Aloe vera-mediated green synthesis of transition metal oxides: structural insights and electrochemical applications in energy storage

The growing demand for sustainable, high-performance energy storage materials has spurred interest in green synthesis strategies. Aloe vera, a phytochemical-rich and eco-friendly biomass, provides a unique platform for fabricating transition metal oxides (TMOs) with tailored properties for supercapacitors and batteries. This review systematically explores the role of bioactive compounds in Aloe vera, such as polysaccharides, flavonoids, phenolic acids, and anthraquinones in reducing, stabilizing, and templating during nanomaterial synthesis. Various green synthesis routes, including carbonization, hydrothermal, sol–gel, and microwave-assisted methods, are discussed, along with their influence on morphology, crystallinity, and electrochemical performance. The review highlights Aloe vera-mediated synthesis of key TMOs (such as NiO, Co3O4, ZnO) and composites, emphasizing structural advantages, defect engineering, and redox activity that enable superior capacitance, energy density, and cycling stability. Comparative analysis demonstrates Aloe vera-assisted methods outperform conventional synthesis in terms of sustainability, cost-effectiveness, and functional efficiency. Finally, critical challenges, such as phytochemical variability, scalability, and reproducibility are examined, and future directions for integrating Aloe vera-based nanomaterials into next-generation energy storage systems are outlined.