# Clay Edges Are Dynamic Proton-Conducting Networks Modulated by Structure and pH

## TL;DR

This study shows that clay edges are dynamic proton conductors influenced by pH and structure, offering new insights into their environmental and chemical roles.

## Contribution

The use of machine learning potentials enables nanosecond-scale simulations revealing dynamic proton behavior on clay edges.

## Key findings

- Montmorillonite edges show amphoteric behavior with pH-dependent protonation and deprotonation.
- Spontaneous proton transfer occurs at neutral pH via direct and solvent-mediated pathways.
- Clay edges act as dynamic proton-conducting networks modulated by structure and solution conditions.

## Abstract

Montmorillonite, a ubiquitous clay mineral, plays a vital
role
in geochemical and environmental processes due to its chemically complex
edge surfaces. However, the molecular-scale acid–base reactivity
of these interfaces remains poorly understood due to the limitations
of both experimental resolution and conventional simulations. Here,
we employ machine learning potentials with first-principles accuracy
to perform nanosecond-scale molecular dynamics simulations of montmorillonite
nanoparticles across a range of pH. Our results reveal clear amphoteric
behavior, with edge sites undergoing protonation in acidic environments
and deprotonation in basic conditions, accompanied by pH-dependent
surface charge regulation. Even at neutral pH, spontaneous and directional
proton transfer events are common, proceeding via both direct and
solvent-mediated pathways. These findings demonstrate that montmorillonite
edges are not static arrays of hydroxyl groups but dynamic, proton-conducting
networks whose reactivity and charge state are modulated by local
structure and solution conditions. This work offers a molecular-level
framework for understanding proton transport and buffering in clay–water
systems, with broad implications for catalysis, ion exchange, and
environmental remediation.