Design, synthesis, and physicochemical study of a biomass-derived CO₂ sorbent 2,5-furan-bis(iminoguanidine)

In this study, the concept of biomass-based direct air capture is proposed, and the aminoguanidine CO₂ chemical sorbent 2,5-furan-bis(iminoguanidine) (FuBIG) was designed, synthesized, and elucidated for the physicochemical properties in the process of CO₂ capture and release. Results showed that the aqueous solution of FuBIG could readily capture CO₂ from ambient air and provided an insoluble tetrahydrated carbonate salt FuBIGH₂(CO₃) (H₂O)₄ with a second order kinetics. Hydrogen binding modes of iminoguanidine cations with carbonate ions and water were identified by single-crystal X-ray diffraction analysis. Equilibrium constant (K) and the enthalpies (ΔH) for CO₂ absorption/release were obtained by thermodynamic and kinetic analysis (K₇ = 5.97 × 10⁴, ΔH₇ = -116.1 kJ/mol, ΔH₈ = 209.31 kJ/mol), and the CO₂-release process was conformed to the geometrical phase-boundary model (1-(1-α)^1/3 = kt). It was found that the FuBIGH₂(CO₃) (H₂O)₄ can release CO₂ spontaneously in DMSO without heating. Zebrafish models revealed a favorable biocompatibility of FuBIG.