High-efficiency selective removal of U(VI) by phosphate-functionalized graphitic carbon nitride activated using guanidine phosphate

Given the efficient reaction of P-containing species with radionuclide U(VI), phosphate-modified carbon nitrides (GPCNs) were prepared with enhanced surface areas (16.9-102.0 m(2)/g) and abundant phosphate groups (15.8-9.1 at% of P) and applied to capture aquatic U(VI). GPCNs presented a fast equilibrium of 8 h, efficient capture capability (maximum 333.5 mg/g at pH 5.0 and T 278 K), excellent selectivity and favorable reusability. The enrichment of U(VI) from the artificial nuclide wastewater (101.5 mg/g) and seawater (89.3 mg/g) were evaluated. Spectroscopic studies proved that the formation of hydrogen uranite was dominant for the high-efficiency selective sorption of U(VI). Under the illumination of visible-light, GPCNs showed a similar to 4.9-fold faster kinetics for the photocatalytic reduction of U(VI) than CNs. Moreover, the origin of the photocatalytic activity of GPCNs including the role of phosphate modification was also discussed in detail. This study provided a valuable reference for the facile preparation of porous phosphate-modified carbon nitrides as well as a meaningful option for the extraction of radionuclides from aqueous solutions.