Fig. 2.

Enzymatic liquid membrane design and mechanism of CO₂ capture and separation. a The membrane is fabricated by formation of ~1-µm-deep oriented arrays of 8 nm diameter cylindrical silica [SiO₂] mesopores within the larger 50–150-nm pore channels of a 50-μm-thick porous alumina [Al₂O₃] Whatman^© Anodisc support. b Using atomic layer deposition and oxygen plasma processing (described in text and Fig. 4) the silica mesopores are engineered to be hydrophobic (trimethylsilyl (Si(CH₃)₃) surface groups) except for an 18-nm-deep region at the pore surface, which is hydrophilic (≡Si-OH surface groups). Via capillary condensation, CA enzymes and water spontaneously fill the hydrophilic mesopores to form an array of nano-stabilized CA enzymes with an effective CA concentration >10× of that achievable in solution. CA catalyzes the capture and dissolution of CO₂ as carbonic acid (HCO₃^–) moieties at the upstream surface and regeneration of CO₂ at the downstream surface (see Fig. 1c). The high concentration of CA and short diffusion path length maximizes capture efficiency and flux