Multifunctional Cd(II) Metal–Organic Framework with Abundant Lewis Acidic and Basic Sites: Selective Gas Adsorption and Separation, CO₂ Catalytic Fixation, and Fluorescence Recognition of Uric Acid

The development of new porous materials for the selective adsorption and fixation of CO₂, as well as the selective capture of C₂H₂, is essential for environmental protection and energy security. Herein, a versatile coordination polymer, {[Cd(btbpa)(H₂O)]·3H₂O·4NMP·DMA}_<i>n</i> (<b>Cd-btbpa</b>, H₂btbpa = 4,4'-bis(1<i>H</i>-1,2,4-triazole-1-yl)-[1,1'-biphenyl]-3,3'-dicarboxylic acid), has been prepared, which not only exhibits good chemical and thermal stability but also possesses adaptive nanochannels. Gas uptake studies disclosed the selective adsorption properties of MOF <b>Cd-btbpa</b> for CO₂ and C₂H₂ over other gases (N₂, CH₄, C₂H₄, and C₂H₆), contributing to a record-high IAST selectivity of ca. 3905 (50/50 of CO₂/CH₄, v/v). The adsorption selectivity values for C₂H₂/C₂H₄ and CO₂/N₂ at 298 K are 2.14 and 41.79, respectively. Breakthrough experiments were carried out to confirm its practical application value for CO₂/CH₄, CO₂/N₂, and C₂H₂/C₂H₄ separation. In addition, it can drive heterogeneous cycloaddition of CO₂ with various epoxides under mild conditions (75 °C, 1 atm) and boost the yield of produced cyclic carbonates almost to 100% for the epoxides such as 1,2-epoxybutane and epichlorohydrin. Besides, <b>Cd-btbpa</b> shows excellent recognition ability for uric acid (UA) with high <i>K</i>_SV (3.9378 × 10⁴ M^-1) and sensitivity (LOD: 0.14 μM).