Decomposition of environmentally persistent trifluoroacetic acid to fluoride ions by a homogeneous photocatalyst in water

Decomposition of trifluoroacetic acid (TFA) was achieved with a tungstic heteropolyacid photocatalyst H₃PW₁₂O₄₀· 6H₂O in order to develop a technique for measures against TFA stationary sources. This is the first example of C-F bond cleavage in an environmentally harmful perfluoromethyl-group-containing compound using a homogeneous photocatalyst. The catalytic reaction proceeds in water at room temperature under UV-visible light irradiation in the presence of oxygen. The system produces only F^- ions and CO₂; the (mole of formed F^-)/(mole of decomposed TFA) and (mole of formed CO₂)/(mole of decomposed TFA) ratios were 2.91 and 2.09, respectively. GC/MS measurements showed no trace of other species such as environmentally undesirable CF₄, which is the most stable perfluorocarbon and has a very high global warming potential. When the (initial TFA)/(initial catalyst) molar ratio was 20:1, the turnover number of TFA decomposition reached 5.58 by 72 h of irradiation, accompanying with no catalyst degradation. The catalytic reaction mechanism can be explained by a redox reaction between the catalyst and TFA, involving a photo-Kolbe process.