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Synthesis and photocatalysis of mesoporous anatase TiO2 powders incorporated Ag nanoparticles
ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 69 (2008) 633–636 www.elsevier.com/locate/jpcs
Synthesis and photocatalysis of mesoporous anatase TiO2 powders incorporated Ag nanoparticles Hong-Wen Wang, Hsiu-Chu Lin, Chien-Hung Kuo, Yue-Ling Cheng, Yun-Chieh Yeh Department of Chemistry, Center for Nanotechnology, R&D Center for Membrane Technology, Chung-Yuan Christian University, ChungLi 320, Taiwan, ROC
Abstract Deposition of Ag nanoparticles on mesoporous anatase TiO2 powders as well as on commercial TiO2 powders via reduction of Ag+ solution was performed and their photocatalytic activities were investigated. Photocatalytic activities of Ag/TiO2 were evaluated by UV–vis test on degrading of methylene blue aqueous solution. For the synthesized mesoporous TiO2 powders, the catalytic activity was found to be increased as the amount of Ag nanoparticles increased. However, for the commercial TiO2 powders, the catalytic activity decreased as the amount of Ag increased. X-ray was employed to characterize the crystalline phase of synthesized Ag/TiO2 powders. Particle sizes and morphologies of Ag/TiO2 powders were investigated by transmission electron microscopy (TEM). Distribution of Ag in TiO2 powders was revealed by element mapping under element dispersive X-ray analysis (EDAX). It is inferred that the Ag nanoparticles reduce the recombination of electron–hole pairs and therefore enhance the photocatalytic activity of the synthesized mesoporous TiO2 powders. However, the Ag nanoparticles retard the photocatalytic activity of commercial TiO2 powders by shielding their effective surface area (only 7.0 m2/g) for accessing light. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Nanostructures; B. Chemical synthesis; D. Microstructure; D. Optical properties
1. Introduction The photocatalytic activity of semiconductor is due to the photo-induced electrons and the corresponding positive holes in the materials [1,2]. These energetically excited species are mobile and capable of initiating many photocatalytic reactions. They are unstable, and the recombination of photo-generated electrons and holes can occur very rapidly, dissipating the input energy as heat. In fact, the photocatalytic efficiency depends on the competition between the surface charge carrier transfer rate and the electron–hole recombination rate [2]. If the recombination rate is so fast (o0.1 ns), then there is not enough time for any other reactions to occur and result in no photocatalytic activity. TiO2 is considered to be the most potential material for the photocatalytic purposes due to its exceptional optical and electronic properties. The photoCorresponding author.
E-mail address: [email protected] (H.-W. Wang). 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.07.052
generated electrons and holes have relatively long life (around 250 ns) in TiO2 [3]. They also exhibit chemical stability, nontoxicity, and low cost [2,3]. Many metals, such as Pd, Pt, Rh, Ru, have been investigated [4–11] to improve the photocatalytic efficiency of TiO2. The deposition of metals on the surface of TiO2 would produce traps to capture the photo-induced electrons or holes, leading to the reduction of electron–hole recombination and thus improving the photocatalytic efficiency [12]. The sizes, morphologies, structures, and properties of the resultant metal and TiO2 particles greatly depend on the preparation conditions [13]. In the present work, formation of Ag nanoparticles on TiO2 powders was carried out by a simple chemical reduction method. The photocatalytic activities of TiO2 and Ag-incorporated TiO2 were evaluated by degrading the aqueous solution of methylene blue. Modification of photocatalytic effect due to the incorporation of Ag nanoparticles upon commercial TiO2 and mesoporous TiO2 was reported.
ARTICLE IN PRESS 634
H.-W. Wang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 633–636
2. Experimental The chemicals used were sodium citrate (499%), sodium borohydride (498%), and silver perchloratare (AgClO4, 499.9%), all from Aldrich. Commercial TiO2 powders with a particle size around 200 nm was purchased for comparison (BET surface area E7 m2/g, Showa, Japan). The mesoporous TiO2 powders were synthesized using a micelle-templated sol–gel process [14], where hydration and condensation of titanium tetraisopropoxide (TTIP) took place in the presence of organic surfactant, tetradecylamine, which was used as a self-assembly micelle. Anatase mesoporous TiO2 powders were formed after removal of organics by firing at 400 1C for 3 h. For the reduction of Ag+ to Ag and depositing them on the TiO2 powders, sodium citrate, sodium borohydride (NaBH4, reducing agent), and the solution of titania were first mixed by stirring for 15 min. The solution of titania was prepared by adding 0.2 g commercial TiO2 or synthesized mesoporous TiO2 powders into 40 ml de-ionized water, respectively. A series amount of silver perchlorate (AgClO4) were dissolved in 10 ml de-ionized water, and dropwise into above 40 ml titania solution which was ultrasonically dispersed and ice-bathed for 1 h. Finally, the Ag/TiO2 powders were separated from the solution by centrifugation. The powdered catalysts were freeze-dried for 8 h before the characterization of photocatalytic effect. Photocatalytic reactions were carried out in a box using 120 w UV–vis (main wavelength around 360 nm) as a light source. Fifty milliliters of methylene blue solution with a concentration of 10 5 M mixed with 0.2 g TiO2 powder was used for the evaluation of photocatalytic effect. During the 2 h irradiation, the color of the methylene blue was gradually fading. Then, the powdered catalyst was immediately separated by centrifugation and the supernatant was collected in a quartz cuvette. The optical absorbance of the supernatant in a quartz cuvette was analyzed using a UV–vis spectrometer (Shimadzu UV-1700). The size and morphology of Ag/TiO2 powders were observed by transmission electron microscopy (TEM; JEM 2010 at 200 kV) and scanning electron microscopy (SEM; Hitachi S300N). Element Ag mapping and semi-quantitative analysis using element dispersive X-ray analysis (EDAX) is carried out in order to evaluate the distribution and quantity of Ag nanoparticles on TiO2 powder. The BET surface area was determined by multipoint BET method (Micrometric ASAP 2010) using the adsorption data in the relative pressure (P/P0) range of 0.05–0.3.
Fig. 1. XRD patterns of Ag/TiO2: (a) Ag nanoparticles by reduction of Ag+ solution, (b) synthesized mesoporous TiO2, (c) synthesized 1.35% Ag/mesoporous TiO2, (d) commercial TiO2, (e) synthesized 1.35% Ag/commercial TiO2.
3. Results and discussion
Fig. 2. (a) Synthesized mesoporous TiO2, surface area: 71.2 m2/g, type IV isotherm; (b) synthesized 1.35% Ag/mesoporous TiO2, surface area: 9.1 m2/g, type I isotherm; (c) commercial TiO2, surface area: 7.0 m2/g, type I isotherm.
Fig. 1(a)–(e) show the XRD diffraction peaks for studied samples. All peaks in Fig. 1(b)–(e) are the peaks of anatase phase, where commercial TiO2 (comm.TiO2) has much sharper peaks than those of synthesized mesoporous TiO2 (meso.TiO2). The crystal sizes of synthesized meso.TiO2 were 27 nm using Scherrer’s equation. The Ag phase is
evident for specimen without TiO2, as shown in Fig. 1(a). This proves that the present method is effective for the formation of Ag nanoparticles. However, Ag phase is not found in the XRD patterns of Ag/TiO2 powders due to low-weight percentage (Ag o1.35 wt%). Fig. 2 shows the
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Fig. 3. (a) TEM images of synthesized 1.35% Ag/mesoporous TiO2, location of Ag nanoparticles is pointed by arrows; (b) SEM image of 1.35% Ag/mesoporous TiO2 powders; (c) Ag element mapping for SEM image in (b).
BET isotherms for the studied samples. It is clear that the synthesized meso.TiO2 has the highest surface area (71.2 m2/g). After incorporating of Ag nanoparticles, the pores of meso.TiO2 powders are filled (type IV isotherm changes to type I) and low surface areas (9.1 m2/g) result. The comm.TiO2 has the lowest surface area, being around 7.0 m2/g. Fig. 3(a) shows the TEM micrograph for the synthesized Ag/meso.TiO2 powder, where 100–200 nm mesoporous spheres consisted of 20–30 nm TiO2 nanocrystals are identified. Homogeneous incorporated Ag nanoparticles in the meso.TiO2 frameworks were observed as the dark dots, as indicated by arrows in Fig. 3(a). SEM and EDAX of Ag element mapping is carried out in order to evaluate the distribution of Ag and its quantity, as shown in Fig. 3(b) and (c), respectively. Semi-quantitative analysis shows that a weight percentage of 1.23 wt% Ag is present for this 1.35% Ag/TiO2 specimen, indicating consistency of initial composition and completeness of reduction of Ag+. Fig. 4(A) and (B) shows the photocatalytic effect with increasing Ag content for the synthesized Ag/meso.TiO2 and Ag/comm.TiO2, respectively. Fig. 4(A) shows apparently that the presence of Ag nanoparticles enhances the photocatalytic activity of synthesized meso.TiO2. However, Fig. 4(B) demonstrates a reduced photocatalytic activity of comm.TiO2 as the Ag nanoparticles increases. Optimal Ag concentration for synthesized meso.TiO2 was found to be
at 1.35 wt%. The poor photocatalytic effect of pristine meso.TiO2 is attributed to their relatively poor crystallinity of anatase. The crystalline defects on meso.TiO2 would act as the recombination centers for electrons and holes [15]. Fig. 5 shows the photo-degradation effect for the two Ag/TiO2 photocatalysts calculated from Fig. 4(A) and (B). Fig. 5 shows that the pristine comm.TiO2 has the highest photocatalytic degradation effect. The high photocatalytic activity of comm.TiO2 is ascribed to the highly crystallized anatase phase which has little defects. However, after the deposition of silver nanoparticles, the catalytic activity reduced. This reduction was thought to be due to that the Ag nanoparticles will cover and occupy the surface area of comm.TiO2, which is relatively small (only 7 m2/g), and therefore reduce the photocatalytic activity by shielding the effective UV light for photogenerating electrons and holes. Similar behaviors observed for sol–gel Ag/TiO2 photocatalysts were also reported by Xin et al. [12], where increasing Ag species initially increased the enhancement of photocatalytic effect and then gradually reduced. 4. Conclusion Photocatalytic effects of commercial TiO2 and synthesized mesoporous TiO2 were investigated after deposition of silver nanoparticles. The silver nanoparticles inserted
ARTICLE IN PRESS 636
H.-W. Wang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 633–636
Fig. 4. The photocatalytic degradation of aqueous methylene blue solution by TiO2 or Ag/TiO2 catalysts. (A) Synthesized mesoporous TiO2 and (B) commercial TiO2. (a) Methylene blue solution without TiO2, (b) pristine TiO2, (c) 0.27% Ag/TiO2, (d) 0.68% Ag/TiO2, (e) 1.35% Ag/TiO2, (f) 2.7% Ag/TiO2.
coverage and occupation of the surface areas of commercial TiO2 decreases its photocatalytic activity. Acknowledgments The financial support to this research by the NSC 932113-M-033-006 and the Center-of-Excellence Program on Membrane Technology, the Ministry of Education are gratefully appreciated. References
Fig. 5. Photocatalytic degradation effect for commercial TiO2 and synthesized mesoporous TiO2 after loading of Ag nanoparticles, data calculated from Fig. 4(A) and (B).
into the pores of mesoporous TiO2 powders and reduced its surface area, however, enhanced its photocatalytic effect by prolonging the lifetime of photogenerated electron–hole pairs. The commercial TiO2 has a low surface area but exhibits well crystalline anatase phase, which is able to degrade the methylene blue reasonably. However, the
[1] G.B. Saupe, T.Y. Zhao, J. Bang, N.R. Yesu, G.A. Carballo, R. Ordonez, T. Bubphamala, Microchem. J. 81 (2005) 156. [2] M.I. Litter, Appl. Catal. B: Environ. 23 (1999) 89. [3] M. Zhou, J. Yu, B. Cheng, H. Yu, Mater. Chem. Phys. 93 (2005) 159. [4] M. Bowker, D. James, P. Stone, R. Bennett, N. Perkins, L. Millard, J. Greaves, A. Dickinson, J. Catal. 217 (2003) 427. [5] T. Sano, S. Kutsuna, N. Negishi, K. Takeuchi, J. Mol. Catal. A 189 (2002) 263. [6] H. Kominami, F. Akitoshi, M. Shinya, I. Hiroyuki, K. Yoshiya, Busho, Catal. Lett. 76 (2001) 31. [7] V. Vamatheva, R. Amal, D. Beydoun, G. Low, S. McEvoy, J. Photochem. Photobiol. A148 (2002) 233. [8] R. Jin, W. Gao., J. Chen, H. Zeng, F. Zhang, Z. Liu, N. Guan, J. Photochem. Photobiol. A162 (2004) 585. [9] L.L. Perissinotti, M.A. Brusa, M.A. Grela, Langmuir 17 (2001) 8422. [10] M. Penpolcharoen, R. Amal, M. Brungs, J. Nanopart. Res. 3 (2001) 289. [11] Y.X. Li, G. Lu, S. Li, J. Photochem. Photobiol. A152 (2002) 219. [12] B. Xin, L. Jing, Z. Ren, B. Wang, H. Fu, J. Phys. Chem. B 109 (2005) 2805. [13] Z. Zhang, X. Song, R. Zhang, M. Zhang, F. Liu, Eur. J. Inorg. Chem. (2005) 1643. [14] Y. Miyake, T. Kondo, J. Chem. Eng. Jpn. 34 (2001) 319. [15] Q. Zhang, L. Gao, J.K. Guo, Appl. Catal. B: Environ. 26 (2000) 207.
Journal of Physics and Chemistry of Solids 69 (2008) 633–636 www.elsevier.com/locate/jpcs
Synthesis and photocatalysis of mesoporous anatase TiO2 powders incorporated Ag nanoparticles Hong-Wen Wang, Hsiu-Chu Lin, Chien-Hung Kuo, Yue-Ling Cheng, Yun-Chieh Yeh Department of Chemistry, Center for Nanotechnology, R&D Center for Membrane Technology, Chung-Yuan Christian University, ChungLi 320, Taiwan, ROC
Abstract Deposition of Ag nanoparticles on mesoporous anatase TiO2 powders as well as on commercial TiO2 powders via reduction of Ag+ solution was performed and their photocatalytic activities were investigated. Photocatalytic activities of Ag/TiO2 were evaluated by UV–vis test on degrading of methylene blue aqueous solution. For the synthesized mesoporous TiO2 powders, the catalytic activity was found to be increased as the amount of Ag nanoparticles increased. However, for the commercial TiO2 powders, the catalytic activity decreased as the amount of Ag increased. X-ray was employed to characterize the crystalline phase of synthesized Ag/TiO2 powders. Particle sizes and morphologies of Ag/TiO2 powders were investigated by transmission electron microscopy (TEM). Distribution of Ag in TiO2 powders was revealed by element mapping under element dispersive X-ray analysis (EDAX). It is inferred that the Ag nanoparticles reduce the recombination of electron–hole pairs and therefore enhance the photocatalytic activity of the synthesized mesoporous TiO2 powders. However, the Ag nanoparticles retard the photocatalytic activity of commercial TiO2 powders by shielding their effective surface area (only 7.0 m2/g) for accessing light. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Nanostructures; B. Chemical synthesis; D. Microstructure; D. Optical properties
1. Introduction The photocatalytic activity of semiconductor is due to the photo-induced electrons and the corresponding positive holes in the materials [1,2]. These energetically excited species are mobile and capable of initiating many photocatalytic reactions. They are unstable, and the recombination of photo-generated electrons and holes can occur very rapidly, dissipating the input energy as heat. In fact, the photocatalytic efficiency depends on the competition between the surface charge carrier transfer rate and the electron–hole recombination rate [2]. If the recombination rate is so fast (o0.1 ns), then there is not enough time for any other reactions to occur and result in no photocatalytic activity. TiO2 is considered to be the most potential material for the photocatalytic purposes due to its exceptional optical and electronic properties. The photoCorresponding author.
E-mail address: [email protected] (H.-W. Wang). 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.07.052
generated electrons and holes have relatively long life (around 250 ns) in TiO2 [3]. They also exhibit chemical stability, nontoxicity, and low cost [2,3]. Many metals, such as Pd, Pt, Rh, Ru, have been investigated [4–11] to improve the photocatalytic efficiency of TiO2. The deposition of metals on the surface of TiO2 would produce traps to capture the photo-induced electrons or holes, leading to the reduction of electron–hole recombination and thus improving the photocatalytic efficiency [12]. The sizes, morphologies, structures, and properties of the resultant metal and TiO2 particles greatly depend on the preparation conditions [13]. In the present work, formation of Ag nanoparticles on TiO2 powders was carried out by a simple chemical reduction method. The photocatalytic activities of TiO2 and Ag-incorporated TiO2 were evaluated by degrading the aqueous solution of methylene blue. Modification of photocatalytic effect due to the incorporation of Ag nanoparticles upon commercial TiO2 and mesoporous TiO2 was reported.
ARTICLE IN PRESS 634
H.-W. Wang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 633–636
2. Experimental The chemicals used were sodium citrate (499%), sodium borohydride (498%), and silver perchloratare (AgClO4, 499.9%), all from Aldrich. Commercial TiO2 powders with a particle size around 200 nm was purchased for comparison (BET surface area E7 m2/g, Showa, Japan). The mesoporous TiO2 powders were synthesized using a micelle-templated sol–gel process [14], where hydration and condensation of titanium tetraisopropoxide (TTIP) took place in the presence of organic surfactant, tetradecylamine, which was used as a self-assembly micelle. Anatase mesoporous TiO2 powders were formed after removal of organics by firing at 400 1C for 3 h. For the reduction of Ag+ to Ag and depositing them on the TiO2 powders, sodium citrate, sodium borohydride (NaBH4, reducing agent), and the solution of titania were first mixed by stirring for 15 min. The solution of titania was prepared by adding 0.2 g commercial TiO2 or synthesized mesoporous TiO2 powders into 40 ml de-ionized water, respectively. A series amount of silver perchlorate (AgClO4) were dissolved in 10 ml de-ionized water, and dropwise into above 40 ml titania solution which was ultrasonically dispersed and ice-bathed for 1 h. Finally, the Ag/TiO2 powders were separated from the solution by centrifugation. The powdered catalysts were freeze-dried for 8 h before the characterization of photocatalytic effect. Photocatalytic reactions were carried out in a box using 120 w UV–vis (main wavelength around 360 nm) as a light source. Fifty milliliters of methylene blue solution with a concentration of 10 5 M mixed with 0.2 g TiO2 powder was used for the evaluation of photocatalytic effect. During the 2 h irradiation, the color of the methylene blue was gradually fading. Then, the powdered catalyst was immediately separated by centrifugation and the supernatant was collected in a quartz cuvette. The optical absorbance of the supernatant in a quartz cuvette was analyzed using a UV–vis spectrometer (Shimadzu UV-1700). The size and morphology of Ag/TiO2 powders were observed by transmission electron microscopy (TEM; JEM 2010 at 200 kV) and scanning electron microscopy (SEM; Hitachi S300N). Element Ag mapping and semi-quantitative analysis using element dispersive X-ray analysis (EDAX) is carried out in order to evaluate the distribution and quantity of Ag nanoparticles on TiO2 powder. The BET surface area was determined by multipoint BET method (Micrometric ASAP 2010) using the adsorption data in the relative pressure (P/P0) range of 0.05–0.3.
Fig. 1. XRD patterns of Ag/TiO2: (a) Ag nanoparticles by reduction of Ag+ solution, (b) synthesized mesoporous TiO2, (c) synthesized 1.35% Ag/mesoporous TiO2, (d) commercial TiO2, (e) synthesized 1.35% Ag/commercial TiO2.
3. Results and discussion
Fig. 2. (a) Synthesized mesoporous TiO2, surface area: 71.2 m2/g, type IV isotherm; (b) synthesized 1.35% Ag/mesoporous TiO2, surface area: 9.1 m2/g, type I isotherm; (c) commercial TiO2, surface area: 7.0 m2/g, type I isotherm.
Fig. 1(a)–(e) show the XRD diffraction peaks for studied samples. All peaks in Fig. 1(b)–(e) are the peaks of anatase phase, where commercial TiO2 (comm.TiO2) has much sharper peaks than those of synthesized mesoporous TiO2 (meso.TiO2). The crystal sizes of synthesized meso.TiO2 were 27 nm using Scherrer’s equation. The Ag phase is
evident for specimen without TiO2, as shown in Fig. 1(a). This proves that the present method is effective for the formation of Ag nanoparticles. However, Ag phase is not found in the XRD patterns of Ag/TiO2 powders due to low-weight percentage (Ag o1.35 wt%). Fig. 2 shows the
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Fig. 3. (a) TEM images of synthesized 1.35% Ag/mesoporous TiO2, location of Ag nanoparticles is pointed by arrows; (b) SEM image of 1.35% Ag/mesoporous TiO2 powders; (c) Ag element mapping for SEM image in (b).
BET isotherms for the studied samples. It is clear that the synthesized meso.TiO2 has the highest surface area (71.2 m2/g). After incorporating of Ag nanoparticles, the pores of meso.TiO2 powders are filled (type IV isotherm changes to type I) and low surface areas (9.1 m2/g) result. The comm.TiO2 has the lowest surface area, being around 7.0 m2/g. Fig. 3(a) shows the TEM micrograph for the synthesized Ag/meso.TiO2 powder, where 100–200 nm mesoporous spheres consisted of 20–30 nm TiO2 nanocrystals are identified. Homogeneous incorporated Ag nanoparticles in the meso.TiO2 frameworks were observed as the dark dots, as indicated by arrows in Fig. 3(a). SEM and EDAX of Ag element mapping is carried out in order to evaluate the distribution of Ag and its quantity, as shown in Fig. 3(b) and (c), respectively. Semi-quantitative analysis shows that a weight percentage of 1.23 wt% Ag is present for this 1.35% Ag/TiO2 specimen, indicating consistency of initial composition and completeness of reduction of Ag+. Fig. 4(A) and (B) shows the photocatalytic effect with increasing Ag content for the synthesized Ag/meso.TiO2 and Ag/comm.TiO2, respectively. Fig. 4(A) shows apparently that the presence of Ag nanoparticles enhances the photocatalytic activity of synthesized meso.TiO2. However, Fig. 4(B) demonstrates a reduced photocatalytic activity of comm.TiO2 as the Ag nanoparticles increases. Optimal Ag concentration for synthesized meso.TiO2 was found to be
at 1.35 wt%. The poor photocatalytic effect of pristine meso.TiO2 is attributed to their relatively poor crystallinity of anatase. The crystalline defects on meso.TiO2 would act as the recombination centers for electrons and holes [15]. Fig. 5 shows the photo-degradation effect for the two Ag/TiO2 photocatalysts calculated from Fig. 4(A) and (B). Fig. 5 shows that the pristine comm.TiO2 has the highest photocatalytic degradation effect. The high photocatalytic activity of comm.TiO2 is ascribed to the highly crystallized anatase phase which has little defects. However, after the deposition of silver nanoparticles, the catalytic activity reduced. This reduction was thought to be due to that the Ag nanoparticles will cover and occupy the surface area of comm.TiO2, which is relatively small (only 7 m2/g), and therefore reduce the photocatalytic activity by shielding the effective UV light for photogenerating electrons and holes. Similar behaviors observed for sol–gel Ag/TiO2 photocatalysts were also reported by Xin et al. [12], where increasing Ag species initially increased the enhancement of photocatalytic effect and then gradually reduced. 4. Conclusion Photocatalytic effects of commercial TiO2 and synthesized mesoporous TiO2 were investigated after deposition of silver nanoparticles. The silver nanoparticles inserted
ARTICLE IN PRESS 636
H.-W. Wang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 633–636
Fig. 4. The photocatalytic degradation of aqueous methylene blue solution by TiO2 or Ag/TiO2 catalysts. (A) Synthesized mesoporous TiO2 and (B) commercial TiO2. (a) Methylene blue solution without TiO2, (b) pristine TiO2, (c) 0.27% Ag/TiO2, (d) 0.68% Ag/TiO2, (e) 1.35% Ag/TiO2, (f) 2.7% Ag/TiO2.
coverage and occupation of the surface areas of commercial TiO2 decreases its photocatalytic activity. Acknowledgments The financial support to this research by the NSC 932113-M-033-006 and the Center-of-Excellence Program on Membrane Technology, the Ministry of Education are gratefully appreciated. References
Fig. 5. Photocatalytic degradation effect for commercial TiO2 and synthesized mesoporous TiO2 after loading of Ag nanoparticles, data calculated from Fig. 4(A) and (B).
into the pores of mesoporous TiO2 powders and reduced its surface area, however, enhanced its photocatalytic effect by prolonging the lifetime of photogenerated electron–hole pairs. The commercial TiO2 has a low surface area but exhibits well crystalline anatase phase, which is able to degrade the methylene blue reasonably. However, the
[1] G.B. Saupe, T.Y. Zhao, J. Bang, N.R. Yesu, G.A. Carballo, R. Ordonez, T. Bubphamala, Microchem. J. 81 (2005) 156. [2] M.I. Litter, Appl. Catal. B: Environ. 23 (1999) 89. [3] M. Zhou, J. Yu, B. Cheng, H. Yu, Mater. Chem. Phys. 93 (2005) 159. [4] M. Bowker, D. James, P. Stone, R. Bennett, N. Perkins, L. Millard, J. Greaves, A. Dickinson, J. Catal. 217 (2003) 427. [5] T. Sano, S. Kutsuna, N. Negishi, K. Takeuchi, J. Mol. Catal. A 189 (2002) 263. [6] H. Kominami, F. Akitoshi, M. Shinya, I. Hiroyuki, K. Yoshiya, Busho, Catal. Lett. 76 (2001) 31. [7] V. Vamatheva, R. Amal, D. Beydoun, G. Low, S. McEvoy, J. Photochem. Photobiol. A148 (2002) 233. [8] R. Jin, W. Gao., J. Chen, H. Zeng, F. Zhang, Z. Liu, N. Guan, J. Photochem. Photobiol. A162 (2004) 585. [9] L.L. Perissinotti, M.A. Brusa, M.A. Grela, Langmuir 17 (2001) 8422. [10] M. Penpolcharoen, R. Amal, M. Brungs, J. Nanopart. Res. 3 (2001) 289. [11] Y.X. Li, G. Lu, S. Li, J. Photochem. Photobiol. A152 (2002) 219. [12] B. Xin, L. Jing, Z. Ren, B. Wang, H. Fu, J. Phys. Chem. B 109 (2005) 2805. [13] Z. Zhang, X. Song, R. Zhang, M. Zhang, F. Liu, Eur. J. Inorg. Chem. (2005) 1643. [14] Y. Miyake, T. Kondo, J. Chem. Eng. Jpn. 34 (2001) 319. [15] Q. Zhang, L. Gao, J.K. Guo, Appl. Catal. B: Environ. 26 (2000) 207.