Pore-Functionalized and Hydrolytically Robust Cd(II)-Metal-Organic Framework for Highly Selective, Multicyclic CO2 Adsorption and Fast-Responsive Luminescent Monitoring of Fe(III) and Cr(VI) Ions with Notable Sensitivity and Reusability.

Abstract

Metal-organic frameworks (MOFs) show a distinctive pre-eminence over other heterogeneous systems for adsorption of carbon dioxide (CO2) gas and fluorescence detection of water contaminating ions, where integration of both these attributes along with enhancement of pore functionality and water stability is crucial for potential applications related to environmental remediation. Pore functionalization has been achieved in a 2-fold interpenetrated, mixed-ligand Cd(II)-framework [Cd1.5(L)2(bpy)(NO3)]·2DMF·2H2O (CSMCRI-5) (HL = 4-(4-carboxyphenyl)-1,2,4-triazole, bpy = 4,4'-bipyridine, DMF = dimethylformamide, CSMCRI = Central Salt & Marine Chemicals Research Institute) by utilizing a bifunctional ligand HL. The bpy-pillared framework, containing diverse Cd(II) nodes, optimum sized voids, and free N-atom affixed one-dimensional porous channels, shows notable structural robustness in diverse organic solvents and water. In spite of a negligible surface area, the activated MOF (5a) exhibits good CO2 uptake and highly selective CO2 adsorption over N2 (259.94) and CH4 (14.34) alongside minor loss during multiple CO2 adsorption-desorption cycles. Luminescence studies demonstrate extremely selective and ultrafast sensing of Fe3+ ions in the aqueous phase with notable quenching (1.13 × 104 M-1) as well as an impressive 98 ppb limit of detection (LOD). Importantly, Fe3+ detection is exclusively retained under simulated physiological conditions. The framework further serves as a quick-responsive scaffold for toxic CrO42- and Cr2O72- anions, where individual quenching constants (CrO42-: 1.73 × 104 M-1; Cr2O72-: 5.42 × 104 M-1) and LOD values (CrO42-: 280 ppb; Cr2O72-: 320 ppb) rank among the best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress vivid monitoring of all these aqueous pollutants by a handy paper-strip method, besides outstanding applicability of 5a toward their recyclable detection. Mechanism of selective quenching is comprehensively investigated in light of the absorption of the excitation/emission energy of the host framework by an individual studied analyte.