Upcycling of Solid Waste into Carbon Nanotubes for Supercapacitors

The rapid accumulation of solid waste—including plastics, agricultural residues, electronic waste, industrial by-products, and biomedical discards—has become a critical environmental concern. Recent advancements have transformed this challenge into an opportunity by utilizing such waste as cost-effective and abundant carbon sources for synthesizing carbon-based nanomaterials (CBNs), including graphene, fullerenes, carbon dots, and carbon nanotubes (CNTs). Among these, CNTs are particularly promising due to their remarkable mechanical strength, thermal stability, and electrical conductivity, making them highly suitable for energy storage applications such as supercapacitors. This chapter focuses on the upcycling of diverse solid waste sources into CNTs and examines their application in supercapacitor systems. While notable progress has been achieved, challenges such as maintaining product consistency and developing scalable synthesis routes persist. Due to their distinctive structure and exceptional physicochemical properties, CNTs are increasingly recognized for their potential in energy storage and conversion. This chapter further outlines the key obstacles and research priorities necessary to advance the structural tuning, performance optimization, and functionalization of CNTs for next-generation energy technologies.