Visualizing Dynamic Environmental Processes in Liquid at Nanoscale via Liquid-Phase Electron Microscopy

Abstract

Visualizing the structure and processes in liquids at the nanoscale is essential for understanding the fundamental mechanisms and underlying processes of environmental research. Cutting-edge progress of in situ liquid-phase (scanning) transmission electron microscopy (LP-S/TEM) and inferred possible applications are highlighted as a more and more indispensable tool for visualization of dynamic environmental processes in this Perspective. Advancements in nanofabrication technology, high-speed imaging, comprehensive detectors, and spectroscopy analysis have made it increasingly convenient to use LP S/TEM, thus providing an approach for visualization of direct and insightful scientific information with the exciting possibility of solving an increasing number of tricky environmental problems. This includes evaluating the transformation fate and path of contamination, assessing toxicology of nanomaterials, simulating solid surface corrosion processes in the environment, and observing water pollution control processes. Distinct nanoscale or even atomic understanding of the reaction would provide dependable and precise identification and quantification of contaminants in dynamic processes, thus facilitating trouble-tracing of environmental problems with amplifying complexity.

Interfacial Liquid Water on Graphite, Graphene, and 2D Materials

“…However, the TEM images neither resolved the molecular-scale structure at the surface nor the interfacial liquid structure inside the carbon nanotube. The development of specific liquid cells for electron microscopy enabled the observation of particle nucleation and growth. ,,, Atomic-scale resolution images of nanoconfined water between two graphene layers were interpreted as “square ice”, a phase of water having a symmetry different from the conventional tetrahedrally geometry of hydrogen bonding between water molecules . Other authors attributed the observed structure to contamination by salt crystals …”

“…(b) Schematic diagram of a liquid cell TEM setup. Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”

“…Several techniques have been applied to study the interaction and properties of water with graphite and 2D materials surfaces. Chiefly, among them were water contact angle, − ,,,− X-ray reflectivity, ,, electron microscopy, − vibrational sum-frequency-generation spectroscopy, ,− X-ray spectroscopies, ,, AFM methods, − 3D AFM, ,,,,,− and impedance methods. ,,, The experimental techniques were complemented by a variety of theoretical and molecular dynamics methods. ,− ,− Nanofluidic channels made from two-dimensional crystals enabled the fabrication of devices that relied on the interfacial liquid water properties. , Those devices were also applied to study the interaction of water with graphene and hexagonal boron nitride surfaces. , …”

Imaging Metal/Metal Oxide Electrocatalyst Transformations in Liquids

“…Fourth, from the aspect of the study systems, the pH, temperature, precursor, and ligands in liquid cells would influence the structure and morphology evolution of electrocatalysts. − Recent breakthroughs on steady-state induced self-organization and phase transformation of micrometer-scale colloids, in which the strategy involves arranging chiral nanoparticles into closely packed achiral superlattices, could provide a chiral bias to direct nanoparticle assemblies with corner-to-edge connections . So far, the study systems are mainly limited to the inorganic metal/metal oxide nanoparticle; the visualization of bioelectrochemical process is virtually unexplored.…”

Observing the Evolution of Metal Oxides in Liquids

“…[120,139,174] Thus, control experiments with different dose rates or liquid cells are essential in distinguishing these artifacts. [175] The low-dose-optimized TEM technique also reduces the accumulated electron dose and optimizes the imaging conditions. [170,176] Hence, the electron beam effect's detection, modeling, and quantification should be pursued in future works.…”