Amorphous Iron Oxide Research Articles

Excellent antibiotic degradation through PMS activation via bio derived Fe-Mn oxides with tunable defect concentration: Synergy between singlet oxygen oxidation and electron transfer

Regulating the defect sites and structural composition of metal-based metal catalysts is an effective strategy to improve the activity of activating PMS to degrade pollutants. Herein, bio derived Fe/Mn composite oxides (BFMO) rich in oxygen vacancy composed of crystalline manganese oxide coated with amorphous iron oxide was prepared through microbial mediation, and used for PMS activation in the degradation of tetracycline (TC). After 60 minutes reaction, the removal rate of TC achieved 92.4 %−98.8 % within wide pH range of 3–12. Besides, this system has outstanding anti-interference ability to common ions and humic acid (HA). The outstanding catalytic performance stemmed from the non-radical pathway for producing singlet oxygen (1O2) and electron transfer, facilitated by defect-rich polyvalent Mn and amorphous Fe species. Polyvalent Mn species accelerate the electron transfer process, and its surface defect structure further promotes the adsorption of pollutants on the surface of the materials. The redox cycle of Fe3+/Fe2+ was accelerate via electron-rich groups. This study explored the synergy triggered by microbe-mediated defect sites and structure-dependent, providing a design strategy for environmental remediation of PMS activated by Fe/Mn based bimetallic catalysts with strong resistance to environmental interference.

Seasonal alternation of soil phosphorus saturation in rice-wheat rotation systems under multiple fertilization strategies

The rice-wheat rotation system has been shown to improve agricultural productivity with associated economic benefits. The degree of phosphorus saturation (DPS) refers to saturation of soil sorption sites with phosphorus (P), and reflects the tendency of soil P fixation or release. A current knowledge gap is to investigate how a rice-wheat rotation system affects soil DPS, which is closely related to P loss to the environment. In the present field study, a rice-wheat rotation was established and different fertilization treatments were implemented, and the Anthrosol soils collected from the rice season and the wheat season, were evaluated. Sequential extraction, Langmuir model, and structural equation modeling were used to reveal the proportion of P fractions, P sorption capacity, and the relationships between the degree of P saturation and soil properties, in order to reveal the geochemical mechanisms of P transformation. A higher degree of P saturation is always found in the rice season soils rather than in the wheat season soils, which should be attributed to the lower P retention capacity and the higher presence of P in forms with greater mobility potential in the rice season soils. The reduction of the proportion of residual P fraction coupled with the enhancement of NaHCO3-P/NaOH-P/HCl-P fractions indicated a prevalence of P mobilization due to flooding during the rice planting period. Simultaneously, lower P sorption capacity was also found in the rice season soils. Structural equation modelling was able to confirm that the change of P sorption capacity together with the enhancement proportion labile P in total P, and mobilization of soil residual P combined to affect the degree of P saturation. Management interventions, such as flooding, induced changes from crystalline iron oxides to amorphous iron oxides and this may have enhanced the release of P retained by crystalline iron oxides, which contributed to the mobilization of P in the soils after the rice season. This knowledge can be utilized to avoid P losses to the environment, while still achieving efficient P utilization.

The Origin and Nature of Magnetic Particles From Soils and Sediments Constrained by Hydrodynamics and Geochemistry Around a Tropical Lagoon System

AbstractMagnetic iron oxides are commonly enriched in soils and sediments on Earth's surface. Magnetic properties are widely employed in soil taxonomy, sediment tracing and paleoclimate reconstruction as indicators of associated pedogenic and depositional processes. However, in coastal regions, frequent shifts in pedogenesis and diagenesis accompanied by changes in hydrodynamic and geochemical conditions from land to sea can influence the formation and preservation of magnetic particles in sediment sequences. To discern the origin and nature of magnetic particles driven by these processes, we systematically examined soils and sediments around a tropical lagoon that has been closing for two hundred years. We found that the finest superparamagnetic particles are enriched along with hematite from inland soils with high‐Fe and high‐Al backgrounds, which was driven by pedogenesis. Single‐domain ferrimagnetic particles are enriched along with amorphous iron oxides in the lagoon with high‐Mg and high‐Mn backgrounds, which was driven by early diagenesis in quiet and reducing depositional environments. Coarse titanomagnetite particles are strongly enriched in inshore sediments with high‐Si and high‐Ti backgrounds, which was driven by seawater elutriation. However, magnetic particles in barrier bar soils have mixed features depending on the neighboring environment. Identifying magnetic particles derived from different soils and sediments in tropical coastal regions can assist in tropical coastal paleoclimate and paleoenvironment reconstruction on the basis of magnetic properties along coastal sediment sequences.

Milk vetch returning combined with lime materials alleviates soil cadmium contamination and improves rice quality in soil-rice system

Milk vetch (Astragalus sinicus L.) returning and lime materials is employed as an effective strategy for remediating cadmium (Cd)-contaminated paddy fields. However, the combined effects of them on alleviating Cd pollution and the underlying mechanisms remain poorly explored. Therefore, this study investigated the impact of these combined treatments on soil properties, iron oxides, iron plaque, mineral elements, and amino acids through a field experiment. The following treatments were employed: lime (LM), limestone (LS), milk vetch (MV), MV + LM (MVLM), and MV + LS (MVLS), and a control (CK) group with no materials. Results demonstrated that treatments significantly decreased soil available Cd by 19.40–32.55 %, 10.20–39.58 %, and 25.36–40.66 % at tillering, filling, and maturing stages compared to CK, respectively. Moreover, exchangeable Cd was transformed into more stable fractions. Compared with individual treatments, MVLM and MVLS treatments further decreased available Cd and exchangeable Cd. Overall, Cd in brown rice was reduced by 18.97–77.39 % compared with CK. And the Cd in iron plaque decreased by 14.12–31.14 %, 24.65–61.60 %, 2.6–38.28 % across three stages. Furthermore, soil pH, dissolved organic carbon, and cation exchange capacity increased, along with 0.22–62.09 % and 0.57–10.66 % increases in free and amorphous iron oxide contents at all stages, respectively. Compared with lime alone, the integration of MV returning facilitated increased formation of Fed, Feo and enhanced the antagonistic effect among grain Ca with Cd; Additionally, it increased AAs in brown rice, improving rice quality and potentially reducing Cd transport. Mantel tests and Partial least squares path modeling revealed a significant positive correlation between Cd in IP and rice Cd uptake and a significant negative correlation between available Cd, Fed and Feo. These findings provide valuable insights into the mechanisms involved in mitigating soil Cd bioavailability using integrated approaches with MV returning and lime materials.

Vascular plants and biocrusts ameliorate soil properties serving to increase the stability of the Great Wall of China

The Great Wall, as a World Heritage Site, is constructed with rammed earth and is currently facing the threat of erosion from wind and rain. Vascular plants and biocrusts are the main coverings of the Great Wall, and their role in mitigating soil erosion has attracted increased amounts of attention; however, the understanding of their underlying mechanisms is limited. Here, we conducted an extensive survey of vascular plants, biocrusts, soil properties (soil organic and inorganic binding materials, aggregates, and texture), soil aggregate stability, and soil erodibility at the top of the Great Wall in four different defensive zones in Northwest China. Vascular plants covered 13.6 % to 63.9 % of the tops of the Great Wall, and their rich diversity was mainly derived from perennial herbs. Moss, lichen, and cyanobacterial crusts collectively covered 36.3 % to 67.8 % of the top of the Great Wall. Redundancy analysis and structural equation modeling revealed that the synergistic effects of vascular plants and biocrusts enhanced soil aggregation stability (including geometric mean diameter, GMD; water-stable macroaggregate content, R) by increasing the accumulation of soil organic carbon (SOC), amorphous iron oxide (Feo), and amorphous alumina (Alo) and promoting the formation of macroaggregates (ASD>0.25 mm) and microaggregates (ASD0.053-0.25 mm). Furthermore, soil erodibility was primarily influenced negatively by the synergistic promotion of SOC accumulation by vascular plants and biocrusts and positively by the reduction in soil sand (PSD>0.05 mm) content by biocrusts. Our work highlights the mechanisms and importance of vascular plants and biocrusts as natural covers for altering the intrinsic properties of soil for the protection of the Great Wall. These findings provide reliable theoretical support for the protection of the Great Wall from erosion by vascular plants and biocrusts and offer new insights for the conservation of global earthen sites and similar wall habitats.

Controllable Growth of Crystal Facets Enables Superb Cycling Stability of Anode Material for Potassium Ion Batteries

AbstractTo enrich the crystal growth strategies for the booming applications concerning lattice structure, a preferred facet‐growth method is proposed for solvothermal synthesis of target (BiO)2CO3 in the two‐phase system. The dominant crystal phase can be regulated from α‐Fe2O3 to (BiO)2CO3 by properly increasing dosage of Bi feedstock, and the optimized composite is composed of (BiO)2CO3 nanocrystal (≈10 nm) and amorphous iron oxide (defined as “FOB‐50”). Based on experimental characterizations and theoretical calculations, the highly matched lattice between (006)/(0012) facets of α‐Fe2O3 and {010} facet group of (BiO)2CO3 involving orientation of Fe─O─Fe bond and Bi─O─Bi bond is verified to facilitate the interaction between the above facets, resulting in preferred growth of {010} dominated by (040) facet in (BiO)2CO3 and its composites. The structural merits can not only enable the FOB‐50‐based electrodes to achieve a high capacity and unprecedentedly stable cyclic performances for 1500 cycles/a long time‐span of 32 months as anode materials, but also ensure the full‐cell to well inherit the electrochemical features of the cathode in potassium ion batteries (PIBs). This work can provide new insight into lattice regulation for bismuth‐based materials and expand their application as electrodes for high performance PIBs and lithium ion batteries.

Zinc isotope fractionation during coprecipitation with amorphous iron (hydr)oxides

Coprecipitation facilitates the incorporation of Zn into the lattice of Fe (hydr)oxide, which is a crucial mechanism causing low Zn bioavailability in widespread Zn-deficient soils. Zn isotopes are a potential indicator of the coprecipitation of Zn and Fe (hydr)oxides in soils. However, the Zn isotope fractionation caused by coprecipitation with amorphous Fe (hydr)oxides (e.g., ferrihydrite) and the impact of environmentally relevant conditions remain unknown. Here, the molecular mechanism and impact factor of Zn isotope fractionation during Zn2+-Fe3+ coprecipitation under natural soil conditions (including different pH values and initial Zn/Fe ratios) were investigated by combining isotope ratio measurements, extended X-ray absorption fine structure (EXAFS) analyses, and density functional theory (DFT) geometry optimization. The results show that aqueous Zn (Znaq) can be complexed on the ferrihydrite surface (Znads) with positive isotope fractionation (Δ66Znads–aq = 0.42 ± 0.09 ‰) or directly incorporated into the ferrihydrite lattice with slightly negative isotope fractionation (Δ66Znstru-aq = −0.08 ± 0.03 ‰). In addition, over time, the surface-complexed Zn can further transform to a layered structure on the surface but exhibits limited Zn isotope fractionation. According to Zn K-edge EXAFS, the Zn isotope fractionation of surface complexation and incorporation of Znaq are related to the decrease in the Zn–O bond strength in the order surface complexed Zn (RZn–O = 2.00 Å) > aqueous Zn (RZn–O = 2.08 Å) > directly incorporated Zn (RZn–O = 2.06–2.07 Å with slight distortion). The limited Zn isotope fractionation associated with the transformation of Znads is related to the reconfiguration of Znads during the nucleation of octahedral Zn layer structures. Furthermore, the primary process controlling Zn isotope fractionation is different under varying experimental conditions, leading to distinct Zn isotope fractionation between the bulk solid and solution during Zn–Fe coprecipitation. Low pH values (5.0–6.0) and initial Zn/Fe ratios (0.01–0.02) favor the direct precipitation of Znaq, resulting in slightly negative Zn isotope fractionation between the bulk solid and solution. In contrast, high pH values (7.0–7.5) and initial Zn/Fe ratios (0.1–0.2) favor surface complexation and the transformation of Znads, leading to heavy Zn isotope enrichment in the bulk solid. These findings offer novel insights into the primary mechanism through which Fe (hydr)oxides regulate Zn bioavailability in Zn-deficient soils and provide experimental evidence supporting the potential application of Zn isotopes as an indicator for comprehending the fate of Zn controlled by Fe (hydr)oxides in soils.

Cu1−Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate

AbstractThe electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3−) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3− to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen‐containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH‐neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3−. Herein, we constructed a Cu1‐Fe dual‐site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero‐valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3− removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L−1 NO3−−N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3− adsorption on Fe sites and strengthened water activation on single‐atom Cu sites, decreasing the energy barrier for the rate‐determining step of *NO‐to‐*NOH. This work develops a novel strategy of fabricating dual‐site catalysts to enhance the electrosynthesis of NH3 from NO3−, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Cu1-Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate.

The electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3 -) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3 - to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen-containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH-neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3 -. Herein, we constructed a Cu1-Fe dual-site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero-valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3 - removal efficiency of 94.8 % and NH3 selectivity of 99.2 % under neutral pH and nitrate concentration of 50 mg L-1 NO3 --N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3 - adsorption on Fe sites and strengthened water activation on single-atom Cu sites, decreasing the energy barrier for the rate-determining step of *NO-to-*NOH. This work develops a novel strategy of fabricating dual-site catalysts to enhance the electrosynthesis of NH3 from NO3 -, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Conservation tillage enhances the sequestration and iron-mediated stabilization of aggregate-associated organic carbon in Mollisols

Conservation tillage practices, which involve minimal or no soil disturbance and crop residue retention, are known to help preserve soil organic carbon (SOC). However, the mechanisms underlying the minerals-mediated chemical and physical stabilization of SOC remain unclear. Here, a long-term field experiment was initiated in 2012 to investigate the effects of tillage managements on the contents and chemical composition of SOC density fractions, iron oxides transformation and aggregate stability in Mollisols. We utilized three treatments: conventional tillage (CT) without crop residue, reduced tillage (RT) and no tillage (NT) with straw mulching. Compared to CT, RT and NT significantly increased SOC content by 13.6 % and 17.9 % in the 0–20 cm soil layer due to an increase in the aromatic compound contents. Furthermore, NT and RT increased the mean weight diameter by 17.7 % and 10.7 %, respectively, indicating increased aggregate stability compared to CT. Additionally, the contents of amorphous iron oxides (Feo) and complex iron oxides (Fep) increased under NT and RT by 10.6–14.4 % and 12.7–41.1 %, respectively, in bulk soil and silt + clay fractions within macroaggregates (>0.25 mm). The contents of Feo and Fep were strongly positively correlated with aggregate stability (p < 0.001, r2 = 0.64), and promote the physical protection of SOC. Both NT and RT enhanced the aromatic-C content and aromatic-C/aliphatic-C ratio by 13.6 %–24.6 % and 16.5 %–38.9 % in macroaggregates compared with CT. Moreover, the aromatic-C/aliphatic-C ratio increased with increasing Feo plus Fep contents (p < 0.001, r2 = 0.73), which led to an increased in the recalcitrant-C proportion, and this shift was benefit for the accumulation of mineral-associated OC. These results indicate that long-term conservation tillage can augment the accessibility of Fe for binding C, possibly by forming organo-Fe complexes, which subsequently improve soil aggregation, and thus promoted the chemical stability and long-term sequestration of SOC in Mollisols of Northeast China.

Accumulation and ecological risk assessment of diazinon in surface sediments of Baiyangdian lake and its potential impact on probiotics and pathogens

Diazinon is an organophosphorus pesticide widely used in agriculture and household pest control, and its use also poses several environmental and health hazards. In this study, we investigated the spatial and temporal distribution of diazinon in Baiyangdian, evaluated its potential ecological risk and toxicity to aquatic organisms based on RQ (Risk quotient) and TU (Toxic unit) analysis, and assessed the potential effects of diazinon accumulation on probiotics and pathogens based on statistical analysis of high-throughput sequencing data. The results showed that diazinon in Baiyangdian posed a low to moderate chronic risk to sediment-dwelling organisms and a low toxicity effect on aquatic invertebrates, which was mainly concentrated in October and human-intensive areas. Meanwhile, increases in sediment electrical conductivity (EC), amorphous iron oxides content and phenol oxidase activity favored diazinon accumulation in sediments, whereas the opposite was the case for sediment organic carbon, β-1,4-glucosidase, phosphatase, catalase and pH, suggesting that environmental indicators play a key role in the behavior and distribution of diazinon. In addition, diazinon in heavily contaminated areas seem to inhibit the rare probiotics (Bifidobacterium adolescentis and Serratia sp.), while promoted dominant pathogens (e.g., Burkholderia cenocepacia), which can lead to increased disease risk to humans and ecosystems, disruption of ecological balance and potential health problems. However, probiotic Streptomyces xiamenensis resist to diazinon would be a potential degrader for diazinon remove. In conclusion, this study unveiled the effects of diazinon pollution on wetland ecosystems, emphasizing ecological impacts and potential health concerns. In addition, the discovery of diazinon resistant probiotics provided new insights into wetland ecological restoration.

Interaction of rice root Fe plaque with radial oxygen loss enhances paddy-soil N2O emission by increasing •OH production and subsequently inhibiting N2O reduction

Amorphous iron (Fe) oxides are commonly deposited on rice roots, forming a distinctive Fe plaque, which has been observed as a notable hotspot for increased nitrous oxide (N2O) emission from paddy fields. However, the precise mechanisms underlying this phenomenon have remained uncertain. We hypothesized that the interaction between Fe plaque and rice root radial oxygen losses (ROL) leads to the generation of hydroxyl radical (•OH), thereby inhibiting N2O reduction and increasing N2O emission. To test this hypothesis, we transplanted rice seedlings with induced Fe plaque coating alongside those without Fe plaque coating into the same paddy soil. The results showed that paddy soil with Fe plaque-coated rice seedlings exhibited significantly higher concentrations of •OH and increased N2O emission rates, but a reduced abundance of the microbial N2O reduction gene (nosZ), compared to paddy soil with Fe plaque-free rice seedlings. These observed differences in N2O emission disappeared when we introduced an •OH scavenger into the paddy soil or shaded the rice leaves to reduce ROL. Furthermore, the supplementation of Fe (II) into the paddy soil with Fe plaque-free rice seedlings markedly increased •OH concentrations and N2O emissions. Our results demonstrate that Fe plaque, in conjunction with rice root ROL, facilitates •OH generation through the Fenton reaction. This •OH production effectively inhibits microbial N2O reduction, ultimately leading to increased N2O emissions from paddy soils. Our study uncovers a new mechanism whereby Fe plaque enhances N2O emissions from paddy soil. Minimizing Fenton reactions on Fe plaque may offer a promising strategy for reducing N2O emissions from paddy fields.

Organic fertilizer enhances soil aggregate stability by altering greenhouse soil content of iron oxide and organic carbon

Both soil organic carbon (SOC) and iron (Fe) oxide content, among other factors, drive the formation and stability of soil aggregates. However, the mechanism of these drivers in greenhouse soil fertilized with organic fertilizer is not well understood. In a 3-year field experiment, we aimed to investigate the factors which drive the stability of soil aggregates in greenhouse soil. To explore the impact of organic fertilizer on soil aggregates, we established four treatments: no fertilization (CK); inorganic fertilizer (CF); organic fertilizer (OF); and combined application of inorganic and organic fertilizers (COF). The application of organic fertilizer significantly enhanced the stability of aggregates, that is it enhanced the mean weight diameter, geometric mean diameter and aggregate content (%) of >0.25 mm aggregate fractions. OF and COF treatments increased the concentration of SOC, especially the aliphatic-C, aromatic-C and polysaccharide-C components of SOC, particularly in >0.25 mm aggregates. Organic fertilizer application significantly increased the content of free iron oxide (Fed), amorphous iron oxide (Feo), and non-crystalline Fe in both bulk soil and aggregates. Furthermore, non-crystalline Fe showed a positive correlation with SOC content in both bulk soil and aggregates. Both non-crystalline Fe and SOC were significantly positively correlated with >2 mm MWD. Overall, we believe that the increase of SOC, aromatic-C, and non-crystalline Fe concentrations in soil after the application of organic fertilizer is the reason for improving soil aggregate stability.

Efficient co-stabilization of arsenic and cadmium in farmland soil by schwertmannite under long-term flooding-drying condition

Simultaneously stabilizing of arsenic (As) and cadmium (Cd) in co-contaminated soil presents substantial challenges due to their contrasting chemical properties. Schwertmannite (Sch) is recognized as a potent adsorbent for As pollution, with alkali modification showing promising results in the simultaneous immobilization of both As and Cd. This study systematically investigated the long-term stabilization efficacy of alkali-modified Sch in Cd–As co-contaminated farmland soil over a 200-day flooding-drying period. The results revealed that As showed significant mobility in flooded conditions, whereas Cd exhibited increased soil availability under drying phases. The addition of Sch did not affect the trends in soil pH and Eh fluctuations; nonetheless, it led to an augmentation in the levels of amorphous iron oxides and SO42− concentration in soil pore water. At a dosage of 0.5% Sch, there was a notable decrease in the mobility and soil availability of As and Cd under both flooding (34.5% and 53.6% at Day 50) and drying conditions (27.0% and 29.4% at Day 130), primarily promoting the transformation of labile metal(loid) fraction into amorphous iron oxide-bound forms. Throughout the flooding-drying treatment period, Sch maintained stable mineral morphology and mineralogical phase, highlighting its long-term stabilization effect. The findings of this study emphasize the promising application of Sch-based soil remediation agents in mitigating the challenges arising from As–Cd co-contamination. Further research is warranted to explore their application in real farmland settings and their impact on the uptake of toxic metal(loid)s by plants.

Deciphering the spatial heterogeneity of groundwater arsenic in Quaternary aquifers of the Central Yangtze River Basin

Significant spatial variability of groundwater arsenic (As) concentrations in South/Southeast Asia is closely associated with sedimentogenesis and biogeochemical cycling processes. However, the role of fine-scale differences in biogeochemical processes under similar sedimentological environments in controlling the spatial heterogeneity of groundwater As concentrations is poorly understood. Within the central Yangtze Basin, dissolved organic matter (DOM) and microbial functional communities in the groundwater and solid-phase As-Fe speciation in Jianghan Plain (JHP) and Jiangbei Plain (JBP) were compared to reveal mechanisms related to the spatial heterogeneity of groundwater As concentration. The optical signatures of DOM showed that low molecular terrestrial fulvic-like with highly humified was predominant in the groundwater of JHP, while terrestrial humic-like and microbial humic-like with high molecular weight were predominant in the groundwater of JBP. The inorganic carbon isotope, microbial functional communities, and solid-phase As-Fe speciation suggest that the primary process controlling As accumulation in JHP groundwater system is the degradation of highly humified OM by methanogens, which drive the reductive dissolution of amorphous iron oxides. While in JBP groundwater systems, anaerobic methane-oxidizing microorganisms (AOM) coupled with fermentative bacteria, iron reduction bacteria (IRB), and sulfate reduction bacteria (SRB) utilize low molecular weight DOM degradation to drive biotic/abiotic reduction of Fe oxides, further facilitating the formation of carbonate associated Fe and crystalline Fe oxides, resulting in As release into groundwater. Different biogeochemical cycling processes determine the evolution of As-enriched aquifer systems, and the coupling of multiple processes involving organic matter transformation‑iron cycling‑sulfur cycling-methane cycling leads to heterogeneity in the spatial distribution of As concentrations in groundwater. These findings provide new perspectives to decipher the spatial variability of As concentrations in groundwater.

Comprehensive insight into the transformation mechanism of Cd fractionation in the components of paddy soils under cysteine leaching

Cadmium (Cd) contamination in paddy soils poses a serious threat to agricultural production and human health. In this study, cysteine was selected as the leaching agent for remediating Cd-contaminated paddy soils because of its effective, low cost and ecofriendly characteristics. Microcosmic simulation experiment was using to investigate the fate of Cd and elucidate the transformation mechanism of Cd in the key components of paddy soil under cysteine leaching. Results showed that the total Cd removal rate of paddy soils reached 46.8–87.4% under the optimal conditions. This was mainly attributed to the decrease of exchangeable fraction (F1), carbonate bound fraction (F2), iron/manganese-bound fraction (F3) and organic matter bound fraction (F4) of Cd. After cysteine leaching, soil fertility was promoted due to the increase in nitrate nitrogen (NN), ammonia nitrogen (AN), available phosphorus (AP) and organic matter (OM). pH, CaCO3, available potassium (AK), NN, AP, amorphous iron oxides (Feo) were the main contributors to Cd fractionation transformation. The desorption of Cd from ferrihydrite (Fh) and goethite (Gt) surfaces is hypothesized to stem from dual mechanisms: the dissolution due to the low solution pH and the reducibility of cysteine, which facilitated the conversion of Fh and Gt to hematite (Hm). And the -SH complexation also ascribed to the activation of Cd bound by Fe-OH in Fh and Gt and oxygen-containing functional groups in humic acid (Ha). For chlorite (Ch), the primary driver for Cd desorption was identified as an ion-exchange process, whereby electrostatically adsorbed Cd2+ were replaced by H+ produced by cysteine protonation.

Rare earth elements in clay-sized fractions: Implications for weathering fingerprint from parent materials to soils

Rare earth elements (REEs) have gained attention as tracers of pedogenic processes over the last few decades. Clay-sized fractions (CSFs, < 2 μm) may play a crucial role in hosting REEs. To better understand the pedochemical signals of REEs in clay-sized phases, such as iron oxides and phyllosilicates, we analyzed REE speciation in CSFs of carbonate rocks (limestone), clastic rocks (sandstone and shale), and their derived saprolites. Our results quantified the REE content (41.2–144.6 mg kg−1) and speciation in CSFs of parent materials, revealing that REEs were primarily hosted in amorphous iron oxides (Feox1), followed by crystalline iron oxides (Feox2) and phyllosilicates. Compared to parent materials, saprolites derived from carbonate rocks exhibited more than a two-fold enrichment of REEs in major clay-sized phases, confirming the role of CSFs as REE sinks during carbonate rock weathering. Furthermore, the initial REE patterns of CSFs of carbonate rocks underwent alteration throughout the weathering process, likely due to water–mineral interactions. Our findings suggest that REEs in CSFs record the weathering fingerprint for soils derived from carbonate rocks, while they are indicative of provenance for soils originating from clastic rocks.

Friction‐Reducing and Anti‐Wear Mechanism of BP/Nano‐Fe3O4 Nanocomposite as a Lubricant Additive in Soybean Oil

ABSTRACTAs an emerging two‐dimensional material, black phosphorus (BP) has excellent tribological properties, but the poor dispersion of BP in oil inhibits its application in friction to some extent. Surface modification is one of the effective methods to solve the dispersibility of BP, and the use of nano‐Fe3O4 dotted on the surface of BP improves the dispersion stability of BP in soybean from 3 days to about 15 days. Compared with pure soybean oil, friction coefficient and wear rate of the addition of 0.12 wt% BP/Fe3O4 are reduced 65% and 78%, respectively. To elucidate the excellent tribological mechanisms of BP/Fe3O4 as additives in soybean oil, the compositional and structural characterisation of the abrasion mark surface was studied accordingly. On the one hand, soybean oil reacts with BP/Fe3O4 to form a composite tribo‐film during the scraping process. This tribo‐film composed of amorphous carbon, iron oxide and phosphorus oxide nitrides prevents direct contact between the sliding interfaces. On the other hand, BP and Fe3O4 nanoparticles form a mechanical rollerball structure, which can further reduce interfacial friction and wear through synergistic lubrication. The results provide new insights into the design of additives in biomass lubricating oils and propose new application prospects for BP in the field of lubricating additives.

Zero-valent iron in phosphate removal: Unraveling the role of particle size and dissolved oxygen

The effect of particle size and dissolved oxygen (DO) on zero-valent iron (ZVI) oxidation needs further study to propose strategies for improving phosphate (P) removal performance. In this study, batch and column experiments were conducted to investigate P removal by ZVI with five different particle sizes under aerobic and anaerobic conditions. The oxidation status of ZVI before and after the reaction was characterized. Under aerobic conditions, as ZVI size increased, the P removal rate initially increased and then decreased, while the difference in P removal was not obvious under anaerobic conditions. Furthermore, the P removal rate exhibited a significant positive correlation with the degree of ZVI oxidation (R2 = 0.877, p = 0.008), highlighting its pivotal role in P removal. The ZVI size and DO on ZVI oxidation primarily affect the types and quantities of iron corrosion products (FeCPs). Under aerobic conditions, the ZVI with small particle sizes (ZVIsps) (50 nm, 500 nm, and 5 μm) tended to form passivation layers composed of amorphous iron oxide (ap-FexOy) and FePO4, limiting ZVI oxidation and resulting in lower P removal rates (17.6%). Conversely, in situations with less passivation, amorphous iron hydroxides (ap-FexOHy) play a dominant role in the P removal process. The 50 μm ZVI eventually generated lepidocrocite (γ-FeOOH) under aerobic conditions, this sufficient oxidation was also the reason for its high P removal rate. Therefore, future research and applications of ZVI materials in P removal should concentrate on enhancing ZVI corrosion and regulating the formation of suitable FeCPs.

Formation of iron-rich phyllosilicates in the FeO–SiO2–H2O system during hydrothermal synthesis as a function of pH

Abstract The formation of iron-rich phyllosilicates can occur at different natural or engineered settings. In this study, the influence of pH in the hydrothermal synthesis of iron-rich phyllosilicates was investigated in the pH range 8.50–12.10 after the ageing of the precursor. The synthesized samples were characterized by powder X-ray diffraction, Raman and Mössbauer spectroscopies and transmission electron microscopy. Three domains of pH were identified, and these correlated with silica availability and its speciation in the solution. The formation of 1:1-type FeIII/FeII phyllosilicate was observed between pH 9.67 and 10.75. Above pH 10.75, two types of phyllosilicate-like mineral phases were observed. In addition to 1:1-type FeIII/FeII phyllosilicate, 2:1-type FeIII/FeII phyllosilicate was observed. Below pH 9.67, mainly amorphous silica and iron oxides were observed. The findings show that pH governed the crystallinity and nature of the obtained phyllosilicate-like phases.