Amorphous Iron Oxide Research Articles

Amorphous iron oxides protect aggregate-associated organic carbon from microbial utilization and decomposition evidenced from the natural abundance of 13C

Iron oxides play a critical role in promoting organic carbon sequestration through adsorption or co-precipitation. However, the effects of iron oxide types on the stabilization of aggregate-associated organic carbon are still poorly understood. We investigated the distribution of crystalline iron oxides (Fec), amorphous iron oxides (Feo), δ13C and Fe-bound OC in soil aggregate fractions of red earth (Ferrisol). The results showed that the δ13C values in microaggregate and silt+clay fractions were significantly lower than macro- and mesoaggregate (p < 0.05). The contents of Feo and Fe-bound OC in the microaggregate and silt+clay fractions were significantly higher than macro- and masoaggregate fractions (p < 0.05), while the content of Fec increased with the increase of aggregate size. The OC: Fe molar ratio of Feo was higher than Fec in all aggregate fractions. The FTIR spectroscopy analyses showed that polysaccharides had the highest proportion of all OC functional groups and increased with the increase of aggregate size. Likewise, the ratio of aromatic-C/aliphatic-C increased with the increase of aggregate size. Both Feo and Fe-bound OC had a significant negative correlation with δ13C values in microaggregate and silt+clay fractions, while Fec had no significant correlation with δ13C values in all aggregate fractions. Furthermore, the Fe-bound OC and fFe-bound OC were positively correlated with Feo and negatively correlated with Fec in all aggregate fractions. This study highlighted the importance of Feo in the sequestration of aggregate-associated organic carbon and confirmed the hypothesis that the SOC in microaggregates and silt+clay underwent less cycles of microbial utilization due to the protection of Feo, thereby limiting the molecular structure complexity and aromaticity of SOM.

The Nature of Iron Oxide Distribution in Some Calcareous and Gypsiferous Soils

The study area is located within two regions. The first site in Tikrit city (Tikrit University) represents gypsiferous soils and the second site represents calcareous soils in Erbil Governorate. Two pedons were chosen in Tikrit P1 (rainfed) and P2 (cultivated), and two other pedons in Erbil P3 (rainfed) and P4 ( cultivated) . Tikrit pedons showed presence of gypsum crystals of spindle and lenticular type with a length ranging between (0.2 -0.5) mm , the pores type of vughs and chamber, while the dominance of the planer and interconnected chamber pores in Erbil pedons. Iron oxides appeared in different forms of single discrete particles or Ferriargillans cutan especially in Erbil's pedons, The values ​​of iron oxides varied, as the dominance of the total, free ,and the amorphous iron oxides in Erbil pedons were ranged between (8.77 -12.81), (8.17 - 10.30), (6.82 - 9.19) g.kg-1, respectively, compared with the iron oxides themselves for Tikrit pedons, which ranged between (2.98 - 5.39), (2.45 - 4.86), (1.19 - 2.67) g.kg-1, respectively. While the amorphous iron oxide values ​​showed an increasing in the Tikrit pedons compared with Erbil pedons, as their values ​​in Tikrit ranged between (1.26 - 2.19) g. kg -1 while in Erbil pedons ranged between (1.01 – 1.81) g. kg -1.

Sequential modifications of the surface of hematite (α-Fe2O3) photoanodes with amorphous nickel iron oxide (NiFeOx) and cobalt phosphate (Co-Pi)

We prepared Hematite (α-Fe2O3)-based photoanodes, treated by either an amorphous NiFeOx coating or a cobalt-phosphate co-catalyst (Co-Pi) or both, and investigated the role of each treatment in the improvement of the PEC performances. We found that the PEC performances of the films in which both Co-Pi or NiFeOx were deposited on the surface of Hematite were much higher than that of bare Hematite regardless of the order of the treatments, which could be attributed to the synergistic effect on the enhancement of the charge transfer efficiency. Particularly, the film in which the surface of hematite was coated with NiFeOx, then Co-Pi was loaded on it, showed the excellent long-term stability, alleviating the shortcoming of the NiFeOx coating. In addition, we found that the treatments of either Co-Pi or NiFeOx resulted in the enhancement of the charge transfer efficiencies and the generation of the additional component arising from the trapped holes in Co-Pi (NiFeOx), separated from the surface states in hematite, which are beneficial for the enhancement of the PEC performance.

Transport and transformation of arsenic in coastal aquifer at the scenario of seawater intrusion followed by managed aquifer recharge

Release of contaminants from aquifers at the coastal area is of increasing concern, but remains unclear due to the complex groundwater dynamics and hydrochemistry. Specifically, frequently occurring seawater intrusion and the subsequent engineering measures of managed aquifer recharge (MAR) could alter the groundwater regime, which might affect the fate and behaviors of contaminants. In this work, we investigated the transport and transformation of arsenic (As) in the coastal aquifer at the scenario of seawater intrusion followed by the injection-based MAR process. Results showed that seawater intrusion induced 10.3% more release of aqueous As in aquifers, which was attributed to the competitive desorption as a result of elevated anion concentration and pH, and the reduction of As(V) to As(III) due to the reduced redox potential and enriched As-reducing bacteria. Furthermore, seawater intrusion inhibited the recrystallization of iron (hydr)oxides and instead facilitated its conversion to iron sulfide with lower affinity to As. The subsequent MAR introduced oxygenated recharge water into aquifers and increased the redox potential, leading to the dissolution of iron sulfide followed by formation of amorphous iron (hydr)oxides. However, the competitive desorption of As with rich HCO3− under increased pH dominated continuous increase in the aquifer aqueous As during MAR process. A constructed numerical model for describing As transport based on the experimental data showed that As transported along the interface between seawater and freshwater, and MAR enhanced the release of As and expanded the spread range of As. Our findings reveal that both seawater intrusion and subsequent MAR could cause the release, transport, and transformation of As, which provides new insight on the understanding of geochemical process of As in coastal aquifers.

Impacts of wet-dry alternations on cadmium and zinc immobilisation in soil remediated with iron oxides

Chemical immobilisation is extensively used for in-situ remediation of heavy metals contaminated soil. Immobilised heavy metals could be reactivated by multiple factors such as pH, moisture, temperature, rainfall, etc., among which rainfall is very important, especially acid rain in southern China. Wet-dry alternations were used to simulate the leaching of metals by rainwater. The variation of cadmium (Cd) and zinc (Zn) speciation distribution in soil immobilised with iron oxides (goethite (GE) and 2-line ferrihydrite (GLS)) was investigated. The impacts of wet-dry alternations on the properties of the soil and amendments were also assessed. In the soil without amendments (OS) and amended with GE (GS), the stable fractions were reactivated and transformed into labile fractions under wet-dry alternations. In the soil amended with GLS (LS), the exchangeable and carbonate-bound Cd decreased while the soluble, Fe–Mn oxide bound and organic bound Cd increased. The carbonate-bound Zn was transformed into the Fe–Mn oxide-bound Zn. Transformation from the amorphous iron oxide into crystalline iron oxide in GS and LS were 4.9% and 5.3%. The Pearson correlation analysis showed that the soil pH and the iron-oxide speciation were strongly correlated with Cd/Zn fractions in the soil. The specific surface area, pore volume and adsorption capacity of the iron oxides decreased by 9.26%, 38.89% and 62–73% (for GE), 1.88%, 22.22% and 26–55% (for GLS). The altered soil properties and morphological differences between the two iron oxides under wet-dry alternations were important reasons for Cd/Zn reactivation.

LEAVES IN IRON OXIDE: REMARKABLE PRESERVATION OF A NEOGENE FLORA FROM NEW CALEDONIA

Abstract A Neogene hematite-goethite concretionary ‘ironstone' horizon in laterized fluvial sediments in the Massif du Sud of New Caledonia yields abundant fossil dicotyledonous angiosperm leaves. The leaves are preserved in iron oxide, mainly goethite, which replicates the morphology and anatomy of the leaf tissues and comprises 73% of the matrix. Organic remains are minimal and associated with aluminosilicate clay. Leaf tissues are preserved three-dimensionally in multiple ways including casts/molds, permineralization/petrifaction, and replacement. Although the mesophyll is less well preserved, reflecting its greater susceptibility to decay, cellular details of vascular and epidermal tissues are commonly evident. Analyses of leaves from an analogous modern setting reveal the early encrustation and impregnation of tissues by amorphous iron-oxides and clays in association with a microbial biofilm. We propose a taphonomic model in which the fossil leaves, like their modern counterparts, were permeated by iron oxides due to the high availability of iron derived from weathering of ultramafic basement. In contrast to the iron-rich aluminosilicate coatings that form in relatively iron-poor settings, the unusually high concentration of dissolved iron oxides permitted rapid anatomical preservation.

Arsenic speciation transformation in soils with high geological background: New insights from the governing role of Fe.

In soils, the speciation transformation of As were inherently related to the behaviors of iron (oxyhydr) oxides. It is poorly understood that the effects of the transformation of iron (oxyhydr) oxides coupled with As speciation transformation during dissimilatory Fe(III) reduction (DIR) involving with humic substances (HS) as electron donor or shuttle in soils with high arsenic geological background. In this study, the relationships between the transformation of iron (oxyhydr)oxides and As speciation transformation were investigated according to the response between continuously As speciation monitoring and iron (oxyhydr) oxides identification during DIR in the soils. The results showed that F4 (arsenic incorporated with amorphous iron (oxyhydr)oxides including ferrihydrite and schwertmannite) and F5 (arsenic incorporated with crystalline iron (oxyhydr)oxides including hematite and magnetite) were the main source and sink for As(III)Dissolved during DIR. During the incubation period, Fe(II) was the dominant driving force for the reduction of As(V) in the water-soil system. The XRD analysis indicated the changes of iron oxides such as ferrihydrite, schwertmannite, hematite and magnetite were closely related to the release and reduction of As, and those iron oxides could play governing roles for As speciation transformation during DIR in soils. Different from the known mechanism in low As concentrations, a limiting effect of As concentration on iron oxides transformation was found in our incubation experiments using soils with high As geological background (∼1000mg/kg). This work provides new insights for Fe as governing role in As speciation transformation in soils with high arsenic geological background by firstly identifying the corresponding iron (oxyhydr)oxides in operationally defined arsenic speciation incorporated with iron oxides.

Facile Synthesis of Multi-Channel Surface-Modified Amorphous Iron Oxide Nanospheres as High-Performance Anode Materials for Lithium-Ion Batteries

Based on the synergistic effect of ripening and hydrogen ion etching in a hydrothermal solution, a simple, facile, and low-cost new strategy was demonstrated to prepare multi-channel surface-modified amorphous Fe2O3 nanospheres as anodes for Li-ion batteries in this study. Compared with polycrystalline Fe2O3, the conversion reaction between amorphous Fe2O3 and lithium ions has a lower Gibbs free energy change and a stronger reversibility, which can contribute to an elevation in the cycle capability of the electrode. Meanwhile, there are abundant active sites and more effective dangling bonds/defects in amorphous materials, which is beneficial to promote charge transfer and lithium-ion migration kinetics. The Galvanostatic intermittent titration analysis results confirmed that the amorphous Fe2O3 electrode had a higher Li+ diffusion coefficient. In addition, the surfaces of the amorphous nanospheres are corroded to produce multiple criss-cross channels. The multi-channel surface structure can not only increase the contact area between Fe2O3 nanospheres and electrolyte, but also reserve space for volume expansion, thereby effectively alleviating the volume change during the intercalation-deintercalation of lithium ions. The electrochemical performance showed that the multi-channel surface-modified amorphous Fe2O3 electrode exhibited a higher specific capacity, a more stable cycle performance, and a narrower voltage hysteresis. It is believed that amorphous metal oxides have great potential as high-performance anodes of next-generation lithium-ion batteries.

The effect of iron oxide types on the photochemical transformation of organic phosphorus in water

Iron oxides play an important role in the transport and transformation of organic phosphorus in aquatic environments. However, the effect of different types of iron oxide on the environmental fate of organic phosphorus has remained unclear. In this study, the photodegradation of the organic phosphorus compound adenosine triphosphate (ATP) via the activity of crystalline (goethite) and amorphous (ferrihydrite) iron oxides was investigated. It was found that ATP was photodegraded by goethite, resulting in the release of dissolved inorganic phosphate under simulated sunlight irradiation. The concentration of ATP on goethite decreased by 75% after 6 h of simulated sunlight irradiation, while the concentration of ATP on ferrihydrite decreased by only 22%. ATR-FTIR spectroscopy revealed that the intensity of the peaks for the P–O and PO stretching vibrations in the goethite−ATP complex decreased significantly more after simulated sunlight irradiation than did those for the ferrihydrite treatment. Combined with the higher TOC/TOC0 values for the goethite treatment, the results indicate that a more vigorous photochemical reaction took place in the presence of goethite than with ferrihydrite. Reactive oxygen species analysis also showed that hydroxyl and superoxide anion radicals were generated when goethite was exposed to simulated sunlight irradiation, while ferrihydrite did not exhibit this ability. Overall, this study highlights that the type of iron oxide is an important factor in the transformation of organic phosphorus in aquatic environments.

A new insight into Cd reduction by flooding in paddy soil: The different dominant roles of Fe and S on Cd immobilization under fluctuant pe + pH conditions

The unsteady comprehensive system of pe + pH strongly affects the fate of Cd in paddy soils. However, the specific pe + pH threshold determining Cd bioavailability is largely unknown especially considering the roles of Fe and S reduction. The experiment set different water managements to obtain paddy soil samples with unstable pe + pH, and chemical analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterization were applied to reveal the dynamic process and mechanism about how Fe and S controlled Cd mobilization. The results showed that low pe + pH was favorable to soil Cd immobilization. Compared with high and medium pe + pH, the exchangeable Cd content decreased by 67.57 % and 64.71 % at low pe + pH, respectively. The XPS results showed that the contents of Fe(II) and S(−II) increased to 65.1 % and 75.2 % at low pe + pH condition, which was higher than that in other treatments. In the process of flooding for reducing Cd mobility, first it was attributed to the formation of amorphous iron oxides that can provide amount of adsorption sites for Cd. After then, S2− began to play a dominant role to combine with Cd2+ to form CdS with continuous decreased pe + pH. Therefore, Fe and S played the different dominant roles on Cd immobilization in paddy soil, and soil pe + pH value could work as a threshold.

The microbial impact on U, Pu, Np, and Am immobilization on aquifer sandy rocks, collected at the deep LRW injection site

In this work the analysis of biogeochemical factors influencing on immobilization of Np, U, Pu and Am on rocks taken from a depth of 450 m in a deep repository of liquid radioactive waste of the Siberian Chemical Combine is carried out. It was found that the development of microbial processes on aquiferous sandy rocks leads to a significant increase in the sorption efficiency of Np and U due to the formation of microbial biofilms and new biogenic mineral phases (Fe sulfides, Fe carbonates, amorphous iron oxides). The high values of Pu immobilization did not deteriorate and the effect on quantitative Am immobilization was negligible, but it led to an increase in the low-desorbed fraction. It is important to note the role of amorphous SiO2, formed after the biogenic dissolution of the clay fraction, in the distribution of U, Np and Am bond forms on rock samples. Development of microbial processes can lead to a redox potential decreasing, which leads to the formation of biogeochemical barrier zones for actinides in reduced oxyhydroxide forms. Thus, complex multifactorial models of radionuclide migration should be based not only on the Kd model and various hydrodynamic parameters of facilities, but also on data obtained from detailed laboratory investigation of the influence of microbial processes on Kd taking into account geochemical conditions determining the intensity of biological processes in the water-rock system.

Topography-dependent formation and transformation of lithogenic and pedogenic iron oxides on a volcano under a tropical monsoon climate

Volcanoes are widely distributed on the surface of the Earth and on other planets. Volcanic activities play a key role in the long-term evolution of the planetary atmosphere and geomorphology. Iron oxides on volcanoes often exist as the products of rapid magmatic oxidation driven by earlier lithogenesis or the weathering of primary iron-bearing minerals driven by later pedogenesis. The antiferromagnetic (AFM) and ferrimagnetic (FM) particles associated with the formation and transformation of iron oxides dominate the color and magnetism of soil and can potentially serve as an indicator to trace these processes. In this study, we systematically investigated the subsoils derived from a Pliocene volcano under a tropical monsoon climate. We observed that the crystalline iron oxides are differentiated along the leeward and windward slopes, while amorphous iron oxides are mainly differentiated along the shady and sunny slopes. The AFM hematite is more concentrated on the purplish top and the reddish leeward slopes, while the AFM goethite is more concentrated on the yellowish windward slopes. Coarser FM particles accompanied by lithogenic hematite form via early lithogenesis at the top, while more fine FM particles are concentrated on the leeward slopes with the neoformation of pedogenic hematite. Fewer but finer FM particles form with goethite on the windward slopes. These results suggest that FM particles could coexist with AFM hematite via lithogenesis or pedogenesis and that goethite would be a more reasonable pedogenic indicator in volcanic regions.

Straw residue incorporation and potassium fertilization enhances soil aggregate stability by altering soil content of iron oxide and organic carbon in a rice–rape cropping system

AbstractBoth iron (Fe) oxide and soil organic carbon (SOC) content, among other factors, drive the development and subsequent stability of soil aggregates. However, the mechanism of these drivers in paddy‐upland rotation systems with straw residue incorporation is not well understood. In this multiyear (2011–2017) trial, we sought to study the factors which drive the stability of soil aggregates in such a rice‐rape (RR) agronomic system. In order to examine the effect of straw residue incorporation and potassium fertilization on soil aggregation dynamics, we divided our trial into four treatments: inorganic phosphorus (P) and nitrogen (N) fertilizer; inorganic NPK fertilizer; inorganic NP fertilizer plus straw residue; and inorganic NPK fertilizer plus straw residue. Treatments which incorporated straw residue significantly increased both the geometric mean diameter (GMD) and the mean weight diameter (MWD) of soil aggregates. Soil aggregate stability was greater after rape harvest than after rice harvest, while SOC shows the opposite trend. Straw residue incorporation increased the SOC and, specifically, concentrations of aliphatic‐C and aromatic‐C, particularly in aggregates greater than 0.25 mm. Straw residue addition significantly increased both the amorphous (Feo) and complex iron oxide (Fep) contents of soil. In both bulk soil and in aggregates greater than 5 mm, SOC and Fep were positively correlated with MWD, while in aggregates less than 5 mm, Feo was positively correlated with MWD. Overall, we suggest that the increased concentrations of SOC, alkane‐C, Feo, and Fep in soils after incorporation of straw residue were responsible for increasing soil aggregate stability.

Time effects of rice straw and engineered bacteria on reduction of exogenous Cu mobility in three typical Chinese soils

Globally, copper (Cu) accumulation in soils is a major environmental concern. Agricultural organic waste and some bacterial species can readily absorb metals in an eco-friendly manner, and thus are commonly used in metal-contaminated soil remediation. This study investigates the change in Cu fractions during the aging process and the time effects of rice straw (RS) and engineered bacteria (EB) ( Pseudomonas putida X4/pIME) on reduction of Cu mobility. Three typical Chinese soils (red, cinnamon, and black soils) were incubated with RS or RS + EB in the presence of exogenous Cu for 24 months. The soil physicochemical properties, reactive soil components, Cu fractions, and Cu mobility were determined over time. The Cu mobility factor (MF) values were the lowest in the black soil (6.4–9.2) because of its high organic carbon and clay contents. The additions of both RS and RS + EB accelerated Cu stabilization during the aging process in all three soils. The Cu MF values decreased with time during the initial 20 months; however, the MF values increased thereafter in all soils, which might be due to the reduction of humic substances and amorphous iron oxides and the increase in iron oxides complexed on the organic matter. The reduction rates of Cu MF were similar after 16, 24, and more than 24 months in the red, cinnamon, and black soils, respectively, indicating that RS and RS + EB could limit Cu mobility at different times in various soils. The RS treatment showed the greatest efficiency in reducing Cu mobility in the red, cinnamon, and black soils after 12, 12, and 8 months of incubation, respectively. The RS + EB treatment was more efficient than the RS treatment in the red soil during the initial 8 months of the incubation period. Our study provides theoretical support for Cu risk assessments and RS supplementation for Cu remediation in different soils.

Evaluation of Sc Concentrations in Ni-Co Laterites Using Al as a Geochemical Proxy

Scandium (Sc) is used in several modern industrial applications. Recently, significant Sc concentrations (~100 ppm) were reported in some nickel-cobalt lateritic ores, where Sc may be valuably co-produced. However, Sc is typically not included in routine analyses of Ni-Co ores. This contribution examines the relevance of using routinely analysed elements as geochemical proxies for estimating Sc concentration and distribution. Three Ni-Co lateritic deposits from New Caledonia were investigated. In each deposit, Sc is well correlated with Al2O3. The slopes of deposit-scale Sc-Al2O3 regression lines are remarkably controlled by the composition of enstatite from the parent peridotite. In all deposits, maximum Sc enrichment occurs in the yellow limonite, above the highest Ni and Co enrichment zones. Sc- and Al-bearing crystalline goethite is predominant in the oxide-rich zones, though Sc shows a higher affinity for amorphous iron oxides than Al. We propose that, in already assayed Ni-Co lateritic ores, the concentration and distribution of Sc can be estimated from that of Al. Deposit-scale Sc-Al2O3 correlations may be determined after analysing a limited number of spatially and chemically representative samples. Therefore, mining operators may get a first-order evaluation of the Sc potential resource in Ni-Co lateritic deposits at low additional costs.

Control the greenhouse gas emission via mediating the dissimilatory iron reduction: Fulvic acid inhibit secondary mineralization of ferrihydrite

Reducing methane emission is of great importance to control the global greenhouse effect. Dissimilatory iron reduction (DIR) coupling of organic matter decomposition may suppress methane production via reducing primary electron donors available for methanogenesis. However, during DIR, the amorphous iron oxides (e.g., ferrihydrite) are easy to transform into more stable crystalline iron minerals, which slowdowns the rate of DIR. Humic substance (HS) with redox activity has been extensively reported to facilitate DIR via “electron shuttles” mechanism, yet little known about the effect of HS on mediating the mineralization of iron oxides and the subsequent influences on DIR and methanogenesis. To clarify this, ferrihydrite and fulvic acid (FA) (as the model substance of HS) were supplied to anaerobic methanogenesis systems. Results showed that FA could significantly decrease the formation of crystalline iron oxides, enhance DIR rate by 13.72% and suppress methanogenesis by 25.13% compared to ferrihydrite supplemented only. By X-ray absorption spectra analysis, it was found that FA could complex with ferrihydrite via forming a Fe-C/O structure on the second shell of Fe atom. Quantum chemical calculation further confirmed that FA reduced the adsorption energy between Fe(II) and ferrihydrite. Our study suggested that rational use of HS to mediate mineralization pathway of iron oxides could efficiently improve the availability of iron oxides to drive DIR and control the conversion of organics into CH4 in natural or engineered systems.

Amorphous iron oxides anchored on BiOCl nanoplates as robust catalysts for high-performance photo-Fenton oxidation

Semiconductor supported iron oxides are highly promising catalysts to remove organic pollutants in photo-Fenton. Development of robust composite catalysts with both high activity and stability is essential. In this work, amorphous iron oxide layers are uniformly and tightly anchored on two-dimensional (2D) BiOCl nanoplates through post precipitation-deposition and subsequent low-temperature thermal treatment at 150–350 °C. A low iron loading amount (1–2 wt.%) is sufficient to make the resulted composite (BiOCl-Fe) catalysts superior in photo-Fenton oxidation of phenol (10 mg/L) with high mineralization efficiency (up to about 80% in 60 min). The low-temperature thermal treatment can significantly enhance the stability of catalysts with much less iron leached and high photo-Fenton performance maintained. The intimate contact between the amorphous iron oxide layers and the 2D BiOCl nanoplates could guarantee the fluent electron transfer and efficient activation of H2O2 at interfaces. Compared with the pristine BiOCl, the BiOCl-Fe catalysts possess faster separation of the charge carriers. The predominant active species turns from O2•– in photocatalysis to HO• in the photo-Fenton catalysis. This research could provide enhanced understanding on the synthesis of robust catalysts and the structure optimization of BiOCl supported iron oxides for photo-Fenton.

Heterogeneous Fenton catalyst based on clay decorated with nano-sized amorphous iron oxides prevents oxidant scavenging through surface complexation

• Crystalline and amorphous Fe-oxide-clay composites were compared as Fenton catalysts. • Nano-sized amorphous iron-oxide-clay best-promoted phenanthrene oxidation. • A stable H 2 O 2 complex was formed with the amorphous iron-oxide-clay surface. • Single oxygen was primarily responsible for phenanthrene degradation. • Oxidation of phenanthrene was achieved with minimal H 2 O 2 waste. Heterogeneous Fenton catalysts based on iron-oxides are of great interest due to their low cost and high reactivity. Herein, the activity of nano-sized amorphous iron-oxide particles deposited on montmorillonite clay (MMT) was compared to crystalline hematite and magnetite-coated MMT. Hematite, magnetite, and their respective clay composites showed little catalytic activity and almost no phenanthrene (PHE) oxidation at circumneutral pH - in part, due to the decomposition of hydrogen peroxide. In contrast, the amorphous iron oxide (Fe)-MMT, showed very high catalytic activity (over 60% PHE degradation in 60 min) with only minimal consumption of H 2 O 2 (3.3%). In-depth characterization of the Fe-MMT coupled with kinetic and mechanistic experiments was performed to understand the reaction pathway and mechanism. The results suggest that initially H 2 O 2 is complexed to the nano-sized iron oxide catalytic sites on the surface, forming a stable Fe-MMT-H 2 O 2 complex that is activated primarily when the pollutant is introduced. The reactive species, ∙OH and 1 O 2 , were detected upon the diffusion of PHE to the surface - leading to oxidation and mineralization with a minimal decomposition of H 2 O 2 . Quenching experiments further revealed that 1 O 2 played an important role in the extensive mineralization of PHE. The amorphous Fe-MMT also exhibited high stability and performance in semi-continuous cycle batch experiments. Thus, this low-cost and simple Fe-MMT catalyst was found to be highly efficient towards the activation of H 2 O 2 , oxidizing PHE rapidly while reducing radical scavenging and unwanted side reactions. These findings, regarding the role of amorphous phases in the reactivity of iron-oxides, have the potential to improve the design and implementation of solid Fenton catalysts for pollutant remediation in engineered and natural systems.

Effects of organic acids on heavy metal release or immobilization in contaminated soil

In order to explicit the environmental activity of heavy metals affected by different organic acids in soil, a batch incubation experiment was explored to investigate the influence of high relative molecular mass organic acid (HMWOA) (humic acid and fulvic acid) and low relative molecular mass organic acid (LMWOA) (threonic acid and oxalic acid) on the release or immobilization of Pb, Cu and Cd in soils. Results showed that LMWOA, especially threonic acid, had a good performance in the release of Pb, Cu and Cd from soils, and decrease in the fractions of HOAc-extractable, reducible and oxidable Pb, Cu and Cd. Conversely, HMWOA, especially humic acid, decreased the release of Pb, Cu and Cd, while it increased the fractions of HOAc-extractable, reducible and oxidable Pb, Cu and Cd, indicating that HMWOA can immobilize heavy metals. The release of Pb, Cu and Cd caused by LMWOA was attributed to the dissociation of soil organic matter and amorphous iron oxides since the total organic carbon and the water-soluble iron increased. The immobilization of Pb, Cu and Cd by HMWOA was attributed to the adsorption onto HMWOA followed by amorphous iron since HMWOA resulted in a significant decrease of zeta potential and an increase of amorphous iron oxide. It can be concluded that LMWOA has a potential application in soil washing remediation, while HMWOA can be used in the immobilization remediation for heavy metals contaminated soils.

Nanoarchitectonics of Illite-Based Materials: Effect of Metal Oxides Intercalation on the Mechanical Properties.

Clay minerals inevitably interact with colloidal oxides (mainly iron and aluminum oxides) in the evolution of natural geomaterials. However, the interaction between the clay minerals and the colloidal oxides affecting the stability and the strength of geotechnical materials remains poorly understood. In the present work, the interaction between the clay minerals and the colloidal oxides was investigated by reaction molecular dynamics simulations to explore the mechanical properties of illite-based materials. It was found that the metal atoms of the intercalated amorphous iron and aluminum oxides interact with oxygen atoms of the silica tetrahedron at the interface generating chemical bonds to enhance the strength of the illite-based materials considerably. The deformation and failure processes of the hybrid illite-based structures illustrated that the Al–O bonds were more favorable to the mechanical properties’ improvement of the hybrid system compared with Fe–O bonds. Moreover, the anisotropy of illite was greatly improved with metal oxide intercalation. This study provides new insight into the mechanical properties’ improvement of clay-based materials through metal oxides intercalation.