- Email: [email protected]
Silver nano-islands on glass fibers using heat segregation method
Materials Chemistry and Physics 113 (2009) 63–66
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Silver nano-islands on glass fibers using heat segregation method Nafiseh Sharifi a , Nima Taghavinia a,b,∗ a b
Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran 14588, Iran Physics Department, Sharif University of Technology, Tehran 14588, Iran
a r t i c l e
i n f o
Article history: Received 19 March 2008 Received in revised form 2 July 2008 Accepted 3 July 2008 Keywords: Silver Glass fibers Heat treatment Coatings
a b s t r a c t A new method for fabrication of silver nano-islands on glass fibers using a top-down process is introduced. A thin layer of silver chemically coated on the surface of the glass fibers evolves into silver islands by heat treatment. The effect of the concentration of the initial solution and the temperature were investigated. Segregation was more clearly observed for lower solution concentrations and higher temperatures. The temperature of 500 ◦ C was found optimum where separated islands form. At higher temperatures, the coagulation and burial of silver islands occur. Scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS) and diffused reflectance spectroscopy (DRS) were used for characterization. Glass fibers loaded with silver nanoparticles are ideal for anti-bacterial air purifiers. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Glass fibers can be found in automobile engine compartments; furnaces; air conditioning units; acoustical wall; ceiling panels and architectural partitions. Glass fibers are useful, in particular due to their high ratio of surface area to weight [1,2]; and therefore, are suitable supports for catalysts, including silver nano-islands, which are employed as anti-bacterial materials. The anti-bacterial property of silver is improved when the size of silver particles decreases and its effective surface area increases. Silver nanoparticles have been widely studied for anti-bacterial applications, as well as other applications such as biosensors, chemical sensors, catalysis, surface enhanced Raman spectroscopy (SERS) and fluorescence spectroscopy [3–8]. Different methods have been used to grow silver nanoparticles. The usual chemical method, that is a bottom-up approach, is to collect, consolidate, and fashion individual atoms and molecules into a larger structure [9]. This is carried out by a sequence of chemical reactions controlled by catalysts [9], chemical reduction [10–12], photochemical reduction [13–16] and radiolysis [17,18]. The opposite approach, i.e. the top-down approach, starts with a large-scale object or pattern and gradually reduces its dimension or dimensions [9]. Top-down methods have not been frequently used for metal nanoparticles preparation. There are however reports on dispersion of large particles into nanosizes using laser ablation [19].
In this study, we report a top-down method, which results in silver nano-islands on the surface of glass fibers using heat treatment. The method is based on the formation of a thin layer of silver on the surface of the fibers using the chemical reduction of Ag complexes. By heat treatment, the silver layer starts to segregate and silver islands form on the surface of the fibers. The dependence of the process on temperature and solution concentration was investigated. Silver islands loaded on glass fibers are ideal for use in anti-bacterial air purifiers. 2. Experimental A thin layer of silver was chemically coated on the fibers. The adhesion and quality of coating depend on the cleaning of fibers. The fibers were washed in 37% HF acid for about 5 min to etch-clean the surface. A typical synthesis involves the following steps: ammonium hydroxide (Guangdong Guanghua, 25%) was slowly dropped into 10 mL of a 0.5 M AgNO3 (Acros) solution. The solution initially turned turbid and then became transparent. The following reactions seem to occur: 2AgNO3 + 2NH4 OH → Ag2 O(s) ↓ + 2NH4 NO3 + H2 O +
−
+
Ag2 O + 4NH4 + 2OH → 2[Ag(NH3 )2 ] + 3H2 O
0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.07.026
(2)
The solution turned dark brown, after adding some drops of a 1 M KOH (Wako) solution. It was made transparent again by addition of ammonium hydroxide. About 0.2 g of glass fibers were put in the resulting solution. 10 mL of a solution of 0.7 M sucrose (C12 H22 O11 , Merck) was then added. Silver complexes were reduced on the surface of fibers and a thin layer of silver formed [20]: Ag(NH3 )2 + (aq) + RCHO(aq) → Ag(s) + RCOOH(aq)
∗ Corresponding author. Tel.: +98 21 6616 4532; fax: +98 21 6602 2711. E-mail address: [email protected] (N. Taghavinia). URL: http://sharif.ir/∼taghavinia (N. Taghavinia).
(1)
(3)
where R represents C11 H21 O10 . The fibers were then removed from the solution and sonicated in order to detach the remained Ag2 O sediments away and then they were rinsed with water. All steps of the process were performed in dark. Silvery fibers were dried at room temperature and were heat-treated in an oven at different temperatures for 30 min. Similar experiments were carried out with lower solution
64
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
Fig. 1. SEM images of typical silvery fibers before heat-treatment at different magnifications.
Fig. 2. SEM images of fibers heat-treated at (A, a) 300 ◦ C, (B, b) 400 ◦ C, (C, c) 500 ◦ C, (D, d) 600 ◦ C and (E, e) 700 ◦ C.
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
65
Fig. 3. SEM images of fibers heat-treated at 500 ◦ C prepared at different AgNO3 concentrations: (a) [AgNO3 ] = [C]; (b) [AgNO3 ] = [C/5]; (c) [AgNO3 ] = [C/10]; and (d) size distribution of picture (c).
Fig. 4. DRS spectra for samples prepared at different AgNO3 concentrations (a, b): heat-treated at (a) 200 ◦ C and (b) 500 ◦ C. At different heat-treatment temperatures (c, d) and two different concentrations: (c) C/2 and (d) C/20. The graphs were shifted against each other.
66
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
concentrations. The concentrations are denoted as [C/n]; where n is the degree of dilution, compared to the mentioned concentration. The surface morphology and composition were investigated using scanning electron microscopy (SEM) (Philips, XL30) and energy dispersive X-ray spectroscopy (EDS) (CamScan, MV2300). Diffuse reflectance spectroscopy (DRS) was performed using AvaSpec-2048TEC spectrometer. The light source was a combination of a 78 W deuterium lamp and a 5 W halogen lamp, coupled to the spectrometer using optical fibers.
3. Results and discussion Fig. 1 shows SEM images of silvery fibers before heat-treatment, at different magnifications. The average diameter of the fibers is 5 m. White spots observed on the silvery fibers are silver oxide sediments, which have remained on the fibers. All over the surface of fibers is thoroughly coated by silver, as evidenced by EDS measurements. Glass fibers consist of 57% silica, 41% alumina and 2% titania and calcium oxide. Fig. 2 shows SEM images of samples heat-treated at different temperatures. The initial concentration was the highest ([C]). The fine structure of samples is clearly visible in the high-magnification SEM images. At 300 ◦ C, the uniform layer of silver on the glass fibers (Fig. 1) starts to segregate. By increasing the temperature of heat treatment, more segregation of layers takes place. At 500 ◦ C, completely separated silver islands form on the surface of glass fibers. It is observed that at 600 ◦ C, silver islands coagulate together and form larger islands, which consist of smaller islands. Therefore, the separation of islands increases. At this temperature, glass fibers begin to deform and partially soften, and the diffusion of the coagulated silver islands into the glass fibers occurs. Most parts of the coagulated silver islands have been buried into the fibers when the temperature is 700 ◦ C. Fig. 3 illustrates SEM images of silver islands on the surface of fibers at different concentrations while the temperature of heat treatment was adjusted at 500 ◦ C. By decreasing the concentration of the initial solution, the separation of islands is more evident. Fig. 3d shows the size distribution of silver islands of Fig. 3c. The diameters of the islands range between 150 nm and 400 nm. Fig. 4 demonstrates typical DRS spectra of the silvery glass fibers heat-treated at 200 ◦ C and 500 ◦ C, for different concentrations (a, b) and at different temperatures for two fixed concentrations (c, d). The collective oscillation of conduction electrons of silver nanoparticles causes the surface plasmon absorption peak at around 400 nm. At 200 ◦ C and the highest concentrations (C, C/2), a peak at around 360 nm appears, which is related to bulk Ag, while the surface plasmon peak is not observed. Therefore, at low temperatures and high concentrations silver islands are not formed on the glass fibers. For lower concentrations at 200 ◦ C, the surface plasmon peak at around 400 nm suggests the formation of silver islands (Fig. 4a). At 500 ◦ C, the absorption band at around 400–410 nm is observed for all concentrations. This demonstrates the presence of the silver nano-islands on the glass fibers. The peaks are narrower for lower concentrations. This indicates that at lower concentrations more separated islands have formed (Fig. 4b). At concentration of C/2, a peak at around 360 nm is observed for heat treatments at 400 ◦ C and below. This demonstrates that no silver islands have formed at these conditions due to large amount of deposition. At 500 ◦ C and 600 ◦ C silver nano-islands are formed, jus-
tified by the existence of surface plasmon peak at around 400 nm. At 700 ◦ C, the surface plasmon peak weakens, since at this temperature the glass fibers begin to deform and the islands penetrate into the fibers. Finally at 800 ◦ C, the surface plasmon peak completely disappears, which indicated the complete burial of silver islands into the fibers (Fig. 4c). These results confirm the SEM images in Fig. 2. The effect of temperature at a low concentration (C/20) is displayed in Fig. 4d. For low concentrations, silver islands are formed on the glass fibers even before heat treatment. Surface plasmon peak is clearly observed at around 400 nm. In contrast with C/2 sample, silver islands are buried into the fibers at lower temperatures as the surface plasmon peaks disappear at the temperatures 600 ◦ C and higher. 4. Conclusion A procedure consisting of the deposition of glass fibers with a thin layer of silver, followed by heat treatment was used to produce silver nano-islands on the surface of glass fibers. Both concentration of the coating solution and the temperature of heat treatment were found effective in the morphology of the islands formed on the surface. Smaller and more resolved islands have been formed for lower concentrations. At very low concentrations, islands form even with no heat treatment. Increasing the temperature enhances the segregation and helps the formation of nanoparticles. However, at high temperatures the coagulation of islands and also burial into the surface take place. The temperature of 500 ◦ C was found optimum, where at all concentrations the islands form. References [1] K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, Elsevier Scientific, New York, 1973. [2] V.B. Gupta, V.K. Kothari, Manufactured Fibre Technology, Chapman and Hall, London, 1997. [3] M.M. Miranda, B. Pergolese, A. Bigotto, A. Giusti, M. Innocenti, J. Mater. Sci. Eng. C 27 (2007) 1295. [4] A.R. Shahverdi, A. Fakhimi Pharm, H.R. Shahverdi, S. Minaian, Nanomed.: Nanotechnol. Biol. Med. 3 (2007) 168. [5] H. Guo, S. Tao, Sens. Actuators B 123 (2007) 578. [6] L. Balan, J.P. Malval, R. Schneider, D. Burget, J. Mater. Chem. Phys. 104 (2007) 417. [7] J.R. Morones, J.L. Elechiguerra, A. Camacho, K. Holt, J.B. Kouri, Nanotechnology 16 (2005) 2346. [8] K.H. Cho, J.E. Park, T. Osaka, S.G. Park, J. Electrochim. Acta 51 (2005) 956. [9] C.P. Pools, F.J. Owens, Introduction to Nanotechnology, Wiley Interscience Publication, Wiley & Sons, New Jersey, 2003. [10] J.A. Creighton, C.G. Blatchford, M.G. Albrecht, J. Chem. Soc., Faraday Trans. 2 75 (1979) 790. [11] P.C. Lee, D. Meisel, J. Phys. Chem. 86 (1982) 3391. [12] M.V. Roldan, A. Frattini, O. de Sanctis, H. Troiani, N. Pellegri, J. Appl. Surf. Sci. 254 (2007) 281. [13] A. Henglein, J. Chem. Mater. 10 (1998) 444. [14] S.K. Ghosh, S. Kundu, M. Mandal, S. Nathand, T. Pal, J. Nanopart. Res. 5 (2003) 577. [15] T. Sato, H. Onaka, Y. Yonezawa, J. Photochem. Photobiol. A: Chem. 127 (1999) 83. [16] S. Dunn, P.M. Jones, D.E. Gallardo, J. Am. Chem. Soc. 129 (2007) 8724. [17] A. Henglein, M. Giersig, J. Phys. Chem. B 103 (1999) 9533. [18] S.H. Choi, S.H. Lee, Y.M. Hwang, K.P. Lee, H.D. Kang, J. Radiat. Phys. Chem. 67 (2003) 517. [19] T. Tsuji, Y. Okazaki, M. Tsuji, J. Photochem. Photobiol. A: Chem. 194 (2008) 247. [20] Y. Yin, Z.Y. Li, Z. Zhong, B. Gates, Y. Xia, S. Venkateswaran, J. Mater. Chem. 12 (2002) 522.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Silver nano-islands on glass fibers using heat segregation method Nafiseh Sharifi a , Nima Taghavinia a,b,∗ a b
Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran 14588, Iran Physics Department, Sharif University of Technology, Tehran 14588, Iran
a r t i c l e
i n f o
Article history: Received 19 March 2008 Received in revised form 2 July 2008 Accepted 3 July 2008 Keywords: Silver Glass fibers Heat treatment Coatings
a b s t r a c t A new method for fabrication of silver nano-islands on glass fibers using a top-down process is introduced. A thin layer of silver chemically coated on the surface of the glass fibers evolves into silver islands by heat treatment. The effect of the concentration of the initial solution and the temperature were investigated. Segregation was more clearly observed for lower solution concentrations and higher temperatures. The temperature of 500 ◦ C was found optimum where separated islands form. At higher temperatures, the coagulation and burial of silver islands occur. Scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS) and diffused reflectance spectroscopy (DRS) were used for characterization. Glass fibers loaded with silver nanoparticles are ideal for anti-bacterial air purifiers. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Glass fibers can be found in automobile engine compartments; furnaces; air conditioning units; acoustical wall; ceiling panels and architectural partitions. Glass fibers are useful, in particular due to their high ratio of surface area to weight [1,2]; and therefore, are suitable supports for catalysts, including silver nano-islands, which are employed as anti-bacterial materials. The anti-bacterial property of silver is improved when the size of silver particles decreases and its effective surface area increases. Silver nanoparticles have been widely studied for anti-bacterial applications, as well as other applications such as biosensors, chemical sensors, catalysis, surface enhanced Raman spectroscopy (SERS) and fluorescence spectroscopy [3–8]. Different methods have been used to grow silver nanoparticles. The usual chemical method, that is a bottom-up approach, is to collect, consolidate, and fashion individual atoms and molecules into a larger structure [9]. This is carried out by a sequence of chemical reactions controlled by catalysts [9], chemical reduction [10–12], photochemical reduction [13–16] and radiolysis [17,18]. The opposite approach, i.e. the top-down approach, starts with a large-scale object or pattern and gradually reduces its dimension or dimensions [9]. Top-down methods have not been frequently used for metal nanoparticles preparation. There are however reports on dispersion of large particles into nanosizes using laser ablation [19].
In this study, we report a top-down method, which results in silver nano-islands on the surface of glass fibers using heat treatment. The method is based on the formation of a thin layer of silver on the surface of the fibers using the chemical reduction of Ag complexes. By heat treatment, the silver layer starts to segregate and silver islands form on the surface of the fibers. The dependence of the process on temperature and solution concentration was investigated. Silver islands loaded on glass fibers are ideal for use in anti-bacterial air purifiers. 2. Experimental A thin layer of silver was chemically coated on the fibers. The adhesion and quality of coating depend on the cleaning of fibers. The fibers were washed in 37% HF acid for about 5 min to etch-clean the surface. A typical synthesis involves the following steps: ammonium hydroxide (Guangdong Guanghua, 25%) was slowly dropped into 10 mL of a 0.5 M AgNO3 (Acros) solution. The solution initially turned turbid and then became transparent. The following reactions seem to occur: 2AgNO3 + 2NH4 OH → Ag2 O(s) ↓ + 2NH4 NO3 + H2 O +
−
+
Ag2 O + 4NH4 + 2OH → 2[Ag(NH3 )2 ] + 3H2 O
0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.07.026
(2)
The solution turned dark brown, after adding some drops of a 1 M KOH (Wako) solution. It was made transparent again by addition of ammonium hydroxide. About 0.2 g of glass fibers were put in the resulting solution. 10 mL of a solution of 0.7 M sucrose (C12 H22 O11 , Merck) was then added. Silver complexes were reduced on the surface of fibers and a thin layer of silver formed [20]: Ag(NH3 )2 + (aq) + RCHO(aq) → Ag(s) + RCOOH(aq)
∗ Corresponding author. Tel.: +98 21 6616 4532; fax: +98 21 6602 2711. E-mail address: [email protected] (N. Taghavinia). URL: http://sharif.ir/∼taghavinia (N. Taghavinia).
(1)
(3)
where R represents C11 H21 O10 . The fibers were then removed from the solution and sonicated in order to detach the remained Ag2 O sediments away and then they were rinsed with water. All steps of the process were performed in dark. Silvery fibers were dried at room temperature and were heat-treated in an oven at different temperatures for 30 min. Similar experiments were carried out with lower solution
64
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
Fig. 1. SEM images of typical silvery fibers before heat-treatment at different magnifications.
Fig. 2. SEM images of fibers heat-treated at (A, a) 300 ◦ C, (B, b) 400 ◦ C, (C, c) 500 ◦ C, (D, d) 600 ◦ C and (E, e) 700 ◦ C.
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
65
Fig. 3. SEM images of fibers heat-treated at 500 ◦ C prepared at different AgNO3 concentrations: (a) [AgNO3 ] = [C]; (b) [AgNO3 ] = [C/5]; (c) [AgNO3 ] = [C/10]; and (d) size distribution of picture (c).
Fig. 4. DRS spectra for samples prepared at different AgNO3 concentrations (a, b): heat-treated at (a) 200 ◦ C and (b) 500 ◦ C. At different heat-treatment temperatures (c, d) and two different concentrations: (c) C/2 and (d) C/20. The graphs were shifted against each other.
66
N. Sharifi, N. Taghavinia / Materials Chemistry and Physics 113 (2009) 63–66
concentrations. The concentrations are denoted as [C/n]; where n is the degree of dilution, compared to the mentioned concentration. The surface morphology and composition were investigated using scanning electron microscopy (SEM) (Philips, XL30) and energy dispersive X-ray spectroscopy (EDS) (CamScan, MV2300). Diffuse reflectance spectroscopy (DRS) was performed using AvaSpec-2048TEC spectrometer. The light source was a combination of a 78 W deuterium lamp and a 5 W halogen lamp, coupled to the spectrometer using optical fibers.
3. Results and discussion Fig. 1 shows SEM images of silvery fibers before heat-treatment, at different magnifications. The average diameter of the fibers is 5 m. White spots observed on the silvery fibers are silver oxide sediments, which have remained on the fibers. All over the surface of fibers is thoroughly coated by silver, as evidenced by EDS measurements. Glass fibers consist of 57% silica, 41% alumina and 2% titania and calcium oxide. Fig. 2 shows SEM images of samples heat-treated at different temperatures. The initial concentration was the highest ([C]). The fine structure of samples is clearly visible in the high-magnification SEM images. At 300 ◦ C, the uniform layer of silver on the glass fibers (Fig. 1) starts to segregate. By increasing the temperature of heat treatment, more segregation of layers takes place. At 500 ◦ C, completely separated silver islands form on the surface of glass fibers. It is observed that at 600 ◦ C, silver islands coagulate together and form larger islands, which consist of smaller islands. Therefore, the separation of islands increases. At this temperature, glass fibers begin to deform and partially soften, and the diffusion of the coagulated silver islands into the glass fibers occurs. Most parts of the coagulated silver islands have been buried into the fibers when the temperature is 700 ◦ C. Fig. 3 illustrates SEM images of silver islands on the surface of fibers at different concentrations while the temperature of heat treatment was adjusted at 500 ◦ C. By decreasing the concentration of the initial solution, the separation of islands is more evident. Fig. 3d shows the size distribution of silver islands of Fig. 3c. The diameters of the islands range between 150 nm and 400 nm. Fig. 4 demonstrates typical DRS spectra of the silvery glass fibers heat-treated at 200 ◦ C and 500 ◦ C, for different concentrations (a, b) and at different temperatures for two fixed concentrations (c, d). The collective oscillation of conduction electrons of silver nanoparticles causes the surface plasmon absorption peak at around 400 nm. At 200 ◦ C and the highest concentrations (C, C/2), a peak at around 360 nm appears, which is related to bulk Ag, while the surface plasmon peak is not observed. Therefore, at low temperatures and high concentrations silver islands are not formed on the glass fibers. For lower concentrations at 200 ◦ C, the surface plasmon peak at around 400 nm suggests the formation of silver islands (Fig. 4a). At 500 ◦ C, the absorption band at around 400–410 nm is observed for all concentrations. This demonstrates the presence of the silver nano-islands on the glass fibers. The peaks are narrower for lower concentrations. This indicates that at lower concentrations more separated islands have formed (Fig. 4b). At concentration of C/2, a peak at around 360 nm is observed for heat treatments at 400 ◦ C and below. This demonstrates that no silver islands have formed at these conditions due to large amount of deposition. At 500 ◦ C and 600 ◦ C silver nano-islands are formed, jus-
tified by the existence of surface plasmon peak at around 400 nm. At 700 ◦ C, the surface plasmon peak weakens, since at this temperature the glass fibers begin to deform and the islands penetrate into the fibers. Finally at 800 ◦ C, the surface plasmon peak completely disappears, which indicated the complete burial of silver islands into the fibers (Fig. 4c). These results confirm the SEM images in Fig. 2. The effect of temperature at a low concentration (C/20) is displayed in Fig. 4d. For low concentrations, silver islands are formed on the glass fibers even before heat treatment. Surface plasmon peak is clearly observed at around 400 nm. In contrast with C/2 sample, silver islands are buried into the fibers at lower temperatures as the surface plasmon peaks disappear at the temperatures 600 ◦ C and higher. 4. Conclusion A procedure consisting of the deposition of glass fibers with a thin layer of silver, followed by heat treatment was used to produce silver nano-islands on the surface of glass fibers. Both concentration of the coating solution and the temperature of heat treatment were found effective in the morphology of the islands formed on the surface. Smaller and more resolved islands have been formed for lower concentrations. At very low concentrations, islands form even with no heat treatment. Increasing the temperature enhances the segregation and helps the formation of nanoparticles. However, at high temperatures the coagulation of islands and also burial into the surface take place. The temperature of 500 ◦ C was found optimum, where at all concentrations the islands form. References [1] K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, Elsevier Scientific, New York, 1973. [2] V.B. Gupta, V.K. Kothari, Manufactured Fibre Technology, Chapman and Hall, London, 1997. [3] M.M. Miranda, B. Pergolese, A. Bigotto, A. Giusti, M. Innocenti, J. Mater. Sci. Eng. C 27 (2007) 1295. [4] A.R. Shahverdi, A. Fakhimi Pharm, H.R. Shahverdi, S. Minaian, Nanomed.: Nanotechnol. Biol. Med. 3 (2007) 168. [5] H. Guo, S. Tao, Sens. Actuators B 123 (2007) 578. [6] L. Balan, J.P. Malval, R. Schneider, D. Burget, J. Mater. Chem. Phys. 104 (2007) 417. [7] J.R. Morones, J.L. Elechiguerra, A. Camacho, K. Holt, J.B. Kouri, Nanotechnology 16 (2005) 2346. [8] K.H. Cho, J.E. Park, T. Osaka, S.G. Park, J. Electrochim. Acta 51 (2005) 956. [9] C.P. Pools, F.J. Owens, Introduction to Nanotechnology, Wiley Interscience Publication, Wiley & Sons, New Jersey, 2003. [10] J.A. Creighton, C.G. Blatchford, M.G. Albrecht, J. Chem. Soc., Faraday Trans. 2 75 (1979) 790. [11] P.C. Lee, D. Meisel, J. Phys. Chem. 86 (1982) 3391. [12] M.V. Roldan, A. Frattini, O. de Sanctis, H. Troiani, N. Pellegri, J. Appl. Surf. Sci. 254 (2007) 281. [13] A. Henglein, J. Chem. Mater. 10 (1998) 444. [14] S.K. Ghosh, S. Kundu, M. Mandal, S. Nathand, T. Pal, J. Nanopart. Res. 5 (2003) 577. [15] T. Sato, H. Onaka, Y. Yonezawa, J. Photochem. Photobiol. A: Chem. 127 (1999) 83. [16] S. Dunn, P.M. Jones, D.E. Gallardo, J. Am. Chem. Soc. 129 (2007) 8724. [17] A. Henglein, M. Giersig, J. Phys. Chem. B 103 (1999) 9533. [18] S.H. Choi, S.H. Lee, Y.M. Hwang, K.P. Lee, H.D. Kang, J. Radiat. Phys. Chem. 67 (2003) 517. [19] T. Tsuji, Y. Okazaki, M. Tsuji, J. Photochem. Photobiol. A: Chem. 194 (2008) 247. [20] Y. Yin, Z.Y. Li, Z. Zhong, B. Gates, Y. Xia, S. Venkateswaran, J. Mater. Chem. 12 (2002) 522.