Photo-Induced Bismuth Single Atoms on TiO₂ for Highly Efficient Photocatalytic Defluorination of Perfluorooctanoic Acid: Ionization of the C-F Bond

Single-atom catalysts (SACs), as a newcomer in the fieldof nanocatalysis,have gained intensive interest due to their excellent activities.In this study, single bismuth (Bi) atom-decorated TiO2 catalysts(N-Bi/TiO2) are synthesized by the simple UV irradiationmethod using Bi(NO3)(3) as the precursor. Characterizationsconfirmed that single Bi atoms were homogeneously dispersed on thesurface of TiO2. BiOCl nanoclusters were formed on TiO2 (Cl-Bi/TiO2) when BiCl3 was used asthe precursor. Both N-Bi/TiO2 and Cl-Bi/TiO2 demonstrated excellent performance for the defluorination of perfluorooctanoicacid (PFOA) under a UV 254 nm irradiation. A deep defluorination ofPFOA was obtained by N-Bi/TiO2 with a defluorination ratioof 85% under a xenon lamp irradiation for 4 h. Moreover, a relativelyhigh defluorination of 65% for PFOA over N-10Bi/TiO2 remainedafter recycling use for 4 times. Cl-10Bi/TiO2 also demonstrateda good performance for the defluorination of PFOA under xenon lampirradiation, with an obtained defluorination ratio of 76% for 4 h.The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)demonstrated that Bi single atoms induced the ionization of the C-Fbond of PFOA, leading to the deep defluorination of PFOA. Density-functionaltheory (DFT) and finite-difference time-domain (FDTD) calculationsfurther revealed the ionization of PFOA on N-10Bi/TiO2,which is due to the high electric field concentration near Bi singleatoms. These findings provide a new approach for manipulating thephotocatalytic activity of TiO2-based composites and broadenthe knowledge regarding the heterogeneous activation of the C-Fbond.