The photocatalytic reduction of U(VI) into U(IV) by ZIF-8/g-C3N4 composites at visible light.

The development of new photocatalyst towards the highly efficient photo-reduction of U(VI) was highly desirable. In this study, ZIF-8/g-C3N4 photocatalyst was fabricated to photo-reduce U(VI) from aqueous solutions under different water chemistry. It is demonstrated that ZIF-8/g-C3N4 exhibited the fast-photocatalytic rate (completely photoreduction within 30 min), high photocatalytic activity (Kd > 105 mL/g) and superior chemical stability (No significant decrease after fifth cycles). The photoreduction rate of U(VI) significantly decreased with increasing pH, H2O2 radicals and photo-generated electrons play an important role in U(VI) photoreduction by quenching experiments and ESR analysis. According to XPS and XANES analysis, adsorbed U(VI) was partly photo-reduced into U(IV) by ZIF-8/g-C3N4 photocatalyst. The highly efficient removal of U(VI) on ZIF-8/g-C3N4 photocatalyst was attributed to the synergistic effect of ZIF-8 and g-C3N4 photocatalyst. The present study may provide a new strategy to apply new photocatalyst for in-situ photoreduction of U(VI) in actual environmental remediation.