Powerful uranium extraction strategy with combined ligand complexation and photocatalytic reduction by postsynthetically modified photoactive metal-organic frameworks

Uranium enrichment is perhaps the most critical chemical process throughout the nuclear fuel cycle including uranium mining, uranium extraction from seawater, used fuel reprocessing and disposal, and environmental contamination remediation. New uranium extraction technology is still highly desirable at current stage, although a variety of extraction methods have been established and developed in the past several decades but all with clear demerits. Herein we present a new uranium extraction strategy with combined ligand complexation and photocatalytic reduction based on postsynthetically functionalized metal-organic frameworks (MOFs). The highly robust and photoactive MOF PCN-222 is modified with phosphono- and amino groups that can capture U(VI) from solution. Upon visible light irradiation, the photo-induced electrons from the MOF host can efficiently reduce U(VI) pre-enriched in MOF, affording neutral uranium species that evacuate the MOF structure and regenerating the active site readily for capturing additional U(VI). This auto-recycled process offers an ultrahigh uranium extraction capacity not limited by the number of adsorption sites and more importantly an extra uranium uptake selectivity over these non-redox-active competing metal cations, and can be utilized for uranium separation over extremely wide uranium concentrations and pH ranges, showing a powerful application potential.