Dodecyldimethylamine N-oxide Intercalation

Langmuir , 1998, 14 (24), pp 6969–6973. DOI: 10.1021/la980173q. Publication Date (Web): October 29, 1998. Copyright © 1998 American Chemical Societ...
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Langmuir 1998, 14, 6969-6973

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Preparation of Smectite/Dodecyldimethylamine N-oxide Intercalation Compounds Makoto Ogawa* PRESTO, Japan Science and Technology Corporation, and Institute of Earth Science, Waseda University, Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-8050, Japan

Nagayuki Kanaoka† and Kazuyuki Kuroda†,‡ Department of Applied Chemistry, Waseda University, Ohkubo 3-4-1, Shinjuku-ku, Tokyo 169-8555, Japan, and Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, Nishiwaseda 2-8-26, Shinjuku-ku, Tokyo 169-0051, Japan Received February 10, 1998. In Final Form: June 19, 1998 The adsorption of dodecyldimethylamine N-oxide into the interlayer space of Na-saponite was investigated. The Na-saponite/dodecyldimethylamine N-oxide intercalation compounds were prepared as supported and unsupported films. Intercalation compounds with two different arrangements of the intercalated dodecyldimethylamine N-oxide were obtained, depending on the adsorbed amounts. When the adsorbed amount was greater than 400 mmol/100 g of clay, the intercalated dodecyldimethylamine N-oxide took a paraffin type bilayer. On the other hand, the intercalated dodecyldimethylamine N-oxide molecules are thought to arrange as a bimolecular coverage with their alkyl chains parallel to the silicate sheet when the added amount of dodecyldimethylamine N-oxide was 100 mmol/100 g of clay. The coadsorption of tris(2,2′-bipyridine)ruthenium(II) with dodecyldimethylamine N-oxide was achieved. The luminescence characteristics of tris(2,2′-bipyridine)ruthenium(II) revealed that there are certain interactions between the adsorbed tris(2,2′-bipyridine)ruthenium(II) and dodecyldimethylamine N-oxide in the interlayer space of saponite. Since the products have been obtained as highly transparent supported and self-standing films, the intercalation of dodecyldimethylamine N-oxide is a way to control the adsorbed states of cationic dyes on the surface of smectites.

Introduction Intercalation of guest species into layered inorganic solids is a way of producing ordered inorganic-organic assemblies with unique microstructures controlled by host-guest and guest-guest interactions.1,2 Recently, photophysical and photochemical properties of intercalation compounds have attracted increasing interest.3,4 Among possible layered host materials, the smectite group of layered clay minerals provides attractive features such as large surface area, swelling behavior, and ion exchange properties for organizing organic guest species.5,6 The surface modification of smectites with the intercalation of organoammonium ions has been employed so far to construct novel functional inorganic-organic hybrid materials.7 The microporous tetramethylammonium/ saponite has been prepared and used as a support of quinizarin8 and p-nitroaniline9 to show photochemical hole burning and nonlinear optical properties, respectively. For the introduction of poorly water soluble species, the hydrophilic interlayer space of smectites has been modified * To whom correspondence should be addressed at the Institute of Earth Science. † Department of Applied Chemistry. ‡ Kagami Memorial Laboratory for Materials Science and Technology. (1) Intercalation Chemistry; Whittingham, M. S., Jacobson, A. J., Eds.; Academic Press: New York, 1982. (2) Progress in Intercalation Research; Mu¨ller-Warmuth, W., Scho¨llhorn, R., Ed.; Kluwer Academic Publishers: Dordrecht, 1994. (3) Ogawa, M.; Kuroda, K. Chem. Rev. 1995, 95, 399. (4) Thomas, J. K. Acc. Chem. Res. 1988, 21, 275. (5) Van Olphen, H. An Introduction to Clay Colloid Chemistry, 2nd ed.; Wiley-Interscience: New York, 1977. (6) Theng, B. K. G. The Chemistry of Clay Organic Reactions; Adam Hilger: London, 1974. (7) Ogawa, M.; Kuroda, K. Bull. Chem. Soc. Jpn. 1997, 70, 2593.

to be hydrophobic by replacing the interlayer exchangeable cations with cationic surfactants. These organoammonium/clays have been studied as a precursor for the pillared clay,10 selective adsorbates,11 membranes,12 supports for catalysts13 and photoactive species,14-24 and so on. However, the processing of the organoammonium/ clays into thin films, which is an ideal morphology for their photochemical applications, is not so simple and may often result in less ordered films with low optical quality. In this paper, we report the preparation of saponite/ dodecyldimethylamine N-oxide (abbreviated as C12AO) (8) Ogawa, M.; Handa, T.; Kuroda, K.; Kato, C.; Tani, T. J. Phys. Chem. 1992, 96, 8116. (9) Ogawa, M.; Takahashi, M.; Kuroda, K. Chem. Mater. 1994, 6, 715. (10) Galarneau, A.; Barodawalla, A.; Pinnavaia, T. J. Nature 1995, 374, 529. Galarneau, A.; Barodawalla, A.; Pinnavaia, T. J. Chem. Commun. 1997, 1661. (11) Boyd, S. A.; Lee, J. F.; Mortland, M. M. Nature 1988, 333, 345. Lee, J. F.; Mortland, M. M.; Chiou, C. T.; Kile, D. E.; Boyd, S. A. Clays Clay Miner. 1990, 38, 113. (12) Okahata, Y.; Shimizu, A. Langmuir 1989, 5, 954. (13) Hu, N.; Rusling, J. F. Anal. Chem. 1991, 63, 2163. (14) Seki, T.; Ichimura, K. Macromolecules 1990, 23, 31. (15) Tomioka, H.; Itoh, T. J. Chem. Soc., Chem. Commun. 1991, 532. (16) Takagi, K.; Kurematsu, T.; Sawaki, Y. J. Chem. Soc., Perkin Trans. 2 1991, 1517. (17) Ogawa, M.; Fujii, K.; Kuroda, K.; Kato, C. Mater. Res. Soc. Symp. Proc. 1991, 233, 89. (18) Ogawa, M.; Kimura, H.; Kuroda, K.; Kato, C. Clay Sci. 1996, 10, 57. (19) Ogawa, M.; Shirai, H.; Kuroda, K.; Kato, C. Clays Clay Miner. 1992, 40, 485. (20) Ogawa, M.; Aono, T.; Kuroda, K.; Kato, C. Langmuir 1993, 9, 1529. Ogawa, M.; Wada, T.; Kuroda, K. Langmuir 1995, 11, 4598. (21) Ito, K.; Fukunishi, K. Chem. Lett. 1997, 357. (22) Ahmadi, M. F.; Rusling, J. F. Langmuir 1995, 11, 94. (23) Sasaki, M.; Fukuhara, T. Photochem. Photobiol. 1997, 66, 716. (24) Ogawa, M.; Takahashi, M.; Kato, C.; Kuroda, K. J. Mater. Chem. 1994, 4, 519.

10.1021/la980173q CCC: $15.00 © 1998 American Chemical Society Published on Web 10/29/1998

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intercalation compounds as a novel type of surfactantmodified clays. Since C12AO is a nonionic surfactant, the intercalation behavior is expected to be different from those of the cationic surfactants formed by cation exchange mechanisms. Moreover, the intercalation compounds have been obtained as thin films with good optical quality equivalent to that of tetramethylammonium/saponite24 which has been utilized for the photochemical hole burning8 and nonlinear optical studies.9 The coadsorption of C12AO with the tris(2,2′-bipyridine)ruthenium(II) complex ion, abbreviated as [Ru(bpy)3]2+, was investigated. [Ru(bpy)3]2+ was used as the guest species because of its unique combination of chemical stability, luminescence, and so on.25 Since the spectroscopic features of [Ru(bpy)3]2+ are environmentally sensitive, photochemical and photophysical investigations are useful for the study of surface phenomena. In other words, one can modify the attractive properties of [Ru(bpy)3]2+ by introducing it into appropriate matrixes. Along this line, the photochemical and photophysical characteristics of [Ru(bpy)3]2+ adsorbed on smectites have been investigated so far.3,4,26-39 The spectroscopic characteristics of the adsorbed [Ru(bpy)3]2+ were expected to reflect the change in the microenvironments caused by the coadsorption of C12AO. Experimental Section Materials. Na-saponite (Sumecton SA supplied from Kunimine Industries Co., the ideal formula was (Na0.49Mg0.14)0.77+[(Si7.20Al0.80)(Mg5.97Al0.03)O20(OH)4]0.77-, very minute particles synthesized by a hydrothermal reaction)24 was used as the host material. The cation exchange capacity of Na-saponite is 70 mequiv/100 g of host. Dodecyldimethylamine N-oxide (abbreviated as C12AO; 30% in water, Fluka) and tris(2,2′-bipyridine)ruthenium(II) chloride hydrate (obtained from Aldrich) were used without further purification. Sample Preparation. The aqueous clay suspension was mixed with an aqueous solution of C12AO (1.0 × 10-2 M) and allowed to react at room temperature. The amount of clay was determined by the molar ratio of C12AO to clay. For the preparation of thin films, the aqueous mixture was cast on a glass substrate and dried in air. The self-standing thin films were prepared by drying a more concentrated aqueous mixture (the concentration of C12AO was 1.0 × 10-1 M) on a Teflon plate (25) Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin Complexes; Academic Press: London, 1992. (26) Habti, A.; Keravis, D.; Levitz, P.; Van Damme, H. J. Chem. Soc., Faraday Trans. 2 1984, 80, 67. (27) DellaGuardla, R. A.; Thomas, J. K. J. Phys. Chem. 1983, 87, 990. (28) Schoonheydt, R. A.; de Pauw, P.; Vliers, D.; de Schryver, F. C. J. Phys. Chem. 1984, 88, 5113. (29) Ghosh, P. K.; Bard, A. J. J. Phys. Chem. 1984, 88, 5519. (30) (a) Joshi, V.; Ghosh, P. K. J. Am. Chem. Soc. 1989, 111, 5604. (b) Joshi, V.; Ghosh, P. K. J. Chem. Soc., Chem. Commun. 1987, 789. (c) Joshi, V.; Kotkar, D.; Ghosh, P. K. Curr. Sci. 1988, 57, 567. (31) Krenske, D.; Abdo, S.; Van Damme, H.; Cruz, M.; Fripiat, J. J. J. Phys. Chem. 1980, 84, 2447. (32) Abdo, S.; Canesson, P.; Cruz, M.; Fripiat, J. J.; Van Damme, H. J. Phys. Chem. 1981, 85, 797. (33) Turro, N. J.; Kumar, C. V.; Grauer, Z.; Barton, J. K. Langmuir 1987, 3, 1056. (34) Kuykendall, V. G.; Thomas, J. K. J. Phys. Chem. 1990, 94, 4224. (35) Nakamura, T.; Thomas, J. K. Langmuir 1985, 1, 567. (36) (a) Nijs, H.; Cruz, M.; Fripiat, J.; Van Damme, H. J. Chem. Soc., Chem. Commun. 1981, 1026. (b) Nijs, H.; Cruz, M.; Fripiat, J.; Van Damme, H. J. Phys. Chem. 1983, 87, 1279. (c) Detellier, C.; Villemure, G. Inorg. Chim. Acta 1984, 86, L19. (d) Detellier, C.; Villemure, G.; Kodama, H. Can. J. Chem. 1984, 63, 1139. (e) Villemure, G.; Bazan, G.; Kodama, H.; Szabo, A. G.; Detellier, C. Appl. Clay Sci. 1987, 2, 241. (f) Van Damme, H.; Nijs, H.; Fripiat, J. J. J. Mol. Catal. 1984, 27, 123. (g) Van Damme, H.; Bergaya, F.; Habti, A.; Fripiat, J. J. J. Mol. Catal. 1983, 21, 223. (37) Yamagishi, A. J. Coord. Chem. 1987, 16, 131. (38) Ogawa, M.; Inagaki, M.; Kodama, N.; Kuroda, K.; Kato, C. J. Phys. Chem. 1993, 97, 3819. (39) Awaluddin, A.; DeGuzman, R. N.; Kumar, C. V.; Suib, S. L.; Burkett, S. L.; Davis, M. E. J. Phys. Chem. 1995, 99, 9886.

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Figure 1. X-ray diffraction patterns of the cast films of (a) Na-saponite and (b-e) the Na-saponite/C12AO intercalation compounds where the loading amounts of C12AO are (a)100, (b) 400, (c)700, and (d) 1000 mmol/100 g of clay. and dried moderately. In a typical experiment, 1.0 mL of the aqueous mixture was deposited on an area of approximately 13 cm2. For preparation of the [Ru(bpy)3]2+/Na-saponite/C12AO intercalation compound, [Ru(bpy)3]2+ was intercalated first, and then C12AO was allowed to react with the [Ru(bpy)3]2+/Nasaponite. The intercalation of [Ru(bpy)3]2+ onto Na-saponite was carried out by a conventional ion exchange method. The amount of [Ru(bpy)3]2+ was 1 mmol/100 g of saponite, to avoid the effect of the intermolecular interactions of [Ru(bpy)3]2+. This low loading amount of [Ru(bpy)3]2+ does not cause significant change of the dispersibility of saponite in water. After the sample was washed, the intercalation of C12AO into the interlayer space of the [Ru(bpy)3]2+/Na-saponite intercalation compound was done in the way mentioned above. Characterization. X-ray powder diffraction patterns of the products were recorded on a Rigaku RINT 1100 diffractometer using Mn-filtered Fe KR radiation. Visible absorption spectra of the films were recorded on a Shimadzu UV-3101PC spectrophotometer. Infrared spectra of the samples in KBr disks were recorded on a Perkin-Elmer FT-1640 Fourier transform infrared spectrophotometer. Differential thermal analysis (DTA) and thermogravimetric analyses (TGAs) were performed on Shimadzu DT-30 and TGA-40 instruments, respectively, with the heating rate 10 °C min-1 and R-alumina as the standard. Luminescence spectra were recorded on a Hitachi F-4500 fluorospectrophotometer in the range 500-800 nm with the excitation at 475 nm. Luminescence lifetimes were measured by a single-photon counting technique on a Horiba NFL-700 time-resolved luminescence spectrometer equipped with a hydrogen lamp.

Results and Discussion The aqueous suspensions of Na-saponite and C12AO were transparent, showing that the silicate layers are swollen to give small colloidal particles. The organoammonium/clays tend to flocculate in water due to their hydophobicity. On the contrary, the aqueous mixtures of Na-saponite and C12AO were stable suspensions. When the aqueous suspensions of Na-saponite and C12AO were cast, transparent thin films formed on the substrate. During the drying, the adsorbed water molecules are evaporated and nonvolatile C12AO remained in the interlayer space of saponite to give intercalation compounds. The X-ray diffraction patterns of the reaction products between Na-saponite and C12AO at different mixing ratios are shown in Figure 1. The basal spacing increased with the addition of C12AO. When the amount of C12AO was 100 mmol/100 g of clay, which is similar to the typical

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Figure 2. Photograph of the film of the Na-saponite/C12AO intercalation compound prepared on a glass substrate.

cation exchange capacity of smectites, the basal spacing was 1.8 nm. Since the thickness of the silicate layer is approximately 1.0 nm, the expansion of the interlayer space was determined to be 0.8 nm. When dodecylammonium ions were intercalated into the interlayer space of smectites, the interlayer separation was approximately 0.8 nm, where the dodecylammonium ions were arranged as a bimolecular layer with their alkyl chains parallel to the silicate layers. The expansion of the interlayer space by 0.8 nm by the intercalation of C12AO (100 mmol/100 g of clay) suggested that the intercalation of C12AO took place in the interlayer space and that the intercalated C12AO arranged as a bimolecular layer in the interlayer space of Na-saponite with its alkyl chains parallel to the silicate layers. On the other hand, the basal spacings were much larger (ca. 3.6-3.9 nm) when the added amounts of C12AO were 400, 700, and 1000 mmol/100 g of clay. The larger d(001) values were thought to reflect the difference in the arrangements of the intercalated C12AO. Judging from the size of C12AO, the intercalated C12AO has a paraffin type arrangement in the interlayer space of Na-saponite. It has been reported that aliphatic alcohols and amines take paraffin type arrangements in the interlayer space of smectites.40-42 The basal spacings observed in the present system are consistent with those reported for the smectite/dodecylamine and smectites/dodecyl alcohol intercalation compounds. Since the size of the C12AO is close to those of dodecylamine and dodecyl alcohol, the microstructure of the Na-saponite/C12AO intercalation compounds is thought to be similar to those of the smectite/ dodecylamine and smectites/dodecyl alcohol intercalation compounds. It was estimated that the intercalated C12AO forms a bilayer with its alkyl chains inclined to the silicate sheet at approximately 60°. When the added amount of C12AO was 400 mmol/100 g of clay, a broad subsidiary peak with the d value 1.8 nm was observed, suggesting two different arrangements (paraffin type and flat bilayer) of C12AO in the product. (40) Brindley, G. W. Clay Miner. 1965, 5, 95. (41) Brindley, G. W.; Ray, S. Am. Miner. 1964, 49, 106. (42) Ogawa, M.; Kato, K.; Kuroda, K.; Kato, C. Clay Sci. 1990, 8, 31.

With increasing amount of C12AO, the transition from flat bilayer to paraffin type arrangements occurred. When the added amount of C12AO was 1000 mmol/100 g of clay, the X-ray diffraction peak due to C12AO, which did not intercalate into the interlayer space, was observed in the XRD pattern of the cast film. This indicates that the maximum amount of C12AO units to be intercalated is approximately 700 mmol/100 g of clay. The photograph of the thin film of the Na-saponite/C12AO intercalation compound (when the ratio of C12AO is 700 mmol/100 g of clay) is shown in Figure 2. For further characterization, self-standing films of the Na-saponite/C12AO intercalation compounds were prepared by casting the aqueous mixture on a Teflon Petri dish. The photograph of the self-standing film is shown in Figure 3. Since the film is thick compared with the supported films mentioned previously, the film is relatively turbid. The thermal analyses were conducted for the selfstanding film. The TGA and DTA curves of the selfstanding film of the Na-saponite/C12AO intercalation compound are shown in Figure 4. In the TGA curve, a weight loss was observed at around 100-200 °C. Endothermic peaks were observed in the DTA curve at that temperature range, showing that the intercalated C12AO molecules were desorbed at 100-200 °C. Besides the thermal properties, the intercalated C12AO can be easily removed by immersing the Na-saponite/ C12AO intercalation compounds in ethanol at room temperature. These characteristics are apparently different from those of the organoammonium/smectites, where the intercalated organoammonium ions are usually stable at temperatures below 250 °C and leaching the intercalated organoammonium ions by organic solvent is not so easy. The observed stability of the intercalated C12AO in the interlayer space of Na-saponite restricts its applications. The immobilization of photo- and electroactive species is a possible way. However, the introduction of these species into the Na-saponite/C12AO intercalation compounds cannot be accomplished by the methods reported for the organoammonium/clays. The photo- and electroactive species have been introduced into the interlayer spaces of the organoammonium/clays by the

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Figure 3. Photograph of the self-standing film of the Na-saponite/C12AO intercalation compound.

Figure 4. TGA and DTA curves of the self-standing film of the Na-saponite/C12AO intercalation compound.

reactions between the presynthesized organoammonium/ clays and guest species in solutions12-15,22,23 and in the solid state.17-21 To overcome this limitation, coadsorbing guest species should be adsorbed prior to the intercalation of C12AO. Since the cationic guest species are strongly bound to the negatively charged silicate layers with electrostatic interactions and do not deintercalate upon the intercalation of C12AO, the possible effect of coadsorption of C12AO on the states of the preadsorbed [Ru(bpy)3]2+ was investigated. Photochemical and photophysical properties of [Ru(bpy)3]2+ on clay minerals and other layered materials have been investigated extensively.3,4,26-39,43 The adsorbed states of [Ru(bpy)3]2+ on the surfaces of smectites have successfully been controlled by the coadsorption of [Zn(bpy)3]2+, [Co(bpy)3]2+, and poly(vinyl pyrrolidone).29,38,39 In the present system, the adsorption of C12AO was expected to alter the states of the adsorbed [Ru(bpy)3]2+ on saponite. The adsorption of [Ru(bpy)3]2+ on Na-saponite was conducted by a conventional ion exchange method. The change in the XRD pattern upon the intercalation of C12AO, when the amounts of added [Ru(bpy)3]2+ and C12AO were 1 and 400 mmol/100 g of clay, respectively, is shown in Figure 5. To avoid the flocculation of clay particles and minimize the dye-dye interactions, the amount of [Ru(bpy)3]2+ was adjusted to 1 mmol/100 g of

Figure 5. X-ray diffraction patterns of the [Ru(bpy)3]2+/Nasaponite intercalation compounds before and after the intercalation of C12AO. The adsorbed amounts of [Ru(bpy)3]2+ and C12AO are 1 and 400 mmol/100 g of clay.

clay. The basal spacing of the [Ru(bpy)3]2+/Na-saponite intercalation compound increased from approximately 1.4 nm to 3.8 nm, showing that the C12AO molecules have been intercalated into the interlayer space of the [Ru(bpy)3]2+/Na-saponite intercalation compound. The amount of C12AO to be intercalated into the [Ru(bpy)3]2+/Nasaponite intercalation compound was lower if compared with those (700 mmol/100 g of clay) intercalated into the original Na-saponite. It was thought that the adsorbed [Ru(bpy)3]2+ prevents the access of C12AO to the silicate surface. A further decrease in the adsorbed amount of C12AO was observed with increasing loading amount of [Ru(bpy)3]2+. The luminescence spectra of the [Ru(bpy)3]2+/Na-saponite intercalation compound before and after the intercalation of C12AO are shown in Figure 6. The luminescence LMCT band of [Ru(bpy)3]2+ did not change significantly upon the adsorption on Na-saponite. This is consistent with those reported for related [Ru(bpy)3]2+layered silicate systems.28,38 By the coadsorption of C12AO, the luminescence maximum shifted toward the shorter wavelength region from 596 to 581 nm. When the

Preparation of Intercalation Compounds

Figure 6. Luminescence spectra of the [Ru(bpy)3]2+/Nasaponite intercalation compounds before and after the intercalation of C12AO. The adsorbed amounts of [Ru(bpy)3]2+ and C12AO are 1 and 400 mmol/100 g of clay.

loading amount of C12AO was 100 mmol/100 g of clay, an [Ru(bpy)3]2+/Na-saponite/C12AO intercalation compound with the basal spacing of approximately 1.7 nm was obtained. A similar luminescence blue shift from 596 to 583 nm was observed by the intercalation of C12AO. Since the luminescence lifetime (ca. 1 ms) of [Ru(bpy)3]2+ did not change by the intercalation of C12AO, self-quenching due to [Ru(bpy)3]2+ aggregation is negligible in the present system. Accordingly, the luminescence shifts by the C12AO intercalation were ascribed to the change in the surroundings of moleculary dispersed [Ru(bpy)3]2+ on the saponite surface. When [Ru(bpy)3]2+ was incorporated in the micelle,44 the luminescence maxima shifted toward red. Colo´n and co-workers found a concentration dependence of the absorption and the luminescence maxima for [Ru(bpy)3]2+ intercalated in zirconium phosphate sulfophenylphosphonate with different loadings and attributed the spectral shifts to a hydrocarbon-like environment both to neighboring bpy and to the hydrophobic nature of the phenyl rings.43c On the other hand, Wheeler and Thomas observed a luminescence blue shift upon the adsorption of [Ru(bpy)3]2+ on colloidal silica and explained that the rigid nature of the environment prevented the excited state from fully relaxing to cause the emission blue shift.45 The [Ru(bpy)3]2+ adsorbed on TiO2 and SiO2 also showed luminescence blue shifts due to the attachment to the surface.46,47 When [Ru(bpy)3]2+ was adsorbed in cellulose, (43) (a) Vliers, D. P.; Schoonheydt, R. A.; de Schrijver, F. C. J. Chem. Soc., Faraday Trans. 1 1985, 81, 2009. (b) Vliers, D. P.; Collin, D.; Schoonheydt, R. A.; de Schryver, F. C. Langmuir 1986, 2, 165. (c) Colo´n, J. L.; Yang, C.-Y.; Clearfield, A.; Martin, C. R. J. Phys. Chem. 1988, 92, 5777. (d) Colo´n, J. L.; Yang, C.-Y.; Clearfield, A.; Martin, C. R. J. Phys. Chem. 1990, 94, 874. (e) Giannelis, E. P.; Nocera, D. G.; Pinnavaia, T. J. Inorg. Chem. 1987, 26, 203. (f) Nakato, T.; Sakamoto, D.; Kuroda, K.; Kato, C. Bull. Chem. Soc. Jpn. 1992, 65, 322. (g) Nakato, T.; Kusunoki, K.; Yoshizawa, K.; Kuroda, K.; Kaneko, M. J. Phys. Chem. 1995, 99,17896. (h) Jakubiak, R.; Francis, A. H. J. Phys. Chem. 1996, 100, 362. (i) Ogawa, M.; Maeda, N. Clay Miner., in press. (44) Kunjappu, J. T.; Somasundaran, P.; Turro, N. J. J. Phys. Chem. 1990, 94, 8464. (45) Wheeler, J.; Thomas, J. K. J. Phys. Chem. 1982, 86, 4540. (46) Kajiwara, T.; Hashimoto, K.; Kawai, T.; Sakata, T. J. Phys. Chem. 1982, 86, 4516. (47) Dvorak, O.; De Armond, M. K. J. Phys. Chem. 1993, 97, 2646.

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the luminescence spectra changed around the melting point of the cellulose.48 It was supposed that an increased possibility for relaxation in a more fluid state caused the spectral shift. Incavo and Dutta have reported that the [Ru(bpy)3]2+ adsorbed in zeolite Y exhibits luminescence blue shifts upon dehydration.49 They concluded that the highly polar environment within the zeolite, without the mediation from water molecules, serves to destabilize and raise the energy of the dipolar excited state. In the present system, the coadsorbed C12AO gave a rigid environment for the [Ru(bpy)3]2+ in the interlayer space probably due to the ordered microstructures of the intercalated C12AO. The polarity of the hydrophilic head group of C12AO may also affect the excited state of [Ru(bpy)3]2+. A similar luminescence shift from 596 to 583 nm was observed for the aqueous suspension of the [Ru(bpy)3]2+/ Na-saponite intercalation compound by the addition of C12AO. This spectral shift indicates the added C12AO interacts with the silicate layer even in the presence of solvent. The coadsorption of C12AO reported in the present paper was proved to be a way to control the photoprocesses of [Ru(bpy)3]2+ on the surface of smectites. However, the amounts of cointercalating C12AO decreased with an increase in the adsorbed amounts of [Ru(bpy)3]2+. This again limits the applicability of the saponite/C12AO intercalation compounds as immobilizing media for photoactive species. It was thought that the preadsorbed [Ru(bpy)3]2+ ions covered the surface of saponite to prevent the dispersion of saponite into water and the intercalation of C12AO. Conclusions Na-saponite/C12AO intercalation compounds have been prepared as supported and unsupported films. C12AO forms a paraffin type bilayer in the interlayer space of Na-saponite when the adsorbed amount of C12AO was greater than 400 mmol/100 g of clay. On the other hand, the intercalated C12AO is thought to arrange as a bimolecular coverage with the alkyl chain parallel to the silicate sheet when the added amount of C12AO was 100 mmol/100 g of clay. The thin films deposited on a transparent support showed transparency applicable for spectroscopic studies. Coadsorption of [Ru(bpy)3]2+ with C12AO has been achieved and characterized by the changes in the basal spacing as well as the variation of the luminescence characteristics of the adsorbed [Ru(bpy)3]2+. Since the products have been obtained as highly transparent supported and self-standing films, the intercalation of C12AO is a way to control the adsorbed states of cationic dyes on the surface of smectites. Acknowledgment. The present work was partially supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture. Waseda University also supported us financially as a Special Project Research. LA980173Q (48) Milosauljevic, B. H.; Thomas, J. K. Chem. Phys. Lett. 1985, 114, 133. (49) Incavo, J. A.; Dutta, P. K. J. Phys. Chem. 1990, 94, 3075.