Green and Efficient Fabrication of Polydopamine/Mega-Carbonic Anhydrase Coatings for Direct Air CO ₂ Capture

Carbonic anhydrase (CA) had immense potentials in addressing the escalating atmospheric carbon dioxide (CO2) levels; however, it was hindered by poor stability, high purification costs, and difficult recycling. A novel one-pot polydopamine (PDA)–Fe2+ coating strategy was proposed to immobilize “mega-CA”, namely, the nanosized SazCA-ferritin assemblies (nsSazCA-F) with an exceptionally large size (21 nm × 21 nm × 21 nm) and ultrahigh molecular weight (1224 kDa). Leveraging low-concentration Fe2+ to accelerate dopamine polymerization on porous nickel foam (NF), a hierarchically porous PDA-Fe2+-nsSazCA-F@NF coating was fabricated within 20 min, demonstrating 82.5% activity retention after 10 reuse cycles and a significantly extended half-life of 70.7 ± 3.9 days (55% improvement compared to free enzymes) at 30 °C and pH 8.0. Furthermore, an integrated PDA-Fe2+-nsSazCA-F@NF coating–Chlorella system was developed for direct air CO2 capture, achieving a 58% increase in Chlorella biomass and a 60% enhancement in the CO2 fixation rate over 8 days, which offered a novel paradigm for achieving air carbon neutrality. The proposed strategy presents a promising approach for efficient immobilization of “mega-enzymes”, providing a new solution for clean production and sustainable carbon cycling technologies.