Immobilization of carbonic anhydrase on poly(ionic liquid) composite membranes for CO2 absorption by gas-liquid membrane contactors

In our current climate crisis, an impressive global effort is being deployed to develop and implement technologies to mitigate CO2 emissions. For instance, CO2 capture and storage/utilization (CCUS) will be fundamental during the energy transition. In the context of CCUS, the enzyme carbonic anhydrase (CA) has gained growing attention because it acts as a green catalyst in CO2 capture by absorption. A few works investigated the preparation of membranes with immobilized CA for CO2 capture by gas-liquid membrane contactors. Although these biocatalytic membranes exhibited improvements in the CO2 capture rate, limited immobilization strategies and carriers have been investigated so far. This work describes the fabrication, characterization, and testing of novel composite membranes with immobilized CA for CO2 capture. The membranes were comprised of a hydrophilic poly(ionic liquid) (PIL) top layer coated on a porous poly(vinylidene fluoride) (PVDF) support. The layer was prepared by in-situ polymerization of an ionic liquid monomer solution cast on the PVDF. CA was easily immobilized on the PIL layer by physical adsorption. The immobilized enzyme's catalytic activity was evaluated to identify the optimum formulation of the PIL layer (monomer and cross-linker concentrations) and immobilization protocol (enzyme concentration in the buffer solution and pH). Despite the immobilization protocol's simplicity, the enzyme was strongly bonded as the enzyme-loaded membranes could be reutilized 10 times while retaining above 90% of their initial activity. These membranes were further characterized by SEM, EDX, ATR-FTIR, TGA, DSC, zeta potential, and water contact angle. Moreover, the biocatalytic composite membranes were tested in a gas absorption set-up to demonstrate their applicability. They showed an increase in the overall mass transfer coefficient with respect to the pristine support by a factor of 2.5, making them interesting candidates for promoting CO2 capture.