From fruit waste to advanced nanomaterials: Energy-efficient MWCNT synthesis and characterization

This study reports a sustainable approach for synthesizing carbon nanotubes from fruit waste through a two-step process involving slow pyrolysis followed by microwave-assisted synthesis. Biochar obtained at different pyrolysis temperatures (300, 400, and 500 °C) was used as the carbon precursor, while ferrocene served as the catalyst at varying weight ratios with biochar. The synthesized fruit waste-derived carbon nanotubes exhibited the characteristic multi-walled tubular morphology with nanoscale diameters, as confirmed by microscopic and spectroscopic analyses. Structural characterization revealed that both pyrolysis temperature and catalyst ratio had a significant influence on carbon nanotube properties, including crystallinity, degree of graphitization, and yield. Higher pyrolysis temperatures generally produced carbon nanotubes with improved structural order, smaller average diameters, and higher product yield, while the catalyst ratio played a critical role in determining the extent of graphitic ordering. The results demonstrate that fruit waste is not only an abundant and low-cost carbon source but also a promising sustainable feedstock for nanomaterial synthesis. Furthermore, the energy and cost analysis indicates that this method is not only comparable to conventional CNT synthesis methods but, in certain cases, offers better energy efficiency and economic feasibility, thereby enhancing its potential for future applications. Overall, this work provides a green and sustainable pathway for transforming agricultural residues into high-value carbon nanomaterials.