Shape controlled ZIF-8 crystals for carbonic anhydrase immobilization to boost CO2 uptake into aqueous MDEA solution

Metal-organic frameworks (MOFs) have been extensively studied as candidate materials for enzyme immobilization over recent years. In this work, carbonic anhydrase was immobilized in ZIFs by “in situ” immobilization method. The growth state of ZIF-8 was adjusted by adjusting the ratio of Zn2+and 2-Hmim to obtain crystals with different morphologies (cubic-, dodecahedral- and leaf-shape). In addition, different surfactants (cationic surface-active agent, an-ionic surfactant, and non-ionic surface-active agent) were added as “shape-inducing agents” to further regulate the crystal shapes, thus affecting the activity of enzyme immobilization in ZIFs. Through CO2 absorption test, it was found that the thick leaf-shaped CA/ZIF-L-(PVP) induced by PVP had a higher relative activity (150%) than other shapes (cubic, dodecahedral, “burr puzzle” shape, “interpenetration leaves” shape, etc.) of immobilized enzymes. In addition, CA/ZIF-L-(PVP) exhibited excellent reusability and stability, which maintained a relative activity of 131% after 5 cycles, and remained approximately 99% relative activity after 15 days at 40 °C in MDEA solution.