The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

To address the on-going climatic crisis primarily caused by excessive carbon dioxide emissions, many carbon dioxide removal (CDR) techniques have been proposed and been experimented on. Among many others, biological pathway via enhancement of photosynthesis is believed to be one of the scalable CDR options. This study proposes a potential CDR method by enhancing the photosynthetic carbon fixation capacity of microalgae through the assembly of metal-organic frameworks (MOFs) on the surface of spirulina. Specifically, a hydrophobic and water-stable ZIF-8-NH₂ was synthesized using a mixed-ligand approach and added to the cultivation system of Spirulina platensis. The FT-IR results indicate that the ZIF-8-NH₂ nanoparticles are likely self-assembled through hydrogen bonding between the primary amine groups in their structure and the carbonyl groups of the proteins in the S. platensis cell membrane. By measuring the changes in dry cell weight and optical density of the microalgae after MOF assembly, the photosynthetic carbon fixation capacity of S. platensis@ZIF-8-NH₂ was evaluated. When the addition concentration of MOF is 25 ppm, the maximum dry cell weight of S. platensis@ZIF-8-NH₂ is 149% higher than that of the regular S. platensis. Moreover, the CO₂ biofixation rate of S. platensis@ZIF-8-NH₂ is 170% higher than that of the regular S. platensis. Furthermore, the concentration of HCO₃^- in the culture system significantly influences the photosynthetic carbon fixation by microalgae assembled by MOF. Therefore, the assembly of ZIF-8-NH₂ on the surface of S. platensis clearly enhances the photosynthetic carbon fixation capacity of the microalgae, which can effectively promote the absorption and utilization of environmental CO₂ by microalgae.