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In surface and near-surface weathering environments, the mobilization and partial loss of palladium (Pd) under oxidizing and weakly acidic conditions has been attributed to aqueous chloride complexation. However, prior work has also observed that a portion of Pd is retained by iron (oxyhydr)oxides in the weathering zone. The effect chloride has on the relative amount of Pd mobilization versus retention by iron (oxyhydr)oxides is currently unclear. We studied the effect of chloride complexation on Pd(II) adsorption to two iron (oxyhydr)oxides, hematite and 2-line ferrihydrite, at pH 4. Increasing chloride concentration suppresses Pd adsorption for both hematite and ferrihydrite, which display similar binding affinities under the conditions studied. Thermodynamic modeling of aqueous Pd speciation indicates that greater suppression of binding to iron (oxyhydr)oxides should occur than is observed because of the strength of Pd-Cl complexation, implying that additional interactions at the mineral surface are counteracting this effect. While increasing dissolved chloride concentration does not measurably impact mineral surface charging, extended X-ray absorption fine structure (EXAFS) spectra indicate that ternary Pd-Cl surface complexes form on both hematite and ferrihydrite. The number of Cl ligands in the surface species increase at greater chloride concentration. A mixture of bidentate and monodentate surface species are indicated by the EXAFS spectra, although the fitting uncertainties precludes determining whether these vary in relative abundance with chloride concentration. In order to offset the effect of strong aqueous Pd-Cl complexation and align with our EXAFS results, a surface complexation model developed for Pd adsorption to hematite involves a mixture of three ternary surface complexes containing 1, 2, and 3 chloride ligands. Our results show that Pd is mobilized as a chloride complex in platinum group element-rich weathering zones. As a result, porewater chloride concentrations are thus a dominant control on Pd retention by iron (oxyhydr)oxides in these weakly acidic environments.

A comprehensive set of single-component and binary isotherms were collected for ethanol/water adsorption into the siliceous forms of 185 known zeolites using grand-canonical Monte Carlo simulations. Using these data, a systematic analysis of ideal/real adsorbed-solution theory (IAST/RAST) was conducted and activity coefficients were derived for ethanol/water mixtures adsorbed in different zeolites based on RAST. It was found that activity coefficients of ethanol are close to unity while activity coefficients of water are larger in most zeolites, indicating a positive excess free energy of the mixture. This observation can be attributed to water/ethanol interactions being less favorable than water/water interactions in the single-component adsorption of water at comparable loadings. The deviation from ideal behavior can be highly structure-dependent but no clear correlation with pore diameters was identified. Our analysis also demonstrates the following: (1) accurate unary isotherms in the low-loading regime are critical for obtaining physically sensible activity coefficients; (2) the global regression scheme to solve for activity model parameters performs better than fitting activity models to activity coefficients calculated locally at each binary state point; and (3) including the dependence on adsorption potential offers only a minor benefit for describing binary adsorption at the lowest fugacities. Finally, the Margules activity model was found incapable of capturing the non-ideal adsorption behavior over the entire range of fugacities and compositions in all zeolites, but for conditions typical of solution-phase adsorption, RAST predictions using zeolite-specific or even bulk Margules parameters provide an improved description compared to IAST.

Optimizing group-V doping and Se alloying are two main focuses for advancing CdTe photovoltaic technology. We report on nanometer-scale characterizations of microelectronic structures of phosphorus (P)-doped CdSeTe devices using a combination of two atomic force microscopy-based techniques, namely, Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). KPFM on device cross-section images distribution of the potential drop across the device. SSRM taken on a delaminated front interface and further beveling into absorber bulk reveals local distributions of doping polarity and carrier concentration. The KPFM and SSRM imaging corroborate each other, suggesting that nonuniform doping revealed by SSRM is associated with nonuniform potential features observed by KPFM. These detrimental microelectronic structures were improved by enhancing P-doping. The large nonuniform potential drop and deep overall n–p transition in the device without doping were mitigated to potential fluctuation around the front interface and n–p transition depth of ~100 nm by low-level P-doping and further mitigated to scarce and slight irregular potential and p-weighed doping at the interface by high-level P-doping. These characterizations imply sophisticated defect chemistry, atomic structure, and associated electronic structure in CdTe with Se alloying and group-V doping together and further point to the direction for improving device efficiency by mitigating and ultimately eliminating the nonuniform doping and irregular potential.

Noble gas transport through geologic media has important applications in the prediction and characterization of measured gas signatures related to underground nuclear explosions (UNEs). Retarding processes such as adsorption can cause significant species fractionation of radionuclide gases, which has implications for measured and predicted signatures used to distinguish radioxenon originating from civilian nuclear facilities or from UNEs. Accounting for the effects of variable water saturation in geologic media on tracer transport is one of the most challenging aspects of modeling gas transport because there is no unifying relationship for the associated tortuosity changes between different rock types, and reactive transport processes such as adsorption that are affected by the presence of water likewise behave differently between gas species. In this study, we perform numerical diffusive-adsorptive transport simulations to estimate gas transport parameters associated with bench-scale laboratory diffusion cell experiments measuring breakthrough in zeolitic and non-zeolitic rocks for a gaseous mixture of xenon, krypton, and SF₆ at varying degrees of water saturation (S_w ). Counter-intuitive transport behavior was observed in the zeolitic rock experiments whereby breakthrough concentrations were significantly higher when the core was partially saturated (S_w = 17 %) than under dry (S_w = 0 %) conditions. Breakthrough of xenon was especially retarded in the dry core – likely due to comparatively high affinity of xenon for zeolitic adsorption sites – and estimated effective diffusion coefficients for all gases were approximately an order of magnitude lower than what is predicted by porosity-tortuosity models. We propose the counter-intuitive behavior observed is because water infiltration of zeolite nanopores reduces both the adsorptive capacity of the rock and the tortuosity of connected flow paths. We developed a two-site competitive kinetic Langmuir adsorption reaction for the porous media transport simulator in order to constrain transport parameters within zeolitic tuff, where differential adsorption to zeolite and non-zeolite pores was observed. We determined that liquid saturation-dependent diffusive-adsorptive transport is affected by subtle and at times competing processes that are specific to different gases, which have a significant overall influence on effective transport parameters.

Designing catalysts with well-defined active sites with chemical functionality responsive to visible light has significant potential for overcoming scaling relations limiting chemical reactions over heterogeneous catalyst surfaces. Visible light can be leveraged to facilitate the removal of strongly bound species from well-defined single cationic sites (Rh) under mild conditions (323 K) when they are incorporated within a photoactive perovskite oxide (Rh-doped SrTiO₃). CO, a key intermediate in many chemistries, forms stable geminal dicarbonyl Rh complexes (Rh⁺(CO)₂), that could act as site blockers or poisons during a catalytic cycle. For the first time, we demonstrate that CO removal can occur at mild temperatures (323 K) under low-energy red light (635 nm) irradiation, which is not possible for supported isolated-site Rh catalysts (0.2 wt % Rh/γ-Al₂O₃). Photolysis of supported Rh⁺(CO)₂ complexes (e.g., 0.2 wt % Rh/γ-Al₂O₃) has been demonstrated but is limited to high energy UV photons. Rigorous kinetic experiments elucidate disparate mechanisms for CO photodepletion from Rh-doped SrTiO₃ and supported isolated site Rh/γ-Al₂O₃. CO photodepletion from supported isolated site Rh/γ-Al₂O₃ involves a direct metal to ligand charge transfer mechanism, whereas Rh-doped SrTiO₃ is governed by electron–hole pair formation in the perovskite. We show that under visible, low-energy red light, surface Rh species in Rh-doped SrTiO₃ introduce midgap energy states above the valence band that facilitate electronic excitations leading to surface CO removal. Isolated Rh sites in Rh-doped SrTiO₃ also exhibit exceptional stability under multiple CO photodepletion cycles. Altogether, incorporating single sites into photoactive perovskite oxides is an effective strategy to influence surface chemistries with visible light.

Porous adsorbents are a promising class of materials for the direct air capture of CO₂ (DAC). Practical implementation of adsorption-based DAC requires adsorbents that can be used for thousands of adsorption–desorption cycles without significant degradation. We examined the potential degradation of adsorbents by a mechanism that appears to have not been considered previously, namely, ozonolysis by trace levels of ozone from ambient air. We focused on amine-appended metal–organic frameworks, specifically amine-functionalized Mg₂(dobpdc), as a representative DAC adsorbent. Estimates based on the number of amine sites in these adsorbents and the ozone concentration in air suggest that degradation by ozone may be relevant over thousands of adsorption–desorption cycles if reactions with adsorbed ozone are fast. We used density functional theory calculations to estimate reaction rates for amine groups and carbon–carbon double bonds in amine-functionalized Mg2(dobpdc).

Carbon dioxide removal (CDR) technologies will play a significant role in limiting global warming if implemented on a large scale. Direct air capture (DAC) is a scalable approach for removing atmospheric carbon, yet the true scope of its scalability remains unclear due to the early stage of technology development and high first plant costs. This study provides groundwork for understanding the technoeconomic trade-offs in developing DAC systems using laminate-structured gas–solid contactors, encompassing the analysis of both contactor and process design spaces. The robust mass transfer and process models outlined in this study provide tools for evaluating DAC processes and designing DAC plants based on cost and energy analysis. First, the key contactor geometrical parameters are identified to understand the CO₂ productivity–energy demand trade-offs, where geometries yielding higher mass transfer rates can achieve higher CO₂ productivities at the expense of energy consumption by fans and steam use. Next, a detailed process parametric study is conducted for DAC systems coupled with steam-assisted temperature-vacuum swing adsorption (S-TVSA) to visualize the trade-offs in the multidimensional design space. The main cost driver dramatically changes over different process conditions, but the operating cost prevailed on the Pareto front, with potential to operate as low as 150 $/tonne-CO₂ (within the cost range of 148–504 $/tonne-CO₂ in this study where the DAC system is coupled with industrial facilities for steam production).

Scaling minerals, such as barite, can cause detrimental consequences for oil/gas pipelines and water systems, but their formation can be inhibited by organic chelators such as ethylenediaminetetraacetic acid (EDTA). Here, we resolve how EDTA affects sorption and desorption of Pb at the barite (001) surface using a combination of X-ray scattering and microscopy measurements. In the presence of EDTA, Pb incorporated in the topmost part of the barite surface and adsorbed as inner-sphere complexes on the surface. In barite saturated solutions containing [Pb] ≥ 100 μM, overgrowth films grew along step edges. These films were exclusively monolayer thick, indicating that their growth was a self-limiting process. Approximately half of the Pb was removed after 14.5 h reaction with a Pb-free EDTA solution where most of the desorption occurred to adsorbed Pb rather than incorporated Pb. Dissolution proceeded primarily via step retreat and etch pit formation in EDTA, but in deionized water, the secondary phase was quickly removed within 3 min. Together these results suggest EDTA binds to both the surface and Pb in solution, which limits Pb sorption. However, EDTA binding to the surface also inhibits removal of the secondary phase that formed at higher Pb concentrations.

Self-assembled organic nanotubes (ONTs) have been actively examined for various applications such as chemical separations and catalysis owing to their well-defined tubular nanostructures with distinct chemical environments at the wall and internal/external surfaces. Adsorption of heavy metal ions onto ONTs plays an essential role in many of these applications, but it has rarely been assessed quantitatively. Herein, we investigated interactions between Cu²⁺ and single-/quadruple-wall bolaamphiphile-based ONTs having inner carboxyl groups with different inner diameters, COOH-ONT_10nm and COOH-ONT_20nm. We first examined the effects of Cu²⁺ on their nanotubular structures using SAXS, STEM, and AFM. COOH-ONT_10nm was stable in aqueous Cu²⁺ solution in contrast to COOH-ONT_20nm owing to the presence of polyglycine-II-type hydrogen bonding networks within its wall. Subsequently, we studied the Cu²⁺ adsorption behavior of COOH-ONT_10nm by monitoring the concentration of unbound Cu²⁺ using linear sweep anodic stripping voltammetry. The Cu²⁺ adsorption was quick, attributable to efficient Cu²⁺ partitioning through the open ends of the ONT, followed by fast Cu²⁺ diffusion in the uniform, relatively large nanochannel. More importantly, the Cu²⁺ adsorption capacity and affinity of COOH-ONT_10nm were measured at different pH using the Langmuir adsorption model. The adsorption capacity was similar at the pH range examined, showing the participation of approximately 25% of the inner carboxyl groups in the adsorption. The adsorption affinity increased with pH, indicating the essential role of the deprotonated carboxyl groups in the Cu²⁺ adsorption. Most interestingly, the Langmuir adsorption constant was significantly higher than those of previously reported synthetic adsorbents and planar monolayer based on carboxyl binding sites. The high Cu²⁺ affinity of the ONT was attributable to the highly dense binding sites on the well-defined nanoscale concave structure of the inner channel. Furthermore, these results provide a valuable guideline to designing self-assembled nanomaterials for efficient chemical separations, detection, and catalysis.

In this report, we describe the photoluminescence of a homoleptic uranium(IV) alkoxide complex. Excitation of [Li(THF)]₂[U^IV(O^tBu)₆] leads to the first example of photoluminescence from a well-defined actinide complex originating from an f–f excitation, supported by second order multiconfigurational electronic structure calculations including spin–orbit coupling. These calculations show strong spin–orbit coupling between the excited triplet and singlet states for the 5f-orbital manifold, which leads to a long-lived excited state lifetime of 0.85 s at low temperature. The photophysical properties of homoleptic uranium(V) and uranium(VI) tertbutoxide complexes are also presented; we find that oxidation of the uranium(IV) alkoxide results in quenching of luminescence in [Li(THF)][U^V(O^tBu)₆] and [U^VI(O^tBu)₆]. This is attributed to competing ligand to metal charge transfer absorption processes shifted to lower energy upon oxidation of the actinide center, which mask the relevant f–f transitions in the visible region of the electronic absorption spectrum.