Metal cadmium is expected to be generated upon light irradiation. Thus, its role in the defluorination reaction was experimentally studied. The generation of the metal cadmium on the NC surface was confirmed by a change in solution color from yellow to dark brown upon light irradiation. The dark brown color persisted throughout the reaction and gradually faded over a day after the termination of light irradiation. This long lifetime of metal cadmium is inconsistent with the fact that the transient species contributing to the defluorination reaction are generated within a few seconds or tens of seconds. Notably, although the formation of metal cadmium was promoted by the addition of cadmium precursors (CdCl2 or Cd(CH3COO)2), the overall deF% decreased (remaining nearly constant for Cd(CH3COO)2) with the addition of these precursors (Supplementary Fig. and). These observations demonstrate that metal cadmium was not involved in the main pathways of defluorination reactions.