1362
J. Phys. Chem. 1983, 87, 1362-1369
Sonoluminescence and Sonochemical Reactions of Aqueous Carbon Tetrachloride Solutions P. K. Chendke and H. S. Fogler' Department of Chemical Engineering, The University of Michigan, Ann Arbor, Michlgan 48109 (Received: May 10, 1982; In Final Form: November 4, 1982)
The sonoluminescenceintensity and its spectral distribution, and the sonochemicalyields from saturated aqueous solutions of carbon tetrachloride, were measured simultaneously. The variation of these quantities with static pressure was also determined for static pressures ranging from 1 to 20 atm. The sonoluminescence intensity was found to increase linearly with increasing percentage saturation of CC14 in water. The intensity of sonoluminescence was found to depend on the static pressure, while its spectral distribution remained virtually independent of the static pressure. The increased luminescence in the presence of CC1, is shown to be due to chemiluminescence and not due to blackbody radiation. The products of the sonochemical decomposition that were detected were HCl and HOC1. The sonoluminescence intensity was found to be linearly related to the yield of the sonochemical decomposition products over the entire pressure range.
Introduction The acoustic cavitation in a liquid is the nucleation, growth, and collapse of cavitation bubbles. The rapid collapse produces high temperatures and pressures in the interior of the bubbles and leads to the formation of free radicals, the synthesis of chemical compounds, and the emission of a faint luminescence (sonoluminescence). Bubble Temperature and Sonoluminescence. Srinivasanl fitted the spectral distribution of sonoluminescence to Wein's law and estimated a temperature inside the collapsing bubble of 11000 K for both argon- and heliumsaturated water while Gunther et a1.2 obtained a much lower estimate of the bubble temperature, 6000 K, for xenon-saturated water. Recently, Saxena and N y b ~ r g , ~ Taylor and Jarman,4 and Sehgal et al.5 have shown the sonoluminescence of water to consist predominantly of the radiative recombination of excited molecules and free radicals (H, OH) (chemiluminescence) in the bubble interior. consequently the fitting of a blackbody distribution of a luminescence of nonblackbody origin (such as chemiluminescence) yields a color temperature associated with that luminescence and not the bubble temperature as suggested by earlier workers.l$ Even the concept of a color temperature associated with sonoluminescence is subject to the reservation that the luminous source consists of bubbles of varying sizes that are not in thermodynamic equilibrium due to their periodic growth and collapse. Subject to these reservations, the concept of color temperature is still useful in characterizing the spectral distribution of sonoluminescence, with a lower color temperature indicating a shift in the spectral distribution to longer wavelengths. Sonoluminescence and Sonochemical Reactions. #en ultrasonic cavitation is induced in a liquid, one can observe the presence of sonochemical reactions as well as sonoluminescence. The dependences of these two phenomena on variables such as the liquid temperature, ambient pressure, nature of the dissolved gas, and ultrasonic intensity are similar. Processes which increase sonoluminescence (e.g., dissolving noble gases in the liquid) also
increase sonochemical reaction yields. Similarly, processes which decrease sonoluminescence (e.g., increasing the liquid temperature) also decrease the sonochemical yields. This is indicative of the effect of these parameters on the bubble dynamics, number of bubbles, and conditions of temperature and pressure within collapsing cavitation bubbles. A simultaneous measurement of the luminescence intensity and the chemical yield in a cavitation field is, therefore, necessary to determine their interrelationship, if any. The addition of carbon tetrachloride and carbon disulfide to water increases sonoluminescence by factors of 3 and 10, respectively.6 Aqueous carbon tetrachloride solutions also yield various chlorine products such as HC1, HOC1, C2C14,and C2C16,' while aqueous carbon disulfide solutions yield H2S and colloidal sulf~r.*9~ The mechanism by which CCll and CS2 increase the sonoluminescence of water is not well understood, although various speculations have been offered. For example, Weyl and Marboe'O suggested that the presence of nonpolar compounds such as CC14 and CS2 weakens the structure of water, thus enhancing cavitation and sonoluminescence, but offered no experimental evidence to substantiate their suggestion. This explanation of the enhancement of the sonoluminescence of water by a nonpolar compound is inadequate in view of the fact that, recently, Sehgal et d.ll have shown that benzene, which is also nonpolar and is a radical scavenger, diminishes sonoluminescence when added to aqueous solutions. The degree of reduction follows the Stern-Volmer equation I,/I = 1 (1) where Io represents the sonoluminescence intensity in the absence of the quenching molecule X, p is a constant dependent on the specific reaction rate constants, and I is the sonoluminescence intensity a t a concentration of the quenching molecule. The Stern-Volmer equation adequately describes the sonoluminescence of aqueous solutions with aliphatic alcohols or benzene as radical sca-
(1) D. Srinivasan and L. V. Holroyd, J. AppE. Phys., 32, 446 (1961). (2) V. P. Gunther, E. Heim, and H. IJ. Borgsstedt, Z. Electrochem., 68, 43 (1959). (3) T. K. Saxena and W. L. Nyborg, J. Chem. Phys., 53, 1722 (1970). (4) K. J. Taylor and P. D. Jarman, Aust. J. Phys., 23, 310 (1970). (5) C. Sehgal, R. G. Sutherland, and R. E. Verall, J.Phys. Chem., 84, 388 (1980).
(6) P. Jarman, Proc. R. SOC.London, 73,628 (1959). (7) L. A. Spurlock and S. B. Reifsneider, Chern. Eng. Prog., Symp. Ser., No. 109, 27, 67 (1971). (8) R. 0. Prudhomme, J. Chem. Phys., 46, 318 (1949). (9) S. C. Srivastava, Nature (London),182, 4627 (1958). (10) W. A. Weyl and E. C. Marboe, Research (London),2,21 (1949). (11) C. Sehgal, R. P. Steer, R. G. Sutherland, and R. E. Verall, J.Phys. Chem., 81, 2618 (1977).
0022-3654/83/2087- 1362W 1.5010
+ px
0 1983 American
Chemical Society
The Journal of Physical Chemistry, Vol. 87, No. 8, 1983
Sonoluminescence and Sonochemical Reactions
vengers and as collisional quenching agents in the conmol/L.l1 centration range of 0-2 x Sonoluminescence in Shock Tubes. A continuous spectrum was observed from CC1,-argon mixtures in shock tubed2 and also from the implosion of partially evacuated glass spheres containing a mixture of water vapor and CCl,.l3 Fairbairn and Gaydon12attributed the luminescence from CCl, to the formation of C and C2particles and also to emission resulting from the combination of halogen atoms. Schmid13 attributed the increased luminescence from imploding glass spheres containing CCl, vapor to chemiluminescence, although no specific scheme was suggested nor were the emitting species identified. A shock wave, a bubble implosion, and the collapse of a cavitation bubble all result in the generation of high temperatures and pressures. Thus, the presence of CCl, is likely to affect the luminescence associated with all these phenomena in a similar manner. For CS2 in shock tubes, the linear dependence of the emission intensity on the CS2concentration was explained by Arnold, Brownlee, and Kimbell’, with the following scheme: CS2 + M CS2*
kl
k-1
k2*
CS2* + M
CS2
(2)
+ hv
(3) One finds that for the CS2 the luminescence intensity in the shock tube is given by 1st = [klk2*(CS2)(M)I/[k-,(M) + k2*1 (4) where (CS,) = concentration of CS2 in the shock tube (mol/cm3), (CS2*)= concentration of electronically excited CS2 (mol/cm3), and (M) = concentration of third body (mol/cm3). ISt= intensity of luminescence from the shock tube. When k-,(M) > k2* or when (M) is constant, eq 4 simplifies to 1st a ( ( 3 2 ) (5) Hence, the intensity of luminescence is linearly proportional to the CS2 concentration in the shock tube. Effect of Static Pressure. Almost all the previous investigations of sonoluminescence and sonochemical yields have been conducted at atmospheric pressure. The study by Finch15 on the sonoluminescence of water over a 1-8atm pressure range is the only reported attempt to investigate the phenomena a t higher static pressures and is restricted to the measurement of total intensity only. The effect of higher static pressure on another cavitation-related phenomena-the disintegration of yeast cells during ultrasonic irradiation-was studied by Neppiras and Hughes.16 They found that, as the static pressure was increased, the percentage of yeast cells destroyed first increased, then decreased, and then increased again. The reason for the local minimum is not well understood. Sonochemistry of H20-CC14-Nz. A number of investigators have studied the ultrasonically induced decomposition of carbon tetrachloride in aqueous solutions a t atmospheric pressure. The variables studied include the acoustic intensity and nature of the dissolved gas,17J8 (12)A. R. Fairbairn and A. G. Gaydon, Proc. R. SOC.London, Ser. A , 239,464 (1957). (13)J. Schmid, Acustica, 12,70 (1963). (14)S.J. Arnold, W. G. Brownlee, and G. H. Kimbell, J.Phys. Chem., 72,4344(1968). (15)R. D. Finch, Br. J . App. Phys., 16, 1543 (1965). (16)E. A. Neppiraa and D. E. Hughes, BiotechnoL Bioeng., 6, 247 (1964). (17)V. Griffing and D. Sette, J. Chem. Phys., 23, 3, 503 (1955). (18)M.E.Fitzgerald, V. Griffing, and J. Sullivan, J. Chem. Phys., 25, 5,926 (1956). ’
1363
concentration of carbon tetrachloride in solution, and product The HOCl yield from the decomposition of CCl, in water was observed to increase linearly with the applied ultrasonic intensity over the 0-7 W/cmz intensity range.17 A qualitatively similar result was obtained by Fitzgerald et al.,18 although these authors did not measure the ultrasonic intensity quantitatively. The HOCl yield was also found to vary with the dissolved gas with the trends being Ar > Ne > N2 > C0,17and Ar > Ne > He > O2> N218 The product distribution resulting from the sonochemical decomposition of CCl, in water consisted of HC1, HOC1, C2C16,CO, and C02.19 In addition to these products, the presence of trace amounts of C2C14has also been reported.21 However, the rate of production of CzC14 was approximately 1/14 the rate of production of C2C16 and consequently C2C14could only be detected when long irradiation times were used (>90 min).21 The mechanism proposed by Prakash and SrivastavaZ0 for the decomposition of carbon tetrachloride in water is 2CC14 CCl, CCl,
-
C2Cl, + C1,
+ 2H20
+ H20
-
-
CO
(6)
+ 4HC1
(7)
+ C12 + 2HC1
(8)
CO
For CCl,-rich solutions or aqueous solutions containing excess CC14, reaction 6 is reported to be favored while reactions 7 and 8 are favored for saturated aqueous solutions of CC14.20In aqueous solutions, the C12that is produced is converted to HOCl and HC1 as given in reaction 9. Clz
+ H20
-
HOCl
+ HC1
(9)
Data on the extent of hydrolysis of C12 in aqueous solutions are reported by Whitez2 and are tabulated elsewhereaZ3For the experimental conditions in the study (C12 < 100 ppm and pH > 3.5)) it was found that the extent of hydrolysis exceeds 99.9%. Hence, all the C12 produced due to the decomposition of CCl, is in the form of HOCl and HC1. No studies have been reported in the literature on the effect of enhanced static pressures on the product distribution of the sonochemical decomposition of carbon tetrachloride. Relationship between Sonoluminescence and Sonochemistry. Although the similarity between sonoluminescence and the chemical effects of cavitation has long been detailed studies have not been undertaken to relate these two phenomena. Prudhomme and Guilmart25studied the sonoluminescence and the formation of hydrogen peroxide from water saturated with various noble gases. The sonoluminescence intensity was reported qualitatively, but their data indicate that both luminescence and hydrogen peroxide formation increased with dissolved gas in the order He < Ne < Ar < Kr < Xe. A linear relationship between the sonoluminescence intensity and hydrogen peroxide formation from water (19)L.A. Spurlock and S. B. Reifsneider, J . Am. Chem. Soc., 92,21, 6112 (1970). (20)S.Prakash and S. C. Srivastava, Z . Phys. Chem. (Leipzig), 208, 127 (1958). (21)B. H. Jennings and S. N. Townsend, J. Phys. Chem., 65, 1574 (1961). (22)G. C. White, ‘Handbook of Chlorination”, Van Nostrand-Reinhold Co., New York, 1972,p 184. (23)P. K. Chendke, Ph.D. Thesis, University of Michigan, Ann Arbor, MI,1982. (24)R. Hickling, J . Acoust. SOC.Am., 35, 11, 1833 (1963). (25)R. 0. Prudhomme and Th. Guilmart, J. Chim. Phys. Phys.-Chim. Biol., 54, 336 (1957).
1364
The Journal of Physical Chemistry, Vol. 87, No. 8, 1983
Chendke and Fogler
TABLE I: Normalized Spectral Distribution in the Presence of Carbon Tetrachloride % CC1,
filter band, nm 348.5-371 .O 385.7-415.0 4 21.5-4 86.5 502.0-560.5 547.5-600.0 total a
._
satn in aq soln
0
25
50
75
100
pure CC1,
two phase
CC1, rich
1.00 1.00 1.00 1.00 1.00 1.00
1.14 0.98 1.14 1.11 1.14 1.43
1.38 1.70 1.51 1.44 1.52 1.97
1.39 1.49 2.00 1.85 1.70 2.4 2
1.40 1.63 2.24 2.18 2.03 2.80
1.00 1.38 2.62 3.42 1.66a 3.61
1.37 2.56 4.49 8.25 3.84a 5.99
2.19 3.59 4.94 7.18 3.39a 6.38
Measured with a filter transmitting in the 566.0-585.0-nm range.
containing dissolved oxygen was reported by Parke and Taylor.26 They also reported a linear dependence of sonoluminescence on the amount of iodine liberated from water-potassium iodide-oxygen and water-potassium iodide-carbon tetrachloride-air solutions. Griffing and Sette" studied the effect of ultrasonic intensity on the sonoluminescence of aqueous solutions of carbon tetrachloride. In addition, they measured the yield of chlorine at varous ultrasonic intensities for solutions having compositions similar to those used in the sonoluminescence studies. By cross plotting the sonoluminescence intensity against the sonochemical yield a t various ultrasonic intensities, Griffing and Settel' found a linear relationship. It should be noted, however, that the sonoluminescence and sonochemical yields were not measured simultaneously on the same sample but, instead, different samples were used. In each of the above studies, the investigators did not quantify the sonoluminescence data by determining the spectral distribution. In the present work, the influence of carbon tetrachloride on the sonoluminescence of water was studied by measuring the luminescence intensity within the spectral range of 165-650 nm and determining its spectral distribution for aqueous solutions ranging from 0% to 100% CCl, saturation. The effect of CCl, concentration on the sonoluminescence intensity and its spectral distribution has not been previously reported. In addition, the total sonoluminescence intensity (165-650 nm) and its spectral distribution were measured simultaneously with the yield of chlorine products from saturated aqueous solutions of carbon tetrachloride containing dissolved nitrogen. In another phase of this work, the effect of elevated static pressures between 1and 20 atm on total sonoluminescence intensity, its spectral distribution, and the CCl, reaction product distribution was studied. In addition to the determination of the relationship between total luminescence and total chlorine yield a t elevated static pressure, the spectral distribution allows the determination of the effect of static pressure on the color temperature of the luminescence. Such an extensive study has not been previously reported. Apparatus a n d Procedure The apparatus and procedure for measuring sonoluminescence intensity is described e l s e ~ h e r e . ~ ~ , ~ ' The products of decomposition of aqueous carbon tetrachloride solutions that were detected were HC1 and HOC1. The concentration of HOCl was determined by the addition of 0.5 N KI to the solution and by titration of liberated iodine with 0.05 N sodium thiosulfate using a starch indicator. The total acid (HC1 + HOCl) was determined by titration with 0.05 N sodium hydroxide. The HC1 was obtained by the difference of these two titrations. For a few selected runs, a complete product analysis was (26) A. V. M. Parke and D. Taylor, J . Chem. SOC.,4, 4442 (1956). (27) P. K. Chendke and H. S. Fogler, J . Phys. Chem., submitted.
carried out with a Beckman Model GC-2A gas chromatograph equipped with hydrogen flame detector. A 4 ft long, l / , in. diameter Porapak P column was used to separate compounds. With this arrangement, the carbon tetrachloride concentration before and after ultrasonic irradiation could be measured. All the samples were irradiated for a total of 15 min, during which time two spectral distributions could be obtained. Longer irradiation times caused a significant drop in the sonoluminescence intensity due to the depletion of carbon tetrachloride and the erosion of the titanium tip and, therefore, were undesirable. A t the end of the irradiation the concentrations of the products of decomposition were determined by titration. As mentioned earlier, the sonoluminescence intensity of saturated aqueous solutions of carbon tetrachloride decreases with irradiation time due to a depletion of the carbon tetrachloride. This causes a decrease in the intensities measured by the various interference filters, and the order in which the filters are used influences the spectral distribution significantly. To correct for this, we measured the total intensity at frequent intervals and normalized all the spectral intensities to a constant total intensity. This procedure eliminated the influence of the depleting carbon tetrachloride concentration and the order of the measurements with the filters. Results a n d Discussion Variation of Intensity with CCl, Concentration. The relative sonoluminescence intensity and its spectral distribution for solutions of carbon tetrachloride in water and different degrees of saturation are given in Table I. The total intensity of luminescence (165-650 nm) increased with the amount of CCl, in solution according to the linear relationship I / Z , = [l f 0.21 + [0.018 f O.OOS]S (10) where Z = intensity of sonoluminescence of the solution, Zo = intensity of sonoluminescence of water, and S = percent CCl, saturation. Pure CCl,, a two-phase solution of 50% water and 50% CCl, by volume, and a saturated solution of water in CCl, luminesced with intensities 3.6, 6.0, and 6.4 times greater than that of water, respectively. However, the investigations of solutions of HzO in CC1, suffer from two experimental difficulties. First, the solutions have a lower heat capacity (specific heat 0.198 cal/g compared to 1.0 cal/g for water) leading to a rapid rise in the liquid temperature during ultrasonic irradiation despite the use of a cooling coil. Secondly, the two-phase solution rapidly forms a translucent emulsion due to the dispersion of droplets during ultrasonic irradiation, thereby interfering with the transmission of the luminescence. To delineate the effect of CCl, on the sonoluminescence of water, it is necessary to examine the spectral distributions of solutions containing various concentrations of CC1,. The relative enhancement of the sonoluminescence in different spectral regions is compared for various solutions
The Journal of Physical Chemistry, Vol. 87, No. 8, 1983
Sonoluminescence and Sonochemical Reactions
by using the spectrum of pure water as a reference, as shown in Table I. The degree of enhancement due to the presence of CCl, was not uniform over the entire spectrum. As the amount of CCl, in solutions increases, the spectral region where the maximum enhancement in sonoluminescence intensity occurs is shifted toward longer wavelengths. The pulse radiolysis of pure liquid CCl, with 100-MeV electrons produces an absorption spectrum of the CC14+ ion in the spectral region of 300-600 nm with a maximum near 500 nm.28 In sonoluminescence, the recombination of the CC14+ ion with an electron would result in an emission spectrum having a maximum a t longer wavelengths and would be consistent with the results shown in Table I. In the absence of more precise information regarding the chemical intermediates and emitting species, a quantitative description is not possible a t this time, although a qualitative model of the process is described below. The linear increase of the sonoluminescence of water with CCl, concentration suggests a scheme similar to that proposed by Arnold et al.I4 for the luminescence from CS2 in shock tubes. If the chemiluminescence from CCl, is due to the recombination of the CC14+cation with an electron, we would have by a scheme similar to eq 2-4 k3
M
+ CC4 CCl,+ + e-
k-3
+ e- + M CCl, + hv
CC14+
k4*
r
32
0
1365
I
0
’
I
1
0 1
9 12 15 18 STATIC PRESSURE, atmospheres
3
6
2f
Figure 1. Variation of sonoluminescence intensity of H,O-CCI,-N, solutions with static pressure. 0
(11)
(12)
where M = third body (H20,N2, or CC,). The sonoluminescence intensity due to CCl, is then given by Iccl, = [K,K,*(M)(CCl,)l/[k-,(M) + K4*1 (13) or Icci,
a
[CCbI
(14)
where [CCl,] = concentration of CCl, in the cavitation bubble. For aqueous solutions of CC,, we assume Raoult’s law to hold and the concentration of CCl, in the bubble to be linearly related to the concentration of CCl, in the liquid. Hence, the sonoluminescence intensity of aqueous carbon tetrachloride solutions would increase linearly with CC, concentration in the solution. The suggested scheme explains the increase in sonoluminescence intensity due to the presence of CCl, and is consistent with the shift of the sonoluminescence spectra of aqueous solutions to longer wavelengths (500 nm) in the presence of CCl,. Variation of Total Sonoluminescence Intensity with Static Pressure. Measurements of the intensity and spectral distribution of sonoluminescence of saturated aqueous solutions of carbon tetrachloride containing dissolved nitrogen are reported in Table 11. The total intensity was measured by a photomultiplier sensitive over the 165-650-nm wavelength range. The spectral distribution was measured by using a serious of five narrow band interference filters with a half-bandwidth of about 10 nm. The sonoluminescence data given in Table I1 were obtained for static pressures ranging from 1 to about 2 atm. The dependence of the total sonoluminescence intensity on static pressure is shown in Figure 1. The intensity increases with static pressure from 1 to about 6 atm, decreases to a local minimum at 8 atm, and then increases to a second and larger peak at about 12 atm. For pressures (28) R. Cooper and J. K. Thomas, “Radiation Chemistry”, Vol. 11, R. F. Gould, Ed., American Chemical Society, Washington, DC, 1968,Adu. Chem. Ser., No. 82, p 351.
!I o
6 9 12 15 la STATIC PRESSURE, otmospheres
3
21
Figure 2. Effect of static pressure on sonoluminescence intensity.
greater than 12 atm, there is a rapid decrease in the sonoluminescence intensity reaching almost to extinction at 18 atm. However, some residual luminescence does remain even a t 20 atm. This pressure dependence of sonoluminescence closely parallels that of another cavitationrelated phenomenon-the disintegration of yeast cells when irradiated with ultrasonic waves reported by Neppiras and Hughes.16 The cause for the decrease in sonoluminescence at pressures near 8 atm is not well understood. To understand the phenomena, we measured the acoustic intensity delivered by the transducer at various pressures. A measured volume of saturated aqueous solution of carbon tetrachloride was introduced into the reactor and saturated with nitrogen gas at various pressures. The ultrasound was turned on and the rise in liquid temperature due to irradiation was measured with copper-constantan thermocouple as a function of time. The ultrasonic intensity (cal/min) varied with static pressure as shown in Figure 2. The intensity increased with static pressure over a range of 1-6.5 atm, reached a broad plateau, and then decreased for static pressure greater than 15 atm. A comparison of figures 1 and 2 shows that over the pressure range of 1-6 atm both sonoluminescence intensity and acoustic intensity increase, with the sonoluminescence increasing by 290% and acoustic intensity increasing by 260% over the corresponding values at 1 atm. For pres-
Stat lc P r e s s u r e . A t m o s ~ h e r e s Spectral B a n d nm - n m
1 0
1 0
2 7
3 7
4 1
6 1
4 4
6 1
7 8
7 8
348.5
371.0
50. 1
33.0
27.4
55 6
62.4
73.5
133.8
178. 1
44 6
52 0
nfl5.7
415 0
76,2
61.6
47 3
118 9
107 0
162 0
1'39 9
227.4
94.7
96 Q
47 I . 5
486.5
121.6
118.5
108.3
264 9
178 8
799.5
345.6
363.0
173.6
166.0
502 .O
560.0
129.8
142.0
87.7
294.9
187.5
342.9
368.6
342.8
198.9
179 6
547.5
600,O
80.3
50.9
67.2
75.3
63.7
122.8
120.7
158.7
64. 1
64.9
348,5
371.0
45.1
27.6
15.0
68.6
57.9
68.8
145 5
158.3
31 , 2
50 2
91.1
61.3
385.7
415.0
82.0
56.8
46.3
119.6
102.0
156.5
224.4
237.9
421.5
486.5
109.5
121.1
78. 1
201.0
175
309.5
345 9
374.6
157.6
126 2
188.9
360. I
349 1
319.8
205.5
198.6
502 0
560.0
127.8
154.0
94.3
199.3
547 5
600.0
78.8
60.0
63.3
69.7
60.5
127.8
124.4
153.6
69.9
66 5
6208
5955
5743
9920
OG05
14428
17914
18871
8124
8767
9.2
9 5
Stattc P r c s s u r e . Atmospheres Spectral R a n d nm
-
m r
10 7
11.2
11 9
12 9
13 2
14 6
16 3
18.0
73.5
2 2
42
1
1 0
348.9
071 0
72.7
61 5
157 3
96.8
139.6
137 7
45.7
4 3
385 7
415.0
140.9
177 9
2?3 4
280.3
307.5
259.3
53.3
14.2
,121 4
486.5
240.4
214.5
378 5
568 7
574 0
501. I
89 2
40 2
80 8
3 7
502 0
560.0
209.3
374.9
4C2.1
043 8
717.4
488 5
89.1
66 1
87.3
7.0
547 5
GOO. 0
93.3
120.1
142 G
243.2
237 3
206 8
28.3
30 1
29 0
3.8
133 2
48 2
8 7
13 7
1.4
Second Spectrum 348.5
371 . O
385.7
415.0
421.5
486.5
93 4
107.5
245.3
308.7
296 6
229 1
53 7
19.1
33 5
2.2
345 9
695.4
546 7
498.6
67 Q
38.9
57 7
4.1
517 5
89.6
52.8
115.7
7 4
53 3
(02.4
130.7
151 9
239.4
322.5
46. 1
502.C
560.0
318.1
342.5
404 3
033.8
726.8
547.5
600.0
101.8
104. 1
139 1
325.3
245.1
211 2
27.5
20.9
22 0
1,8
12027
12029
18257
23571
26960
22767
4324
2667
3234
224
sures greater than 6 atm, sonoluminescence and acoustic intensity show no direct proportionality. Dependence of Carbon Tetrachloride Concentration and Static Pressure o n t h e Color Temperature of Sonoluminescence. Planck's equation relating the spectral distribution of intensity as a function of wavelength to a blackbody temperature is given in eq 15 IA = C1(X)-5[exp(C2/XT) - 11-1 (15) where Ix = spectral intensity between X and X + dx, X = wavelength, C1, Cz = constants, and T = blackbody temperature. In the visible region of the spectrum, exp(C,/XT) >> 1 and eq 15 can be simplified to Wien's law
I , = C,(X)-' exp(-C,/XT) (16) with errors ranging from 3.5% a t 300 nm to 7.0% at 600
nm a t a temperature of 5000 K. By plotting In (IAX5) vs. 1 / X , one can obtain a straight line of slope - C z / T from which the color temperature T is estimated. If the sonoluminescence is caused by blackbody radiation, the temperature, T , is the blackbody temperature of the source. However, if the sonoluminescence originates from other processes (e.g., chemiluminescence), the estimate T i s called the color temperature of luminescence. In the case of chemiluminescence, therefore, T does not correspond to the thermodynamic temperature of the bubble contents but is a parameter which is still useful in characterizing the spectral distribution of the luminescence. For example, a lower value of T would indicate the shift of the spectral distribution intensities toward longer wavelengths. CC1, Concentration Dependence. If the sonoluminescence from aqueous solutions of carbon tetrachloride were
The Journal of Physical Chemistry, Vol. 87, No. 8, 1983
Sonoluminescence and Sonochemical Reactions
TABLE 111: Influence of the CC1, Concentration on the Color Temperature of Sonoluminescence
CCl, satn, %
color temp,
K
color temp,
K
CCl, satn, %
H,O-Rich Solutions 0
5300 5200 5100
25 50
distilled CCl, 50% CCl, + 50% H,O
4900 4700
75
100
CC1,-Rich Solutions satd H,O in CCl,
4200 3600
4300
to resemble a blackbody, as assumed by Srinivasan’ and Gunther,, the total intensity at a given temperature can be obtained from Stefan’s law
where Zba = total intensity of a blackbody at temperature T and 0 = Stefan’s constant. Table I11 shows the temperatures obtained by fitting Wien’s law to the sonoluminescence from aqueous carbon tetrachloride solutions. The temperature range from 5300 K for water, 4700 K for a saturated aqueous solution of CCl,, and 4200 K for distilled CCl,. If the sonoluminescence spectra were of a blackbody origin, we have from eq 17
I,,[H,O-CCl,]/(I,,[H,O])
= (4700)4/(5300)4= 0.6
(18) while the experimental results give
I,~[H,O-CC1,1/(I,,[H,OI)
= 2.8
(19)
There is even a greater discrepancy when the carbon tetrachloride rich solutions are considered. For example = (4200)4/(5300)4= 0.4
Z,,[CCl,]/(Z~t,[H,O]]
(20)
and the experimentally determined ratio is
1367
~tOtal[CCLI/ ~ ~ t O t a ~= ~6.0 ~ Z ~ l ~ (21) While the total intensity of luminescence decreases with decreasing temperature for a blackbody, the experimental results show the sonoluminescence to increase with decreasing temperature. This lack of agreement suggests that the sonoluminescence is not blackbody radiation but is due to chemiluminescence. The temperatures determined by fitting a blackbody radiation law to sonoluminescence, therefore, yields a color temperature associated with the luminescence. The decrease in the color temperature with increasing CCl, concentration is due to the shift of the spectral distribution toward longer wavelengths. Static Pressure Dependence. The spectral distribution of sonoluminescence from H20-CC14-N2 solutions a t pressures ranging from 1 to 20 atm is given in Table 11. A linear regression to relate the color temperature to the static pressure yields a correlation coefficient of 0.14. Consequently, a test based on the Student’s t statistics at the 99% confidence interval indicated no relationship between the static pressure and the sonoluminescence color temperature. The color temperature (rounded off to the nearest 100 K) of sonoluminescence over the pressure range of 1-10 atm was determined to be 4900 f 600 K. The fact that the sonoluminescence intensity changes with static pressure, while the color temperature associated with the spectral distribution is independent of static pressure, suggests that the number of cavitation bubbles is dependent on static pressure. This dependency is similar to that obtained for the sonoluminescence of water at various static pressures.23 Sonochemistry of H,O-CCl,-N,. All the liquid samples were ultrasonically irradiated for a period of 15 min and the concentration of products resulting from the decomposition of the CCl, was determined. As seen from eq 6-8, the chlorine-containing products are Clz, HCl, and C2C1,. At the experimental conditions, C2C16is a solid while C12 undergoes hydrolysis to yield HC1 and HOC1. In Table IV the concentrations of C1- and OC1- (mg/L) obtained after 15 min of ultrasonic irradiation at various static pressures are reported. This dependence of the product
TABLE IV: Products Resulting from the Sonochemical Decomposition of H,O-CCl,-N, Solutions at Various Static Pressures Concentration mg/l iter
I
Static Pressure, Atmospheres
1
.o
1
.o
2.7
3.7
4.1
4.4
6 .1
6 .1
7.8
7.8
oc 1
16.5
15.4
14.2
17.0
16.8
18.4
28.2
30.1
14.9
16. 1
c1
39,4
37.9
47.0
41.5
50.5
48.1
54,3
50.0
42 . O
39.5
OCl+Cl
55.9
53.4
61.2
58.5
67.4
66.5
82.4
89.2
56.9
55.7
Cl/OCl
2.39
2.46
3.31
2.44
3.00
2.61
1.92
1.96
2.82
2.45
Concentration mg/ 1 1 ter
Statlc Pressure, Atmospheres 9.2
9.5
10 2
11.2
11 9
12.9
13.2
14 . 6 I 1 6 3
I 1 8 0
oc 1
20.4
19.9
23.4
86,9
39.0
32.8
16.3
17.9
14.2
8.9
c1
48.4
45.7
55.0
C0.8
63.1
63.5
23.3
26.6
24.1
16.5
OCl+Cl
68.8
65.6
78.4
97.7
102.1
96.3
‘39.5
44,5
38.3
25.4
1.48
1.70
1 85
Cl/OCl
2,37
2.30
2.35
1 65
1 .c2
1.94
1.42
1368
The Journal of Physical Chemistry, Vol. 87, No. 8, 1983
Chendke and Fogler
3212 0-
16t
u
I - Sonolum
Intensity
~ ~ S o n o c h eYield m Y,:Sonochem Yield a t 1ATM
l 2 F
YG
i
w LT
01
0
1 04
I
08
12
1 '6
20
I 24
I
28
32
I
36
40
I/[,
I
L
0
0 3
Figure 4. Relationship between sonoluminescence and sonochemical yields at elevated static pressures.
\
201-
Some of the free C1 radicals produced by the reaction in eq 23 could react with water to give HC1.
0 6 9 i2 15 18 STATIC PRESSURE, atmospheres
3
21
C1+ HzO
Figure 3. Effect of static pressure on sonoluminescence and sonochemical reactions.
TABLE V : Gas-Chromatographic Detection of CCl, Conversion during Ultrasonic Irradiation
c1
detected
atm
before irrad
after irrad
as HOCl + HCL, mg/L
1.0 6.1 7.8 11.2 19.7
98.5 97.0 100.0 100.0 100.0
91.0 77.0 88.0 73.0 91.8
53.4 89.2 55.7 97.7 18.6
press.,
HCI, '3 7.4 12.5 7.6 13.2 2.5
7.5 20.0 12.0 27.0 8.3
yields on the static pressure is shown in Figure 3. For a few runs, a complete gas-chromatographic analysis was attempted to identify products of decomposition other than HOCl and HCl. Although it was possible to measure the C C 4 concentration before and after irradiation, no other compounds such as C2C14or CzC&were detected by the chromatograph. The absence of C2C14is supported by the results of Spurlock and Reifsneider,lgwho also failed to detect any CZClfion irradiation of aqueous CCl, solutions. The solid C2Clfiwas mixed with the metal particles eroded from the tip and, thus, the gravimeteric analysis performed by Spurlock and Reif~neider'~ was not possible. From the CCl, concentrations before and after ultrasonic irradiation, the amount decomposed in 15 min was determined. The data are given in Table V and show that the extent of decomposition ranged from 7 % at the atmospheric pressure to 27% at 11.2 atm. The ratio (Cl-)/(OCl-) has a maximum value of about 3 and decreases with increasing pressure. Consequently, the generation of HOCl and HC1 described by eq 6 and 9 cannot be the dominant reactions since the ratio of (Cl-)/(OCl-) will always be 1. While eq 7 and 8 could account for greater amounts of HC1, there are also other possibilities. One such sequence of reactions is cc1, CCl, + c1 (22)
-
-
e1 + cc14 c1*+ cc1, 2cc1, c2c1,
(23) (24)
HCl
+ OH
(25)
In addition, it is known that both H and OH radicals under the conditions found in collapsing cavities could also react with CC14 to produce HC1 and HOCl, e.g.
+ CC1, OH + C C 4 H
original CC1, consumed due to irrad, 70
original CC1, converted to HOCl +
-
-
-
CC13 + HCl
(26)
CC13 + HOCl
(27)
Consequently the ratio (Cl-)/ (OC1-) will depend on the relative rates of reactions given by eq 7, 8, and 22-27. Relationship between Sonoluminescence and Sonochemical Yields. The similarity between sonoluminescence and the sonochemical reactions in a cavitation bubble is readily apparent from Figure 3. In Figure 4,the ratio of the sonoluminescence intensity at a given pressure to the intensity at atmospheric pressure is plotted vs. the ratio of the sonochemical yields at the same pressure to the sonochemical yield at atmospheric pressure. A linear regression line is drawn in Figure 4 to show the relationship between sonoluminescence and sonochemical reactions. Griffing and Sette" found a similar relationship between the sonoluminescence and sonochemical yields in their study at atmospheric pressure. This study reveals that the linear relationship between sonoluminescence and sonochemical yields holds over the entire range of pressures studied (1-20 atm). Conclusions (1)The sonoluminescence intensity of aqueous solutions was found to increase linearly with the degree of carbon tetrachloride concentration in the 0-100% saturation range. A saturated solution of CCl, in H 2 0 luminesced with an intensity 2.8 times that of water. (2) It is postulated that the increased sonoluminescence in the presence of CCll is due to the recombination continua CCl,+ + e- CCl, + h u . The observed shift of the maximum in the sonoluminescence spectra to 500 nm is consistent with the hypothesis that the increased luminescence is due to the recombination of CCl,+ and an electron. (3) The spectral distribution of sonoluminescence is shown not to follow a blackbody distribution law and is attributed to chemiluminescence. (4) The sonoluminescence intensity, spectral distribution, and sonochemical yields from saturated aqueous solutions of CC1, were measured simultaneously over a
-
J. Phys. Chem. 1983, 87, 1369-1377
pressure range of 1-20 atm. The sonoluminescence intensity was determined to be linearly related to the yield of sonochemical decomposition over the entire range of pressures (1-20 atm). (5) The sonoluminescence intensity changed by a factor of about 6 over the entire pressure range while the spectral distribution of sonoluminescence was found to be independent of the pressure.
1389
(6) The color temperature of sonoluminescence was estimated to be 4900 f 600 K over the entire pressure range. This is in agreement with the fact that the spectral distribution of sonoluminescence was independent of pressure. Registry No. CC14, 56-23-5; HzO,7732-18-5;HC1, 7647-01-0; HOC1, 7790-92-3.
Chemical Effects of Ultrasound on Aqueous Solutions. Formation of Hydroxyl Radicals and Hydrogen Atoms Kelsuke Maklno, Magdl M. Mossoba, and Peter Rlesr' Laboratory of P8thophysioiogy National Cancer Institute, N8tion8l Institutes of Health, Eethesd8, Maryland 20205 (Received: September 23, 1982)
Direct evidence for the formation of .OH and -H in the cavitation bubbles produced by ultrasound in argonsaturated aqueous solutions is presented. The methods of spin trapping with 5,5-dimethyl-l-pyrroline 1-oxide (DMPO), 4-[ [ (l,l-dimethylethyl)imino]methyl]-l-methylpyridinium N-oxide (PYBN), and 2-methyl-N-(4pyridinylmethylene)-2-propanamineN,N'-dioxide (POBN) combined with ESR were used for the detection of .OH and .H. With either DMPO or PYBN, the OH and H spin adducts were obtained, and with POBN, the H adduct was observed. These results were confirmed by sonolysis of D20 solutions containing the same spin traps. By studying the competition reactions for .OH and .H between the spin traps, DMPO and POBN, and .OH and .H scavengers [O,, formate, thiocyanate, benzoate, methanol, ethanol, 1-propanol, 2-methyl-2propanol, acetone, 2-methyl-2-nitrosopropane (MNP)], we obtained further verification for the formation of .OH and .H. Sonolysis of aqueous solutions containing DMPO or POBN in the presence of air suppressed formation of H adducts but not that of OH-DMPO. The unusually large effects of acetone and MNP on the spin adduct yields could be explained either by the scavenging of radicals in the gas phase of the cavitation bubbles or by preventing the collapse of the gas bubbles during cavitation and thus reducing radical formation. From the results of the present work, it was inferred that -OH and .H are formed in the cavitation bubbles.
Introduction The study of chemical effects of ultrasound on biological systems1 is of interest because of the widespread applications of ultrasound in diagnosis and therapy in medi~ i n e . ~The - ~ collapsing cavities which occur during sonolysis lead to chemical damage and sonoluminescence due to the production of high local instantaneous temperatures and pressures.&'O The threshold for cavitation increases with increasing frequency and also depends on factors such as the number of motes (nonwettable particles), nature of the dissolved gases, and the techniques for cavitation dete~tion.~Jl-l~ It has been proposed that ultrasound-induced reactions in aqueous solutions involve free-radical mechanisms due to the formation of hydroxyl radicals (.OH) and hydrogen atoms (-H).14-23 The effect of volatile scavengers on the formation of hydrogen peroxide during the sonolysis of aqueous solutions was studied by Wei~s1er.l~ It was inferred that H202is formed by the recombination of .OH. However, Anbar and Pecht found that nonvolatile scavengers, in contrast to volatile organic solutes, do not affect the production of H202and concluded that H202is not formed from .OH.17 Weissler also studied ultrasound hydroxylation of benzoic acid which was reported to be due to the formation of .OH by ~1trasound.l~ Anbar and Pecht found that, when deuterated formate anions were sonolyzed in aqueous solutions, HD was produced and the yield Member N I H E S R Center.
of HD was independent of solute concentrations, suggesting that -H is formed from water by sonolysis.18 Verrall (1) Elipiner, I. E. "Ultrasound, Physical Chemistry and Biological Effects"; Consultants Bureau: New York, 1964. (2) Distasio, J. I. "Ultrasonics as a Medical Diagnostic Tool"; Noyes Data Corporation: Park Ridge, NJ, 1980. (3) Kremkau, F. W. "Diagnostic Ultrasound, Physical Principles and Exercises"; Grune and Stratton: New York, 1980. (4) Kremkau, F. W. J . Clin. Ultrasound 1979, 7, 287. (5) Weissler, A. J. Acoust. SOC. Am. 1953, 25, 651. (6) Weissler, A. In "Encyclopedia of Chemical Technology"; Kirk, P. E.; Othmer, D. F., Ed.; Wiley-Interscience: New York, 1978. (7) Weissler, A,; Cooper, H. W.; Synder, S. J. Am. Chem. SOC.1950, 72, 1769. (8) Weissler, A.; Pecht, I.; Anbar, M. Science 1965, 150, 1288. (9) Moon, S.; Duchin, L.; Conney, J. V. Tetrahedron Lett. 1979, 41, 3917. (10) Sehgal, C. M.; Wang, S. Y. J . Am. Chem. SOC.1981, 103, 6606. (11) Hill, C. R. J. Acoust. SOC.Am. 1972, 52, 667. (12) Armour, E. P.; Corry, P. M. Radiat. Res. 1982,89, 369. (13) Apfel, R. E. In "Methods of ExperimeriLal Physics"; Academic Press: New York, 1981; Vol. 19, Chapter 7, p 355. (14) Weissler, A. J . Am. Chem. SOC.1959, 81, 1077. (15) Weissler, A. Nature (London) 1962, 193, 1070. (16) Anbar, M.; Pecht, I. J. Chem. Phys. 1964, 40, 608. (17) Anbar, M.; Pecht, I. J. Phys. Chem. 1964, 68, 352. (18) Anbar, M.; Pecht, I. J . Phys. Chem. 1964, 68, 1460. (19) Anbar, M.; Pecht, I. J. Phys. Chem. 1964, 68,, 1462. (20) Anbar, M.; Pecht, I. J . Phys. Chem. 1967, 71, 1246. (21) Reifsneider; S. B.; Spurlock, L. A. J. Am. Chem. SOC.1973, 95, 299. (22) Mead, E. L.; Sutherland, R. G.;Verrall, R. E. Can. J. Chem. 1975, 53, 2394. (23) McKee, J. R.; Christman, C. L.; O'Brien, W. D., Jr.; Wang, S. Y. Biochemistry 1977, 16, 4651.
This article not subject to US. Copyright. Published 1983 by the American Chemical Society
