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

TL;DR

This study uses advanced simulations to show that montmorillonite clay edges are dynamic, proton-conducting networks whose reactivity varies with pH and structure, impacting environmental and catalytic processes.

Contribution

It introduces a first-principles accuracy machine learning approach to reveal the molecular-scale proton transfer mechanisms at clay edges across different pH levels.

Findings

Edge sites protonate in acid, deprotonate in base

Spontaneous proton transfer occurs at neutral pH

Edges act as dynamic, proton-conducting networks

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: edge sites undergo protonation in acidic environments and deprotonation in basic conditions. 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 is 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.