Catalytic synthesis of nitrogen-doped multi-walled carbon nanotubes using layered double hydroxides as catalyst precursors

The nitrogen (N)-doped carbon (CN_x) nanotubes were synthesized by pyrolysis of ethyl-enediamine with Ni_1.07Mg1.01AlO3.58, Ni _1.99Mg_0.29AlO_3.78, and Ni_2.31Mg _0.08AlO_3.89 mixed oxides as catalysts at 650°C. Those mixed oxides were obtained by calcination of corresponding layered double hydroxide precursors (LDHs). Structure and composition of LDHs and mixed oxides were characterized by X-ray diffraction (XRD) and Inductively coupled plasma spectrum. X-ray photoelectron spectroscopy and transmission electron microscope were used to characterize the N content, proportion of pyridine-like N structure and morphology of CN_x nanotubes. The results showed that the tubes grown with Ni₂₃₁Mg_0.08AlO_3.89 as catalysts had more obvious bamboo-like structure, larger diameter than those grown with Ni_1.07Mg_1.01AlO_3.58 and Ni _1.99Mg_0.29AlO_3.78. The N content and proportion of graphitic-like N structures increased with the content of Ni ₂₊ increasing in LDH precursors. The morphology, N content and pyridine-like N structures for CN_x nanotubes can be controlled to a certain extent by varying the content of Ni₂₊ in LDH precursors.