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Natural occurring ferrihydrite (Fh) nanoparticles have varying degrees of crystallinity, but how Fh crystallinity affects its transformation behavior remains elusive. Here, we investigated the Fe(II)-catalyzed transformation of Fh with different degrees of crystallinity (i.e., Fh-2h, Fh-12h, and Fh-85C). X-ray diffraction patterns of Fh-2h, Fh-12h, and Fh-85C exhibited two, five, and six diffraction peaks, respectively, indicating the order of crystallinity: Fh-2h < Fh-12h < Fh-85C. Fh with the lower crystallinity has a higher redox potential, corresponding to the faster Fe(II)-Fh interfacial electron transfer and Fe(III)labile production. With the increase of initial Fe(II) concentration ([Fe(II)aq]int.) from 0.2 to 5.0 mM, the transformation pathways of Fh-2h and Fh-12h change from Fh â lepidocrocite (Lp) â goethite (Gt) to Fh â Gt, but that of Fh-85C switches from Fh â Gt to Fh â magnetite (Mt). The changes are rationalized using a computational model that quantitatively describes the relationship between the free energies of formation for starting Fh and nucleation barriers of competing product phases. Gt particles from the Fh-2h transformation exhibit a broader width distribution than those from Fh-12h and Fh-85C. Uncommon hexagonal Mt nanoplates are formed from the Fh-85C transformation at [Fe(II)aq]int.= 5.0 mM. The findings are crucial to comprehensively understand the environmental behavior of Fh and other associated elements.
Assuntos
Compostos Férricos , Ferro , Oxirredução , Minerais , Óxido Ferroso-Férrico , CatáliseRESUMO
Transformation of metastable Fe(III) oxyhydroxides is a prominent process in natural environments and can be significantly accelerated by the coexisting aqueous Fe(II) (Fe(II)aq). Recent evidence points to the solution mass transfer of labile Fe(III) (Fe(III)labile) as the primary intermediate species of general importance. However, a mechanistic aspect that remains unclear is the dependence of phase outcomes on the identity of the metastable Fe(III) oxyhydroxide precursor. Here, we compared the coupled evolution of Fe(II) species, solid phases, and Fe(III)labile throughout the Fe(II)-catalyzed transformation of lepidocrocite (Lp) versus ferrihydrite (Fh) at equal Fe(III) mass loadings with 0.2-1.0 mM Fe(II)aq at pH = 7.0. Similar to Fh, the conversion of Lp to product phases occurs by a dissolution-reprecipitation mechanism mediated by Fe(III)labile that seeds the nucleation of products. Though for Fh we observed a transformation to goethite (Gt), accompanied by the transient emergence and decline of Lp, for initial Lp we observed magnetite (Mt) as the main product. A linear correlation between the formation rate of Mt and the effective supersaturation in terms of Fe(III)labile concentration shows that Fe(II)-induced transformation of Lp into Mt is governed by the classical nucleation theory. When Lp is replaced by equimolar Gt, Mt formation is suppressed by opening a lower barrier pathway to Gt by heterogeneous nucleation and growth on the added Gt seeds. The collective findings add to the mechanistic understanding of factors governing phase selections that impact iron bioavailability, system redox potential, and the fate and transport of coupled elements.
Assuntos
Compostos Férricos , Minerais , Catálise , Óxido Ferroso-Férrico , OxirreduçãoRESUMO
Increasing CO2 emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO2 have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO2 concentrations, ferric oxide loading, and dolomite (CaMg(CO3)2) availability. The results showed that abiotic and biotic processes interactively mediate CO2 acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO2 stress on microbial activity, possibly via pH control that transforms the inhibitory CO2 to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H+) consumption during iron reduction and H+ generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO2 to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO3) under elevated CO2, supporting its incorporation into solids. The results of these CO2-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO2 acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO2 sequestration, and modeling of carbon flux).
Assuntos
Compostos Férricos , Ferro , Compostos Férricos/química , Ferro/química , Dióxido de Carbono , Bicarbonatos , Carbonatos/química , Minerais , OxirreduçãoRESUMO
Ferrihydrite (Fh) is generally associated with dissolved organic matter (DOM) in natural environments due to a strong sorption affinity at circumneutral pH and its high specific surface area. In suboxic conditions, aqueous Fe(II) (Fe(II)aq) can catalyze transformation of Fh into more stable crystalline Fe(III) phases, but how DOM influences the transformation kinetics and pathway is still unclear. Using citrate as a surrogate, we have examined Fh transformation with 1 mM Fe(II)aq and 0-60 µM citrate at pH 7.2. We focus on quantifying the time-dependent concentrations of sorbed Fe(II), structural Fe(II), and a key intermediate species, labile Fe(III) (Fe(III)labile), resulting from interfacial electron transfer (IET), and how these species correlate with the evolution of lepidocrocite (Lp), magnetite (Mt), and goethite (Gt) products. Low concentrations of citrate significantly impact the proportions of Lp/Gt, and the collective results reveal that its effect is primarily through its ability to complex labile Fe(III) and thereby disrupt polymerization into product crystallites, as opposed to modifying the surface properties of Fh or inhibiting IET. The emergence of a Mt coprecipitate is observed in the transformation experiments with 5-10 µM citrate, when the Fe(II)/Fe(III)labile ratio on/near the Fh surface is close to 0.5, the stoichiometric Fe(II)/Fe(III) ratio in Mt. At the molecular level, the findings suggest that citrate, and by extension DOM, can modify the relative rates of olation and oxolation reactions that assemble labile Fe(III) into various product minerals.
Assuntos
Compostos Férricos , Ferro , Catálise , Citratos , Ácido Cítrico , Minerais , OxirreduçãoRESUMO
Adsorption kinetics and conformational changes of a model protein, bovine serum albumin (BSA, 0.1, 0.5, or 1.0 g/L), on the surface of hematite (α-Fe2O3) particles in 39 ± 9, 68 ± 9, and 103 ± 8 nm, respectively, were measured using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. As the particle size increases, the amount of adsorbed BSA decreases, but the loss in the helical structure of adsorbed BSA increases due to the stronger interaction forces between adsorbed BSA and the larger particles. On 39 or 68 nm hematite particles, refolding of adsorbed BSA can be induced by protein-protein interactions, when the protein surface coverage exceeds certain critical values. Two-dimensional correlation spectroscopy (2D-COS) analysis of time-dependent ATR-FTIR spectra indicate that the increase in the amount of adsorbed BSA occurs prior to the loss in the BSA helical structure in the initial stage of adsorption processes, whereas an opposite sequence of the changes to BSA conformation and surface coverage is observed during the subsequent refolding processes. Desorption experiments show that replacing the protein solution with water can quench the refolding, but not the unfolding, of adsorbed BSA. A kinetic model was proposed to quantitatively describe the interplay of adsorption kinetics and conformational change, as well as the effects of particle size and initial protein concentration on the rate constants of elementary steps in protein adsorption onto a mineral surface.
Assuntos
Soroalbumina Bovina , Adsorção , Compostos Férricos , Cinética , Conformação Proteica , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de SuperfícieRESUMO
Dissolution behavior of isolated and aggregated hematite particles in 10, 36, and 103 nm, respectively, was investigated using in situ liquid cell transmission microscopy (LCTEM). The high spatial and temporal resolution of LCTEM enables us to differentiate the respective effects of primary particle size, crystal defects, and aggregation state on particle dissolution. At similar electron-beam irradiation parameters, the initial surface-area normalized dissolution rates ( RSA,Int) of isolated 10, 36, and 103 nm particles are 4.64 ± 3.60, 0.91 ± 0.44, and 0.24 ± 0.04 mg m-2 s-1, respectively. Interface free energy, calculated from the measured RSA,Int, decreases with the decreasing primary particle size. No preferential etching occurs on 10 nm, defect-free nanoparticles, whereas dissolution preferentially originates from crystal defects on 103 nm particles. In dissolution of aggregated particles, dissolution occurs more rapidly on the particles that are more accessible to bulk solution than the others inside the aggregate. As dissolution proceeds, dendritic aggregates break into several smaller aggregates that respectively shrink into even smaller and more compact aggregates, followed by reaggregation together. This study directly shows microscopic dissolution behavior of isolated and aggregated particles in different primary particle sizes, which is important to understand bioavailability, transport, and fate of nanoparticles in aquatic systems.
Assuntos
Compostos Férricos , Microscopia Eletrônica de Transmissão , Tamanho da Partícula , SolubilidadeRESUMO
The initial aggregation kinetics of hematite nanoparticles (NPs) that were conjugated with two model globular proteins-cytochrome c from bovine heart (Cyt) and bovine serum albumin (BSA)-were investigated over a range of monovalent (NaCl) and divalent (CaCl2) electrolyte concentrations at pH 5.7 and 9. The aggregation behavior of Cyt-NP conjugates was similar to that of bare hematite NPs, but the additional electrosteric repulsion increased the critical coagulation concentration (CCC) values from 69 mM to 113 mM in NaCl at pH 5.7. An unsaturated layer of BSA, a protein larger than Cyt, on hematite NPs resulted in fast aggregation at low salt concentrations and pH 5.7, due to the strong attractive patch-charge interaction. However, the BSA-NP conjugates could be stabilized simply by elevating salt concentrations, owing to the screening of the attractive patch-charge force and the increasing contribution from steric force. This study showed that the aggregation state of protein-conjugated NPs is proved to be completely switchable via ionic strength, pH, protein size, and protein coverage. Macroscopic Cu(II) sorption experiments further established that reducing aggregation of hematite NPs via tailoring ionic strength and protein conjugation could promote the metal uptake by hematite NPs under harsh conditions.
Assuntos
Compostos Férricos/química , Nanopartículas/química , Proteínas/química , Adsorção , Animais , Bovinos , Citocromos c/química , Eletrólitos/química , Concentração de Íons de Hidrogênio , Cinética , Concentração Osmolar , Soroalbumina Bovina/química , Cloreto de Sódio/química , Água/químicaRESUMO
The aggregation behavior of 9, 36, and 112 nm hematite particles was studied in the presence of OmcA, a bacterial extracellular protein, in aqueous dispersions at pH 5.7 through time-resolved dynamic light scattering, electrophoretic mobility, and circular dichroism spectra, respectively. At low salt concentration, the attachment efficiencies of hematite particles in all sizes first increased, then decreased, and finally remained stable with the increase of OmcA concentration, indicating the dominant interparticle interaction changed along with the increase in the protein-to-particle ratio. Nevertheless, at high salt concentration, the attachment efficiencies of all hematite samples gradually decreased with increasing OmcA concentration, which can be attributed to increasing steric force. Additionally, the aggregation behavior of OmcA-hematite conjugates was more correlated to total particle-surface area than primary particle size. It was further established that OmcA could stabilize hematite nanoparticles more efficiently than bovine serum albumin (BSA), a model plasma protein, due to the higher affinity of OmcA to hematite surface. This study highlighted the effects of particle properties, solution conditions, and protein properties on the complicated aggregation behavior of protein-nanoparticle conjugates in aqueous environments.
RESUMO
Aggregation of nanoparticles impacts their reactivity, stability, transport, and fate in aqueous environments, but limited methods are available to characterize structural features and movement of aggregates in liquid. Here, liquid cell transmission electron microscopy (LCTEM) was utilized to directly observe the size, morphology, and motion of aggregates that were composed of 9 and 36 nm hematite nanoparticles, respectively, in water or NaCl solution. When mass concentrations were same, the aggregates of 9 nm nanoparticles were statistically more compact and slightly larger than those of 36 nm nanoparticles. Aggregates in both samples were typically nonspherical. Increasing ionic strength resulted in larger aggregates, and also enhanced the stability of aggregates under electron-beam irradiation. In water, small aggregates moved randomly and approached repeatedly to large aggregates before final attachment. In NaCl solution, small aggregates moved directly toward large aggregates and attached to the latter quickly. This observation provided a direct confirmation of the DLVO theory that the energy barrier to aggregation is higher in water than in salt solutions. This study not only presented the influences of particle size and ionic strength on aggregation state, but also demonstrated that LCTEM is a promising method to link aggregation state to dynamic processes of nanoparticles.
Assuntos
Microscopia Eletrônica de Transmissão , Nanopartículas/química , Concentração Osmolar , Tamanho da Partícula , SoluçõesRESUMO
Soil organic matter (SOM) and clay minerals are important sinks for reactive heavy metals (HMs) and exogenous hydrogen ions (H+). Therefore, HMs are likely to be released into soil porewater under acid rainfall conditions due to the competitive adsorption of H+. However, negligible Lead, Zinc, and Cadmium (<6 ) in the Pb/Zn smelter soil were leached, and the effects of SOM and clay minerals on HMs leaching were unclear. Herein, the H+ consumption and HMs redistribution on SOM and clay minerals were quantitated by the multi-surface model and density functional theory calculations to reveal the roles of SOM and clay minerals in alleviating HMs' leaching. Clay minerals consumed 43.2 %-52.0 % of the exogenous H+, serving as the dominant sink for the exogenous H+ due to its high content and hindering H+ competitive adsorption on SOM. Protonation of the functional groups constituted >90 % of the total H+ captured by clay minerals. Meanwhile, some H+ also competed with HMs for adsorption sites on clay minerals due to its 0.497-fold to 1.54-fold higher binding energies than HMs, resulting in the release of HMs. On the contrary, SOM served as an accommodator for taking over the released HMs from clay minerals. The HMs complexation on the low-affinity sites (R-L-) of SOM was responsible for the recapture of HMs. In Ca-enriched soil, the released HMs were also recaptured by SOM via ion exchange on the R-L-Ca+ and the high-affinity sites (R-H-Ca+) sites due to the 30.8 %-178 % higher binding energies of HMs on these sites than those of Ca. As a result, >63.4 % of the released HMs from clay minerals were transferred to the SOM. Thus, the synergy of SOM and clay minerals in alleviating the leaching of HMs in Pb/Zn smelter soils cannot be ignored in risk assessment and soil remediation.
RESUMO
Due to the diverse controlling factors and their uneven spatial distribution, especially atmospheric deposition from smelters, assessing and predicting the accumulation of heavy metals (HM) in crops across smelting-affected areas becomes challenging. In this study, integrating HM influx from atmospheric deposition, a boosted regression tree model with an average R2â¯>â¯0.8 was obtained to predict accumulation of Pb, As, and Cd in wheat grain across a smelting region. The atmospheric deposition serves as the dominant factor influencing the accumulation of Pb (28.2â¯%) and As (31.2â¯%) in wheat grain, but shows a weak influence on Cd accumulation (12.1â¯%). The contents of available HM in soil affect HM accumulation in wheat grain more significantly than their total contents in soil with relative importance rates of Pb (14.4â¯%â¯>â¯8.2â¯%), As (30.9â¯%â¯>â¯4.0â¯%), and Cd (55.0â¯%â¯>â¯16.9â¯%), respectively. Marginal effect analysis illustrates that HM accumulation in wheat grain begins to intensify when Pb content in atmospheric dust reaches 5140â¯mg/kg and available Cd content in soil exceeds 1.15â¯mg/kg. The path analysis rationalizes the cascading effects of distances from study sites to smelting factories on HM accumulation in wheat grain via negatively influencing atmospheric HM deposition. The study provides data support and a theoretical basis for the sustainable development of non-ferrous metal smelting industry, as well as for the restoration and risk management of HM-contaminated soils.
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Engineering black carbon (e.g. biochar) has been widely found in natural environments due to natural processes and extensive applications in engineering systems, and could influence the geochemical processes of coexisting arsenic (AsV) and FeII, especially when they are exposed to oxic conditions. Here, we studied time-varying kinetics and efficiencies of AsV immobilization by solid-phase FeII (FeIIsolid) and FeIII (FeIIIsolid) in FeII-AsV-biochar systems under both anoxic and oxic conditions at pH 7.0, with focuses on the effects of biochar surface and biochar-derived dissolved organic carbon (DOC). Under anoxic conditions, FeII could rapidly immobilize AsV via co-adsorption onto biochar surfaces, which also serves as the dominant pathway of AsV immobilization at the initial stage of reaction (0-5 min) under oxic conditions at high biochar concentrations. Subsequently, with increasing biochar concentrations, FeIIIsolid precipitation from aqueous FeII (FeIIaq) oxidation (5-60 min) starts to play an important role in AsV immobilization but in decreased efficiencies of AsV immobilization per unit iron. In the following stage (60-300 min), FeIIsolid oxidation is suppressed and leads to AsV release into solutions at >1.0 g·L-1 biochar. The decreasing efficiency of AsV immobilization over time is attributed to the gradual release of DOC into solution from biochar particles, which significantly inhibit AsV immobilization when FeIIIsolid is generated from FeIIsolid oxidation in the vicinity of biochar surfaces. Specifically, 4.06 mg·L of biochar-derived DOC can completely inhibit the immobilization of AsV in the 100 µM FeII system under oxic conditions. The findings are crucial to comprehensively understand and predict the behavior of FeII and AsV with coexisting engineering black carbon in natural environments.
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The leachability of heavy metals (HMs) in tailings is significantly affected by multivariate factors associated with environmental conditions. However, the leaching patterns of HMs in molybdenum (Mo) tailings due to environmental change and cumulative influences of multi-leaching factors remain unclear. The leaching behaviors of HMs in Mo tailings were studied through static leaching tests. The key leaching factors were discussed via simulating acid rain leaching scenario in terms of global and local environmental conditions. The potential risk factors were identified, and their cumulative influences on the leachability of HMs were evaluated with boosted regression trees (BRT) and generalized additive model (GAM) analyses. Environmental factors showed interactive effects on the leachability of HMs in tailings. The leachability of HMs in tailings decreased significantly with the interaction of increasing liquid/solid (L/S) ratio and pH. Rebound of leachability was observed with high L/S ratio (> 60) and long-time leaching (> 30 h). L/S ratio and pH were the most sensitive factors to the leachability of HMs with the corresponding contribution of 40.8% and 27.1%, respectively, followed by leaching time and temperature (~ 16%). The total contribution of global climate-associated factors, i.e., L/S ratio, leaching time, and temperature to the leachability of HMs was up to 70%, while leachate pH shared the other 30%. With the increase of persistent heavy rain in summer globally, As and Cd were found to having higher leaching risks than the other HMs in tailings, although an obvious decrease in their leachability was obtained due to the improvement of acid rain pollution in China. The study provides a valuable method for the identification of potential risk factors and their associations with the leaching behaviors of HMs in tailings under the background of obvious improvement on acid rain pollution in China and global climate change.
Assuntos
Chuva Ácida , Metais Pesados , Poluentes do Solo , Poluentes do Solo/análise , Metais Pesados/análise , Poluição Ambiental , Fatores de Risco , MolibdênioRESUMO
Substantial fractions of extracellular enzymes are intimately associated with soil minerals, which may protect enzymes from denaturation, precipitation, proteolysis, or microbial consumption in soil environments. However, how mineral surface properties affect enzyme-mineral interactions and enzymatic activity of enzymes associated to mineral surface is still unclear. In the present study, adsorption behavior, conformational change, and enzymatic activity of ß-glucosidase (BG) on hematite (001) face and (104) face, respectively, were investigated using in situ attenuated total reflectance FTIR spectroscopy and batch experiments. ß-glucosidase undergoes greater conformational changes upon adsorption onto hematite (104) face than on hematite (001) face, probably due to the stronger protein-surface interactions on (104) face with the relatively higher surface hydroxyl density. On the other hand, the amount of BG sorbed on hematite (001) face was nearly two times higher than that on hematite (104) at the end of the 150-min adsorption experiments, due to the higher extent of conformational change in ß-glucosidase on hematite (104) face. Correspondingly, the initial rate of cellobiose hydrolysis by per gram of ß-glucosidase adsorbed on hematite (104) face was 1.7 times higher than that on hematite (001) face. However, when the density of hematite particles was same, the extent of cellobiose hydrolysis was 1.2 times higher on hematite (001) face than that on the (104) face, because of the higher adsorbed amount of ß-glucosidase on the former. This study decoupled the effects of mineral surface properties on adsorption kinetics and conformational changes of soil enzymes bound to soil minerals and provided new insights into the correlation between mineral surface properties and catalytical activity of mineral-associated enzymes in soil environments.