Basicity-tuned graphitic carbon nitride supported MgO heterogeneous catalysts for efficient transesterification of groundnut oil to biodiesel

• Triglyceride transesterification using MgO catalyst produced a conversion rate of 27.5 % prior to process optimization. • Basicity-tuned MgO/g-C 3 N 4 50 wt% composite yielded 52 % biodiesel conversion prior to process optimization. • Experimental validation of the process, optimized by RSM yielded a biodiesel conversion of 94 % for MgO/g-C 3 N 4 . • GC–MS characterization of MgO/g-C 3 N 4 catalyzed groundnut oil biodiesel show presence of wide spectrum fatty acid esters. • MgO/g-C 3 N 4 catalyzed groundnut oil biodiesel conforms to ASTM-D6751 standard biodiesel specifications. Quality and quantity of biodiesel derived from oil depend on the type of feedstock and the transesterification process. To maximize biodiesel production efficiency and ensure the desired fuel quality, it is crucial to develop and optimize feedstock-specific production processes. This study reports on the transesterification of groundnut oil using a heterogeneous catalyst. Magnesium oxide (MgO) and its composites with graphitic carbon nitride (g-C 3 N 4 ) at 10, 30, and 50 wt% (MG10, MG30, MG50) were used. The composite catalyst combines basic sites from MgO and Lewis acid sites from the nitrogen atoms in the g-C 3 N 4 triazine unit, giving rise to synergistic effects that enhances biodiesel production. MgO nanoparticles were synthesized via precipitation, followed by calcination at 500 °C, and MgO/g-C 3 N 4 composites were prepared by grinding at different ratios. Morphological and structural studies confirmed material characteristics. BET analysis indicated an increased surface area of 71.39 m 2 /g, enhancing catalytic activity, while SEM revealed the agglomerated g-C 3 N 4 and the cubic morphology of MgO. Response surface methodology was used to optimize catalyst loading, temperature, and reaction time parameters. The optimal conditions for biodiesel conversion using MG50 composite was determined to be methanol/oil ratio of 6:1, 2.5 wt% catalyst loading, 41.7 °C reaction temperature and spanning 52 min of reaction, yielding 94 % efficiency. GC–MS analysis confirmed successful transesterification, identifying key fatty acid esters such as ethyl oleate (34.72 %) and hexadecanoic acid methyl ester (7.69 %). This work supports further research into feedstock-specific catalysts for industrial biodiesel applications.