Water-Stable Two-Dimensional Metal–Organic Framework Nanostructures for Fe3+ Ions Detection

A novel two-dimensional (2D) metal–organic framework (MOF), {[Cd­(hsb-2)­(2-obdc)]·2H2O}n (HSB-W7), has been assembled from Cd­(II) and the mixed ligands of hydrogenated Schiff base hsb-2 (1,2-bis­(4′-pyridylmethylamino)-ethane) and dicarboxylate 2-obdc (2-hydroxybenzene-1,4-dicarboxylate) via the diffusion method under mild conditions. By changing the synthetic approach with the IISEM (instant in situ exfoliation method), nanoscale MOFs (nanoMOFs) HSB-W7-Ns, HSB-W7-Ns1 and HSB-W7-NR, have also been rapidly and massively fabricated from the MOF precursors in one-pot and one-step manner under aqueous solution. These as-synthesized nanoMOFs had the same 2D crystal structure; however, they displayed diverse nanostructures from 2D rectangular nanosheets with different sizes to 1D nanorods stacked in spheres. Such morphology variations were tuned just by adjusting the initial concentration of the precursors during their nanoMOFs synthesis. Because of the exceptional water stability and strong blue fluorescence, nanoMOFs HSB-W7-Ns, HSB-W7-Ns1 and HSB-W7-NR can serve as fluorescent sensors to selectively and sensitively detect the presence of Fe3+ ions in water. All the nanoMOFs showed much higher detection performance for Fe3+ ions than that of their bulk MOF crystals, of which the HSB-W7-Ns MOF nanosheets with elongated rectangle morphology was the best. This work provides a new strategy for the morphology engineering of MOF nanostructures, which also offers an opportunity to improve the performance of MOFs.