Supporting information for
Complete mineralization of perfluorooctanoic acid (PFOA) by γ-irradiation in aqueous solution
Ze Zhang1,*, Jie-Jie Chen1,*, Xian-Jin Lyu1, Hao Yin2, Guo-Ping Sheng1, **
1CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, 2Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, 230026, China
* These authors contributed equally to this work.
** Corresponding author:
Dr. Guo-Ping Sheng, Fax: +86-551-63601592; E-mail:
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Mechanism of PFOA decomposition in alkaline solution. The Step O2 in Table S2 is obtained by simultaneously adding the OH– on the both sides of Step 2 in Table 3, presenting the same thermodynamic parameters. Then the radical C6F13CF2· in alkaline solution reacts with O·– to form unstable anion C6F13CF2O–, which undergoes F– elimination to form C6F13COF with ΔGO5ө of 0.018 eV, almost reaching reaction equilibrium. Following this, O·– will attack and cleave the C=O bond to form an anion radical C6F13CF(O–)O·, which can be easily attacked by eaq-. Then, PFHpA (C6F13COO-) is spontaneously formed by releasing the F– with a negative ΔGO7ө of -5.038 eV.
Some alternative reactions of PFOA degradation by irradiation. The possible cleavage mechanism of C-F bonds by eaq- is illustrated as Eq. S1 in Table S3. According to the proposed mechanisms of PFOA degradation by UV irradiation reported previously1, the released F– is from the CF2 at the ortho position of carboxyl. But the positive ΔGS1ө from DFT calculations indicates that the reaction is not a spontaneous process. The probable mechanism for cleavage of C-F bond by eaq- might be proceeded with an extra energy, such as UV irradiation. This result agrees well with the experimental results that only eaq- might not cleave the C-F bond efficiently. Moreover, the possible decarboxylation reaction, which generates perfluorooctyl and CO2 via the ·OH radical (Eq. S2 in Table S3), is also investigated. The overall reaction free energy is -0.810 eV, which is more positive than the value (-3.059 eV, Table 3) of the eaq- mediated reduction. This implies that the eaq- plays more important role in the initial step of the end group elimination.
Previous studies indicated that the oxidative degradation of PFOA and PFOS usually began in the elimination of the end group2-3. In this study, the other possible reactions (Eq. S3 and S4 in Table S3) as the initial step are also examined by DFT calculations. However, both reactions have more positive ΔGө. These possible mechanisms have been investigated for PFOS in a previous study, indicating that the reactions have high activation barriers4. Thus, it is difficult to proceed the completely mineralization of PFOA by ·OH radical only, which is in agreement with the experimental results.
Table S1 | Structural characteristics of reactants and intermediate products in PFOA degradation in aqueous solution
l(C7-F14) / l(C7-F15) / θ(F14-C7-F15) / l(C8-O1) / l(C8-O2)
C7F15COO- / 1.383 / 1.380 / 106.555 / 1.258 / 1.253
l(C7-F14) / l(C7-F15) / θ(F14-C7-F15)
C6F13CF2· / 1.331 / 1.331 / 112.383
l(C7-F14) / l(C7-F15) / θ(F14-C7-F15) / l(C7-O) / l(O-H)
C6F13CF2OH / 1.383 / 1.358 / 107.742 / 1.351 / 0.979
l(C7-F14) / l(C7-F15) / θ(F14-C7-F15) / l(C7-O)
C6F13CF2O– / 1.487 / 1.478 / 100.067 / 1.236
l(C7-F14) / l(C7-O) / θ(O-C7-F14)
C6F13COF / 1.350 / 1.189 / 123.814
l(C7-F14) / l(C7-O1) / l(C7-O2) / l(O1-H)
C6F13CF(OH)O· / 1.409 / 1.390 / 1.321 / 0.984
l(C7-F14) / l(C7-O1) / l(C7-O2)
C6F13CF(O–)O· / 1.501 / 1.319 / 1.321
l(C6-F12) / l(C6-F13) / θ(F12-C6-F13) / l(C7-O1) / l(C7-O2)
C6F13COO- / 1.360 / 1.361 / 108.748 / 1.390 / 1.321
Table S2 | Calculated thermodynamic characteristics of the PFOA degradation by radical eaq- and O·– in alkaline solution
(eV) / ΔH
(eV) / ΔS
(×10-3 eV/K)
O1 / C7F15COO– + eaq-→ C7F15COO·2– / -2.217 / -2.105 / 0.376
O2 / C7F15COO·2– + H2O → C7F15CO· + 2OH– / -1.008 / -0.978 / 0.102
O3 / C7F15CO· → C6F13CF2· + CO / 0.166 / 0.329 / 0.547
O4 / C6F13CF2· + O·– → C6F13CF2O– / -0.019 / -0.001 / 0.060
O5 / C6F13CF2O– → C6F13COF + F– / 0.018 / 0.008 / -0.035
O6 / C6F13COF + O·– → C6F13CF(O–)O· / -0.041 / 0.006 / 0.157
O7 / C6F13CF(OH)O·– + eaq- → C6F13COO– + F– / -5.038 / -5.035 / 0.012
Table S3 | Calculated thermodynamic properties of alternative mechanisms of PFOA degradation individually by radical eaq- or ·OH in aqueous solution generated through γ-ray irradiation
(eV) / ΔH
(eV) / ΔS
(×10-3 eV/K)
S1: C7F15COO– + eaq-→·C7F14COO– + F–* / 0.033 / 0.053 / 0.070
S2: C7F15COO– + ·OH → C7F15· + OH– + CO2 / -0.810 / -0.830 / -0.068
S3: C7F15COO– + ·OH →·OC7F14COO– + HF / -1.354 / -1.576 / -0.743
S4: C7F15COO– + ·OH → C4F9OH + ·C3F6COO– / -0.949 / -1.117 / -0.565
* The F– is from the CF2 at the ortho position of carboxyl as shown in Figure S3a
Figure S1 | MS of the intermediate products in PFOA degradation by radical eaq- and ·OH in aqueous solution generated through γ-ray irradiation, (a) PFOA, C7F15COOH, (b) PFHpA, C6F13COOH, (c) PFHxA, C5F11COOH, (d) PFPeA, C4F9COOH, (e) PFBA, C3F7COOH, (f) PFPA, C2F5COOH.
Figure S2 | Optimized structures of reactants and intermediate products in PFOA degradation in aqueous solution with eaq- and ·OH generated by γ-ray irradiation, (a) C7F15COO-, (b) C6F13CF2·, (c) C6F13CF2OH, (d) C6F13COF, (e) C6F13CF(OH)O·, and (f) C6F13COO-
Figure S3 | Optimized structures of reactants and possible intermediate products in PFOA degradation individually by radical eaq- or ·OH in aqueous solution generated from γ-ray irradiation, (a) ·C7F14COO– and F–, (b) C7F15COO– and ·OH, (c) C7F15·, CO2, and OH–, (d) ·OC7F14COO– and HF, and (e) C4F9OH and ·C3F6COO–
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