Atomic-Scale Mapping of Interfacial Water on Oxide Surfaces via Proton-Resolved NMR and Ab Initio Simulations

Understanding the molecular structure of water at solid–liquid interfaces is essential for advancing catalysis, energy conversion, and environmental technologies. However, directly characterizing interfacial water species in excess liquid water remains a major experimental challenge. Here, we introduce a new strategy that combines high-resolution 1H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy with first-principles molecular dynamics simulations to resolve and assign the chemical environments of interfacial water and hydroxyl species on hydrated titanium dioxide (TiO2) nanoparticles. Using partial proton–deuteron exchange and fast MAS techniques, we achieve site-specific detection of surface-bound H2O and OH groups at the solid–liquid interface. This enables a detailed atomistic assessment of surface hydration states under ambient conditions. Our results reveal that the fully hydrated anatase (101) TiO2 surfaces are positively protonated and exhibit hydrophobic behavior, a counterintuitive finding with significant implications for interfacial reactivity. The approach developed in this work is widely applicable for unraveling complex hydration structures at oxide–water interfaces with molecular resolution.