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

## TL;DR

The paper introduces a new method to study water at oxide surfaces, revealing unexpected protonation and hydrophobic behavior on titanium dioxide.

## Contribution

A novel combination of proton-resolved NMR and simulations to map interfacial water at atomic scale.

## Key findings

- Fully hydrated TiO2 surfaces are positively protonated.
- Surface exhibits hydrophobic behavior under ambient conditions.
- Method enables molecular-level hydration analysis on oxide surfaces.

## Abstract

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.