CARBON NANOTUBES: SYNTHESIS, PROPERTIES, AND MULTIDISCIPLINARY APPLICATIONS A COMPREHENSIVE REVIEW

Carbon nanotubes (CNTs) have become one of the most versatile classes of nanomaterials in the last three decades, due to their outstanding mechanical strength, tunable electrical conductivity, high thermal stability and large accessible surface area. CNTs are cylindrical, sp2-hybridized carbon nanostructures. This review summarizes recent work on the synthesis, structure, and physicochemical behavior of single-walled and multi-walled carbon nanotubes, with special attention to arc discharge, laser ablation, and chemical vapor deposition routes, as well as post-synthesis purification and covalent or non-covalent functionalization strategies to improve dispersibility and biocompatibility. Based on these basic principles, four key application areas are discussed in the review: (i) biomedical applications, including targeted and controlled drug delivery, gene therapy, tissue engineering scaffolds, biosensing and photothermal or photodynamic cancer therapy; (ii) electrocatalytic and energy applications including fuel cells, batteries, electrochemical sensors and CO2 electroreduction; (iii) polymer-matrix composites produced by melt mixing, solution mixing, in-situ polymerization and additive manufacturing, which produce lightweight materials with improved mechanical, electrical and thermal properties for aerospace, automotive, construction and electronics applications; and (iv) natural nanotubular clay analogues such as halloysite that provide a lower-cost, more abundant alternative platform for carbon capture and environmental remediation. Toxicological issues such as biodegradability, dispersibility and long-term biocompatibility remain impediments to translation. The research finds that ongoing improvement in scalable synthesis, reproducible functionalization, and application-specific material design will be necessary for carbon nanotubes to move from laboratory-scale demonstrations to widely deployed industrial and clinical applications.