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 Å3, 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
Å3. 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.