Aqueous interfaces of oxides are ubiquitous on our planet, playing a key role in the ecosphere: for example, protonation/deprotonation of silicates in water dominates the weathering process that shapes the Earth landscape, and serves as the major sink in global carbon cycle. In modern industrial applications, oxide/water interfaces also host many important reactions, such as the oxygen evolution in renewable energy schemes. However, accurate knowledge about these interfaces still lacks at the molecular level, due to difficulties in accessing buried oxide surfaces. In this presentation, we report an experimental scheme enabling in situ vibrational spectroscopy of oxide surfaces in liquid water. Application to the silicon oxide/water interface has allowed us to reveal the emergence of new pathways from reactions with water. In synergy with ab initio (DFT-based) molecular dynamics and metadynamics simulations, we uncovered a surface reconstruction, triggered by deprotonation of surface hydroxylated groups, that led to unconventional five-coordinated silicon species. Our investigation furthermore demystifies the multimodal chemistry of aqueous silica discovered decades ago, bringing in new information that we believe is capable to radically modify our current understanding.

Unveiling surface chemistry of oxide surfaces in liquid water by coupling SFG spectroscopy and DFT-based molecular dynamics simulations

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