Optimization and Characterization of Biodiesel Production From Non‐Edible Brassica deflexa Seed Oil Using a Plant‐Assisted Iron Oxide Nanocatalyst

The present study explores non‐edible Brassica deflexa seed oil as an alternative feedstock for biodiesel production using a plant‐assisted iron oxide nano‐catalyst prepared from green chili pedicel and calyx extract. The seed oil showed an oil content of 32% and a low free fatty acid value of 0.042 wt.%, indicating its suitability for single‐step transesterification. The synthesized Fe 2 O 3 nanocatalyst was characterized through XRD, EDX, SEM, FTIR, and zeta potential analysis. XRD confirmed the crystalline nature of the catalyst with an average crystallite size of 14.71 nm, while EDX showed Fe as the dominant element with 68.92 wt.%. SEM analysis revealed aggregated spheroidal particles with a porous, sponge‐like surface morphology, suggesting the presence of accessible catalytic sites. Zeta potential analysis indicated a surface charge of −7.25 mV, showing a negatively charged catalyst surface and supporting its dispersion stability during catalytic application. Biodiesel production was optimized using response surface methodology based on Box–Behnken design. The highest biodiesel yield of 96.3% was achieved at a methanol‐to‐oil ratio of 9:1, catalyst loading of 0.80 wt.%, reaction temperature of 70°C, and reaction time of 120 min. Formation of fatty acid methyl esters was confirmed by FT‐IR, GC–MS, and NMR analyses, with GC–MS identifying 20 methyl ester compounds in the produced biodiesel. Fuel property assessment showed that the biodiesel satisfied selected quality parameters, including acid value and sulfur content; however, further purification and process refinement are required to improve properties such as flash point and viscosity. Overall, the findings suggest that B. deflexa seed oil has potential as an under‐utilized non‐edible feedstock for biodiesel production, while further studies on moisture control, catalyst benchmarking, engine performance, and techno‐economic feasibility are needed before large‐scale application.