Driving CO₂ to a Quasi-Condensed Phase at the Interface between a Nanoparticle Surface and a Metal–Organic Framework at 1 bar and 298 K

Abstract

We demonstrate a molecular-level observation of driving CO 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 CO 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 CO is observed at the interface. The high surface concentration leads CO molecules to be in close proximity with the probe molecules on the metal surface (4-methylbenzenethiol), and transforms CO molecules into a bent conformation without the formation of chemical bonds. Such linear-to-bent transition of CO is unprecedented at ambient conditions in the absence of chemical bond formation, and is commonly observed only in pressurized systems (>10 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 CO conversion and ambient solid-gas operation.

Favoring the unfavored: Selective electrochemical nitrogen fixation using a reticular chemistry approach

“…The overgrowth of ZIF on metallic nanoparticles using our fabrication protocol generates nanoscopic interfacial cavities at the interface between the catalyst surface and the polycrystalline ZIF coating (fig. S2, F to H) ( 18 ). Collectively, these interfacial cavities and MOF’s intrinsic micropores are essential for accumulating N 2 and other reactant molecules at the catalytic surface for NRR, as affirmed from surface-sensitive SERS detections of chemical species located near/at the bifunctional plasmonic and electrocatalytically active metallic surfaces (fig.…”

“…3E ). Consequently, N 2 gas reactants infuse the ZIF scaffold selectively and eventually concentrate near the electrocatalyst surface driven by the thermodynamically favorable sorption at the interfacial cavities and ZIF’s micropores ( 18 ). The close proximity of N 2 molecules and ethanol (proton source) to the catalytic surface facilitates both intermolecular and surface interactions, eventually activating the electrochemical heterogeneous reduction of N 2 molecules to ammonia when an external voltage is applied.…”

“…It is noteworthy that the temporal positive shift of a reducing peak is a direct indication of the growing ease of N 2 electrochemical reduction. We attribute this phenomenon to the continuous sorption of reactants into a pseudo high-pressure microenvironment within the nanoscopic interfacial cavities ( 18 ), where reactants are forced near the electrocatalytic surface to improve reactants’ accessibility and enhance catalyst-gas interaction necessary for NRR. Under sustained N 2 gas flow, this accumulation of reactants at the electrocatalyst surfaces ensures the abundance of N 2 molecules to fuel NRR, which is observed from the consistent peak current of 1.43 μA with <3% change over 45 consecutive cycles ( Fig.…”

Understanding the Role of Metal–Organic Frameworks in Surface‐Enhanced Raman Scattering Application

“…[45] Lee et al reported that under ambient conditions of 0.987 atm and 298 K, real-time surface-enhanced Raman scattering spectroscopy was used to monitor the changes of CO 2 molecules on the Ag@ZIF-8 substrate. [46] A >18-fold enhancement of CO 2 was observed at the interface. The CO 2 molecules transformed into a bent conformation, changing from the gas phase to the quasi-condensed phase, which meant that the cavity MOFs formed at the solid can form a microhigh pressure environment at the interface of the nanoparticle@MOF substrate (Figure 8A,B).…”

“…Reproduced with permission. [46] Copyright 2017, American Chemical Society. C) Schematic diagram of gas-liquid reaction in the interfacial cavity.…”