Carbonic anhydrase immobilized on Zn(II)-geopolymer membrane for CO2 capture

Inorganic membranes are widely used in water filtration and gas separation due to their many advantages. In this work, we proposed an innovative approach for enzyme immobilization using a geopolymer based tubular inorganic membrane (GM) as a carrier. The GM has abundant mesopores, excellent mechanical strength and strong stability for continuous flow systems in biocatalysis field, and carbonic anhydrase (CA) was successfully loaded into this mesoporous membrane using adsorption-crosslinking method, relying on the excellent ion exchange capacity of geopolymers and large number of hydroxyl groups naturally present in the membrane's mesopores. The results of the immobilization experiments showed that the immobilized enzyme composite membrane (GZnM-CA) could achieve 63.7% enzyme recovery. This is a significant improvement over the enzyme recoveries obtained on organic membranes which are typically less than 50%. In stability tests, the membrane retained more than 90.0% relative activity after 10 consecutive uses. In the CO2 capture assay, the CO2 capture efficiency developed dramatically under the catalytic of GZnM-CA. To our delight, the membrane has excellent separation capability for CO2 gas mixtures, especially at low CO2 concentrations, achieving 99.90% CO2 removal rate, and this result can be maintained for a long period of time in a pH = 8.0 environment.