Light-driven methane conversion: unveiling methanol using a TiO2/TiOF2 photocatalyst

Abstract

A TiO₂/TiOF₂ composite has been synthesized through a hydrothermal method and characterized using X-ray diffraction, Raman spectroscopy, UV-vis diffuse reflectance, SEM-EDX, TEM, and N₂ adsorption–desorption isotherms. The percentage of exposed facet [001] and the composition of TiO₂/TiOF₂ in the composite were controlled by adjusting the amount of HF and hydrothermal temperature synthesis. Three crucial factors in the photocatalytic conversion of methane to methanol, including the photocatalyst, electron scavenger (FeCl₂), and H₂O₂ were evaluated using a statistical approach. All factors were found to have a significant impact on the photocatalytic reaction and exhibited a synergistic effect that enhanced methanol production. The highest methanol yield achieved was 0.7257 μmole h⁻¹ g_cat⁻¹. The presence of exposed [001] and fluorine (F) in the catalyst is believed to enhance the adsorption of reactant molecules and provide a more oxidative site. The Fenton cycle reaction between FeCl₂ and H₂O₂ was attributed to reducing recombination and extending the charge carrier lifetime. Incorporating Ag into the TiO₂/TiOF₂ catalyst results in a significant 2.2-fold enhancement in methanol yield. Additionally, the crucial involvement of hydroxyl radicals in the comprehensive reaction mechanism highlights their importance in influencing the process of photocatalytic methane-to-methanol conversion.