ACS Earth and Space Chemistry最新文献

{"title":"The Stability of Nd Hydroxyl Complexes at Near Neutral to Alkaline pH from 25 to 75 °C: Implications for Monazite Solubility in Hydrothermal Aqueous Fluids","authors":"Hannah J. Han,&nbsp;Alexander P. Gysi","doi":"10.1021/acsearthspacechem.5c00328","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.5c00328","url":null,"abstract":"<p>Speciation of rareearth elements (REE) in aqueous fluids controlstheir mobilization during fluid-rock interaction. Thermodynamic modelingprovides important insights into the factors controlling REE mobilityand fractionation in aqueous fluids, in which aqueous REE hydroxylcomplexes are particularly important across a broad pH range. However,the stability of these REE hydroxyl complexes remains poorly determineddue to limited experimental data above ambient temperature. In thiswork, UV–vis spectrophotometry experiments were conducted todetermine the cumulative hydrolysis constants for neodymium (Nd) from25 to 75 °C in near-neutral to alkaline solutions. The colorindicator <em>m</em>-cresol purple was used to determine <em>in situ</em> pH. Alkaline NaOH-bearing aqueous solutions weredoped with varying initial Nd concentrations (0 to ∼0.155 mmol/kg),which resulted in the release of protons (H⁺) and pH decreaseduring hydrolysis of Nd³⁺ according to Nd³⁺ + <em>n</em>H₂O = Nd(OH)_<em>n</em>³^{– <em>n</em>} + H⁺. The average OH^– ligand number coordinated toNd³⁺ was found to increase from 1.0 to 1.6 at 25 °Cand from 1.2 to 2.8 at 75 °C over a pH range from 6.3 to 9.0.The measured speciation shows an increased predominance of Nd(OH)₃⁰ over the Nd(OH)₂⁺ and Nd(OH)²⁺ species with increased temperature and pH. The increasingcumulative formation constants (log*β°_<em>n</em>, <em>n</em> = 1 to 3) retrieved from 25 to 75 °Cdiffer by 0.1 to 1.9 logarithmic units in comparison to existing thermodynamicdatabases. These updated thermodynamic data have important implicationsfor geochemical modeling of the speciation of Nd hydroxyl complexesand the solubility of monazite as a function of pH.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1832–1842"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiolytic Processing of CH4:CO2:NH3 Ices by Swift Heavy Ions: Coupled C–H–O-N Chemistry","authors":"Ana Lucia Ferreira de Barros,&nbsp;Yahia Murhej,&nbsp;Italo Prazeres,&nbsp;Davi Viana Doreste,&nbsp;Enio Frota da Silveira,&nbsp;Hermann Rothard,&nbsp;Alicja Domaracka","doi":"10.1021/acsearthspacechem.6c00104","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00104","url":null,"abstract":"<p>The chemical evolution of CH₄:CO₂:NH₃ astrophysical ice analogs was investigated underirradiationby 538 MeV ⁶⁴Ni²⁴⁺ ions at 14 K, simulatingthe effects of heavy cosmic rays in dense interstellar environments.Molecular changes were monitored <em>in situ</em> using Fouriertransform infrared (FTIR) spectroscopy. A progressive depletion ofthe precursor species was observed with increasing ion fluence, accompaniedby the formation of a diverse set of products, including CO, H₂O, C₂H₆, C₂H₄,CH₃OH, H₂CO, HCOOH, HCOO^–,OCN^–, and N₂O. The evolution of columndensities revealed an initial rapid growth phase followed by saturation,reflecting the competition between formation and destruction processes.Destruction and formation cross sections were derived assuming first-orderkinetics, and the corresponding radiochemical yields were determined.CO exhibited the highest formation yield, indicating that CO₂ dissociation is one of the dominant irradiation-induced processes,while the efficient production of CH₃OH, H₂CO,OCN^–, and N₂O demonstrated the simultaneousoperation of carbon-, oxygen-, and nitrogen-bearing reaction pathways.An atomic budget analysis indicated that a significant fraction ofdissociated atoms was not accounted for in the observed infrared-activespecies, suggesting the formation of more complex or refractory compounds.These findings demonstrate the key role of heavy-ion processing indriving chemical complexity in interstellar ices, promoting the formationof oxygen- and nitrogen-bearing organic species of astrochemical andprebiotic relevance.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1895–1912"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Behavior of Water-to-Air Trace Gas Exchange for Ammonia and Amines at Low Wind Speeds Using Chemical Ionization Mass Spectrometry","authors":"Christine Troller,&nbsp;Stephen D. Archer,&nbsp;Coty N. Jen","doi":"10.1021/acsearthspacechem.6c00080","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00080","url":null,"abstract":"<p>Ammonia (NH₃) and alkylamines play criticalroles inatmospheric aerosol chemistry, influencing cloud formation, Earth’sradiative balance, and air quality. Despite significant contributionsfrom water-based sources, associated emissions of ammonia and alkylaminesremain poorly characterized, especially in freshwater environments.As such, this lack of understanding complicates efforts to accuratelypredict ammonia and amine fluxes from aquatic sources. For example,the widely used two-film resistance model often leads to substantialmisestimation of these fluxes under low-wind conditions. Compoundingthis uncertainty, Henry’s Law, which is commonly applied tothese compounds, relies on published Henry’s Law constantsthat can differ by more than 2 orders of magnitude, further resultingin inaccurate modeling of the water-to-air transfer of these highlypolar gases. In this study, we experimentally investigate the real-timetrace gas exchange (i.e., flux) of ammonia and alkylamines in modelaqueous solutions (10^–9 to 10^–5 M) across the air–water interface using a custom flux measurementsystem (FMS) coupled with a hydronium chemical ionization mass spectrometer(CIMS). Carrier gas velocities ranged from 10^–4 to10^–3 m s^–1 to examine how lowwind speeds influence emission rates. Observed gas concentrationswithin the FMS headspace were compared to theoretical concentrationspredicted by the two-film resistance model and Henry’s Law.Our findings provide direct experimental evidence of ammonia and alkylaminegas exchange from aqueous systems in low wind conditions, helpingto constrain their emission behavior and refine our understandingof aquatic contributions to the atmosphere.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1843–1854"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kinetic and H Atom Product Study of the C + C6H6 Reaction at Low Temperatures","authors":"Kevin M. Hickson,&nbsp;Jean-Christophe Loison","doi":"10.1021/acsearthspacechem.6c00169","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00169","url":null,"abstract":"<p>The reactions of atomic carbon in its ground electronicstate configuration,C(³P), are potentially important processes in astrochemistrydue to the large abundance of C(³P) atoms in the interstellarmedium (ISM) and its high overall reactivity toward a wide range ofmolecules. Although benzene, C₆H₆, has not beendetected in the dense ISM, its presence at high abundance levels isinferred through the detection of functionalized derivatives. Herewe present a combined experimental and astrochemical modeling investigationof the gas-phase C(³P) + C₆H₆ reaction.Experimentally, rate constants were determined over the 50–296K range using the Laval nozzle technique coupled with pulsed laserphotolysis and laser-induced fluorescence for C(³P) generationand detection, respectively. Product yields of atomic hydrogen, H(²S), were also measured at 177 and 296 K to provide some informationon the product channels of the reaction. The measured rate constantsare very large, between 3.3 and 5.7 × 10^–10 cm³ s^–1, indicating the fast, barrierlessnature of the reaction, while the H atom yields are all below 10%when compared to the C(³P) + C₂H₄ reference reaction. As the C(³P) + C₆H₆ reaction is not currently included in astrochemical databases,its influence on the simulated abundances of C₆H₆ and related species was tested using a gas-grain model of denseinterstellar clouds. The C(³P) + C₆H₆ reaction is shown to be the main loss process for interstellar benzene,while different hypotheses regarding the product channels are discussedin the context of observations to shed light on the preferred formationpathways.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1974–1985"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distinguishing Natural and Anthropogenic Cadmium Sources for Regional Pollution Zoning: A Two-Stage Machine Learning Framework","authors":"Zilun Gou,&nbsp;Jin Ma,&nbsp;Meng Qi,&nbsp;Qiyuan Liu,&nbsp;Wenhao Zhao,&nbsp;Fei Wu,&nbsp;Chengshuai Liu,&nbsp;Jie Li","doi":"10.1021/acsearthspacechem.6c00133","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00133","url":null,"abstract":"<p>Widespreadcadmium (Cd) anomalies in soil and associated pronouncedspatial heterogeneity in high-geochemical background regions are primarilyattributed to the superimposed effects of natural enrichment and anthropogenicdisturbances. These superimposed effects hinder accurate identificationand management of critical pollution zones. To address this issue,a pollution differential (PD) indicator was developed based on theDBSCAN algorithm to delineate the distinct pollution patterns arisingfrom the superimposed effects. By integrating the DBSCAN-derived resultswith bivariate local indicators of spatial association analysis, criticalpollution zones predominantly influenced by mining, manufacturing,and agricultural activities were effectively identified. The PD indicatorwas subsequently transformed into model-interpretable structured data,serving as an input that captures heterogeneity information for thesubsequent prediction stage. Validation using an independent dataset demonstrated that incorporating the PD indicator significantlyimproved model predictive performance and generalization, achievinga testing <em>R</em>² RMSE of 0.86 and 0.13, respectively.Considering the inconsistency in Cd content and its bioavailability,an anthropogenic activity-oriented spatial prediction of Cd distributionwas further generated using the optimized model after excluding theinfluence of natural enrichment. The two-stage model developed inthis study provides an enhanced framework for identifying criticalpollution zones, thereby supporting more effective pollution preventionand control strategies in high-geochemical background regions.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 8","pages":"1955–1963"},"PeriodicalIF":2.6,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decadal-Scale Hydrothermal Alteration of Basalt: Implications for Long-Term Reactivity in Subsurface Technologies","authors":"Marie N. M. Gibson*,&nbsp;Vincent R. Lamberti,&nbsp;Emily T. Nienhuis*,&nbsp;C. Heath Stanfield,&nbsp;Yuntian Teng,&nbsp;Harshvardhan Chopra,&nbsp;José Marcial,&nbsp;Tan Tai Vo,&nbsp;Son T. Dang,&nbsp;Quin R. S. Miller* and H. Todd Schaef,&nbsp;","doi":"10.1021/acsearthspacechem.6c00057","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00057","url":null,"abstract":"<p >Global demands to secure critical mineral supply chains, manage water resources, and store energy long-term require innovative resource management strategies. Subsurface basalt reservoirs potentially offer an unconventional dual-purpose approach to mining and energy storage, where compressed air energy storage can be coupled with water remediation strategies for the extraction of economically important and environmentally relevant elements. This study utilizes static batch experiments conducted on Columbia River Basalt Group samples to evaluate long-term fluid–rock interactions relevant to coupled subsurface applications. Samples were reacted under elevated temperature and pressure conditions, for 296 and 4061 days, providing a unique data set to assess geochemical evolution, element partitioning, and aqueous chemistry over decadal time scales. The alteration was dominated by silicate, aluminosilicate, and oxide phases. Progressive hydrothermal alteration increased the cation exchange capacity through the formation of secondary minerals (e.g., clays and zeolites), influencing solute retention, ion exchange behavior, and aqueous chemistry. Grain-scale and bulk analyses revealed selective cation release and retention patterns, establishing a mechanistic baseline for predicting element mobility. These geochemical constraints inform the prospective use of enhanced metal recovery for critical resources (e.g., Mn, Mg, Ti, and Fe) and associated water quality impacts, providing a foundation for the design and management of engineered fluid–rock systems in unconventional basalt reservoirs.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 7","pages":"1732–1741"},"PeriodicalIF":2.6,"publicationDate":"2026-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148452252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Theoretical and Experimental IR Spectra of Astronomical PAHs and PANHs in the 2000–1650 cm–1 Range (∼5–6 μm)","authors":"Akant Vats*,&nbsp;Andrew L. Mattioda and Alessandra Ricca,&nbsp;","doi":"10.1021/acsearthspacechem.6c00033","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00033","url":null,"abstract":"<p >Recent James Webb Space Telescope observations reveal unprecedented details in the 2000–1650 cm^–1 (∼5–6 μm) region, including the well-known 5.25 and 5.75 μm bands. This range, dominated by overtone and combination bands mainly involving C–H out-of-plane (CH_oop) bending fundamentals, provides a powerful yet underexplored probe of astronomical polycyclic aromatic hydrocarbons (PAHs) and their nitrogen-containing analogues (PANHs). We present a combined experimental and theoretical investigation of 27 neutral PAHs and PANHs using matrix-isolation spectroscopy and second-order vibrational perturbation theory to disentangle effects of PAH structures and nitrogen substitution in the 2000–1650 cm^–1 region. Coupling among the underlying fundamentals subdivides this region, accommodating the distinct characteristics of the 5.25 and 5.75 μm bands. The higher-frequency subregion (2000–1870 cm^–1; 5.00–5.35 μm) reflects PAH edge topology, where the highest-frequency band shifts from quartet + bay structures (∼5.13 μm) to quartet+solo (∼5.18 μm) and pericondensed PAHs (∼5.20 μm), consistent with the relatively stable astronomical 5.25 μm band. The lower-frequency subregion (1870–1650 cm^–1; 5.35–6.06 μm) shows greater structural variability, consistent with the composite 5.75 μm band. Nitrogen substitution broadens the spectral distribution by shifting bands by ∼10 cm^–1. From our neutral PAHs/PANHs set, we infer that the 5–6 μm region reflects contributions from neutral astronomical PAHs, dominated by pericondensed PAHs, with secondary contributions from catacondensed PAHs with limited quartets and increasing solos. Contributions from irregular edges containing quartets C–H groups and nitrogen-substitution are modest. A corresponding study of cations is needed to fully characterize the 5–6 μm emission, disentangling cation and neutral contributions from the CH_oop region.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 7","pages":"1685–1701"},"PeriodicalIF":2.6,"publicationDate":"2026-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.acs.org/doi/pdf/10.1021/acsearthspacechem.6c00033","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148452253","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nontailpipe Particulate Matter from Brake Wear, Tire Tread, and Road Dust: Environmentally Persistent Free Radicals, Reactive Oxygen Species, and Oxidative Potential","authors":"Sukriti Kapur,&nbsp;B. Sage Lauper-Cook,&nbsp;Kasey C. Edwards,&nbsp;Lena Gerritz,&nbsp;David Herman,&nbsp;Madeline E. Cooke,&nbsp;Adam E. Thomas,&nbsp;Lisa M. Wingen,&nbsp;Véronique Perraud,&nbsp;Tsuyoshi Ito,&nbsp;Hiroyuki Hagino,&nbsp;Junichi Hosoya,&nbsp;Tazuko Morikawa,&nbsp;Andrea De Vizcaya Ruiz,&nbsp;Michael T. Kleinman,&nbsp;James N. Smith and Manabu Shiraiwa*,&nbsp;","doi":"10.1021/acsearthspacechem.6c00076","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00076","url":null,"abstract":"<p >Nontailpipe emissions including brake and tire wear and resuspended road dust have become emerging concerns in traffic air pollution. It is thus important to understand the health-related properties of nontailpipe particulate matter (PM) as it becomes a major contributor to traffic air pollution. Here we characterize the chemical composition, reactive oxygen species (ROS) formation, and oxidative potential of ambient PM collected next to two highways in California, as well as laboratory-generated PM from brake wear particles (BWPs), cryogenically milled tire tread (CMTT) from fresh and used tires, used tire tread particles, and road dust. The major metal components are found to be iron, barium and copper in BWPs, zinc in CMTT, and crustal elements such as aluminum, calcium, potassium, and sodium in road dust. CMTT is found to contain environmentally persistent free radicals (EPFRs), while BWPs and road dust do not contain detectable amounts of EPFRs. Ambient traffic PM generates hydroxyl radicals (^•OH) and carbon-centered organic radicals upon extraction in water, while BWPs exclusively generate ^•OH, consolidating findings by previous studies. CMTT and road dust exhibit relatively low ROS formation and PM oxidative potential. BWPs generated from three different brakes of varying Cu content show that a higher Cu content leads to higher ROS formation and higher oxidative potential as measured by dithiothreitol (DTT) decay and ^•OH formation in surrogate lung fluid. These results provide useful insights into health-related properties of nontailpipe PM, supporting that regulation of Cu in brake materials would help reduce potential health effects of BWPs.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 7","pages":"1742–1754"},"PeriodicalIF":2.6,"publicationDate":"2026-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148452217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depositional Environment and Organic Matter Accumulation Mechanism along the Southwestern Marginal Yangtze Platform (South China) during the Middle Devonian: Implications for Low Content of Organic Matter","authors":"Zijun Ren,&nbsp;Niuniu Zou*,&nbsp;Daquan Zhang,&nbsp;Yi Chen,&nbsp;Xia Feng,&nbsp;Zhilong Ye,&nbsp;Yuanyan Yin,&nbsp;Yuheng Peng and Luyang Dong,&nbsp;","doi":"10.1021/acsearthspacechem.6c00077","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.6c00077","url":null,"abstract":"<p >To determine the sedimentary environment of the black shales in the Middle Devonian Huohong Formation in the southwestern marginal Yangtze Platform and analyze the controlling factors of organic matter accumulation, this study selects the black shales from the southwestern marginal Yangtze Platform and conducts comprehensive analyses including total organic carbon (TOC), major and trace element. The TOC range from 0.26% to 1.27%, averaging 0.53%, indicating a low organic matter content. Redox-sensitive and paleowater depth indicator elements (Mo &lt; 5 ppm, Co &lt; 40 ppm, Cu &lt; 90 ppm, Ba &lt; 1000 ppm) suggest that relatively shallow depositional water depths. Redox indicators (U/Th &lt; 0.75, V/Cr &lt; 2.0, Ni/Co &lt; 5) suggest that the oxic sedimentary environment. The Mo/TOC &lt; 4.5 reveals strong water restriction, while paleosalinity indicators (S/TOC &gt; 0.5) reveals a saline-brackish water environment. The Lower Ti/Al (0.007–0.012) implies limited terrigenous clastic input, and the CIA values (46.40–72.85) indicate a paleoclimatic shift from warm-humid to cold-arid conditions in the provenance area. The paleoproductivity indicators P/Ti &lt; 0.34 and biogenic Ba (Ba_bio) &lt; 200 ppm indicates low paleoproductivity. The (La/Yb)_N far from 1 reflects a relatively low sedimentation rate. The Al–Fe–Mn ternary diagram and Al/(Al + Fe + Mn) &gt; 0.4 and (Fe + Mn)/Ti &lt; 15 confirm the absence of significant hydrothermal activity during deposition. The low organic matter content is mainly controlled by two factors: the oxic environment is unfavorable for organic preservation, and insufficient nutrient supply resulted in low paleoproductivity, limiting organic input. Additionally, slow sedimentation enhanced organic consumption in sediments. This study established an organic matter accumulation model for the Middle Devonian Huohong Formation shales and concludes that the depositional conditions were unfavorable for organic enrichment.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 7","pages":"1755–1769"},"PeriodicalIF":2.6,"publicationDate":"2026-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148452218","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Speciation of Iron in Soil Including Structural Fe(II)/Fe(III) Ratios in Phyllosilicates by X-ray Absorption Fine Structure Spectroscopy","authors":"Yoshio Takahashi*,&nbsp;Yuki Shimizu*,&nbsp;Sakura Sato,&nbsp;Yoko Masuda,&nbsp;Hirotomo Ohba,&nbsp;Noriko Yamaguchi,&nbsp;Yasuhiro Niwa,&nbsp;Yuta Ijichi,&nbsp;Takehiro Hirayama,&nbsp;Haibo Qin and Keishi Senoo,&nbsp;","doi":"10.1021/acsearthspacechem.5c00393","DOIUrl":"https://doi.org/10.1021/acsearthspacechem.5c00393","url":null,"abstract":"<p >Soil is a complex system where iron (Fe) speciation plays a key role in redox reactions and biogeochemical processes. However, quantitative evaluation of the Fe(II)/Fe(III) ratio in phyllosilicates, which constitute a major Fe reservoir in soils, has remained challenging. In this study, we developed a method to quantify Fe speciation in soils using linear-combination fitting (LCF) of X-ray absorption fine structure (XAFS) spectra with four end members: ferrihydrite, Fe(II)-bearing biotite, Fe(III)-bearing montmorillonite, and adsorbed Fe²⁺ as hydrated Fe²⁺ (outer-sphere complex). Principal component analysis confirmed that these four components are sufficient to reproduce Fe K-edge X-ray absorption near-edge structure (XANES) spectra of various soil and sediment samples under both oxic and anoxic conditions. The LCF-XAFS results showed that phyllosilicates account for 40–70% of total Fe in the studied samples, and the ratio of Fe(II) and total Fe in the octahedral layer in phyllosilicates (= Fe(II)_phy/Fe_total-phy ratio) varies systematically with redox conditions. Under reducing conditions, ferrihydrite was partially dissolved and replaced by adsorbed Fe²⁺, while the Fe(II)_phy/Fe_total-phy ratio increased significantly. The speciation results were consistent with those obtained by Mössbauer spectroscopy and sequential extraction within ∼10% difference. Furthermore, μ-XANES analysis revealed spatial heterogeneity of Fe speciation at the micrometer scale, demonstrating that the Fe(II)_phy/Fe_total-phy ratio in phyllosilicates reflects local redox conditions within soils. These results indicate that the Fe(II)_phy/Fe_total-phy in phyllosilicates can serve as a quantitative proxy for redox conditions in soils and sediments.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":"10 7","pages":"1666–1684"},"PeriodicalIF":2.6,"publicationDate":"2026-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148452207","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}