Visible Light‐Responsive Sulfone‐Based Covalent Organic Framework as Metal‐Free Nanoenzyme for Visual Colorimetric Determination of Uranium

Abstract

Covalent organic framework (COF) has been attracting considerable attention as a novel crystalline material owing to its extended π‐electron conjugation and excellent spectral behavior. In this study, we present an imine‐linked two‐dimensional (2D) crystalline sulfone‐based covalent organic framework (TAS‐COF) synthesized by 2,4,6‐triformylphloroglucinol (Tp) and 3,7‐ diaminodibenzo[b,d]thiophene (DAS) via a Schiff base condensation reaction. The benzothiophene sulfone endows the as‐synthesized TAS‐COF with excellent oxidase‐like activity under visible light irradiation, ascribed to the generation of superoxide radicals (O2•−) by photo‐generated electron transfer. TAS‐COF can efficiently oxidase the colorless substrate 3,3′,5,5′‐tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) when exposed to visible light, and the presence of uranium (UO22+) leads to clear color fading due to the coordination between the imine of oxTMB and UO22+. A colorimetric strategy is thus developed for UO22+ determination with a detection limit of 0.07 μmol L−1. Moreover, a paper‐based visual sensing platform is also constructed to offer simple and fast UO22+ content evaluation in water samples. The present study not only provides a promising strategy to prepare visible light‐triggered COF‐based metal‐free nanoenzymes but also extends the applications of COF material in radionuclide detection.