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. Cyanide-based photocatalysts show promise for efficient uranium removal, but their green synthesis remains a significant challenge. Herein, we develop a γ-irradiation-induction 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-ray coupled diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy reveal morphological evolution via imidazole ring cleavage and –CN formation kinetics during irradiation. Research indicates that –CN-functionalized ZIF-8 exhibits 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⁻¹, higher than that for most existing MOF-type photocatalysts. In situ DRIFT spectroscopy revealed the intermediates of the uranium photoreduction 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.