Structural transformation and performances of green rust for water decontamination: A review.

Electrochemical hydrogen peroxide and enzymatic glucose sensors based on silver‑copper (I)-nanoparticles-oxidized green rust nanohybrids

Alkaline hydrothermal vents are plausible environments for the emergence of life on Earth. By means of a simplified analogical reconstruction of the vent-ocean interface of these systems reproducing early Earth conditions, we show that iron (oxy-hydr)oxide minerals may have carried out proto-bioenergetic processes driven by pH and redox gradients. The initial pH gradient precipitates the iron (oxy-hydr)oxide mineral barriers (magnetite, green rust and amakinite) and yields reducing conditions, enabling the production of metallic iron at room temperature via the disproportionation of Fe2+ to Fe3+ and Fe0. The crystallographic association of Fe0 surrounded by magnetite suggests the coupling of Fe3+ / H2 co-production at ambient temperature by amakinite oxidation with the thermodynamically unfavorable reduction of Fe2+ to Fe0. This abiotic disproportionation process coupling exergonic and endergonic reactions may serve as a proto-bioenergetic mechanism increasing the non-equilibrium reduction state of the system and offers an interesting analog of the biological electronic bifurcation reaction, the free energy coupling being a fundamental thermodynamic trait of life-as-we-know-it.

Green rust (GR) isa mixed-valent Fe-layered double hydroxide (Fe­(II)–Fe­(III)-LDH)mineral that is prevalent in reducing geochemical environments, whereit exhibits high sorption and redox reactivity. Here, we examinedthe morphology and chemistry of individual GR particles with nanoscaleresolution in the presence and absence of Ni­(II)aq at reactiontimes between 1 h and 3 months using scanning transmission electronmicroscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDXS).During the first day of reaction, sorbed Ni­(II) accumulated alongsideFe in ∼10 nm thick rims around the GR particle edges, consistentwith the formation of mixed Ni­(II)/Fe­(II)–Fe­(III)-LDH. After3 months, the rims were thinner and contained less Ni­(II) despitea doubling of the sorbed load, suggesting sequestration of Ni­(II)sorbates into the bulk during aging. Sequential extractions similarlyprovided evidence for declining levels of sorbed Ni­(II) at the GRsurface with time, concurrent with increasing levels inside the mineralbulk. The combined STEM-EDXS and extraction results demonstrate chemicaland structural variations across GR particle surfaces and redistributionof Ni­(II) sorbates during aging over time scales of days–weeks.These findings provide new mechanistic insights into the processescontrolling the partitioning and mobility of trace metals in reducinggeochemical systems.

Nanoenabled phosphorus fertilizers offer controlled release to improve phosphorus utilization efficiency (PUE) and reduce environmental impact, but their performance, particularly in alkaline soils, remains limited. Herein, a P-delivery nanoplatform (PDN) was constructed utilizing a nanoscale magnesium phosphate (nMgP)-supported iron-based layer double hydroxide (green rust, GR) nanocomposite. Its efficacy was evaluated in maize grown in P-deficient soils with pH values of 4.9 and 8.5. Soil-applied PDN (180 mg P/kg soil) significantly enhanced maize photosynthesis by 31.6-32.5% and fresh biomass by 6.9-27.3%, with agronomic efficacy (AE) increasing by 21.1-39.3% over conventional P fertilizers (CPFs). Crucially, lower PDN doses (45-90 mg P/kg soil) could improve maize growth as effectively as CPFs (180 mg P/kg soil), enhancing PUE by 1.6-2.0 times and AE by 159.8-189.5%. Mechanistically, PDN integrated GR-optimized nMgP dissolution, GR-mediated passivation suppression, and GR-P ligand-exchange, synergistically sustaining rhizosphere P bioavailability to minimize leaching and enhance P uptake by maize. Moreover, PDN conversion to bioavailable P species in the rhizosphere could drive the proliferation of beneficial bacteria, creating a growth-enhancing feedback loop. This work presents a new strategy for designing nanomaterials as P-delivery platforms to optimize PUE in crop production, promoting the development of environment-friendly nanoenabled agriculture.

In-situ formation of green rust during Fe(II) coagulation: Dual reductive and adsorptive pathways for dyeing wastewater treatment.

Abstract Ultraviolet (UV) photooxidation has been considered a viable pathway to oxidize aqueous ferrous iron expected to have been present in early Martian surface waters. This reaction has been proposed to have created iron mineral deposits in Meridiani Planum as well as Gale Crater and would have affected chemical conditions such as pH and dissolved iron concentrations. Previous experimental work has not focused on the influence of atmospheric CO 2 on aqueous ferrous iron photooxidation. Atmospheric CO 2 would have been an important factor since climate models require high pCO 2 (in addition to other greenhouse species) to stabilize liquid water on the ancient surface environment of Mars. In this work, we conducted two types of irradiation experiments under anoxic conditions, with solutions containing ∼100 ppm (1–2 mM) iron and 0–35 mM dissolved inorganic carbon (DIC) at initial pH varying between 3 and 8. Utilizing two experimental setups revealed the importance of DIC within these solutions in determining the fate of iron. When the solutions experience CO 2 degassing, pH increases in a predictable manner and iron is removed from solution and precipitates as carbonate green rust and magnetite. When DIC remains in solution in the absence of degassing effects, the pH changes and iron losses were minimized. Under these conditions, UV‐ induced iron photooxidation does not occur. These results imply that under the assumption of a 1 bar CO 2 atmosphere, ferrous iron in surface environments would not have been photooxidized and would have remained as a stable species in solution in the absence of other oxidants.

Transport of green rust and biochar mixtures in porous media for in-situ remediation of chlorinated ethylenes.

Novel ECOMF system: In situ ferrate generation for contaminant removal and fouling mitigation in brackish water desalination.

A novel approach based on PEM electrolysis technology for iron recovery from acid mine drainage: performance and mechanism.

Simple preparation of floating magnetic particles for oil recovery using the ferrite production process in the presence of long-carbon-chain surfactants.

Iron electrocoagulation (EC) is promising for selenium(VI) removal from water. This study investigated the performance of flow-through iron EC under environmentally relevant conditions. The influence of water composition on Se removal and the mechanisms by which water components affect Se removal were studied. The individual effects of major anions (bicarbonate, sulfate, and nitrate) and humic acid on selenate removal were examined under pH 8 anoxic conditions, at which selenate removal was previously demonstrated to be effective in a simple water composition. Bicarbonate inhibited Se removal by promoting the formation of less reactive iron solids (carbonate-containing green rust). Sulfate inhibited the oxidation and transformation of iron solids, thereby limiting their reactivity with selenate. Nitrate and humic acid had a smaller impact on Se removal compared to bicarbonate and sulfate. Building on the work with individual constituents, flow-through EC was applied to treat challenge waters that represent mining discharge, agricultural runoff, and flue-gas desulfurization wastewater. Sulfate and ionic strength were major inhibitors for Se removal in those waters, and an iron dose of 240 mg/L was required for effective Se removal. Pretreatment to remove sulfate improved the EC performance for Se removal from agriculture and mining wastewater, but it had little effect for flue-gas desulfurization wastewater. The impact of major anions and humic acid on solids formation, redox, and adsorption in flow-through EC processes provided valuable insights into removal mechanisms and practical guidance for predicting EC performance in real-world water treatment.

Effects of different natural organic matter on catalytic properties of green rust: Mechanism and environmental significance.

Abstract The fuel additive and pesticide 1,2-dibromoethane (DBA) is a problematic organic pollutant found in soil and aquifers. Remediation methods face drawbacks because of undesirable by-products and slow rates of removal. Biochars (BCs) are catalysts of reductive dehalogenation in anoxic environments by the layered iron(II)-iron(III) hydroxide green rust (GR). However, so far, such catalytic properties have generally only been observed for BCs produced from animal substrates, while BCs from easily available plant substrates, seem to lack these properties. In this study, the potential of CO2 activation to enhance the catalytic properties of plant-substrate BCs was tested, specifically for BCs from barley straw (BARST), soybean meal (SOYM), wheat straw (WHST) and eelgrass (Zostera marina, ZOST). All BCs were tested for catalyzing reductive debromination of DBA with GR as the reductant. CO2 activation led to clear increases in the extent of DBA debromination (after 7 days) by a factor of 1.5, 8.8, 3.3, and 2.1 for GR reactions with BARST, SOYM, WHST, and ZOST BCs respectively. Changes in BC properties were observed upon CO2 activation, and these varied between substrates, making it difficult to define the key properties that led to the observed reactivity increase. However, surface polarity, structural defects and the presence of surface O and N functional groups were identified as key BC properties regulating the extent of DBA sorption and degradation. The findings of this study contribute to the optimization of BC mediators for reduction of halogenated pollutants. Graphical abstract

Arsenic immobilization in soils and sediments is primarilycontrolledby its sorption onto or incorporation into reactive soil minerals,such as iron (oxyhydr)­oxides. However, coexisting ions (e.g., dissolvedbicarbonate, phosphate, silica, and organic matter) can negativelyimpact the interaction of the toxic arsenate species with iron (oxy)­hydroxides.Of special note is inorganic phosphate, which is a strong competitorfor sorption sites due to its analogous chemical and structural natureto inorganic arsenate. Much of our understanding of this competingnature between phosphate and arsenate focuses on the impact on mineralsorption capacities and kinetics. However, we know very little abouthow coexisting phosphate will alter the stability and transformationpathways of arsenate-bearing Fe (oxyhydr)­oxides. In particular, thelong-term fate and behavior regarding arsenate immobilization areunknown under anoxic conditions. Here, we document, through mineraltransformation reactions, the immobilization of both phosphate (P)and arsenate [As­(V)] in secondary mineral products and characterizetheir changing compositions during the transformations. We did thiswhile controlling the initial P/As­(V) ratios. Our results documentthat, in the absence or at low P/As­(V) ratios, the initial ferrihydriterapidly transforms to green rust sulfate (GRSO4), which further transforms into magnetite after 180 days. Meanwhile,high P/As­(V) ratios resulted in a mixture of GRSO4 and vivianite, with magnetite as a minor fraction. Invariably,the speciation and partitioning of As­(V) were also affected by theP/As­(V) ratio. A higher P/As­(V) ratio also led to a faster partialreduction of mineral-bound As­(V) to As­(III). The most important findingis that the initial ferrihydrite-bound As­(V) became structurally incorporatedinto magnetite [low P/As­(V) ratio] or vivianite [high P/As­(V) ratio]and was thus immobilized and not labile. Overall, our results highlightthe influence of coexisting phosphate in controlling the toxicityand mobility in anoxic, Fe2+-rich subsurface settings,such as contaminated aquifers.

Excessive intake of fluorine (F) over time can lead to acute or chronic fluorosis. In this study, a novel FeIII-CeIV-based layered hydroxide composite (DD-LHC) was synthesized and applied in both batch and column modes to develop new adsorbent materials and to obtain efficient removal of fluorine (F) anions from wastewater. DD-LHC achieved better adsorption results and material stability compared to green rusts (GR, FeII-FeIII hydroxide). The maximum adsorption capacity of DD-LHC for F- was 44.68 mmol·g-1, obtained at an initial pH of 5 and initial concentration of 80 mM. The substitution of CeIV for FeII in the intercalated layered structure of GR potentially changed the reaction pathways for F- removal, which are typically dominant in the layered double hydroxides (LDHs) of FeII-FeIII. The molecular structure of layered hydroxides combined with the three-dimensional (3D) metal frame of Fe-O-Ce was integrated into DD-LHC, resulting in nanoscale particle morphologies distinct from those of GR. The pseudo-first-order kinetic model effectively described the whole adsorption process of DD-LHC for F-. DD-LHC exhibited notable selectivity for F- across a wide pH range. The removal process of F- by DD-LHC was dominated by Ce-F coordination bonds, with additional influences from auxiliary pathways to different extents.

Unveiling the dual role of calcium peroxide in enhancing green rust-catalyzed arsenite oxidation and stabilization.

Simultaneous removal of Cr(VI), As(III), and sulfanilamide via an e-barrier electrochemical system: A pilot study.

Biogeochemical controls on iron speciation and cycling across upland to shoreline gradients in freshwater and estuarine coastal soils (Lake Erie and Chesapeake Bay, United States).

Geological structures known as alkaline hydrothermal vents (AHVs) likely displayed dynamic energy characteristics analogous to cellular chemiosmosis and contained iron-oxyhydroxide green rusts in the early Earth. Under specific conditions, those minerals could have acted as non-enzymatic catalysts in the development of early bioenergetic chemiosmotic energy systems while being integrated into the membrane of AHV-produced organic vesicles. Here, we show that the simultaneous addition of two probable AHV components, namely nickel and amino acids, impacts green rust's physico-chemical properties, especially those required for its incorporation in lipid vesicle's membranes, such as decreasing the mineral size to the nanometer scale and increasing its hydrophobicity. These results suggest that such hydrophobic nano green rusts could fit into lipid vesicle membranes and could have functioned as a primitive, inorganic precursor to modern chemiosmotic metalloenzymes, facilitating both electron and proton transport in early life-like systems.