Visualizing Hidden Nanoscale Dynamic Chemistry in Surface Liquid Layers at Solid–Liquid Interfaces

Deciphering the dynamic chemistry of solid-liquid interfaces at the nanoscale is fundamental to understanding processes underpinning natural and engineered water purification. Yet, capturing these transient interfacial transformations remains elusive due to the spatial and temporal limitations of conventional techniques. Here, we introduce a multimodal high-resolution electron microscopy platform that unites liquid-phase electron microscopy, cryo-electron microscopy, electron tomography, electron energy loss spectroscopy, and X-ray energy-dispersive spectroscopy into a single integrative framework. This approach couples cryogenic immobilization, interface-resolved tracking, and ambient tomography to resolve the evolving structure, composition, and valence chemistry of liquid-interacting surfaces. Using model iron nanoparticles exposed to NaAuCl₄, NiCl₂, and Na₂SeO₃ solutions, we reveal nanoscale variations in layer thickness governed by interfacial charge, the spatial distribution of elemental valence states within the liquid phase, and the ionic mediation of interfacial architecture. Beyond enabling real-time-to-three-dimensional mapping of interface dynamics, this method offers an unprecedented window into the chemical evolution of reactive interfaces. Its broad applicability across nanomaterial-pollutant systems underscores its potential as a universal platform for advancing mechanistic understanding in catalysis, environmental remediation, and beyond.