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

Abstract

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 via a green synthesis, employing Aloe vera 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 Aloe vera-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 Aloe vera assisted Co3O4 as a promising electrode material for supercapattery applications.