Pore Wall-Functionalized Luminescent Cd(II) Framework for Selective CO2 Adsorption, Highly Specific 2,4,6-Trinitrophenol Detection, and Colorimetric Sensing of Cu2+ Ions

Astute combination of basic functionality and luminescence property can pursue multifunctional metal–organic frameworks (MOFs) with assorted applications such as selective CO2 adsorption, specific detection of explosive nitro compounds, and toxic metal ion sensing. The bifunctional ligand 4-(4-carboxyphenyl)-1,2,4-triazole (HL) is used to build the framework [Cd­(L)2]·(DMF)0.92 (1) (L = L–1, DMF = N,N′-dimethylformamide), having a free N atom decorated porous channel. The solvothermal synthesis is extended to produce three isoskeletal frameworks in diverse solvents, where pore size maximizes in 2 by employing N,N′-diethylformamide solvent. The activated framework [Cd­(L)2] exhibits strong CO2 affinity with good CO2/N2 selectivity, and shows minimum CO2 loss during five adsorption–desorption cycles. Sensing studies for nitro-aromatic compounds in DMF reveal highly specific detection of 2,4,6-trinitophenol (TNP) with remarkable quenching (KSV = 9.3 × 104 M–1) and low limit of detection (LOD: 0.3 ppm). The quenching mechanism is ascribed to the combined existence of static and dynamic quenching plus resonance energy transfer. The activated framework further shows highly selective luminescent detection of Cu2+ ions with a quenching constant of 4.4 × 103 M–1 and very low LOD of 3.9 ppm. The detection of Cu2+ ions accompanies a visible color change in solution and solid phase, which validates the present system as a potential colorimetric Cu2+ sensor. Of note is that bifunctional sensor shows excellent reusability toward TNP and Cu2+ detection. Overall, selective and multicycle CO2 adsorption, together with efficient sensing of both TNP and Cu2+ ion, manifest this pore-functionalized MOF as a versatile material for sustainability.