Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

Abstract

Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic-and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems. A second key advance is new experimental evidence for what scientists hypothesized but could not test previously, namely, interfacial chemical reactions are frequently driven by "anomalies" or "non-idealities" such as defects, nanoconfinement, and other nontypical chemical structures. Third, progress in computational chemistry has yielded new insights that allow a move beyond simple schematics, leading to a molecular model of these complex interfaces. In combination with surfacesensitive measurements, we have gained knowledge of the interfacial structure and dynamics, including the underlying solid surface and the immediately adjacent water and aqueous ions, enabling a better definition of what constitutes the oxide− and silicate−water interfaces. This critical review discusses how science progresses from understanding ideal solid−water interfaces to more realistic systems, focusing on accomplishments in the last 20 years and identifying challenges and future opportunities for the community to address. We anticipate that the next 20 years will focus on understanding and predicting dynamic transient and reactive structures over greater spatial and temporal ranges as well as systems of greater structural and chemical complexity. Closer collaborations of theoretical and experimental experts across disciplines will continue to be critical to achieving this great aspiration.

Uncovering the Dominant Role of an Extended Asymmetric Four-Coordinated Water Network in the Hydrogen Evolution Reaction

“…Additionally, from analysis of the potential-dependent in situ SEIRA spectra at the water concentration of 10 m, it is found that only the peaks at 3622 and 3433 cm –1 show obvious Stark shifts, while the peak at 3241 cm –1 does not (Figure D and E). These indicate that weakly hydrogen-bonded and asymmetric four-coordinated water are closer to the electrode surface and more sensitive to the local electric field than symmetric four-coordinated water, which aligns with Bañuelos et al that there is a disrupted hydrogen-bonding network at the interface in comparison to the bulk . Simultaneously, the δ(O–H) shows a blue-shift from 1636 to 1651 cm –1 (Figure D and E), indicating that the water near the electrode surface does undergo large structural changes to form a more and more strong water network in the EDL under negative polarized electric fields.…”

“…Owing to the enhanced local electromagnetic field of the nanostructured Au substrate, surface-enhanced infrared absorption spectroscopy (SEIRAS) enables direct access to molecule-level information on surface species, − especially for sensitively probing interfacial water because of the large extinction coefficient of water in the mid-infrared range. Nevertheless, it is difficult to accurately distinguish the structural information from the Stern layer and the diffuse layer because the excited surface plasma attenuates exponentially within 10 nm from the Au film, although great progress has been made in this field by nonlinear optical methods. − Herein, the nonaqueous 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquids , (ILs, [BMIM]­[BF 4 ]) were introduced to separate the coupling of water with varied structures in the EDL. Further, based on the affinity differences of water and ILs for the Au electrode and the different orientation responses to bias potential, the water interacting with the electrode surface and the outer water were successfully distinguished.…”

Dissolution of Selected Trace Elements from Simulated Atmospheric Aerosol Aging and Human Exposure of Mineral Dust and Coal Fly Ash

“…This result emphasizes that the rate of dissolution in the strong acid extraction procedure is affected to a higher degree by the mineralogy, morphology, and density of defects than surface area only, as shown in a number of studies for Fe. ,, Within the fly ash samples, there are negative linear trends for DTE SA with increasing surface area for Fe and Mn, and positive linear trends for Cu, Pb, and As. These results clearly show the differences in the dissolution mechanisms of metal oxides in fly ash samples despite the same experimental conditions, which needs further investigation to disentangle the role of surface area from the roles of mineralogy and surface defects . The following section describes results from simulated dark atmospheric aging experiments as a function of pH without and with catechol and oxalic acid as proxies for reactive WSOC.…”

Quantifying the Impact of Electric Fields on the Local Structure and Migration of Potassium Ions at the Orthoclase (001) Surface

“…Depending on the pH and composition of the aqueous solution, most mineral surfaces will bear a net electrical charge due to specific ion adsorption, which is subsequently neutralized by a diffuse swarm of surrounding counterions. Stern layer ions making up the near-surface region are generally located within the first two water monolayers (MLs) (∼6 Å), whereas the diffuse layer lies beyond. , This electrical double-layer (EDL) concept provides a useful framework for understanding interfacial properties that impact reactivity, such as the adsorption capacity, redox potential, and interparticle forces that cause them to aggregate/disaggregate. − EDL properties thus play an important role in a variety of contexts including catalysis, cement corrosion, aquatic geochemistry, , and the transport of metals in soil and sedimentary rocks. , …”