispersed noble metal nanoparticles such as Ag, Au and Pt, because the nanoscale noble metals are usually a classic high-performance heterogeneous catalysts [6–8]. So far, various methods have been successfully applied to coat or deposit metal particles onto TiO2 nanostructured surfaces. These methods include chemical reduction [9], deposition precipitation method [10] and photodeposition [11]. However, the fabrication processes including introduction of reducing reagents, UV irradiation or templates to the system means a much more complicated, and might bring about impurities in the final product. Therefore, it is a challenge to develop more convenient methods to prepare noble metal-coated TiO2 without other impurities. To our knowledge, the sol–gel process plus hydrothermal treatment is one of the relatively convenient and simple methods to introduce foreign metallic ions into TiO2 nanostructured surfaces [12,13]. ⁎ Corresponding author. Fax: +86 592 2184655. E-mail address: [email protected] (C. Lin). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.055
Recently, we had successfully decorated carbon nanotubes with platinum nanoparticles by a novel route in the presence of ethylene glycol [14]. In this letter, we report the fabrication of highly dispersive size-controlled Ag nanoparticles supported on TiO2 nanostructured surface by a simple process based on combining the sol–gel method with hydrothermal method. The effect of the alkali concentration on the morphology and size of Ag/TiO2 is investigated. And a formation mechanism of Ag nanoparticles supported on TiO2 nanostructured surface is also discussed. 2. Experimental section 2.1. Preparation of Ag/TiO2 powders The Ag/TiO2 powders were similarly prepared using a modified sol–gel method as described in our previous work [15]. In a typical synthesis, a 0.2 g solid AgNO3 was dissolved in 20 mL of ethanol, followed by addition of mixture containing 8 mL of tetra-n-butyl titanate, 80 mL of ethanol, 4 mL of ethyl acetoacetate. Then 1 mL distilled water was added by dropwise to the above mixed solution in the absence of light, the mixed solution was successively stirred for 4 h until a clear and transparent sol was obtained. Subsequently, the sol was dried at 353 K to get xerogel, which was grinded and calcined at 723 K for 2 h. 2.2. Preparation of TiO2 nanostructures with Ag nanoparticles The as-synthesized Ag/TiO2 powders (300 mg) were added into 20 mL 5–10 M NaOH and dispersed uniformly, then transferred to a 30 mL Teflon-lined stainless autoclave and heated to 403 K for 48 h. The obtained precipitates were firstly filtered and washed with distilled water, then centrifuged to separate the powder from the solution. This procedure was repeated for several times until the pH
Y. Lai et al. / Materials Letters 62 (2008) 3688–3690
3689
(HRTEM, Philips Tecnai F30). The chemical composition was characterized with a scanning ESCA microprobe system (XPS, PHI Quantum 2000) with Al Kα radiation source. The binding energies were normalized to the signal for adventitious carbon at 285.0 eV. The X-ray powder diffraction (XRD) analysis was carried out by a Panalytical X'pert PRO diffractometer with Cu Kα radiation source. 3. Results and discussion
Fig. 1. XRD spectra of the as-prepared Ag/TiO2 nanostructures. Titanate nanotubes (a) and Ag/TiO2 nanotubes (b) and nanosheets (c) by hydrothermal treatment in 10 M and 5 M NaOH, respectively.
of washing water close to neutral. Finally, the Ag-loaded powder was filtered and dried at 353 K for 6 h. 2.3. Structure and morphology characterization The morphologies of Ag-supported TiO2 nanostructures were observed using high-resolution transmission electron micrograph
The XRD patterns of the metal Ag nanoparticles coated TiO2 nanostructures are shown in Fig. 1. Peaks marked “A” and “O” correspond to anatase phase and orthorhombic system of titanate, respectively. It can be seen that the samples exhibit well-crystallized anatase phase. The transition of crystalline phase from the orthorhombic system to anatase TiO2 take place readily in the hydrothermal processes with the impregnation of silver metal because titanate nanostructures possess a large surface area and more defects. Diffractive peaks indexed to metal Ag can be found at 2θ = 44.3° (200), 64.2° (220) and 77.5° (311), indicating that the silver ions are effectively reduced into metal Ag. The peaks around 10° and 28° (corresponding to an orthorhombic titanate system) are significantly weakened and shifted towards a higher angle value, which indicates an interlayer distance change in structure with the introduction of silver metal [16]. TEM analyses give further and direct evidence of the Ag nanoparticles on different TiO2 nanostructured morphologies with respect to various NaOH concentrations. When the hydrothermal treatment was carried out in 10 M NaOH, the typical HRTEM images of the synthesized TiO2 nanotube with Ag nanoparticles are shown in Fig. 2a. It can be seen that abundant metal Ag nanoparticles are highly dispersed on the exterior nanotube surface without aggregation. Fig. 2b shows a representative high magnification TEM image of an individual nanotube. Besides a uniform outer diameter about 10 nm and the length up to several hundreds nanometers, the nanotube has a hollow structure with opening ends. Moreover, it can be clearly seen that part of the Ag nanoparticles are encapsulated in the inner nanotube. This confirms nanotube is rolled up by an alkali-treated specimen with a sheet shape to encapsulate silver nanoparticles. The TEM statistical analysis reveals that the size of nanoparticles is distributed mostly in a range of 4–8 nm.
Fig. 2. HRTEM images of the as-prepared Ag/TiO2 nanotubes and nanosheets. Low magnification and its high-magnified individual Ag/TiO2 nanotube (a, b) and Ag/TiO2 nanosheet (c, d).
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Y. Lai et al. / Materials Letters 62 (2008) 3688–3690 (367.8 eV) or AgO (367.4 eV) was observed, indicating that Ag specie coated on TiO2 nanostructures is of metallic nature [17,18]. These results are in good agreement with the XRD characterization. We conclude that the mechanism for the deposition of silver nanoparticles on different TiO2 nanostructures is as follow. While Ag/TiO2 gel powders were calcined at 723 K for 2 h, the Ag+ ion introduced by sol–gel process could not enter into the lattice of anatase phase due to its larger radius than that of Ti4+ ion. So the dispersed Ag+ ions would move towards the nanotubes surface under the action of heat. Furthermore, due to the high redox potential, Ag+ ions gradually reduced into metallic state Ag (0) by heat and TiO2 photocatalytic reduction [12]. Since the Ag–O bonding is much weaker than Ti–O and Ag–Ag bonding and Ag atom possesses higher surface free energy than TiO2 [19], the free Ag atoms will have the tendency to aggregate into metallic Ag nanoparticles. When the TiO2 power of anatase crystallites is treated with NaOH aqueous solution, the crystallites are exfoliated into layered crystalline sheets. Both sides of these sheets have many dangling bonds that should be saturated in the alkali solution. If a higher concentration of NaOH aqueous solution is used, the structure of the obtained products can be changed to nanotube. The sheet structure is unstable because of its high surface-to-volume ratio or system energy. Rolling of the sheet to tube can reduce the number of surface dangling bonds and thus decrease its system energy. Therefore, the Ag nanoparticles supported on the sheet surface can be encapsulated into the nanotube, as shown in the above HRTEM images.
4. Conclusions In this work, we report a facile strategy to synthesize highly dispersive Ag species nanoparticles on TiO2 nanotubes or nanosheets in large scale. Various characterization studies prove the synthesis of Ag species nanoparticles are all in metallic state without the introducing of other impurities of Ag oxide species. A possible mechanism is proposed to explain the formation of Ag nanoparticles on TiO2 nanostructured surface. In addition, we believe that the synthetic route can be a promising choice for large-scale synthesis of noble metal nanoparticles supported on TiO2 nanostructured materials. Acknowledgments The financial support from the National Nature Science Foundation of China (50571085) and the Key Scientific Project of Fujian Province, China (2005HZ01-3) is gratefully acknowledged. References Fig. 3. XPS spectrum of the Ag/TiO2 powder. (a) Overall spectrum; (b) Original and Guassian fitted high-resolution curves of the Ag 3d region.
HRTEM image (Fig. 2c) shows the Ag/TiO2 nanosheets by hydrothermal treatment in 5 M NaOH solution. It is found that the uniform metal Ag nanoparticles are in close contact with the TiO2 nanosheet support. High magnification TEM image clearly demonstrate that abundant nanoparticles coated on the nanosheets with homogeneous dispersion and narrow size dispersion (Fig. 2d). The size of nanoparticles is distributed mostly in a narrow range of 2–5 nm. Therefore, the morphology of the Ag/TiO2 nanostructures can be controlled by adjusting the concentration of NaOH solution. The chemical states of elements in the Ag particles coated TiO2 were analysed by Xray photoelectron spectroscopy (XPS). Fig. 3 shows the survey XPS spectrum of the Ag nanoparticles coated TiO2 nanotube and high-resolution XPS spectrum of Ag 3d. On its survey spectrum (Fig. 3a), it clearly indicated that Ti, O, Na and Ag elements exist in the Ag nanoparticles coated TiO2 nanotube, no trace of any impurity is observed except for a small amount of adventitious carbon from XPS instrument itself. The binding energy values of Ti 2p3/2 and O 1s peaks show that they are in the ranges 458.2–458.8 eV and 530.0–530.2 eV, respectively. These values can be attributed to Ti4+and O2−in TiO2. Fig. 3b is the high-resolution original and guassian fitted XPS curves of Ag 3d region. The original XPS curve can be well fitted by two peaks centered at 368.2 eV and 374.2 eV corresponding to Ag 3d5/2 and Ag 3d3/2, respectively. No peak corresponding to Ag2O
[1] Schulz J, Roucoux A, Patin H. Chem Rev 2002;102:3757–78. [2] Lai YK, Sun L, Chen C, Nie CG, Zuo J, Lin CJ. Appl Surf Sci 2005;252:1101–6. [3] Lai YK, Sun L, Chen YC, Zhuang HF, Lin CJ, Chin JW. J Electrochem Soc 2006;153:123–7. [4] Xu MW, Bao SJ, Zhang XG. Mater Lett 2005;59:2194–8. [5] Lai YK, Lin CJ, Wang H, Huang JY, Zhuang HF, Sun L. Electrochem Commun 2008;10:387–91. [6] Ma RZ, Sasaki T, Bando Y. J Am Chem Soc 2004;126:10382–8. [7] Huang JG, Kunitake T, Onoue S. Chem Commun 2004;8:1008–9. [8] Tada H, Teranishi K, Inubushi YI, Ito S. Langmuir 2000;16:3304–9. [9] Kamat PV, Flumiani M, Dawson A. Colloids Surf A-Physicochem Eng Asp 2002;202:269–79. [10] You XF, Chen F, Zhang JL, Anpo M. Catal Letters 2005;102:247–50. [11] Chan SC, Barteau MA. Langmuir 2005;21:5588–95. [12] Epifani M, Giannini C, Tapfer L, Vasanelli L. J Am Ceram Soc 2000;85:2385–93. [13] Miao L, Ina Y, Tanemura S, Jiang T, Tanemura M, Kaneko K, et al. Surf Sci 2007;601:2792–9. [14] Wang Y, Xu X, Tian ZQ, Zong Y, Cheng HM, Lin CJ. Chem Eur J 2006;12:2542–9. [15] Shen GX, Chen YC, Lin L, Lin CJ, Scantlebury D. Electrochim Acta 2005;50:5083–9. [16] Ma XQ, Feng CX, Jin ZS, Guo XY, Yang JJ, Zhang ZJ. J Nanopart Res 2005;7:681–3. [17] Stathatos E, Lianos P. Langmuir 2000;16:2398–400. [18] Sano T, Negishi N, Uchino K, Tanaka J, Matsuzawa S, Takeuchi K. J Photochem Photobiol A-Chem 2003;160:93–8. [19] Vitos L, Ruban AV, Skriver HL, Kollar J. Surf Sci 1998;411:186–202.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
A facile method for synthesis of Ag/TiO2 nanostructures Yuekun Lai, Yicong Chen, Huifang Zhuang, Changjian Lin ⁎ Key Laboratory for Physical Chemistry of Solid Surfaces and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China
A R T I C L E
I N F O
Article history: Received 8 December 2007 Accepted 8 April 2008 Available online 23 April 2008 Keywords: Titanium dioxide nanostructure Ag nanoparticle Sol–gel Hydrothermal process
A B S T R A C T A facile sol–gel and hydrothermal process has been developed to prepare the Ag nanoparticles supported TiO2 nanostructures. The chemical composition and structure of the products have been characterized systematically with XRD, HRTEM and XPS spectrum. The results indicate that Ag species nanoparticles dispersed uniformly on the TiO2 nanostructured surface are of metallic nature. A possible mechanism has been proposed to explain the formation of silver nanoparticles on TiO2 nanostructures with high dispersion. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Titanium dioxide (TiO2) has attracted tremendous interest due to its intriguing optical, electrical and photochemical properties, such as the excellent properties of photoelectrochemistry and photocatalytic activity [1–3]. However, for practical application, the photocatalytic activity and photoresponse behavior of TiO2 are very much needed to be further improved. Compared with regular particles, the TiO2-based solids with nanoscale dimensions and high morphological specificity, e. g. nanosheets or nanotubes may offer a unique reaction vessel for nanoscale photoactive building devices due to its high specific surface area. In recent years, great efforts have been devoted to the design and fabrication of nanostructured systems with tunable physical–chemical properties for advanced photocatalytic applications [4,5]. It is of great interest to encapsulate or adorn the TiO2 nanostructures with highly dispersed noble metal nanoparticles such as Ag, Au and Pt, because the nanoscale noble metals are usually a classic high-performance heterogeneous catalysts [6–8]. So far, various methods have been successfully applied to coat or deposit metal particles onto TiO2 nanostructured surfaces. These methods include chemical reduction [9], deposition precipitation method [10] and photodeposition [11]. However, the fabrication processes including introduction of reducing reagents, UV irradiation or templates to the system means a much more complicated, and might bring about impurities in the final product. Therefore, it is a challenge to develop more convenient methods to prepare noble metal-coated TiO2 without other impurities. To our knowledge, the sol–gel process plus hydrothermal treatment is one of the relatively convenient and simple methods to introduce foreign metallic ions into TiO2 nanostructured surfaces [12,13]. ⁎ Corresponding author. Fax: +86 592 2184655. E-mail address: [email protected] (C. Lin). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.04.055
Recently, we had successfully decorated carbon nanotubes with platinum nanoparticles by a novel route in the presence of ethylene glycol [14]. In this letter, we report the fabrication of highly dispersive size-controlled Ag nanoparticles supported on TiO2 nanostructured surface by a simple process based on combining the sol–gel method with hydrothermal method. The effect of the alkali concentration on the morphology and size of Ag/TiO2 is investigated. And a formation mechanism of Ag nanoparticles supported on TiO2 nanostructured surface is also discussed. 2. Experimental section 2.1. Preparation of Ag/TiO2 powders The Ag/TiO2 powders were similarly prepared using a modified sol–gel method as described in our previous work [15]. In a typical synthesis, a 0.2 g solid AgNO3 was dissolved in 20 mL of ethanol, followed by addition of mixture containing 8 mL of tetra-n-butyl titanate, 80 mL of ethanol, 4 mL of ethyl acetoacetate. Then 1 mL distilled water was added by dropwise to the above mixed solution in the absence of light, the mixed solution was successively stirred for 4 h until a clear and transparent sol was obtained. Subsequently, the sol was dried at 353 K to get xerogel, which was grinded and calcined at 723 K for 2 h. 2.2. Preparation of TiO2 nanostructures with Ag nanoparticles The as-synthesized Ag/TiO2 powders (300 mg) were added into 20 mL 5–10 M NaOH and dispersed uniformly, then transferred to a 30 mL Teflon-lined stainless autoclave and heated to 403 K for 48 h. The obtained precipitates were firstly filtered and washed with distilled water, then centrifuged to separate the powder from the solution. This procedure was repeated for several times until the pH
Y. Lai et al. / Materials Letters 62 (2008) 3688–3690
3689
(HRTEM, Philips Tecnai F30). The chemical composition was characterized with a scanning ESCA microprobe system (XPS, PHI Quantum 2000) with Al Kα radiation source. The binding energies were normalized to the signal for adventitious carbon at 285.0 eV. The X-ray powder diffraction (XRD) analysis was carried out by a Panalytical X'pert PRO diffractometer with Cu Kα radiation source. 3. Results and discussion
Fig. 1. XRD spectra of the as-prepared Ag/TiO2 nanostructures. Titanate nanotubes (a) and Ag/TiO2 nanotubes (b) and nanosheets (c) by hydrothermal treatment in 10 M and 5 M NaOH, respectively.
of washing water close to neutral. Finally, the Ag-loaded powder was filtered and dried at 353 K for 6 h. 2.3. Structure and morphology characterization The morphologies of Ag-supported TiO2 nanostructures were observed using high-resolution transmission electron micrograph
The XRD patterns of the metal Ag nanoparticles coated TiO2 nanostructures are shown in Fig. 1. Peaks marked “A” and “O” correspond to anatase phase and orthorhombic system of titanate, respectively. It can be seen that the samples exhibit well-crystallized anatase phase. The transition of crystalline phase from the orthorhombic system to anatase TiO2 take place readily in the hydrothermal processes with the impregnation of silver metal because titanate nanostructures possess a large surface area and more defects. Diffractive peaks indexed to metal Ag can be found at 2θ = 44.3° (200), 64.2° (220) and 77.5° (311), indicating that the silver ions are effectively reduced into metal Ag. The peaks around 10° and 28° (corresponding to an orthorhombic titanate system) are significantly weakened and shifted towards a higher angle value, which indicates an interlayer distance change in structure with the introduction of silver metal [16]. TEM analyses give further and direct evidence of the Ag nanoparticles on different TiO2 nanostructured morphologies with respect to various NaOH concentrations. When the hydrothermal treatment was carried out in 10 M NaOH, the typical HRTEM images of the synthesized TiO2 nanotube with Ag nanoparticles are shown in Fig. 2a. It can be seen that abundant metal Ag nanoparticles are highly dispersed on the exterior nanotube surface without aggregation. Fig. 2b shows a representative high magnification TEM image of an individual nanotube. Besides a uniform outer diameter about 10 nm and the length up to several hundreds nanometers, the nanotube has a hollow structure with opening ends. Moreover, it can be clearly seen that part of the Ag nanoparticles are encapsulated in the inner nanotube. This confirms nanotube is rolled up by an alkali-treated specimen with a sheet shape to encapsulate silver nanoparticles. The TEM statistical analysis reveals that the size of nanoparticles is distributed mostly in a range of 4–8 nm.
Fig. 2. HRTEM images of the as-prepared Ag/TiO2 nanotubes and nanosheets. Low magnification and its high-magnified individual Ag/TiO2 nanotube (a, b) and Ag/TiO2 nanosheet (c, d).
3690
Y. Lai et al. / Materials Letters 62 (2008) 3688–3690 (367.8 eV) or AgO (367.4 eV) was observed, indicating that Ag specie coated on TiO2 nanostructures is of metallic nature [17,18]. These results are in good agreement with the XRD characterization. We conclude that the mechanism for the deposition of silver nanoparticles on different TiO2 nanostructures is as follow. While Ag/TiO2 gel powders were calcined at 723 K for 2 h, the Ag+ ion introduced by sol–gel process could not enter into the lattice of anatase phase due to its larger radius than that of Ti4+ ion. So the dispersed Ag+ ions would move towards the nanotubes surface under the action of heat. Furthermore, due to the high redox potential, Ag+ ions gradually reduced into metallic state Ag (0) by heat and TiO2 photocatalytic reduction [12]. Since the Ag–O bonding is much weaker than Ti–O and Ag–Ag bonding and Ag atom possesses higher surface free energy than TiO2 [19], the free Ag atoms will have the tendency to aggregate into metallic Ag nanoparticles. When the TiO2 power of anatase crystallites is treated with NaOH aqueous solution, the crystallites are exfoliated into layered crystalline sheets. Both sides of these sheets have many dangling bonds that should be saturated in the alkali solution. If a higher concentration of NaOH aqueous solution is used, the structure of the obtained products can be changed to nanotube. The sheet structure is unstable because of its high surface-to-volume ratio or system energy. Rolling of the sheet to tube can reduce the number of surface dangling bonds and thus decrease its system energy. Therefore, the Ag nanoparticles supported on the sheet surface can be encapsulated into the nanotube, as shown in the above HRTEM images.
4. Conclusions In this work, we report a facile strategy to synthesize highly dispersive Ag species nanoparticles on TiO2 nanotubes or nanosheets in large scale. Various characterization studies prove the synthesis of Ag species nanoparticles are all in metallic state without the introducing of other impurities of Ag oxide species. A possible mechanism is proposed to explain the formation of Ag nanoparticles on TiO2 nanostructured surface. In addition, we believe that the synthetic route can be a promising choice for large-scale synthesis of noble metal nanoparticles supported on TiO2 nanostructured materials. Acknowledgments The financial support from the National Nature Science Foundation of China (50571085) and the Key Scientific Project of Fujian Province, China (2005HZ01-3) is gratefully acknowledged. References Fig. 3. XPS spectrum of the Ag/TiO2 powder. (a) Overall spectrum; (b) Original and Guassian fitted high-resolution curves of the Ag 3d region.
HRTEM image (Fig. 2c) shows the Ag/TiO2 nanosheets by hydrothermal treatment in 5 M NaOH solution. It is found that the uniform metal Ag nanoparticles are in close contact with the TiO2 nanosheet support. High magnification TEM image clearly demonstrate that abundant nanoparticles coated on the nanosheets with homogeneous dispersion and narrow size dispersion (Fig. 2d). The size of nanoparticles is distributed mostly in a narrow range of 2–5 nm. Therefore, the morphology of the Ag/TiO2 nanostructures can be controlled by adjusting the concentration of NaOH solution. The chemical states of elements in the Ag particles coated TiO2 were analysed by Xray photoelectron spectroscopy (XPS). Fig. 3 shows the survey XPS spectrum of the Ag nanoparticles coated TiO2 nanotube and high-resolution XPS spectrum of Ag 3d. On its survey spectrum (Fig. 3a), it clearly indicated that Ti, O, Na and Ag elements exist in the Ag nanoparticles coated TiO2 nanotube, no trace of any impurity is observed except for a small amount of adventitious carbon from XPS instrument itself. The binding energy values of Ti 2p3/2 and O 1s peaks show that they are in the ranges 458.2–458.8 eV and 530.0–530.2 eV, respectively. These values can be attributed to Ti4+and O2−in TiO2. Fig. 3b is the high-resolution original and guassian fitted XPS curves of Ag 3d region. The original XPS curve can be well fitted by two peaks centered at 368.2 eV and 374.2 eV corresponding to Ag 3d5/2 and Ag 3d3/2, respectively. No peak corresponding to Ag2O
[1] Schulz J, Roucoux A, Patin H. Chem Rev 2002;102:3757–78. [2] Lai YK, Sun L, Chen C, Nie CG, Zuo J, Lin CJ. Appl Surf Sci 2005;252:1101–6. [3] Lai YK, Sun L, Chen YC, Zhuang HF, Lin CJ, Chin JW. J Electrochem Soc 2006;153:123–7. [4] Xu MW, Bao SJ, Zhang XG. Mater Lett 2005;59:2194–8. [5] Lai YK, Lin CJ, Wang H, Huang JY, Zhuang HF, Sun L. Electrochem Commun 2008;10:387–91. [6] Ma RZ, Sasaki T, Bando Y. J Am Chem Soc 2004;126:10382–8. [7] Huang JG, Kunitake T, Onoue S. Chem Commun 2004;8:1008–9. [8] Tada H, Teranishi K, Inubushi YI, Ito S. Langmuir 2000;16:3304–9. [9] Kamat PV, Flumiani M, Dawson A. Colloids Surf A-Physicochem Eng Asp 2002;202:269–79. [10] You XF, Chen F, Zhang JL, Anpo M. Catal Letters 2005;102:247–50. [11] Chan SC, Barteau MA. Langmuir 2005;21:5588–95. [12] Epifani M, Giannini C, Tapfer L, Vasanelli L. J Am Ceram Soc 2000;85:2385–93. [13] Miao L, Ina Y, Tanemura S, Jiang T, Tanemura M, Kaneko K, et al. Surf Sci 2007;601:2792–9. [14] Wang Y, Xu X, Tian ZQ, Zong Y, Cheng HM, Lin CJ. Chem Eur J 2006;12:2542–9. [15] Shen GX, Chen YC, Lin L, Lin CJ, Scantlebury D. Electrochim Acta 2005;50:5083–9. [16] Ma XQ, Feng CX, Jin ZS, Guo XY, Yang JJ, Zhang ZJ. J Nanopart Res 2005;7:681–3. [17] Stathatos E, Lianos P. Langmuir 2000;16:2398–400. [18] Sano T, Negishi N, Uchino K, Tanaka J, Matsuzawa S, Takeuchi K. J Photochem Photobiol A-Chem 2003;160:93–8. [19] Vitos L, Ruban AV, Skriver HL, Kollar J. Surf Sci 1998;411:186–202.