Catalytic Activity of Microcystis aeruginosa in Fe-Co-MOFs System for Efficient CO2 Fixation and High-Value Conversion

The enrichment efficiency during the high-value conversion of carbon dioxide still presents certain limitations in practical applications. Iron-cobalt-based metal-organic framework (MOF) nanoparticles, which exhibit lower toxicity to Microcystis aeruginosa, have been successfully introduced into microalgae solutions to address the issue of low CO2 concentration in interfacial reactions. When 1,4-naphthalenedicarboxylic acid was employed as an organic ligand under synthesis conditions of 130°C, pH 3.5, and a reaction time of 15 h, the resulting MOF exhibited a CH₄ yield of 92.6 μmol g⁻¹ h⁻¹ in the photocatalytic system at room temperature (25°C). The combination of Microcystis aeruginosa with the optimal Fe-Co-MOFs system achieved a selectivity of up to 96.1 % in converting CO2 into CH4. When Microcystis aeruginosa was cultured in a modified medium with a pH of 6.78 and 5 mg of NDC-T130 at 25°C for 12 h, an OD600 of 0.192 ± 0.01 was observed. The CH₄ yield from the Microcystis aeruginosa-NDC-T130 co-culture composite system was 1.46 times that of the Fe-Co-MOFs. Density-functional theory calculations indicate that carbon dioxide molecules preferentially adsorb on the crystal surfaces of (CoFe2)O4 (113) and (Co0.457Fe0.543)(Co1.543Fe0.457)O4 (311), with the Co site being more likely to serve as the reactive site for CO2 photoreduction to CH4 within the Fe-Co-MOFs. Transcriptome analysis demonstrates that MOFs enhance the dark reactions of microalgae and facilitate further CO2 fixation for photosynthesis and electron transfer, which are crucial for improving the high-value CO2 conversion efficiency of this system. This strategy provides both experimental and theoretical support for iron-based MOFs as photocatalytic materials, regardless of CO2 concentration.