Green synthesis of <i>Aloe vera</i>-assisted Co₃O₄ nanostructures: structural, electronic, optical, and electrochemical insights for supercapattery applications

Green synthesis is an emerging and sustainable approach for developing functional nanomaterials using environmentally benign resources. In this work, cobalt oxide (Co₃O₄) nanostructures were successfully synthesized <i>via</i> a green synthesis, employing <i>Aloe vera</i> gel as a natural reducing and stabilizing agent. This phytochemical-assisted synthesis eliminates the need for hazardous chemicals and offers a cost-effective, eco-friendly alternative for nanomaterial fabrication. The resulting Co₃O₄ exhibited a phase-pure spinel structure with an average crystallite size of ∼32 nm, as confirmed by synchrotron X-ray diffraction (XRD), and showed excellent thermal stability with only 3.5% weight loss up to 750 °C (TGA). FTIR analysis revealed strong Co-O stretching vibrations along with <i>Aloe vera</i>-derived surface functionalities, indicating successful templating and stabilization. X-ray photoelectron spectroscopy (XPS) confirmed the coexistence of Co²⁺/Co³⁺ oxidation states, surface hydroxyls, and chemisorbed oxygen features that contribute to a redox-active, defect-rich surface. X-ray absorption spectroscopy (XAS) further supported these findings by revealing oxidation state distribution, crystal field splitting, and strong Co-O hybridization. Additionally, UV-Vis spectroscopy showed a direct band gap of 3.65 ± 0.10 eV, suggesting good electronic quality with low intrinsic defect density. Electrochemical studies demonstrated excellent performance, with specific capacitance values of 450.7 F g^-1 at 1 mV s^-1 and 467.9 F g^-1 at 0.5 A g^-1, along with outstanding cycling stability (83% retention) and 100% coulombic efficiency after 3000 cycles at 10 A g^-1. These results highlight the synergistic contributions of green synthesis and intrinsic structural-electronic properties, establishing <i>Aloe vera</i> assisted Co₃O₄ as a promising electrode material for supercapattery applications.