Surface Sulfur Research Articles

“Grafting from” Enabled Stretchable and Highly Fluorescent Carbon Quantum Dot–Polyisoprene Elastomers

Achieving polymer nanocomposites with improved elasticity and stable mechanical and fluorescence properties remains challenging due to the aggregation tendency of fluorescent carbon nanomaterials, particularly for a polymer with no functional groups. To alleviate the aforementioned issues, the “grafting from” method can be employed via covalent bonding design. Herein, we exploit the “grafting from” method coupled with reversible fragment-added chain transfer polymerization to construct soft polyisoprene (PI) chains onto a photostable nitrogen, sulfur, and phosphorus-doped carbon quantum dot (NSP–CQD) surface for the preparation of flexible fluorescent NSP–CQDs-grafted-polyisoprene (NSP–CQDs-g-PIx) nanocomposite films. By tuning the molecular weight of PI in NSP–CQDs-g-PIx (x = 8, 13, and 18 kg mol–1), the elastic and mechanical properties can be tailored. Upon an intense tensile cyclic test, the NSP–CQDs-g-PI18K generates remarkable elasticity, indicated by the absence of permanent deformation or residual strain even after multiple loading–unloading tests up to 50 times. Moreover, compared with the blending method that tends to cause reduced photoluminescence properties due to the NSP–CQD agglomeration, the grafting method intelligibly maintains the fluorescence property. This study concludes that “grafting from” is a feasible method for fabricating CQD-loaded composites, which have great potential to meet the demand for advanced stretchable and flexible organic electronic devices.

Dual Integrating Oxygen and Sulphur on Surface of CoTe Nanorods Triggers Enhanced Oxygen Evolution Reaction.

The bottleneck of large-scale implementation of electrocatalytic water-splitting technology lies in lacking inexpensive, efficient, and durable catalysts to accelerate the sluggish oxygen evolution reaction kinetics. Owing to more metallic features, transition metal telluride (TMT) with good electronic conductivity holds promising potential as an ideal type of electrocatalysts for oxygen evolution reaction (OER), whereas most TMTs reported up to now still show unsatisfactory OER performance that is far below corresponding sulfide and selenide counterparts. Here, the activation and stabilization of cobalt telluride (CoTe) nanoarrays toward OER through dual integration of sulfur (S) doping and surface oxidization is reported. The as-synthesized CoO@S-CoTe catalyst exhibits a low overpotential of only 246mV at 10mAcm-2 and a long-term stability of more than 36h, outperforming commercial RuO2 and other reported telluride-based OER catalysts. The combined experimental and theoretical results reveal that the enhanced OER performance stems from increased active sites exposure, improved charge transfer ability, and optimized electronic state. This work will provide a valuable guidance to release the catalytic potential of telluride-based OER catalysts via interface modulating engineering.

Spatial shifting of COVID-19 clusters and disease association with environmental parameters in India: A time series analysis

BackgroundThe viability and virulence of COVID-19 are complex in nature. Although the relationship between environmental parameters and COVID-19 is well studied across the globe, in India, such studies are limited. This research aims to explore long-term exposure to weather conditions and the role of air pollution on the infection spread and mortality due to COVID-19 in India. MethodDistrict-level COVID-19 data from April 26, 2020 to July 10, 2021 was used for the study. Environmental determinants such as land surface temperature, relative humidity (RH), Sulphur dioxide (SO2), Nitrogen dioxide (NO2), Ozone (O3), and Aerosol Optical Depth (AOD) were considered for analysis. The bivariate spatial association was used to explore the spatial relationship between Case Fatality Rate (CFR) and these environmental factors. Further, the Bayesian multivariate linear regression model was applied to observe the association between environmental factors and the CFR of COVID-19. ResultsSpatial shifting of COVID-19 cases from Western to Southern and then Eastern parts of India were well observed. The infection rate was highly concentrated in most of the Western and Southern regions of India, while the CFR shows more concentration in Northern India along with Maharashtra. Four main spatial clusters of infection were recognized during the study period. The time-series analysis indicates significantly more CFR with higher AOD, O3, and NO2 in India. ConclusionsCOVID-19 is highly associated with environmental parameters and air pollution in India. The study provides evidence to warrant consideration of environmental parameters in health models to mediate potential solutions. Cleaner air is a must to mitigate COVID-19.

Sodium sulfosalicylate activation mechanism on sulfidation flotation of smithsonite using dodecylamine as a collector

In this work, the sulfidation-dodecylamine flotation effects of smithsonite using sodium sulfosalicylate activation were investigated by micro-flotation, atomic force microscopy (AFM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and fourier transform infrared spectrometer (FTIR). The micro-flotation results showed that the sodium sulfosalicylate significantly promoted the sulfidation flotation of smithsonite using dodecylamine as a collector and increased the flotation recovery by around 26 %. The AFM analysis showed that the enhanced sulfurized smithsonite surface roughness Rq increased from 3.80 to 5.82, and the height of the hill-shaped materials on the smithsonite surface was greatly increased after enhanced sulfidation, reaching 41.4 nm. The SEM-EDS analysis revealed that the concentration of sulfur atoms on the sulfurized smithsonite surface enhanced by sodium sulfosalicylate was almost twice that of the direct sulfurized smithsonite surface. The ToF-SIMS analysis indicated that more ZnS was generated on the smithsonite surface and penetrated the smithsonite interior after enhanced sulfidation than after direct sulfidation. The results of FTIR indicated that the addition of sodium sulfosalicylate increased the adsorption of dodecylamine on the smithsonite surface after sulfidation by Na2S·9H2O. The mechanism by which sodium sulfosalicylate activated the smithsonite surface was proposed and verified. In this mechanism, the sulfosalicylic acid ion chelated with Zn2+ to form Zn(SSA)22+ complexes. These complexes react with S ions to form ZnS, which is adsorbed on the smithsonite surface, increasing the sulfide content on the mineral surface, and finally promoting the collection of dodecylamine.

Selective C-Br bond activation for decabromodiphenyl ether photo-debromination via sulfur vacancies enriched zinc indium sulfides

Activation of carbon-halogen bonds is vital for realizing the degradation of halogenated pollutants. Herein, zinc indium sulfides ZnxIn2Sx+3 (x = 1, 2 and 3) with different sulfur vacancies concentration were constructed to achieve photocatalytic decabromodiphenyl ether (BDE209) debromination. Under irradiation, ZnIn2S4 had the most outstanding degradation ability to BDE209, attributing to its abundant surface sulfur vacancies. The sulfur vacancies not only can narrow the forbidden band to increase light absorption and utilization, but more importantly, serve as active sites for the adsorption and activation of C-Br of BDE209. Interestingly, the removal of the first bromine atom from BDE209 on sulfur vacancies behaved as a meta-selective debromination process. The selectivity of meta-debromination is as high as 70%, superior to that on oxygen vacancies enriched photocatalyst. It can be ascribed to the larger vacancy space of sulfur to better accommodate bromine atoms in BDE209, which helps to stabilize the meta-bromine adsorption configuration of BDE209 on sulfur vacancies. Meanwhile, the intermediate configuration is further stabilized under the assistance of the S…Br halogen bond by surrounding sulfur atom at the catalytic interface. This work sheds light on the great potential of larger element vacancies to activate C-halogen bonds in photocatalytic treatment of halogenated pollutants.

One-Step Synthesis of Sulfur-Doped Nanoporous Carbons from Lignin with Ultra-High Surface Area, Sulfur Content and CO2 Adsorption Capacity

Lignin is the second-most available biopolymer in nature. In this work, lignin was employed as the carbon precursor for the one-step synthesis of sulfur-doped nanoporous carbons. Sulfur-doped nanoporous carbons have several applications in scientific and technological sectors. In order to synthesize sulfur-doped nanoporous carbons from lignin, sodium thiosulfate was employed as a sulfurizing agent and potassium hydroxide as the activating agent to create porosity. The resultant carbons were characterized by pore textural properties, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The nanoporous carbons possess BET surface areas of 741-3626 m2/g and a total pore volume of 0.5-1.74 cm3/g. The BET surface area of the carbon was one of the highest that was reported for any carbon-based materials. The sulfur contents of the carbons are 1-12.6 at.%, and the key functionalities include S=C, S-C=O, and SOx. The adsorption isotherms of three gases, CO2, CH4, and N2, were measured at 298 K, with pressure up to 1 bar. In all the carbons, the adsorbed amount was highest for CO2, followed by CH4 and N2. The equilibrium uptake capacity for CO2 was as high as ~11 mmol/g at 298 K and 760 torr, which is likely the highest among all the porous carbon-based materials reported so far. Ideally adsorbed solution theory (IAST) was employed to calculate the selectivity for CO2/N2, CO2/CH4, and CH4/N2, and some of the carbons reported a very high selectivity value. The overall results suggest that these carbons can potentially be used for gas separation purposes.

Electrochemical synthesis of fluorescence-enhanced carbon dots with multicolor emission via surface nitrogen and sulfur modulation for information encryption applications

Elucidating the mechanism of surface nitrogen and sulfur modulation in multicolor carbon dots via electrochemical methods for information encryption applications.

ZnIn2S4 with oxygen atom doping and surface sulfur vacancies for overall water splitting under visible light irradiation

The synergistic effect of sulfur vacancies and oxygen doping can increase the photogenerated carrier lifetime and inhibit carrier recombination in the bulk, which enhances the photocatalytic overall water splitting activity of ZnIn2S4 significantly.

Development of an ultrafast photo-switch device using surface passivated nanocrystalline CdS thin film

The development of an ultrafast optical switch is demonstrated in this work using a surface passivated nanocrystalline cadmium sulfide (CdS) thin film. The optical switching ratio of the Ag/CdS/Ag device, after surface passivation with nitrocellulose, is 2.1 × 104 in just 0.4 ms under a constant bias of 10 V and blue light (380 nm) of intensity ∼7.4 mW/cm2, which is 100 times higher than the native device. This is because the surface sulphur vacancy defects are suppressed, increasing the concentration of photo-generated free carriers.

Enhancement of xanthate adsorption on lead-modified and sulfurized smithsonite surface in the presence of ammonia

The contribution of ammonia to the sulfurization of Cu and Zn oxide minerals has been widely investigated, but the practical role of ammonia in the xanthate adsorption that directly determines the flotation of minerals has not been clearly confirmed. In this work, the promotion performance of NH3·H2O for xanthate adsorption onto the smithsonite surface was visually exhibited through adsorption density detection and the relating adsorption mechanism was revealed in terms of adsorption behavior and structure. Ultraviolet–visible spectroscopy and infrared spectroscopy tests showed that NH3·H2O treatment significantly increased the adsorption density of xanthate, with an increasing value of approximately 0.52 mg/m2 on the smithsonite surface at the initial xanthate concentration of 300 mg/L. With NH3·H2O treatment, the zeta potential of smithsonite particles increased, which was attributed to the chemisorption of Zn–NH3 complex cations on the mineral surface; such increased potential enhenced the proximity and adsorption probability for xanthate anions on the mineral surface through electrostatic attraction. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis indicated that Pb–xanthate was the main xanthate product chemisorbed onto the Pb-modified and sulfurized smithsonite surface; NH3·H2O effectively increased the number of Pb sites on the surface and facilitated the transformation of the Pb(II)–S state to the Pb(II) xanthate state, resulting in an increase of Pb–xanthate content on smithsonite surface. Thus, NH3·H2O improved the hydrophobicity and increased the flotation recovery of smithsonite by approximately 10% in the Pb ion-modified sulfurization–xanthate system.

Activating molybdenum carbide via a surface sulfur modification to enhance hydrogen evolution activity

Molybdenum carbide (Mo2C) was regarded as one of the most promising catalysts for hydrogen evolution reaction (HER) due to its Pt-like electronic structure. In practice, however, the catalytic performance of Mo2C is always hampered by the inevitable oxidation on its surface. Herein, we developed a simple and efficient strategy to improve the HER activity of Mo2C using sulfur as a "modifier", in which sulfur atoms were used to replace a portion of the oxygen atoms in the surface oxide layer to activate the surface. The experimental results demonstrated that a moderate sulfur modification could significantly improve the HER performance. Theoretical studies further revealed that the strong hydrogen bonding of Mo atoms in the oxide layer is the primary reason that impairs HER performance, whereas the S modification can shift down the d-band center of Mo, effectively weakening the Mo-H bond. As expected, the S-modified Mo2C exhibited superior performance, affording a low overpotential of 117 mV at 10 mA cm−2 for catalyzing the HER in 0.5 M H2SO4. This work provides a convenient and effective way for the development of transition metal carbide catalysts.

Investigation on Dynamic Changes in the Morphology and Fluorescence Properties of Sulfur Quantum Dots.

Sulfur quantum dots (SQDs), an emerging metal-free quantum dot, which has received intense research interest owing to their unique optical property, good solubility, excellent biocompatibility, and facile synthetic approach. Herein, using sodium hypochlorite as the etching agent, we investigate how it functions and transforms sulfur powder to SQDs and affects the dynamics, photoluminescence, and size changes of SQDs by controlling the reaction time. Precise control of reaction time allows SQDs to be tuned between green and blue (from 515 to 420 nm) with size distribution ranging from 2.0 to 20 nm as well as the occurrence of a distinctive irregular rodlike structure. Surface functional groups and element analysis reveal that the core size and surface oxidizing sulfur species both contribute to the versatile PL properties. Morevoer, we propose a tentative formation mechanism that relies on the oxidizing sulfur surface state and quantum size effect, offering a theoretical and experimental foundation for investigation of we propose a tentative formation mechanism that relies on the oxidizing sulfur surface state and quantum size effect, offering a theoretical and experimental foundation for investigation of the formation and modulation of SQDs.

Surface reconstruction and sulfur vacancies engineering in pentlandite for improving hydrogen evolution reaction

Transition metal sulfide pentlandite, (Fe, Ni)9S8, emerges as a prominent catalyst for electrolytic hydrogen evolution reaction (HER) owing to high conductivity and stability. In order to investigate the effect of sulfur (S) vacancy content on the HER activity of (Fe, Ni)9S8 for optimal HER activity, controlled levels of S vacancies need to be generated. Herein, Fe5Ni4S8−x electrocatalysts toward HER were developed through surface reconstruction and S vacancy engineering through a simple heat treatment method. The surface reconstruction could regulate the surface structure to be more stable and lead to a higher number of exposed active sites. S vacancies provided an Fe–Ni synergistic effect to facilitate the hydrogen adsorption, further improving catalytic activity. The optimal Fe5Ni4S8−xelectrocatalyst exhibited the overpotential of 107 mV at 10 mA cm−2 in acidic media. Tafel slope and electrochemical impedance spectroscopy further demonstrate that the proposed thermal treatment to modulate the S vacancy content is a feasible approach to further accelerate the HER kinetics. This study provides valuable insights for the rational formulation of high-efficiency pentlandite electrocatalysts.

Performance enhancement of elemental mercury removal from syngas over Fe7SC sorbent: Experimental and theoretical studies

In this study, a Fe7SC sorbent was prepared via hydrothermal impregnation and used to eliminate Hg0 from simulated syngas. A certain amount of oxygen was introduced to induce targeted H2S oxidation to form active surface sulfur species for the enhanced capture of Hg0 over Fe7SC. The effects of the introduced oxygen, temperature, and syngas composition (H2S, CO, H2, and H2O) on Hg0 adsorption performance were investigated. X-ray photoelectron spectroscopy, Hg0-temperature programmed desorption, and density functional theory calculations were performed to elucidate the Hg0 removal mechanism. Fe7SC exhibited a superior Hg0 removal performance (approximately 99.2%) in the presence of H2S + O2 at 150 °C. The interaction between H2S and the introduced oxygen was responsible for its superior Hg0 capture capacity. CO and H2 suppressed Hg0 adsorption, and H2O inhibited Hg0 removal owing to competitive adsorption. Results of the Bangham kinetic analysis indicate that Hg0 surface chemisorption is the primary rate-controlling step. Hg0 adsorption on the Fe7SC sorbent may follow the Eley–Rideal mechanism, in which the active sulfur species generated from H2S oxidation react with gaseous Hg0 to form HgS.

Sulfur-doped NiCo carbonate hydroxide with surface sulfate groups for highly enhanced electro-oxidation of urea

NiCo-based hydroxides are promising catalysts for urea oxidation reaction. To further enhance their catalytic performance, the combined effect of nonmetal heteroatom doping and surface functional groups on their catalytic behaviors deserves to be evaluated. Herein, as a proof of concept, both the sulfur-doped NiCo(OH)2CO3 with surface sulfate groups (SS-NiCo) and the surface-sulfated NiCo(OH)2CO3 (S-NiCo) are synthesized by hydrothermal method. The effect of sulfur doping and surface sulfate treatment on the morphology, crystal structure, electronic structure and electrochemical properties is comprehensively studied. It is found that both the incorporation of sulfur into the crystal structure and the introduction of surface sulfate groups can tune the electronic structure and thus promotes the intrinsic activity of the NiCo(OH)2CO3. Additionally, the surface sulfate groups can effectively reduce the series resistance and thus enhance the charge transfer/reaction kinetics. The optimized SS-NiCo catalyst delivers a current density of 100 mA cm−2 at 1.34 V vs RHE, which is much smaller than those of the S-NiCo (1.38 V) and the pristine NiCo(OH)2CO3 (1.43 V). In addition, the SS-NiCo catalyst shows good performance in the urea-assisted water electrolysis for hydrogen production.

Surface Passivation of III-V GaAs Nanopillars by Low-Frequency Plasma Deposition of Silicon Nitride for Active Nanophotonic Devices.

Numerous efforts have been devoted to improve the electronic and optical properties of III-V compound materials via reduction of their nonradiative states, aiming at highly efficient III-V sub-micrometer active devices and circuits. Despite many advances, the poor reproducibility and short-term passivation effect of chemical treatments, such as sulfidation and nitridation, requires the use of protective encapsulation methods, not only to protect the surface, but also to provide electrical isolation for device manufacturing. There is still a controversial debate on which combination of chemical treatment and capping dielectric layer can best reproducibly protect the crystal surface of III-V materials while being compatible with readily available semiconductor-foundry plasma deposition methods. This work reports on a systematic experimental study on the role of sulfide ammonium chemical treatment followed by dielectric coating (either silicon oxide or nitride) in the passivation effect of GaAs/AlGaAs nanopillars. Our results conclusively show that, under ambient conditions, the best surface passivation is achieved using ammonium sulfide followed by encapsulation with a thin layer of silicon nitride by low-frequency plasma-enhanced chemical deposition. Here, the sulfurized GaAs surfaces, high level of hydrogen ions, and low-frequency (380 kHz) excitation plasma that enable intense bombardment of hydrogen, all seem to provide a combined active role in the passivation mechanism of the pillars by reducing the surface states. As a result, we observe up to a 29-fold increase of the photoluminescence (PL) integrated intensity for the best samples as compared to untreated nanopillars. X-ray photoelectron spectroscopy analysis confirms the best treatments show remarkable removal of gallium and arsenic native oxides. Time-resolved micro-PL measurements display nanosecond lifetimes resulting in a record-low surface recombination velocity of ∼1.1 × 104 cm s-1 for dry-etched GaAs nanopillars. We achieve robust, stable, and long-term passivated nanopillar surfaces, which creates expectations for remarkable high internal quantum efficiency (IQE > 0.5) in nanoscale light-emitting diodes. The enhanced performance paves the way to many other nanostructures and devices such as miniature resonators, lasers, photodetectors, and solar cells, opening remarkable prospects for GaAs active nanophotonic devices.

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism.

As the solid waste by-product from the delayed coking process, high-sulfur petroleum coke (HSPC), which is hardly used for green utilization, becomes a promising raw material for Hg0 removal from coal-fired flue gas. The effects of the physical–chemical evolution of HSPC on Hg0 removal are discussed. The improved micropores created by pyrolysis and KOH activation could lead to over 50% of Hg0 removal efficiency with the loss of inherent sulfur. Additional S-containing and Br-containing additives are usually introduced to enhance active surface functional groups for Hg0 oxidation, where the main product are HgS, HgBr, and HgBr2. The chemical–mechanical activation method can make additives well loaded on the surface for Hg0 removal. The DFT method is used to sufficiently explain the micro-scale reaction mechanism of Hg0 oxidation on the surface of revised-HSPC. ReaxFF is usually employed for the simulation of the pyrolysis of HSPC. However, the developed mesoporous structure would be a better choice for Hg0 removal in that the coupled influence of pore structure and functional groups plays a comprehensive role in both adsorption and oxidation of Hg0. Thus, the optimal porous structure should be further explored. On the other hand, both internal and surface sulfur in HSPC should be enhanced to be exposed to saving sulfur additives or obtaining higher Hg0 removal capacity. For it, controllable pyrolysis with different pyrolysis parameters and the chemical–mechanical activation method is recommended to both improve pore structure and increase functional groups for Hg0 removal. For simulation methods, ReaxFF and DFT theory are expected to explain the micro-scale mechanisms of controllable pyrolysis, the chemical–mechanical activation of HSPC, and further Hg0 removal. This review work aims to provide both experimental and simulational guidance to promote the development of industrial application of Hg0 adsorbent based on HSPC.

Voltammetric investigation on iron-(nickel-)sulfur surface under conditions for the emergence of life

Iron (II) sulfide minerals have gained attention in the last decades due to their relevance in hypotheses for the emergence of life on the early Earth around 4 billion years ago. In the submarine vent theory, it has been proposed that those minerals, especially mackinawite, had a key role in prebiotic processes. Those are estimated to be present in a natural electrochemical setting, analogous to a chemiosmotic one, formed in the interface between the early ocean and the interior of the alkaline hydrothermal systems, the early vent-ocean interface. To evaluate this and other hypotheses, voltammetric studies were performed to better understand the electrochemical behavior of minerals under conditions analogous to the vent-ocean interface. The preliminary results presented here indicate that, in the potential range estimated to exist in that interface, mackinawite can transition to other mineral phases and may posibly coexist with other minerals, resulting from its oxidation. This can create a local chemical diversity. In addition, it has been tested a protocol for Ni incorporation in mackinawite structure, resulting in a surface that showed an interesting behavior in the presence of CO2, although definitive experiments showed necessary for a deeper comprehension of that behavior. Overall, the results are consistent with previous results on electrocatalytical properties of Fe-Ni-S materials for CO2 reduction, and also could lead to the emergence of a protometabolism on early Earth.

Experimental and theoretical analysis of elemental mercury removal from syngas over Fe-Ti spinel

A magnetic Fe-Ti spinel sorbent was synthesized by the co-precipitation method and applied to remove gaseous Hg0 from syngas. A superior Hg0 removal performance was achieved in the temperature range of 120–180 °C, and the highest an average removal efficiency of was approximately 95% at 150 °C under simulated syngas. H2S was adsorbed on the Fe-Ti spinel surface，which generated active sulfur species, and enhanced the Hg0 removal efficiency significantly. CO, H2 and H2O variably suppressed the Hg0 removal performance. H2S-pretreatment, X-ray photoelectron spectroscopy (XPS) and Hg0-temperature programmed desorption (Hg0-TPD) results demonstrated that Hg0 reacted with H2S over Fe-Ti spinel followed the Eley-Rideal mechanism, in which gas-phase Hg0 reacted with the active surface sulfur species generated from H2S oxidation and formed surface-bonded HgS. The surface Fe3+ and surface-active oxygen species were involved in the H2S and Hg0 adsorption and transformation process. Stability and regeneration cycling experiments indicated that Fe-Ti spinel exhibited excellent stability for Hg removal and great regeneration ability. Density functional theory (DFT) calculations showed that H2S underwent strong chemisorption on the Fe-Ti spinel surface with an adsorption energy of −116.988 kJ/mol, and then H2S further dissociated on the sorbent surface to generate active sulfur species, which reacted strongly with gas-phase Hg0 to form HgS.

Mineralogy and geochemistry of hot spring deposits at Námafjall, Iceland: Analog for sulfate soils at Gusev crater, Mars

AbstractIceland’s Námafjall geothermal area exhibits a range of alteration environments. Geochemical and mineralogical analyses of fumaroles and hot springs interacting with Holocene basaltic lavas at Hverir, and with Pleistocene hyaloclastites atop nearby Námaskarð hill, reveal different patterns of alteration depending on water-rock ratio, degree of oxidation, and substrate composition and age. The focus of this study is on the mineral deposits at and near hot springs at Hverir and Námaskarð. Surface samples, and samples collected from shallow pits in the alteration aprons adjacent to hot springs, were analyzed by X-ray diffraction (XRD) and X-ray fluorescence (XRF) to constrain the differences in composition with both distance and depth. Fluids were analyzed in the field for their environmental parameters and sampled for cation and anion analysis. Fluid analyses revealed uniformly acidic conditions but with site-to-site variation in other parameters such as temperature, salinity, and conductivity. Solid phases identified include amorphous silica, pyrite, elemental sulfur, and kaolinite in the muds, surrounded by Fe2+-sulfate and then Fe3+-sulfate efflorescence, following a redox gradient pattern involving the oxidation of sulfur and then iron with increasing distance. Shallow pits excavated near two Námaskarð hot springs reveal a shallow oxidation front, with sulfide-rich materials below a thin surface of sulfates and elemental sulfur. Silica phases include amorphous silica and quartz. Quartz likely reflects diagenetic maturation of earlier-formed amorphous silica, under surface hydrothermal conditions.The high iron content of the substrate basalt and the prevalence of Fe-sulfates and Fe-oxides among the alteration products make this geothermal area an especially useful analog for potential martian hydrothermal environments. In particular, these sulfate-rich deposits adjacent to volcanic, acidic hot springs could provide a helpful comparison for sulfur-rich soils in the Columbia Hills on Mars, where some of the same minerals have been identified (e.g., ferricopiapite) or inferred (e.g., rhomboclase).