Photocatalytic and Photochemical Processes on the Surface of Uranyl-modified Oxides: An in Situ XPS Study

•The lability of uranium on the surface of porous supports correlates with the photocatalytic activity under visible light.•A fast and reversible two-electron transition (U6+ ↔ U4+) occurs on TiO2 under visible light and exposure to oxygen.•A slower and only one-electron transition (U6+ ↔ U5+) occurs on the surface of Al2O3 or SiO2 oxides.•The TiO2 supported with uranyl ions has a high stability and oxidizes organic compounds with a high photonic efficiency.