Duo Song

Results of first-principles simulations of aqueous solution layers (with and without reactiveFeaq2+) adsorbed on the protonated (001) and (012) crystal surfaces of hematite (Fe2O3) are presented. PBE+U calculations show that the ground-state magnetic structures of both surfaces remain consistent with the bulk antiferromagnetic ordering and that the stable terminations are O-terminated. With these terminations, the calculated interlayer spacings in the bulk just beneath the surfaces agree with experiment to within 4.9%. AIMD simulations with spin order were performed using both PBE+U and SCAN gradient corrections. Results from the two methods are in semiquantitative agreement. At the hematite/water interfaces, the average OD···OA (donor oxygen to acceptor oxygen) distance for hydrogen bonds and the corresponding OD–H···OA angle are ∼2.8 Å and 158°, respectively, close to values in bulk water. The vibrational power spectrum indicates that interfacial water in our simulations exhibits a mixed liquid-like behavior and features of a more strongly hydrogen-bonded structure. The (001) surface structure is consistent with several CTR models, whereas for the (012) surface, the structure agrees with one of the CTR models but deviates from two others. The calculated distance between the first hydration layer and the outermost surface oxygen, however, is consistently larger than experimental estimates. This reveals significant discrepancies in the X-ray reflectivity measurements, likely due to unmodeled surface defects. For the (001) surface, the first-layer height is 2.59 Å by PBE+U and 2.51 Å by SCAN, compared with an experimental value of 1.9 ± 0.6 Å. For the (012) surface, a single adsorbed water layer at 2.34 Å is found, whereas experimental studies report two absorbed water layers with the first located at ∼1.0 Å and the second between 1.4 Å and 2.6 Å from the surface. AIMD simulations of Fe2+ adsorption reveal distinct site preferences at the two hematite interfaces. On the (001) surface, the adsorbed Fe2+ achieves 6-fold coordination by forming three bonds with surface hydroxyl groups and three with water molecules, whereas on the (012) surface it bonds to only two hydroxyls and four water molecules. Projected density of states (PDOS) analysis shows that the energy gap between Fe2+ states and surface oxygen bands is ∼0.5 eV on the (001) surface but ∼1.5 eV on the (012) surface. The greater delocalization of the HOMO into the (001) surface, together with these PDOS features, suggests that absorption and electron transfer are more favorable on (001) than on (012), consistent with their surface magnetic structures.

Gibbsite (α-Al(OH)₃, sometimes designated as γ-Al(OH)₃) plays a crucial role in the chemistry of aluminum in the environment and industry, yet its crystallization behavior under multianionic conditions is not well understood. In this study, we investigate how six common anions─fluoride (F^-), chloride (Cl^-), bromide (Br^-), nitrate (NO₃^-), sulfate (SO₄^2-), and phosphate (PO₄^3-)─influence the mineralization, structure, and morphology of gibbsite at room temperature. The results show that PO₄^3-, SO₄^2-, and F^- strongly inhibit gibbsite formation, stabilizing amorphous or alternative crystalline phases such as nordstrandite and cryolite. On the contrary, Cl^-, Br^-, and NO₃^- allow partial to complete crystallization of gibbsite without significant morphological changes. Solid-state ²⁷Al magic angle spinning nuclear magnetic resonance provides crucial insight into aluminum coordination environments in both crystalline and amorphous phases, distinguishing between octahedral, pentahedral, and tetrahedral Al species. The density functional theory calculations reveal a direct correlation between the Al-X bond strength and the inhibition of crystallization, following the order: PO₄^3- > SO₄^2- > F^- > NO₃^- > Cl^- > Br^-. These findings offer molecular-scale insights into anion-specific effects on aluminum hydroxide nucleation and transformation, improving the understanding of gibbsite formation and aluminum cycling in soils, phosphate retention, contaminant immobilization, and waste treatment strategies in nuclear and industrial settings. These insights can also guide the controlled synthesis of aluminum hydroxide materials with tailored crystallinity and morphology via liquid-assisted methods.

Polymer additives [like polyethylene oxide (PEO)] are widely used for smooth electrode deposition in aqueous zinc and many other battery systems. However, the precise mechanism by which they regulate morphology and suppress dendrite formation remains unclear. In this study, the knowledge gap is addressed by using in situ electrochemical atomic force microscopy to directly observe the interfacial evolution during Zn electrodeposition and polymer adsorption on Cu substrates in the presence of varying concentrations of ZnSO ₄ and PEO. Contrary to previous literature assumptions, which emphasize the binding to the growing Zn crystal surfaces or Zn ²⁺ ions, the results demonstrate that PEO smooths Zn films by promoting nucleation of (002)‐oriented Zn platelets through interactions with the Cu substrate. Density functional theory simulations support this finding by showing that PEO adsorption on Cu modifies the interfacial energy of Zn/Cu/electrolyte interfaces, favoring the stabilization of Zn (002) on the Cu substrate, as well as confines Zn electrodeposition to a narrow near‐surface region. These findings elucidate a novel design principle for electrode smoothing, emphasizing the importance of substrate selection paired with polymer additives that exhibit an attractive interaction with the substrate but minimal interaction with growing crystals, offering a mechanistic perspective for improved battery performance.

This study demonstrates REE fractionation through structural incorporation into iron minerals, like goethite, and the underlying physical mechanism.

Hematite's common (001) and (012) facets are frequently used in model studies of lead (Pb) adsorption behavior, but there is a lack of research on the high-energy facets, e.g., (104), present in nature. Also, few studies have attempted to connect the molecular details of facet-specific Pb adsorption to the macroscopic uptake behavior. To address these knowledge gaps, we investigated Pb(II) adsorption behaviors on facet-engineered hematite nanoparticles dominated by (001), (104), and (116). Adsorption experiments revealed significant variations in Pb(II) uptake among the three samples, with (001) demonstrating the highest capacity and (116) showing the best adsorption efficiency when normalized to the specific surface area. Adsorption kinetics followed the pseudo-second-order model, indicating that the adsorption process is governed mostly by chemisorption. Adsorption isotherms were well fitted by the Langmuir model, indicating that uptake proceeds until roughly monolayer adsorption. Detailed characterization revealed Pb(II) was adsorbed as single atoms with complex inner-sphere binding modes that varied across different facets, indicating that adsorption is both structurally and energetically facet-dependent. Coadsorption experiments further demonstrated Cu²⁺, Zn²⁺, and humic acid significantly promoted Pb(II) adsorption. This study advances the understanding of hematite surface reactivity in controlling macroscopic wet adsorption behaviors, providing valuable insights into the environmental fate of Pb(II).

Iron oxide minerals regulate the flux of electrons in the environment and are important hosts for trace and minor, yet critical, elements. Here, we present the first evidence of a direct link between the local coordination environments of Ni and Zn and the redox properties of their host phase goethite (α-FeOOH), the most abundant Fe(III) (oxyhydr)oxide at Earth's surface. We used aqueous redox measurements to show that the redox potential E_H⁰, and hence the mineral's stability, follows the order: pure goethite ≥ Zn-goethite > Ni-goethite. Parallel X-ray absorption and scattering measurements demonstrate, using quantum-informed analysis, that the local coordination environment of the smaller impurity, Ni, causes more bulk strain energy than Zn, which nearly accounts for the difference in E_H⁰ between Ni- and Zn-goethite. Our theory-informed, experimental study reveals how two common impurities affect the stability of goethite with implications for the biogeochemical reactivity of Fe(III) (oxyhydr)oxide in mediating elemental and electron fluxes in the environment.

New technologies in chemical separations are urgently needed to meet the surging demand for critical materials that has strained supply chains and threatened environmental damage. Here we propose a paradigm for separations via reaction-diffusion coupling, demonstrating broad applicability to unconventional feedstocks. Using this approach, we separate iron, neodymium, and dysprosium ions from model feed stocks of permanent magnets, which are typically found in electronic wastes. Feedstock solutions were placed in contact with a hydrogel loaded with potassium hydroxide and/or dibutyl phosphate, resulting in complex precipitation patterns as the various metal ions diffused into the reaction medium. Specifically, we observed the precipitation of up to 40 mM of iron from the feedstock, followed by the enrichment of 73% dysprosium, and the extraction of >95% neodymium product at a further distance from the solution-gel interface. We designed a series of experiments and simulations to determine the relevant ion diffusivities, DNd = 5.4×10-10 and DDy = 5.1×10-10 m2/s, and precipitation rates, kNd = 1.0×10-5 and kDy = = 5.0×10-3 m9mol-3s-1, which enabled a numerical model to be established for predicting the distribution of products in the reaction medium. Our proof-of-concept study validates reaction-diffusion coupling as an effective and versatile approach for critical materials separations, without relying on ligands, membranes, resins, or other specialty chemicals.