Mixed-linker Strategy Toward Enhanced Photoreduction-Assisted Uranium Recovery from Wastewater and Seawater

Integrating multi-functionality into metal-organic frameworks (MOFs) has attracted growing attention as it plays a critical role in realizing the potential of MOFs for a wide variety of applications. Owing to the ultrahigh surface areas and porosity, MOFs have been recognized as potential adsorbents for uranium capture through chemical chelation of uranyl ions (UO22+). As a new type of photocatalyst, however, these MOFs are rarely applied in uranium recovery by photocatalytic reduction of soluble U(VI) to the less soluble U(IV), which is largely due to the limited visible light harvesting as well as the poor separation and transfer of photo-generated carriers. Herein, we present a facile one pot synthetic route to incorporate photo-responsive Ni(II)-centered porphyrin (TCPP(Ni)) ligands into UIO-66-NH2 (TCPP(Ni) subset of MOF) while maintaining the crystal structure and ultrahigh chemical stability. TCPP(Ni) not only provides strong visible light harvesting but also improves the charge transfer from excited ligands to Zr-oxo clusters. Consequently, the mixed-linker strategy boosts the photoreduction of soluble U(VI) to the less soluble U(IV) for uranium immobilization. After optimization, TCPP(Ni) subset of MOF-3 presents excellent selective uranium capture from wastewater and natural seawater through combined complexation and photoreduction. Strikingly, after immersing in natural seawater for 25 days, a high uranium sorption capacity of 8.95 +/- 0.39 mg-U/g-Ads can be achieved together with good antibacterial ability. This work provides a promising strategy to improve the photoreduction potential of MOF adsorbents for uranium capture.