Efficient photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticle modified titanium dioxide

Perfluorooctanoic acid (PFOA) is potentially toxic and exceptionally stable attributed to its robust CF bond, which is hard to be removed by UV/TiO₂ systems. In this research, bismuth nanoparticle (Bi NP) modified titanium oxides (Bi/TiO₂) were synthesized by a simple photochemical deposition-calcination method and were applied as photocatalysts for the first time to degrade PFOA. The removal rate of 50 mg/L PFOA reached 99.3 % with 58.6 % defluorination rate after 30 min of irradiation via a mercury lamp. Bi/TiO₂ exhibited superior performance in PFOA degradation compared to commercial photocatalysts (TiO₂, Ga₂O₃, Bi₂O₃ and In₂O₃). In addition, Bi/TiO₂ showed high degradation activity under actual sunlight, achieved 100 % removal rate and 59.3 % defluorination rate within 2 h. Bi NPs increase the light trapping ability of Bi/TiO₂ and promote the separation of photogenerated electron-hole pairs via local surface plasmon resonance (LSPR) effect, which results in more photogenerated holes (h⁺) and hydroxyl radicals (OH). Combined with DFT calculations and intermediate detections, the degradation reaction is initiated from the oxidation of the PFOA carboxyl group via h⁺, followed by the loss of the CF₂ unit step by step with the participation of OH. This work presents a novel approach for the practical implementation of TiO₂-based photocatalysts to achieve highly efficient photocatalytic degradation of perfluorocarboxylic acids (PFCAs).