4598
Langmuir 1995,11, 4598-4600
Intercalation of Pyrene into Alkylammonium-Exchanged Swelling Layered Silicates: The Effects of the Arrangements of the Interlayer Alkylammonium Ions on the States of Adsorbates Makoto Ogawa,**+JTetsuya Wads,$ and Kazuyuki KurodaSJl
The Institute of Physical and Chemical Research (RIKE", Hirosawa 2-1, Wako-shi, Saitama 351-01, Japan, Department of Applied Chemistry, Waseda University, Ohkubo-3, Shinjuku-ku, Tokyo 169, Japan, and Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, Nishiwaseda 2-8-26, Shinjuku-ku, Tokyo 169, Japan Received May 26, 1995. I n Final Form: August 14, 1995
Introduction Photoprocesses of aromatic hydrocarbons adsorbed on various solid surfaces have revealed important information on the surface properties of solids. For example, fluorescence of pyrene has been used as a measure of the mobility of molecules on surfaces and the polarity of environments. The microstructure of various supramolecular systems both natural and synthetic has been studied using spectroscopic probe mole~ules.l-~ Swelling layered silicates such as the smectite group of layered clay minerals possess various attractive features such as the swelling behavior, ion exchange properties, adsorptive properties, and large surface area4for studies on organizingphotoactive specie^.^,^ If a clay mineral has metal cations in the cation exchange sites, its surface is hydrophilic and is often not a good adsorbent for poorly water-soluble organic species which cannot compete with highly polar water for adsorption on the clay mineral surfaces. However, when the interlayer metal cations are replaced by organoammonium cations, the surfaces of the clays are substantially modified to become strongly ~rganophilic.~ The organophilic clays have been studied as ads or bent^,^,^ catalysts,1°controlled permeability membranes,ll and rheology controlling agents.12 Recently, immobilization of photoactive species in the interlayer spaces of alkylammonium-exchanged montmorillonites has been reported.l3-lg It has been revealed that the
' The Institute of Physical and Chemical Research (RIKEN). Present Address: Institute of Earth Science, Waseda University, Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-50,Japan 8 Department of Applied Chemistry, Waseda University. 'I Kagami Memorial Laboratory for Materials Science and Technology, Waseda University. (1)Photochemistry in Organized & ConstrainedMedia; Ramamurthy, V.. Ed.: VCH Publishers. Inc.: New York. 1991. '(2) Turro, N. J.; Gratzel, M.; Braun, A.'M. Angew. Chem., Int. Ed. Engl. 1980,19,675. (3)Winnik, F. Chem. Rev. 1993,93,587. (4) Theng, B. K. G. The Chemistry of Clay Organic Reactions; Adam Hilger: London, 1974. (5)Ogawa, M.; Kuroda, K. Chqm. Reu. 1995,95, 399. (6)Thomas, J. K. Ace. Chem. Res. 1988,21,275. (7)Jordan, J.W. J. Phys. Colloid Chem. 1950,54,294. ( 8 ) Boyd, S. A.; Lee, J. F.; Mortland, M. M. Nature 1988,333,345. (9)Bondarenko,S.V.;Zhukova,A. I.: Tarasevich.Y. I. J . Chromatom 1982,241,281. (10)Rusling, J.F.Acc. Chem. Res. 1991,24, 75. (11)Okahata, Y.; Shimizu, A. Langmuir 1989,5,954. (12) Jones, T.R. Clay Miner. 1983,18, 399. (13)Seki, T.; Ichimura, K. Macromolecules 1990.23,31. (14)Tomioka, H.; Itoh, T. J. Chem. SOC.,Chem. Commun. 1991,532. (15) Takagi, K.; Kurematsu, T.; Sawaki, Y. J . Chem. SOC.,Perkin Trans. 2 1991.1517. (16)Ogawa,'M.;Fujii, K.;Kuroda, K.; Kato, C. Mater. Res. SOC.Symp. Proc. 1991,233, 89. (17)Ogawa, M.; Shirai, H.; Kuroda, K.; Kato, C. Clays Clay Miner. 1992,40,485.
Table 1. The Basal Spacings and the Adsorbed Amounts of the Alkylammonium Ions for the Alkylammonium-Exchanged Materials
host
basal spacing/ nm
ODTMA-saponite DMDODA-saponite ODTMA-TSM DMDODA-TSM
1.5 2.2 2.2 3.2
adsorbed amount of alkylammonium ions/ (milliequiv/100 g silicate) 67 89
105
assembly of the intercalated alkylammonium ions acts as a novel support for organizing organic molecules. We have successfully introduced aromatic hydrocarbons (naphthalene, anthracene1' and pyrene9 into alkylammonium-montmorillonites by solid-solid reactions.20 Interestingly, the adsorbed states of pyrene and anthracene differ depending on the intercalated alkylammonium ions. In order to investigate the difference further, layered silicates with different cation exchange capacities were used as the host materials. In this paper, we will report the intercalation of pyrene into alkylammonium-saponite and fluor-tetrasilicic micas and discuss the effect of the arrangements of the interlayer alkylammonium ions on the states of the adsorbed pyrene.
Experimental Section Sodium-saponite (Sumecton SA supplied from Kunimine Industries Co., synthesized by a hydrothermal reaction), synthetic sodium-fluor-tetrasilicic mica (abbreviated as Na-TSM, supplied by Topy Ind. Co.) and sodium-montmorillonite (Kunipia F, Kunimine Industries Co.; reference clay sample (The Clay Science Society of Japan)) were used as the host materials. The cation exchange capacities of Na-saponite, Na-TSM, and Namontmorillonite are 70, 120, and 119 milliequiv/100 g of host, respectively. Octadecyltrimethylammonium- and dimethyldioctadecylammonium ( C I E H ~ ~ ( C H ~and ) ~ N (C18H37)2(CH&Nf; + abbreviated as ODTMA- and DMDODA-,respectively) exchanged TSMs, montmorillonites, and saponites were prepared by a conventional ion exchange method using aqueous solutions of the appropriate organoammonium chlorides. Intercalation of pyrene into these alkylammonium silicates was carried out by solid-solid reaction^.^^.'^ The reaction products were characterized by X-ray diffraction, emission spectra, etc. as reported previously.18
Results and Discussion The basal spacings and the amounts of adsorbed alkylammonium ions of the alkylammonium-saponite and TSMs are listed in Table 1. Judging from the cation exchange capacity of the host materials, the interlayer sodium cations were replaced with organoammoium ions quantitatively. From the observed basal spacings, alkylammonium ions are arranged as pseudo-trimolecular layers with their alkyl chains parallel to the silicate sheet in ODTMA-TSM as is schematically shown in Figure la.21 For DMDODA-TSM, two types of arrangements are expected; one is monomolecularcoverage with the alkyl chains inclined to the silicate sheets at ca. 53" and the other is bimolecular coverage with the alkyl chains inclined to the silicate sheet at ca. 23" (Figure lb). Thus, the (18)Ogawa, M.; Aono, T.; Kuroda, K.; Kato, C. Langmuir 1993,9, 1529. (19)Ahmadi, M. F.;Rusling, J. F. Langmuir 1995,11, 94. (20) Ogawa, M.; Kuroda, K.; Kato, C. Chem. Lett. 1989,1659.Ogawa, M.;Handa, T.; Kuroda, K.; Kato, C. Chem. Lett. 1990,71.Ogawa, M.; Kato, K.; Kuroda, K.; Kato, C. Clay Sci. 1990,8, 31. Ogawa, M.; Hashizume,T.; Kuroda, K.; Kato, C. Inorg. Chem. 1991,30,584. Ogawa, M.; Handa, T.; Kuroda, K.; Kato, C. Chem. Lett. 1992,365.Ogawa, M.; Nagafusa, Y.; Kuroda, K.; Kato, C. Appl. Clay Sci. 1992,7,291. (21) Lagaly, G. Clay Miner. 1981,16, 1.
0743-746319512411-4598$09.00/0 0 1995 American Chemical Society
Langmuir, Vol. 11, No. 11, 1995 4599
Notes pseudo-trimolecularlayer
paraffintype
(a)
(b)
(C)
Figure 1. Schematic drawing for the arrangements of the
.-
c,
alkylammonium ions in the interlayer spaces.
v)
C c Q) ,
C
28/'
(FeKa)
Figure 3. The X-ray diffraction patterns of (a) DMDODATSM and (b-d) the DMDODA-TSM-pyrene intercalation compounds in which pyrendC18 = 1/10 (b), l/6 (c), and U0.34
(a).
28/'
(FeKa)
Figure 2. The X-ray diffraction patterns of (a) DMDODAsaponite and (b-d) the DMDODA-saponite-pyrene intercalation compounds in which pyrendC18 = 1/10 (b), l/6 (c), and ll0.24 (d).
arrangements of the alkylammonium ions intercalated in TSM are similar to those in montmorillonite. On the other hand, due to the difference in the cation exchange capacity (directly correlated to the layer charge density), the arrangements of the interlayer alkylammonium ions in saponite are different. The intercalated DMDODA ions are arranged as pseudo-trimolecular layers with their alkyl chains parallel to the silicate sheets. Since the arrangements of the DMDODA ions differ depending on the layer charge density of the hosts, the adsorption behavior of pyrene will give information on the different states of adsorbed aromatic molecules reported previously. It is difficult to estimate the arrangements of the ODTMA ions in the interlayer space of saponite because the observed basal spacing (1.5 nm) is just between those expected for the bimolecular and monomolecular coverage of the alkyl chains in the interlayer space. Due to the lower number of alkyl chains in the interlayer space, lower hydrophobicity is expected for the ODTMA-saponite. The X-ray diffraction patterns of the reaction products between the DMDODA-saponite and pyrene are shown in Figure 2. After the reaction, a new broad d(001) diffraction peakwith a basal spacingofca. 3.3 nm appeared and the intensity of the d(001) diffraction peak due to the unreacted DMDODA-saponite (d(001) = 2.2 nm) decreased. Thus, pyrene molecules were intercalated into the interlayer space of the DMDODA-saponite by the solid-solid reaction. On the other hand, solid-state intercalation of pyrene into ODTMA-saponite was unsuccessful. It is consistent with the results reported previously on the solid-state intercalation of naphthalene and anthracene into alkylammonium-montmorillonites. Lower hydrophobicity of the interlayer spaces of ODTMAsaponite is thought to be responsible for the observed reactivity.
After the reaction between ODTMA-TSM and pyrene, a new d(001) diffraction peak with a basal spacing of ca. 3.6 nm appeared and the intensity of the d(001)diffraction peak due to the unreacted ODTMA-TSM (d(001) = 2.2 nm) decreased. The increased amount of pyrene caused the 3.6 nm increase of the d(001)peak and the appearance of the peaks due to excess pyrene crystal in the XRD pattern of the product. Intercalation of pyrene into DMDODA-TSM gave a different result. The change in the XRD patterns with the increase in the ratio of pyrene to host is shown in Figure 3. After the reaction with pyrene, the d(001) diffraction peak of DMDODA-TSM shifted toward the lower 28 region, showing the expansion of the interlayer space. The basal spacings increased gradually up to 4.1 nm depending on the relative amount of added pyrene. Larger amountsof pyrene did not lead to W h e r expansion of the interlayer space; and the excess amount of pyrene was detected by XRD. This behavior is similar to that observed for the intercalation of anthracene and pyrene into the alkylammonium-montmorillonites.18 Thus, pyrene was intercalated into the interlayer spaces. of the DMDODA-saponite, ODTMA-TSM, and DMDODA-TSM. The changes in the XRD patterns upon the intercalation of pyrene are classified into two types by the arrangements of the interlayer alkylammonium ions. The spectroscopic behavior of the products showed the different states of the intercalated species. When pyrene is forced into close proximity or in high concentration solution, excited state dimers (excimers)are observed. 1-3 The ratio of excimer to monomer fluorescence intensity obtained from emission spectra is often utilized as a measure of pyrene mobility and proximity. The emission spectra (excitationwavelength is 310 nm) of DMDODAsaponite-pyrene, ODTMA-TSM-pyrene, and DMDODA-TSM- pyrene intercalation compounds, in which the amounts of adsorbed pyrene were almost identical (the ), are shown in Figure ratio of pyrene/alkyl chain = 1/622 4. The emission spectra showed no excitation wavelength dependence. In the spectra, monomer fluorescence with (22) In order to compare the emission spectra, the loaded amount of pyrene was adjusted on the basis of the amountof the interlayer alkyl chain.
Notes
4600 Langmuir, Vol. 11, No. 11, 1995
/ nm Figure 4. The emission spectra of (a) the DMDODAsaponite-pyrene, (b) the ODTMA-TSM-pyrene, and (c) the DMDODA-TSM-pyrene intercalationcompounds (pyrendC18 Wavelength
= ll6).
Table 2. The Ratio of Excimer to Monomer Fluorescence Intensity (ZE/lhl)
relative amount of pyrene PylC18 = PyIC18 = PylC18 = host DMDODA-saponite ODTMA-TSM DMDODA-TSM
ODTMA-montmorillonite DMDODA-montmorillonite
1130
1/10
116
0.084 0.17 0.051
0.30 0.22 0.10 0.25 0.082
0.50 0.34 0.16 0.49 0.12
vibrational structure was observed at around 400 nm together with the broad peak due to excimer emission (500 nm). From the fluorescence spectra of the intercalation compounds, the ratios of excimer to monomer ( Z ~ Z Mwere ) determined and the values are listed in Table 2. The value observed for the DMDODA-saponite-pyrene intercalation compound (0.50) is relatively high if compared with that (0.12) for the DMDODA-montmorillonite system. As reported previously, the adsorbed anthracene and pyrene molecules are thought to be aggregated in the interlayer space of ODTMA-montmorillonite while those in DMDODA-montmorillonite are dispersed. From the 1dIh.1value observed for the DMDODA-saponite-pyrene intercalation compound, the intercalated pyrene molecules are thought to be aggregated in the interlayer space of DMDODA- saponite. On the other hand, the Z d Z M values were 0.34and 0.16 for the ODTMA- and DMDODA-TSM systems, respectively. The ratio for the DMDODA-TSM system is ‘12
that for the ODTMA-TSM system, suggesting that the adsorbed pyrene molecules are isolated in the interlayer space of DMDODA-TSM if compared with those doped in ODTMA-TSM. This intercalation behavior of pyrene into TSMs is similar to that into montmorillonites.’* It should be noted here that the emission intensity observed for the TSM systems is much higher than that observed for the montmorillonite systems. The impurities such as iron atoms which are involved in montmorillonite are thought to quench the excited state of the adsorbed pyrene. When the loaded amounts of pyrene were changed to the ratios of pyrene/alkyl chain = 1/10 and 1/30, the tendency to form excimers is similar to that when the amounts of pyrene were pyrene/alkyl chain = 1/6. The I ~ Z values M observed when the amounts of pyrene were changed to pyrene/alkyl chain = 1/10 and 1/30 are also listed in Table 2. In ODTMA-montmorillonite, ODTMATSM, and DMDODA-saponite, the adsorbed pyrene molecules tend to form excimers while those in the DMDODA-montmorillonite and TSM are dispersed. The intercalation of pyrene into the alkylammonium silicates studied here is classified into two types: (1)the intercalation of pyrene into DMDODA-saponite, ODTMA-montmorillonite, and ODTMA-TSM, where the interlayer alkylammonium ions are arranged as apseudotrimolecular layer and (2) the intercalation into DMDODA-montmorillonite and DMDODA-TSM, where the intercalated alkylammonium ions form a paraffin type aggregate. In type 1,the adsorbed pyrene tends to form an excimer while the adsorbed pyrene is dispersed molecularly in type 2. It has been shown that the arrangements of the interlayer alkylammonium ions play an important role in the difference in the states of the adsorbed pyrene. In other words, the adsorbed states of pyrene can be controlled microscopically by changing the arrangements of the alkylammonium ions in the interlayer spaces. This can be achieved by the selection of the size of the alkylammonium ions and the layer charge density of the host materials.
Acknowledgment. This work was supported in part by a grant for “Special Researcher’s Basic Science Program” from the Science and Technology Agency of the Japanese Government. LA950408N
