Real-Space Visualization of CO2 Capture, Diffusion, and Release in Surface-Confined Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) show significant potential for addressing the urgent demand for high-efficiency carbon dioxide (CO2) capture and conversion. However, gaining mechanistic insights into CO2 diffusion processes and host-guest interactions within MOFs remains largely unexplored, due to the challenges associated with atomic-scale imaging. Here, we directly visualize the binding configurations of CO2 molecules and their dynamic evolution in real space and real time within surface-confined MOFs by combining in situ CO2 dosing with atomic-resolution scanning probe microscopy. Bond-resolved imaging reveals two distinct CO2 adsorption configurations, arising from the interactions between flat adsorbed CO2 and ligand/metal coordination sites of MOFs. Well-organized CO2 patterns composed of alternating triangular and rhombic subunits are clearly identified within the MOF pores. Temperature-dependent measurements further identify characteristic regimes associated with early stages of CO2 capture, diffusion, and release. Furthermore, we show how a sudden increase of CO2 concentration would cause the instability and even collapse of MOFs. These observations highlight the dynamic and nonequilibrium nature of CO2 capture in surface-confined MOFs and demonstrate the power of real-space approaches for elucidating gas adsorption and diffusion mechanisms at the molecular scale.