Photocatalytic Oxidative Desulfurization of Coal Using Cu-TiO2/Fe3O4 Nanocomposites: Kinetic and Reusability Studies

Abstract

Coal plays a crucial role as a primary energy source in meeting global energy demands. However, the high sulfur content of coal poses environmental and health risks due to release of sulfur dioxide during combustion. Conventional desulfurization methods have limitations in efficiency and reusability. In this study, the utilization of magnetically separable Cu TiO2/Fe3O4 nanocomposite as photocatalysts with various molar ratios of Fe3O4 to TiO2 (0.5:1, 1:1, and 2:1), synthesized via modified sol-gel method for efficient sulfur removal from coal under direct sunlight represents an innovative approach in this field. The as-prepared photocatalyst was characterized using various analytical techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The X-ray diffraction (XRD) analysis of the composite revealed diffraction peaks corresponding to both Fe3O4 and TiO2. Additionally, energy dispersive X-ray spectroscopy (EDX) spectra verified composite's composition by detecting elemental signatures of Fe, Ti, and O. Scanning electron microscopy image of Cu-TiO2/Fe3O4 magnetic nanocomposite revealed spherical, non-uniform, and slightly dispersed agglomerated particles. The UV-Vis DRS spectroscopy showed a broadened absorption spectrum with increased absorption intensity and decreased band gap energies as compared to Cu-TiO2 photocatalyst. The photoluminescence (PL) data showed a decrease in e-/h+ recombination rate for composites compared with Cu-TiO2 photocatalyst. Magnetic nanocomposites were employed as photocatalysts for oxidative desulfurization of sulfur from coal under sunlight irradiation. 3.0% Cu-TiO2/Fe3O4 (1:1) nanocomposite as photocatalyst showed a superior photocatalytic activity with 73.30% sulfur removal efficiency with catalyst dosage of 150mg/500mg of coal, 20 ml of oxidant and 5 h of irradiation time. The recyclability studies demonstrated the high stability of 3.0% Cu-TiO2/Fe3O4 (1:1) nanocomposite after five cycles of repetitive uses. The photocatalytic oxidation desulfurization system proved to be viable for environmental applications, effectively eliminating sulfur from coal.