Water-Robust Zinc–Organic Framework with Mixed Nodes and Its Handy Mixed-Matrix Membrane for Highly Effective Luminescent Detection of Fe³⁺, CrO₄^2–, and Cr₂O₇^2– in Aqueous Solution

Abstract

Metal–organic frameworks (MOFs) and MOF-based composites as luminescent sensors with excellent economic practicability and handy operability have attracted much attention. Herein, we designed and fabricated a porous Zn-based MOF, [Zn(OBA)2(L1)·2DMA]n [1; H2OBA = 4,4′-oxybis(benzoic acid), L1 = 2,4,6-tris(4-pyridyl)pyridine, and DMA = N,N-dimethylacetamide], with mixed nodes under solvothermal conditions, and the pore size of 5.9 Å was calculated from N2 adsorption isotherms by using a density functional theory model. The as-synthesized compound 1 is stable in different boiling organic solvents and water solutions with a wide pH range of 2–12 and exhibits intense luminescence emission at 360 nm under excitation of 290 nm. Significantly, compound 1 shows high selective detection of Fe3+, CrO42–, and Cr2O72– in aqueous solution even under the interference of other ions. Compound 1 can quickly sense these ions in a short time and has a striking sensitivity toward Fe3+ with an ultralow limit of detection (LOD) of 1.06 μM. The relatively low LODs for CrO42– and Cr2O72– are 3.87 and 2.37 μM, respectively, compared to the reported works. Meanwhile, compound 1 can be reused to detect Fe3+, CrO42–, and Cr2O72– six times by simple regeneration. Considering the practicability, a mixed-matrix membrane (MMM) incorporated compound 1 and poly(methyl methacrylate) has been constructed. This MMM displays quick detection of Fe3+, CrO42–, and Cr2O72– and prompt regeneration by lifting from the analyte. This useful MMM shows a comparable LOD below 4.35 μM for these ions. This work presents a cost-effective Zn-based MOF as a functional platform for simple but useful sensing of Fe3+, CrO42–, and Cr2O72– in aqueous solution.

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