Subcritical Water-Driven Complete Mineralization of Silane Coupling Agents with Short Perfluoroalkyl Chains

Abstract

The decomposition of CF₃CH₂CH₂Si-(OMe)₃ and C₄F₉CH₂CH₂Si-(OMe)₃typical fluorinated silane coupling agents used for surface modificationwas investigated in subcritical water for potential waste treatment applications. When CF₃CH₂CH₂Si-(OMe)₃ was heated in subcritical water with no additive at 350 °C, only a small amount of fluoride (F^-) was produced. In contrast, virtually complete mineralization of CF₃CH₂CH₂Si-(OMe)₃ was achieved in the presence of KMnO₄. Specifically, after treatment with 0.50 mmol of KMnO₄ for 6 h, the F^- yield reached 100%, and the residual total organic carbon in the reaction solution was reduced to 4% of the initial carbon content of CF₃CH₂CH₂Si-(OMe)₃. Furthermore, under the same reaction conditions, quasi-complete mineralization of C₄F₉CH₂CH₂Si-(OMe)₃ was also attained, with an F^- yield of 96% and a remaining TOC ratio of 2%.

1

Effect of KMnO₄ amount on the formed amounts of F^– and TOC in the reaction solution. CF₃CH₂CH₂Si­(OMe)₃ (46.8–55.0 μmol) was heated at 350 °C with KMnO₄ under argon for 6 h. For 0.25 mmol of KMnO₄, two replicate runs were carried out.

2

Effect of temperature on the formed amounts of F^– and TOC in the reaction solution. CF₃CH₂CH₂Si­(OMe)₃ (46.7–60.9 μmol) was heated with 0.25 mmol of KMnO₄ under argon for 6 h. For 350 °C, two replicate runs were carried out.

3

Effect of reaction time on the formed amounts of F^– and TOC in the reaction solution. CF₃CH₂CH₂Si­(OMe)₃ (42.6–48.6 μmol) was heated at 350 °C with 0.25 mmol of KMnO₄ under argon. For 4.5 and 6 h, two replicate runs were carried out.

4

Temperature dependence of the amounts of TF and F^– in the reaction solution. CF₃CH₂CH₂Si­(OMe)₃ (46.7–60.9 μmol) was heated with 0.25 mmol of KMnO₄ under argon for 6 h. For 350 °C, two replicate runs were carried out.

5

XPS spectra of the resulting solid: (a) F 1s, (b) C 1s and K 2p, and (c) Si 2p regions. CF₃CH₂CH₂Si­(OMe)₃ (48.6 μmol) was heated 350 °C with 0.25 mmol of KMnO₄ under argon for 6 h. The resulting solid was dried and subjected to the measurement.

6

XRD patterns of the solids generated from the reactions of CF₃CH₂CH₂Si­(OMe)₃ with 0.25 mmol of KMnO₄ at 350 °C for (a) 3 h and (b) 6 h. Initial CF₃CH₂CH₂Si­(OMe)₃ amounts were 46.5 and 48.6 μmol for panels (a) and (b), respectively.

7

Effect of KMnO₄ amount on the formed amounts of F^– and TOC in the reaction solution. C₄F₉CH₂CH₂Si­(OMe)₃ (32.6–42.9 μmol) was heated at 350 °C with KMnO₄ (0–0.50 mmol) under argon for 6 h.

8

Effect of KMnO₄ amount on the formed amounts of F^– and TF in the reaction solution. C₄F₉CH₂CH₂Si­(OMe)₃ (32.6–42.9 μmol) was heated at 350 °C with KMnO₄ under argon.

9

Temperature dependence of the formed amounts of F^– and TOC in the reaction solution. C₄F₉CH₂CH₂Si­(OMe)₃ (35.0–37.2 μmol) was heated with 0.25 mmol of KMnO₄ under argon for 6 h.

10

XPS spectra of the resulting solid: (a) F 1s, (b) C 1s and K 2p, and (c) Si 2p regions. C₄F₉CH₂CH₂Si­(OMe)₃ (35.0 μmol) was heated 350 °C with 0.25 mmol of KMnO₄ under argon for 6 h. The resulting solid was dried and subjected to the measurement.

11

XRD pattern of the solid generated from the reaction of C₄F₉CH₂CH₂Si­(OMe)₃ (35.0 μmol) with 0.25 mmol of KMnO₄ at 350 °C for 6 h.