Pressure-induced amorphization and porosity modification in a metal-organic framework.

The impact of modest, industrially accessible pressures (0-1.2 GPa) on the structure and porosity of the zeolitic imidazolate framework Zn(2-methylimidazole)(2), ZIF-8, was investigated using in situ powder X-ray diffraction in combination with sorption measurements for pressure-treated samples. The framework is highly compressible, with a bulk modulus (K = -V partial differential P/partial differential V) of 6.52(35) GPa, the most compressible metal-organic framework (MOF) documented to date. The framework undergoes an irreversible pressure-induced amorphization following compression beyond 0.34 GPa. The pressure-amorphized ZIF-8 remains porous, although the sorption characteristics are distinctly altered compared to the pristine material. As such, pressure can provide a new route to systematically modify the sorption behavior and other functional properties of MOFs, a nontraditional form of postsynthetic modification. Importantly, pressure modification of MOFs is effective at lower pressures than in other porous materials (e.g., zeolites) and, as such, is easily scalable and industrially relevant.