Rapid and selective uranium extraction from aqueous solution under visible light in the absence of solid photocatalyst

Extraction of uranium from radioactive waste-water is of significant importance for environmental protection and the recovery of uranium resource. Different from the previous reports to use the solid absorbent/photocatalyst for U(VI) removal, herein, we proposed a new eco-friendly method for the rapid and selective extraction of uranium from aqueous solutions under visible light without solid materials. At optimal pH value and in the presence of organics like alcohols, the U(VI) could be extracted efficiently to form brown uranium solid over wide uranium concentrations under anaerobic condition and visible light, by utilizing the excitation of the given U(VI) species. With comprehensive modelling of the electronic ultraviolet-visible (UV-Vis) properties, it is proved that pH adjusting towards U(VI) could induce efficient ligand-to-metal-charge-transfer (LMCT) within the uranyl complex under visible light and the reduction of U(VI) to form U(V), which can be transformed into U(IV) via disproportionation reaction. The resulting U(IV) in solid phase makes the extraction much more convenient in operation. More importantly, the excellent selectivity for uranium extraction over interfering alkali metal ions, transition metal ions and the lanthanide metal ions shows a powerful application potential.