sp2-c linked Cu-based metal-covalent organic framework for chemical and photocatalysis synergistic reduction of uranium

The reduction of hexavalent uranium to tetravalent uranium is an effective strategy for controlling uranium contamination in wastewater. Herein, a –CC-bonded metal-covalent organic framework (Cu-TMT) was synthesized via the Aldol condensation reaction by using the metal cluster Cu3(PyCA)3 and 2,4,6-trimethyl-1,3,5-triazine (TMT) for the chemical and photocatalytic synergistic reduction of uranium. In the Cu-TMT, the low-valent Cu in the metal clusters provides the framework with numerous distributed redox sites being capable of chemically reducing UVI. Meanwhile, the encapsulating Cu clusters in long-range ordered frameworks can provide fast transport channels for intramolecular charge transfer and effectively inhibit electron/hole complexation, making Cu-TMT suitable for photocatalytic reduction of uranium. The chemical reduction of uranium by Cu-TMT was verified under light-avoidance conditions, reaching 659.5 mg g−1. After exposure of Cu-TMT to light, the amount of reduced uranium further increases to 1438.8 mg g−1 with 98.1 % removal rate of actual uranium containing wastewater. This study not only expands the range of applications of variable valence metal covalent organic frameworks, but also provides unique insights into the effective combination of chemical and photocatalytic reduction strategies for removing UVI in a single material.