Preparation of coal-based carbon nanotubes using catalytical pyrolysis: A brief review

In view of the Chinese government's “30–60 target” for “carbon peak, carbon neutral” coal utilization, the persistent bottleneck problems in coal consumption of low utilization efficiency, serious environmental pollution, and high carbon emissions have once again become critical issues. The preparation of advanced carbon materials with coal as the precursor can realize the clean, efficient, and low-carbon utilization of coal resources. Coal is a natural low-cost carbon source with a rich aromatic structure that can be used for the preparation of carbon nanomaterials with excellent physical and chemical properties via arc discharge, laser ablation, chemical vapor deposition, and catalytic pyrolysis. In this study, coal-based carbon nanotubes (CNTs) were investigated. First, progress in research on CNTs prepared by conventional, microwave, and plasma-catalyzed pyrolysis methods were discussed in depth. Second, the effects of metal catalysts, including alkali metals, transition metals, and other metals, on the preparation of CNTs were analyzed. Third, the formation mechanisms of the catalytic pyrolysis of CNTs, namely, “Tip growth” and “Base growth” models, “Step growth” model, and “Particle-Wire-Tube growth” model, were summarized. Finally, the current challenges and future direction in the development for preparing coal-based CNTs were explored.