3423
J . Phys. Chem. 1992,96. 3423-3428 Fe substitutes primarily in the CuO layers, it is apparent that the interaction between the CuO and BiO layers must determine in part the superstructure. We suggest that the Cu apical oxygen which directly links the CuO and BiO layers (Figure 1) probably drives the disorder in the superstructure as a consequence of the difference in the Fe-O-Bi versus Cu-O-Bi bonding. The significance of the CuO and BiO lattice mismatch has also been discussed in previous diffraction investigations where it was suggested that the superstructure could be eliminated by substitution of the larger Pb2+ ( r = 1.33 A) cation for Bi3+( r = 1.17 A) in the BiO layer. In these studies no modulation was detected in diffraction data obtained on Pb-substituted Bi2Sr2CuOyand BiPbSr2MOy(M = Mn, Fe, Co) material^.^^"^ Comparison of the STM and electron diffraction data for the Fe-doped system indicates that this conclusion may not be correct. We find that the superlattice peaks do become weaker with Fe substitution (as with Pb doping); however, the STM data demonstrate that this is due to increased disorder in the superlattice which reduces and ultimately eliminates the long-range coherence needed to observe d i f f r a ~ t i o n . ~STM ~ can thus provide unique insight into the microstructure of these materials. Lastly, we consider further the atomic structure of the BiO layer of Bi2,2Sr,,sCuOy,Bi2.2Srl,sC~0,gFe0,10y, and Bi2Sr2CaCu208.In all three materials the average lattice constant observed in the STM images, 3.8 A, could correspond to the Bi-Bi or 0-0 distance. The similarity in the atomic structures suggests that the surface electronic states near the Fermi level, which are imaged by the STM, are similar for these three compounds. In contrast, recent photoemission spectroscopy (PES) data indicate that the T bands of the Bi-O layer do not cross the Fermi level (Le., they are unoccupied) in Bi2Sr2CuOy but are partially filled in B~,S~,C~CU~O Since , . ~ ~it is possible that different crystal (33) Manivannan, V.;Gopalakrishnan, J.; Rao, C. N. R. Phys. Reo. B 1991, 43, 8686. (34)Tarascon, J. M.; Page, Y.Le; McKinnon, W. R.; Ramesh, R.; Eibschutz. M.: TseleDis. E.: Wana. E.;Hull. G. W. Phvsica C 1990. 167. 20. (35) Fukushima, N.;Niu, k.; Nakamura, S.;Tikeno, S.;Hayashi, M.; Ando. K. Physica C 1989, 159, 771. (36)STM studis of Pbsubstituted Bigr,CuO, show that a superstructure
is present in these materials, although it exhibits significant disorder. The modulation is not detected by diffraction measurements since it lacks long range coherence: Liu, J.; Lieber, C. M. Unpublished results.
preparations may also contribute to the electronic character of the BiO layer, we cannot make a certain conclusion from the PES data at this point.10.12*16It will be important in the future to investigate by STM compositionally similar crystals that have electronically distinct BiO layers (these could be prepared using different annealing conditions) to address this point. There are, however, significant differences in the BiO layer atomic structure imaged in the pure and Fe-substituted materials. These differences indicate that either the surface BiO layer structure and/or electronic states are locally perturbed by the Fe in the underlying Cu(Fe)O layer or that the STM detects directly electronic states in the Cu(Fe)O layer. At present, we cannot unambiguously distinguish between these possibilities, although studies of the distance dependence of tunneling may resolve this que~tion.I~*~’
Conclusions In summary, STM has been used to characterize the surface structure of cleaved single crystals of Bi2,2Srl,sCuOyand Bi2,zSrI,8CuosFeo,10y with atomic resolution for the first time. High-quality atomic resolution images of the BiO layer of Biz,2Sr,,8CuOy show an incommensurate superstructure with a period of 25.1 f 0.3 A and an average atomic lattice spacing of 3.8 f 0.2 A. The atomic structure in these images is ordered and shows no evidence for local distortions due to Sr2+substitution and/or extra oxygen in the BiO layer. The substitution of Cu with Fe causes distortions in the surface atomic structure and superstructure. Analyses of real-space images, 2DFT power spectra, and electron diffraction data show that the superstructure retains on average its one-dimensional character. The real-space STM data provide, however, detailed insight into the changes in the microstructure caused by Fe doping that cannot be detected by diffraction-based techniques. These data indicate that a mismatch between the BiO and CuO lattices is probably the dominant factor causing the one-dimensional modulation, although other effects may perturb this structure. Acknowledgment. C.M.L. acknowledges support of this work by the National Science, David and Lucile Packard, Alfred P. Sloan, and Camille and Henry Dreyfus Foundations. ~~~
~
~~
( 3 7 ) Zhang, Z . ; Lieber, C. M. J . Phys. Chem. 1992, 96, 2030
Collection Optics of TiO, Photocatalyst on Hollow Glass Microbeads Floating on Oil Slicks I. Rosenberg,* J. R. Brock,* and A. Heller* Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (Received: October 9, 1991; In Final Form: December 19, 1991)
We analyze the optics of sunlight collection in hollow glass microbead attached TiO, particles floating on oil slicks, photoassisting their dissolution. This technology uses glass microbeads that float on the oil slick. The microbeads are partially coated with a layer of 3.0-3.3-eV bandgap Ti02,a known catalyst for the photoassisted oxidation of organics. The fraction of the UV solar irradiance (A = 360 nm) directly and indirectly exciting the Ti02 photocatalyst is calculated. It is shown that a glass microbead collects most of the sunlight, channeling it to the attached photocatalyst particles. Therefore, 30-40% coverage of the microbeads is optimal for photodissolving oil slicks. Here, the collection optics of the floating, coated microbeads is analyzed.
Introduction Our p r o p 4 method developed for solar-awisted oxidation of oil slicks involves the use of the classical semiconducting photocatalyst titanium dioxide. Upon absorption of a photon, an electron-hole pair is generated in the Ti0, microcrystal. The
electron may react with surface-adsorbed oxygen, reducing it to hydrogen peroxide; the hole oxidizes adsorbed water to OH radicals and photons; the O H radicals oxidize in turn adsorbed organic compounds. Titanium dioxide is denser than either oil or seawater; the density of the anatase phase is 3.8, and that of
0022-3654/92/2096-3423%03.00/0 0 1992 American Chemical Society
Rosenberg et al.
3424 The Journal of Physical Chemistry, Vol. 96, No. 8, 1992
I
bead, n = l . 5 3
Figure 2. Schematic diagram of the trajectories of several rays absorbed by bead-attached TiO, crystallites.
strongly UV-light-absorbing crudes. Figure 1. Hollow glass microbead partially covered by titanium dioxide floating in oil; half of the bead surface is irradiated by direct sunlight. The depth of immersion is 0.1%) (Dis the external diameter of the bead).
rutile is 4.3. To keep the titanium dioxide at the air/oil interface, it is attached to a low-density, floating material. Specifically, for experimental purposes we have attached the photocatalyst particles to commercially available inexpensive hollow glass microbeads of about 80-” diameter. To determine the fraction of the solar UV flux captured by the Ti02-coated hollow glass microbeads of arbitrary diameter floating at the oil/air interface, the optics of the system is analyzed. The procedures and results of this analysis are presented here. First, the optical model is briefly described, followed by exposition of the theory used in the analysis. The collection optics depends on the complex refractive indexes of the glass, of the Ti02, and of the oil in the UV band of interest-that is, 35&360 nm. Depending on their composition, the aluminosilicateglasses used have real indexes ranging from 1.48 to 1.73 at 350 nm. Both the literature and our measurements show that crude oils absorb strongly in the UV. The absorbances of three crude oils (Arab light, Arab heavy, Basrah light) at 350 nm are in the range (1.5-3.0) X lo4 cm-l. Thus a 2-pm-thick layer of one of these crudes absorbs 95% of the solar UV flux at 35&360 nm. Therefore, it is essential that the hollow glass beads have sufficiently low density to float on the surface at the air/oil interface.
Description of the Model For the purpose of modeling we consider hollow beads of arbitrary diameter with shells made of perfectly transparent aluminosilicate glass and a shell thickness about 10%of the diameter. The depth of immersion of a bead in an oil slick depends on the viscosity of the oil and its surface properties (which both vary with age of slick,12J3temperature,14 etc.) as well as on the density of the bead itself. Therefore, for our initial estimate, we will assume that the bead is floating as shown in Figure 1. The incoming radiation was taken to be monochromatic of unit intensity at 360 nm and made an angle of 45O with the surface. The photon flux absorbed by the Ti02 particles has two components, an outer and inner flux, as indicated by Figure 1. The outer flux involves absorption of solar photons that pass only through the atmosphere, for example, ray A, Figure 2. The inner flux is composed of photons refracted into the bead at the air-glass interface and are subsequently absorbed by the attached Ti02, for example, ray B or ray C, Figure 2. The collection of sunlight is analyzed for beads at varying photocatalyst coverages and varying immersion in the
”ry
We first analyze the optimum coverage of the microbead surface by the photocatalyst, Ti02. We define an effectiveness function E of microbead coverage by monocrystals of Ti02: E = (labsorb/linc)
/ (STiOz/Sbead)
l a h r b / l i n c is the fraction of the incident solar flux at 360 nm absorbed by the Ti02. STo,/Sbdis the fraction of the microbead surface area covered by T i 0 2 monocrystals. The absorption of light depends on the position on the microbead surface of the Ti02 layer relative to the zenith angle of the sun. Therefore, we have performed a series of calculations for different Ti02 monocrystal beadsurface distributions and coverages. We introduce an angular absorption function (AAF) that relates the absorbed light with the Ti02 monocrystal layer’s “center” polar angle A(+) for a layer of area S. Assuming that occupation of all positions on the bead’s surface by the Ti02layer have uniform probabilities, we can consider an angle-averaged absorption A, by a Ti02 crystalline layer (regardless of its position on the glass bead); Aav depends for optically thick crystallites only on the covered area T of the bead. This is Aav(q
= 1/r J~*A(T,+) d+
(1)
where A( T,+) is the amount of energy absorbed by a Ti02 layer of area T with its center at the polar angle Similarly, for microbeads of irregular shape it is necessary to define
+.
where u and u are the current coordinates of the microbead surface and dS is a surface element. It also may be necessary to consider the probability distribution P(u,u) of the position of the Ti02 crystallite layer on the surface of the bead. P(u,u) will depend on physical and chemical factors such as surface tension, density of the oil, the way the photocatalyst is attached to the bead, etc. So, eq 2 can be generalized as Aav(q
=
S,A(T,W)
P(U,U)
a/Ju S
(3)
For example, when the monocrystal Ti02 layer is thick and the glass microbead shell is thin enough so that their weights are comparable, the Ti02 layer is likely to be found at the submerged pole of the microbead. In this case P(u,u) would be P(u,u) = 6(u - 240) 6(u - uo) (4)
The Journal of Physical Chemistry, Vol. 96, No. 8, 1992 3425
Collection Optics of T i 0 2 Photocatalyst
b '"1
330
340
350
360
370
W wavelenght, nm
Faure 5. Absorbance of several Middle East crudes: m, Arab light; +, Arab heavy; m, Basrah light. 1464 280
.
,
.
, 320
300
340
360
400
380
d
Wivclcnth (nm)
Figure 3. Dispersion of oil and fused quartz. A, oil; B, fused quartz. 18
17
16
270
Figure 6. Absorbed UV fraction A (6)for 2% ( O ) , 4% (+), and 6% (W)
1
of bead surface coverage by Ti02. Arrow shows the direct solar flux.
is
15
I 4
20
60
40
Cwnpwion (mole% ofAI 0 2
90
1
Figure 4. Refractive indexes of aluminosilicate glasses as a function of their relative composition.
where uo and uo are the coordinates of the submerged layer -center" and 6 designates the 6-function. Thus, from (4)and (3)
= A(T,uo,uo)
(5)
The solar flux incident on the glass microbead is reflected and refracted according to the hell's law and the Fresnel formulas (separately for the s and p components). It is a function of the indexes of refraction of the glass (N= 1.53),' oil (N= 1.56)2and T i 0 2 for rutile (N= 3.87))s' at X = 360 nm. [Here and below, (1) Bansal, N. P.; Doremus, R. H. Handbook of Glass Properties; Academic Press: Orlando, FL, 1986; Table 16.17. (2) Al'perovich, L. I.; Komarova, A. 1.; Narziev, B. N.; Pushkarev, V. N. Sou. 1. Appl. Spectrosc. 1918, 28, 491-494.
by the term index of refraction will refer only to its real part.] For silica glass and oil the variation in the indexes with wavelength, Le., dispersion in the near UV does not e x 4 1% (Figure 3). However, the index of aluminosilicate glasses (A1203-Si02) depends strongly on their alumina content (Figure 4). In our model any T i 0 2 monocrystallite layer is considered to be continuous, having boundaries that are parallel to the surface of the bead and thick enough to absorb all of the photons with energies exceeding the bandgap. Provided the bead density is much less than the density of the oil, the beads are floating on the surface as shown in Figure 1. The authors measured the UV absorbance of some crude oil sampks from the Middle East. The results of these measurements arc presented in Figure 5. This shows that the W light is strongly absorbeel by the crudes. As described above, in the calculations we considered a norn u a l i d paralkl incident radiation, with the wavelength set at X = 360 nm. The.characteristic distances are considerably larger than A, so that diffraction may be neglected and Monte Carlo methods5 with geometric optics6*'are applied. We calculated the (3) Palic, E. D. Handbook of Optical Conrtants of Solids; Academic Press: Orlando, FL, 1985; Table XIV. (4) Cardona, M.; Harbeke, G. fhys. Rev. A 1965, 137, 1467-1494. (5) Shreider, I. U.A. Method of statistical testing, Monte Carlo method Elsevier: Amsterdam, 1964. (6) Born, M.; Wolf, E. Principles of Optics; Electromagnetic Theory of Propagation, Interference and Difjraction of Light; Pergamon: New York, 1980.
3426 The Journal of Physical Chemistry, Vol. 96, No. 8, 1992
\
Rosenberg et al.
90
.Aav=.654 .Aav=.578 Aav=.438
-oil 270
Figure 7. Absorbed UV fraction A (4) for 34%(El), 50%(4), and 66% (m) of bead surface coverage by Ti02. Arrow shows the direct solar flux.
Figure 9. Hollow glass microbead partially covered by titanium dioxide deeply immersed in oil. The depth of immersion is 0.850 ( 0 is the external diameter of the bead).
0.0
0.2
0.4
0.6
Fraction of microbead surfacecoated
0.8
1 .o
Figure 8. Calculated fraction of the incident solar UV flux absorbed by the titanium dioxide coating as a function of the area of the microbead coated by the Ti02 photocatalyst. A, floating microbeads, shown in Figure 1; B, immersed microbeads, shown in Figure 8.
fraction of the incident UV flux absorbed by a crystalline layer of Ti02 as a function of the fraction of the microbead surface covered.
Results The results of the numerical analysis for Ti02 layers sited at a set of arbitrary positions on the microbead surface covering 2%, 496, and 6% of the surface are shown in Figure 6. The larger the area covered, the more circular AAF becomes. Results for layers that occupy 34%, 5096,6696 of the surface are presented in Figure 7. Obviously, the AAF of the bead totally covered by T i 0 2 is a perfect circle (a perfect sphere in three dimensions). At total coverage, A, = 0.65 and absorption is independent of the optical properties of the glass bead. Upon complete coverage of the microbead surface by a Ti02 layer, it is necessary to consider only the absorption and reflection of the incident light by the Ti02 crystallites. At full coverage a substantial 35% of the incident light is scattered by the layer because of the large difference between the indexes of refraction of rutile (N = 3.87) and air (N = 1). We have also calculated the fraction of the solar UV flux absorbed by the photocatalyst for intermediate values of T i 0 2 coverages & i 0 2 / S & d as shown in Figure 8A. This fraction is almost linear for ratios between 0 and 0.45, meaning that as long as S T i 0 2 / S & d is less than 0.5, the separated areas coated by the photocatalyst absorb incident light independently. When the coated area increases from 0.45 to 1.O, the E function is no longer (7) Vasicek, A. Optics of Thin Films; North-Holland: Amsterdam, 1960, pp 26-59.
linear, indicating interaction between the Ti02 covered areas, Le., / S b d reaches 0.7, the effectiveness function shading. When STio is at its maximum of E,,, = 0.65. Here part of the light passes through the uncoated portion of the glass shell (30% of the bead area) and is absorbed at the Ti02-glass interface, as for rays B and C of Figure 2. A further increase in the fraction of the Ti02 covered area increases the reflection of incident light from the surface of the microbead, decreases the amount of light collected by the microbead shell, consequently causing a drop in thefraction of incident photons absorbed by the TiO, coating. Calculations for Ti02 layers of irregular form and large area show that the effectiveness of absorption depends, within the accuracy of *OS%, depends only on the area of the layer and not on its shape. While this was obvious on the linear part of the absorption curve, for coverages exceeding 0.45 it required proof. As they are, the results are now valid for any arbitrary statistical distribution of the coverage by TiOz crystallites on the surface of the bead. The optical characteristics of different crude oils vary from light to heavy oils.* For X = 360 nm, the extinction is generally in the 1700-65OO-~m-~ range. Hence, the characteristic absorption lengths are 6 and 1.5 pm for light and heavy crudes, respectively. Therefore, the light is refracted and collected by the partial TiO, layer, enters at the air-glass interface but not at the oil-glass interface. Calculations confirm that, to a first approximation, the average absorption A, by the photocatalyst is proportional to the incident flux at the air-glass interface. We have also considered the case where a microbead is almost totally immersed in an oil layer, as shown in Figure 9; in this case most of the attached photocatalysts is immersed in the highly absorbing crude oil layer. The AAFs shown in Figure 6 for a microbead with most of its surface above the oil layer change to those shown in Figure 10 for the nearly submerged microbead. The AAFs become more stretched and decrease in value because the incident flux pencil is narrowed. They are less symmetrical with respect to the incident flux direction because the whole optical system becomes less symmetrical. Corresponding values of average absorption are shown in the same figure. The effectiveness of the photocatalyst layer for this case is shown in Figure 8B. It reaches its maximum E,,, = 0.35 when S T i 0 2 / S b d equals to 0.7-i.e., (8) Zolotarev, V. M.; Kitushkina, I. A.; Sutovsky, S. M. Sou. Oceunol. 1978,17,736-739.
.
The Journal of Physical Chemistry, Vol. 96, No. 8, 1992 3421
Collection Optics of TiO2 Photocatalyst
iction coverage
IS
14
9
sa
0 6 5
m
82
98
270
Figure 10. Absorbed UV fraction A (4) for 2% (a), 4% (e),and 6%
(m) of bead surface coverage by T i 0 2 Arrow shows the direct solar flux.
-
1
.
4
r
6
.
;
'
'1 0
Thichess of !he shell (in prccnr IO the h a " D)
Figure 12. Calculated fraction of the incident 360-nm solar flux absorbed by the titanium dioxide coating as a function of the thickness of the shell of the beads.
/
13
1 4
1 5
16
1 7
1 8
19
Index oirchaction of glass
Figure 11. Calculated fraction of the incident 360-nm solar flux absorbed by the titanium dioxide coating as a function of the index of refraction of the glass of the beads.
at the value derived for the first case (Figure SA). This means that an increase in the fraction of the microbead surface covered by the photocatalyst does not increase the fraction of absorbed light by the photocatalyst; it only increases the fraction of the scattered light. This conclusion also bears on the design of photoreactors where it is unlikely that the fully Ti0,-coated glass surface will be optimal for efficiency. Analysis of the optimum optical parameters of the floating microbead of Figure 1, Le., the optimal index of refraction of the glass microbead and the optimal thickness of its shell, shows that the fraction of light absorbed by the photocatalyst depends only slightly on these parameters, (Figures 11 and 12).
Conclusion The efficiency of UV light collection by a TiO, photocatalyst layer on an aluminosilicate glass microbead peaks near 70% coverage layer, where about 65% of the direct sunlight is absorbed. At greater coverage the collection efficiency decreases because of reflection. About half of the incident solar UV flux is collected at 40% Ti0, coverage. In this case, most of the light absorbed by TiOz particles comes from inside the microbead. The solar UV ray now passes into the glass at a region that is not coated
by TiO, and undergoes multiple reflections and refractions inside the microbead until it reaches a T i 0 2 coated area where it is absorbed. This means that the Ti0, particles will act as an effective photocatalyst, no matter where they are positioned on the bead, as long as they contact oil. This conclusion is valid for afloating bead of any size. A question has been raised as to the validity of the model given here in the event that the beads may tumble and become coated with an oil layer which would prevent capture of UV light by the attached Ti0,. Beads may be designed so that tumbling will not decrease efficiency and oxidation of oil will occur. From an engineering point of view, because T i 0 2 is more expensive than the microbeads, it is possible to coat only about one-third of the microbead surface yet still collect half the UV photons (Figure 8, the ascent part of the upper curve A). Bemuse of the strong absorption of UV light by crude oils, it is essential that the microbeads be sufficiently light, that they float with a minimum of their surface immersed in the oil. If microbeads were expensive relative to the titanium dioxide needed, about 70%of the surface should be covered by TiO, in order to maximize the collection of UV photons by the photocatalyst; in this case, about 65% of the direct UV flux would be collected by the TiOz layer. Some factors were not considered in this study. The scattered light field at the surface of the oil was not taken into consideration9J0nor was the dependence of UV light flux on the atmospheric mass (zenith angle of the sun)." The UV sunlight spectrum near the oil-air interface needs to be examined. Information on the TiOz (rutile and anatase) optical dispersion properties is sometimes contradictory and needs to be verified. The glass of the microbeads, considered here to be absolutely transparent may actually absorb because of Fe3+impurities. The case of very thin oil filmsI2 (9) Plass, G. N.; Kattawar, G. W.; Guinn, J. A. Appl. Opt. 1976, 15, 13 26- 13 39. (10) Guinn, J. A.; Plass, G. N.; Kattawar, G.W. Appl. O p f . 1979, 18, 701-7 13. (11) Hundbook of geophysics; Campen, C. F., et al., Eds.;Macmillan: New York, 1960; pp 16-18 to 16-20.
( I 2) Rasmussen, D. Oil Spill Conference; American Petroleum Institute: Washington, DC, 1985; pp 243-249. (13) Carsin. M . J . L. Ann Hydrogruph. 1980, 754, 1980; pp 19-43. (14) Gorkina, I. A.; Afanac'eva, N. A. Sou. Trudy COIN 1979, 149, 73-77.
J . PAYS.Chem. 1992, 96, 3428-3435
3428
of a thiclcness comparable to the average microbead diameter needs to be investigated. In spite of these omissions, however, the principal results concerning the optics of the glass microbeads covered by monocrystal T i 0 2 are valid.
Acknowledgment. We thank Dr. Schechter for numerous helpful discussions. We would also like to thank Dr. Bezman from Chevron for providing us with samples of the crude oils. We are grateful to the Department of Energy for the support of this work.
Thionine in the Cage of Zeolite L Cion Calzaferri* and Niklaus Cfelkr Institute for Inorganic and Physical Chemistry, University of Bern, CH-3000 Bern 9, Switzerland (Received: October 14, 1991)
The room temperature exchange isotherm of thionine (TH') in aqueous potassium zeolite L dispersions shows that TH+ can exchange up to 7.5% of the cations belonging to the main channel from which an average thionintthionine center to center distance of 27 A is calculated. This corresponds to a 0.2 M TH' concentration with respect to the zeolite L volume. We conclude that the maximum number of TH+ that can be incorporated is limited by the space available in the channel. Even at these high concentrations the electronic spectrum is that of a monomer. It is more structured than in diluted aqueous or alcoholic solutions, thus indicating the restricted freedom in the channel. The spectrum observed just after mixing the dye with a zeolite L dispersion is that of aggregates, easily recognized by the sudden color change from blue to purple. With time the short-wavelength absorption decreases and the monomer spectrum develops. Intercalation kinetics is slow at room temperature in the case of a potassium zeolite L and takes about 2 weeks to be completed. It is much faster at 70 OC where it takes about 10 h for a potassium zeolite and only about 1 h for a proton zeolite. We have observed that the acid-base behavior of thionine in the channels of a proton zeolite L is comparable to that otherwise observed in 2.5 M hydrochloric acid. Methylene blue and ethylene blue being slightly larger than thionine do not show any cage effect since they do not go into the main channel of zeolite L. Their electronic spectra observed even after 2 weeks are those of aggregates. We conclude that they remain adsorbed at the outside of the zeolite particles because the geometry of a zeolite L does not allow the formation of parallel dimers inside the main channel.
introduction The van der Waals radii of the thionine molecule 1 are about 7.2 X 15 AZ.This suggests that it should fit into the main channel of a zeolite L which has an opening of about 7.1 A,1shown in Scheme I. Thionine is a cationic dye and this is why it can fill R
R
I
I@
R
R
H
in the cylinder shaped cage by ion exchange. A channel of 200 nm length, the average size of commercially available zeolite L particles, is long enough to swallow up to 100 dye molecules one after the other, resulting in concentrations of about 0.2 mol jL. Methylene blue 2 and ethylene blue 3 are molecules of similar structure and shape but slightly larger. formula 1
formula 1'
l:R=H 2: R = CHI 3: R = CZH5
1': R = H 2': R = CHI 3': R CZHS
* Author to whom correspondence should be addressed.
SCHEME I: Schematic View of a Tbionine Molecule in the Main Chanoe' Of Zeolite
*
Photochemical and photophysical properties of these molecules have been studied extensively in homogeneous2-" and in heterogeneous environment.12-'6 Thus we know enough to meaningfully investigate their interactions with a zeolite environment. The characteristic differences between the electronic absorption spectra (1) Meier, W. M.; Olson, D. H. Arlus ojZeolire Srrucrure Types; Butterworths, London, 1987; p 88. (2) Rabinowitch, E.; Eptein, L. F. J . Am. Chem. SOC.1941, 63, 69. (3) Haugen, G. R.; Hardwick, E. R. J . Phys. Chem. 1963, 67, 725. (4) Faure, J.; Bonneau, R.; Joussot-Dubien, J. Phorochem. Phorobiol. 1967, 6, 33 1 . ( 5 ) Sommer, ,U.; Kramer, H. E. A. Phorochem. Phorobiol. 1971,13,387. (6) Constanciel, R.; Chalvet, 0.;Rayez, J. C. Theor. Chim. Acru 1975, 37, 305. (7) Dewey, T. G.; Wilson, P. S.; Turner, D. H. J . Am. Chem. Soc. 1978, 100, 4550. (8) Braswell, E. J . Phys. Chem. 1968, 72, 2477. (9) Mukerjee, P.; Ghosh, A. K. J . Am. Chem. Soc. 1970, 92, 6403. (10) Valdes-Aguilera, 0.; Necken, D. C. Acc. Chem. Res. 1989, 22, 171. (I 1) Spencer, W.; Sutter, J. R. J . Phys. Chem. 1979, 83, 1573. (12) Bergmann, K.; OKonski, C. T. J . Phys. Chem. 1963, 67, 2169. ( 13) Vitagliano, V. In Chemicul ond Biol~'cu1 Applicariw of Relaxcrrion Specrromerry; Wyn-Jones, Ed.; D. Reidel: Dordrecht, Holland, 1975; pp 437-466. (14) Archer, M. D.; Ferreira, M. I. In Phorochemicul Conuersion and Sroruge of Solar Energy; Connolly, J. S.,Ed.; Academic Press: New York, 1981; pp 2201-228. Albery, W. J.; Bowen, R.; Archer, M. D.; Ferreira, M. I . J . Phorochem. 1979, 11, 27. (15) Cenens, J.; Schoonheydt, R. A. Clays Cluy Miner. 1988, 36, 214. (16) Sunwar, C. B.; h e , H. J . Colloid. fnrerface Sci. 1990, 136, 54.
0022-3654/92/2096-3428S03.00/00 1992 American Chemical Society
