Mechanism insights into the facet-dependent photocatalytic degradation of perfluorooctanoic acid on BiOCl nanosheets

Photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS) remains insufficient. It is vital to investigate the structure-activity relationship between exposed facets and photocatalytic activity of PFAS. In this study, BiOCl nanosheets with predominantly exposed {010} or {001} facets (i.e. {010}-BiOCl or {001}-BiOCl) were synthesized via the hydrothermal method and applied for the photodegradation of perfluorooctanoic acid (PFOA). We observed that the degradation rate constant of PFOA via the {010}-BiOCl (0.0954 min(-1)) was 2.64-fold better than that of the {001}-BiOCl (0.0361 min(-1)) in photocatalytic activity. Density functional theory calculation results revealed that the higher catalytic activity of {010}-BiOCl was attributed to the in-situ generated surface oxygen vacancies (OVs) and the strong interaction with PFOA molecules via the bidentate adsorption configuration. {010}-BiOCl nanosheets with OVs exhibited the highest adsorption capacity (55.6 mg g(-1)h(-1)) and lowest adsorption energy (-0.399 eV) for PFOA molecules. The electron spin resonance spectroscopy and radical scavenging experiments showed that both photogenerated holes and surface hydroxyl radicals were generated on {010} facets that contributed to the degradation of PFOA; while only photogenerated holes were formed on {001} facets. Interestingly, F- ions as the by-products were prone to attaching to the BiOCl facets to block the catalytic sites. To recover the catalytic performance, we adopted a simple chemical precipitation approach to precipitate the F- by using Ca2+ ions. Our findings provide fundamental insights into the interface reactions during the photocatalytic degradation of PFOA.

Automated summary

The photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS) using BiOCl nanosheets with {010} or {001} facets showed that {010}-BiOCl exhibited higher catalytic activity compared to {001}-BiOCl in the degradation of perfluorooctanoic acid (PFOA). The higher catalytic activity of {010}-BiOCl was attributed to the in-situ generated surface oxygen vacancies and strong interaction with PFOA molecules. Furthermore, the nanosheets with {010} facets showed the highest adsorption capacity and lowest adsorption energy for PFOA molecules, while photogenerated holes and surface hydroxyl radicals on {010} facets played a significant role in the degradation process. Additionally, F- ions as by-products tended to block the catalytic sites but could be removed using a simple chemical precipitation approach with Ca2+ ions to recover the catalytic performance.