Facet-dependent Heterogeneous Fenton Reaction Mechanisms on Hematite Nanoparticles for (Photo)catalytic Degradation of Organic Dyes.

Although heterogeneous photo-Fenton reactions on nanoparticulate iron oxides effectively degrade organic pollutants, the underlying surface mechanisms remain debated. Here, we demonstrate how these pathways are modulated by specific hematite crystal facets. To investigate the influence of particle surface structure, methylene blue (MB) adsorption and photodegradation kinetics are examined using facet-engineered hematite nanoparticles with distinct exposed facets.

Structure and Dynamics of Water and Ions at Quartz (101) and (001) Surfaces under Applied Electric Fields from Molecular Simulations.

Electrical double layer (EDL) models are commonly adopted as a framework for understanding electrokinetic properties at mineral-fluid interfaces but the dynamics of ion and water mobilities are typically not well known. Extending the previous work performed at equilibrium conditions, here it is examined how applied electric fields induce mobilities of monovalent and divalent ions at hydroxylated quartz (001) and (101) interfaces with various electrolyte solutions (NaCl, KCl, and CaCl). The simulations reveal how the diffusion coefficients depend on the orientation and magnitude of the applied electric field, with a particularly strong effect for fields applied parallel to the quartz surfaces.

Vibrational sum frequency generation spectroscopy reveals the inertness of chromium oxide (001) surfaces.

Nanoengineered metal oxides such as Cr(III)-oxide (chromia) films have diverse potential applications in corrosion inhibition, remediation, energy generation, catalysis, data storage, and biological and environmental systems. Concerns about material degradation or oxidation to toxic chromate necessitate an understanding of chromia/aqueous interfaces, beginning with their hydroxylation and hydration behavior. Vibrational sum-frequency generation spectroscopy (vSFG) provides specific molecular-level information about water at the oxide/aqueous junction with high surface selectivity.

Rapid Screening of Single-Atom Catalyst Synthesis Conditions Using ToF-SIMS and Facet-Dependent Single-Crystal Substrates.

Single-atom catalysts (SACs) offer superior catalytic performance compared with traditional nanoparticle catalysts but are challenging to develop because of the need for extensive optimization and specialized characterization techniques. This study presents a rapid and versatile method for detecting synthesis conditions and elucidating the deposition mechanisms of SACs on various substrates. By depositing active elements (Au, Cu, Ni, and Rh) on facet-specific single-crystalline substrates (CeO, TiO, MgO, and AlO) and employing time-of-flight secondary ion mass spectroscopy (ToF-SIMS), we assessed facet-dependent deposition behaviors and identified optimal conditions for solution-based SAC synthesis.

Facet-Dependent Adsorption of Pb(II) on Hematite (001), (116), and (104) Surfaces.

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.

Single rhenium atoms on nanomagnetite: Probing the recharge process that controls the fate of rhenium in the environment.

Understanding the redox transitions that control rhenium geochemistry is central to paleoredox and geochronology studies, as well as predicting the fate of chemically similar hazardous oxyanions in the environment such as pertechnetate. However, detailed mechanistic information regarding rhenium redox transitions in anoxic systems is scarce. Here, we performed a comprehensive laboratory study of rhenium redox transitions on variably oxidized magnetite nanoparticle surfaces.

Carbon-Mediated Oxygen Vacancy Creation at Hematite Interfaces.

Nanoscale iron oxides (e.g., hematite (α-FeO)) have unique properties, such as enhanced chemical reactivity and high surface area, when compared with their bulk counterparts.

Boosting Hydrogenation of CO Using Cationic Cu Atomically Dispersed on 2D γ-AlO Nanosheets.

The continuous development of novel catalytic approaches is crucial for advancing efficient CO hydrogenation processes. Drawing inspiration from single-atom catalysis and 2D materials, we designed a new 2D single-atom catalyst with excellent thermal stability by thermally treating Cu-adsorbed γ-AlOOH nanosheets, which yielded a Cu/γ-AlO catalyst with high activity in the hydrogenation of CO-yielding methanol (CHOH), dimethyl ether (DME), and CO as products. The active Cu sites are monodispersed and highly stable due to their cationic oxidation state and their substitution for pentacoordinated aluminum (Al) sites on particle surfaces.

Water flipping and the oxygen evolution reaction on FeO nanolayers.

Hematite photoanodes are promising for the oxygen evolution reaction, however, their high overpotential (0.5-0.6 V) for water oxidation and limited photocurrent make them economically unviable at present.

Impacts of Focused Ion Beam Processing on the Fabrication of Nanoscale Functionalized Probes.

Herein, we examine the impact of Ga ion kinetic energy and the target material type on the extent of ion implantation and structural damage in atomic force microscopy probes made of AlO and ZnO manufactured by focused ion beam using scanning transmission electron microscopy and energy-dispersive X-ray mapping. Penetration of Ga into the AlO lattice induced structural distortions and amorphization. For the ZnO probes, Ga is uniformly dispersed across the surface, resulting in the formation of distinct clusters.

Carbonation of MgO Single Crystals: Implications for Direct Air Capture of CO.

Direct air capture (DAC) may be feasible to remove carbon dioxide (CO) from the atmosphere at the gigaton scale, holding promise to become a major contributor to climate change mitigation. Mineral looping using magnesium oxide (MgO) is potentially an economical, efficient, and sustainable pathway to gigaton-scale DAC. The hydroxylation and carbonation of MgO determine the efficiency of the looping process, but their rates and mechanisms remain uncertain.

pH-dependent reactivity of water at MgO(100) and MgO(111) surfaces.

Facet-dependent surface charging of metal oxides in water dominates the ion transport behavior across the interface, in turn impacting many natural and industrial processes such as adsorption, the formation and stabilization of nanoparticle suspensions, corrosion, and heterogeneous catalysis. Here we investigated the pH-dependent surface chemistry of two low-index MgO single crystal surfaces, namely MgO(100) and MgO(111), using vibrational sum frequency generation (vSFG) spectroscopy. This allowed us to evaluate facet-dependent pH effects on the hydration and hydroxylation at the solid/aqueous interface and point-of-zero charge (PZC) values.

Mechanism of Fe(II) Chemisorption on Hematite(001) Revealed by Reactive Neural Network Potential Molecular Dynamics.

Atomic-scale understanding of important geochemical processes including sorption, dissolution, nucleation, and crystal growth is difficult to obtain from experimental measurements alone and would benefit from strong continuous progress in molecular simulation. To this end, we present a reactive neural network potential-based molecular dynamics approach to simulate the interaction of aqueous ions on mineral surfaces in contact with liquid water, taking Fe(II) on hematite(001) as a model system. We show that a single neural network potential predicts rate constants for water exchange for aqueous Fe(II) and for the exergonic chemisorption of aqueous Fe(II) on hematite(001) in good agreement with experimental observations.

Effect of Co Irradiation on Boehmite Dissolution in Caustic Solutions.

Here, we examine how radiation impacts the dissolution behavior of boehmite by subjecting dry nanoparticles of different sizes to Co γ radiation and subsequently analyzing their dissolution behavior in caustic solutions as a function of temperature. The measured kinetics show that irradiation with an amount 228.24 Mrad significantly slows the dissolution rate, particularly for smaller sizes at lower temperatures.

Mineral-associated organic matter is heterogeneous and structured by hydrophobic, charged, and polar interactions.

The formation of mineral-associated organic matter (MAOM) is a key phenomenon that may explain the slow turnover rates of carbon in soil organic matter (SOM). Despite this, important details pertaining to the structure and dynamics of MAOM remain unknown. In the present study, we use replica-exchange molecular dynamics simulations to gain insight into the structure of MAOM on the surface of prototypical phyllosilicate clay and Fe-oxide minerals, montmorillonite and goethite, fine-grained minerals that strongly impact soil carbon dynamics in temperate and tropical regions, respectively.

Understanding Trace Iron and Chromium Incorporation During Gibbsite Crystallization and Effects on Mineral Dissolution.

Incorporation of pollutants, e.g., heavy metals, or critical elements, e.

Machine learning the electric field response of condensed phase systems using perturbed neural network potentials.

The interaction of condensed phase systems with external electric fields is of major importance in a myriad of processes in nature and technology, ranging from the field-directed motion of cells (galvanotaxis), to geochemistry and the formation of ice phases on planets, to field-directed chemical catalysis and energy storage and conversion systems including supercapacitors, batteries and solar cells. Molecular simulation in the presence of electric fields would give important atomistic insight into these processes but applications of the most accurate methods such as ab-initio molecular dynamics (AIMD) are limited in scope by their computational expense. Here we introduce Perturbed Neural Network Potential Molecular Dynamics (PNNP MD) to push back the accessible time and length scales of such simulations.

Resolving intermediates during the growth of aluminum deuteroxide (Hydroxide) polymorphs in high chemical potential solutions.

Aluminum hydroxide polymorphs are of widespread importance yet their kinetics of nucleation and growth remain beyond the reach of current models. Here we attempt to unveil the reaction processes underlying the polymorphs formation at high chemical potential. We examine their formation in-situ from supersaturated alkaline sodium aluminate solutions using deuteration and time-resolved neutron pair distribution function analyses, which indicate the formation of individual Al(OD) layers as an intermediate particle phase.

Uncovering the Size-Dependent Thermal Solid Transformation of Akaganéite.

Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, in-situ heating techniques are employed in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite 1D nanostructures with varying diameters. These findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (γ-FeO) and subsequent crystal growth.

Anionic Effects on Concentrated Aqueous Lithium Ion Dynamics.

The dynamics, orientational anisotropy, diffusivity, viscosity, and density were measured for concentrated lithium salt solutions, including lithium chloride (LiCl), lithium bromide (LiBr), lithium nitrite (LiNO), and lithium nitrate (LiNO), with methyl thiocyanate as an infrared vibrational probe molecule, using two-dimensional infrared spectroscopy (2D IR), nuclear magnetic resonance (NMR) spectroscopy, and viscometry. The 2D IR, NMR, and viscosity results show that LiNO exhibits longer correlation times, lower diffusivity, and nearly 4 times greater viscosity compared to those of the other lithium salt solutions of the same concentration, suggesting that nitrite anions may strongly facilitate structure formation via strengthening water-ion network interactions, directly impacting bulk solution properties at sufficiently high concentrations. Additionally, the LiNO and LiNO solutions show significantly weakened chemical interactions between the lithium cations and the methyl thiocyanate when compared with those of the lithium halide salts.

Effect of impurities on radical formation in gibbsite radiolysis.

The generation and stabilization of gamma radiation-induced hydrogen atoms in gibbsite (Al(OH)) nanoplates is directly related to the nature of residual ions from synthetic precursors used, whether nitrates or chlorides. The concentration of hydrogen atoms trapped in the interstitial layers of gibbsite is lower and decays faster in comparison to boehmite (AlOOH), which could affect the management of these materials in radioactive waste.

Facet-dependent dispersion and aggregation of aqueous hematite nanoparticles.

Nanoparticle aggregates in solution controls surface reactivity and function. Complete dispersion often requires additive sorbents to impart a net repulsive interaction between particles. Facet engineering of nanocrystals offers an alternative approach to produce monodisperse suspensions simply based on facet-specific interaction with solvent molecules.

Development and application of hybrid AIMD/cDFT simulations for atomic-to-mesoscale chemistry.

Many important chemical processes involve reactivity and dynamics in complex solutions. Gaining a fundamental understanding of these reaction mechanisms is a challenging goal that requires advanced computational and experimental approaches. However, important techniques such as molecular simulation have limitations in terms of scales of time, length, and system complexity.

Photolysis of Dissolved Organic Matter over Hematite Nanoplatelets.

Solar photoexcitation of chromophoric groups in dissolved organic matter (DOM), when coupled to photoreduction of ubiquitous Fe(III)-oxide nanoparticles, can significantly accelerate DOM degradation in near-surface terrestrial systems, but the mechanisms of these reactions remain elusive. We examined the photolysis of chromophoric soil DOM coated onto hematite nanoplatelets featuring (001) exposed facets using a combination of molecular spectroscopies and density functional theory (DFT) computations. Reactive oxygen species (ROS) probed by electron paramagnetic resonance (EPR) spectroscopy revealed that both singlet oxygen and superoxide are the predominant ROS responsible for DOM degradation.