Exploring the frontiers of carbon nanotube synthesis techniques and their potential applications in supercapacitors, gas sensing, and water purification

In the last few decades, there have been major developments in the field of nanotechnology, particularly in the synthesis of materials at nanoscales, with numerous potential applications. Carbon nanotubes (CNTs) are sp2 hybridized tube-like structures, now gaining significant attention in various technological applications due to their intriguing physio-chemical and electronic properties. This review encompasses the recent developments in CNT synthesis techniques, with a special focus on the chemical vapor deposition method over arc discharge and laser ablation. The twenty-first century's unceasing quest for efficient and sustainable energy storage solutions has spurred the development of supercapacitors, in which CNTs exhibit unprecedented potential due to their large surface area and high electrical conductivity. For instance, MWCNTs composited with Ni-Co bimetallic hydroxide doped with rare earth elements Lai+ give the 4396.0 F g-1 highest specific capacitance at a current density of 1 A g-1, maintaining 70.31 % of their capacitance after 3000 cycles. Moreover, their utilization as gas sensors has revolutionized environmental monitoring by virtue of their sensitivity, selectivity and rapid response to harmful gases. An MWCNT-WS2 composite possesses a superior selectivity along with a 7 % response to NO gas exposure at a concentration of 5 ppb. Additionally, carbon nanotubes have proven to contribute to addressing the pressing need for effective water purification technologies, leveraging their unique structural and adsorptive properties to remove contaminants from water sources. The AC-MWCNTs-ZnO composite achieved the highest adsorption capacity for MB dye at 1250 mg g-1, with a removal efficiency of 89.5 % and a high surface area of 1723.64 m2 g-1. CNT-based materials offer high adsorption capacities for contaminants, including organic pollutants, heavy metals, pharmaceuticals and dyes. Despite these advancements, CNT-based composites face challenges such as high production costs, low stability, limited selectivity, and issues related to safe disposal or recycling. Additionally, the potential health risks associated with CNTs, particularly concerning toxicity and bioaccumulation, necessitate thorough investigation. Nonetheless, the diverse range of applications underscores the critical role of CNTs in addressing contemporary challenges in energy, environmental protection, and sensing technologies.