Carbonic anhydrase-embedded ZIF-8 membrane reactor with improved the recycling and stability for efficient CO₂...

Carbonic anhydrase (CA) enzyme-based absorption technology for CO₂ capture has been intensively investigated. However, low solubility of CO₂ and poor stability of CA severely limits its industrial utilization. Here, hydrolyzed polyacrylonitrile (PAN) membrane (HPAN) was first modified by polyethyleneimine (PEI) with a large number of amino groups, which has a strong affinity for CO₂. Then, ZIF-8 was grown in situ on the surface of HPAN/PEI membrane by using the metal chelation of PEI and Zn²⁺. In this process, CA was embedded inside ZIF-8 by co-precipitation (CA@HPAN/PEI/ZIF-8). The resultant CA@HPAN/PEI/ZIF-8 exhibited high catalytic activity for CO₂ capture compared with free CA, which was due to the synergistic enhancement of CO₂ capture by PEI and ZIF-8 with high affinity to CO₂ and enzymatic catalysis. The yield of CaCO₃ by CA@HPAN/PEI/ZIF-8 in the process of one-time conversion of CO₂ was 13.6-fold higher than free CA. Furthermore, the CA@HPAN/PEI/ZIF-8 showed better thermal stability, storage and reusability than free CA. Free CA retained only 18.3 % of its original activity after 18 days of storage, whereas CA@HPAN/PEI/ZIF-8 remained 48.7 % of its original activity. The total CaCO₃ yield by CA@HPAN/PEI/ZIF-8 was 74.9-fold that of free CA after 8 consecutive rounds of CO₂ conversion.