Zr(IV)-Based Metal-Organic Framework with T-Shaped Ligand: Unique Structure, High Stability, Selective Detection, and Rapid Adsorption of Cr₂O₇^2– in Water

Abstract

Dichromate is known for severe health impairments to organisms. New and valid strategies have been developed to rapidly detect and efficiently remove this pollutant. Constructing stable luminescent metal-organic frameworks (MOFs) for dichromate recognition and removal from aqueous solution could provide a feasible resolution to this problem. Herein, a new luminescent Zr(IV)-MOF, Zr₆O₄(OH)₇(H₂O)₃(BTBA)₃ (BUT-39, BUT = Beijing University of Technology) was constructed through the reaction of a newly designed functionalized T-shaped ligand 4,4',4″-(1 H-benzo[ d]imidazole-2,4,7-triyl)tribenzoic acid (H₃BTBA) with zirconium salt. BUT-39 has a unique porous framework structure, in which Zr₆ cluster acts as a rare low-symmetric 9-connected node and BTBA^3- as a T-shaped 3-connected linker. As far as we know, this represents the first case of a (3,9)-connected Zr(IV)-MOF. BUT-39 could retain its framework integrity in boiling water, 2 M HCl aqueous solution, and pH 12 NaOH aqueous solution. Due to its good water stability and strong fluorescent emission, BUT-39 is then employed in fluorescence sensing for various ions in aqueous solution and shows good performance toward Cr₂O₇^2- selectively, at a low concentration and a short response time (<1 min). Simultaneously, it also exhibits excellent capacity to rapidly capture Cr₂O₇^2- (within 1 min) with a high uptake up to 1 mmol g^-1. Taking advantage of its excellent stability, sensitive and selective sensing, as well as rapid and high adsorption, BUT-39 is expected to be useful in Cr₂O₇^2- detection in and removal from water.