▎ 摘　　要

Graphene-carbon nanotube (G-CNT) hybrids were synthesized by a one-step chemical vapor deposition process using a mixed catalyst of MgO and Fe/MgO. MgO layers acted as templates for the growth of graphene, and Fe particles on the MgO layers catalyzed the growth of single or double-walled CNTs. The G-CNT hybrids had porous structures with hierarchical pore distributions due to the composition of graphene with CNT network. Superparamagnetism with a saturation magnetization of 2.7 emu/g was found in the G-CNT hybrids due to the existence of Fe3C nanoparticles of size similar to 3 nm. The graphene to CNT ratio was conveniently changed by varying the MgO to Fe/MgO ratio, as characterized by Raman analysis and specific surface area measurements. Furthermore, a simplified synthesis of G-CNT hybrids was demonstrated by using MgO supported Fe or Ni catalysts with a low metal concentration. (C) 2012 Elsevier Ltd. All rights reserved.