Boosting charge transfer of COF/g-C3N4 composites for highly synergetic photocatalytic removal of U(VI), Cr(VI) and BPA

The combined pollution of radionuclides, heavy metals and organics during uranium mining (i.e., association/coexist with heavy metals) or reprocessing of spent fuel (i.e., organic extraction) has become a prominent issue nowadays. Herein, the synergetic removal mechanism of U(VI), Cr(VI) and bisphenol(BPA) on porous covalent organic framework/graphitic carbon nitride (COF/g-C 3 N 4 ) was investigated using optical, microscopic and spectroscopic techniques. Compared to g-C 3 N 4 (1%), the high photocatalytic reduction (77%) and the excellent stability (90% after 5 recycles) of U(VI) on COF/g-C 3 N 4 could be attributed to the highly efficient separation of photogenerated carrier and wide response range of COF/g-C 3 N 4 under visible light (low band gap of 1.98 eV). In the ternary system, the increased removal of U(VI) on COF/g-C 3 N 4 was due to the consumption of h + by Cr(VI) and BPA, whereas the further increase of Cr(VI) and BPA inhibited U(VI) removal due to the competition of active sites. The interaction mechanism of U(VI) on COF/g-C 3 N 4 was ascribed to superoxide radicals by trapping and XPS analysis. These findings are crucial for the actual application of COF/g-C 3 N 4 on simultaneous removal of radionuclides, heavy metals and organic in complexed systems. Graphical abstract