Amin Alamdari
A series of triple-component PTA-Y%/GO-X%/UiO-66(Zr) hybrid is designed, where GO uniquely mediates electron transfer between Zr sites and PTA, enabling a dual-path radical generation mechanism and exceptional stability under ultrasonic irradiation. The composites were synthesized via a hydrothermal method for the purpose of removing indole (IND) from model fuel under sono-assisted oxidative denitrogenation (SODN). These materials were developed by encapsulating phosphotungstic acid (PTA) into a composite catalyst consisting of graphene oxide (GO) and a UiO-66(Zr) metal-organic framework (MOF). A comprehensive characterization of the synthesized composites was performed, employing FE-SEM, FT-IR, XRD, EDX, BET, and TGA. The study comprehensively evaluated the impact of multiple parameters on catalytic performance, including PTA content, the GO-to-MOF ratio, process time, catalyst dosage, O/N molar ratio, temperature, initial concentration of IND, the presence of an aromatic co-solvent, solution pH, the catalytic performance of other nitrogen-containing compounds (NCCs) such as quinoline (QUI) and carbazole (CBZ), and selectivity to IND. The PTA-3%/GO-15%/UiO-66(Zr) catalyst demonstrated optimal SODN performance for a model fuel. The effect is ascribed to the material's substantial BET of 721.75 m²/g, combined with a significant V p of 0.3481 cm³/g, a rapid k of 0.075 min⁻¹, and low E a of 19.93 kJ/mol. This high efficacy is driven by the ultrasonic, GO, Zr 4 ⁺, and an oxidant, which facilitates the generation of reactive radicals. Optimal conditions for IND removal were achieved using the PTA-3%/GO-15%/UiO-66(Zr) composite, yielding a high IND removal of 100% at a 1.5 g/L catalyst amount, MeOH volume to fuel volume ratio of 0.5, oxidant to nitrogen molar ratio of 4, an initial concentration of 500 ppm, solution pH of 8, and a temperature of 55°C at 20 min. The reusability of the composite was successfully demonstrated through regeneration with ethanol, maintaining over 92.4% efficiency in IND removal after five regeneration cycles. The effectiveness of a catalyst with H 2 O 2 relies on its ability to generate reactive oxygen species. A new catalytic cycle for Zr-based MOFs proposes that unsaturated zirconium sites activate H 2 O 2 , leading to the formation of a peroxometallic complex. This complex decomposes under heat to produce hydroxyl and superoxide radicals, which are the potent agents responsible for oxidizing the target compounds. A parallel pathway involving PTA nanoparticles also generates these same radicals. Overall, the studies confirm that the synthesized PTA-3%/GO-15%/UiO-66(Zr) composite exhibits significant potential for the efficient elimination of NCCs from fuel.