“Dual waste-derived magnetic geopolymer nanocatalyst for simultaneous biodiesel and colorless glycerol production under ultrasonic-electrical assisted transesterification”

This study presents the development and application of a magnetically separable core–shell nanocatalyst, denoted MAG-BPDDA-MgO@GP-CoreShell, for sustainable biodiesel production via an integrated transesterification/ultrasonic-electrical shock (TRANS/US-ESH) process. The catalyst was prepared by pharmaceutical-grade magnesium oxide (MgO) tablets and potassium-rich ash derived from banana peel and donkey dung (BPDDA), immobilized on a Fe₃O₄/mesoporous silica/geopolymer core–shell, functionalized by cold oxygen plasma. The novelty of this work lies on the simultaneous utilization of pharmaceutical and agricultural waste as catalytic active agents combined with a plasma-functionalized magnetic core–shell structure, which results enhanced catalytic activity and easy magnetic recovery. Characterization by XRD, FTIR, BET, TGA, FESEM, and VSM verified the successful synthesis of a mesoporous catalyst with a significant surface area of 58.4 m 2 /g and strong magnetic properties. Under the optimized conditions estimated by Response Surface Methodology (65.5 °C, 5.1 wt% catalyst, 1.7 methanol-to-oil volume ratio, and 129.6 min), the catalyst achieved a biodiesel yield of 96.1%. Gas chromatography analysis showed a FAME content of 98.86%, while the catalyst activity retained 76.6% of its initial after four reuse cycles. Response Surface Methodology (RSM) were used to model the production yield R = 0.99 represent aproprate crrlation between experimental and predicted values. These findings demonstrate that the proposed catalyst offers an efficient and sustainable approach for waste cooking oil conversion while promoting the valorization of pharmaceutical and agricultural wastes.