Photoreductive defluorination of trifluoroacetic acid (TFA) in the aqueous phase by hydrated electrons

Abstract

Due to its extremely high stability and continuous accumulation in the environment, which lead to a widespread environmental distribution, trifluoroacetic acid (TFA) is a global concern in ecosystems. In this study, TFA was decomposed through photoreduction by hydrated electrons (e_(aq)⁻) with potassium iodide (KI) as a mediator in the aqueous phase. The reaction proceeded under irradiation at 254 nm in a solution with the following parameters: pH 11.0, anoxic conditions and room temperature (25℃). In 48 h, 91.4% ± 1.1% of the fluoride ions (F⁻) on all the TFA molecules in the UV/KI system were released, indicating the effective defluorination of TFA. Kinetic analysis indicated that TFA decomposition fit the first-order model with a rate constant of 0.147 ± 0.014 h⁻¹. The optimal reaction conditions were 0.2 mM KI, 0.05 mM TFA and pH 11.0. In addition to fluoride ions (F⁻) and CO₂, other intermediates, including formic acid (HCOO⁻) and acetic acid (CH₃COO⁻), were identified and quantified in the aqueous phase by Ion chromatography (IC), and small amounts of gas-phase CF₃H and CF₄ were detected by gas chromatography-mass spectrometry (GC/MS). Finally, possible TFA degradation pathways were proposed. This method may be effective for the treatment of TFA in aquatic environments.

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