Carbon nano-onions(CNOs)are typically 3 to 50 nm in diameter with successive layers of graphene around a hollow or filled core 0.7 to 5 nm in diameter.They have high conductivity and relatively large specific surface area,with unique physical properties,and have been widely investigated.CNOs were derived from catalytic cracking of methane in our study,the hollowed CNOs and CNOs that with catalytic inside were efficiently separated through two main methods.(i)CNOs were calcined at 500 ℃ in air for 2 h and then manipulate the nitric acid reflux.The XRD patterns showed the iron inside the core was oxidized to be Fe2 O3 and the CNOs broke with a tip opened or into the semicircle was observed from the TEM images.Finally the impurity appeared on the surface or on the top ends of the CNOs and it was removed by using HNO3(60%)reflux at 80 ℃for 2 h.Once the metal was removed from the core under high temperature the graphitic carbon reassemble into more stable material,including collapsing into smaller-particles.(ii)using carbon monoxide treated CNOs,during this process,[Ni,Fe] alloy in the core were transferred to carbonyl metal [Ni(CO)4/Fe(CO)5 ] which were gaseous phase and removed by volatilization and this mechanism was proposed.What is more,size selective growth of palladium nano-particles 2-7 nm in diameter on the surface of carbon nano-onions(CNOs)in water involves pretreating the CNOs with p-phosphonic acid calix arene then PdCl4 2-followed by dynamic thin film processing under hydrogen in a vortex fluidic device will also be conducted.