Parametric Investigation of Single‐Walled Carbon Nanotube Growth on Co/CaO Catalysts Derived from Waste Eggshells

Abstract The use of eggshell‐derived CaO as a sustainable catalyst support for single‐walled carbon nanotube (SWCNT) synthesis offers environmental and economic benefits. However, controlling Co nanoparticle dispersion and stability on CaO support remains a challenge. This study explored the synthesis of SWCNTs on Co/E‐CaO‐H catalysts obtained by calcination–hydration–dehydration (C–H–D) treatment of eggshells. Optimized conditions, including catalyst calcination temperature of 400 °C, catalyst reduction temperature of 550 °C, and SWCNT growth temperature of 800 °C, enabled the formation of well‐dispersed 2–3 nm Co nanoparticles, critical for SWCNT growth. Raman spectroscopy confirmed the successful synthesis of SWCNTs with low D/G ratios (down to 0.06) and strong radial breathing mode (RBM) peaks. With 1 wt% Co loading on Co/E‐CaO‐H, the catalyst produced a carbon yield of 7.1wt% C/g Co, while minimizing aggregation and defects. DFT calculations and catalyst characterization revealed that E‐CaO‐H support provides a chemically reactive surface with abundant O 2− sites, which facilitate the stabilization of Co 3 O 4 . The partial reduction of well‐dispersed Co 3 O 4 produced small Co nanoparticles, effectively serving as nucleation sites for SWCNT growth. This study demonstrates eggshell‐derived CaO as an effective, eco‐friendly catalyst support, offering a sustainable approach for SWCNT synthesis.