Hydrolytically Stable Zr-Based Metal–Organic Framework as a Highly Sensitive and Selective Luminescent Sensor of Radionuclides

Abstract

Effective detections of radionuclides including uranium and its predominant fission products, for example, iodine, are highly desired owing to their radiotoxicity and potential threat to human health. However, traditional analytical techniques of radionuclides are instrument-demanding, and chemosensors targeted for sensitization of radionuclides remain limited. In this regard, we report a sensitive and selective sensor of UO 2 2+ and I − based on the unique quenching behavior of a luminescent Zr-based metal−organic framework, Zr 6 O 4 (OH) 4 (OH) 6 (H 2 O) 6 (TCPE) 1.5 • (H 2 O) 24 (C 3 H 7 NO) 9 (Zr-TCPE). Immobilization of the luminescent tetrakis(4-carboxyphenyl)ethylene (TCPE 4− ) linkers by Zr 6 nodes enhances the photoluminescence quantum yield of Zr-TCPE, which facilitates the effective sensing of radionuclides in a "turn-off" manner. Moreover, Zr-TCPE can sensitively and selectively recognize UO 2 2+ and I − ions with the lowest limits of detection of 0.67 and 0.87 μg/kg, respectively, of which the former one is much lower than the permissible value (30 μg/L) defined by the U.S. EPA. In addition, Zr-TCPE features excellent hydrolytic stability and can withstand pH conditions ranging from 3 to 11. To facilitate real-world applications, we have further fabricated polyvinylidene fluoride-integrating Zr-TCPE as luminescence-based sensor membranes for on-site sensing of UO 2 2+ and I − .

Enhancing Dynamic Spectral Diffusion in Metal-Organic Frameworks Through Defect Engineering

“…These patterns also diverge from that of the TCPE-based MOF reported with she topology (SI Figure S48); the divergent topologies for Zr-TCPE frameworks are likely due to the different Zr precursors used herein (ZrCl4) and in previous work (ZrOCl2). 45 Nonetheless, the comparable SEM images of Zr-TCPE-FA( 50) and Zr-TCPE-FA(200), representative samples of Form 1 and Form 2, respectively, confirm that the two phases are likely topologically similar (SI Figure S26). For Form 1, a gradual broadening of the reflections due to a decrease in crystallinity was observed above 50 equiv., which is not expected given the increase in crystallinity that is generally observed when higher equivalents of acid modulators are employed.…”

“…50 The combination of Zr6 nodes and 4-connected linkers (TCPE 4− ) can potentially crystallize in csq (akin to PCN-128), 51 scu (akin to NU-901), 52 ftw (akin to PCN-94), 53 or she topologies. 45 For csq and scu topologies, there are two possible orientations of the TCPE 4− linkers relative to the largest pore aperture, with the alkenes either parallel or perpendicular to the pore direction (SI Figures S45-S46). The simulated patterns corresponding to structures with scu topologies matched most closely to the experimental PXRD patterns of Zr-TCPE-FA (50) and Zr-TCPE-FA(200) and were chosen for further examination (SI Figures S47).…”

“…Notably, Pawley refinement using the unit cell parameters corresponding to the reported Zr-TCPE MOF with she topology led to poor fits to the experimental data for both Forms, confirming that they are topologically distinct (SI Figures S14-15). 45 Indexing and Rietveld refinement of the experimental patterns were carried out to obtain potential structural models for both forms of Zr-TCPE. For the more crystalline Form 2, further optimization of the initial scu structure and the addition of two bidentate formate molecules per cluster produced an orthorhombic structure (Zr6 (3-O)4(3-OH)4(HCO2)2(TCPE)2(OH)2(H2O)2) in the Cmmm space group with a = 30.34 (17) Å, b = 17.50(7) Å, and c = 12.00(3) Å (Figure 2c, d; SI Section 3).…”

“…This linker has been previously employed to prepare frameworks from Zn, 16,24 Cd, 16 La, Nd, 23 and UO2, 21,22 but its incorporation into a Zr-based MOF (with she topology) was only reported during the preparation of this manuscript. 45 A series of Zr-TCPE MOFs were initially synthesized at 120 °C for 48 h using ZrCl4 as a metal precursor, formic acid (FA) as a modulator, H2O to facilitate Zr6 cluster formation, and N,N-dimethylformamide (DMF) as a solvent (Figure 1a, SI Section 2c). Varying equivalents (0-200 equiv.)…”

“…Importantly, the crystallinity and PL intensity of Zr-TCPE-FA(50) and Zr-TCPE-FA(200) were also retained after suspension in water for 48 h, indicating that these materials are promising for applications under aqueous conditions (Figure S28). 45,[56][57][58] In order to elucidate the origins of the unexpected shift in emission color as a function of phase and modulator equivalents, steady-state PL spectra of all samples were first collected (Figure 4d-f). The maximum PL emission wavelength of all samples was similar to that of H4TCPE (524 nm), supporting that linker-based emission dominates in these materials.…”