Developing a Bifunctional Copper-Organic Framework for Fluorescence Turn-on Hg²⁺ Sensing and Catalyzing CO₂ Cycloaddition Reaction

Abstract

Metal–organic frameworks attract great attention because they show great potential for applications such as catalysis and luminescence sensing. Herein, a novel copper–organic framework, [Cu2.5(OH)(nia)2(Bibt)1.5]n, known as CuBN, was hydrothermally prepared based on the self-assembly of 4,7-bis(1H-imidazole-1-yl) benzo-[2,1,3]thiadiazole (Bibt), 5-(1,8-naphthalimido)-isophthalic acid (H2nia), and CuCl2·2H2O. CuBN exhibited a 4, 8-connected sqc 3D porous framework with a binuclear copper oxygen cluster unit and the point symbol of {34 48 512 64}{32 42 52}. CuBN can work as an efficient luminescent sensor for Hg2+ via a turn-on fluorescence change. Fluorescent data shows that CuBN has high selectivity to Hg2+ among various metal ions, and the detection limit is low, down to 9.52 nM. The turn-on sensing behavior can be mainly attributed to the Hg2+-promoted framework collapsing and subsequent binding to the ligand Bibt. In addition, CuBN exhibits the capability of promoting the chemical fixation of CO2 to cyclic carbonates under mild conditions (0.1 mol % catalyst loading, 2 mol % TBAB, 1 atm of CO2, 24 h, 80 °C and without solvent) with up to 97% yield and good reusability.