Diamagnetism of carbon onions probed by NMR of adsorbed water

We measured the 1 H chemical shift of water molecules adsorbed on defect sites of carbon onions and compared it with the shifts of bulk water and water adsorbed by chemically-derived graphene, graphene oxide and nanodiamond. The positions of 1H resonances for insulator nanodiamond and graphene oxide are close to that of bulk water, while water molecules adsorbed by graphene, and particularly by carbon onions, reveal a significant deviation in chemical shift from that of bulk water, which can be attributed to the diamagnetic screening effect of the conducting graphene layers. This conclusion is supported by a pronounced correlation established in our experiments between the proton chemical shifts and diamagnetic contribution to the magnetic susceptibility.