Copper-Doped Zinc Sulfide Nanocrystals for Near-Ultraviolet and Visible-Light Driven Decomposition of Perfluoroalkyl Compounds

Developing methods capable of decomposing per- and polyfluoroalkyl substances (PFASs) into fluoride ions under mild conditions would not only help mitigate the global PFAS contamination crisis but also provide a technological foundation for recycling fluorinated materials. Here, we show that zinc sulfide (ZnS) nanocrystals, an inexpensive, low-toxicity, and readily scalable semiconductor, can decompose perfluorooctanesulfonic acid (PFOS), one of the most recalcitrant and strictly regulated PFASs, under both UV and near-visible light-emitting diode (LED) irradiation. Using acetate-capped ZnS nanocrystals, we achieve up to 62% overall defluorination after 24 h of 365 nm light irradiation. Moreover, visible-light-induced photocatalytic defluorination of PFOS was achieved by doping Cu ions into ZnS nanocrystals. Mechanistic studies suggest that both single-photon and higher-order reductive pathways contribute to PFOS defluorination, with transient absorption data being consistent with hydrated-electron formation under UV excitation. A continuous-flow photoreactor using ZnS nanocrystals maintained PFOS removal and measurable defluorination over several days. These results identify ZnS nanocrystals as promising photocatalysts for LED-driven PFAS degradation.