Robust interaction of ZnO and TiO 2 nanoparticles with layered graphitic carbon nitride for enhanced photocatalytic oxidative desulfurization of fuel oil: mechanism, performance and stability.

Sulfur compounds in fuel such as thiophene, benzothiophene and dibenzothiophene are the primary source of SO x emissions, leading to environmental pollution and acid rain. In this study, we synthesized a layered oxygen-doped graphitic carbon nitride (OCN) structure and integrated ZnO and TiO 2 nanoparticles onto the OCN surface through a microwave-assisted sol-gel method. The X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) results confirmed a robust interaction between the ZnO and TiO 2 nanoparticles and the oxygen-doped g-C 3 N 4 (OCN) surface, as indicated by the formation of C-N-Ti and C-O-Ti bonds. This interaction notably improved the optoelectronic properties of the ZnO-TiO 2 /OCN composite, yielding increased visible light absorption, reduced charge recombination rate, and enhanced separation and transfer of photogenerated electron-hole pairs. The oxygen doping into the CN network could alter the band structure and expand the absorption range of visible light. The ZnO-TiO 2 /OCN photocatalyst demonstrated remarkable desulfurization capabilities, converting 99.19% of dibenzothiophene (DBT) to dibenzothiophene sulfone (DBT-O 2 ) at 25 °C, and eliminating 92.13% of DBT from real-world fuel oil samples. We conducted in-depth analysis of the factors impacting the redox process of DBT, including the ZnO ratio, initial DBT concentration, catalyst dosage, stability, and O/S molar ratio. Radical trapping experiments established that ˙O 2 - , ˙OH and h + radicals significantly influence the reaction rate. The obtained results indicated that the ZnO-TiO 2 /OCN photocatalyst represents a promising tool for future fuel oil desulfurization applications.