Driving CO₂ to a Quasi-Condensed Phase at the Interface between a Nanoparticle Surface and a Metal-Organic Framework...

We demonstrate a molecular-level observation of driving CO₂ molecules into a quasi-condensed phase on the solid surface of metal nanoparticles (NP) under ambient conditions of 1 bar and 298 K. This is achieved via a CO₂ accumulation in the interface between a metal-organic framework (MOF) and a metal NP surface formed by coating NPs with a MOF. Using real-time surface-enhanced Raman scattering spectroscopy, a >18-fold enhancement of surface coverage of CO₂ is observed at the interface. The high surface concentration leads CO₂ molecules to be in close proximity with the probe molecules on the metal surface (4-methylbenzenethiol), and transforms CO₂ molecules into a bent conformation without the formation of chemical bonds. Such linear-to-bent transition of CO₂ is unprecedented at ambient conditions in the absence of chemical bond formation, and is commonly observed only in pressurized systems (>10⁵ bar). The molecular-level observation of a quasi-condensed phase induced by MOF coating could impact the future design of hybrid materials in diverse applications, including catalytic CO₂ conversion and ambient solid-gas operation.