Immobilization of uranyl ions in water by covalent organic frameworks: In-situ utilization of the photocatalytic produced H2O2

Abstract

The photocatalytic extraction of uranyl (UO22+) ions from aqueous solutions using covalent organic frameworks (COFs) represents a promising approach for mitigating environmental concerns and recovering uranium resources. In this study, benzotrithiophene (BTT)-based COFs with electron donor–acceptor structures were synthesized to harness photocatalytic capabilities. Under visible light, the synergistic effect of COF-BTT-TAPB and methanol achieved UO22+ removal efficiencies of 99 % and 92 % (at an initial U concentration of 50 ppm) with and without N2 pretreatment. Notably, even in the absence of a sacrificial agent, COF-BTT-TAPB can remove 36 % of UO22+ from water. The photocatalytic mechanism for UO22+ immobilization on COF-BTT-TAPB does not involve the conventional reduction of U(VI). Instead, the formation of the solid-state (UO2)O2(H2O)2 results from an in-situ reaction between UO22+ and H2O2, the latter produced through visible light-induced catalysis on the COF-BTT-TAPB surface. Additionally, UO22+ can be photoexcited under visible light, undergoing a homogeneous reaction with methanol in the presence of O2 to produce (UO2)O2(H2O)2. This study presents a novel approach for extracting UO22+ from aqueous solutions by leveraging photocatalytically generated H2O2.