Efficient reduction of uranyl under aerobic conditions by sodium and potassium co-doped carbon nitride

It is still a challenge for photocatalytic reduction of uranyl and maintaining catalyst stability under aerobic conditions. Herein, a catalyst of sodium–potassium co-doped g-C3N4 (CD-NaK) was obtained to remove Hexavalent Uranium (U(VI)) by photocatalytic reduction under aerobic conditions. And the CD-NaK was characterized by XRD, XPS and other methods. Furthermore, DFT calculations and XRD revealed that Na was doped in-plane while K was doped in-plane and interlayer, enhancing holes and electrons separation performance. Moreover, the removal rate of U(VI) could be achieved nearly 100% after 20 mins of visible irradiation in the presence of air over CD-NaK(30). The photocatalytic activity has the order: CD-NaK(30) > SD-Na > SD-K > CN. Additionally, when the atmosphere of the reaction system was air, the photocatalytic activity of CD-NaK(30) to uranyl was 4.6 times higher than that of pure nitrogen atmosphere in the present of benzyl alcohol, and CD-NaK(30) displayed good reusability and stability with the removal rate > 96% even after five cycles. Interestingly, the effect of the amount of oxygen on catalytic reduction and the role of oxygen were elucidated. Finally, a novel uranyl reduction mechanism has been supposed.