Bio-metal organic frameworks (Zn, Fe, Ni–Glu) as green catalysts for oleic acid esterification into biodiesel

The depletion of petroleum resources and environmental concerns drive the need for sustainable, renewable energy. Biodiesel, produced via fatty acid esterification, is a promising alternative to conventional diesel. Metal-organic frameworks (MOFs) are appealing solid-phase catalysts, but they often rely on unsustainable synthetic ligands. This study addresses that by using glutamic acid, a natural amino acid, to synthesize three bio-MOFs: ZnGlu (zinc-glutamate), FeGlu (iron-glutamate), and NiGlu (nickel-glutamate). The methods used were spontaneous hydrothermal, hydrothermal, and solvothermal (at elevated temperature and pressure), yielding 63.65 %, 9.87 %, and 45.94 %, respectively. Characterization involved Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) to confirm differences. Though NiGlu had the highest surface area (236.71 m 2 /g), its catalytic performance was low, possibly due to blocked active sites. ZnGlu, by contrast, converted 87.5 % of oleic acid to biodiesel under optimal conditions (5 % catalyst, 65°C, 360 min). These results suggest that catalytic efficiency depends on surface area, pore purity, metal stability, and active-site accessibility. Therefore, ZnGlu bio-MOF shows strong potential as an environmentally friendly catalyst for biodiesel.