Integrating biomass valorization and clean energy: Exocarp‐derived nano‐catalyst for sustainable biodiesel production from Martynia annua L.

The escalating prices and dependence on fossil fuels have intensified the climatic deterioration worldwide, pushing researchers to focus on renewable and sustainable energy. Biodiesel is an ideal substitute to conventional fuels with the potential to tackle rising energy demands. The present study emphasizes exploring the possibility of Martynia annua L. seed oil for biodiesel production. The process of transesterification was facilitated using green Al 2 O 3 nano‐catalyst synthesized from the waste exocarp of Martynia annua fruit. Characterization of the synthesized phyto‐nanocatalyst was performed by using XRD, DRS, FTIR, SEM, DLS, and EDX techniques. Reaction conditions for transesterification were optimized using response surface methodology with a Box–Behnken Design comprising 29 experimental runs. At an oil‐to‐methanol ratio of 1:12, a catalyst loading of 0.50 wt% for 100 min and at 75°C, maximum biodiesel yield (95.2%) was achieved. The physico‐chemical properties of M. annua biodiesel including density (0.857 kg/L), acid value (0.35 mg KOH/g), cloud point (−14°C), viscosity (3.81 mm 2 /s), flash point (96°C), sulfur content (0.00723 wt%), and the pour point (−10°C) were consistent with international biodiesel standards. Thus, the finding indicates that M. annua seed oil can serve as a potential feedstock for biodiesel production, while its fruit exocarp can be used for nanocatalyst synthesis, offering a cheap and viable approach to reduce production cost and support a closed‐loop production system. Engine‐based studies are further recommended to assess its suitability for use in automobile engines.