Nanostructured TiON-based semiconductor photocatalysts have been developed with various compositions and in various forms, which extend the absorption band-edge of TiO 2 into the visible-light region with improved stability, photocatalytic effi ciency, and ease of the doping process. Metal-ion modifi cation has strong eff ects on the optical and photocatalytic properties of TiON photocatalysts, and greatly enhances photoactivity of TiON under visible-light illumination if the metal-ion-additive concentration is optimized.
By combining sol–gel process with templating, nanostructured photocatlysts have been synthesized into fi brous and porous forms to meet the specifi c requirements for water and air purifi cation. With TiON-based photocatalysts, visible-light-induced photocatalytic degradation and disinfection have been successfully achieved. These nanostructured photocatalysts have shown great promise in a wide range of optical and photochemical solutions, especially for environmental controls.
Although visible-light photocatalysts have shown great promise in degrading organics and microbials in water, a number of great challenges still remain and require attention in the future work. First of all, the mechanism of the interaction between microorganisms with photocatalysts needs to be examined in details to gain the clear understanding of the disinfection eff ect and provide guidelines for future water treatment design based on photocatalysis. Second, much of the work so far has been focused on TiO 2 and very few other material systems have been investigated. There is a strong need to explore other material systems with improved photocatalytic performance under visible-light illumination. Third, there are early indications that chemical modifi cations of the photocatalysts may enhance photocatalytic activities selectively. If confi rmed, it would be possible to tailor the photocatalyst to specifi c environmental applications. Fourth, new and improved methods are needed to synthesize photocatalysts into various forms at low costs to meet the needs of diff erent environmental applications. For example, various forms of semiconductor-based photocatalysts (particularly nanotubes, nanowires, and nanosized three-dimensional structures) may be explored as photoelectrocatalytic sensors for rapid monitoring and control of environmental pollutants. Finally, broader environmental applications should be explored. For example, the photocatalytic disinfection of various microorganisms, such as fungi or viruses, should be investigated, which is very important to the human health, environmental protection, and agriculture area.
Savage_Ch02.indd 33
Savage_Ch02.indd 33 11/11/2008 2:14:31 PM11/11/2008 2:14:31 PM
References
1. A. Fujishima and K. Honda, “Electrochemical photolysis of water at a semiconductor electrode,” Nature , Vol. 238, pp. 37–38, 1972.
2. J.R. Bolton, “Solar photoproduction of hydrogen: a review,” Solar Energy , Vol. 57, pp. 37–50, 1996.
3. S.U.M. Khan and J. Akikusa, “Photoelectrochemical splitting of water at nanocrystalline n -Fe 2 O 3 thin-fi lm electrodes,” The Journal of Physical Chemistry B , Vol. 103, pp. 7184–
7189, 1999.
4. J. Akikusa and S.U.M. Khan, “Stability and photoresponse of nanocrystalline n-TiO 2 and n-TiO 2 /Mn 2 O 3 thin fi lm electrodes during water splitting reactions,” Journal of the Electrochemical Society , Vol. 145, pp. 89–93, 1998.
5. S.U.M Khan and J. Akikusa, “Photoelectrolysis of water to hydrogen in p-SiC/Pt and p-SiC/
n-TiO 2 cells,” International Journal of Hydrogen Energy , Vol. 27, pp. 863–870, 2002.
6. O. Khaselev and J.A. Turner, “A monolithic photovoltaic–photoelectrochemical device for hydrogen production via water splitting,” Science , Vol. 280, pp. 425–427, 1998.
7. S. Licht, B. Wang, S. Mukerji, T. Soga, M. Umeno, and H. Tributsch, “Effi cient solar water splitting, exemplifi ed by RuO 2 -catalyzed AlGaAs/Si photoelectrolysis,” The Journal of Physical Chemistry B , Vol. 104, pp. 8920–8924, 2000.
8. B. O’Regan and M. Gratzel, “A low-cost, high-effi ciency solar cell based on dye-sensitized colloidal TiO 2 fi lms,” Nature Vol. 353, pp. 737–740, 1991.
9. G.R. Comte and M. Gratzel, “A contribution to the optical design of dye-sensitized nanocrystalline solar cells,” Solar Energy Materials and Solar Cells , Vol. 58, pp. 321–336, 1999.
10. G. Sauve´, M.E. Cass, S.J. Doig, I. Lauermann, K. Pomykal, and N.S. Lewis, “High quantum yield sensitization of nanocrystalline titanium dioxide photoelectrodes with cis-dicyanobis (4,4’-dicarboxy-2,2’-bipyridine)osmium(II) or tris(4,4’-dicarboxy-2,2’-bipyridine)osmium(II) complexes,” The Journal of Physical Chemistry B , Vol. 104, pp. 3488–3491, 2000.
11. M.R. Hoff man, S.T. Martin, W. Choi, and D.W. Bahnemann, “Environmental applications of semiconductor photocatalysis,” Chemical Reviews , Vol. 95, pp. 69–96, 1995.
12. N.S. Frank and A.J. Bard, “Heterogeneous photocatalytic oxidation of cyanide and sulfi te in aqueous solutions at semiconductor powders,” The Journal of Physical Chemistry , Vol. 81, pp. 1484–1488, 1977.
13. A. Hagfeldt and M. Graetzel, “Light-induced redox reactions in nanocrystalline systems,”
Chemical Reviews , Vol. 95, pp. 49–68, 1995.
14. H. Einaga, S. Futamura, and T. Ibusuki, “Photocatalytic decomposition of benzene over TiO 2 in a humidifi ed airstream,” Physical Chemistry Chemical Physics , Vol. 1, pp. 4903–4908, 1999.
15. A. Fujishima, T.N. Rao, and D.A. Tryk, “Titanium dioxide photocatalysis,” Journal of Photochemistry and Photobiology C , Vol. 1, pp. 1–21, 2000.
16. A.L. Linsebigler, G. Lu, and J.T. Yates, Jr, “Photocatalysis on TiO 2 surfaces: principles, mechanisms, and selected results,” Chemical Reviews , Vol. 95, pp. 735–758, 1995.
17. K. Hashimoto, H. Irie, and A. Fujishima, “TiO 2 photocatalysis: a historical overview and future prospects,” Japanese Journal of Applied Physics , Vol. 44, pp. 8269–8285, 2005.
18. A.K. Ghosh and H.P. Maruska, “Photoelectrolysis of water in sunlight with sensitized semiconductor electrodes,” Journal of the Electrochemical Society , Vol. 124, pp. 1516–1522, 1977.
19. W. Choi, A. Termin, and M.R. Hoff mann, “The role of metal ion dopants in quantum-sized TiO 2 : correlation between photoreactivity and charge carrier recombination dynamics,” The Journal of Physical Chemistry , Vol. 98, pp. 13669–13679, 1994.
20. M. Anpo, “Photocatalysis on titanium oxide catalysts: approaches in achieving highly Effi cient reactions and realizing the use of visible light,” Catalysis Surveys from Japan , Vol. 1, pp. 169–179, 1997.
Savage_Ch02.indd 34
Savage_Ch02.indd 34 11/11/2008 2:14:31 PM11/11/2008 2:14:31 PM
21. V. Subramanian, E. Wolf, and P.V. Kamat, “Semiconductor–metal composite nanostructures:
to what extent do metal nanoparticles improve the photocatalytic activity of TiO 2 fi lms?”
The Journal of Physical Chemistry B , Vol. 105, pp. 11439–11446, 2001.
22. R.G. Breckenridge and W.R. Hosler, “Electrical properties of titanium dioxide semiconductors,” Physical Review , Vol. 91, pp. 793–802, 1953.
23. D.C. Cronemeyer, “Infrared absorption of reduced rutile TiO 2 single crystals,” Physical Review , Vol. 113, pp. 1222–1226, 1959.
24. R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, and Y. Taga, “Visible-light photocatalysis in nitrogen-doped titanium oxides,” Science , Vol. 293, pp. 269–271, 2001.
25. H. Irie, Y. Watanabe, and K. Hashimoto, “Nitrogen-concentration dependence on photocatalytic activity of TiO 2-x N x powders,” The Journal of Physical Chemistry B , Vol. 107, pp. 5483–5486, 2003.
26. T. Lindgren, J.M. Mwabora, E. Avendaủo, J. Jonsson, C.G. Granqvist, and S.E. Lindquist,
“Photoelectrochemical and optical properties of nitrogen doped titanium dioxide fi lms prepared by reactive DC magnetron sputtering,” The Journal of Physical Chemistry B , Vol.
107, pp. 5709–5716, 2003.
27. Irie, Watanabe, and Hashimoto, “Nitrogen-concentration dependence,” pp. 5483–5486.
28. S. Sakthivel and H. Kisch, “Photocatalytic and photoelectrochemical properties of nitrogen- doped titanium dioxide,” ChemPhysChem , Vol. 4, pp. 487–490, 2003.
29. C. Burda, Y. Lou, X. Chen, A.C.S. Samia, J. Stout, and J.L. Gole, “Enhanced nitrogen doping in TiO 2 nanoparticles,” Nano Letters , Vol. 3, pp. 1049–1051, 2003.
30. S. Yin, Q. Zhang, F. Saito, and T. Sato, “Preparation of visible light-activated titania photocatalyst by mechanochemical method,” Chemistry Letters , Vol. 32, pp. 358–359, 2003.
31. O. Diwald, T.L. Thompson, T. Zubkov, E.G. Goralski, S.D. Walck, and J.T. Yates,
“Photochemical activity of nitrogen-doped rutile TiO 2 (110) in visible light,” The Journal of Physical Chemistry B , Vol. 108, pp. 6004–6008, 2004.
32. S.W. Yang and L. Gao, “New method to prepare nitrogen-doped titanium dioxide and its photocatalytic activities irradiated by visible light,” Journal of the American Ceramic Society , Vol. 87, pp. 1803–1805, 2004.
33. C.D. Valentin, G. Pacchioni, and A. Selloni, “Origin of the diff erent photoactivity of N-doped anatase and rutile TiO 2 ,” Physical Review B , Vol. 70, pp. 85–116, 2004.
34. C. Lettmann, K. Hildenbrand, H. Kisch, W. Macyk, and W.F. Maier, “Visible light photodegradation of 4-chlorophenol with a coke-containing titanium dioxide photocatalyst,”
Applied Catalysis B , Vol. 32, pp. 215–227, 2001.
35. S. Livraghi, A. Votta, P. Cristina, and E. Giamello, “The nature of paramagnetic species in nitrogen doped TiO 2 active in visible light photocatalysis,” Chemical Communications , pp.
498–500, 2005.
36. S. Livraghi, M.C. Paganini, E. Giamello, A. Selloni, C.D. Valentin, and G. Pacchioni,
“Origin of photoactivity of nitrogen-doped titanium dioxide under visible light,” Journal of the American Chemical Society , Vol. 128, pp. 15666–15671, 2006.
37. S.U.M. Khan, M. Al-Shahry, and W.B. Ingler, “Effi cient photochemical water splitting by a chemically modifi ed n-TiO 2 ,” Science Vol. 297, pp. 2243–2245, 2002.
38. S. Sakthivel and H. Kisch, “Daylight photocatalysis by carbon-modifi ed titanium dioxide,”
Angewandte Chemie International Edition , Vol. 42, pp. 4908–4911, 2003.
39. H. Irie, Y. Watanabe, and K. Hashimoto, “Carbon-doped anatase TiO 2 powders as a visible- light sensitive photocatalyst,” Chemistry Letters , Vol. 32, pp. 772–773, 2003.
40. K. Noworyta and J. Augustynski, “Spectral photoresponses of carbon-doped TiO 2 fi lm electrodes,” Electrochemical and Solid-State Letters , Vol. 7, pp. E31–E33, 2004.
41. H. Wang and J.P. Lewis, “Eff ects of dopant states on photoactivity in carbon-doped TiO 2 ,”
Journal of Physics: Condensed Matter , Vol. 17, pp. L209–L213, 2005.
42. W. Wang, P. Serb, P. Kalck, and J.L. Faria, “Visible light photodegradation of phenol on MWNT-TiO 2 composite catalysts prepared by a modifi ed sol–gel method,” Journal of Molecular Catalysis A: Chemical , Vol. 235, pp. 194–199, 2005.
Savage_Ch02.indd 35
Savage_Ch02.indd 35 11/11/2008 2:14:31 PM11/11/2008 2:14:31 PM
43. L. Lin, W. Lin, Y.X. Zhu, B.Y. Zhao, Y.C. Xie, Y. He, and Y.F. Zhu, “Uniform carbon- covered titania and its photocatalytic property,” Journal of Molecular Catalysis A: Chemical , Vol. 236, pp. 46–53, 2005.
44. M.E. Rinco´n, M.E. Trujillo-Camacho, and A.K. Cuentas-Gallegos, “Sol–gel titanium oxides sensitized by nanometric carbon blacks: comparison with the optoelectronic and photocatalytic properties of physical mixtures,” Catalysis Today , Vol. 107–108, pp. 606–611, 2005.
45. T. Umebayashi, T. Yamaki,, H. Itoh, and K. Asai, “Band gap narrowing of titanium dioxide by sulfur doping,” Applied Physics Letters , Vol. 81, pp. 454–456, 2002.
46. T. Umebayashi, T. Yamaki, S. Tanaka, K. Asai, “Visible light-induced degradation of methylene blue on S-doped TiO 2 ,” Chemistry Letters , Vol. 32, pp. 330–331, 2003.
47. T. Umebayashi, T. Yamaki, S. Yamamoto, A. Miyashita, S Tanaka, T. Sumita, and K. Asai,
“Sulfur-doping of rutile-titanium dioxide by ion implantation: photocurrent spectroscopy and fi rst-principles band calculation studies,” Journal of Applied Physics , Vol. 93, pp. 5156–5160, 2003.
48. T. Ohno, T. Mitsui, and M. Matsumura, “Photocatalytic activity of S-doped TiO 2 photocatalyst under visible light,” Chemistry Letters , Vol. 32, pp. 364–365, 2003.
49. T. Yamamoto, Y. Yamashita, I. Tanaka, F. Matsubara, and A. Muramatsu, “Electronic states of sulfur doped TiO 2 by fi rst principles calculations,” Material Transactions , Vol. 45, pp. 1987–19890, 2004.
50. J.C. Yu, J.G. Yu, W.K. Ho, Z.T. Jiang, and L.Z. Zhang, “Eff ects of F - doping on the photocatalytic activity and microstructures of nanocrystalline TiO 2 powders,” Chemistry of Materials , Vol. 14, pp. 3808–3816, 2002.
51. G.R. Torres, T. Lindgren, J. Lu, C.G. Granqvist, and S.E. Lindquist, “Photoelectrochemical study of nitrogen-doped titanium dioxide for water oxidation,” The Journal of Physical Chemistry B , Vol. 108, pp. 5995–6003, 2004.
52. R. Nakamura, T. Tanaka, and Y. Nakato, “Mechanism for visible light responses in anodic photocurrents at N-doped TiO 2 fi lm electrodes,” The Journal of Physical Chemistry B , Vol.
108, pp. 10617–10620, 2004.
53. J.Y. Lee, J. Park, and J.H. Cho, “Electronic properties of N- and C-doped TiO 2 ,” Applied Physics Letters , Vol. 87, pp. 011904, 2005.
54. Q. Li, R. Xie, E.A. Mintz, and J.K. Shang, “Eff ect of precursor ratio on synthesis and optical absorption of TiON photocatalytic nanoparticles,” Journal of the American Ceramic Society , Vol. 90, pp. 1045–1050, 2007.
55. J. Tauc, R. Grigorovici, and A. Vancu, “Optical properties and electronic structures of amorphous germanium,” Physica Status Solidi , Vol. 15, pp. 627–637, 1966.
56. P.G. Wu, C.H. Ma, and J.K. Shang, “Eff ects of nitrogen doping on optical properties of TiO 2 thin fi lms,” Applied Physics A , Vol. 81, pp. 1411–1417, 2005.
57. S.I. Shah, W. Li, C.P. Huang, O. Jung, and C. Ni, “Study of Nd 3+ , Pd 2+ , Pt 4+ , and Fe 3+
dopant eff ect on photoreactivity of TiO 2 nanoparticles,” Proceedings of the National Academy of Sciences of the United States of America , Vol. 99, pp. 6482–6486, 2002.
58. Q. Li, R. Xie, E.A. Mintz, and J.K. Shang, “Enhanced visible-light photocatalytic degradation of humic acid by palladium oxide-sensitized nitrogen-doped titanium oxide,”
Journal of the American Ceramic Society , Vol. 90, pp. 3863–3868, 2007.
59. Q. Li, W. Liang, and J.K. Shang, “Enhanced visible-light absorption from PdO nanoparticles in nitrogen-doped titanium oxide thin fi lms,” Applied Physics Letters , Vol. 90, pp. 63–109, 2007.
60. Q. Li, M. A. Page, B. J. Marinãs, and J. K. Shang, “Treatment of coliphage MS2 with palladium-modifi ed nitrogen-doped titanium oxide photocatalyst illuminated by visible light,” Environmental Science & Technology, Vol. 42, pp. 6148–6153, 2008.
61. P. Wu, PhD dissertation, University of Illinois at Urbana–Champaign, May 2007.
Savage_Ch02.indd 36
Savage_Ch02.indd 36 11/11/2008 2:14:31 PM11/11/2008 2:14:31 PM
62. P. Wu, R. Xie, J. A. Imlay, and J. K. Shang, “Visible-light-induced photocatalytic inactivation of bacteria by composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide,” Applied Catalysis B: Environmental, 2008, submitted.
63. 63. P. Wu, R. Xie, and J. K. Shang, “Enhanced visible-light photocatalytic disinfection of bacterial spores by palladium-modifi ed nitrogen-doped titanium oxide,” Journal of the American Ceramic Society, Vol. 91, pp. 2957–2962, 2008.
Savage_Ch02.indd 37
Savage_Ch02.indd 37 11/11/2008 2:14:31 PM11/11/2008 2:14:31 PM
39
Savage et al. (eds.), Nanotechnology Applications for Clean Water, 39–46,
© 2009 William Andrew Inc.
Film- and Membrane-Based Photocatalysis for Water Treatment
Hyeok Choi ,1 Souhail R. Al-Abed ,1 and Dionysios D. Dionysiou 2
1 National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH, USA 2 Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA