Crystalline Iron Oxides Research Articles

Iron Oxide Nanoparticles with Supramolecular Ureido-Pyrimidinone Coating for Antimicrobial Peptide Delivery.

Antimicrobial peptides (AMPs) can kill bacteria by disrupting their cytoplasmic membrane, which reduces the tendency of antibacterial resistance compared to conventional antibiotics. Their possible toxicity to human cells, however, limits their applicability. The combination of magnetically controlled drug delivery and supramolecular engineering can help to reduce the dosage of AMPs, control the delivery, and improve their cytocompatibility. Lasioglossin III (LL) is a natural AMP form bee venom that is highly antimicrobial. Here, superparamagnetic iron oxide nanoparticles (IONs) with a supramolecular ureido-pyrimidinone (UPy) coating were investigated as a drug carrier for LL for a controlled delivery to a specific target. Binding to IONs can improve the antimicrobial activity of the peptide. Different transmission electron microscopy (TEM) techniques showed that the particles have a crystalline iron oxide core with a UPy shell and UPy fibers. Cytocompatibility and internalization experiments were carried out with two different cell types, phagocytic and nonphagocytic cells. The drug carrier system showed good cytocompatibility (>70%) with human kidney cells (HK-2) and concentration-dependent toxicity to macrophagic cells (THP-1). The particles were internalized by both cell types, giving them the potential for effective delivery of AMPs into mammalian cells. By self-assembly, the UPy-coated nanoparticles can bind UPy-functionalized LL (UPy-LL) highly efficiently (99%), leading to a drug loading of 0.68 g g-1. The binding of UPy-LL on the supramolecular nanoparticle system increased its antimicrobial activity against E. coli (MIC 3.53 µM to 1.77 µM) and improved its cytocompatible dosage for HK-2 cells from 5.40 µM to 10.6 µM. The system showed higher cytotoxicity (5.4 µM) to the macrophages. The high drug loading, efficient binding, enhanced antimicrobial behavior, and reduced cytotoxicity makes ION@UPy-NH2 an interesting drug carrier for AMPs. The combination with superparamagnetic IONs allows potential magnetically controlled drug delivery and reduced drug amount of the system to address intracellular infections or improve cancer treatment.

Investigation of linear and non-linear optical features of crystalline and non-crystalline iron oxide thin films for optoelectronic purposes

Spray pyrolysis at various temperatures was employed to produce non-crystalline and crystalline iron oxide (α-Fe2O3) thin films on glass. The amorphous and crystalline characteristics of α-Fe2O3 thin films were affirmed via X-ray diffraction analysis. With low deposition times (5 min) and at various substrate temperatures, iron oxide seems almost in a non-crystalline structure. As for the increase in deposition time (40 min), the crystallinity’s degree was enhanced. According to Tauc’s law, the direct gap energy Ed for both the amorphous and the crystalline phases, were found to be 1.95 and 2.125 eV, respectively. Moreover, the indirect gap energy, Ein = 1.65 and 1.71 eV were obtained for the amorphous phases and the crystalline phases, respectively. The linear and non-linear optical features of amorphous and crystalline structure were meticulously and adaptably detailed. It is observed that the behavior of the refractive index n (λ) and extinction coefficient k (λ) of the crystalline state was lower than that of the amorphous state. The real and imaginary linear dielectric constant and also the thin film quality factor were estimated for both the amorphous and crystalline states as well as the volume and surface energy loss functions for the crystalline and amorphous states. In conclusion, amorphous and crystalline α-Fe2O3 nanocrystalline films improved their optical properties, making them potential candidates for multifunctional applications such as optoelectronics and spintronics electronics devices.

Fate of Cd during mineral transformation by sulfate-reducing bacteria in clay-size fractions from soils with high geochemical background

Sulfate-reducing bacteria (SRB) can immobilize heavy metals in soils through biomineralization, and the parent rock and minerals in the soil are critical to the immobilization efficiency of SRB. To date, there is little knowledge about the fate of Cd associated with the parent rocks and minerals of soil during Cd immobilized by SRB. In this study, we created a model system using clay-size fraction of soil and SRB to explore the role of SRB in immobilizing Cd in soils from stratigraphic successions with high geochemical background. In the system, clay-size fractions (particle size < 2 µm) with concentration of Cd (0.24–2.84 mg/kg) were extracted from soils for bacteria inoculation. After SRB reaction for 10 days, the Cd fraction tended to transform into iron-manganese bound. Further, two clay-size fractions, i.e., the non-crystalline iron oxide (Fe-OX) and the crystalline iron oxide (Fe-CBD), were separated by extraction. The reaction of SRB with them verified the transformation of primary iron-bearing minerals into secondary iron-bearing minerals, which contributed to Cd redistribution. This study shows that SRB could exploit the composition and structure of minerals to induce mineral recrystallization, thereby aggravating Cd redistribution and immobilization in clay-size fractions from stratigraphic successions with high geochemical background.

Spatial Differentiation Characteristics and Evaluation of Cu and Cd in Paddy Soil around a Copper Smelter.

To accurately evaluate the distribution and bioavailability of potentially toxic elements (PTEs) such as Cu and Cd in farmlands near a copper smelter, we determined the total concentrations (Cu-T and Cd-T), various speciation concentrations of Cu and Cd and physicochemical properties of 18 paddy soil (or colloid) samples in Guixi town, Jiangxi province, China. The results showed that the concentrations of Cu-T and Cd-T in the soil around the smelter far exceeded the standard limits. Specifically, Cu ranged from 97.47 to 1294.63 mg·kg-1, with a coefficient of variation (CV) of 0.95; Cd ranged from 0.14 to 9.06 mg·kg-1, and the CV was 1.68. Furthermore, the pollution of PTEs continued to accumulate, posing a significant risk to the environment and human health. The findings from the analysis of soil and colloid indicated that the distribution characteristics of Cu and Cd speciations did not align with the total concentrations. The highest pollution points were found to be shifted to the residual fraction of Cu, organic fraction, and crystalline iron oxide fraction of Cd in soil. The dominant fraction of Cu in colloid was the amorphous iron oxide fraction, whereas Cd was the crystalline iron oxide fraction. The assessment of Cu and Cd migration (MR) revealed that Cd posed a greater ecological risk. Further examination of the properties of iron oxides in soil and colloid revealed that they played a crucial role in the migration and transformation of soil PTEs.

Dominant Aggregate Binding Agent Dynamics of Quaternary Ancient Red Soils under Different Land Use Patterns

The cementation mechanisms and processes of aggregate binding agents are important in understanding aggregate formation. However, the role of threshold values and the proportions of organic and inorganic binding agents in aggregate formation remain unclear. This research investigated the dominant aggregate binding agent dynamics in a sequence comprising buried ancient red soil unaffected by modern climate changes and human activities, alongside nearby exposed Quaternary ancient red soils subjected to different land use patterns influenced by these factors in northeastern China. By analyzing soil age, aggregate compositions, and organic/inorganic indicators of binding agents, including soil organic matter (SOM), free iron oxide (Fed), poorly crystalline iron oxide (Feo), crystalline iron oxide (Fed-Feo), and total clay particles (TCL), we determined the relative contributions of different binding agents using redundancy analysis (RDA). The results revealed that the buried ancient red soil did not contain dominant binding agents in the aggregate formation before 91.01 ka BP. Due to denudation, the buried ancient red soil was exposed at the surface and experienced the importation of soil organic matter, weathering of silicate-bound iron oxides, and crystallization of poorly crystalline iron oxides resulting from the effects of different land use patterns from 91.01 ka to the present. Under the influence of binding agent dynamics, dominant binding agents in the exposed Quaternary ancient red soils’ aggregate formation changed into SOM and Fed. When the C/(Fed-Feo) molar ratio was less than 2.13, Fed-Feo was the dominant aggregate binding agent. When the C/(Fed-Feo) molar ratio was greater than 2.13, SOM was the dominant aggregate binding agent. The results of this study improve our understanding of aggregate formation and the relationship between soil organic matter and iron oxides.

Methylene Blue Dye Adsorption on Iron Oxide-Hydrochar Composite Synthesized via a Facile Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels' Waste.

The toxicity of dyes has a long-lasting negative impact on aquatic life. Adsorption is an inexpensive, simple, and straightforward technique for eliminating pollutants. One of the challenges facing adsorption is that it is hard to collect the adsorbents after the adsorption. Adding a magnetic property to the adsorbents makes it easier to collect the adsorbents. The current work reports the synthesis of an iron oxide-hydrochar composite (FHC) and an iron oxide-activated hydrochar composite (FAC) through the microwave-assisted hydrothermal carbonization (MHC) technique, which is known as a timesaving and energy-efficient method. The synthesized composites were characterized using various techniques, such as FT-IR, XRD, SEM, TEM, and N2 isotherm. The prepared composites were applied in the adsorption of cationic methylene blue dye (MB). The composites were formed of crystalline iron oxide and amorphous hydrochar, with a porous structure for the hydrochar and a rod-like structure for the iron oxide. The pH of the point of zero charge (pHpzc) of the iron oxide-hydrochar composite and the iron oxide-activated hydrochar composite were 5.3 and 5.6, respectively. Approximately 556 mg and 50 mg of MB dye was adsorbed on the surface of 1 g of the FHC and FAC, respectively, according to the maximum adsorption capacity calculated using the Langmuir model.

Comparing Indicators of Carbon Cycling Under Different Climatic Regions of Iran

ABSTRACT Dissolved organic carbon (DOC) and soil respiration (SR) are essential in carbon cycling and storage. Consequently, proper soil management requires knowledge of factors influencing DOC and SR in soil. The main objective is to identify the most critical indicators that control DOC and SR in the major climatic regions of Iran. The carbon cycling of sixteen pedons from six study sites with different soil moisture and temperature regimes was measured. Soil samples were collected from various genetic horizons to assess their physicochemical properties. Stepwise multiple linear regression (MLR) models were conducted on all horizons and B horizon properties (representing the subsoil) to identify the strongest correlation with DOC and SR. The MLR model revealed that organic carbon (OC) was negatively affected by pH, electrical conductivity (EC), amorphous and crystalline iron oxide contents in all horizons (R2 = 0.69), EC, and cation exchange capacity (CEC) in B horizons (R2 = 0.62). On the other hand, SR was negatively affected by pH, EC, soil water content, and clay contents in all horizons (R2 = 0.67), and calcium carbonate equivalent (CCE), pH, and sodium adsorption ratio in B horizons (R2 = 0.67). The most important indicators associated with carbon cycling included EC and pH in the different soil types of Iran. This study contributes to improving crop yield and mitigating soil degradation, mainly by controlling and managing salinity and pH threats for soil fertility to increase carbon storage in such climatic regions.

Pedogenesis at the coastal arid-hyperarid transition deduced from a Late Quaternary chronosequence at Paposo, Atacama Desert

Under hyperarid climate conditions, pedogenesis is driven by the atmospheric deposition and subsequent accumulation of easily to moderately soluble salts forming extreme types of Aridisols. In contrast, the processes and timescales of soil formation in coastal desert environments are as yet not well understood. Therefore, a soil chronosequence at the arid-hyperarid transition in the south-central coastal Atacama Desert is investigated. We measured physicochemical soil parameters of shallow soil profiles on four generations of a multi-stage alluvial fan system, assisted by micromorphological analysis, allowing to deduce the soil-forming processes. We further established a geochronological framework by applying 10Be cosmogenic nuclide exposure dating on the abandoned surface generations, which allowed to infer the timescales for soil formation. The results indicate initial yet clearly identifiable pedogenesis occurring since MIS 5e–c. Along the Late Quaternary chronosequence, physicochemical soil properties show decreasing trends with growing age for the median grain size, salinity, long-term pH development, and CaCO3 contents. Contrarily, organic carbon, the ratio of organic to total phosphorus, the redness, and the contents of total and poorly crystalline pedogenic iron oxides tend to increase with age. This provides evidence for soil formation under an arid to hyperarid coastal climate characterized by (i) redistribution of salts by leaching causing topsoil desalinization; (ii) decalcification coupled with (iii) dealkalinization in totally decalcified horizons; (iv) accumulation of soil organic matter; (v) initial rubification through formation of pedogenic iron oxides (i.e. hematite); and (vi) initial loamification that, in turn, might have impeding effects on the translocation of soil constituents on timescales larger than 105 a. Furthermore, in situ pedogenesis might be superimposed considerably by aeolian dust influx. At Atacama’s south-central coast, the state of pedogenic alteration scales with the cumulative precipitation received throughout the entire Late Quaternary, yet evolved strongest between MIS5 and the MIS4/3-transition.

Competing Magnetic Interactions and Field-Induced Metamagnetic Transition in Highly Crystalline Phase-Tunable Iron Oxide Nanorods.

The inherent existence of multi phases in iron oxide nanostructures highlights the significance of them being investigated deliberately to understand and possibly control the phases. Here, the effects of annealing at 250 °C with a variable duration on the bulk magnetic and structural properties of high aspect ratio biphase iron oxide nanorods with ferrimagnetic Fe3O4 and antiferromagnetic α-Fe2O3 are explored. Increasing annealing time under a free flow of oxygen enhanced the α-Fe2O3 volume fraction and improved the crystallinity of the Fe3O4 phase, identified in changes in the magnetization as a function of annealing time. A critical annealing time of approximately 3 h maximized the presence of both phases, as observed via an enhancement in the magnetization and an interfacial pinning effect. This is attributed to disordered spins separating the magnetically distinct phases which tend to align with the application of a magnetic field at high temperatures. The increased antiferromagnetic phase can be distinguished due to the field-induced metamagnetic transitions observed in structures annealed for more than 3 h and was especially prominent in the 9 h annealed sample. Our controlled study in determining the changes in volume fractions with annealing time will enable precise control over phase tunability in iron oxide nanorods, allowing custom-made phase volume fractions in different applications ranging from spintronics to biomedical applications.

Removal of arsenic from contaminated soils by combining tartaric acid with dithionite: An efficient composite washing agent

In the context of the increasing global problem of arsenic (As) contamination in soils, an efficient remediation method is urgently needed to alleviate it. In this study, a composite washing agent consisting of 0.2 mol L−1 dithionite and 0.05 mol L−1 tartaric acid (TA) in a 1:1 mixing volume ratio was prepared and used in the remediation of arsenic-contaminated soils. The results showed that the removal efficiency of arsenic was 62.47% in soil 1 at a concentration of 134 mg kg−1 and 70.08% in soil 2 at a concentration of 70 mg kg−1. Dithionite achieved greater release of the arsenic associated with amorphous hydrous oxides of iron and aluminium (F3) and arsenic associated with crystalline hydrous oxides of iron and aluminium (F4) forms of arsenic by the reductive dissolution of iron oxides, while also reducing Fe3+. TA released some arsenic in the specifically adsorbed (F2) and F3 forms through acidic effects. The mechanism of arsenic removal from the composite washing agent was found to be a synergistic effect between dithionite and TA. The TA complexation formed Fe-TA complexes with Fe2+ in solution, preventing the formation of new iron mineral phases and reducing the readsorption or precipitation of arsenic to the soil surface. Meanwhile, the formation of Fe-TA complexes kept the iron oxides dissolved, allowing more iron oxide-bound arsenic (F3 +F4) to be released. This study showed that combining TA with dithionite is a promising technology for remediating arsenic-contaminated soils because of its high efficiency.

Evidence for preservation of organic carbon interacting with iron in material displaced from retrogressive thaw slumps: Case study in Peel Plateau, western Canadian Arctic

In northern high latitudes, rapid warming is set to amplify carbon-climate feedbacks by enhancing permafrost thaw and biogeochemical transformation of large amounts of soil organic carbon. However, between 30 % and 80 % of permafrost soil organic carbon is considered to be stabilized by geochemical interactions with the soil mineral pool and thus less susceptible to be emitted as greenhouse gases. Quantification of the nature of and controls on mineral-organic carbon interactions is needed to better constrain permafrost-carbon-climate feedbacks, particularly in ice-rich environments resulting in rapid thaw and development of thermokarst landforms. On sloping terrain, mass wasting features called retrogressive thaw slumps are amongst the most dynamic forms of thermokarst. These multi-decadal disturbances grow due to ablation of an ice-rich headwall, and their enlargement due to warming of the Arctic is mobilizing vast stores of previously frozen materials. Here, we investigate headwall profiles of seven retrogressive thaw slumps and sediments displaced from these mass wasting features from the Peel Plateau, western Canadian Arctic. The disturbances varied in their headwall height (2 to 25 m) and affected land surface area (<1 to > 30 ha). We present total and water extractable mineral element concentrations, mineralogy, and mineral-organic carbon interactions in the headwall layers (active layer, permafrost materials above an early Holocene thaw unconformity, and Pleistocene-aged permafrost tills) and in displaced material (suspended sediments in runoff and material accumulated on the debris tongue). Our data show that the main mechanism of organic carbon stabilization through mineral-organic carbon interactions within the headwall is the complexation with metals (mainly iron), which stabilizes 30 ± 15 % of the total organic carbon pool with higher concentrations in near-surface layers compared to deep permafrost. In the displaced material, this proportion drops to 18 ± 5 %. In addition, we estimate that up to 12 ± 5% of the total organic carbon is stabilized by associations to poorly crystalline iron oxides, with no significant difference between near-surface layers, deep permafrost and displaced material. Our findings suggest that the organic carbon interacting with the sediment mineral pool in slump headwalls is preserved in the material mobilized by slumping and displaced as debris. Overall, up to 32 ± 6 % of the total organic carbon displaced by retrogressive thaw slumps is stabilized by organo-mineral interactions in this region. This indicates that organo-mineral interactions play a significant role in the preservation of organic carbon in the material displaced from retrogressive thaw slumps over years to decades after their development resulting in decadal to centennial scale sequestration of this retrogressive thaw slump-mobilized organic carbon interacting with the soil mineral pool.

Coupled effects of sedimentary iron oxides and organic matter on geogenic phosphorus mobilization in alluvial-lacustrine aquifers

The organic matter (OM) biodegradation and reductive dissolution of iron oxides have been acknowledged as key factors in the release of geogenic phosphorus (P) to groundwater. However, the coupled effects of natural OM with iron oxides on the mobilization of geogenic P remain unclear. Groundwater with high and low P concentrations has been observed in two boreholes in the alluvial-lacustrine aquifer system of the Central Yangtze River Basin. Sediment samples from these boreholes were examined for their P and Fe species as well as their OM properties. The results show that sediments from borehole S1 with high P levels contain more bioavailable P, particularly iron oxide bound P (Fe-P) and organic P (OP) than those from borehole S2 with low P levels. Regarding borehole S2, Fe-P and OP show positive correlations with total organic carbon as well as amorphous iron oxides (FeOX1), which indicate the presence of Fe-OM-P ternary complexes, further evidenced by FTIR results. In a reducing environment, the protein-like component (C3) and terrestrial humic-like component (C2) will biodegrade. In the process of C3 biodegradation, FeOX1 will act as electron acceptors and then undergo reductive dissolution. In the process of C2 biodegradation, FeOX1 and crystalline iron oxides (FeOX2) will act as electron acceptors. FeOX2 will also act as conduits in the microbial utilization pathway. However, the formation of stable P-Fe-OM ternary complexes will inhibit the reductive dissolution of iron oxides and OM biodegradation, thus inhibiting the mobilization of P. This study provides new insights into the enrichment and mobilization of P in alluvial-lacustrine aquifer systems.

Cooperative effect of slow-release ferrous and phosphate for simultaneous stabilization of As, Cd and Pb in soil

The different chemical behavior of anionic As and cationic Cd and Pb makes the simultaneous stabilization of soils contaminated with arsenic (As), cadmium (Cd), and lead (Pb) challenging. The use of soluble, insoluble phosphate materials and iron compounds cannot simultaneously stabilize As, Cd, and Pb in soil effectively due to the easy re-activation of heavy metals and poor migration. Herein, we propose a new strategy of “cooperatively stabilizing Cd, Pb, and As with slow-release ferrous and phosphate”. To very this theory, we developed ferrous and phosphate slow-release materials to simultaneously stabilize As, Cd, and Pb in soil. The stabilization efficiency of water-soluble As, Cd and Pb reached 99% within 7d, and the stabilization efficiencies of NaHCO3-extractable As, DTPA-extractable Cd and Pb reached 92.60%, 57.79% and 62.81%, respectively. The chemical speciation analysis revealed that soil As, Cd and Pb were transformed into more stable states with the reaction time. The proportion of residual fraction of As, Cd, and Pb increased from 58.01% to 93.82%, 25.69 to 47.86%, 5.58 to 48.54% after 56 d, respectively. Using ferrihydrite as a representative soil component, the beneficial interactions of phosphate and slow-release ferrous material in stabilizing Pb, Cd, and As were demonstrated. The slow-release ferrous and phosphate material reacted with As and Cd/Pb to form stable ferrous arsenic and Cd/Pb phosphate. Furthermore, the slow-release phosphate converted the adsorbed As into dissolved As, then the dissolved As reacted with released ferrous to form a more stable form. Concurrently, As, Cd and Pb were structurally incorporated into the crystalline iron oxides during the ferrous ions-catalyzed transformation of amorphous iron (hydrogen) oxides. The results demonstrates that the use of slow-release ferrous and phosphate materials can aid in the simultaneous stabilization of As, Cd, and Pb in soil.

Transformations of Ferrihydrite-Extracellular Polymeric Substance Coprecipitates Driven by Dissolved Sulfide: Interrelated Effects of Carbon and Sulfur Loadings.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

Functionalized Pt nanoparticles between α/γ-Fe2O3 and MXene for superior acetone sensing

Crystalline iron oxide (Fe2O3) shows great potential for acetone detection in multiple applications such as monitoring air pollution and diagnosing diabetes. α-Fe2O3 or γ-Fe2O3 are generally used as sensing materials. Here, we report a sol-gel method followed by a thermal treatment to control the phases formation of mesoporous iron oxide. We have found that mixed α/γ-Fe2O3 phases exhibit enhanced sensing performances toward acetone. Moreover, as α/γ-Fe2O3 is coupled with 2D materials of MXene (Ti3C2Tx), the agglomeration of Fe2O3 nanoparticles is prevented and the number of active sites for chemical absorption increased. Furthermore, the p-n heterojunctions lead to the enhancement of their response up to 148 towards 200 ppm of acetone at 200 °C. Additionally, Pt nanoparticles were be easily incorporated in between α/γ-Fe2O3 and MXene to reduce the operating temperature down to 160 °C, while maintaining a very high response (307 towards 200 ppm) and lowering the detection limit to 0.5 ppm, thanks to the catalytic properties Pt nanoparticles.

Role of Al substitution in the reduction of ferrihydrite by Shewanella oneidensis MR-1.

Substitution of aluminum under natural environmental conditions has been proven to inhibit the transformation of weakly crystalline iron (oxyhydr)-oxides towards well crystalline iron oxides, thereby enhancing their long-term stability. However, exploration on the role of aluminum substitution in bacteria-mediated iron oxides transformation is relatively lacking, especially in the anaerobic underground condition where iron (oxyhydr)-oxides are easy to reduced. In this study, we selected four different levels of substitution aluminum prevalent in iron oxides under natural conditions, which are 0mol%, 10mol%, 20mol%, and 30mol% (mol Al/mol (Al + Fe)) respectively. With the presence of Shewanella oneidensis MR-1, we conducted a 15-day anaerobic microcosm experiment in simulated groundwater conditions. The experiment data suggested that aluminum substitution result in a decrease in bio-reduction rate constants of ferrihydrite from 0.24 in 0mol% Al to 0.17 in 30mol% Al. Besides, when containing substituted aluminum, secondary minerals produced by biological reduction of ferrihydrite changed from magnetite to akaganeite. These results were attributed to the surface coverage of Al during the reduction process, which affects the contact between S. oneidensis MR-1 and the unexposed Fe(III), thus inhibiting the further reduction of ferrihydrite. Since iron (oxyhydr)-oxides exhibit a strong affinity on multiple kinds of pollutants, results in this study may contribute to predicting the migration and preservation of contaminants in groundwater systems.

Effects of annealing temperature on the magnetic properties of highly crystalline biphase iron oxide nanorods

We report on the effects of annealing temperatures ranging from 225 °C to 325 °C on the magnetic properties of high aspect ratio iron oxide nanorods consisting of a ferrimagnetic Fe3O4 phase and an antiferromagnetic α-Fe2O3 phase in an as-prepared state. Annealing at the aforementioned temperatures under a constant flow of O2 for 3 h leads to an increment of the volume fraction of the antiferromagnetic α-Fe2O3 phase and concomitant enhancement of the crystallinity of the ferrimagnetic Fe3O4 phase. These opposing effects compete with each other, resulting in a decrease in global magnetization with increasing the annealing temperature. The desirable magnetic properties are achieved for the sample annealed at 250 °C. For all samples investigated, we observed an increase in low field magnetization at low temperatures after the sample is field cooled in the presence of a 1T magnetic field, which we attribute to the ordering of macro-spins of the weakly ordered antiferromagnetic α-Fe2O3 phase in the presence of the cooling field. Our study will pave the way for determining the optimal conditions to enhance the magnetic characteristics in iron oxide nanorods, which will enable its use in spintronics and biomedical applications.

Green rust sulfate transformation under the impact of Cr(VI) and oxalic acid: Mechanism and environmental significance

Green rust (GR), as one of mixed-valent iron [Fe(II)-Fe(III)] minerals, has received a significant attention in recent years because it is an intrinsic and essential part of biogeochemical cycling of heavy metals and DOM. The transformation of GR is a key factor in altering the environmental behavior of heavy metals, and therefore, prediction of such transformation is critical for managing environmental quality. DOM and heavy metals are recognized to have a significant impact on iron oxide transformation. However, detailed information on these phenomena and mechanisms are still limited. In this study, Cr(VI) and oxalic acid (OA) widely distributed in the natural environment were selected representatives of heavy metals and DOM. The mechanism of their influence on GR transformation and their environmental significance were clarified. GR transformed to feroxyhyte under the impact of Cr(VI) and OA, and feroxyhyte did not transform to more crystalline iron oxides after 7 days. However, OA enhanced Fe dissolution and Cr(VI) reduction while weakening the immobilization of Cr on GR. SEM results demonstrated that OA addition resulted in the collapse of the feroxyhyte structure. SEM-EDS data indicated that Cr and OA were adsorbed on GR, suggesting that this can be an essential pathway for C and Cr sequestration during GR transformation. This study reveals Cr(VI) not only favors the formation of feroxyhyte, but also stabilizes the mineral to prevent transformation and meanwhile indicates the mechanisms of organic matter interactions with iron oxide and the environmental behavior of C and Cr during the iron oxide transformation processes.

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.

Scanning pulsed laser ablation in liquids: An alternative route to obtaining biocompatible YbFe nanoparticles as multiplatform contrast agents for combined MRI and CT imaging

Ytterbium ferrites are being used in many promising applications, such as visible-light photocatalysis, solar cells, magnetooptic devices, electro-magnetic equipment, etc., due to their fantastic ferroelectric and ferromagnetic properties. However, despite their good magnetic and radiopaque features, the use of ytterbium ferrites as multiplatform contrast agents in magnetic resonance imaging (MRI) and X-ray computed tomography (CT) is still under-developed. This is mainly due to difficulties in obtaining stable and biocompatible aqueous colloidal dispersions of ytterbium ferrite nanoparticles. In order to overcome this limitation, this work explores an eco-friendly method to directly synthesize such dispersions by liquid-assisted pulsed laser ablation of ytterbium ferrite massive targets. First, orthorhombic bulk YbFeO3 targets were obtained by a reaction-sintering method. Then, colloidal dispersions of nanoparticles were produced directly in both distilled water and ethanol by irradiating the bulk YbFeO3 targets with high-power infrared nanosecond lasers pulses. A battery of techniques has been used to characterize the as synthesized YbFeO3 targets and colloidal dispersions of YbFe nanoparticles to determine their composition, structure, magnetic properties, X-ray attenuation potentials, and colloidal properties. Moreover, the biocompatibility of the systems was also analysed by MTT cell viability assay. Results indicated that the use of distilled water as ablation medium yields colloidal dispersions consisted mainly of paramagnetic ytterbium ferrite nanoparticles. Contrarily, the use of ethanol as solvent leads to colloidal dispersions of polycrystalline nanoparticles with both ferromagnetic and paramagnetic behaviour, due to the coexistence, in each nanoparticle, of ytterbium ferrite, ytterbium oxide, and iron oxide crystalline phases. Both colloidal dispersions exhibit also high biocompatibility and suitable X-ray attenuation properties. Moreover, they show bio-safe hydrodynamic sizes (lower than 200 nm) with acceptable overall hydrodynamic polydispersity index values (under 0.4), being stable in water for several weeks. These results pave the way for the future evaluation of Yb–Fe based nanoparticles as multiplatform contrast agents in multimodal MRI and CT imaging.