Finally, the nano-onion NPs had an average EEO2 of ~3.6 x 10 -3 , but the individual NP EEO2 values varied by over two orders of magnitude, from near zero for two NPs (Figs. and), to one NP with the highest EEO2 of the entire set of carbon NPs. As discussed above, we believe that the inherent reactivity of perfect onion surfaces is near zero, and interpret the high reactivity of some nano-onion NPs to be the presence of defective or non-onionstructure carbon on the surface.