Per- or polyfluoroalkyl substances (PFAS) are a class of chemicals featuring strong C-F bonds which are used in a wide range of industries for their durability and heat-, water- and oil-resistant properties. It is these properties that also make PFAS impervious to environmental breakdown, posing a risk to the environment and human health.1 Degradation strategies which can effectively cleave the C-F bonds (mineralizing PFAS) are, therefore, a global research priority.
This research describes the novel synthesis of zinc sulfide (ZnS) and its use in photocatalysis to leverage the C-F reduction pathway to degrade PFAS.
ZnS has an intrinsically high reduction potential, and when it is excited with UV-A light, it has sufficient potential to cleave C-F bonds via direct electron transfer.2
For the first time, ZnS nanoparticles were synthesized via a supercritical synthesis method (without the presence of urea), on a gram-scale. These materials were rigorously characterized by XRD, DRS, SEM, TEM and EDS to confirm their structural and photo-physical properties.
Perfluorooctane sulfonate (PFOS), a notoriously persistent PFAS compound, was used for photocatalytic testing and degradation products were monitored by LC-MS, 19F NMR, and ISE. The production of fluoride (F-) was tracked as an indicator of successful C-F bond cleavage and PFAS mineralization.
The results are promising, showing nearly 80% of PFOS mineralized within 24 h of illumination in a batch reactor and full mineralization within just over 4 h of illumination in a continuous circulating flow reactor.3 We also demonstrate mineralization of various PFAS compounds as well as an AFFF contaminated field sample. This research demonstrates a viable method of PFAS degradation, contributing to the development of sustainable technologies for environmental remediation. Furthermore, photocatalysis provides a non-specific method of bond breaking, allowing this research to be transferred to a broad range of pollutant and environmental remediation applications.