Fe Hydroxides Research Articles

In Situ Quantification of the Active Sites, Turnover Frequency, and Stability of Ni–Fe (Oxy)hydroxides for the Oxygen Evolution Reaction

In Situ Quantification of the Active Sites, Turnover Frequency, and Stability of Ni–Fe (Oxy)hydroxides for the Oxygen Evolution Reaction

Polymorphs Fe hydroxides nanostructures growth via green route: Effect of olive leaves extract surfactant

Many researchers have shifted their interest towards eco-friendly, cost effective and green-based metal oxide nanoparticles. In this work, the formation of various hydroxides (Goethite, Protohematite and Feroxyhyte) is investigated during a green simple synthesis process. The major challenge is to follow the effect of Olive Leaves Extract (OLE) concentration. The OLE surfactant is used as a reduced agent to fabricate three samples with different amounts of OLE and the synthesis process is devised into three steps of dissolution, complexation (hydroxylation) and decomposition. The prepared materials are characterized structurally and/or morphologically by X-ray diffraction (XRD), Field emission-scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray Photoelectrons Spectroscopy (XPS), Thermo-gravimetric Analysis (TGA), Specific surface area analysis (BET) and Residual Gas Analysis (RGA). The increase of OLE concentration induces an increase of the surface area and finally the formation of well-ordered Fe hydroxide phase. Moreover a mechanism of Fe oxides formation is proposed.

Production of Cr(VI) from CrxFe1–x(OH)3 precipitates and NOM-Cr(III) colloids upon reaction with H2O2 under oxic conditions

Cr(III)-Fe(III) hydroxides (CrxFe1–x(OH)3 precipitates) and NOM-Cr(III) colloids are common products of Cr(VI) reduction during remediation and natural processes. However, re-oxidation of Cr(III) to Cr(VI) can undermine remediation efforts. Nevertheless, until now, less is known about the oxidation of Cr(III) from naturally occurring Cr(III) (i.e., CrxFe1–x(OH)3 precipitates and NOM-Cr(III) colloids) by H2O2. Here, we examined the oxidation of Cr(III) from Cr0.5Fe0.5(OH)3 and NOM-Cr(III) colloids by H2O2 under oxic conditions. Batch experiments demonstrated that Cr(VI) generation via Cr(III) oxidation from both Cr0.5Fe0.5(OH)3 and NOM-Cr(III) colloids increased with increasing H2O2 concentration. Increasing pH and addition of Fe2+ promoted Cr(III) oxidation, but the promoting effect of pH was more significant on Cr0.5Fe0.5(OH)3, whereas the promoting effect of Fe2+ was significant on NOM-Cr(III) colloids. By evaluating the effects of Fe species on Cr(VI) generation from Cr0.5Fe0.5(OH)3 and NOM-Cr(III) colloids, we proposed that an intermediate reactive Fe species formed during the reaction with H2O2 activated Cr(III) oxidation. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analyses collectively supported that the surface structural Fe in CrxFe1–x(OH)3 precipitates might contribute to the formation of reactive Fe species that promoted Cr(III) oxidation. In contrast, the decomposition of complexed NOM from NOM-Cr(III) colloids enabled the formation of Cr(III)-H2O2 complex that is favorable for subsequent Cr(III) oxidation. Results gained from this study provide a complete understanding of the long-term stability of naturally occurring Cr(III) under environmentally relevant conditions.

Electrolyte optimization of alkaline aqueous redox flow battery using iron-2,2-bis(hydroxymethyl)-2,2′,2′-nitrilotriethanol complex as active material for anolyte

In this study, optimal electrolyte condition of alkaline aqueous redox flow battery (ARFB) using iron-2,2-bis(hydroxymethyl)-2,2′,2′-nitrilotriethanol (Fe(BIS-TRIS)) and Ferrocyanide as redox couple is determined. Especially, the optimal condition of anolyte, including Fe(BIS-TRIS) and potassium hydroxide (KOH), is deeply explored. As a result, the stability of the anolyte is improved by controlling (i) the mixing ratio of metal to a ligand for the synthesis of Fe(BIS-TRIS) complex and (ii) the concentration of KOH, which is linked to hydroxyl (OH–) ion concentration. By systematic analysis, it is revealed that 2.75 M OH– ions are needed for the synthesis of 0.5 M Fe(BIS-TRIS) complex, while an additional 1.75 M OH– ions are further required to remain the anolyte stable. When the performance of ARFB using the redox couple prepared with the optimized anolyte is measured, its energy efficiency and discharging capacities are 78.6 % and 40.4 Ah L-1 at 80 mA cm−2. This implies that its performance can be compatible with those of conventional vanadium RFB. Conclusively, it is confirmed that Fe(BIS-TRIS) is viable active material for ARFB and the ARFB performance benefit induced by Fe(BIS-TRIS) is outstanding.

Disparate relationships between pH and goethite-water 18O/16O and D/H fractionation factors

For goethites synthesized at low (∼1–2) and high (∼13–14) extremes of pH, the values of 1000ln18αgt-w at ca. 25 °C are, respectively, +6.2(±0.6) and + 0.9(±0.6). Note that 18αgt-w = (18O/16O)gt/(18O/16O)w and gt = goethite (α-FeOOH); w = liquid water. A steady-state, flux-balance model indicates that this pH-related difference in values of 1000ln18αgt-w arises because of an effectively irreversible oxygen flux associated with aqueous Fe(III) hydroxide adsorption on, and incorporation in, goethite during growth at crystal surfaces. The model predicts that the transition from a low-pH to a high-pH value of 1000ln18αgt-w is relatively abrupt. At 22 to 25 °C, extant data indicate that the transition occurs in the interval of pH from about 6 to 8. Consequently, uncertainty about the pH of ancient waters could be a factor in interpretations of goethite δ18O values. However, an experimentally determined equation for the temperature dependence of 1000ln18α(LpH) has been applied with apparent success to natural goethites that formed in the presence of meteoric waters (18α(LpH) = low-pH 18αgt-w). This suggests that those ancient waters may have been acidic (pH < 6) in the immediate environments of goethite crystallization.Published values of D/H fractionation between synthetic goethite and water (Dαgt-w) show no systematic effect of either pH or temperature (T) over a range of pH from 1 to 14 and a range of T from 22 °C to 62 °C. Within these ranges, the average value of Dαgt-w is 0.905(±0.005) – a value which seems to characterize the D/H fractionation observed in natural goethites. If hydrogen in transitional, chemisorbed Fe(III) hydroxides – represented here as Fe(OH)3A – rapidly exchanges D/H with ambient water during crystal growth, there is a model-based expectation that Dαgt-w will not be affected by pH. This postulated D/H exchange would cease when Fe(OH)3A irreversibly transitions to FeOOH during crystallization – i.e., when Fe, O, and H are incorporated in the structure of the growing crystal.Thus, the flux balance model suggests that the observed dichotomy in the effects of pH on 18αgt-w and Dαgt-w is a result of distinctly different exchangeabilities of 18O/16O and D/H in transitional Fe(III) hydroxides that are chemisorbed on growing surfaces of goethite crystals. Observed values of 18αgt-w and Dαgt-w may represent steady-state – but not necessarily thermodynamic equilibrium – distributions of isotopes between H2O and the oxygen or hydrogen in the interiors of crystallizing goethites. Nevertheless, these steady-state values of Dαgt-w and 18αgt-w are generally reproducible and systematically relate δ18O and δD values of goethite to environmental variables.

Iron‑sulfur geochemistry and acidity retention in hydrologically active macropores of boreal acid sulfate soils: Effects of mitigation suspensions of fine-grained calcite and peat

Acid sulfate soils discharge large amounts of sulfuric acid along with toxic metals, deteriorating water quality and ecosystem health of recipient waterbodies. There is thus an urgent need to develop cost-effective and sustainable measures to mitigate the negative effects of these soils. In this study, we flushed aseptically-prepared MQ water (reference) or mitigation suspensions containing calcite, peat or a combination of both through 15-cm-thick soil cores from an acid sulfate soil field in western Finland, and investigated the geochemistry of Fe and S on the surfaces of macropores and in the solid columnar blocks (interiors) of the soil columns. The macropore surfaces of all soil columns were strongly enriched in total and HCl-extractable Fe and S relative to the interiors, owing to the existence of abundant Fe oxyhydroxysulfates (schwertmannite and partly jarosite) as yellow-to-brownish surface-coatings. The dissolution/hydrolysis of Fe oxyhydroxysulfates (predominantly jarosite) on the macropore surfaces of the reference columns, although being constantly flushed, effectively buffered the permeates at pH close to 4. These results suggest that Fe oxyhydroxysulfates accumulated on the macropore surfaces of boreal acid sulfate soils can act as long-lasting acidification sources. The treatments with mitigation suspensions led to a (near-)complete conversion of jarosite to Fe hydroxides, causing a substantial loss of S. In contrast, we did not observe any recognizable evidence indicating transformation of schwertmannite. However, sulfate sorbed by this mineral might be partially lost through anion-exchange processes during the treatments with calcite. No Fe sulfides were found in the peat-treated columns. Since Fe sulfides can support renewed acidification events, the moderate mineralogical changes induced by peat are desirable. In addition, peat materials can act as toxic-metal scavengers. Thus, the peat materials used here, which is relatively cheap in the boreal zone, is ideal for remediating boreal acid sulfate soils and other similar jarosite-bearing soils.

Synthesis of layered zinc-aluminium double hydroxides modified with metal ions as photocatalysts with enhanced sorption properties

In the article the process of Fe, Co, Ni and Cu hydroxides modified nanoparticles of layered double hydroxides (LDH) based on Zn and Al (Zn-Al LDH) was successfully presented. The precipitation method allowed to obtain nanoparticles of high crystallinity with lateral dimensions below 100 nm and thickness below 20 nm. The photocatalytic activity of the modified LDH in the degradation process of quinoline yellow was over 99%, while for the unmodified LDH the efficiency was only 30%. The study confirmed that modification of LDH with divalent ions had a significant effect on both photocatalytic and sorption properties. Furthermore, the study also investigated the effect of the nature of the type of light on the photodegradation efficiency.

Genesis of the Florida Canyon Nonsulfide Zn Ores (Northern Peru): New Insights Into the Supergene Mineralizing Events of the Bongará District

Abstract The Florida Canyon Zn deposit in the Bongará Province of northern Peru consists of sulfide and nonsulfide mineralizations within dolomitized strata of the Triassic Chambará Formation, a member of the Triassic-Jurassic Pucará Group. The nonsulfide mineralization, which represents one third of the total resource, formed by supergene alteration of Mississippi Valley-type sulfide bodies. The nonsulfide assemblages occur in stratabound or fault-related, discordant zones that mimic the shapes of the former sulfide zones. Two nonsulfide facies can be distinguished: facies 1 – red zinc ores, which are characterized by smithsonite, or hemimorphite-dominant bodies that formed by direct replacement of primary sulfide assemblages, and facies 2 – white zinc ores, which are characterized by masses of colloform smithsonite formed by replacement of wall rock. The facies are distinct in bulk chemical composition and stable isotope geochemistry. Facies 1 shows high concentrations of Zn, Pb, Fe, Ge, Mn, and As, whereas facies 2 shows only high Zn and Cd concentrations. Enrichments in Ge, which have been reported in other Zn deposits of the Bongará Province, are associated with hemimorphite, Fe hydroxides, and remnant sphalerite in facies 1. The δ13C and δ18O signatures of smithsonite in both facies suggest that meteoric waters infiltrating the precursor sulfide bodies were affected by kinetic fractionation and originated from multiple sources at different altitude.

Contribution of sedimentary organic matter to arsenic mobilization along a potential natural reactive barrier (NRB) near a river: The Meghna river, Bangladesh

Elevated dissolved arsenic (As) concentrations in the shallow aquifers of Bangladesh are primarily caused by microbially-mediated reduction of As-bearing iron (Fe) (oxy)hydroxides in organic matter (OM) rich, reducing environments. Along the Meghna River in Bangladesh, interactions between the river and groundwater within the hyporheic zone cause fluctuating redox conditions responsible for the formation of a Fe-rich natural reactive barrier (NRB) capable of sequestering As. To understand the NRB's impact on As mobility, the geochemistry of riverbank sediment (<3 m depth) and the underlying aquifer sediment (up to 37 m depth) was analyzed. A 24-hr sediment-water extraction experiment was performed to simulate interactions of these sediments with oxic river water. The sediment and the sediment-water extracts were analyzed for inorganic and organic chemical parameters. Results revealed no differences between the elemental composition of riverbank and aquifer sediments, which contained 40 ± 12 g/kg of Fe and 7 ± 2 mg/kg of As, respectively. Yet the amounts of inorganic and organic constituents extracted were substantially different between riverbank and aquifer sediments. The water extracted 6.4 ± 16.1 mg/kg of Fe and 0.03 ± 0.02 mg/kg of As from riverbank sediments, compared to 154.0 ± 98.1 mg/kg of Fe and 0.55 ± 0.40 mg/kg of As from aquifer sediments. The riverbank and aquifer sands contained similar amounts of sedimentary organic matter (SOM) (17,705.2 ± 5157.6 mg/kg). However, the water-extractable fraction of SOM varied substantially, i.e., 67.4 ± 72.3 mg/kg in riverbank sands, and 1330.3 ± 226.6 mg/kg in aquifer sands. Detailed characterization showed that the riverbank SOM was protein-like, fresh, low molecular weight, and labile, whereas SOM in aquifer sands was humic-like, older, high molecular weight, and recalcitrant. During the dry season, oxic conditions in the riverbank may promote aerobic metabolisms, limiting As mobility within the NRB.

Attenuation of antimony in groundwater from the Xikuangshan antimony mine, China: Evidence from sulfur and molybdenum isotope study

The Xikuangshan (XKS) mine, an antimony mine that has been active for more than a century, was chosen for a detailed antimony hydrogeochemical study because of the historical antimony contamination in local bedrock aquifers. Hydrochemical data, δ34S values of dissolved SO42−, and δ98Mo values were analyzed to identify the predominant geochemical processes affecting Sb attenuation within the aquifers. Groundwater from the adits at the XKS Sb mine reflects an oxidizing environment and has pH values between 6.81 and 8.89 because of the sufficient acid-neutralizing effect of carbonates. The decrease in Sb concentrations along the groundwater flow direction and the highly coloured deposits in the adits indicate Fe and Mn oxides have a significant capacity for Sb sorption. The δ34S values of the groundwater indicate that reductive dissolution of Fe(III) hydroxides is not the dominant process controlling Sb mobilization. Furthermore, the δ34S values and weak-alkaline groundwater corporately suggest that Sb adsorption on and desorption from Fe/Mn (hydr)oxides may both occur, with adsorption being more significant than desorption with respect to Sb attenuation in groundwater. The δ98Mo values of the groundwater further demonstrate that this adsorption is relatively significant in terms of Sb attenuation, and that competitive adsorption may occur between Sb and As in groundwater at the XKS Sb mine. Overall, the hydrochemistry analysis, especially the S and Mo isotope evidences collectively elucidate that the attenuation of Sb in groundwater from the XKS Sb mine are influenced by several geochemical processes, including: (1) more adsorption on than desorption from Fe/Mn (hydr)oxides; (2) competitive adsorption of arsenic; and (3) dilution with low-Sb groundwaters. This study demonstrates that hydrochemical analyses, particularly S and Mo isotope studies, are useful for tracking Sb attenuation in groundwater from antimony-contaminated mine areas.

Phosphate mineral solubility controls on cassava root exudates, rhizosphere nutrient availability, and plant nutrient accumulation

Phosphorus (P) is the most limiting essential nutrient in soil-plant systems; its availability is mainly dependent on host cationic metals/nutrients. However, P mineral solubility impacts plant root exudates and P solubility in the rhizosphere zone, with both P and host plant nutrient accumulation in the plant being poorly understood. This work developed the acid-washed-sand-hydroponic-hybrid technique to examine root exudates (protons and organic acid), P fractions, and nutrient accumulation in cassava exposed to P mineral with different solubilities (FePO4, Ca3(PO4)2, KH2PO4, and to no P addition). The root-to-shoot biomass data demonstrated that the cassava responded equally to different P minerals. Nevertheless, the P minerals substantially influenced the root proton and organic acid effluxes, with protons being the primary constituent released from the roots, corresponding to 99.75% of the total release of protons and organic acid. The sparingly soluble FePO4 and Ca3(PO4)2 treatments induced cassava to release fewer protons (449 and 480 μmol L−1 h−1 g−1 fresh weight root, respectively) from the roots than the highly soluble KH2PO4 treatment (630 μmol L−1 h−1 g−1 fresh weight root). The KH2PO4 treatment promoted higher oxalic acid release from the roots (3.31 μmol L−1 h−1 g−1 fresh weight root) than other treatments. The P fractions based on the sequential extraction technique revealed that the easily dissolved H2PO4− ion from the KH2PO4 compound could readily react with dissolved Fe in the sand material, possibly forming P bound to the Fe hydroxide fraction. Nevertheless, the positive relationship between the P bound to the Fe hydroxide and the P concentration in different plant parts (R2 = 0.39–0.89) showed that the newly formed Fe-bound P fraction could be available for plant assimilation. Notably, the Fe, Ca, and K concentrations in the plant parts were abundant in the respective FePO4, Ca3(PO4)2, and KH2PO4 treatments. Overall, the different P minerals considerably regulated the release of protons and ligands from cassava roots, with the released protons potentially promoting the release of the host metal of P minerals through the proton-promoted dissolution of the host metal oxides. In contrast, the released organic anions could enhance plant P availability by a ligand-exchange mechanism. This study highlighted the importance of phosphate minerals and their host metals in triggering root proton and organic ligand effluxes and in improving P availability and the P and cationic uptake by plants.

New method for efficient removal of Cr(VI) by recoverable magnetic nitrogen-doped carbon aerogel microspheres: Kinetics and mechanism

• The nZVI and N co-doped magnetic carbon aerogel composites were synthesized. • nZVI@NCA900 displayed high Cr(VI) removal capacity of 266.79 mg·g −1 at 318 K. • Cr(VI) can be reduced to Cr(III) by nZVI and N-containing functional groups. • Simulation results by DFT prove that N-doped show positive effect. • The nZVI@NCA could provide magnetism after several adsorption and desorption cycles. The efficient removal of hexavalent chromium from solution is a challenging task, in this paper, the nZVI and nitrogen co-doped magnetic carbon aerogel microsphere composites (nZVI@NCAs) were prepared via the microemulsion polymerization and subsequent carbonization process, and were expected to satisfactory performance in the removal of Cr(VI). From batch experiments, the Cr(VI) removal process by nZVI@NCA900 fitted better with the pseudo-second-order model. The optimal nZVI@NCA900 was superior to that of most magnetic carbon-substrate composites, displaying high Cr(VI) adsorption capacity of 266.79 mg·g −1 at 318 K. Additionally, it was found that Cr(VI) was reduced to the low-toxicity Cr(III) from the results analyzed by XPS, and nZVI@NCA900 exhibited Cr(VI) reduction performance of 33.92% Cr(VI) reduced to Cr(III). The reaction between the nZVI@NCAs and Cr(VI) was pH-dependence, endothermic and spontaneous. Removal mechanisms might involve multiple processes. The nZVI particles on the surface acted as reductants to reduce Cr(VI) to Cr(III) and form Cr(III)/Fe(III) hydroxides to precipitate on nZVI@NCAs. Simulation results by DFT prove that N is an active site and show positive effect in the adsorption system. N atoms were used as active sites to stabilize the interaction with Cr(VI) via adsorption attributed to electrostatic and act as electron donors for reduction of Cr(VI). The nZVI particles encapsulated by carbon aerogels could provide magnetic stability after acid reaction, which was beneficial to the separation of adsorbents after reaction and reuse for many cycles. These results provide a new view for developing magnetic carbon materials to remove Cr(VI) from contaminated water.

Evaluation of the dual-process approach for in-situ groundwater arsenic removal

ABSTRACT While the worldwide distribution of geogenic arsenic (As)-affected groundwater is highly overlapped with the areas with abundant groundwater, utilization of As-contained groundwater is an inevitable compromise in those areas where surface water is not enough for irrigation. Since the occurrence of As in groundwater is often accompanied by high iron (Fe) contents, the facilitation of As and Fe precipitation without adding additional oxidizers and adsorbents is considered an environmental-friendly approach to removing As in groundwater. In the present study, the oxidation/filtration dual-process with sprinkling height of 25 cm and 120 kg filter media efficiently increased the dissolved oxygen (DO) concentration (0.36–1.52 mg/L) and oxidation–reduction potential (ORP) (24–63 mV), which facilitated the formation of Fe oxides and As co-precipitation. The correlation of As removal efficiencies with their respective flow rates indicated that a decrease in groundwater Fe and an increase of Fe in sands and gravels filters as the flow rate increased evidenced the rapid oxidation of Fe to form the Fe hydroxides. In a 40-hour continuous aeration/filtration operation, As and Fe concentrations in groundwater were reduced by 79.5% and 64.88% within 40 hrs, respectively. The ease of filter replacement and cost-effectiveness in operation can be the major attractions and innovations for future field practices.

Amorphous Fe hydroxide nanoparticles embedded in Ni3S2 as high-efficiency and low-cost electrocatalysts for oxygen evolution reaction

For hydrogen production from water splitting, the development of low-cost while high-efficiency electrocatalysts for oxygen evolution reaction (OER) is of great significance. Here, via facile hydrolysis at room temperature, amorphous Fe hydroxide nanoparticles are attached to the Ni3S2 which is intergrown in situ on nickel foam, forming a novel hierarchical system of Fe(OH)3@Ni3S2/NF as outstanding electrocatalysts for OER. By changing the immersion time (0.5, 1, and 2 days) of the synthesized Ni3S2/NF and the Fe3+concentrations (10, 30 and 50 mM), the optimized material of Fe(OH)3@Ni3S2/NF-D1–30 (D1 refers to the immersion time of one day, and 30 means the Fe3+concentration of 30 mM) exhibits excellent OER performance in alkaline medium (1 M KOH). Making good use of interfacial interaction and synergistic effect between Fe(OH)3 and Ni3S2, this novel catalyst require extremely low overpotentials of 173 and 242 mV to achieve the current densities of 10 and 50 mA cm−2, and the Tafel slope of 45 mV dec−1 is even smaller than that (66 mV/dec) of RuO2/NF. At the same time, the Fe(OH)3@Ni3S2/NF-D1–30 exhibits extraordinary strong durability (≥ 80 h) at the high current density of 50 mA cm−2. The presence of Fe hydroxide nanoparticles in amorphous state brings out more active sites, and the interface between Fe(OH)3 and Ni3S2 may accelerate the electron transport, which both contribute to the improved OER performance. This study offers neoteric research ideas for the design and fabrication of novel OER electrocatalysts by constructing interfacial structure of nanomaterials, thus having far-reaching value.

Peach Gum‐Derived S,N Co‐Doped Nanoporous Carbon Coupled with Layered Double (Ni, Fe) Hydroxide for Efficient Bifunctional Oxygen Electrocatalysis in Zn‐Air Batteries

AbstractLow‐cost and high activity bifunctional oxygen electrocatalysts are at the heart of developing advanced rechargeable Zn‐air batteries (ZABs), but the challenges are great. Herein, a highly efficient hybrid catalyst, consisting of S, N co‐doped nanoporous carbon (SNC) coupled with in‐situ growth layered double (Ni, Fe) hydroxide (LDH), was derived from the biomass peach gum by a series of treatments, including hydrothermal carbonization, alkali activation, S/N co‐doping and metal‐coprecipitation process. Benefiting from the coexistence of active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the hybrid (NiFe‐LDH/SNC) reveals excellent bifunctional electrocatalytic activity with a small ΔE of 794 mV. Furthermore, as the cathode bifunctional catalyst for ZAB, the battery with NiFe‐LDH/SNC displays a large open‐circuit voltage of 1.36 V, a high power density/specific capacity of 100 mW cm−2/816 mAh gZn−1, and superior cycling durability up to 500 h at a charge/recharge current density of 2 mA cm−2, indicating its great application potential in the rechargeable metal‐air batteries.

Investigation on the correlation between ferrous ion and the floatability of pyrite with different oxidation degrees

This work aims to establish the quantitative relationship between the surface oxidation state of pyrite and flotation performance. In this paper, an efficient method was proposed to prepare pyrite with different oxidation degrees. Flotation tests show that the floatability of pyrite decreased with prolonging the oxidation time. Tof-SIMS results reveal that the main component on the oxidized pyrite surface is Fe hydroxides or oxides. XPS analysis confirms that Fe(OH)2 and FeOOH are the main formula of Fe species, and the ratio of Fe2+/Total Fe agrees well with the floatability of pyrite with different oxidation degrees, which can be taken as an index to develop the flotation performance of pyrite. DFT simulation calculation further demonstrates the reliability of Fe(OH)2 as the active site. This study provides essential surface chemistry evidence for correlating the surface species with the floatability of pyrite with different oxidation states through quantitative analysis of various intermediate products.

Why CoCrFeMnNi HEA could not passivate in chloride solution? – A novel strategy to significantly improve corrosion resistance of CoCrFeMnNi HEA by N-alloying

This work elaborated the underlying mechanism for the non-passivation of CoCrFeMnNi HEA in chloride solution based on the dissolution-diffusion-deposition model. A novel N-alloying strategy was proposed to significantly improve the corrosion resistance of CoCrFeMnNi HEA. Modelling results indicated that N could consume H+ and relieve the acidification on the surface of HEA, thus accelerating deposition of Cr and Fe oxides and hydroxides. Thereby, the nucleation rate and growth rate of passive film were apparently enhanced after N-alloying, which agreed well with the less defective and thinner passive film. Finally, the element selection for designing corrosion resistant HEAs was recommended.

Eco-utilization of steel slag: Preparation of Fe-based calcium silicate hydrate and its application in As(V) removal

Arsenic (As), a carcinogenic heavy metal, is a toxic environmental pollutant that threatens human and environmental health. Here, a cost-effective and high-performance Fe-based calcium silicate hydrate (Fe-CSH) was synthesized through a one-step alkaline activation process using steel slag as an in situ Ca and Fe source to treat As(V)-containing solutions. The synthesized Fe-CSH exhibited a flower-like structure with numerous interleaving nanosheets, which provided abundant adsorption sites. More importantly, this compound could remove large quantities of As(V) from wastewater, achieving maximum adsorption capacities of up to 141.5 mg/g at a pH of 5. The adsorption kinetics were consistent with a Langmuir isotherm model and followed pseudo-second-order and intra-particle diffusion kinetics. Thermodynamics analyses indicated that the adsorption process was spontaneous and feasible. XRD, FTIR, SEM, TEM, and XPS analyses indicated that the outstanding adsorption performance of the Fe-CSH could be due to the release of Ca2+ and OH– from this material. The released Ca2+ reacted with arsenate ions via coprecipitation, whereas OH– promoted the generation of Fe hydroxide from iron ions, which adsorb As(V) by forming stable bidentate surface complexes. Ultimately, a potential process was proposed for the remediation of As-containing wastewater using hierarchically structured Fe-CSH derived from steel slag. The “trash-to-treasure” strategy implemented for the repurposing of steel slag and the remediation of As-contaminated wastewater are both conducive to sustainable development.

Nanoemulsion-Coated Ni-Fe Hydroxide Self-Supported Electrode as an Air-Breathing Cathode for High-Performance Zinc-Air Batteries.

To improve the energy conversion efficiency and durability of zinc-air batteries (ZABs) for large-scale implementations, here we propose an "air-breathing" strategy to significantly enlarge triple-interfaces with intensified mass transfer. By dip-coating the aerophilic perfluorochemical compounds (PFC) and amphiphilic ionomers into the self-supported electrodes, (1) the high solubility of O2 in the PFC nanoemulsions greatly increases triple-phase boundaries and facilitates the efficient supply/removal of O2 from the electrolyte; (2) the ionomers with hydrophobic and hydrophilic functionalities enable fast gas, water, and ion transport to the triple-phase boundaries; and (3) the self-supported electrode without binder ensures fast electron transfer while the firm integration prevents catalyst shedding. By applying this strategy, the ZABs show a high power density of 115 mW cm-2 and a narrow discharge/charge gap of 0.64 V at 10 mA cm-2 and a long-cycling durability (over 1000 h). This work provides a universal approach to promote gas-evolving reactions for electrochemical applications.

Limited roles of anthropogenic activities on arsenic mobilization in groundwater from the Yinchuan Basin, China

Arsenic (As) pollution in groundwater is an extremely concerning issue all over the world, because it has brought many negative health effects on people. However, the impact of anthropogenic activities on the formation of high As groundwater is poorly understood. Seventy-nine groundwater samples and seven surface water samples were taken along two transects in the Yinchuan Basin, China, to trace effects of anthropogenic activities on distribution of high As groundwater by using artificial sweeteners. The sampling campaign showed that, in 47% of samples, As concentrations exceeded the WHO drinking water guideline (10 μg/L). Both acesulfame and sucralose were detected in the groundwater samples, and concentrations in samples from the transect of the upper stream of regional groundwater were generally higher than those from the transect of the middle stream. Both acesulfame and sucralose in all studied groundwater samples had the detection rate (DR) > 7 and the detection frequency (DF) > 90%, indicating that they can be used as tracers to reflect anthropogenic activities. Higher As groundwater samples generally had lower concentrations of the artificial sweeteners and vice versa, showing that the influence of anthropogenic activities on high As concentration was limited. Geological processes are the main reason for the formation of high As groundwater. High As groundwaters were characterized by moderate reducing conditions, and the reductive dissolution of Fe(III) hydroxides led to the release of the adsorbed As into groundwater. Additionally, As desorption was another process to mobilize As under the conditions of elevated pH and/or high HCO3−. This study provides an insight into relative contribution of anthropogenic activities and hydrogeochemical conditions to As enrichment in groundwater, and highlights the necessity in protecting low As groundwater highly vulnerable to human activities in high As-groundwater areas.