Large-scale CVD synthesis of nitrogen-doped multi-walled carbon nanotubes with controllable nitrogen content on a CoxMg1−xMoO4 catalyst

High-purity nitrogen-doped multi-walled carbon nanotubes (MWCNTs) have been produced with a yield of more than 30 times the amount of the catalyst, using CoxMg1−xMoO4 as catalyst and a methane–hydrogen–ammonia mixture as precursor. By controlling the flow-rate of ammonia during the chemical vapor deposition, the nitrogen concentration of 0.6 at.% to 3.2 at.% was obtained. X-ray photoelectron spectroscopy reveals that three different structures of the nitrogen atoms are involved in the nitrogen-doped MWCNTs, among which a graphite-like structure is dominant in these MWCNTs. Thermal gravimetric analyses show that the purity of the as-prepared MWCNTs is over 95%. High-resolution transmission electron microscopy analyses indicate that the MWCNTs have high graphitization degree. Our experimental results showed that the CoxMg1−xMoO4 catalyst is ideal for the synthesis of high-quality nitrogen-doped MWCNTs because of its high catalytic activity.