Remediation of thiophenes from liquid fuel via ultrasound-assisted oxidative desulfurization using a magnetic MgFe2O4@CQD nanocatalyst

Abstract

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 ΔG of ∼82 kJ mol⁻¹ and ΔS 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.