Dynamic Surface Incorporation of Pb Ions at the Actively Dissolving Calcite (104) Surface.

The reaction of dissolved Pb with calcite surfaces at near-equilibrium conditions involves adsorption of Pb and precipitation of secondary heteroepitaxial Pb-carbonate minerals. A more complex behavior is observed under far-from-equilibrium conditions, including strong inhibition of calcite dissolution, development of microtopography, and near-surface incorporation of multiple monolayers (ML) of Pb without precipitation of secondary phases [where 1 ML ≡ 1 Ca/20.2 Å, the crystallographic site density of the calcite (104) lattice plane].

Visualizing the Internal Nanocrystallinity of Calcite Due to Nonclassical Crystallization by 3D Coherent X-Ray Diffraction Imaging.

The internal crystallinity of calcite is investigated for samples synthesized using two approaches: precipitation from solution and the ammonium carbonate diffusion method. Scanning electron microscopy (SEM) analyses reveal that the calcite products precipitated using both approaches have a well-defined rhombohedron shape, consistent with the euhedral crystal habit of the mineral. The internal structure of these calcite crystals is characterized using Bragg coherent diffraction imaging (BCDI) to determine the 3D electron density and the atomic displacement field.

Dynamic Inhibition of Calcite Dissolution in Flowing Acidic Pb Solutions.

Reactions of mineral surfaces with dissolved metal ions at far-from-equilibrium conditions can deviate significantly from those in near-equilibrium systems due to steep concentration gradients, ion-surface interactions, and reactant transport effects that can lead to emergent behavior. We explored the effect of dissolved Pb on the dissolution rate and topographic evolution of calcite (104) surfaces under far-from-equilibrium acidic conditions (pH 3.7) in a confined single-pass laminar-flow geometry.

Unraveling pH-Dependent Changes in Adsorption Structure of Uranyl on Alumina (012).

Mitigating uranium transport in groundwater is imperative for ensuring access to clean water across the globe. Here, resonant anomalous X-ray reflectivity is used to investigate the adsorption of uranyl on alumina (012) in acidic aqueous solutions, representing typical U concentrations of contaminated water near mining sites. The analyses reveal that U adsorbs at two distinct heights of 2.

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite-Water Interface by Adsorption of Rb and Halides (Cl , Br , I ) at High Salinity.

The front cover artwork is provided by Argonne National Laboratory. The image shows the arrangement of correlated cations and anions at a charged solid surface in contact with highly concentrated electrolyte solutions. Read the full text of the Research Article at 10.

Systematic observations of enhanced oil recovery and associated changes at carbonate-brine and carbonate-petroleum interfaces.

Enhanced oil recovery (EOR) from carbonates is obtained by injection of controlled ionic strength brines containing "active ions" (e.g., SO, Mg, Ca).

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite-Water Interface by Adsorption of Rb and Halides (Cl , Br , I ) at High Salinity.

Classical electric double layer (EDL) models have been widely used to describe ion distributions at charged solid-water interfaces in dilute electrolytes. However, the chemistry of EDLs remains poorly constrained at high ionic strength where ion-ion correlations control non-classical behavior such as overcharging, i. e.

Carbonate Coprecipitation for Cd and Zn Treatment and Evaluation of Heavy Metal Stability Under Acidic Conditions.

Mining wastes or combustion ash are materials of high carbon sequestration potential but are also known for their toxicity in terms of heavy metal content. To utilize such waste materials for engineered carbon mineralization purposes, there is a need to investigate the fate and mobility of toxic metals. This is a study of the coprecipitation of metals with calcium carbonate for environmental heavy metal mitigation.

Y(III) Sorption at the Orthoclase (001) Surface Measured by X-ray Reflectivity.

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of the Y concentration, [Y], at pH 7 and 5.

Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)-Water Interface.

The interactions of heavy metals with minerals influence the mobility and bioavailability of toxic elements in natural aqueous environments. The sorption of heavy metals on covalently bonded minerals is generally well described by surface complexation models (SCMs). However, understanding sorption on sparingly soluble minerals is challenging because of the dynamically evolving chemistry of sorbent surfaces.

Water Adsorption on Mica Surfaces with Hydrophilicity Tuned by Counterion Types (Na, K, and Cs) and Structural Fluorination.

The stability of adsorbed water films on mineral surfaces has far-reaching implications in the Earth, environmental, and materials sciences. Here, we use the basal plane of phlogopite mica, an atomically smooth surface of a natural mineral, to investigate water film structure and stability as a function of two features that modulate surface hydrophilicity: the type of adsorbed counterions (Na, K, and Cs) and the substitution of structural OH groups by F atoms. We use molecular dynamics simulations combined with in situ high-resolution X-ray reflectivity to examine surface hydration over a range of water loadings, from the adsorption of isolated water molecules to the formation of clusters and films.

Ion correlations drive charge overscreening and heterogeneous nucleation at solid-aqueous electrolyte interfaces.

Classical electrical double layer (EDL) models are foundational to the representation of atomistic structure and reactivity at charged interfaces. An important limitation to these models is their dependence on a mean-field approximation that is strictly valid for dilute aqueous solutions. Theoretical efforts to overcome this limitation are severely impeded by the lack of visualization of the structure over a wide range of ion concentration.

Molecular-scale origins of wettability at petroleum-brine-carbonate interfaces.

Wettability control of carbonates is a central concept for enhanced petroleum recovery, but a mechanistic understanding of the associated molecular-scale chemical processes remains unclear. We directly probe the interface of calcium carbonate (calcite) with natural petroleum oil, synthetic petroleum analogues, and aqueous brines to understand the molecular scale behavior at this interface. The calcite-petroleum interface structure is similar whether or not calcite was previously exposed to an aqueous brine, and is characterized by an adsorbed interfacial layer, significant structural changes within the calcite surface, and increased surface roughness.

Direct recovery of interfacial topography from coherent X-ray reflectivity: model calculations for a 1D interface.

The use of coherent X-ray reflectivity to recover interfacial topography is described using model calculations for a 1D interface. The results reveal that the illuminated topography can be recovered directly from the measured reflected intensities. This is achieved through an analysis of the Patterson function, the Fourier transform of the scattering intensity (as a function of lateral momentum transfer, Q, at fixed vertical momentum transfer, Q).

Nonclassical Behavior in Competitive Ion Adsorption at a Charged Solid-Water Interface.

Ion adsorption at solid-water interfaces is commonly described by interactions between specific surface sites and adsorbed ions in classical models. However, energetic contributions from non-site-specific ion-ion interactions have been less well understood. Here, we report nonclassical behaviors observed during competitive adsorption between Sr and Na/Rb at the negatively charged muscovite mica (001)-water interface, revealing apparent controls of adsorbed ion speciation over the interfacial reactivity.

Oxidation induced strain and defects in magnetite crystals.

Oxidation of magnetite (FeO) has broad implications in geochemistry, environmental science and materials science. Spatially resolving strain fields and defect evolution during oxidation of magnetite provides further insight into its reaction mechanisms. Here we show that the morphology and internal strain distributions within individual nano-sized (~400 nm) magnetite crystals can be visualized using Bragg coherent diffractive imaging (BCDI).

Mechanistic understanding of tungsten oxide in-plane nanostructure growth via sequential infiltration synthesis.

Tungsten oxide (WO) nanostructures with hexagonal in-plane arrangements were fabricated by sequential infiltration synthesis (SIS), using the selective interaction of gas phase precursors with functional groups in one domain of a block copolymer (BCP) self-assembled template. Such structures are highly desirable for various practical applications and as model systems for fundamental studies. The nanostructures were characterized by cross-sectional scanning electron microscopy, grazing-incidence small/wide-angle X-ray scattering (GISAXS/GIWAXS), and X-ray absorption near edge structure (XANES) measurements at each stage during the SIS process and subsequent thermal treatments, to provide a comprehensive picture of their evolution in morphology, crystallography and electronic structure.

Real-time observation of cation exchange kinetics and dynamics at the muscovite-water interface.

Ion exchange at charged solid-liquid interfaces is central to a broad range of chemical and transport phenomena. Real-time observations of adsorption/desorption at the molecular-scale elucidate exchange reaction pathways. Here we report temporal variation in the distribution of Rb species at the muscovite (001)-water interface during exchange with Na.

Reversible Li-Ion Conversion Reaction for a TiGe Alloy in a Ti/Ge Multilayer.

Group IV intermetallics electrochemically alloy with Li with stoichiometries as high as LiM (M = Si, Ge, Sn, or Pb). This provides the second highest known specific capacity (after pure lithium metal) for lithium-ion batteries, but the dramatic volume change during cycling greatly limits their use as anodes in Li-ion batteries. We describe an approach to overcome this limitation by constructing electrodes using a Ge/Ti multilayer architecture.