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chain and a HC chain attached to the same hydrophilic head group. The dependence of the cmc on the chain length of both hydrocarbon and fluorocarbon chain has been studied. The results indicate the following: (1) For F7H1, the compound does not form micelles up to its solubility limit. For F7H2, the solution becomes saturated at a concentration slightly higher than the cmc. (2) For n 1 2, the introduction of each CH2 group to the hydrocarbon chain reduces the cmc by about 35%, and the introduction of each CF2 group to the fluorocarbon chain reduces the cmc by about 75%. (3) For n 1 3, changes in both the 19Fand IH chemical shift upon micelle formation indicate that both the FC and HC chains of the FmHn are incorporated inside the micelle and that the interior of the micelle becoma more FC-rich as n decreases or m increases. (4) The aggregation number of the micelles as estimated from the NMR data is about 10-35. Except for compounds with a short HC chain, the aggregation number decreases with the increase of the length of either chain.
Acknowledgment. This work was supported by the National Science Foundation under Grant No. CTS-98 12806 and the Oklahoma Center for the Advancement of Science & Technology (OCAST) Award No. ARO-075. We gratefully acknowledge the assistance of industrial sponsors of the Institute for Applied Surfactant Research, including Kerr-McGee Corporation, Sandoz Chemicals Corp., E. I. Du Pont de Nemours & Co, and Union Carbide Corp. We are indebted to Dr.Richard G. Weiss for suggesting the procedure in ref 6 regarding the synthesis of the ketones. Registry No. F7HI, 142066-23-7; F7H2, 142066-24-8; F7H3, 142066-25-9; F7H4, 142066-26-0; F7H5, 142066-27-1; F7H6, 14206628-2; F7H7, 142066-22-6; F7H8, 142066-29-3; F7H9, 142066-30-6; F6H6, 142066-31-7; F8H6, 142066-32-8; F9H6, 142066-33-9; C7FI5COC7HI5, 142066-20-4; C7FI5CH(OH)C7HIS, 142066-21-5; ClSO,H, 7790-94-5; pyridine, 110-86-1; pentadecafluorooctanoic acid, 335-67- 1; heptylmagnesium bromide, 13125-66- 1.
References and Notes (1) Winsor, P. A. Trans Faraday SOC.1948, 44, 463. (2) Evans, H. C. J . Chem. SOC.1956, 579. (3) Tadros, Th. F. In Wetting, Spreading, and Adhesion; Padday, J. F., Ed.; Academic Press: New York, 1978; p 423. (4) Shafrin, E. G.; Zisman, W. A. J. Phys. Chem. 1962, 66, 740. (5) Abenin, P. S.;Szonyi, F.; Cambon, A. J. Fluorine Chem. 1991,55, 1. (6) Dishart, K. T.; Levine, R. J. Am. Chem. SOC.1956, 78, 2268. (7) (a) Lee,C.; ORear, E. A.; Harwell, J. H.; Sheffeld, J. A. J . Colloid InterfaceSci. 1990, 137, 296. (b) Fieser, L. F. J. Am. Chem. Soc. 1948, 7, 3232. (8) Aman, E. S.; Serve, D. J. Colloid Interface Sci. 1990, 138, 365. (9) Dreger, E. E.; Keim, G. I.; Miles, G. D.; Shedlovsky, L.;Ross, J. Ind. Eng. Chem. 1944, 36, 610. (10) Carrington, R. A. G.; Evans, H. C. J. Chem. SOC.1957, 1701. (11) Powney, J.; Addition, C. C. Trans. Faraday SOC.1937, 33, 1243. (12) Myers, D. Surfactant Science and Technology; VCH: New York, 1988; Chapter 3. (13) Shinoda, K.; Hato, M.;Hayashi, T. J . Phys. Chem. 1972, 76, 909. (14) Muller, N.; Platko, F. E. J . Phys. Chem. 1971, 75, 547. (15) Guo, W.; Fung, B. M.; Christian, S. D.; Guzman, E. K. In Mixed Surfactant Systems; Holland, P. J., Rubingh, D. N., Eds.; ACS Symposium Series, in press. (16) Mukerjee, P.; Mysels, K. J. In Colloidal Dispersion and Micellar Behavior; Kerker, M., Ed.; ACS Symposium Series 1975,17,239. Mukerjee, P., Yang, A. Y. S. J. Phys. Chem. 1976,80, 1388. (17) Zhu, B. Y.;Zhao, G. X.;Cui, J. G. In Phenomena in Mixed Surfactant Systems; Scamehom, J. F., Ed.; ACS Symposium Series 1986, 311, 173; Ibid. 1986, 311, 185. (18) Sugihara, G.; Nakamura, D.; Okwauchi, M.; Sakai, S.;Kuriyama, K.; Tanaka, M.; Ikawa, Y. Fukuka. Univ. Sci. Rep. 1987, 17, 31. (19) Emsley, J. W.; Feeney, J.; Sutcliffe, L. H. Progress in Nuclear Magneiic Resonance Spectroscopy; Pergamon Press: New York, 1971; Vol. 7, p 11. (20) CRC Handbook of Chemistry and Physics; 70th ed.; Weast, R. C., Ed.; CRC Press: Boca Raton, FL, 1980; section E. (21) Persson, B. 0.;Drakenberg, T.; Lindman, B. J. Phys. Chem. 1979, 83, 301 1. (22) Turro, N. J.; Lee, P. C. C. J . Phys. Chem. 1982,86, 3367. (23) Berr, S.S.; Jones, R. R. M. J . Phys. Chem. 1989, 93, 2555. (24) Rosen, M. J. Surfactants and Interfacial Phenomena; Wiley: New York, 1978; Chapter 3.
Electrochemical Oxidation of Nl(11l)c(4X2)-CO in Alkaline Electrolytes Kuilong Wang; Gary S.Chottiner,**+and Daniel A. Scherson*.* Departments of Physics and Chemistry, Case Western Reserve University, Cleveland, Ohio 441 06 (Received: March 16, 1992; In Final Form: April 27, 1992)
The electrochemical properties of Ni( 11l)c(4X2)-CO surfaces prepared in ultrahigh vacuum (UHV)have been examined in 0.1 M KOH using a UHV electrochemistry transfer system. The results obtained indicate that the CO layer remains intact up to the moment of contact with the electrolyte and can be subsequently electrooxidized quantitatively to yield C02 (e.g., mostly carbonate) as the product.
Introduction A detailed characterization of the electrochemical properties of well-defined electrode surfaces is of crucial importance to the further understanding of structural effects in e1ectrocatalysis.l Much of the interest in this area has centered around the electrooxidation of a variety of small organic compounds, including methanol and formic acid on platinum and on other metal electrodes, because of their potential application in fuel cells.2 These reactions are accompanied by the formation of adsorbed carbon monoxide, a species that blocks surface sites leading to losses in electrocatalytic a~tivity.~ The extraordinary progress made over the past few years toward elucidating important aspects of this ~~
Department of Physics. *Department of Chemistry
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poisoning phenomena is owed primarily to the development of procedures for the preparation of high-quality single-crystal surfaces which do not rely on the use of ultrahigh-vacuum (UHV) surface science techniq~es.~ Particularly noteworthy is the work of Weaver and ceworkers,5who have made extensive use of these methodologies for studying the effects of coverage and applied potential on the binding properties of CO on a number of low-index single-crystal surfaces including Pt, Rh, and Au, using in situ Fourier transform infrared reflection absorption spectroscopy. Although such non-UHV strategies for the preparation of single-crystal surfaces appear to be suitable for fairly noble metals, no simple method has yet been described for more active materials such as Ni and other first-row transition metals. This paper will present voltammetric curves for the electrooxidation of irreversibly adsorbed CO on UHV-prepared Ni( 111) 0 1992 American Chemical Society
The Journal of Physical Chemistry, Vol. 96, No. 16, 1992 6143
Oxidation of Ni( 1 1l)c(4X2)-CO surfacesdisplaying ~ ( 4 x 2 low-energy ) electron diffraction (LEED) patterns in 0.1 M KOH aqueous electrolytes. Particularly relevant to the measurements described herein is the work of Wagner and ROSS,who examined the electrochemical properties of Pt( 111) exposed to CO in UHV.6
Experimental Section The Ni( 11~ ) c ( ~ X ~ ) - ’surfaces’ ~ C O were prepared and characterized in UHV according to well-known proceduresEand transferred by means of an externally actuated set of magnetic and bellows-driven manipulators to a separate UHV-compatible auxiliary chamber where electrochemical measurements can be carried out. This instrument shares many commonalities with those developed in other laboratories9and will be described in detail elsewhere.I0
0.25
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I
-005 000
020
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140
Potential /V vs DHE Results and Discussion Figure 1. First cyclic voltammetric scan in 0.1 M KOH for a Ni( 11 1) Considerable care was exercised to assess whether the UHVsurface transferred to the auxiliary chamber with (curve A) and without prepared Ni( 11~ ) c ( ~ X ~ ) - ’surfaces ~ C O could survive exposure ~ C O Curve B shows the (curve C) a UHV-prepared c ( ~ X ~ ) - ~overlayer. to a moist environment at 1 atm pressure of an inert gas. To this second (and subsequent)scan@)in the positivedirection for either of the end, the UHV-prepared Ni( 11~ ) c ( ~ X ~ ) - ’ surfaces ~ C O were two specimens after a single potential excursion beyond the Ni(OH),/ transferred into the auxiliary chamber, which was then isolated NiOOH redox peak in the same electrolyte (see text). Electrode area 0.785 cm2;scan rate 0.1 V s-I. from the main chamber by closing the connecting gate valve. Ultrapurified argon was then admitted into the auxiliary chamber direction at 1.56 V (see curve B, Figure 1). This supports the to about 1 atm, and shortly thereafter the electrochemical cell view that both the oxidation of CO and the (2-electron) nonfilled with 0.1 M KOH electrolyte was transferred into the same reversible oxidation of the nickel surface are irreversible in this chamber and placed directly under the Ni( 11~ ) c ( ~ X ~ ) - ’ ~ C O potential range.”J* surface at a distance of ca. 3 mm. After 15-20 min the cell was The charge under the CO-related peaks for the Ni(l1 l)c(4X retracted and isolated in a separate compartment, the auxiliary 2)-CO surface, determined by integration, yielded a value of about chamber was pumped down, and the specimen was then trans0.26 mC. This is in very good agreement with that expected for ferred back to the main UHV chamber for further examination. the two-electron oxidation of half a monolayer of CO on Ni( 111) Both the LEED patterns and the m / e = 29 temperature-pro(Le., the coverage of a ~ ( 4 x 2 layer) ) based strictly on the lattice grammed desorption (TPD) features, including the position of the constants of the metal and assuming a perfectly flat surface, i.e., maximum (T,,),overall shape, and area under the TPD peak, were 0.234 mC. It may therefore be concluded that within the time found, within experimental error, to be identical to those obtained scale of the experiments the original c(4X2)-COlayer undergoes for similar specimens prepared and maintained in UHV, Le., quantitative electrooxidation to yield CO, (or more precisely without transfer. The value of T p(ca. 415 10 K) was in good carbonate) as theproduct. Evidence has been obtained that CO agreement with data reported elsewhere for UHV studies of CO elecfrosorbedonto single-crystal Pt( 11l)I3 and Pd( 11l)I4 displays on Ni( 1 1 l).E For a few experiments, the C and 0 AES spectral under certain conditions well-defined superlattices upon emersion features of Ni( 11 ~ ) c ( ~ X ~ ) - ’were ~ C Orecorded before and after from aqueous solutions. Direct proof for the presence of ordered transfer to the electrochemical environment, yielding essentially CO overlayers while the crystals are immersed in the electrolyte identical intensities (for most of the measurements, AES spectra has been obtained by Weaver, Schardt, and -workers in the case of Ni( 11l)c(4X2)-13C0 were not recorded to prevent e-beamof Rh( 111)15using in situ scanning tunneling microscopy. induced CO dissociation). However, no impurities were detected For comparison, curve C in Figure 1 shows the results obtained by AES after the TPD experiments for specimens which had not in a similar experiment involving a bare Ni( 111) surface transbeen analyzed with AES either prior or following the transfer. ferred into the auxiliary chamber without the c(4X2)-CO layer. These observations provide rather conclusive evidence that the As indicated, this curve shows a small peak associated with the Ni( 11l)c(4X2)-”CO surfaces exhibit essentially identical behavior incipient nickel oxidation (at slightly more negative potentials) in UHV before and after the transfer and suggests that the CO as well as a much less prominent feature centered at about the overlayer is preserved intact at least until contact with the elecsame potential at which the shoulder was found for Ni( 11l)ctrolyte is made. (4X2)-CO. This can be attributed to CO present as a contaminant Curve A in Figure 1 shows the first cyclic voltammetric scan in the auxiliary chamber as evidenced by the presence of a m / e of Ni( 11l)c(4X2)-13C0 in 0.1 M KOH obtained shortly after the = 28 peak in TPD spectra obtained in nonelectrochemical UHV electrochemical cell was formed. This curve was recorded by first transfer experiments of the type described above involving bare polarizing the electrode at about 0.20 V vs an internal dynamic Ni( 111) surfaces. A measurement in which the CO coverage (as hydrogen reference electrode (DHE), which corresponds to the determined from the cyclic voltammetry) was (accidentally) below open-circuit potential measured 5 min after contact with the half a monolayer yielded peaks centered at 0.41 and 0.77 of about electrolyte was made, and then scanning the potential linearly in the same height. the positive direction at 0.1 V s-l. The peak at 0.47 V vs RHE Although perhaps fortuitous, the features associated with the is related to the formation of a reversible,hydrated divalent nickel electrooxidation of CO on Ni( 1 11) are very similar to those hydroxide,” i.e., a species capable of undergoing reduction (upon reversing the potential scan) to restore the initial surface conditions. observed for close-to-saturation coverages of CO on polished The shoulder at 0.64 V and a prominent peak at 0.77 V vs. RHE, polycrystalline Pt in 0.1 M NaOH prepared by conventional however, are uncharacteristic of the bare substrate and may be electrochemical techniques. As reported by Kita et a1.I6 the shoulder in this case appears at 0.68, and the larger, much sharper ascribed to the electrooxidation of adsorbed CO. These results feature is centered at 0.72 V vs DHE. provide strong evidence that the reversible hydroxide and the layer of CO can m x k t on the surface over a substantial voltage range. On the basis of the results obtained, it might be envisioned that At more positive potentials the voltammetric scan exhibits a rather the UHV electrochemistry strategy herein described can provide long plateau ascribed to the growth of a nonreversible form of a reliable means for expanding the range of metals onto which nickel hydroxide,l*Le., a surface species that cannot be reduced CO adsorption and electrooxidation can be examined and thus by reversing the voltammetric scan. None of these features are lead to a better understanding of structureactivity relationships for this class of adsorbate/substrate systems. observed in the second cycle after reversing the scan in the positive
*
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Acknowledgment. This work was supported by NASA Lewis Research Center, Brookpark, OH. Registry No. CO, 630-08-0; Ni, 7440-02-0; KOH, 1310-58-3; C02, 124-38-9; C03’-,3812-32-6; ”C, 9118-70-1.
References and Notes (1) Adzic, R. R. In Modern Aspecfs ofElecfrochemistry;White, R. E., Bockris, J. OM., Conway, B. E.,Us.Plenum ; Press: New York, 1990 Vol. 21. (2) Parsons, R.; VanderNoot, T. J . Elecfroanal. Chem. 1988, 257, 9. Iwasita-Vielstich T. In Advances in Electrochemical Science and Engineering; Tobias, C., Gerischer, H., Eds.; Wiley: New York, 1990; Vol. 1. (3) For a general review in the area of CO electrooxidation see: Beden, B.; Lamy, C.; de Tacconi, N. R.; Arvia, A. J. Electrochim. Acfa 1990, 35, 691. (4) Clavilier, J.; Faure, R.; Guinet, G.;Durand, R. J. Electroanal. Chem. 1980,107,205. Hourani, M.; Wieckowski, A. J. Electroanal. Chem. 1987, 227, 259. Zurawski, D.; Rice, L.; Hourani, M.; Wieckowski, A. J . Electroanal. Chem. 1987, 230, 221. (5) Chang, S-C.; Weaver, M. J. J . Phys. Chem. 1991, 95, 5391. (6) Wagner, F.; Ross, P. J . Elecfroanal. Chem. 1988, 250, 301. (7) The Ni(lI1) crystal (Cornell Laboratory) was a thin wafer circular in shape with a surface geometrical area of 0.785 cm2.
(8) Netzer, F. P.; Madey, T. E. J . Chem. Phys. 1982, 76, 710. (9) Hubbard, A. T.; Stickney, J. L.; Rosasco, S.D.; Soriaga, M. P.; Song, D. J. Electroanal. Chem. 1983, 150, 165 and references therein. Wagner, F. T.; Ross, Jr. P. N. J. Electroanal. Chem. 1983, 150, 141 and references therein. Homa, A: S.;Yeager, E.;Cahan, B. D. J. Electroanal. Chem. 1983, 150, 181 and references therein. J. L. Stickney, J. L.; C. B. Ehlers, C. B.J . Vac. Sci. Technol. A 1989, 7, 1801. Wagner, F. T.; Moylan, T. E.J. Electrochem. Soc. 1989,136,2498. Kamrath, M.; Zurawski, D.; Wieckowski, A. Langmuir. 1990.6, 1683 and references therein. Rodriguez, J. F.; Mebrahtu, T.; Soriaga, M. P. J . Electroanal. Chem. 1989,264,291. Leung, L.-W. H.; Gregg, T. W.; Goodman, D. W. Rev.Sci. Instrum. 1991,62, 1857. (10) Wang, K.; Eppell, S.J.; Chottiner, G.S.;Schenon, D. A.; Reid, M. A. submitted to Rev. Sci. Instrum. (1 1) Schrebler-Guzman, R. S.;Vilche, J. R.; Arvia, A. J. Corros. Sci. 1987, 18, 765. Schrebler-Guzman, R. S.;Vilche, J. R.; Arvia, A. J. J . Electrochem. Soc. 1978, 125, 1578. (12) Visintin, A.; Chialvo, A. C.; Triaca, W. E.;Ania, A. J. J . Elecrrwnal. Chem. 1987, 225, 227 and references therein. (13) Zurawski, D.; Wasberg, M.; Wieckowski, A. J . Phys. Chem. 1990, 94. 2076. (14) Berry, G.M.; Bothwell, M. E.;Michelhaugh, S.L.; McBride, J. R.; Soriaga, M. P. J. Chim. Phys. 1991,88, 1591. (15) Yau, S.-L.; Gao, X.;Chang, S.-C.; Schardt, B. C.; Weaver, M. J. J. Am. Chem. SOC.1991, 113,6049.(16) Kita, H.; Shimazu, K.; Kunimatsu, K. J . Electroanal. Chem. 1988, 241, 163.
Multinuclear Magic-Angle Spinning and Double-Rotation NMR Study of the Synthesis and Assembly of a Sodalite Semiconductor Supralattice R. Jelinek, B. F.Chmelka, Materials Sciences Division, Lawrence Berkeley Laboratory, and Department of Chemistry, University of California, Berkeley, California 94720, and Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, California 93106
A. Stein,+and G.A. O h * Advanced Zeolite Materials Research Group, Lash Miller Chemical Loboratories, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada MSS 1 A1 (Received: December 10, 1991; In Final Form: March 2, 1992)
29Simagic-angle spinning, 27Aland Z3Namagic-angle spinning, and double rotation NMR provide structural and electronic details for the newly developed sodalite semiconductor quantum supralattices. The evolution of the nucleation and crystallization processes of sodium halide sodali- is monitored, and the appearanceof anionempty sodalitecages is detected. Subtle changes in the electronic and quadrupolar interactions of sodium and aluminum nuclei occur upon loading chloride, bromide, and iodide into the sodalite cages. The NMR results suggest that the development of electronic coupling occurs throughout the lattice in mixed-halide chloro,iodosodalites. A preference for silver exchange of sodium cations in halide-containing cages, over hydroxideantaining and anionempty sodalitecavities, is detected. Extraction of the isotrOpic chemical shift and quadrupolar contributions to the sodium resonances is achieved by performing the NMR experiments at two magnetic field strengths. The parameters obtained indicate a change in the charge distribution around the sodium nuclei upon exchanging approximately onequarter of the extraframeworkNa+ cations with silver, which parallels other data pointing to the onset of a semiconductor supralattice within the sodalite matrix.
Introduction The Federovian cuboctahedral structure of sodalites enables them to host insulator, semiconductor, or metal cluster guests of uniform size and shape.’ This unique quality confers upon this class of microporous solids potential uses as advanced materials, which may include semiconductor quantum expanded metal or superconducting array^,^ and redox-active supralattices in erasable highdensity optical data storage and processing media! Single-crystal and Rietveld powder X-ray diffraction methods are pivotal in providing atomically precise structural details of solids that display long-range order. Solid-state NMR on the other hand can address structural questions of a more local nature, To whom correspondence should be addressed. ‘Current address: Bayer AG, D-5090 Leverkusen, Germany.
yielding invaluable information on the environment of atomic species in materials having short-range order or amorphous configurations. The use of high magnetic fields, combined with spatial-averaging sample reorientation N M R techniques like magbangle spinning (MAS) and double rotation (DOR), enables one to obtain a wealth of structural information on solid lattices, including open-framework structures like zeolites. Numerous studies have used MAS to examine structural aspects of the framework nuclei 29Si5and 27Al.6 23NaNMR studies concentrating upon the charge-balancing cations have been conducted as weL7 The recently developed DOR technique is additionally useful in probing fine structural details when observing quadrupolar nuclei.* This work concentrates on the application of 29SiMAS, 27Al and 23NaMAS, and DOR, complemented by X-ray diffraction
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