Some perspectives on nitrogen-doped carbon nanotube synthesis from acetonitrile and N,N′-dimethylformamide mixtures

This work reports on the influence of the ratio of sp³ (N,N′-dimethylformamide, DMF) to sp (acetonitrile) hybridised nitrogen within the carbon source used in the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) by means of the floating catalyst chemical vapour deposition method. The physicochemical properties of the N-CNTs were investigated by means of scanning and transmission electron microscopies, textural characteristics, powder X-ray diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis and elemental analysis. When the two nitrogen sources were compared before mixing, it was found that sp³ hybridised nitrogen in DMF was a more effective source for the incorporation of nitrogen atoms (5.87%) than sp hybridised nitrogen in acetonitrile (3.49%). The number of walls within the N-CNT synthesised from the sp³ nitrogen source was tailored by changing the synthesis temperature. Overall, a 1:3 sp³:sp ratio produced N-CNTs with the highest nitrogen content of 9.38% and a general abundance of pyrrolic nitrogen moieties within the samples. The best synthesis temperature in terms of nitrogen content and largest composition of N-CNTs with least residual iron was found to be 900 °C. Varying ratio of sp³:sp hybridised nitrogen is suitable for tailoring the physicochemical properties of N-CNTs towards preferred applications.