Langmuir 2007, 23, 10353-10356
10353
Photochemical Reactions of Ketones to Synthesize Gold Nanorods Koji Nishioka,† Yasuro Niidome,*.†.‡ and Sunao Yamada*.†.‡ Department of Materials Physics and Chemistry, Graduate School of Engineering, Kyushu UniVersity, Moto-oka, Fukuoka 819-0395, Japan, and Department of Applied Chemistry, Faculty of Engineering, Kyushu UniVersity, Moto-oka, Fukuoka 819-0395, Japan ReceiVed May 28, 2007. In Final Form: July 10, 2007 Photochemical synthesis of gold nanorods (NRs) in a micellar solution of hexadecyltrimethylammonium bromide (CTAB) was triggered by photoreactions of ketones. Photoexcitation of gold ions and silver bromide clusters ((AgBr)n) in the absence of ketones did not produce NRs. The initial products of the photoirradiation were probably ketyl radicals, which then initiated reactions to form NRs. NRs formed in darkness, if the reaction solutions were irradiated by UV light for a few minutes, thus indicating that the photochemical products catalyzed NR-formation.
Introduction Gold nanorods (NRs) are rod-shaped nanoparticles prepared by wet-chemical techniques in micellar solutions of cationic amphiphiles. NRs have been attractive research subjects due to remarkable optical properties originating from their anisotropic shapes. That is, NRs exhibit two distinctive absorption bands that are assignable to transverse and longitudinal modes of surface plasmon (SP) oscillation.1 The transverse SP band is located at around 520 nm, whereas the longitudinal SP band is observed in the near-infrared (NIR) having a large absorption coefficient (3500∼4000 (Au atoms)). The peak positions of longitudinal SP bands are tunable as they depend on the shape and volume of NRs in the range of 750∼1300 nm. Theoretical considerations on the SP bands of NRs have already been reported.2-4 Thus, the NR is a new type of NIR pigment that can be used for analytical,5-11 photochemical,12-15 and biochemical16-22 applications. Several methods to prepare homogeneous and shape-controlled NRs have been reported. The methods can be classified into four categories: photochemical,23 templating,24-26 electrochemical,1,27 and seed-mediated28,29 methods. Each method has particular * Author to whom correspondence should be addressed. E-mail:
[email protected];
[email protected]. † Department of Materials Physics and Chemistry. ‡ Department of Applied Chemistry. (1) Yu, Y.-Y.; Chang, S.-S.; Lee, C.-L.; Wang, C. R. C. J. Phys. Chem. B 1997, 101, 6661. (2) Link, S.; Mohamed, M. B.; El-Sayed, M. A. J. Phys. Chem. B 1999, 103, 3073. (3) Brioude, A.; Jiang, X. C.; Pileni, M. P. J. Phys. Chem. B 2005, 109, 13138. (4) Lee, K.-S., El-Sayed, M. A. J. Phys. Chem. B 2005, 109, 20331. (5) Niidome, Y.; Takahashi, H.; Urakawa, S.; Nishioka, K.; Yamada, S. Chem. Lett. 2004, 33, 454. (6) Ueno, K.; Juodkazis, S.; Mino, M.; Mizeikis, M.; Misawa, H. J. Phys. Chem. C 2007, 111, 4180. (7) Rex, M.; Hernandez, F. E.; Campiglia, A. D. Anal. Chem. 2006, 78, 445. (8) (a) Nikoobakht, B.; Wang, J.; El-Sayed, M. A. Chem. Phys. Lett. 2002, 366, 17. (b) Nikoobakht, B.; El-Sayed, M. A. J. Phys. Chem. A 2003, 107, 3372. (9) Suzuki, M.; Niidome, Y.; Terasaki, N.; Inoue, K.; Kuwahara, Y.; Yamada, S. J. J. Appl. Phys. 2004, 43, L554. (10) Hu, X.; Cheng, W.; Wang, T.; Wang, Y.; Wang, E.; Dong, S. J. Phys. Chem. B 2005, 109, 19385. (11) Orendorff, C. J.; Gearheart, L.; Jana, N. L.; Murphy, C. J. Phys. Chem. Chem. Phys. 2006, 8, 165. (12) Niidome, Y.; Urakawa, S.; Kawahara, M.; Yamada, S. J. J. Appl. Phys. 2003, 42, 1749. (13) Pe´rez-Juste, J.; Rodrı´guez-Gonza´lez, B.; Mulvaney, P.; Liz-Marza´n, M. AdV. Funct. Mater. 2005, 15, 1065. (14) Das, M.; Sanson, N.; Fava, D.; Kumacheva, E. Langmuir 2007, 23, 196. (15) Shiotani, A.; Mori, T.; Niidome, T.; Niidome, Y.; Katayama, Y. Langmuir 2007, 23, 4012.
advantages and disadvantages. Nowadays, it is likely the seedmediated method is the most commonly used technique because of its shape-controllability and reproducibility.28,29 The seedmediated method consists of at least two chemical processes, which are the preparation of seed particles that are small (
