The effects of catalyst on the morphology and physicochemical properties of nitrogen-doped carbon nanotubes

• Nitrogen-doped CNTs have been prepared by CVD method using different catalysts.
• The effects of catalyst on the properties of the nanotubes were investigated.
• Changing the catalyst varies the structure of N-CNTs from bamboo-like to hollow channel.
• Changing the catalyst influences the surface properties of N-CNTs.

Doping of carbon nanotubes with foreign elements, such as boron or nitrogen, is one of the most effective ways to change their properties to make them suitable for various applications. As the properties of nitrogen-doped carbon nanotubes (N-CNTs) originate from their structure, it is practical to manipulate their structure during synthesis. We have investigated the influence of catalyst on the chemical surface properties and morphology of N-CNTs. Different catalysts, such as iron, nickel, cobalt and copper, have been tested for the synthesis of N-CNTs. The results revealed strong correlations between the properties of N-CNTs and the growth catalyst. The highest percentage of nitrogen incorporated in the N-CNTs structure was found for the N-CNTs synthesized on the nickel catalyst. The use of nickel, cobalt or copper catalysts led to the formation of N-CNTs with higher numbers of pyrrolic nitrogen doped in the structure, while N-CNTs with higher numbers of quaternary nitrogen were synthesized with the iron catalyst. The N-CNTs synthesized on iron, nickel and copper had a bamboo-shaped structure; and, the majority of the N-CNTs had a hollow-channel structure if synthesized on the cobalt catalyst. A higher yield and lower N-CNT diameter were obtained using cobalt as the growth catalyst.

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