Remediation of thiophenes from liquid fuel <i>via</i> ultrasound-assisted oxidative desulfurization using a magnetic MgFe ₂ O ₄ @CQD nanocatalyst

Magnetic MgFe₂O₄@CQD was developed as a novel nanocatalyst for ultrasound-assisted oxidative desulfurization (UAOD) of thiophenes from fuel. The nanocatalyst was synthesized using an oxidative co-precipitation method and characterized. XRD and XPS confirmed the formation of carbon quantum dots and MgFe₂O₄@CQD and its paramagnetic character was confirmed using the VSM technique. The UAOD tests were designed using the Box-Behnken type of response surface methodology (RSM) and the process was modelled and optimized. The optimum conditions were predicted to be 50 ppm, 0.62, 0.5 g L^-1 and 24 min, respectively, for sulfur concentration, the volumetric ratio of H₂O₂/fuel, catalyst dosage/fuel, and sonication time, leading to a removal rate of 67%. The order of independent factors' importance according to Pareto analysis was as follows: sonication time > nanocatalyst dosage/fuel > sulfur concentration > volumetric ratio of oxidant/fuel. The kinetics of DBT oxidation over MgFe₂O₄@CQD followed a pseudo-first order reaction with an activation energy of 33.94 kJ mol^-1, revealing easy oxidation of DBT. The results of thermodynamic studies exhibited a Δ<i>G</i> of ∼82 kJ mol^-1 and Δ<i>S</i> of ∼-0.17 kJ mol^-1 K^-1 at 298 K, indicating a non-spontaneous reaction. The results demonstrate that magnetic MgFe₂O₄@CQD is a cheap, green, highly effective and recyclable nanocatalyst in the UAOD process for fuel purification.