Ångstrom Scale Pore Engineering in ZIF-62 Glasses by in vacuo Heating-Induced Amorphization

Zeolitic Imidazolate Framework (ZIFs) glasses possess both the intrinsic porosity of Metal–Organic Frameworks (MOFs) and the melt-processability of conventional glasses, thereby representing a new class of porous materials that has already demonstrated established promise across a range of applications. However, unlike the high pore tunability in crystalline MOFs, pore engineering in MOF glasses is challenging due to pore collapse during melting and the overall amorphous structure. Therefore, developing a versatile strategy to tune pores in MOF glasses is of critical importance. This work demonstrates that vacuum-assisted heating allows Ångstrom-scale pore engineering in ZIF-62 glasses. The negative pressure dependence on ZIF-62 glass formation and porosity was systematically investigated by going from ambient pressure to high vacuum (HV, 1×10−10 bar) for heating of ZIF-62. A clear correlation between vacuum strength and final glass pore size is observed. High-Resolution Transmission Electron Microscopy (HRTEM) showed significantly larger porosity in ZIF-62 glasses formed under higher vacuum conditions, further supported by CO2 gas sorption showing an increase in CO2 uptake capacity from 0.29 mmol·g-1 for ZIF-62 to 0.94 mmol·g-1 for agZIF-62HV. Comprehensive characterization (XRD, ED, XPS, IR, Raman, DSC, TGA) confirms the preservation of the chemical environment, and gas sorption reveals changes to the porosity structure. These findings, combined with the unprecedented colorless nature of the resulting glasses, highlight the potential of negative pressure as a parameter to tune the microstructure and porosity in hybrid glasses, which in turn further advances the applicability of these materials in fields where precise structural control is of critical importance, such as catalysis, separation or capture processes, and advanced optics.