ZIF8

ZIF-8, or zeolitic imidazolate framework-8, is a zinc-based metal-organic framework (MOF) belonging to the family of zeolitic imidazolate frameworks. It comprises Zn2+ ions tetrahedrally coordinated to four 2-methylimidazolate (mim) linkers, producing a porous crystalline solid with the sodalite (SOD) topology. The framework creates large internal cages about 11.6 Å in diameter, connected by narrow pore apertures of approximately 3.4 Å, yielding a microporous material with a high surface area.

Synthesis and activation typically involve solvothermal or room-temperature methods using zinc salts and 2-methylimidazole in solvents such as water or methanol. Crystallization occurs over a few hours to days, and activation requires solvent exchange followed by vacuum heating to remove guest molecules, yielding materials with high surface areas often in the 1200–1700 m2/g range.

Properties of ZIF-8 include notable thermal and chemical stability relative to many other MOFs, with reports of stability up to around 500 °C under certain conditions. It shows resistance to many organic solvents and air exposure, though prolonged contact with strong acids or bases and certain aqueous environments can cause degradation. The framework’s hydrophobic pore surfaces, due to the methyl groups on the imidazolate linkers, influence adsorption behavior and contribute to size-selective separations through the relatively small pore window of about 3.4 Å.

Applications encompass gas storage and separations (including hydrogen, carbon dioxide, and hydrocarbons), catalysis and catalytic support, and use as a host for encapsulating functional species or drugs in composite materials. ZIF-8 has become one of the most studied ZIFs because of its accessible synthesis, robust porosity, and versatile utility across adsorption, separation, and materials science.