Breathing Transition and Effective Iodine Adsorption in a Temperature-Responsive Zn-Based Flexible Metal–Organic Framework

A porous and flexible Zn-MOF was synthesized under solvothermal conditions by using the ligand 2,5-furandicarboxylic acid (2,5-FDA). This flexible Zn-MOF demonstrates a temperature-triggered breathing effect. At low temperature (100 K), we obtained the high-symmetry MOF denoted as SM-A with a unit cell volume of 1958 ų, characterized by triangular narrow pore (np) channels. Upon increasing the temperature from 100 K to 298 K, the lower symmetry referred to as SM-B was obtained, featuring rhombic large pore (lp) channels, along with an expanded unit cell volume of 7823 ų. This temperature-induced phase transition involves distortion of the channels and a change in the dimensionality of the framework from 3D (SM-A) to 2D (SM-B). The flexible behavior and phase transition were thoroughly justified with the help of single-crystal X-ray diffraction and differential scanning calorimetry. Additionally, BET analysis revealed a surface area of 85.504 m²/g, with mesopores of 3.05 nm. Leveraging the large-pore channels, SM-B at room temperature was employed as an adsorbent for the removal of hazardous iodine in both the vapor and the solution phases. The discovery of such dynamic MOFs holds potential and may pave the way for novel strategies in advanced applications.