The adsorption of PFOS onto the surface of NCs is crucial for an efficient decomposition reaction. The decrease in the F-NMR signals of PFOS dissolved in the aqueous solution by the addition of CdS NCs indicates that PFOS was promptly adsorbed onto the surface of NCs in the solution (Fig. ). LC-MS analyses revealed that 21% of PFOS were adsorbed on the surface of NCs 5 min after the addition of CdS NCs to the solution for photocatalytic reactions (Supplementary Fig. ). Prior studies have shown that coordinated ligands are displaced under light irradiation, and the readsorption of displaced ligands requires more than several seconds. The photoinduced ligand displacement was observed through proton-NMR ( 1 H-NMR) spectroscopy of the deuterated solution of MPA-capped CdS NCs (Fig. ). Broad peaks at 2.2-3.5 ppm before light irradiation were attributable to the MPA coordinated on the surface of NCs, while several sharp peaks were ascribed to weakly bound or free MPA. The sharp peaks associated with free MPA increased upon irradiation of 405-nm continuous-wave LED light (830 mW cm -2 ) for 5 min. Moreover, the sharp peaks decreased again 1 h after light irradiation. These results indicated that MPA ligands were displaced by light irradiation, and the displaced MPA gradually readsorbed onto the NCs. This ligand displacement most probably facilitates the adsorption of PFOS onto the surface of NCs and accelerates the photodecomposition of PFOS. The timescale of the observed reaction was considerably slower than that reported previously, possibly because the extended duration of light irradiation promoted the persistence of displaced ligands. The reaction between PFOS and hydrated electrons, as well as higher excited states, should be completed within several microseconds. If the ligand displacement reaction plays a pivotal role in driving PFOS decomposition, the decomposition efficiency is expected to be affected by light irradiation conditions slower than seconds. To elucidate the relationship between ligand displacement on the NC surface and PFOS decomposition, we measured the overall deF% under different irradiation conditions. Specifically, the light was irradiated for 10 s and paused for specified intervals (10 s, 1 min, and 2 min, as illustrated in Fig. ). This cycle was repeated to achieve an equivalent total irradiation duration as that of continuous irradiation for 1 h. Moreover, we monitored the solution temperature because it changes based on the duration of irradiation. Following continuous light irradiation for 1 h, the overall deF% was 56% and the solution temperature after the light irradiation was 311 K. The decrease in the solution temperature to 296 K under the same irradiation condition led to a decrease in the overall deF% to 41%.