The rational design of catalytically active sites in porous materials is essential in electrocatalysis. Herein, atomically dispersed Fe‐Nx sites supported by hierarchically porous carbon membranes ...are designed to electrocatalyze the hydrazine oxidation reaction (HzOR), one of the key techniques in electrochemical nitrogen transformation. The high intrinsic catalytic activity of the Fe‐Nx single‐atom catalyst together with the uniquely mixed micro‐/macroporous membrane support positions such an electrode among the best‐known heteroatom‐based carbon anodes for hydrazine fuel cells. Combined with advanced characterization techniques, electrochemical probe experiments, and density functional theory calculation, the pyrrole‐type FeN4 structure is identified as the real catalytic site in HzOR.
Hierarchically porous carbon membrane‐supported atomically dispersed pyrrole‐type FeN4 sites are proposed and verified as real active sites for the hydrazine oxidation reaction.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Learning and studying the structure–activity relationship in the bio‐enzymes is conducive to the design of nanozymes for energy and environmental application. Herein, Fe single‐atom nanozymes ...(Fe‐SANs) with Fe–N5 site, inspired by the structure of cytochromes P450 (CYPs), are developed and characterized. Similar to the CYPs, the hyperoxide can activate the Fe(III) center of Fe‐SANs to generate Fe(IV)O intermediately, which can transfer oxygen to the substrate with ultrafast speed. Particularly, using the peroxymonosulfate (PMS)‐activated Fe‐SANs to oxidize sulfamethoxazole, a typical antibiotic contaminant, as the model hyperoxides activation reaction, the excellent activity within 284 min−1 g−1(catalyst) mmol−1(PMS) oxidation rate and 91.6% selectivity to the Fe(IV)O intermediate oxidation are demonstrated. More importantly, instead of promoting PMS adsorption, the axial N ligand modulates the electron structure of FeN5 SANs for the lower reaction energy barrier and promotes electron transfer to PMS to produce Fe(IV)O intermediate with high selectivity. The highlight of the axial N coordination in the nanozymes in this work provides deep insight to guide the design and development of nanozymes nearly to the bio‐enzyme with excellent activity and selectivity.
Learning the structure–activity relationship of bio‐enzymes is conducive to the design of nanozymes. Herein, Fe single‐atom nanozymes (Fe‐SANs) with Fe–N5 site, inspired by the structure of cytochromes P450 (CYPs), are developed for the hyperoxide activation to degrade micropollutants, and the crucial role of axial N for the activity and selectivity of Fe‐SANs is demonstrated.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Birnessite owing to its negative surface charge and defective structure exhibits high sorption affinities for Cd(II). However, Mn(II) can not only compete for the sorption sites with Cd(II), but also ...react with structural Mn(IV) in birnessite to form Mn(III), and thus, affect Cd(II) immobilization by birnessite. Herein, we investigate effects of Mn(II) on Cd(II) retention and remobilization on two birnessite δ-MnO2 and Mn(III)-rich δ-MnO2 (denoted as HE-MnO2). At pH 5.5, Cd(II) sorption to birnessite was inhibited by Mn(II) addition. Mn(II) addition to δ-MnO2 led to Cd(II) migration from vacant sites to edge sites, forming double-corner sharing (DCS) complexes. Mn(II) introduction to δ-MnO2 led to less stable Cd(II) species formed on birnessite, indicating that Cd(II) was more firmly bound to vacant sites than edge sites of birnessite. Cd(II) formed double-edge sharing (DES) and DCS complexes on HE-MnO2. Mn(II) addition to HE-MnO2 increased the CdMn distance in DES complexes. The stability of adsorbed Cd(II) on HE-MnO2 was slightly elevated due to Mn(II) addition. At pH 7.5, Mn(II) had no effect on Cd(II) sorption and desorption amounts on birnessite. However, low concentration of Mn(II) added to δ-MnO2 induced partial migration of Cd(II) from vacant sites to edge sites while high concentration of Mn(II) added to birnessite led to the formation of amorphous Cd(II)-Mn(III) coprecipitate. These findings imply that aqueous Mn(II) is an important factor in influencing Cd(II) immobilization by birnessite in the environment.
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•Mn(II) addition to δ-MnO2 led to Cd(II) migration from vacant sites to edge sites.•Mn(II) introduction to δ-MnO2 led to less stable Cd(II) species formed on birnessite.•Cd(II) formed edge sharing and cornering sharing complexes on Mn(III)-rich δ-MnO2 regardless of Mn(II) addition.•Cd(II) was more firmly bound to vacant sites than edge sites of birnessite.•High concentration of Mn(II) added to birnessite led to the formation of amorphous Cd(II)-Mn(III) coprecipitate at pH 7.5.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Zn deficiency is a critical problem for many crops and human populations worldwide. Soil biochar amendment has recently been promoted as a sustainable agricultural practice. However, its effect on ...the bioavailability of micronutrients (especially Zn) to crops has not been fully addressed. This study investigated the impact of long-term biochar application in soils on Zn bioavailability to rice and wheat, using field experiments, and batch sorption/desorption experiments, in combination with extended X-ray absorption fine structure spectroscopy (EXAFS). In field soils biochar amendment increased total Zn content, but significantly decreased CaCl2-extractable Zn concentrations. Intriguingly, the uptake of Zn to wheat and rice grains was decreased. At high biochar application rates of 124 and 270t/ha the Zn concentrations in wheat grains (36.6 and 37.5mg/kg) reached a deficient level, lower than the recommended concentration of 45mg/kg. The batch experiments showed that biochar application at a cumulative rate of 10.5, 15.8, 31.5, 124, and 270t/ha significantly increased soil pH and soil organic matter (SOM) content, resulting in greater sorption and lower desorption of Zn. The EXAFS results demonstrated that the main forms of sorbed Zn were outer-sphere Zn complexes, Zn-illite, Zn-kaolinite and Zn-OM. The proportion of Zn-OM increased with increasing biochar application rates, suggesting that higher SOM might be more effective in immobilizing Zn and thus decreasing the Zn bioavailability. These results on the microscopic and macroscopic scales improved our understanding of the Zn bioavailability to crops, and raised potential concerns on the Zn deficiency in agricultural soils with long-term biochar application.
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•Biochar application significantly increased soil pH and soil organic matter.•The application of biochar attenuated Zn mobility in soils and uptake to rice and wheat grains.•The presence of biochar increased the proportion of Zn-OM in soils.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The interaction of Cd and other heavy metals with soil colloidal particles controls the sequestration, mobility and bioavailability of Cd in soils. In this study, the binding (△Gbi) and adsorption ...(△Gad) energies of Cd on colloidal particles of 18 soils were determined by the Wien effect method. The binding energy of Cd on soil colloidal particles varied from 5.3 to 9.9 kJ mol−1, depending on the soil characteristics including pH, Mn‐oxide content and dissolved organic carbon in the soil. The Cd adsorption energy correlated positively with Mn‐oxide content and pH. In parallel, the extended X‐ray absorption fine structure (EXAFS) spectroscopy was used to determine the speciation of Cd in Cd‐saturated soil samples, which revealed that the outer‐sphere Cd was the predominant species, accounting for 32.2–73.7% of the total adsorbed Cd, and positively correlated to the binding and adsorption energies. Humic acid‐Cd (10.4–42.2%) and montmorillonite‐Cd (2.5–51.2%) were also major species that were identified by EXAFS spectroscopy. The toxicity (log EC50) of Cd in soils to three organisms (earthworm, Collembola and Chinese cabbage) was found to correlate positively with the binding energies, indicating the predictive capability of using binding energies of Cd in different soils as an indicator for evaluating Cd bioavailability and toxicity in soils.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The ubiquity and abundance of iron oxides in the subsurface highlight their important roles in influencing the fate and transport of engineered silver nanoparticles (AgNPs). In this study, the ...adsorption behaviors of AgNPs on two naturally occurring iron oxides, goethite and hematite, were investigated under environmentally relevant conditions. The maximum surface coverage of AgNPs on iron oxides ranged between 0.014 and 0.326 mg m −2 depending on the investigated ionic strength and pH. The particle interactions (AgNPs–AgNPs and AgNPs–goethite/hematite) were probed by aggregation kinetics measurements using time-resolved dynamic light scattering and Derjaguin–Landau–Verwey–Overbeek theory calculations, which confirmed the predominant role of heteroaggregation in AgNP adsorption onto iron oxides. Multiple state-of-the-art characterization studies using X-ray absorption spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy, and X-ray diffraction substantiate the dominant electrostatic attractions between AgNPs and iron oxides. Moreover, AgNP dissolution was reduced in the presence of iron oxides. Goethite was more effective than hematite in retaining AgNPs (5.1 to 16.3-fold higher) and inhibiting AgNP dissolution (1.2 to 5.7-fold lower), due to their surface charge differences. Altogether, our findings provide compelling evidence of the dominant role played by electrostatic attractions in AgNP adsorption by iron oxides and of inhibition of AgNP dissolution during the heteroaggregation process, which has important implications for better evaluating the potential environmental impacts and risks of AgNPs in the iron oxide-rich subsurface.
Birnessites are abundant naturally occurring minerals with high sorption and oxidation capacity that could therefore play an important role in antimony (Sb) migration and transformation. There are ...various types of birnessites in the environment. However, little is known about the similarities and differences in Sb oxidation and sorption on birnessites with different properties. In this study, the behavior of Sb oxidation and sorption on two contrasting birnessites (δ-MnO2 and triclinic birnessite (TrBir)) were investigated via batch and kinetic experiments and various spectroscopic techniques. Our results showed that the reaction mechanisms between Sb and the two birnessites were similar. The edge sites of birnessites were responsible for Sb(III) oxidation. Mn(IV) was reduced to Mn(III) and Mn(II), bound with birnessites and released to the solution, respectively. Because of the rapid rate of electron transfer of adsorbed Sb(III) to birnessites, the only Sb species on δ-MnO2 after the oxidation reaction was Sb(V). Sb(V) was adsorbed at the edge sites of birnessites by replacing the OH group of birnessites, forming corner-sharing complexes with birnessites. However, the Sb sorption and oxidation capacities of the two birnessites were significantly different. Poorly-crystallized δ-MnO2 exhibited a much higher oxidation and sorption capacity than well-crystallized TrBir because the former had many more edge sites than the latter. This study reveals the general mechanism of the reaction between Sb and birnessite and indicates that birnessite with a high number of edge sites would exhibit a huge capacity in Sb oxidation and sorption.
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•The reaction mechanisms between Sb and the two birnessite (δ-MnO2 and TrBir) are similar.•The edge sites of birnessite were responsible for Sb(III) oxidation and Sb(V) sorption.•Sb(V) was adsorbed at the edge sites of birnessite, forming corner-sharing complexes with birnessite.•δ-MnO2 was much reactive than TrBir in Sb oxidation and adsorption due to the many more edge sites of δ-MnO2.
The general reaction mechanism between Sb and birnessite and the key properties of birnessite affecting the reaction were revealed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Arsenic (As) and antimony (Sb) are considered as priority environmental pollutants and their accumulation in crop plants particularly in rice has posed a great health risk. This study endeavored to ...investigate As and Sb contents in paired soil-rice samples obtained from Xikuangshan, the world largest active Sb mining region, situated in China, and to investigate As speciation and location in rice grains. The soil and rice samples were analyzed by coupling the wet chemistry, laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), synchrotron-based micro X-ray fluorescence mapping (μ-XRF) and micro X-ray absorption near-edge structure (μ-XANES) spectroscopy. The results of field survey indicated that the paddy soil in the region was co-polluted by Sb (5.91–322.35 mg kg−1) and As (0.01–57.21 mg kg−1). Despite the higher Sb concentration in the soil, rice accumulated more As than Sb indicating the higher phytoavailability of As. Dimethylarsinic acid (DMA) was the predominant species (>60% on average) in the rice grains while the percentage of inorganic As species was 19%–63%. The μ-XRF mapping of the grain section revealed that the most of As was distributed and concentrated in rice husk, bran and embryo. Sb was distributed similarly to As but was not in the endosperm of rice grain based on LA-ICP-MS. The present results deepened our understanding of the As/Sb co-pollution and their association with the agricultural-product safety in the vicinity of Sb mining area.
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•The pollution conditions of sites were classified as sub-polluted (III) or clear (I).•As and Sb contents in rice decreased in the order of root > shoot > husk > grain.•DMA was the predominant species in the rice grains.•As distributed on the periphery and the endosperm of the rice grain.•Sb accumulated on the periphery of the rice grain.
This work clearly investigated the metalloid behaviors in soil-plant system, further contributing to address the food safety issues around the mining areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Both Sb(III) oxidation and resultant Sb(V) sorption took place at the edge sites of δ-MnO2.•Sb(III) oxidation was passivated by generated Mn(II), Mn(III) and manganese antimonate ...precipitation.•Sb(V) sorption on δ-MnO2 was favored by generated Mn(II) and Mn(III).•Sb(V) could bind to δ-MnO2 through Mn(II) bridge.
Manganese (Mn) oxide is considered as a potential regulator of the fate of many contaminants in soil due to its abundance and reactivity. The present study investigated the oxidation and sorption mechanisms of antimony (Sb) on δ-MnO2, by combining batch equilibrium experiments, kinetic experiments and various spectroscopic techniques. The collective results confirmed the high Sb(III)-oxidizing capacity of Mn(IV) sites on δ-MnO2 and the oxidation reaction was proton-driven. However, the oxidation process was gradually inhibited by the accumulation of manganese antimonate precipitates, the production of less reactive Mn(III), and the site-blocking effects of products Mn(II) and Sb(V) on the surface. Different from the direct sorption of Sb(V) by δ-MnO2, the oxidation of Sb(III) destroyed the surface structure of δ-MnO2 and exposed more reactive sites as evidenced by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The stronger Sb(V) sorption along with the oxidation of Sb(III), therefore, could be attributed to several binding modes, i.e., Mn(II) cation bridge, precipitation with Mn(II), along with inner-sphere complexations with surface Mn(IV) and Mn(III) sites. Sb(V) was sorbed at the edge sites of δ-MnO2 forming monodentate mononuclear complex with a configuration of Mn-O(H)-Sb(V) as confirmed by supplementary X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (EXAFS) spectroscopy and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy techniques. The findings altogether help to contribute to a better understanding on the geochemical dynamics of Sb with δ-MnO2 in subsurface environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The sorption mechanism of Cd(II) in 49 soils was fully explored.•Cd(II) sorption capacities were closely related to soil physicochemical properties.•Cd in soils was mainly bound to metal ...(hydro)oxides or existed as CdCO3.
Soil cadmium (Cd) contamination has emerged as an alarming environmental issue worldwide. Chemical reactivity and bioavailability of Cd in soils are highly dependent on soil properties. However, the sorption mechanism of Cd(II) on soils is not yet fully explored. For this purpose, batch sorption experiments, statistical analysis, and extended X-ray absorption fine structure (EXAFS) spectroscopy were integrated to elucidate the Cd(II) sorption mechanism by investigating the Cd(II) sorption behaviors in 49 soils with contrasting physicochemical characteristics and to figure out the influence of soil properties on Cd(II) sorption in soils. The outcomes of this study revealed that the soils from different areas had large differences in their abilities to adsorb Cd(II), while the differences were closely related to the physicochemical properties of soils. Cd(II) sorption capacities were controlled together by pH, metal (hydro)oxides, organic matter, and cation exchange capacity. The soil pH was the most critical factor in connecting Qmax with soil properties. EXAFS results indicated that Cd(II) adsorbed on soils was mainly bound with metal (hydro)oxides or existed as CdCO3 precipitate. The findings of this study provide a theoretical basis for predicting the risk of soil Cd contamination.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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