▎ 摘　　要

By means of a (H2O)-O-18 labeling experiment in combination with mass spectrometry tracking, we studied GO photoreduction. Observation of O-18 labeled O-2 provides direct evidence to confirm that water oxidation occurs during GO photoreduction. In combination with DFT calculations, we propose a mechanism for O-2 and CO2 evolution in the photoreduction of GO.