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.