To confirm the presence of copper (Cu) atom on the support, chemical mapping was conducted of the photocatalyst before and after the reaction by using energy dispersive X-ray spectroscopy (EDX) in low magnification scanning transmission electron microscopy (STEM) mode. As shown in Figure , the EDX elemental maps indicated the presence of Cu (Figure ), dispersed over the g-C3N4 support. The Cu-loading was quantified from various regions over the sample and was found to be 0.1-1 atom%. Furthermore, the highresolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image was used to distinguish the heavier metallic element, Cu, from the lighter support.