Water-Robust Zinc–Organic Framework with Mixed Nodes and Its Handy Mixed-Matrix Membrane for Highly Effective Luminescent Detection of Fe3+, CrO42–, and Cr2O72– 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⁺, CrO₄^2–, and Cr₂O₇^2– 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 CrO₄^2– and Cr₂O₇^2– are 3.87 and 2.37 μM, respectively, compared to the reported works. Meanwhile, compound 1 can be reused to detect Fe³⁺, CrO₄^2–, and Cr₂O₇^2– 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⁺, CrO₄^2–, and Cr₂O₇^2– 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⁺, CrO₄^2–, and Cr₂O₇^2– in aqueous solution.