Catalytic Promotion of CO ₂ Hydration by Mimetic Carbonic Anhydrase/2-Methylimidazole Zinc Salt and Its Effects on the Carbonation and Microstructure of Cement Paste

Cement-based materials offer substantial potential for mineral carbonation, but the slow CO₂ hydration reaction limits sequestration efficiency. In this work, mimetic carbonic anhydrase (mCA), 2-methylimidazole zinc salt (ZIF-8), and a hybrid catalyst (ZIF-8@mCA) were synthesized and evaluated as CO₂ hydration promoters in cement paste. FTIR, XRD, and TG-DSC confirmed that mCA was successfully incorporated into ZIF-8 without altering the framework structure. All three catalysts accelerated CO₂ hydration and enhanced CaCO₃ precipitation. When incorporated at 0.1 wt. % into cement paste subjected to CO₂ mixing and CO₂ pressurized curing, the catalysts modified the hydration and carbonation behavior. Microstructural analyses indicated reduced porosity, increased pore tortuosity, and the formation of a more compact and stable calcium carbonate polymorph. After 3 days of CO₂ pressurized curing, the surface (0-1 mm) CaCO₃ content of the ZIF-8@mCA paste reached 55.5%, more than twice that of the reference. The 1-day compressive and flexural strength under conventional curing were twice those of the reference without catalysts. These results demonstrate that ZIF-8@mCA can serve as a compatible CO₂ hydration catalyst in cement-based systems and can promote accelerated and more uniform carbonation within the investigated curing regime.