Sustainable carbon nanoarchitectonics: a biomass derived carbon nano-onion/magnetite composite as a reusable catalyst for solvent-free synthesis of benzoxazinones and benzthioxazinones

In pursuit of greener and more sustainable chemical transformations, we report the synthesis of a biomass-derived carbon nano-onion/magnetite (CNO/Fe₃O₄) composite using flaxseed oil <i>via</i> a facile, eco-friendly wick pyrolysis method. The resulting nanocomposite exhibits excellent catalytic activity for the solvent-free synthesis of benzoxazinones and benzothioxazinones-pharmacologically relevant heterocycles-with yields of up to 95%. The unique layered architecture of CNOs combined with the magnetic functionality of Fe₃O₄ imparts high surface area, thermal stability, and magnetic recoverability, enabling easy separation and reuse over multiple cycles with minimal activity loss. Comprehensive characterization using FT-IR, XRD, BET, HR-TEM, FE-SEM, EDX, TGA, XPS, and VSM confirmed the structural integrity and composition of the hybrid catalyst. The methodology retains high efficiency at the gram scale, demonstrating its practical scalability. Overall, this study underscores the promise of biomass-derived nanocatalysts in advancing green chemistry through efficient, recyclable, and scalable catalytic systems for the synthesis of value-added compounds.