Full experimental conditions, along with the results of utilizing Cu-CdS NCs, are described in Methods and the supplementary information. The 19-fluorine nuclear magnetic resonance ( 19 F-NMR) spectrum of the reaction solution (deuterated water was used only for NMR measurements) before light irradiation originates from PFOS (Fig. ). After 405-nm light irradiation (830 mW cm -2 ) for 24 h, only an intense sharp peak at -121 ppm was observed, attributable to the fluorine ion. This observation shows that PFOS can be decomposed to fluorine ions by visible-light irradiation. The overall defluorination efficiency (overall deF%, see equation (1) in the Methods section) increased with the increase in the irradiation period and reached almost the unity after 8 h (ranging from 90-100% depending on the experimental condition, Fig. ). The concentration of PFOS in the solution decreased with increase in the irradiation period and reached <0.1% after 8 h. The defluorination efficiency depends on the amounts of NCs and TEOA (Supplementary Fig. ), and the optimized overall deF% were 55%, 70-80%, and 100% for 1-, 2-, and 8h light irradiation, respectively. The quantum efficiency of C-F bond dissociations was determined to be 2.0 × 10 -3 using the overall deF% after 1-h irradiation of 405-nm LED light (details can be found in Supplementary Note 2).