Although sulfide ions and their byproducts may be potential photodegradation products of CdS, the reaction efficiency did not improve even after the addition of sulfide ions (Supplementary Fig. ). This result suggests that sulfur ions and their byproducts were not likely to be involved in the reaction. This defluorination method can be applied to perfluorinated alkyl polymers such as Nafion (Fig. ). Nafion is widely used as an ion-exchange membrane in electrolysis and batteries. For the powder form of Nafion, where the sulfonate groups are -SO2F, the overall deF% under the same experimental condition with PFOS was at most 1.8% after irradiation for 24 h. When the same reaction was performed with Nafion dispersed in a water/ethanol mixture solution by saponification, where the sulfonate groups are -SO3 -, the overall deF% dramatically increased to 81% over 24-h light irradiation. These results demonstrated that nonlinear photoreactions of semiconductor NCs can efficiently decompose perfluoroalkyl polymers, emphasizing the significance of proximity between the NCs and the substrate for the reaction. Furthermore, polytetrafluoroethylene (PTFE) powder can also be defluorinated, although the overall deF% was at most 5% after irradiation for 48 h. Images captured before and after the reactions demonstrated that the surface of the PTFE powder, which is strongly hydrophobic, became hydrophilic and the powder sank into the aqueous solution (Supplementary Fig. ). In other words, PTFE can be defluorinated by visible LED light although the reaction efficiency was relatively low.