Unexpected hydrogenation process in the formation of hydrogenated carbon nano-onions

[Display omitted] •Time-dependent growth of hydrogenated CNOSs by a solvothermal method is presented.•Unexpectedly, hydrogenation degree of CNOSs increases as the reaction time increases.•New insights into our understanding on the formation of hydrogenated CNOSs are given. Study on the formation of hydrogenated carbon nanomaterials is very important for their synthesis and understanding the properties. Here we show the time-dependent growth process of the hydrogenated carbon nano-onion spheres (CNOSs) in a solvothermal method, giving important information on the underlying mechanism for the hydrogenated CNOSs formation. By tuning the reaction time for CNOSs growth, we unexpectedly find that graphitic CNOSs are formed within short reaction time, and then the hydrogenation of CNOSs takes place. The degrees of hydrogenation increase as the reaction time increases, resulting in the hydrogenated CNOSs. This gives new insight into the synthesis of hydrogenated carbon nano-onions, enabling the degree of hydrogenation to be tuned.