Insights into the intrinsic mechanisms underlying the ultra-highly efficient degradation of PFOA over S-scheme heterojunction of Bi7O5F11/BiOF

Perfluorooctanoic acid (PFOA) is refractory owing to the strong C-F bonds and is extremely difficult to be degraded by traditional photocatalysts. In this study, an S-scheme heterojunction was successfully synthesized by incorporating BiOF with wide-bandgap Bi7O5F11. Theoretical calculations, in situ X-ray photoelectron spectroscopy and Kelvin probe force microscopy verified that a build-in electric field was created in the heterojunction, facilitating the separation of electron-hole pairs. Thus, the photoexcited electrons in the conduction-band (CB) of BiOF rapidly recombined with holes in the valence-band (VB) of Bi7O5F11, leading to enrichment of the highly reductive electrons in CB of Bi7O5F11 and strongly oxidative holes in VB of BiOF. Additionally, the strong interaction between Bi7O5F11/BiOF and PFOA is conducive to electron transfer from catalyst surface to PFOA. Thus, BOF-2 displayed superbly-high photoactivity to decompose PFOA. PFOA (5 mg/L) was decomposed within 1 h, and 53% of total-organic-carbon was removed in 2 h of irradiation.