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Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions Mohammad Ghalei, Jun Ma, Uli Schmidhammer, Johan Vandenborre, Massoud Fattahi, and Mehran Mostafavi J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.5b12405 • Publication Date (Web): 17 Feb 2016 Downloaded from http://pubs.acs.org on February 19, 2016
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Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions Mohammad Ghalei1; Jun Ma2, Uli Schmidhammer2, Johan Vandenborre1, Massoud Fattahi1 and Mehran Mostafavi2* 1
SUBATEC UMR 6457. École des Mines de Nantes, CNRS/Université de Nantes, 4, Rue Alfred Kastler, La chantrerie BP 20722, 44307 Nantes cedex 3, France 2 Laboratoire de Chimie Physique/ELYSE, UMR 8000 CNRS /Université Paris-Sud 11, Faculté des Sciences d’Orsay, Bât. 349, 91405 Orsay Cedex, France E-mail: [email protected],
Abstract Highly concentrated potassium carbonate aqueous solutions are studied by picosecond pulse radiolysis with the purpose of exploring the formation processes of carbonate radical CO3•–. The transient absorption band of solvated electron produced by ionizing is markedly shifted from 715 to 600 nm when the solute concentration of K2CO3 is 5 mol L–1. This spectral shift is even more important than that observed for the solvated electron in 10 mol L–1 KOH solutions. The broad absorption band of solvated electron in K2CO3 solutions overlaps with the one of carbonate radical CO3•– formed at ultrashort time. Nitrate ion is used to scavenge the solvated electron and to observe the contribution of carbonate radical CO3•–. The analysis of the amplitude and the kinetics of carbonate radical formation in highly concentrated solutions shows that CO3•– is formed within the electron pulse (7 ps) by two parallel mechanisms: a direct effect on the solute and the oxidation of the solute by water radical hole H2O•+. These two mechanisms are followed by an additional one, by reaction between the solute and OH• radical especially in lower concentration. The radiolytic yield of each process is discussed.
Keywords: Picosecond pulse radiolysis, highly concentrated solution, direct effect, ultrafast kinetics, radiolysis, carbonate radical
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Introduction The carbonate radical CO3•– plays an important role in biological, environmental and chemical systems.1,2,3 In biological systems, the carbonate radical which can be produced by peroxidase activity oxidizes amino acids and proteins by one electron oxidation.4 It can also oxidize the metal center of organo-metallic compounds in the human body. 5 As the bicarbonate ion is abundant in biological systems, and also the carbonate radical can be produced through oxidation of CO2 by nitrogen oxide radical, the study of the carbonate radical is a mandatory issue for the understanding of oxidative damages to biological tissues.6 Although the presence of carbonate radicals in atmosphere is not important, its concentration can reach high values in surface waters.7 The formation of carbonate and bicarbonate radical ions and their reactivity towards OH• and H2O2 have been studied by pulse radiolysis of diluted solutions at room temperature and at elevated temperatures. The rate constant for the reaction between carbonate and OH• forming the CO3•- radical was reported to be 3 × 108 mol L–1 s–1. This electrophilic oxygen centered radical has a redox potential of 1.78 V8 at pH 7; it exhibits an absorption band with maximum at 600 nm and an extinction coefficient of 1970 mol–1 L cm–1. The decay of carbonate radical by disproportionation reaction is relatively slow, and in some conditions the decay is complex with the presence of several reactions. Carbonate solutions can be used in radiochemistry for both oxidation and complexation of transient metals as a method of nuclear waste stabilization.9 For example, it is well-known that highly concentrated carbonate solutions can stabilize the radioactive element Tc. 99mTc is a γ emitter which is used in nuclear medicine for a wide variety of diagnostic tests. In that case, it is important to know the effect of irradiation of the solute. Moreover, its short half-life involves considerable amounts of nuclear fission products which exist mainly as pertechnetate ion (TcO4). Pertechnetate has high mobility and solubility, and in order to prevent the contamination of environment, it must be stabilized by changing the oxidation state and complexation reaction. Although the carbonate concentration is low in environment, the high concentrations of carbonate must be used in in order to stabilize soluble technetium carbonate complex for further studies. However, for a high concentrated solution, the mechanism used in diluted solutions cannot be considered. Our recent studies on picosecond pulse radiolysis of concentrated inorganic aqueous solutions have shown that three mechanisms of oxidation of solute can occur: i) the direct effect of radiation on the solute, in that case the solute lose one electron which can be further solvated; ii) the oxidation of the solute by water radical hole H2O•+, occurring only if the solute is in contact with this radical; iii) the oxidation of the solute by OH• radical. In our previous studies about concentrated sulfuric acid, it was possible to estimate the yield of radical formation through oxidation by water hole through measuring directly the yield of sulfate radical in neat sulfuric acid on the picosecond range. For these systems, it was shown that the electron transfer reaction from the solute to the water hole could be more rapid than a proton transfer reaction.10-16 In the present work, a picosecond pulse radiolysis study of five highly concentrated K2CO3 solutions has been carried out in order to find the time dependent oxidation radiolytic yield in perspective to allowing the evaluation on the redox reactions of solutions containing Tc 2 ACS Paragon Plus Environment
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radioelement containing also high concentration of carbonate anion. 17 For this purpose, the mechanism and the yield of carbonate radical formation are discussed. Experimental method The picosecond pulse radiolysis experiments were performed at the ELYSE facility, University of Paris-Sud. The electron accelerator is described in detail elsewhere. 18 , 19 For the present experiments ELYSE delivers electron pulses with an energy of 7.1 MeV and a charge around 4 nC at a repetition rate of 10 Hz. ELYSE provides electron bunches in this configuration with a typical pulse duration around 7 ps and a rms shot-to-shot jitter less than 1 ps.20,21 The electron pump - optical probe set-up is based on the laser-electron intrinsic synchronization resulting from the laser-triggered photocathode22 and is detailed elsewhere.23,24 A femtosecond Ti:Sapphire amplifier laser output is frequency tripled and used to produce the electron pulse that is accelerated by the radiofrequency fields. About 1 µJ of the laser source was focused into a 6 mm thick CaF2 disk to generate a supercontinuum covering the near UV and visible spectrum that is used as the optical probe. The dose per pulse in neat water was determined by measuring the absorbance of the hydrated electron, Ae − ( λ , t ) , and by considering its initial yield measured aq
–7
at 15 ps to be G(t = 15 ps) = 4.2 × 10 mol J-1.25 Therefore, the dose absorbed in water is given by Dwater (Gy ) =
Ae− (λ , t ) hyd
(1)
ε λ l ρ wG ( t )
where ε is the hydrated electron extinction coefficient (19130 M-1cm-1, at maximum 718 nm),26 l is the optical path in the cell, and ρw is the density of solution. All the measurements were made in a flow cell with a 5 mm optical path collinear to the electron pulse propagation. The absorbance measured for a given species in highly concentrated solutions is given by equation 2.
A(λ, t ) = ε λ lc(t) = ελ lFDW G(t )
(2)
The dose additionally absorbed by the solute in concentrated solutions is obtained by multiplying the absorbed dose in pure water by the dose factor F: F = ρsol (ZK2CO3 p / AK2CO3 + Zwater (100 − p) / Awater )(ZK2CO3 100 / AK2CO3 )−1
where ρsol
(3) is the density of the solution, Z is the number of electrons, A is the mass number,
and p is the weight fraction of the solute per 100 gram of solution. Solutions containing carbonate anions at high concentration and pure water were studied under identical experimental conditions. The relevant parameters of the solutions used in this work are given in Table 1. Measurements were performed at 22.5 °C, the room temperature during the pulse radiolysis experiments.
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Results Figure 1 shows the evolution of the transient absorption of a solution containing 5 mol L–1 carbonate K2CO3 (sample 1). The transient spectra recorded directly after the picosecond electron pulse (20 ps) and at a delay time of 3 ns reveal an important absorption in the visible with a maximum around 600 nm; the typical absorption of the hydrated electron peaking at 715 nm is not seen. It is well known that in the presence of non-reactive metal cation such as K+ (10 mol L–1 in this case) the absorption spectrum of the solvated electron can be shifted to shorter wavelengths, So, it seems that the known strong absorption band of the hydrated electron in this solution overlaps with that of carbonate radical which has an absorption centered around 600 nm. Such a strong shift of the absorption of hydrated electron has never been reported before. It should be noted that the shift of the absorption band of the solvated electron depends on the concentration of the non-reactive metal cation, so the degree of spectral shift for each solution (2, 3, 5 mol L–1) is different. To calculate the radiolytic yield of carbonate radical in picosecond range, it is necessary to obtain the absorption spectra of this radical. Picosecond pulse radiolysis measurements are performed in solution containing 10 mol L–1 KOH (Figure 2) in order to get estimation for the shift of the absorption spectra of the solvated electron in the presence of highly concentrated K+. In this case the radical of carbonate is not formed and the only species absorbing in the visible range is the solvated electron. For 10 mol L–1 KOH solution, the maximum of the absorption band is found to be shifted from 715 to 650 nm showing clearly that the shift is imposed by the presence of high concentration of K+. But the shift is less important (~ 50 nm) than that observed in 5 mol L–1 K2CO3 solution exhibiting a maximum at 600 nm. It is known that the shift of the absorption band of solvated electron depends not only on the metal cation concentration but also on the counter-ion and the composition of the solution. The counter ion being different (OH– instead of CO32–), it can play a different role on the solvent structure around the solvated electron resulting in a different absorption band. The presence of the intense absorption band at 600 nm prevents the direct observation of radical carbonate having an extinction coefficient 10 times lower than hydrated electron at 600 nm. Therefore, the soluble nitrate ion NO3− was selected in highly concentrated carbonate solutions as a scavenger, and its fast reaction with solvated electron or presolvated electron allows suppressing its signal without introducing absorbing additional radicals in the visible range. For the solutions with scavenger containing different concentrations of carbonate, the absorption spectra recorded at 20 ps after the pulse are shown in Figure 3. The amplitudes of the absorption spectra are corrected by normalizing the absorbed dose (see the experimental section). The maximum of the absorption band at 20 ps is located at 600 nm, 620 nm and 650 nm for carbonate solutions with concentrations of 5, 3 and 2 mol L–1, respectively. At this delay the amplitude of the absorption is still very high; it is expected that the absorption spectra contain a contribution of the solvated electron as the scavenging reaction is not terminated. In contrast, when the solvated electron is scavenged totally by NO3– in the three solutions at 3000 ps, the
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amplitude of the absorption is much lower and it shows an identical absorption band of the carbonate radical (Figure 4). The kinetics for the three solutions are reported at 600 nm and 780 nm (Figure 5). The first wavelength (600 nm) corresponds to the absorption of the solvated electron and the species due to the radiolysis of carbonate solution, the second one (780 nm) is only due to the solvated electron. Due to the reaction with NO3-, the decay of solvated electron is fast. At 600 nm the kinetics are very different. For the solutions containing 0.7 M NO3– the decay is almost complete in less than 500 ps. In the solution of 5 mol L–1 with its reduced solubility of NO3–, the scavenger concentration is only limited to 0.3 mol L–1 so that the decay of the solvated electron is correspondingly slower. In that case, the initial absorbance is slightly higher due to the suppressed scavenging reaction of NO3– ion with the pre-solvated electron. In order to determinate the yield of carbonate radical just after the pulse, the contribution of solvated electron absorption is subtracted from the recorded data. As the extinction coefficient of the carbonate radical is very low compared to the one of the solvated electron, we consider that the observed spectral positions of the maxima (600, 625, 650 nm) correspond to the one of solvated electron. For example, the shift is 120 nm for solution containing 5 mol L–1 carbonate. With the shift of the absorption band (in energy scale) and the pure kinetics and amplitude of the solvated electron observed at 780 nm by assuming their band shape and extinction coefficient remain the same, the concentration of solvated electron for each solution can be deduced. The absorption spectra at 20 ps due to the carbonate radiolysis in each solution after subtraction of the contribution of the solvated electron are reported in Figure 6. The spectra are normalized showing that their shape and intensity are very close and are in agreement with the one of the carbonate radical reported in the literature.
Discussion and concluding remarks If we consider that after the electron pulse the same radical of carbonate is formed in three solutions, the time dependent radical yield can be deduced from the kinetics. As reported in Figure 7, the time dependent yield for solution of 5 mol L–1 K2CO3 is different compared to the two others ones. First, the initial yield is higher after the pulse and second, it decreases to reaches almost the same value (3.2 × 10–7 mol J–1) than that of the two other cases. It is interesting to note that at 5 mol L–1 concentration a slight increase of the carbonate radical yield is observed in the first 100 ps. The value is increased from 3.3 × 10–7 mol J–1 to 3.6 × 10–7 mol J-1 and then a slight decrease is observed which can be due to the reaction with solvated electron in spurs. For solutions containing 2 and 3 mol L–1 carbonate solutions, the initial yield of radical carbonate is only 1.3×10–7 mol J–1 and 2 × 10–7 mol J–1, respectively. As reported in highly concentrated solutions, this initial yield is due to the formation of the carbonate radical by direct effect and the reaction of carbonate anion with water hole radical cation. After the pulse, an increase of the carbonate radical yield is observed. It can be interpreted by the reaction of carbonate solutes with OH• radical constituting the third pathway of the radical carbonate formation. To explain this time dependent radical yield, we have to consider that in solution containing 5 mol L–1 carbonate 5 ACS Paragon Plus Environment
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anions, the amount of water is very low: only 9 water molecules are present for each carbonate salt molecule. It can be considered that a large amount of the water molecules are in vicinity of carbonate anions. Therefore, the ionized water is in close contact of the carbonate anion, and the reaction of carbonate anion with water hole contributes efficiently to the formation of the carbonate radical. In that case, as the large amount of the precursor of OH• radical is scavenged by the carbonate anion, the amount of the OH• radical in this solution is low. The slight increase of the yield during the first 100 ps is due to the reaction of the carbonate anion with the OH• radical. But for the lowest concentration (2 mol L–1), 80% of the dose is absorbed by water molecules and the probability of water hole scavenging is low. Therefore, the initial yield of the radical carbonate is low. In that case, the OH• radicals are formed and they react with the carbonate anions forming the additional carbonate radical within 3 ns. It is possible to rationalize these observations by using the following equation for the initial yield of the radical carbonate observed just after the electron pulse: Gobs = fs Gs + α fw GH2O•+
(4)
where fs is the electron fraction of the solute, Gs is direct ionization yield of the solute, fw (=1 – fs) is the electron fraction of the water, GH2O•+ is the yield of water cations formed, and α is the fraction of water cations that react with the solute. Recent simulations of several kinetics in highly concentrated solutions showed that equation 4 with GH2O•+ ~ 4.5×10–7 mol J-1 can fit well the experimental data.27 By using this and by assuming the value of the yield of the direct effect around Gs = 3.5 × 10-7 mol J–1, which is very close to that obtained recently in the case of sulfate and phosphate anions, it is possible to evaluate the value of α. As expected, the fraction of water cations that react with the solute is found to be concentration dependent. It is equal to 22%, 30% and 70% for the solution of 2, 3 and 5 mol L-1 carbonate, respectively. This increase is reasonable because of the decrease of the ratio of water molecule and solute (Table 1). Therefore, it is concluded that by following the kinetics of the carbonate radical, it can be claimed that in the nanosecond time scale at lowest concentration most of the oxidation is due to the OH• radicals: OH• + CO32– → CO3–• + OH(5) which is produced mainly by the following reaction: H2O•+ + H2O → OH• + H3O+ (6) •+ However, ultrafast oxidation of the solute by H2O radical occurs mainly at high solute concentrations. (7) H2O•+ + CO32- → CO3-• + H2O •+ Therefore, the trend to scavenge the H2O radical depends on the competition between proton transfer by the H2O•+ radical and water ((reaction 6) with a rate constant of kpt) and the electron transfer between the H2O•+ radical and the solute (reaction 7 with a rate constant of ket). By considering an oversimplified kinetics model, the following equation can be used:
α≈
ሾுమ ை శ ሿሾௌሿ శ ሾுమ ை ሿሾுమ ைሿ
=
ሾௌሿ ሾுమ
= ܴ ିଵ ைሿ
(8)
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The value of α is higher when R is decrease i.e. the concentration of the solute increases. In conclusion, the yield of CO3•- in highly concentrated carbonate solutions is studied and quantified on the picosecond time scale. The solute concentration was varied and a solvated electron scavenger added in order to distinguish the different contributions and mechanism. The contribution of the absorption band of the solvated electron was carefully subtracted; due to its interaction with the carbonate counter ion resulting in a pair solvated electron and K+, its absorption is markedly blue shifted compared to the one of hydrated electron. The formation of the radical carbonate is originated from three mechanisms: the direct ionization, the reaction with the water hole and the reaction with OH• radical. The contribution of the two first mechanisms is revealed by the initial yield of CO3•- measured just after 7 ps electron pulse and the last one at nanosecond time scale. It is interesting to note that the initial yield of radical carbonate is very different for 3 and 5 mol L-1 solutions. Such a difference cannot be explained by the direct absorption of the dose by the solute, but by the additional reaction with water hole which is very efficient for 5 mol L-1 solution. Eventually, it is worth noting that whatever the mechanism of the radical formation, the yield is almost the same 3 ns after dose deposition. In dilute solutions, the two first mechanisms of oxidation; by direct effect and that by electron transfer with the cation radical of water are fully negligible. Nevertheless, the radical yield of oxidizing species (mainly carbonate and OH• radicals) at 3 ns, even in dilute solutions, is expected to be around 3.2 × 10-7 mol J–1 which is very close to that of OH• radical in neat water.28
Acknowledgement The work was supported by a public grant from University of Paris-Sud “Moyen de Rechreche Mutualisé”. The authors thank Jean-Philippe Larbre and Pierre Jeunesse for their help during the experiments with ELYSE facility.
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Table 1. Solutions and their corresponding physio-chemical parameters. sample 1 2 3 4 5
K2CO3 [mol.L-1] 5 0 2 3 5
KOH Nitrate -1 [mol.L ] [mol.L-1] 0 0 10 0.7 0.7 0.3 -
fs
fw
0.4
0.6
0.2 0.29 0.4
0.8 0.71 0.6
F (g.cm3)
ρsol (g.cm3)
R=[H2O]/[S]
1.11 1.35 1.54
1.12 1.36 1.55
26.39 17.4 9.55
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0.20
20 ps 3000 ps
0.15
0.20
0.10
0.05
Abs / 0.5 cm
Absorbance / 0.5 cm
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600 nm
0.15 0.10 0.05
780 nm
0.00 0
0.00 450
500
500 1000 1500 2000 2500 3000 Time (ps)
550
600
650
700
750
800
λ (nm)
Figure 1. Transient absorption spectra and kinetics observed in 5 mol L–1 K2CO3 aqueous solutions without adding any solvated electron scavenger.
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0.30
20 ps 0.25
3000 ps 0.20
0.15
0.3 600 nm Abs / 0.5 cm
Absorbance / 0.5 cm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.10
0.05
0.2 780 nm
0.1 0.0 0
0.00 400
450
500
550
1000 2000 Time (ps)
600
650
3000
700
4000
750
800
λ (nm)
Figure 2. Transient absorption spectrum of 10 mol L-1 KOH aqueous solution observed at t = 20 ps and t = 3000 ps. Inset: Decay of the solvated electron in KOH solution at 600 and 780 nm.
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0.10
20 ps
5 mol / L K2CO3 0.08
Absorbance / 0.5 cm
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2 mol / L K2CO3 0.06
0.04
3 mol / L K2CO3 0.02
0.00 400
450
500
550
600
650
700
750
800
λ (nm)
Figure 3. Transient absorption spectra observed at 20 ps in K2CO3 solutions of different concentration with nitrate scavenger for the same absorbed dose. The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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0.024
3000 ps 0.020
Absorbance / 0.5 cm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.016
0.012
0.008
2 mol L-1 K2CO3 0.004
3 mol L-1 K2CO3 5 mol L-1 K2CO3
0.000 500
550
600
650
700
750
λ (nm)
Figure 4. Absorption spectra observed at the delay time of 3000 ps in K2CO3 solutions with nitrate scavenger at different concentration for the same absorbed dose. The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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Absorbance at 780 nm (0.5 cm)
0.10
0.08
0.06
0.04
0.02
0.00 0
1000
2000
3000
4000
Time (ps) 0.10
Absorbance at 600 nm (0.5 cm)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0.08
0.06
0.04
0.02
0.00 0
1000
2000
3000
4000
Time (ps)
Figure 5. Kinetics observed for each K2CO3 solution (5 mol L-1, O blue; 3 mol L-1, O red; 2 mol L-1, O black) with NO3- acting as a solvated electron scavenger at 780 nm (top) and 600 nm (bottom). The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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0.020
5 mol L-1 K2CO3 3
0.015
2 0.010
Normalized Absorbance
Absorbance / 0.5 cm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
0.005
5 mol L-1 K2CO3 3 mol L-1 K2CO3 2 mol L-1 K2CO3
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
Energy (eV)
0.000 500
600
700
Wavelength (nm)
Figure 6. Absorption spectra after subtraction of the solvated electron contribution at 20 ps. Inset: Normalized spectra (reported in energy scale) of different carbonate solutions.
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4
0.02
3
0.015
2 mol L-1 3 mol L-1 5 mol L-1
2
1
0.010
0.005
0
Absorbance / 0.5 cm
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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107 Yield of carbonate radicals (mol J-1)
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0 0
1000
2000
3000
4000
Time (ps)
Figure 7. Time dependent radiolytic yield (left scale) (deduced from the time dependent absorption (right scale)) of carbonate radicals in different solutions.
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References 1
Amarjeet Yadav, P.C.M. Carbonate radical anion as an efficient reactive oxygen species: Its reaction with guanyl radical and formation of 8-oxoguanine. Chem. Phys, 2012, 405, 76-98. 2 Liu, Y.; He, X.; Duan, X.; Fu, Y.;, Dionysiou, D.D. Photochemical degradation of oxytetracycline: Influence of pH and role of carbonate radical. Chem. Eng. J. 2015, 276, 113-121. 3 Mazellier, P.; Busset, C.: Delmont, A.; De Laat, J. A comparison of fenuron degradation by hydroxyl and carbonate radicals in aqueous solution. Water res. 2007, 41, 4585-4594. 4 Adams, G., Bisby, R.H., Cundall, R.B, Redpath, J.L., Willson, R.L. Selective free radical reactions with proteins and enzymes: the inactivation of ribonuclease. Rad. Res. 1972, 49, 290-299. 5 Dassanayake, R.S.; Shelley J.T.; Cabelli, D.E.; Brasch, N.E. Pulse Radiolysis and Ultra-HighPerformance Liquid Chromatography/High-Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B12 Derivatives. Chem. Eur. J. 2015, 21, 6409-6419. 6 Lymar, S.; Hunt, I. K. Rapid reaction between peroxonitrite ion and carbon dioxide; implication for biological activity. J. Am Chem. Soc, 1995, 117 8867-8868. 7 Graedel, T.E.; Weschler, C.J. Chemistry within aqueous atmospheric aerosols and raindrops. Rev. Geophys. Space Phys, 1984, 19, 505-539. 8 Bonini, M. G.; and Augusto, O. Carbon dioxide stimulates the production of thiyl, sulfinyl, and disulfide radical anion from thiol oxidation by peroxynitrite J. Biol. Chem. 2001, 276, 9749-9754. 9 Said, K.B.; Seimbille, Y.; Fattahi, M.; Houee-Lévin, C.; Abbé J.C. γ radiation effects on potassium pertechnetate in carbonate media. Appl. Radiat. Isot. 2001, 54, 45-51. 10 Balcerzyk, A.; Schmidhammer, U.; El Omar, A. K.; Jeunesse, P.; Larbre J. P.; Mostafavi. M. Direct and Indirect Radiolytic Effects in Highly Concentrated Aqueous Solutions of Bromide. J. Phys. Chem. A. 2011, 115, 4326-4333. 11 El Omar, A. K.; Schmidhammer, U.; Rousseau, B.; LaVerne, J.; Mostafavi, M. Competition Reactions of H2O•+ Radical in Concentrated Cl- Aqueous Solutions: Picosecond Pulse Radiolysis Study. J. Phys. Chem. A. 2012, 116, 11509-11518. 12 Balcerzyk, A.; LaVerne, J.; Mostafavi, M. Picosecond Pulse Radiolysis of Direct and Indirect Radiolytic Effects in Highly Concentrated Halide Aqueous Solutions. J. Phys. Chem. A. 2011, 115, 9151-9159. 13 Balcerzyk, A.; El Omar, A. K.; Schmidhammer, U.; Pernot, P.; Mostafavi. M. Picosecond Pulse Radiolysis Study of Highly Concentrated Nitric Acid Solutions: Formation Mechanism of NO3• Radical. J. Phys. Chem. A. 2012, 116, 7302-7307. 14 El Omar, A. K.; Schmidhammer, U.; Balcerzyk, A.; LaVerne, J.; Mostafavi, M. Spur Reactions Observed by Picosecond Pulse Radiolysis in Highly Concentrated Bromide Aqueous Solutions. J. Phys. Chem. A. 2013, 117, 2287-2293. 15 Ma, J.; Schmidhammer, U.; Pernot, P.; Mostafavi, M. Reactivity of the Strongest Oxidizing Species in Aqueous Solutions: The Short-Lived Radical Cation H2O•+. J. Phys. Chem. Lett. 2014, 5, 258-261. 16 Ma, J.; Schmidhammer, U.; Mostafavi, M. Picosecond Pulse Radiolysis of Highly Concentrated Sulfuric Acid Solutions: Evidence for the Oxidation Reactivity of Radical Cation H2O•+. J. Phys. Chem. A. 2014, 118, 4030-4037. 17 Ghalei, M.; Vandenborre, J.; Blain, G.; Haddad, F.; Mostafavi, M.; Fattahi, M. Oxidation and/or Reduction of Manganese Species by Gamma-Ray and He2+ Particle Irradiation in Highly Concentrated Carbonate Media. Rad. Phys. Chem. 2016, 119, 142-150.
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Belloni, J.; Monard, H.; Gobert, F.; Larbre, J. -P.; Demarque, A.; De Waele, V.; Lampre, I.; Marignier, J. -L.; Mostafavi, M.; Bourdon, J. C. et al. ELYSE - A Picosecond Electron Accelerator for Pulse Radiolysis Research. Nucl. Instr. and Meth. Phys. Res. A. 2005, 539, 527-539. 19 Marignier, J. L.; De Waele, V.; Monard, H.; Gobert, F.; Larbre, J.-P.; Demarque, A.; Mostafavi, M.; Belloni, J. Time-Resolved Spectroscopy at the Picosecond Laser-triggered Electron Accelerator ELYSE. Rad. Phys. Chem. 2006, 75, 1024-1033. 20 Schmidhammer, U.; De Waele, V.; Marquès, J.-R.; Bourgeois, N.; Mostafavi, M. Single shot linear detection of 0.01-10 THz electromagnetic fields. Appl. Phys. B. 2009, 94, 95-101. 21 De Waele, V.; Schmidhammer, U.; Marquès, J.-R.; Monard, H.; Larbre, J.-P.; Bourgeois, N.; Mostafavi, M. Non-invasive single bunch monitoring for ps pulse radiolysis. Rad. Phys. Chem. 2009, 78, 1099-1101. 22 Belloni, J. ; Crowell, R. A.; Katsumura, Y.; Lin, M.; Marignier, J. -L.; Mostafavi, M.; Muroya, Y.; Akinori, S.; Tagawa, S.; Yoshida, Y.; et al. Ultrafast Pulse Radiolysis Methods. In Recent Trends in Radiation Chemistry, Eds. Wishart, J. F. And Rao, B. S. M World Scientific New Jersey, 2010, P. 121-160. 23 Schmidhammer U.; Pernot P.; De Waele V.; Jeunesse P.; Demarque A.; Murata S.; and Mostafavi M. Distance Dependence of the Reaction Rate for the Reduction of Metal Cations by Solvated Electrons: a picosecond pulse radiolysis study. J. Phys. Chem. A 2010, 114, 12042–12051. 24 Schmidhammer, U.; El Omar, A. K.; Balcerzyk, A.; Mostafavi, M. Transient Absorption Induced by a Picosecond Electron Pulse in the Fused Silica Windows of an Optical Cell. Rad. Phys. Chem. 2012, 81,1715-1719. 25 Muroya, Y.; Lin, M.; Wu, G.; Iijima, H.; Yoshii, K.; Weda, T.; Kudo, H.; Katsumura, Y. A Reevaluation of the Initial Yield of the Hydrated Electron in the Picosecond Time Range. Rad. Phys. Chem. 2005, 72, 169-172. 26 Jou, F. Y.; Freeman, G. R. Shapes of optical spectra of solvated electrons. Effect of pressure. J. Phys. Chem. 1977, 81, 909-915. 27 Ma, J.; Laverne, J.; Mostafavi, M. Scavenging the Water Cation in Concentrated Acidic Solutions. J. Phys. Chem. A. 2015, 119, 10629-10636. 28 El Omar, A. K.; Schmidhammer, U.; Jeunesse, P.; Larbre, J. P.; Lin, M. Z.; Muroya, Y. ; Katsumura, Y. ; Pernot, P.; Mostafavi, M. Time-Dependent Radiolytic Yield of OH. Radical Studied by Picosecond Pulse Radiolysis J. Phys. Chem. A. 2011, 115, 12212-12216.
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107 Yield of carbonate radicals (mol J-1)
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4
Mechanisms of CO3–• formation
3
2
CO32- → CO3–• + eH2O•+ + CO32- → CO3-• + H2O
1
OH• + CO32– → CO3–• + OH0 0
1000
2000
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Article
Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions Mohammad Ghalei, Jun Ma, Uli Schmidhammer, Johan Vandenborre, Massoud Fattahi, and Mehran Mostafavi J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.5b12405 • Publication Date (Web): 17 Feb 2016 Downloaded from http://pubs.acs.org on February 19, 2016
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Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions Mohammad Ghalei1; Jun Ma2, Uli Schmidhammer2, Johan Vandenborre1, Massoud Fattahi1 and Mehran Mostafavi2* 1
SUBATEC UMR 6457. École des Mines de Nantes, CNRS/Université de Nantes, 4, Rue Alfred Kastler, La chantrerie BP 20722, 44307 Nantes cedex 3, France 2 Laboratoire de Chimie Physique/ELYSE, UMR 8000 CNRS /Université Paris-Sud 11, Faculté des Sciences d’Orsay, Bât. 349, 91405 Orsay Cedex, France E-mail: [email protected],
Abstract Highly concentrated potassium carbonate aqueous solutions are studied by picosecond pulse radiolysis with the purpose of exploring the formation processes of carbonate radical CO3•–. The transient absorption band of solvated electron produced by ionizing is markedly shifted from 715 to 600 nm when the solute concentration of K2CO3 is 5 mol L–1. This spectral shift is even more important than that observed for the solvated electron in 10 mol L–1 KOH solutions. The broad absorption band of solvated electron in K2CO3 solutions overlaps with the one of carbonate radical CO3•– formed at ultrashort time. Nitrate ion is used to scavenge the solvated electron and to observe the contribution of carbonate radical CO3•–. The analysis of the amplitude and the kinetics of carbonate radical formation in highly concentrated solutions shows that CO3•– is formed within the electron pulse (7 ps) by two parallel mechanisms: a direct effect on the solute and the oxidation of the solute by water radical hole H2O•+. These two mechanisms are followed by an additional one, by reaction between the solute and OH• radical especially in lower concentration. The radiolytic yield of each process is discussed.
Keywords: Picosecond pulse radiolysis, highly concentrated solution, direct effect, ultrafast kinetics, radiolysis, carbonate radical
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Introduction The carbonate radical CO3•– plays an important role in biological, environmental and chemical systems.1,2,3 In biological systems, the carbonate radical which can be produced by peroxidase activity oxidizes amino acids and proteins by one electron oxidation.4 It can also oxidize the metal center of organo-metallic compounds in the human body. 5 As the bicarbonate ion is abundant in biological systems, and also the carbonate radical can be produced through oxidation of CO2 by nitrogen oxide radical, the study of the carbonate radical is a mandatory issue for the understanding of oxidative damages to biological tissues.6 Although the presence of carbonate radicals in atmosphere is not important, its concentration can reach high values in surface waters.7 The formation of carbonate and bicarbonate radical ions and their reactivity towards OH• and H2O2 have been studied by pulse radiolysis of diluted solutions at room temperature and at elevated temperatures. The rate constant for the reaction between carbonate and OH• forming the CO3•- radical was reported to be 3 × 108 mol L–1 s–1. This electrophilic oxygen centered radical has a redox potential of 1.78 V8 at pH 7; it exhibits an absorption band with maximum at 600 nm and an extinction coefficient of 1970 mol–1 L cm–1. The decay of carbonate radical by disproportionation reaction is relatively slow, and in some conditions the decay is complex with the presence of several reactions. Carbonate solutions can be used in radiochemistry for both oxidation and complexation of transient metals as a method of nuclear waste stabilization.9 For example, it is well-known that highly concentrated carbonate solutions can stabilize the radioactive element Tc. 99mTc is a γ emitter which is used in nuclear medicine for a wide variety of diagnostic tests. In that case, it is important to know the effect of irradiation of the solute. Moreover, its short half-life involves considerable amounts of nuclear fission products which exist mainly as pertechnetate ion (TcO4). Pertechnetate has high mobility and solubility, and in order to prevent the contamination of environment, it must be stabilized by changing the oxidation state and complexation reaction. Although the carbonate concentration is low in environment, the high concentrations of carbonate must be used in in order to stabilize soluble technetium carbonate complex for further studies. However, for a high concentrated solution, the mechanism used in diluted solutions cannot be considered. Our recent studies on picosecond pulse radiolysis of concentrated inorganic aqueous solutions have shown that three mechanisms of oxidation of solute can occur: i) the direct effect of radiation on the solute, in that case the solute lose one electron which can be further solvated; ii) the oxidation of the solute by water radical hole H2O•+, occurring only if the solute is in contact with this radical; iii) the oxidation of the solute by OH• radical. In our previous studies about concentrated sulfuric acid, it was possible to estimate the yield of radical formation through oxidation by water hole through measuring directly the yield of sulfate radical in neat sulfuric acid on the picosecond range. For these systems, it was shown that the electron transfer reaction from the solute to the water hole could be more rapid than a proton transfer reaction.10-16 In the present work, a picosecond pulse radiolysis study of five highly concentrated K2CO3 solutions has been carried out in order to find the time dependent oxidation radiolytic yield in perspective to allowing the evaluation on the redox reactions of solutions containing Tc 2 ACS Paragon Plus Environment
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radioelement containing also high concentration of carbonate anion. 17 For this purpose, the mechanism and the yield of carbonate radical formation are discussed. Experimental method The picosecond pulse radiolysis experiments were performed at the ELYSE facility, University of Paris-Sud. The electron accelerator is described in detail elsewhere. 18 , 19 For the present experiments ELYSE delivers electron pulses with an energy of 7.1 MeV and a charge around 4 nC at a repetition rate of 10 Hz. ELYSE provides electron bunches in this configuration with a typical pulse duration around 7 ps and a rms shot-to-shot jitter less than 1 ps.20,21 The electron pump - optical probe set-up is based on the laser-electron intrinsic synchronization resulting from the laser-triggered photocathode22 and is detailed elsewhere.23,24 A femtosecond Ti:Sapphire amplifier laser output is frequency tripled and used to produce the electron pulse that is accelerated by the radiofrequency fields. About 1 µJ of the laser source was focused into a 6 mm thick CaF2 disk to generate a supercontinuum covering the near UV and visible spectrum that is used as the optical probe. The dose per pulse in neat water was determined by measuring the absorbance of the hydrated electron, Ae − ( λ , t ) , and by considering its initial yield measured aq
–7
at 15 ps to be G(t = 15 ps) = 4.2 × 10 mol J-1.25 Therefore, the dose absorbed in water is given by Dwater (Gy ) =
Ae− (λ , t ) hyd
(1)
ε λ l ρ wG ( t )
where ε is the hydrated electron extinction coefficient (19130 M-1cm-1, at maximum 718 nm),26 l is the optical path in the cell, and ρw is the density of solution. All the measurements were made in a flow cell with a 5 mm optical path collinear to the electron pulse propagation. The absorbance measured for a given species in highly concentrated solutions is given by equation 2.
A(λ, t ) = ε λ lc(t) = ελ lFDW G(t )
(2)
The dose additionally absorbed by the solute in concentrated solutions is obtained by multiplying the absorbed dose in pure water by the dose factor F: F = ρsol (ZK2CO3 p / AK2CO3 + Zwater (100 − p) / Awater )(ZK2CO3 100 / AK2CO3 )−1
where ρsol
(3) is the density of the solution, Z is the number of electrons, A is the mass number,
and p is the weight fraction of the solute per 100 gram of solution. Solutions containing carbonate anions at high concentration and pure water were studied under identical experimental conditions. The relevant parameters of the solutions used in this work are given in Table 1. Measurements were performed at 22.5 °C, the room temperature during the pulse radiolysis experiments.
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Results Figure 1 shows the evolution of the transient absorption of a solution containing 5 mol L–1 carbonate K2CO3 (sample 1). The transient spectra recorded directly after the picosecond electron pulse (20 ps) and at a delay time of 3 ns reveal an important absorption in the visible with a maximum around 600 nm; the typical absorption of the hydrated electron peaking at 715 nm is not seen. It is well known that in the presence of non-reactive metal cation such as K+ (10 mol L–1 in this case) the absorption spectrum of the solvated electron can be shifted to shorter wavelengths, So, it seems that the known strong absorption band of the hydrated electron in this solution overlaps with that of carbonate radical which has an absorption centered around 600 nm. Such a strong shift of the absorption of hydrated electron has never been reported before. It should be noted that the shift of the absorption band of the solvated electron depends on the concentration of the non-reactive metal cation, so the degree of spectral shift for each solution (2, 3, 5 mol L–1) is different. To calculate the radiolytic yield of carbonate radical in picosecond range, it is necessary to obtain the absorption spectra of this radical. Picosecond pulse radiolysis measurements are performed in solution containing 10 mol L–1 KOH (Figure 2) in order to get estimation for the shift of the absorption spectra of the solvated electron in the presence of highly concentrated K+. In this case the radical of carbonate is not formed and the only species absorbing in the visible range is the solvated electron. For 10 mol L–1 KOH solution, the maximum of the absorption band is found to be shifted from 715 to 650 nm showing clearly that the shift is imposed by the presence of high concentration of K+. But the shift is less important (~ 50 nm) than that observed in 5 mol L–1 K2CO3 solution exhibiting a maximum at 600 nm. It is known that the shift of the absorption band of solvated electron depends not only on the metal cation concentration but also on the counter-ion and the composition of the solution. The counter ion being different (OH– instead of CO32–), it can play a different role on the solvent structure around the solvated electron resulting in a different absorption band. The presence of the intense absorption band at 600 nm prevents the direct observation of radical carbonate having an extinction coefficient 10 times lower than hydrated electron at 600 nm. Therefore, the soluble nitrate ion NO3− was selected in highly concentrated carbonate solutions as a scavenger, and its fast reaction with solvated electron or presolvated electron allows suppressing its signal without introducing absorbing additional radicals in the visible range. For the solutions with scavenger containing different concentrations of carbonate, the absorption spectra recorded at 20 ps after the pulse are shown in Figure 3. The amplitudes of the absorption spectra are corrected by normalizing the absorbed dose (see the experimental section). The maximum of the absorption band at 20 ps is located at 600 nm, 620 nm and 650 nm for carbonate solutions with concentrations of 5, 3 and 2 mol L–1, respectively. At this delay the amplitude of the absorption is still very high; it is expected that the absorption spectra contain a contribution of the solvated electron as the scavenging reaction is not terminated. In contrast, when the solvated electron is scavenged totally by NO3– in the three solutions at 3000 ps, the
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amplitude of the absorption is much lower and it shows an identical absorption band of the carbonate radical (Figure 4). The kinetics for the three solutions are reported at 600 nm and 780 nm (Figure 5). The first wavelength (600 nm) corresponds to the absorption of the solvated electron and the species due to the radiolysis of carbonate solution, the second one (780 nm) is only due to the solvated electron. Due to the reaction with NO3-, the decay of solvated electron is fast. At 600 nm the kinetics are very different. For the solutions containing 0.7 M NO3– the decay is almost complete in less than 500 ps. In the solution of 5 mol L–1 with its reduced solubility of NO3–, the scavenger concentration is only limited to 0.3 mol L–1 so that the decay of the solvated electron is correspondingly slower. In that case, the initial absorbance is slightly higher due to the suppressed scavenging reaction of NO3– ion with the pre-solvated electron. In order to determinate the yield of carbonate radical just after the pulse, the contribution of solvated electron absorption is subtracted from the recorded data. As the extinction coefficient of the carbonate radical is very low compared to the one of the solvated electron, we consider that the observed spectral positions of the maxima (600, 625, 650 nm) correspond to the one of solvated electron. For example, the shift is 120 nm for solution containing 5 mol L–1 carbonate. With the shift of the absorption band (in energy scale) and the pure kinetics and amplitude of the solvated electron observed at 780 nm by assuming their band shape and extinction coefficient remain the same, the concentration of solvated electron for each solution can be deduced. The absorption spectra at 20 ps due to the carbonate radiolysis in each solution after subtraction of the contribution of the solvated electron are reported in Figure 6. The spectra are normalized showing that their shape and intensity are very close and are in agreement with the one of the carbonate radical reported in the literature.
Discussion and concluding remarks If we consider that after the electron pulse the same radical of carbonate is formed in three solutions, the time dependent radical yield can be deduced from the kinetics. As reported in Figure 7, the time dependent yield for solution of 5 mol L–1 K2CO3 is different compared to the two others ones. First, the initial yield is higher after the pulse and second, it decreases to reaches almost the same value (3.2 × 10–7 mol J–1) than that of the two other cases. It is interesting to note that at 5 mol L–1 concentration a slight increase of the carbonate radical yield is observed in the first 100 ps. The value is increased from 3.3 × 10–7 mol J–1 to 3.6 × 10–7 mol J-1 and then a slight decrease is observed which can be due to the reaction with solvated electron in spurs. For solutions containing 2 and 3 mol L–1 carbonate solutions, the initial yield of radical carbonate is only 1.3×10–7 mol J–1 and 2 × 10–7 mol J–1, respectively. As reported in highly concentrated solutions, this initial yield is due to the formation of the carbonate radical by direct effect and the reaction of carbonate anion with water hole radical cation. After the pulse, an increase of the carbonate radical yield is observed. It can be interpreted by the reaction of carbonate solutes with OH• radical constituting the third pathway of the radical carbonate formation. To explain this time dependent radical yield, we have to consider that in solution containing 5 mol L–1 carbonate 5 ACS Paragon Plus Environment
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anions, the amount of water is very low: only 9 water molecules are present for each carbonate salt molecule. It can be considered that a large amount of the water molecules are in vicinity of carbonate anions. Therefore, the ionized water is in close contact of the carbonate anion, and the reaction of carbonate anion with water hole contributes efficiently to the formation of the carbonate radical. In that case, as the large amount of the precursor of OH• radical is scavenged by the carbonate anion, the amount of the OH• radical in this solution is low. The slight increase of the yield during the first 100 ps is due to the reaction of the carbonate anion with the OH• radical. But for the lowest concentration (2 mol L–1), 80% of the dose is absorbed by water molecules and the probability of water hole scavenging is low. Therefore, the initial yield of the radical carbonate is low. In that case, the OH• radicals are formed and they react with the carbonate anions forming the additional carbonate radical within 3 ns. It is possible to rationalize these observations by using the following equation for the initial yield of the radical carbonate observed just after the electron pulse: Gobs = fs Gs + α fw GH2O•+
(4)
where fs is the electron fraction of the solute, Gs is direct ionization yield of the solute, fw (=1 – fs) is the electron fraction of the water, GH2O•+ is the yield of water cations formed, and α is the fraction of water cations that react with the solute. Recent simulations of several kinetics in highly concentrated solutions showed that equation 4 with GH2O•+ ~ 4.5×10–7 mol J-1 can fit well the experimental data.27 By using this and by assuming the value of the yield of the direct effect around Gs = 3.5 × 10-7 mol J–1, which is very close to that obtained recently in the case of sulfate and phosphate anions, it is possible to evaluate the value of α. As expected, the fraction of water cations that react with the solute is found to be concentration dependent. It is equal to 22%, 30% and 70% for the solution of 2, 3 and 5 mol L-1 carbonate, respectively. This increase is reasonable because of the decrease of the ratio of water molecule and solute (Table 1). Therefore, it is concluded that by following the kinetics of the carbonate radical, it can be claimed that in the nanosecond time scale at lowest concentration most of the oxidation is due to the OH• radicals: OH• + CO32– → CO3–• + OH(5) which is produced mainly by the following reaction: H2O•+ + H2O → OH• + H3O+ (6) •+ However, ultrafast oxidation of the solute by H2O radical occurs mainly at high solute concentrations. (7) H2O•+ + CO32- → CO3-• + H2O •+ Therefore, the trend to scavenge the H2O radical depends on the competition between proton transfer by the H2O•+ radical and water ((reaction 6) with a rate constant of kpt) and the electron transfer between the H2O•+ radical and the solute (reaction 7 with a rate constant of ket). By considering an oversimplified kinetics model, the following equation can be used:
α≈
ሾுమ ை శ ሿሾௌሿ శ ሾுమ ை ሿሾுమ ைሿ
=
ሾௌሿ ሾுమ
= ܴ ିଵ ைሿ
(8)
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The value of α is higher when R is decrease i.e. the concentration of the solute increases. In conclusion, the yield of CO3•- in highly concentrated carbonate solutions is studied and quantified on the picosecond time scale. The solute concentration was varied and a solvated electron scavenger added in order to distinguish the different contributions and mechanism. The contribution of the absorption band of the solvated electron was carefully subtracted; due to its interaction with the carbonate counter ion resulting in a pair solvated electron and K+, its absorption is markedly blue shifted compared to the one of hydrated electron. The formation of the radical carbonate is originated from three mechanisms: the direct ionization, the reaction with the water hole and the reaction with OH• radical. The contribution of the two first mechanisms is revealed by the initial yield of CO3•- measured just after 7 ps electron pulse and the last one at nanosecond time scale. It is interesting to note that the initial yield of radical carbonate is very different for 3 and 5 mol L-1 solutions. Such a difference cannot be explained by the direct absorption of the dose by the solute, but by the additional reaction with water hole which is very efficient for 5 mol L-1 solution. Eventually, it is worth noting that whatever the mechanism of the radical formation, the yield is almost the same 3 ns after dose deposition. In dilute solutions, the two first mechanisms of oxidation; by direct effect and that by electron transfer with the cation radical of water are fully negligible. Nevertheless, the radical yield of oxidizing species (mainly carbonate and OH• radicals) at 3 ns, even in dilute solutions, is expected to be around 3.2 × 10-7 mol J–1 which is very close to that of OH• radical in neat water.28
Acknowledgement The work was supported by a public grant from University of Paris-Sud “Moyen de Rechreche Mutualisé”. The authors thank Jean-Philippe Larbre and Pierre Jeunesse for their help during the experiments with ELYSE facility.
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Table 1. Solutions and their corresponding physio-chemical parameters. sample 1 2 3 4 5
K2CO3 [mol.L-1] 5 0 2 3 5
KOH Nitrate -1 [mol.L ] [mol.L-1] 0 0 10 0.7 0.7 0.3 -
fs
fw
0.4
0.6
0.2 0.29 0.4
0.8 0.71 0.6
F (g.cm3)
ρsol (g.cm3)
R=[H2O]/[S]
1.11 1.35 1.54
1.12 1.36 1.55
26.39 17.4 9.55
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0.20
20 ps 3000 ps
0.15
0.20
0.10
0.05
Abs / 0.5 cm
Absorbance / 0.5 cm
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600 nm
0.15 0.10 0.05
780 nm
0.00 0
0.00 450
500
500 1000 1500 2000 2500 3000 Time (ps)
550
600
650
700
750
800
λ (nm)
Figure 1. Transient absorption spectra and kinetics observed in 5 mol L–1 K2CO3 aqueous solutions without adding any solvated electron scavenger.
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0.30
20 ps 0.25
3000 ps 0.20
0.15
0.3 600 nm Abs / 0.5 cm
Absorbance / 0.5 cm
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0.10
0.05
0.2 780 nm
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450
500
550
1000 2000 Time (ps)
600
650
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4000
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λ (nm)
Figure 2. Transient absorption spectrum of 10 mol L-1 KOH aqueous solution observed at t = 20 ps and t = 3000 ps. Inset: Decay of the solvated electron in KOH solution at 600 and 780 nm.
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0.10
20 ps
5 mol / L K2CO3 0.08
Absorbance / 0.5 cm
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2 mol / L K2CO3 0.06
0.04
3 mol / L K2CO3 0.02
0.00 400
450
500
550
600
650
700
750
800
λ (nm)
Figure 3. Transient absorption spectra observed at 20 ps in K2CO3 solutions of different concentration with nitrate scavenger for the same absorbed dose. The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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3000 ps 0.020
Absorbance / 0.5 cm
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0.016
0.012
0.008
2 mol L-1 K2CO3 0.004
3 mol L-1 K2CO3 5 mol L-1 K2CO3
0.000 500
550
600
650
700
750
λ (nm)
Figure 4. Absorption spectra observed at the delay time of 3000 ps in K2CO3 solutions with nitrate scavenger at different concentration for the same absorbed dose. The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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Absorbance at 780 nm (0.5 cm)
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Time (ps) 0.10
Absorbance at 600 nm (0.5 cm)
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0.08
0.06
0.04
0.02
0.00 0
1000
2000
3000
4000
Time (ps)
Figure 5. Kinetics observed for each K2CO3 solution (5 mol L-1, O blue; 3 mol L-1, O red; 2 mol L-1, O black) with NO3- acting as a solvated electron scavenger at 780 nm (top) and 600 nm (bottom). The concentration of nitrate is 0.7, 0.7 and 0.3 mol L-1 for 2, 3 and 5 mol L-1 K2CO3 solution, respectively.
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0.020
5 mol L-1 K2CO3 3
0.015
2 0.010
Normalized Absorbance
Absorbance / 0.5 cm
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0.005
5 mol L-1 K2CO3 3 mol L-1 K2CO3 2 mol L-1 K2CO3
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1.8
2.0
2.2
2.4
2.6
2.8
3.0
Energy (eV)
0.000 500
600
700
Wavelength (nm)
Figure 6. Absorption spectra after subtraction of the solvated electron contribution at 20 ps. Inset: Normalized spectra (reported in energy scale) of different carbonate solutions.
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3
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2 mol L-1 3 mol L-1 5 mol L-1
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107 Yield of carbonate radicals (mol J-1)
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0 0
1000
2000
3000
4000
Time (ps)
Figure 7. Time dependent radiolytic yield (left scale) (deduced from the time dependent absorption (right scale)) of carbonate radicals in different solutions.
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References 1
Amarjeet Yadav, P.C.M. Carbonate radical anion as an efficient reactive oxygen species: Its reaction with guanyl radical and formation of 8-oxoguanine. Chem. Phys, 2012, 405, 76-98. 2 Liu, Y.; He, X.; Duan, X.; Fu, Y.;, Dionysiou, D.D. Photochemical degradation of oxytetracycline: Influence of pH and role of carbonate radical. Chem. Eng. J. 2015, 276, 113-121. 3 Mazellier, P.; Busset, C.: Delmont, A.; De Laat, J. A comparison of fenuron degradation by hydroxyl and carbonate radicals in aqueous solution. Water res. 2007, 41, 4585-4594. 4 Adams, G., Bisby, R.H., Cundall, R.B, Redpath, J.L., Willson, R.L. Selective free radical reactions with proteins and enzymes: the inactivation of ribonuclease. Rad. Res. 1972, 49, 290-299. 5 Dassanayake, R.S.; Shelley J.T.; Cabelli, D.E.; Brasch, N.E. Pulse Radiolysis and Ultra-HighPerformance Liquid Chromatography/High-Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B12 Derivatives. Chem. Eur. J. 2015, 21, 6409-6419. 6 Lymar, S.; Hunt, I. K. Rapid reaction between peroxonitrite ion and carbon dioxide; implication for biological activity. J. Am Chem. Soc, 1995, 117 8867-8868. 7 Graedel, T.E.; Weschler, C.J. Chemistry within aqueous atmospheric aerosols and raindrops. Rev. Geophys. Space Phys, 1984, 19, 505-539. 8 Bonini, M. G.; and Augusto, O. Carbon dioxide stimulates the production of thiyl, sulfinyl, and disulfide radical anion from thiol oxidation by peroxynitrite J. Biol. Chem. 2001, 276, 9749-9754. 9 Said, K.B.; Seimbille, Y.; Fattahi, M.; Houee-Lévin, C.; Abbé J.C. γ radiation effects on potassium pertechnetate in carbonate media. Appl. Radiat. Isot. 2001, 54, 45-51. 10 Balcerzyk, A.; Schmidhammer, U.; El Omar, A. K.; Jeunesse, P.; Larbre J. P.; Mostafavi. M. Direct and Indirect Radiolytic Effects in Highly Concentrated Aqueous Solutions of Bromide. J. Phys. Chem. A. 2011, 115, 4326-4333. 11 El Omar, A. K.; Schmidhammer, U.; Rousseau, B.; LaVerne, J.; Mostafavi, M. Competition Reactions of H2O•+ Radical in Concentrated Cl- Aqueous Solutions: Picosecond Pulse Radiolysis Study. J. Phys. Chem. A. 2012, 116, 11509-11518. 12 Balcerzyk, A.; LaVerne, J.; Mostafavi, M. Picosecond Pulse Radiolysis of Direct and Indirect Radiolytic Effects in Highly Concentrated Halide Aqueous Solutions. J. Phys. Chem. A. 2011, 115, 9151-9159. 13 Balcerzyk, A.; El Omar, A. K.; Schmidhammer, U.; Pernot, P.; Mostafavi. M. Picosecond Pulse Radiolysis Study of Highly Concentrated Nitric Acid Solutions: Formation Mechanism of NO3• Radical. J. Phys. Chem. A. 2012, 116, 7302-7307. 14 El Omar, A. K.; Schmidhammer, U.; Balcerzyk, A.; LaVerne, J.; Mostafavi, M. Spur Reactions Observed by Picosecond Pulse Radiolysis in Highly Concentrated Bromide Aqueous Solutions. J. Phys. Chem. A. 2013, 117, 2287-2293. 15 Ma, J.; Schmidhammer, U.; Pernot, P.; Mostafavi, M. Reactivity of the Strongest Oxidizing Species in Aqueous Solutions: The Short-Lived Radical Cation H2O•+. J. Phys. Chem. Lett. 2014, 5, 258-261. 16 Ma, J.; Schmidhammer, U.; Mostafavi, M. Picosecond Pulse Radiolysis of Highly Concentrated Sulfuric Acid Solutions: Evidence for the Oxidation Reactivity of Radical Cation H2O•+. J. Phys. Chem. A. 2014, 118, 4030-4037. 17 Ghalei, M.; Vandenborre, J.; Blain, G.; Haddad, F.; Mostafavi, M.; Fattahi, M. Oxidation and/or Reduction of Manganese Species by Gamma-Ray and He2+ Particle Irradiation in Highly Concentrated Carbonate Media. Rad. Phys. Chem. 2016, 119, 142-150.
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Belloni, J.; Monard, H.; Gobert, F.; Larbre, J. -P.; Demarque, A.; De Waele, V.; Lampre, I.; Marignier, J. -L.; Mostafavi, M.; Bourdon, J. C. et al. ELYSE - A Picosecond Electron Accelerator for Pulse Radiolysis Research. Nucl. Instr. and Meth. Phys. Res. A. 2005, 539, 527-539. 19 Marignier, J. L.; De Waele, V.; Monard, H.; Gobert, F.; Larbre, J.-P.; Demarque, A.; Mostafavi, M.; Belloni, J. Time-Resolved Spectroscopy at the Picosecond Laser-triggered Electron Accelerator ELYSE. Rad. Phys. Chem. 2006, 75, 1024-1033. 20 Schmidhammer, U.; De Waele, V.; Marquès, J.-R.; Bourgeois, N.; Mostafavi, M. Single shot linear detection of 0.01-10 THz electromagnetic fields. Appl. Phys. B. 2009, 94, 95-101. 21 De Waele, V.; Schmidhammer, U.; Marquès, J.-R.; Monard, H.; Larbre, J.-P.; Bourgeois, N.; Mostafavi, M. Non-invasive single bunch monitoring for ps pulse radiolysis. Rad. Phys. Chem. 2009, 78, 1099-1101. 22 Belloni, J. ; Crowell, R. A.; Katsumura, Y.; Lin, M.; Marignier, J. -L.; Mostafavi, M.; Muroya, Y.; Akinori, S.; Tagawa, S.; Yoshida, Y.; et al. Ultrafast Pulse Radiolysis Methods. In Recent Trends in Radiation Chemistry, Eds. Wishart, J. F. And Rao, B. S. M World Scientific New Jersey, 2010, P. 121-160. 23 Schmidhammer U.; Pernot P.; De Waele V.; Jeunesse P.; Demarque A.; Murata S.; and Mostafavi M. Distance Dependence of the Reaction Rate for the Reduction of Metal Cations by Solvated Electrons: a picosecond pulse radiolysis study. J. Phys. Chem. A 2010, 114, 12042–12051. 24 Schmidhammer, U.; El Omar, A. K.; Balcerzyk, A.; Mostafavi, M. Transient Absorption Induced by a Picosecond Electron Pulse in the Fused Silica Windows of an Optical Cell. Rad. Phys. Chem. 2012, 81,1715-1719. 25 Muroya, Y.; Lin, M.; Wu, G.; Iijima, H.; Yoshii, K.; Weda, T.; Kudo, H.; Katsumura, Y. A Reevaluation of the Initial Yield of the Hydrated Electron in the Picosecond Time Range. Rad. Phys. Chem. 2005, 72, 169-172. 26 Jou, F. Y.; Freeman, G. R. Shapes of optical spectra of solvated electrons. Effect of pressure. J. Phys. Chem. 1977, 81, 909-915. 27 Ma, J.; Laverne, J.; Mostafavi, M. Scavenging the Water Cation in Concentrated Acidic Solutions. J. Phys. Chem. A. 2015, 119, 10629-10636. 28 El Omar, A. K.; Schmidhammer, U.; Jeunesse, P.; Larbre, J. P.; Lin, M. Z.; Muroya, Y. ; Katsumura, Y. ; Pernot, P.; Mostafavi, M. Time-Dependent Radiolytic Yield of OH. Radical Studied by Picosecond Pulse Radiolysis J. Phys. Chem. A. 2011, 115, 12212-12216.
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107 Yield of carbonate radicals (mol J-1)
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Mechanisms of CO3–• formation
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CO32- → CO3–• + eH2O•+ + CO32- → CO3-• + H2O
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OH• + CO32– → CO3–• + OH0 0
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