In-situ Cyanide Functionalization of ZIF-8 by γ-Irradiation for Photochemical removal of Uranium

Abstract

Photoreduction conversion of soluble U(VI) to insoluble U(IV) is regarded as an ideal strategy for removing uranium from water. The Cyanide-based photocatalysts shows promises for efficient uranium removal but their green synthesis remain significant challenges. Herein, we develop a γ-irradiation-induced strategy for in-situ -CN generation via imidazole ring opening in ZIF-8 MOFs for uranium photoreduction, circumventing the use of toxic cyanide sources. In-situ transmission electron microscopy (TEM) and in-situ X-rays coupled diffraction infrared Fourier transform (DRIFT) reveal morphological evolution via imidazole ring cleavage and -CN formation kinetics during irradiation. Research indicated that -CN-functionalized ZIF-8 displayed superior uranium photoreduction activity through -CN-UO22+ complexation and promotion of photo-induced electron transfer. Impressively, the uranium extraction capacity reached a value of 1532.4 mg/g, higher than most existing MOF-type photocatalysts. In-situ DRIFT spectroscopy revealed the intermediates of the photoreduction uranium reaction and their adsorption mode with the catalyst, providing a comprehensive mechanistic explanation. This work provides a sustainable pathway for uranium photoreduction and guidance for the green design of MOF-type photocatalysts.