6590
Langmuir 2005, 21, 6590-6595
Fabrication of Densely Packed Titania Nanosheet Films on Solid Surface by Use of Langmuir-Blodgett Deposition Method without Amphiphilic Additives Masaru Muramatsu,† Kosho Akatsuka,† Yasuo Ebina,‡ Kezhi Wang,†,§ Takayoshi Sasaki,‡ Takao Ishida,| Koji Miyake,⊥ and Masa-aki Haga*,† Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan, Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan, Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8564, Japan, and Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan Received February 2, 2005. In Final Form: April 18, 2005 Densely packed exfoliated nanosheet films such as Ti0.91O2, Ti0.8M0.2O2 (M ) Co, Ni), Ti0.6Fe0.4O2, and Ca2Nb3O10 on solid substrates were prepared by the LB transfer method without any amphiphilic additives at the air-water interface. Nanosheet crystallites covered nearly 95% on the solid surface with minimum overlapping of nanosheets. The LB transfer method of the Ti0.91O2 nanosheet monolayer film is applicable for not only hydrophilic substrates such as quartz, silicon, indium-tin oxide (ITO), and glass but also the hydrophobic Au surface. On the basis of these points, the LB transfer method has advantages compared to the alternating layer-by-layer method, which makes use of oppositely charged polyelectrolytes such as poly(ethylenimine) (PEI). Adsorption of hydrophobic Ti0.91O2 nanosheets at the air-water interface is responsible for this LB transfer deposition method. The addition of tetrabutylammonium bromide into the subphase assisted the adsorption, causing an increase in the adsorbed amount of Ti0.91O2 nanosheets at the air-water interface.
Introduction The fabrication of inorganic multilayered films has attracted much attention due to their optical and photochemical applications, such as solar energy conversion.1 In particular, titanium dioxide is one of the most attracting materials from the viewpoint of photoelectrochemical and photocatalytic properties.2,3 Delamination into single sheets is well-known for smectite clay minerals, zirconium phosphonates,4 transition-metal chalcogenides,5 and layered perovskites.6-8 Colloidal single-sheet suspensions of these compounds may be used as sources for the nanocomposites of organic polymer-inorganic layered hosts and self-assembled multilayered films.9-12 * To whom correspondence should be addressed: e-mail
[email protected]. † Chuo University. ‡ National Institute for Materials Science. § Present address: Beijing Normal University, Beijing, PR China. | Advanced Manufacturing Research Institute, AIST. ⊥ Nanotechnology Research Institute, AIST. (1) Decher, G. Multilayer Thin Films; Decher, G., Schlenoff, J. B., Eds.; Wiley-VCH: Weinheim, Germany, 2003; 1. (2) Hagfeldt, A.; Gratzel, M. Acc. Chem. Res. 2000, 33, 269. (3) Choy, J.-H.; Lee, H.-C.; Jung, H.; Hwang, S.-J. J. Mater. Chem. 2001, 11, 2232. (4) Keller, S. W.; Kim, H.-N.; Mallouk, T. E. J. Am. Chem. Soc. 1994, 116, 8817. (5) Taguchi, Y.; Kimura, R.; Azumi, R.; Tachibana, H.; Koshizaki, N.; Shimomura, M.; Momozawa, N.; Sakai, H.; Abe, M.; Matsumoto, M. Langmuir 1998, 14, 6550. (6) Yao, K.; Nishimura, S.; Imai, Y.; Wang, H.; Ma, T.; Abe, E.; Tateyama, H.; Yamagishi, A. Langmuir 2003, 19, 321. (7) Miyamoto, N.; Nakato, T. Langmuir 2003, 19, 8057. (8) Suzuki, H.; Notsu, K.; Takeda, Y.; Sugimoto, W.; Sugahara, Y. Chem. Mater. 2003, 2003, 636-641. (9) Sukpirom, N.; Lerner, M. M. Chem. Mater. 2001, 13, 2179. (10) Hasegawa, N.; Okamoto, H.; Kato, M.; Usuki, A.; Sato, N. Polymer 2003, 44, 2933.
Recently, a lepidocrocite-type layered protonic titanate, HxTi2-x/40x/4O4‚yH2O (x ∼ 0.7; vacancy sites are indicated by 0), was delaminated into colloidal single titanium oxide (Ti0.91O2) nanosheets (thickness 0.75 nm).13-18 A layerby-layer self-assembly method has been applied to prepare multilayer films of Ti0.91O2 nanosheets on a flat or spherical substrate by use of electrostatic interaction between anionic nanosheets and cationic polyelectrolytes.19 On the other hand, the Langmuir-Blodgett (LB) technique was applied to the formation of ultrathin films of a wide variety of inorganic materials such as size-quantized cadmium sulfide and titanium dioxide20 and clay minerals.21,22 Recently, Yamaki and Asai23 reported on ordered nanostructured films composed of alternating layers of cationic dioctadecyldimethylammonium bromide (DODAB) and negatively charged titanium dioxide (Ti0.91O2) nanosheets onto solid substrates, in which the electrostatic interaction (11) Fang, M.; Kim, H. N.; Saupe, G. B.; Miwa, T.; Fujishima, A.; Mallouk, T. E. Chem. Mater. 1999, 11, 1526. (12) Schaak, R. E.; Mallouk, T. E. Chem. Mater. 2000, 12, 2513. (13) Sasaki, T.; Nakano, S.; Yamauchi, S.; Watanabe, M. Chem. Mater. 1997, 9 (2), 602. (14) Sasaki, T.; Watanabe, M. J. Phys. Chem. B 1997, 101, 10159. (15) Sasaki, T.; Watanabe, M. J. Am. Chem. Soc. 1998, 120, 4682. (16) Sasaki, T.; Ebina, Y.; Kitami, Y.; Watanabe, M.; Oikawa, T. J. Phys. Chem. B 2001, 105, 6116. (17) (a) Sasaki, T.; Watanabe, M.; Hashizume, H.; Yamada, H.; Nakazawa, H. J. Am. Chem. Soc. 1996, 118, 8329. (b) Sasaki, T.; Ebina, Y.; Watanabe, M.; Decher, G. Chem. Commun. 2000, 2163. (18) Sakai, N.; Ebina, Y.; Takada, K.; Sasaki, T. J. Am. Chem. Soc. 2004, 126, 5851. (19) Wang, L.; Sasaki, T.; Ebina, Y.; Kurashima, K.; Watanabe, M. Chem. Mater. 2002, 14, 4827. (20) Meldrum, F. C.; Fendler, J. H. Biomimetic Materials Chemistry; VCH Publishers: New York, 1996. (21) Umemura, Y.; Yamagishi, A.; Schoonheydt, R.; Persoons, A.; De Schryver, F. J. Am. Chem. Soc. 2002, 124, 992. (22) Umemura, Y. J. Phys. Chem. B. 2002, 106, 11168. (23) Yamaki, T.; Asai, K. Langmuir 2001, 17, 2564.
10.1021/la050293f CCC: $30.25 © 2005 American Chemical Society Published on Web 06/08/2005
Densely Packed Titania Nanosheet Films
between DODAB and Ti0.91O2 nanosheets at the air-water interface should contribute to the composite monolayer. Similar complexation of the organic ammonium amphiphilic compounds with clay minerals at the air-water surface has been studied extensively by Yamagishi and co-workers.24 In these previous studies, the ionized ammonium groups on the amphiphile at the air-water interface play an important role in forming stable LB films. Here we report an LB deposition method for Ti0.91O2 nanosheets without the use of amphiphiles, onto a variety of substrates such as Au, indium-tin oxide (ITO), and mica, by use of a colloidal Ti0.91O2 nanosheets suspension as a subphase. In the resulting LB film, Ti0.91O2 nanosheets are densely packed, and the Ti0.91O2 monolayer films are stable enough to act as substrates for attachment of additional nanosheet layers. This direct nanosheet transfer method can be applied not only for Ti0.91O2 but also for other relevant nanosheets, such as Ca2Nb3O10 and Ti0.8M0.2O2 (M ) Co, Ni). Experimental Section Materials. The colloidal single Ti0.91O2 nanosheet suspension was prepared from the exfoliation of HxTi2-x/40x/4O4‚yH2O with tetrabutylammonium hydroxide (TBAOH), which was synthesized from the protonation of CsxTi2-x/40x/4O4 by HCl solution (1 mol dm-3) as previously described.13 The concentrations of nanosheets in the suspensions were determined by weighing the amount of Ti0.91O2 residues after evaporation of water. The other nanosheet types, Ca2Nb3O10, Ti0.8M0.2O2 (M ) Co, Ni), and Ti0.6Fe0.4O2, were similarly exfoliated and stored as colloidal solutions. Tetrabutylammonium bromide (TBABr) was a Wako Co. commercial product of high purity and was used without further purification. All other supplied chemicals were of standard reagent-grade quality. Indium-tin oxide- (ITO-) coated glass plates, purchased from Central Glass Co. (surface resistance
