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Environmental Processes at the Solid−Liquid Interface: What Constitutes New Physical Insights?
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illustrative, but by no means exhaustive, examples from each one of these areas which meet the criterion for new physical insights and are therefore suitable for publication in The Journal of Physical Chemistry. Spectroscopy: Nonlinear optical techniques to elucidate molecular orientation, adsorbed functional groups/hydrogenbonding interactions, perturbations of cell membranes by particle interactions, and interfacial electrostatics; ambient XPS to probe composition, bonding state, protonation/deprotonation, surface charge density, and potential; X-ray reflectivity to interrogate the detailed structure of the mineral−water interface and its response to adsorbates; adsorption geometries of organic acids on mineral surfaces probed with ATR-IR. Dynamics/Thermodynamics: Mechanisms of single particle aggregation at solid−liquid interfaces using in situ TEM and other imaging techniques; molecular diffusion at solid−liquid interfaces probed with single-particle tracking; adsorption energies of CO2 on metal oxides and hydrated surface energies of oxides determined by microcalorimetry; influence of electrolytes on the forces between water−solid interfaces probed with AFM. Computations/Modeling: Surface structure of complex metal oxides as a function of stoichiometry; adsorption geometries of oxy-anions; simulations of water transport through membranes as well as particle nucleation and aggregation; solvation of ions at ice−water interfaces, mechanism of crystal growth and crystal growth inhibition, and redox properties. Given the rapid pace at which this field is moving toward developing increased molecular insight for increasingly complex systems, our discussion is, of course, only relevant for the immediate future. We look forward to revisiting this topic in a few years so as to take stock of where the new frontier of environmental physical chemistry at solid−liquid interfaces has moved.
ew physical insights with broad applicability are a key requirement for publication in The Journal of Physical Chemistry. They are critically important to furthering our ability to not only understand and predict environmental phenomena at solid−liquid interfaces but also to control them. The need for new physical insights is motivated not only from a fundamental scientific perspective but also from a recognition that many of the most important environmental processes in natural systems occur at solid−liquid interfaces, ranging from mineral−water to cell-membrane−water interfaces. For example, the sorption− desorption behavior of aqueous species (e.g., ions, organic chemicals) on metal oxides, clays, and soils plays a crucial and often determinant role in mineral growth and transport properties. Similarly, the chemical transformations and cellular uptake of many inorganic and organic pollutants, including nanoparticles, occur at solid−liquid interfaces, processes that have broad implications in toxicity and remediation technologies. Despite the central role that solid−liquid interfaces play in the field of environmental physical chemistry, studying them experimentally or from computation represents a major challenge. Recognizing the intrinsic complexity and heterogeneity of natural systems, model systems are often needed to provide information on the molecular orientation and spatial distribution of water molecules and ions, and their dynamics in response to external stimuli within the electrical double layer. Such information has the potential to help pave the way toward models that go beyond mean field theory to describe charged interfaces. Developing new physical insights also requires us to develop fundamental knowledge not only of the solid interface under aqueous conditions and how its structure responds to changes in composition and solution chemistry, but also of the dynamics and thermodynamics that govern the relevant adsorbate−substrate interactions. Protonation and deprotonation, surface complexation, charge and energy transfer, and other specific interactions among the surface sites and the adsorbing ions and molecules are also in need of atomistic descriptions. To provide an even more detailed atomistic understanding, spatially and temporally resolved atom- and bond-specific information is neededan enormous challenge at the condensed matter interfaces relevant to the field. Given these inherent challenges in probing solid−liquid interfaces, the discovery of new molecular level insights is often facilitated by the development and application of advanced experimental (including imaging), computational, or modeling tools. Synergic interactions between computation, theory/modeling, and experimental efforts are often necessary if experimental results are to be rationalized and underlying factors that contribute to interfacial properties are to be understood. For example, structural determinations by X-raybased techniques are often complemented by theoretical studies. New physical insights into environmental phenomena at solid−liquid interfaces can be obtained using information acquired from a number of different approaches, subdivided for convenience into spectroscopy, dynamics/thermodynamics, and computations/modeling. In the following sections we will give © 2017 American Chemical Society
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D. Howard Fairbrother,* Senior Editor Franz M. Geiger,* Senior Editor AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
D. Howard Fairbrother: 0000-0003-4405-9728 Franz M. Geiger: 0000-0001-8569-4045 Notes
The authors declare no competing financial interest. This Viewpoint is jointly published in The Journal of Physical Chemistry A and C.
Published: August 17, 2017 17045
DOI: 10.1021/acs.jpcc.7b07172 J. Phys. Chem. C 2017, 121, 17045−17045
