Complex Surface Research Articles

Calcined MgFe layered double hydroxides for magnetic separation and enhanced adsorption performance of methyl orange: Mechanism based on the memory effect

This study successfully synthesized magnetic MgFe-layered double oxides (MgFe-LDO-500 °C) by calcining MgFe-layered double hydroxides (MgFe-LDHs) at 500 °C. Calcination temperature was identified as a critical factor for optimizing adsorption capacity and activating a memory effect, with 500 °C being particularly effective. The adsorption performance of MgFe-LDO-500 °C towards methyl orange (MO) in aqueous solutions was evaluated across varying pH levels (2–12), initial MO concentrations (50–1800 mg/L), contact times (0–1440 min), and temperatures (25–45 °C). The results indicated that MgFe-LDO-500 °C adsorption conforms to the pseudo-second-order kinetic and Langmuir models, achieving a theoretical maximum adsorption capacity of 5087.76 mg/g. Characterization through scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Zeta potential analysis revealed that the outstanding adsorption performance of MgFe-LDO-500 °C towards MO involves a combination of electrostatic attraction, memory effect, and surface complexation. Moreover, after four regeneration cycles, the material maintained a 73 % MO removal efficiency and could be efficiently separated using magnetic separation technology. In conclusion, MgFe-LDO-500 °C represents a promising adsorbent for wastewater treatment.

The adsorption of U(VI) on chlorite: batch, modeling and XPS study

Abstract A mechanistic modelling of the adsorption processes onto individual minerals presenting in the near- and far-fields can greatly enhance the credibility of long-term safety assessments of granite-based geological repositories. In this study, the titration and U(VI) adsorption characteristics of chlorite, one of the major minerals of rock fractures, have been studied. Potentiometric titration curves at two ionic strengths (0.1 and 0.4 mol/L NaCl) are successfully interpreted by considering protonation/deprotonation reactions on generic edge sites (≡SOH) in the framework of a non-electrostatic surface complexation model (SCM). The adsorption of U(VI) on chlorite was reached after 24 h, the adsorption kinetics can be described by a pseudo-second-order model. A non-electrostatic SCM with three surface complexes (≡SOUO2 +, ≡SO(UO2)3(OH)5 and ≡SO(UO2)3(OH)7 2−) was set up based on pH edges of U(VI) at adsorption equilibrium in the absence of CO2. Additional, experimental data measured as a function of U(VI) concentration, solid-to-liquid ratio and carbonate concentration were well reproduced by the proposed model. Finally, parallel experiments were conducted using X-ray photoelectron spectroscopy (XPS) to analyze the variation of U(VI) surface species speciation at different pH values. The good agreement between SCM prediction and XPS analysis demonstrates the reliability of the model in predicting and quantifying the radionuclides retention by chlorite.

Computational Investigations of the Detailed Mechanism of Reverse Intersystem Crossing in Inverted Singlet-Triplet Gap Molecules.

Inverted singlet-triplet gap (INVEST) materials have promising photophysical properties for optoelectronic applications due to an inversion of their lowest singlet (S1) and triplet (T1) excited states. This results in an exothermic reverse intersystem crossing (rISC) process that potentially enhances triplet harvesting, compared to thermally activated delayed fluorescence (TADF) emitters with endothermic rISCs. However, the processes and phenomena that facilitate conversion between excited states for INVEST materials are underexplored. We investigate the complex potential energy surfaces (PESs) of the excited states of three heavily studied azaphenalene INVEST compounds, namely, cyclazine, pentazine, and heptazine using two state-of-the-art computational methodologies, namely, RMS-CASPT2 and SCS-ADC(2) methods. Our findings suggest that ISC and rISC processes take place directly between the S1 and T1 electronic states in all three compounds through a minimum-energy crossing point (MECP) with an activation energy barrier between 0.11 to 0.58 eV above the S1 state for ISC and between 0.06 and 0.36 eV above the T1 state for rISC. We predict that higher-lying triplet states are not populated, since the crossing point structures to these states are not energetically accessible. Furthermore, the conical intersection (CI) between the ground and S1 states is high in energy for all compounds (between 0.4 to 2.0 eV) which makes nonradiative decay back to the ground state a relatively slow process. We demonstrate that the spin-orbit coupling (SOC) driving the S1-T1 conversion is enhanced by vibronic coupling with higher-lying singlet and triplet states possessing vibrational modes of proper symmetry. We also rationalize that the experimentally observed anti-Kasha emission of cyclazine is due to the energetically inaccessible CI between the bright S2 and the dark S1 states, hindering internal conversion. Finally, we show that SCS-ADC(2) is able to qualitatively reproduce excited state features, but consistently overpredict relative energies of excited state structural minima compared to RMS-CASPT2. The identification of these excited state features elaborates design rules for new INVEST emitters with improved emission quantum yields.

Significant contribution of the Tianshan lakes to their water storage and water resources

Study regionThe Tianshan region Study focusThe Tianshan region possesses a complex landscape with lakes, and changes in the water storage of these lakes serve as a crucial indicator of climate change. They also represent a significant water resource for the local area, profoundly impacting water resource allocation and playing a pivotal role in understanding the mass balance in the Tianshan region. Nevertheless, there is still a lack of systematic research on the Tianshan lake group. New hydrological insights for the regionThe results reveal that the total lake water storage is exhibiting an increasing trend (0.73±0.10 Gt/a). The Tianshan region experienced two periods of mass anomalies in 2010 and 2016, which were reflected not only in the changes of lake water storage but also in soil moisture, snow water, and even Global Navigation Satellite System (GNSS) displacement fields. These two mass anomalies were closely related to abnormal precipitation resulting from El Niño events (r=0.55, p<0.01). During these two mass anomaly periods, the regional total mass increased by 65.73 Gt and 67.35 Gt. Compared with their contributions to the mass (22% and 14%), the variations in lake area were remarkably slight (0.01% and 0.014%). This study contributes to understanding the sensitivity of lakes to climate responses and underscores the necessity of lake research for water resource management in complex surface environments.

Recent Advances in Machine Learning in Tribology

Tribology, the study of friction, wear, and lubrication, has been a subject of interest for researchers exploring the complexities of materials and surfaces [...]

Galaxies' properties in the Fundamental Plane across time

Using the Illustris-1 and IllustrisTNG-100 simulations, we investigate the properties of the Fundamental Plane (FP), which is the correlation between the effective radius the effective surface intensity and the central stellar velocity dispersion sigma of galaxies, at different cosmic epochs. Our aim is to study the properties of galaxies in the FP and its projections across time, adopting samples covering different intervals of mass. We would like to demonstrate that the position of a galaxy in the FP space strongly depends on its degree of evolution, which might be represented by the beta and $ L'_0$ parameters entering the law. Starting from the comparison of the basic relations among the structural parameters of artificial and real galaxies at low redshift, we obtain the fit of the FP and its coefficients at different cosmic epochs for samples of different mass limits. Then, we analyze the dependence of the galaxy position in the FP space as a function of the beta parameter and the star formation rate (SFR). We find that: 1) the coefficients of the FP change with the mass range of the galaxy sample; 2) the low luminous and less massive galaxies do not share the same FP of the bright massive galaxies; 3) the scatter around the fitted FP is quite small at any epoch and increases when the mass interval increases; 4) the distribution of galaxies in the FP space strongly depends on the beta values ( on the degree of virialization and the star formation rate). The FP is a complex surface that is well approximated by a plane only when galaxies share similar masses and condition of virialization.

Nitrogen and sulfur co-doped mesoporous carbon as an efficient peracetic acid activator for the degradation of 4-chlorophenol: A nonradical mechanism dominated by singlet oxygen

Metal-free peracetic acid (PAA) activators are urgently required due to their low toxicity. Heteroatom doping is beneficial to improve the catalytic performance of carbon materials, but the activation performance of doped carbon materials on PAA and the underlying mechanism have not been reported. Herein, nitrogen and sulfur co-doped mesoporous carbons (NS-MC-x, with x representing the mass ratio of thiourea:mesoporous carbon) were fabricated and used as efficient PAA activators for 4-chlorophenol (4-CP) degradation. The NS-MC-1.0/PAA system can remove > 95 % of 4-CP within 10 min, far more than the MC/PAA system. Co-existing anions show no effect on the degradation of 4-CP, whereas humic acid has a certain degree of inhibition. Singlet oxygen (1O2) primarily drives the degradation of 4-CP, with a secondary contribution from a direct electron transfer process mediated by reactive surface complexes, while the contribution of radicals is minimal. In addition, NS-MC-1.0 exhibits excellent reusability for PAA activation, which is conductive to its practical application. This study facilitates further research on metal-free catalysts for PAA activation and offers fresh perspectives on the utilization of PAA in degrading emerging pollutants.

Influence of Cations on Direct CO2 Capture and Mineral Film Formation: The Role of KCl and MgCl2 at the Air/Electrolyte/Iron Interface.

Uncovering the mechanisms associated with CO2 capture through mineralization is vital for addressing rising CO2 levels. Iron in planetary soils, the mineral cycle, and atmospheric dust react with CO2 through complex surface chemistry. Here, the effect of cations on the growth of carbonate films on iron surfaces was investigated. In situ polarized modulated infrared reflection absorption spectroscopy was used to measure CO2 adsorption and oxidation of iron in MgCl2(aq) and KCl(aq), compared to FeCl2(aq) at the air/electrolyte/iron interface. The cation was found to influence the film composition and growth rates, as corroborated by infrared and photoelectron spectroscopy. In MgCl2(aq), a mixture of hydromagnesite, magnesite, and a Mg hydroxy carbonate film was grown on iron, while in KCl(aq), a potassium-rich bicarbonate film was grown. The cations were found to affect the rates of hydroxylation and carbonation, confirming a specific cation effect on carbonate film growth. In the submerged region, a heterogeneous mixture of lepidocrocite and iron hydroxy carbonate was produced, suggesting that Fe2+ dominates the surface products. Surface roughness measurements from in situ atomic force microscopy indicate iron initially corrodes faster in MgCl2(aq) than KCl(aq), due to the Cl- ions that initiate pitting and corrosion. In this region, cations were not found to affect the morphologies. This study shows surface corrosion is necessary to provide nucleation sites for film growth and that the cations influence the carbonate film, relevant for CO2 capture and planetary processes.

Distinct differences in surface transport between electrolyte-gated (110) and (001) SrTiO3

Electrolyte gating technology has been widely used as an effective tool to study novel physics at complex oxide surfaces and interfaces. Certain emergent phenomena reported in electro-gated SrTiO3 (STO) surfaces are particularly interesting. Here, we report on the disparate electron transport behaviors of electrolyte-gated STO (001) and (110) oriented surfaces. In contrast to the anomalous transport from an insulating state to a Kondo-like state and then metallic states on the (001) surface, with increasing carrier density, the (110) surface always behaves as an insulating state. A comparison study suggests that the oxygen vacancies and localized Ti3+ ions on the (001) surface are scatter carriers, but no such defects are found on the (110) surface. This suggests that these surfaces are intrinsically insulating, and the observed anomalous effects are likely induced by the Ti3+ ions and oxygen vacancies introduced during electrolyte gating. This work sheds light on complicated phenomena in electrolyte-gated STO-based systems.

Material corrosion characteristics of heat-treated SLM-ed Hastelloy X in electrochemical machining process

Selective laser melting (SLM) technology and electrochemical machining (ECM) offer new methods for producing nickel-based superalloys with complex structures and high surface quality, including Hastelloy X parts. However, SLM-fabricated parts exhibit significant anisotropy, and there are no effective criteria for evaluating material corrosion characteristics in actual ECM due to the detachment of research and application, making the parameter selection challenging in actual ECM. To address this issue, this article proposes a comprehensive evaluation system based on the corrosion characteristics in the actual machining process and investigates the effect of heat treatment temperature on the corrosion characteristics of Hastelloy X in ECM. The results show that at a heat treatment temperature of 1000°C, machining efficiency, accuracy, and localization can all be achieved at a good level with good consistency in different directions at the expense of a certain machining accuracy. The 800℃ heat-treated specimen exhibits strong corrosion resistance, providing a significant advantage in machining localization and accuracy. When the heat treatment temperature exceeds the solid solution temperature (more than 1175℃), the mechanical properties and corrosion characteristics of the specimen are significantly degraded. The results of various material testing methods, including electrochemical testing, EBSD, XRD, and EDS indicate that changes in grain size due to recrystallization and the galvanic effect of precipitates are the primary causes of these changes.

Influence of Tool Inclination and Effective Cutting Speed on Roughness Parameters of Machined Shaped Surfaces

Free-form surfaces in the automotive or aviation industry where the future shape of the product will contain complex surfaces raises the question of how to achieve the necessary shape of the required quality in the milling process. One of the methods of their production is the use of 5-axis milling, in which it is necessary to consider not only the input data of the process itself, but also the methodology for evaluating the desired results. Correctly answered questions can thus facilitate the choice of the inclination of the tool when machining parts of the surfaces defined in the experiment. The primary goal of the paper was to monitor the influence of tool inclination on the quality of the machined surface and effective cutting speed by evaluating surface roughness and surface topography. The experiment was designed to show the effect of different tool positions while the feed per tooth fz for the finishing operation remained constant. The best result in terms of surface quality was achieved with a tool inclination of 15° in the cutting process. The most unfavorable result was obtained with a tool axis inclination of zero degrees due to unfavorable cutting conditions.

Construction of highly robust amino orange peel cellulose for Cu2+ adsorption study

ABSTRACT In this paper, a kind of cellulose aerogel (HRCNFs) with high mechanical robustness and durability was prepared by using orange peel cellulose and polyethylenimine, and it was used for high-efficiency adsorption of Cu (II). Fourier analysed the structure and morphology of HRCNFs transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and the pore structure characteristics of the materials were evaluated by BET. The adsorption capacity of HRCNFs as adsorbent to remove Cu (II) ions from aqueous solution was further studied. The maximum adsorption capacity was 167.21 mg/g. Adsorption is mainly a single-layer chemisorption process. Based on FTIR and BET analysis, the adsorption mechanism is the strong surface complexation of amino, carboxyl, and hydroxyl groups with Cu (II). Through many cycles, HRCNFs retain their integrity and high mechanical robustness. Therefore, the synthesised HRCNFs material can be considered a promising adsorbent for the removal of Cu (II) ions from polluted water bodies.

Removal of polystyrene microplastic from aqueous solutions with London Plane bark biochar: Pyrolysis temperature, performance and mechanism

The seasonally shed bark of London Plane tree is an ideal source for biochar due to its high lignin content. Microplastics derived from plastic wastes has become a hot topic due to its potential threats to ecosystems. The aim of this work is to convert the shed bark into efficient London Plane bark biochar (LBC) adsorbents and investigate its application in microplastics adsorption. The effects of pyrolysis temperature on LBC structure, surface properties and microplastic adsorption were investigated and the best adsorption performance of 60.05 mg/L was found at the 550 °C-pyrolyzed LBC. The wet sieve-weighing method was applied to assess the adsorption effect of LBC and verified with thermogravimetric analysis. The adsorption of polystyrene (PS) particles on LBC was in accordance with the Sips isothermal model and the second-order-kinetics model. The robustness of LBCs and the adsorption mechanism were investigated. With the analysis from pore size distribution, SEM images, FTIR and XPS spectra, physical trapping, surface complexation, hydrogen bonding and π-π interaction all play key roles in the adsorption of PS onto the LBC surface. This study not only provides a new approach for the removal of microplastics, but also offers a broad perspective on the treatment of biomass waste.

Understanding adsorption mechanisms and metal ion selectivity of superparamagnetic beads with mesoporous CMK-3 carbon and commercial activated carbon

This study investigates, the adsorption capacities of synthesized magnetic hybrid beads containing ordered mesoporous carbon (CMK-3) and commercial activated carbon (commercial AC) for Cd (II), Ni (II), and Hg (II) ions adsorption in single and ternary systems. The order of maximum adsorption capacity was Cd (II) > Ni (II) > Hg (II) in both beads and systems. L13 beads containing CMK-3 exhibit superior adsorption efficiency compared to L3 beads with commercial AC, attributed to the large surface area, enhanced accessibility to adsorption sites, and the presence of O=C bonds, as well as other elements such as F−. Adsorption of all metal ions was described by Freundlich isotherm in L3 beads in both systems, meanwhile in L13 beads, Langmuir and Freundlich models described adsorption differently in both systems and among metal ions, indicating a more complex process. According to the reported maximum adsorption capacity values, L3 beads exhibit a greater affinity for Hg (II) ions, while L13 beads show a higher affinity for Cd (II) and Ni (II) ions. Adsorption in both beads occurred through several mechanisms involving surface complexation, ion-exchange, precipitation, physical and chemical processes. These findings highlight the importance of material design in optimizing adsorption performance for environmental applications, with potential for further enhancement of adsorption capacities and selectivities through future research.

Results of round robin form measurements of optical aspheres and freeform surfaces

Abstract High-quality aspherical and freeform surfaces are in high demand, and the high-accuracy form measurement of such surfaces is a challenging task. To explore the current status of form measurement systems for complex surfaces such as aspheres and freeforms, interlaboratory comparison measurements are performed. This study presents the pseudonymized results obtained using three different surfaces (metal asphere, glass asphere, toroidal surface) in a total of six different round robins. These results were taken from a total of 13 different measurement instruments based on 9 different measurement principles and operated at 12 different laboratories.&amp;#xD;They were analyzed using a sophisticated procedure that was first developed in 2018 and then refined and tested on simulated data in 2022 to address the challenges of such a comparison at this level of accuracy.&amp;#xD;In the current study, we applied these refined methods to data acquired from tactile and optical point measurements as well as from optical areal measurements. As there are no absolutely measured and very well characterized reference standard aspherical and freeform surfaces available at the accuracy level of a few tens of nanometers root-mean-square, the approximated true forms of the surfaces were derived from the measurements and indicate the manufacturing accuracy of the surface forms. Then, the measurement's differences to the approximated true forms were analyzed, which directly indicate the systematic measurement errors of the instruments.&amp;#xD;By also comparing the approximated true forms from the two different round robins for each surface, additional insights into the reliability and stability of these so-called virtual reference topographies (VRTs) were gained.

Cost-effective synthesis of magnetic graphene oxide nanocomposite from waste battery for the removal of arsenic from aqueous solutions: Adsorption mechanism with DFT calculation

In this study, magnetic graphene oxide (MGO-Fe3O4) nanocomposite was prepared by co-precipitating of FeCl3.6H2O and FeCl2.4H2O on waste battery-derived graphene oxide and used as an adsorbent for the efficient removal of As(III) from aqueous solutions. The prepared nanocomposite was characterized by Fourier transformed infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, zeta potential, and a vibrating sample magnetometer. These characterizations revealed that spare like Fe3O4 nanoparticles (10.5 nm) were decorated on graphene oxide nanosheets and showed excellent saturation magnetization (89.73 emu/g). The adsorption of As(III) by MGO-Fe3O4 was optimized by analyzing various parameters. Experiments showed that 98 % of As(III) was removed at neutral pH in a just 20 min, even though the adsorbent dose was only 0.14 g/L. The adsorption kinetic and isotherm were best fitted with the pseudo-second order kinetic and Frendlich isotherm model. The maximum adsorption capacity (qmax) was found to be 50.2 mg/g at room temperature. Thermodynamic studies showed that the As(III) adsorption process was spontaneous and exothermic in nature. The enhanced adsorption capacity and magnetic properties of MGO-Fe3O4 are crucial in the drinking water treatment process due to the easy magnetic separation of MGO-Fe3O4 from aqueous solution after the adsorption process. Density Functional Theory (DFT) was also used to investigate the interaction between MGO-Fe3O4 and As(III), which further suggested that MGO-Fe3O4 and As(III) mostly interact with each other through surface complexation and hydrogen bonding.

The competition of heavy metals between hyporheic sediments and microplastics of driving factors in the Beiluo River Basin

Both sediments and microplastics (MPs) are medias of heavy metals (HMs) in river ecosystems. This study investigated HMs (Mn, Cr, V, As, Cu, Co, Cd, Pb, and Ni) concentration and driving factors for competitive enrichment between hyporheic sediments versus MPs. The medias basic characteristics indicated that the sediments were mostly sand and rich in Fe2O3; three polymer types were identified, with blue, fragment, less than 500μm being the main types of MPs. The results have shown that the average content of extracted HMs in MPs was much higher than that of the same metals accumulated in sediments. HMs in sediments and MPs reached heavily polluted at some points, among which As and Cd were ecological risks. Electrostatic adsorption and surface complexation, and biofilm-mediated and organic matter complexation were the interaction mechanism of HMs with sediments and MPs. Further, the driving factors affecting the distribution of HMs in the two carriers were analyzed by multivariate statistical analysis. The results demonstrated that carrier characteristics, hydrochemical factors, and the inherent metal load of MPs were the main causes of the high HMs content. These findings improved our understanding of HMs fate and environmental risks across multiple medias. Environmental ImplicationOwing to large specific surface area and hydrophobicity, microplastics adsorb heavy metals (HMs) from the surrounding environment, aggravating potential ecological hazards and posing a threat to aquatic organisms. Many laboratory experiments have confirmed the compound effect of the two, but the attribution of HMs in natural rivers under the influence of multiple factors remains to be studied.This study investigated the distribution of HMs concentrations in different media, assessed HMs pollution in sediments and microplastics, and explained the drivers of uneven HMs concentrations. The finding provides new insights for further understanding of the fate of HMs in ecosystems.

KMnO4 modified magnetic hydrochar for efficient adsorption of malachite green and methylene blue from the aquatic environment

This study exploited magnetic citrus peel hydrochar (MHC) modified by KMnO4 (MHC/Mn) for the removal of methylene blue (MB) and malachite green (MG). Effects of initial concentration, pH, dosage, temperature, and ion strength on MHC/Mn adsorption properties were investigated. The adsorption kinetics, isotherm, and mechanism were further explored. The results indicated that Fe3O4 was successfully embedded and MnO2 was coated on MHC after modification. The experiment data were well fitted to the pseudo-second-order kinetic model and Langmuir isotherm model. Thermodynamic parameters showed that the adsorption of MHC/Mn to MB is spontaneous and endothermic, and the adsorption of MG is spontaneous and exothermic. The mechanism of MB and MG interaction with MHC/Mn includes electrostatic interaction, hydrogen bond, surface complexation, and π-π interaction. The maximum adsorption capacity of MB and MG calculated were 175.63 mg/g and 1402.17 mg/g. After four adsorption–desorption cycles, the removal rate of MB and MG were 85.11 % and 69.29 %. MHC/Mn is an economical and environmentally favorable adsorbent for the removal of MB and MG in wastewater.

Electrochemical characterization of binder effect in natural magnetite electrodes for fluoride removal of well water

This work presents the study of the behavior of magnetite in fluoride electroadsorption. A concern in the fluoride electroadsorption is related to the type of binder, fluoride concentration, pH, and coexisting ions. A graphite/Nafion/magnetite electrode increases the specific capacitance of the surface favoring the surface complexation of anions due to the increase in the effective adsorption surface in this system. There is a tendency to increase the specific capacitance when the concentration and pH increase. The anionic affinity of the system is directly related to the nature of the ions and the hydrated ionic radius, in ions with the same charge, a lower hydrated radius results in a greater possibility of surface complexation. Excess OH− groups increase the accumulation of charge in the double layer, making the surface complexation of the anionic species towards the surface difficult. The selectivity trend is: CO32− > SO42− > F− > Cl− > NO3−.

Understanding arsenic-ulexite interactions in evaporite environments: Evidence from XRPD, micro-XRF, micro-FT-IR, and XPS studies

World-class borate deposits often form from As-rich waters, this study addresses the understudied association of arsenic (As) species with evaporite borates, focusing on the Puna region's borate deposits (Central Andes of Argentina). The research aims to characterize the association between borate minerals and high As concentrations in brines and thermal waters. To achieve this, five borate samples were collected from the Olaroz salt flat nucleus and thermal springs, alongside associated water samples. Comprehensive analytical techniques, including ICP-MS, ICP-OES, synchrotron-based micro-XRF, XRPD, Rietveld analysis, micro-FT-IR, and XPS, were employed to determine bulk and surface chemical compositions, mineral identification, and solid speciation of As and boron. The study reveals that under oxidizing conditions and in absence of organic matter, aqueous arsenic species interact with ulexite through a stepwise process involving charge neutralization, cationic bridge formation, and surface complex formation with polyborate and As(V) oxyanions. However, in environments associated with microbial mats or organic-rich sediments, the dissolved As(V) is reduced to As(III), which forms complexes with functional groups of organic matter. The coexistence of As(III) and As(V) in specific layers suggests potential remediation strategies targeting organic matter for the removal of the more toxic As(III) in similar geological settings.