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 field of 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 irradiation method using Bi(NO3)3 as the precursor. Characterizations confirmed that single Bi atoms were homogeneously dispersed on the surface of TiO2. BiOCl nanoclusters were formed on TiO2 (Cl-Bi/TiO2) when BiCl3 was used as the precursor. Both N-Bi/TiO2 and Cl-Bi/TiO2 demonstrated excellent performance for the defluorination of perfluorooctanoic acid (PFOA) under a UV 254 nm irradiation. A deep defluorination of PFOA was obtained by N-Bi/TiO2 with a defluorination ratio of 85% under a xenon lamp irradiation for 4 h. Moreover, a relatively high defluorination of 65% for PFOA over N-10Bi/TiO2 remained after recycling use for 4 times. Cl-10Bi/TiO2 also demonstrated a good performance for the defluorination of PFOA under xenon lamp irradiation, 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–F bond of PFOA, leading to the deep defluorination of PFOA. Density-functional theory (DFT) and finite-difference time-domain (FDTD) calculations further revealed the ionization of PFOA on N-10Bi/TiO2, which is due to the high electric field concentration near Bi single atoms. These findings provide a new approach for manipulating the photocatalytic activity of TiO2-based composites and broaden the knowledge regarding the heterogeneous activation of the C–F bond.