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Phenol, a common semi-volatile compound associated with different emissions including from plants and biomass burning, as well as anthropogenic emissions and its derivatives, are important components of secondary organic aerosols (SOAs). Gas and aqueous phase reactions of phenol, in the presence of photochemical drivers, are fairly well understood. However, despite observations showing aromatic content within SOA size and mass increases during dust episodes, the heterogeneous reactions of phenol with mineral dusts are poorly understood. In the current study, surface reactions of phenol at the gas/solid interface with different components of mineral dust including SiO2, α-Fe2O3, and TiO2 have been investigated. Whereas reversible surface adsorption of phenol occurs on SiO2 surfaces, for both α-Fe2O3 and TiO2 surfaces, phenol reacts to form a wide range of OH substituted aromatic products. For α-Fe2O3 surfaces that have been nitrated by gas-phase reactions of nitric acid prior to exposure to phenol, unique compounds form on the surface including nitro-phenolic compounds. Moreover, additional surface chemistry was observed when adsorbed nitro-phenolic products were exposed to gas-phase SO2 as a result of the formation of adsorbed nitrite from nitrate redox chemistry with adsorbed SO2. Overall, this study reveals the extensive chemistry as well as the complexity of reactions of prevalent organic compounds leading to the formation of SOA on mineral surfaces.

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Organonitrates (ON) and nitroxy-organosulfates (NOS) are important components of secondary organic aerosols (SOAs). Gas-phase reactions of α-pinene (C10H16), a primary precursor for several ON compounds, are fairly well understood although formation pathways for NOS largely remain unknown. NOS formation may occur via reactions of ON and organic peroxides with sulfates as well as through radical-initiated photochemical processes. Despite the fact that organosulfates (OS) represent a significant portion of the organic aerosol mass, ON and NOS formation from OS is less understood, especially through nighttime heterogeneous and multiphase chemistry pathways. In the current study, surface reactions of adsorbed α-pinene-derived OS with nitrogen oxides on hematite and kaolinite surfaces, common components of mineral dust, have been investigated. α-Pinene reacts with sulfated mineral surfaces, forming a range of OS compounds on the surface. These OS compounds when adsorbed on mineral surfaces can further react with HNO3 and NO2, producing several ON and NOS compounds as well as several oxidation products. Overall, this study reveals the complexity of reactions of prevalent organic compounds leading to the formation of OS, ON, and NOS via heterogeneous and multiphase reaction pathways on mineral surfaces. It is also shown that this chemistry is mineralogy-specific.

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The fate of biomolecules in the environment depends in part on understanding the surface chemistry occurring at the biological-geochemical (bio-geo) interface. Little is known about how environmental DNA (eDNA) or smaller components, like nucleotides and oligonucleotides, persist in aquatic environments and the role of surface interactions. This study aims to probe surface interactions and adsorption behavior of nucleotides on oxide surfaces. We have investigated the interactions of individual nucleotides (dGMP, dCMP, dAMP, and dTMP) on TiO2 particle surfaces as a function of pH and in the presence of complementary and noncomplementary base pairs. Using attenuated total reflectance-Fourier transform infrared spectroscopy, there is an increased number of adsorbed nucleotides at lower pH with a preferential interaction of the phosphate group with the oxide surface. Additionally, differential adsorption behavior is seen where purine nucleotides are preferentially adsorbed, with higher surface saturation coverage, over their pyrimidine derivatives. These differences may be a result of intermolecular interactions between coadsorbed nucleotides. When the TiO2 surface was exposed to two-component solutions of nucleotides, there was preferential adsorption of dGMP compared to dCMP and dTMP, and dAMP compared to dTMP and dCMP. Complementary nucleotide base pairs showed hydrogen-bond interactions between a strongly adsorbed purine nucleotide layer and a weaker interacting hydrogen-bonded pyrimidine second layer. Noncomplementary base pairs did not form a second layer. These results highlight several important findings: (i) there is differential adsorption of nucleotides; (ii) complementary coadsorbed nucleotides show base pairing with a second layer, and the stability depends on the strength of the hydrogen bonding interactions and; (iii) the first layer coverage strongly depends on pH. Overall, the importance of surface interactions in the adsorption of nucleotides and the templating of specific interactions between nucleotides are discussed.

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Uranium-bearing respirable dust can cause various health problems, such as cardiovascular and neurological disorders, cancers, immunosuppression, and autoimmunity. Exposure to elevated levels of uranium is linked to many such health conditions in Navajo Nation residents in northwestern New Mexico. Most studies have focused on the fate of inhaled dust particles (<4 µm) in the lungs. However, larger-sized inhaled particles (10-20 µm) can be cleared to the human gastrointestinal tract (GIT), thereby enabling them to interact with stomach and intestinal fluids. Despite the vital importance of understanding the fate of uranium-bearing solids entering the human GIT and their impact on body tissues, cells, and gut microbiota, our understanding remains limited. This study investigated uranium solubility from dust and sediment samples collected near two uranium mines in the Grants Mining District in New Mexico in two simulated gastrointestinal fluids representing fasting conditions in the GIT: Simulated Gastric Fluid (SGF) and Simulated Intestinal Fluid (SIF). The dissolution of uranium from dust depends on its mineralogy, fluid pH, and composition. The dust samples from the Jackpile mine favored higher solubility in the SIF solution, whereas the sediment samples from the St. Anthony Mine favored higher solubility in the SGF solution. Further, geochemical calculations performed with the PHREEQC modeling program suggested that samples rich in the minerals andersonite, tyuyamunite, and/or autunite have higher uranium dissolution in the SIF solution than in the SGF solution. We also tested the effect of added kaolinite and microcline, which are both present in some samples. The ratio of dissolved uranium in SGF relative to SIF decreases with the addition of kaolinite for all mineral phases but andersonite. With the addition of microcline, the ratio of dissolved uranium in SGF relative to SIF decreases for all the tested uranium minerals. The most prevalent oxidation state of dissolved uranium was computationally determined as +6, U(VI). The geochemical calculations made with PHREEQC agree with the experimentally observed results. Therefore, this study gives insight into the mineralogy-controlled toxicological assessment of uranium-containing inhaled dust cleared to the gastrointestinal tract.

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Organonitrates (ON) are important components of secondary organic aerosols (SOAs). α-Pinene (C10H16), the most abundant monoterpene in the troposphere, is a precursor for the formation of several of these compounds. ON from α-pinene can be produced in the gas phase via photochemical processes and/or following reactions with oxidizers including hydroxyl radical and ozone. Gas-phase nitrogen oxides (NO2, NO3) are N sources for ON formation. Although gas-phase reactions of α-pinene that yield ON are fairly well understood, little is known about their formation through heterogeneous and multiphase pathways. In the current study, surface reactions of α-pinene with nitrogen oxides on hematite (α-Fe2O3) and kaolinite (SiO2Al2O3(OH)4) surfaces, common components of mineral dust, have been investigated. α-Pinene oxidizes upon adsorption on kaolinite, forming pinonaldehyde, which then dimerizes on the surface. Furthermore, α-pinene is shown to react with adsorbed nitrate species on these mineral surfaces producing multiple ON and other oxidation products. Additionally, gas-phase oxidation products of α-pinene on mineral surfaces are shown to more strongly adsorb on the surface compared to α-pinene. Overall, this study reveals the complexity of reactions of prevalent organic compounds such as α-pinene with adsorbed nitrate and nitrogen dioxide, revealing new heterogeneous reaction pathways for SOA formation that is mineralogy specific.

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Chemical contaminants are becoming an increasingly greater concern for water quality and it is well known that interactions with geochemical interfaces impact the fate and transport of these contaminants in the environment. In this study, we investigated the interactions of one such chemical contaminant, monoethanolamine (MEA), with oxide surfaces, particularly titanium dioxide (TiO2) and iron oxide (α-Fe2O3). Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to probe the adsorption behavior of MEA on titanium dioxide (TiO2) and iron oxide (α-Fe2O3) nanoparticles as a function of pH and other environmental conditions including concentration and ionic strength. Both the extent and initial rates of adsorption of MEA on these oxide surfaces increases with increasing pH. Adsorption on these oxide surfaces increases with solution concentration until saturation occurs and MEA adsorbs more readily at higher pH. Furthermore, adsorption decreases with increasing ionic strength, demonstrating the importance of electrostatic interactions to this process. Based on these results, a mechanistic picture emerges for the interaction of MEA with titanium dioxide and iron oxide across a range of pH values. Overall, this study provides important insights into the surface chemistry and interactions between an alkanolamine and geochemical oxide interfaces.

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Iron (Fe) is a growth-limiting micronutrient for phytoplankton in major areas of oceans and deposited wind-blown desert dust is a primary Fe source to these regions. Simulated atmospheric processing of four mineral dust proxies and two natural dust samples followed by subsequent growth studies of the marine planktic diatom Cyclotella meneghiniana in artificial sea-water (ASW) demonstrated higher growth response to ilmenite (FeTiO3) and hematite (α-Fe2O3) mixed with TiO2 than hematite alone. The processed dust treatment enhanced diatom growth owing to dissolved Fe (DFe) content. The fresh dust-treated cultures demonstrated growth enhancements without adding such dissolved Fe. These significant growth enhancements and dissolved Fe measurements indicated that diatoms acquire Fe from solid particles. When diatoms were physically separated from mineral dust particles, the growth responses become smaller. The post-mineralogy analysis of mineral dust proxies added to ASW showed a diatom-induced increased formation of goethite, where the amount of goethite formed correlated with observed enhanced growth. The current work suggests that ocean primary productivity may not only depend on dissolved Fe but also on suspended solid Fe particles and their mineralogy. Further, the diatom C. meneghiniana benefits more from mineral dust particles in direct contact with cells than from physically impeded particles, suggesting the possibility for alternate Fe-acquisition mechanism/s.

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Charge-separated metal-organic frameworks (MOFs) are a unique class of MOFs that can possess added properties originating from the exposed ionic species. A new charge-separated MOF, namely, UNM-6 synthesized from a tetrahedral borate ligand and Co2+ cation is reported herein. UNM-6 crystalizes into the highly symmetric P43n space group with fourfold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO3 - anions within the crystal structure. These NO3 - ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co2+ ) and Lewis base (anions) pairs within the pores and potentially cooperative catalytic activities. For example, UNM-6-Br, the MOF after anion exchange with Br- anions, displays high catalytic activity and stability in reactions of CO2 chemical fixation into cyclic carbonates.

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The recent increase in cardiovascular and metabolic disease in the Navajo population residing close to the Grants Mining District (GMD) in New Mexico is suggested to be due to exposure to environmental contaminants, in particular uranium in respirable dusts. However, the chemistry of uranium-containing-dust dissolution in lung fluids and the role of mineralogy are poorly understood, as is their impact on toxic effects. The current study is focused on the dissolution of xcontaining-dust, collected from several sites near Jackpile and St. Anthony mines in the GMD, in two simulated lung fluids (SLFs): Gamble's solution (GS) and Artificial Lysosomal Fluid (ALF). We observe that the respirable dust includes uranium minerals that yield the uranyl cation, UO2 2+, as the primary dissolved species in these fluids. Dust rich in uraninite and carnotite is more soluble in GS, which mimics interstitial conditions of the lungs. In contrast, dust with low uraninite and high kaolinite is more soluble in ALF, which simulates the alveolar macrophage environment during phagocytosis. Moreover, geochemical modeling, performed using PHREEQC, is in good agreement with our experimental results. Thus, the current study highlights the importance of site-specific toxicological assessments across mining districts with the focus on their mineralogical differences.

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We report the synthesis, characterization, and gas adsorption analyses of a new charge-separated metal-organic framework (MOF), UNM-1 (C52H16BCuF16N4), possessing diamondoid structures, assembled from an anionic tetrahedral borate ligand and cationic Cu(i) metal ion. The resulting MOF structure displays four-fold interpenetration, resulting in high environmental stability, and at the same time possesses relatively large surface area (SABET = 621 m2 g-1) due to the absence of free ions. Gas adsorption measurements revealed temperature-dependent CO2 adsorption/desorption hysteresis and large CO2/N2 ideal selectivities up to ca. 99 at 313 K and 1 bar, suggesting potential applications of this type of charge-separated MOFs in flue gas treatment and CO2 sequestration.

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Over the last several decades, iron has been identified as a limiting nutrient in about half of the world's oceans. Its most significant source is identified as deposited iron-containing mineral dust that has been processed during atmospheric transportation. The current work focuses on chemical and photochemical processing of iron-containing mineral dust particles in the presence of nitric acid, and an organic pollutant dimethyl sulfide under atmospherically relevant conditions. More importantly, ilmenite (FeTiO3) is evaluated as a proxy for the iron-containing mineral dust. The presence of titanium in its lattice structure provides higher complexity to mimic mineral dust, yet it is simple enough to study reaction pathways and mechanisms. Here, spectroscopic methods are combined with dissolution measurements to investigate atmospheric processing of iron in mineral dust, with specific focus on particle mineralogy, particle size, and their environmental conditions (i.e., pH and solar flux). Our results indicate that the presence of titanium elemental composition enhances iron dissolution from mineral dust, at least by 2-fold comparison with its nontitanium-containing counterparts. The extent of iron dissolution and speciation is further influenced by the above factors. Thus, our work highlights these important, yet unconsidered, factors in the atmospheric processing of iron-containing mineral dust aerosol.