Carbon nanotubes: Their role in engineering applications and challenges ahead

Since their discovery in 1991, carbon nanotubes have been of great interest because of their simplicity and ease of synthesis. The novel properties of nanostructure carbon nanotubes such as high surface area, good stiffness, and resilience have been explored in many engineering applications. Research on carbon nanotubes has shown the application in the fields of energy storage, hydrogen storage, electrochemical supercapacitors, field-emitting devices, transistors, nanoprobes and sensors, composite material, and templates. For commercial applications large quantities and high purity of carbon nanotubes are needed. Different types of carbon nanotubes can be synthesized in various ways. The most common techniques currently practiced are arc discharge, laser ablation, chemical vapor deposition, and flame synthesis. The purification of carbon nanotubes is carried out using various techniques mainly oxidation, acid treatment, annealing, sonication, filtering, and chemical functionalization. However, high-purity purification techniques still have to be developed. Real applications are still under development. The authors address the current research on the challenges that are associated with synthesis methods, purification methods, dispersion, and toxicity of carbon nanotubes within the scope of different engineering applications, energy, and environmental impact.