Visible-light-driven oxidative denitrogenation of liquid hydrocarbon fuels over hydrochar-modified TiO2 engineered nanoparticles: The dominant contribution of singlet oxygen

Abstract

Developing engineered photocatalysts for low-temperature oxidation denitrogenation of fuels has sustained appeal in the clean production of oils. In this study, TiO₂ nanoparticle photocatalysts surface-hybridized by hydrochar (HC-TENPs) were prepared through a simple in-situ carbonization. A few nanometers thick hydrochar layer was uniformly coated on the surface of TiO₂ nanoparticles, with Ti-O-C bonding linkage and abundant oxygen vacancy defects at the interface. HC-TENPs/H₂O₂/visible light system can efficiently degrade various nitrogen heterocyclic compounds (pyridine, quinoline, benzoquinoline, pyrrole, indole, and carbazole) at ambient temperatures and pressures. The hydrochar hybridization narrowed the bandgap of photocatalysts, broadened the range of light absorption, and enhanced the separation of photogenerated charge carriers and photoelectric response. Hydroxyl radicals, superoxide radicals, and singlet oxygen are recognized as reactive oxygen species, in which singlet oxygen contributed over 60% to quinoline degradation. The oxygen vacancy defects served as the centers to trap superoxide radicals where they were oxidized to singlet oxygen by holes. The industrial feedstocks and simple production process allow HC-TENP photocatalysts to have great engineering manufacturing prospects. These are expected to meet the practical application in photocatalytic oxidation denitrogenation for fuel oils.