Enhancing ZnTPP performance as a carbonic anhydrase mimic for promoting CO2 absorption via circumferential and axial functionalization

Abstract

Mitigating climate change requires efficient carbon dioxide (CO₂) capture technologies. Carbonic anhydrase (CA), the most efficient enzyme for CO₂ hydration, holds great potential for enhancing CO₂ absorption. However, its high cost and low stability limit large-scale applications. CA mimics present a promising alternative but often suffer from poor dispersibility in absorbents, restricting their catalytic performance. To this end, this study proposes a functional modification strategy to enhance CA mimics by introducing basic hydrophilic groups. Zinc tetraphenylporphyrin (ZnTPP) was selected as a representative CA mimic, and four derivatives were synthesized: peripherally modified ZnTPP with hydroxyl (ZnTPP-OH) and amino (ZnTPP-NH₂) groups, as well as axially coordinated ZnTPP with lysine (ZnTPP-Lysine) and diethylenetriamine (ZnTPP-C₄H₁₃N₃) complexes. Absorption experiments demonstrated that the modified mimics significantly improved CO₂ absorption in both water and a 20 wt% potassium carbonate (K₂CO₃) solution. ZnTPP-OH exhibited the highest efficiency, increasing CO₂ absorption by 38.10 % in water and 28.20 % in K₂CO₃ solution, achieving 2.71- and 1.69-fold enhancements compared to unmodified ZnTPP. Characterization and density functional theory (DFT) calculations confirmed that hydrophilic modification enhanced dispersibility and increased exposure of active sites. Additionally, basic hydrophilic groups provided extra CO₂ adsorption sites, facilitating nucleophilic attack step during the catalytic hydration process.