pH-Stable Zn(II) Coordination Polymer as a Multiresponsive Turn-On and Turn-Off Fluorescent Sensor for Aqueous Medium Detection of Al(III) and Cr(VI) Oxo-Anions

Nowadays, coordination polymers (CPs) are promising candidates as sensory materials for their high sensitivity, improved selectivity, fast responsive nature, as well as good recyclability. However, poor chemical stability often makes their practical usage limited. Herein, employing a mixed ligand approach, we constructed a chemically robust CP, {[Zn2L2(DPA)2]·3H2O}n (IITKGP-70, IITKGP stands for the Indian Institute of Technology Kharagpur), which exhibited excellent framework robustness not only in water but also over a broad range of pH solutions (pH = 3–11). The developed framework displayed high selectivity and sensitivity for the detection of trivalent Al3+ ions and toxic hexavalent Cr(VI)-oxo anions in an aqueous medium. The developed framework exhibited an aqueous medium Al3+ turn-on phenomenon with a limit of detection (LOD) value of 1.29 μM, whereas a turn-off effect was observed for toxic oxo-anions (Cr2O72– and CrO42–) having LOD values of 0.27 and 0.71 μM, respectively. Both turn-on and turn-off mechanisms are speculated via spectroscopic methods coupled with several ex situ studies. Such a multiresponsive nature (both turn-on and turn-off) for aqueous medium detection of targeted cations and anions simultaneously in a single platform coupled with high robustness, ease of scalability, recyclability, and fast-responsive nature makes IITKGP-70 highly fascinating as a sensory material for real-world applications

A Water-Stable Twofold Interpenetrating Microporous MOF for Selective CO₂ Adsorption and Separation

Self-assembly of bent dicarboxylate linker 4,4′-sulfonyldibenzoic acid (H₂SDB) and flexible N,N-donor spacer 1,4-bis­(4-pyridyl)-2,3-diaza-1,3-butadiene (<b>L</b>) with Co­(NO₃)₂·6H₂O forms a twofold interpenetrated <b>{[Co</b>_<b>2</b><b>(SDB)</b>_<b>2</b><b>(L)]·(H</b>_<b>2</b><b>O)</b>_<b>4</b><b>·(DMF)}</b>_{<b><i>n</i></b>}, (<b>IITKGP-6</b>) network via solvothermal synthesis with <i><b>sql</b></i><b>(2,6</b><i><b>L</b></i><b>1)</b> topology, which is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, powder X-ray diffraction (XRD), and single-crystal XRD. The framework is microporous with a solvent-accessible volume of 25.5% and forms a one-dimensional channel along [1–1 0] direction with the dimensions of ∼3.4 × 5.0 Ų. As the stability of metal–organic frameworks (MOFs) in the presence of water is a topic of significant importance while considering them for practical applications, this framework reveals its high stability toward water. The desolvated framework shows modest uptake of CO₂ (50.6 and 37.4 cm³ g^–1 at 273 and 295 K under 1 bar pressure, respectively), with high selectivity over N₂ and CH₄. Ideal adsorbed solution theory calculations show that the selectivity values of CO₂/N₂ (15:85) are 51.3 at 273 K and 42.8 at 295 K, whereas CO₂/CH₄ (50:50) selectivity values are 36 at 273 K and 5.1 at 295 K under 100 kPa. The high CO₂ separation selectivity over N₂ and CH₄ along with its water stability makes this MOF a potential candidate for CO₂ separation from flue gas mixture and landfill gas mixture as well

Immobilization of a polar sulfone moiety onto the pore surface of a humid stable MOF for highly efficient CO2 separation under dry and wet environment through direct CO2-sulfone interaction

The stability of microporous metal–organic frameworks (MOFs) in moist environments must be taken into consideration for their practical implementations, which has been largely ignored thus far. Herein, we synthesized a new moisture-stable Zn-MOF, {[Zn2(SDB)2(L)2]·2DMA}n, IITKGP-12, by utilizing a bent organic linker 4,4′-sulfonyldibenzoic acid (H2SDB) containing a polar sulfone group (−SO2) and a N, N-donor spacer (L) with a Brunauer–Emmett–Teller surface area of 216 m2 g–1. This material displays greater CO2 adsorption capacity over N2 and CH4 with high IAST selectivity, which is also validated by breakthrough experiments with longer breakthrough times for CO2. Most importantly, the separation performance is largely unaffected in the presence of moisture of simulated flue gas stream. Temperature-programmed desorption (TPD) analysis shows the ease of the regeneration process, and the performance was verified for multiple cycles. In order to understand the structure–function relationship at the atomistic level, grand canonical Monte Carlo (GCMC) calculation was performed, indicating that the primary binding site for CO2 is between the sulfone moieties in IITKGP-12. CO2 is attracted to the bonded structure (V-shape) of the sulfone moieties in a perpendicular fashion, where CCO2 is aligned with S, and the CO2 axis bisects the SO2 axis. Thus, the strategic approach to immobilize the polar sulfone moiety with a high number of inherent stronger M–N coordination and the absence of coordination unsaturation made this MOF potential toward practical CO2 separation applications