Carbon Nanotubes from Bio-Waste: Sustainable Synthesis and Applications

Biomass is the only solid, carbon-rich, renewable resource that is abundantly available, geographically diverse, and inherently eco-friendly. As a sustainable precursor, it offers significant potential for the development of high-performance carbon-based nanomaterials, particularly carbon nanotubes (CNTs). This review provides a comprehensive overview of various biomass feedstocks utilized for CNT synthesis, emphasizing their physicochemical properties and suitability as carbon sources for CNT synthesis. It further explores multiple thermochemical conversion techniques, such as pyrolysis, microwave-assisted pyrolysis, and gasification, which generate intermediate carbon-rich materials. Special focus is given to the synthesis pathways of CNTs from bio-waste using the solid–solid–solid (SSS) two-step method, solid–gas–solid (SGS) method, microwave-assisted pyrolysis, and chemical vapor deposition (CVD) methods. Advanced characterization techniques are discussed in detail to assess the morphology, crystallinity, purity, and structural integrity of the biomass-derived CNTs. This review also highlights the intrinsic physical, chemical, and structural properties of CNTs that govern their functionality. Finally, emerging and established applications of biomass-derived CNTs are critically analyzed across diverse domains, such as environmental remediation, adsorption, energy storage devices, catalysis, sensors, and biomedical engineering. This review underscores the promising role of bio-waste-derived CNTs in advancing sustainable nanotechnology and contributing to the circular carbon economy.