Langmuir 1994,10, 70F716
709
Chemical Reactions of Pyrene and Its Chlorinated Derivative on Silica-Alumina Surfaces Induced by Ionizing Radiation Yun Mao, Kai K. I u , ~and J. K. Thomas' Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 Received April 1, 1993. In Final Form: October 7 , 1 9 9 P
Chemical reactions of model compounds pyrene and chloropyrene on silica-alumina surfaces induced by ionizing radiation have been studied. Energy is deposited in the silica-alumina by ionizing radiation, leadingto charge-transfer processesforming radical cations by pyrene, which are observed by steady-state diffuse reflectance and time-resolved absorption spectroscopies. Electron paramagnetic resonance measurements at low temperaturealso confirmthe identificationof this species. Preirradiation of silicaalumina with subsequent addition of the arene also produces the same chemical reaction as that given by the radical cation of the arene. The cationicspeciesare extracted into solutionwhich gives rise to products. High-performanceliquid chromatographyseparationand steady-statespectroscopicstudiesof the products show that a major product is hydroxypyrene with a G value (molecules per 100 eV of energy absorbed) of 0.76. The reaction of the pyrene radical cation with water producesa hydroxy-addition-typefree radical which is a key intermediate in the hydro%is process. Oxygen and ferricyanide which are present in the extraction solution enhance the yield of hydroxypyrene,and earlier studies have shown that thii supports the proposed reaction mechanism.
Introduction Recently, a growing interest has developed in using ionizing radiation for the removal of pollutants in the environment.lB2 It was reported that a prototype of a truckmounted X-ray unit has been used to destroy organic contaminants in the Lawrence Livermore National Laboratory.g Of particular promise is the use of ionizing radiation to remove chlorinated contaminants, where the ionizingradiation removes chlorine atoms from the organic compounds. The fundamental concepts of the action of ionizing radiation on solids are established,c8 although it maybe arguedthat this chemistry is not as well established as that in solution. Early work on the radiation chemistry of material surfaces was concerned mainly with the decomposition of organic compounds, e.g., pentane?JO azoethane,ll isopropylbenzene,12J3and cyclohexane,6and the formation of radical anions and cations of aromatic
* To whom correspondence should be addressed. t Present
address: Hewlett-Packard Co., San Diego, CA 92127. Abstract published in Aduance ACS Abstracts, February 15, 1994. (1) (a)Singh,A;Sagert,N.H.;Boma,J.;Singh,H.;Bennett,G.S.The Use of High-energyRadiation for the Treatment of Waetewater. Proceedings of the 8th Symposium on Wastewater Treatment, Montreal, 1985. (b)Dicheon, L. W.; Lopata, V. J.; Toft-Hall, A; Kremer, W.; Singh, A. Use of Activation Carbon Adsorption. Conjunction with Radiation TreatmentProceeeee,Atomic Energy of Canada Limitad Report AECL9568,1988. (2) Iverson, I. Radiation Technology for a Cleaner Environment. In Proceedings of the 7th Tihiany Symposium on Radiation Chemistry, B u d a p t , 1991; Dobo,J.; Nyikoe, L.; Schiller, R., Eda.;p 491. (3) Chem. Br. Apr 1992,306. (4) Coekelberga, R;Cruco, A.; Frennet, A. Adv. Catal. 1962, 13,55. (S)Kohn, H.-W. The Radiation Chemistry of Surfaces. In The Chemical and Biological Action of Radiations; Haiessinsky, M., Ed.; Maseon et Cie.: Parie, 1967; p 183. (6) Norfold, D. J. Radiat. Res. Rev. 1974,6, 373. (7) !hgomki, Z P. Solid State Pulse Radiolysis. New Trends and Developments in Radiation Chemistry,IAEA-TECDOC-527,1989;p 79. (8) Thomae, J. K. Chem. Rev. 199&93,301. (9) Capfrey, J. M.; Allen, A. 0. J. Phys. Chem. 1968,62, 33. (10) Sutherland,J. W.; Allen, A. 0.J. Am. Chem. Soc. 1961,83,1040. (11) Rabe, J. G.; B. Rabe, J. G.; Allen, A. 0.J. Phys. Chem. 1966,70, 1098, (12) (a) Rojo, E. A.; Hentz, R. R. J. Phys. Chem. 1966, 70,2919. (b) Rojo, E. A.; Hentz, R. R Zbid. 1972, 76,3741. (13) Hentz, R. R.; Wickenden, D.K. J. Phys. Chem. 1969, 73, 817.
compounds on irradiated solids was also reported.1417 Recently, alkane radical cations have been observed also on y-irradiated zeolites.l8 The data are explained basically by energy transfer and chargetransfer from the irradiated solid to the adsorbed molecules;a combination of the two effects is also observed.lg In the case of energy transfer, the energy is transferred to the adsorbed solid rapidly during the irradiation or short& thereafter. Hence, preirradiation of the solid and subsequent addition leads to very little decomposition. In the case of charge transfer, preirradiation of solids leads to trapping of ionic species which can subsequently act via charge transfer with adsorbates, resulting in chemistry. This is similar to what occurs when adsorbed molecules are present during the irradiation. In the present study pyrene (Cl6Hl0, Py) and l-chloropyrene (ClsHgCl,CPy) are selected as model compounds of polycyclic aromatic hydrocarbons, and silica-alumina (SA)is used as a model solid system. The arene is adsorbed on the silica which is then irradiated with ionizing radiation. Species are observed by diffuse reflectance and electron paramagnetic resonance (EPR) spectroscopies, and products are also separated and identified by highperformance liquid chromatography (HPLC).
Experimental Section Silica-alumina (SA)(AldrichChemical)was used as received. The average surface area of the SA,measured by the single-point Brunauel-Emmett-Teller (BET) method (Quanta Chrome, Monosorb),is 304 mVg. The composition of SA is Si02 (87w t %) and Ala08 (13 wt 5%). The main impurities are as follows: Na+, 25 ppm (parta per million); Fe2+/FeS+,15 ppm; NH,+,75 ppm; C1-, 7 ppm. In order to estimate the effect of the impurity (14) Edlund, 0.; Kindell, P.-OJLid, A.; Shimizu, A. J. Chem. Phys. 1967,46,3679. (15) Wong, P. K.; Willard, J. E. J. Phys. Chem. 1968, 72, 2623. (16) Wong, P. K.; Allen, A. 0. J. Phys. Chem. 1969, 74,774. (17) Kamatau, T.; Lund, A. J. Phys. Chem. 1971, 76, 1727. (18) (a) Toriyama, K.; Nunome, K.; I w d , M. J. Am. Chem. Soc. 1987,109,4496. (b)Qm,X.4.; Trifunac, A. D.J. Phys. Chem. 1990,94, 4751. (19) Volkov, A. I.; Volkova, G. G.; Yermolaev, V. K.; Sazonov, L. A. React. Kmet. Catal. Lett. 1982,20, 277, 283.
0743-7463/94/2410-0709$04.50/0 63 1994 American Chemical Society
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710 Langmuir,Vol. 10, No.3, 1994 in the commercial product, silica-alumina was also synthesized according to the literature.a0 The synthesized SA has an average surface area of 291 mVg, and contains a lot less impurities: Na+, 3 ppm; FeZ+/Fes+,
