Beyond zinc porphyrins: Immobilized algal chlorophyllin carboxylates as hydrophilic carbonic anhydrase mimics for recyclable CO2 capture

To address the limitations of synthetic zinc porphyrins (ZnP)—including high hydrophobicity, synthesis cost, and poor reusability—as carbonic anhydrase (CA) mimics, this study utilized chlorophyll a -rich Arthrospira platensis algal powder to synthesize hydrophilic zinc and copper chlorophyllin trisodium salts (Zn/Cu-E6–3Na). These derivatives preserve the metal-porphyrin catalytic center while incorporating three carboxylic groups, significantly improving water solubility. To enhance stability and recyclability, ZIF-8 was employed as a carrier to immobilize the Zn/Cu-E6–3Na via coordination, forming Zn/Cu-E6–3Na@ZIF-8 composites. Characterization confirmed anchoring through dual interactions involving both the central metal ion and carboxyl groups, which also improved the hydrophilicity of ZIF-8. The composites considerably enhanced CO 2 absorption within a potassium carbonate system. Esterase activity assays demonstrated a synergistic effect, with Zn- and Cu-composites reaching 0.14 U and 0.13 U, respectively, outperforming individual components. Furthermore, the composites retained over 62 % of their initial activity after multiple cycles without significant metal leaching, indicating excellent operational stability. This work presents a new approach for CO 2 capture using functional chlorophyll derivatives and proposes an innovative strategy for high-value biomass utilization.