Citrus limetta Peel-Derived Catalyst for Sustainable Production of Biodiesel

[Image: see text] To produce biodiesel from oleic acid (OA), the effectiveness of sweet lemon (Citrus limetta) waste peels as an acidic catalyst in an esterification process is examined in the current work. A biowaste-derived sulfonated carbon-based catalyst is fabricated without high temperatures via a simple one-pot process. Several techniques are used to investigate the chemical components and morphology of the catalyst, including Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET), and N(2) adsorption–desorption. The biodiesel conversion is observed by gas chromatography–mass spectrometry (GC–MS), proton nuclear magnetic resonance (1)H NMR, and carbon nuclear magnetic resonance (13)C NMR. The excellent biodiesel conversion of 96% was obtained using optimized conditions, i.e., 1:20 of OA/MeOH, 5 wt % catalyst loading, 70 °C temperature, and 3 h. The catalyst shows 87% conversion in just 1 h, and the maximum conversion was found to be ≈96%. This high activity of the catalyst can be attributed to the presence of sulfonic groups and its porous nature. The formed catalyst shows excellent catalytic activity up to three cycles.