Fe Lattice Research Articles

Subsurface oxygen at transition metal surfaces: Its direct atom-resolved imaging and role in metal oxidation

Clarifying how oxygen is incorporated into the subsurface region of metal surfaces is a crucial step towards a robust understanding of the initial oxidation of metals. Due to lack of direct atomic-resolution imaging of subsurface oxygen, the atomistic mechanisms of oxygen-metal interactions and the role of subsurface oxygen remain elusive. Here, by state-of-the-art transmission electron microscopy, we demonstrate a direct atom-resolved imaging of subsurface oxygen that is dissolved in the subsurface region of the Fe (001) and Ti (0001) surfaces. It is found that subsurface oxygen occupies the octahedral sites of the Fe and Ti lattices, rather than the tetrahedral sites. First-principles calculations reveal that the octahedral-site occupancy of subsurface oxygen is energetically more favorable compared to the tetrahedral-site occupancy and will facilitate the process of metal oxidation by reducing the formation energy of metal oxides. Our findings clarify the atomistic mechanism of how oxygen attacks metal surfaces for the initiation of oxidation that occurs everywhere in nature.

Ferromagnetism with above-room-temperature Curie temperature in Fe-doped β-Ga2O3 studied by first-principles calculations

Induced by the spin-polarized double-exchange interaction between the 3d orbitals of Fe atoms and O-2p orbitals near the O/Ga vacancy complexes, the origin of magnetism in β-Ga2O3 is investigated by using geometry optimization and energy calculation based on the first-principles generalized gradient approximation Hubbard + U method of density-functional theory. The results show that the formation energy of Fe2+ in the β-Ga2O3 matrix is lower than that of Fe3+, and the system is more stable when the Ga or O vacancies (VGa or VO) are adjacent to the Fe lattice position. It is found that the β-Ga31Fe2+/3+O47 and β-Ga30Fe2+/3+O48 systems all exhibit ferromagnetism with above-room-temperature Curie temperature. β-Ga30Fe2+/3+O48 (i.e., with Fe2+/3+ and VGa) has more spin-polarized O atoms in the same direction. The magnetism originates from the double-exchange interaction of the coupling and hybridization of the Fe-3d state of Fe3+ and the O-2p state, which increases the magnetic moment of the β-Ga30Fe3+O48 system. This study provides a theoretical reference for designing and preparing new β-Ga2O3-based dilute magnetic semiconductors and related spintronic and optoelectronic devices.

Lattice contraction-driven design of highly efficient and stable O–NiFe layered double hydroxide electrocatalysts for water oxidation

The slow progress of the oxygen evolution reaction (OER) is a key challenge in advancing water splitting as a viable technology for sustainable hydrogen production. Utilizing a self-standing NiFe layered double hydroxide (LDH) is a promising approach to address the slow kinetics of OER. Herein, the oxidized Fe2+-containing NiFe-LDH supported on Ni foam (O–NiFe-LDH@NF) is developed through corrosion engineering and aging. The growth mechanism is studied by adjusting urea content, hydrothermal temperature and time. It is revealed that the transformation of Fe2+ to Fe3+ in Fe2+-containing NiFe-LDH and the increase of Fe content leads to lattice contraction. Furthermore, detailed experiments and theoretical simulations illustrate that the substantial Fe content and lattice shrinkage promote the generation of Ni in high oxidation state and enhance the adsorption affinity toward the reaction species. Consequently, O–NiFe-LDH@NF exhibits enhanced OER activity and stability, with an exceptionally low overpotential of 197 mV and 354 mV observed at the current densities of 10 and 500 mA cm−2, respectively, and remarkable stability over 300 h. This approach can be generalized for designing advanced electrocatalysts.

Effects of Mn on the interface bonding and mechanical properties of TiC reinforced steel matrix composites

The addition of alloying elements to the steel matrix during the preparation process can significantly affect the properties of TiC reinforced steel matrix composites. In this study, the effects of Mn on the electronic structure and crystal structure stability of Fe supercells, along with as well as the stability of the TiC/Fe(Mn) interface, were analyzed through first-principles calculations. Additionally, 8 vol% TiC/Fe–C composites were prepared through the master alloy method. The effects of Mn contents (0, 0.8, 1.2, 1.6, and 2.0 wt%) on the interface mismatch and mechanical properties of the composites were investigated. The results revealed that Mn formed a solid solution and generated a stronger Fe–Mn bond compared with the Fe–Fe bond, and no interface chemical reaction occurred. The addition of a small amount of Mn improved the interface bonding between TiC particles and the steel matrix. The TiC particles were uniformly distributed in the matrix at the grain boundaries, with only a small amount dispersed within the grains. The TiC particles and steel matrix exhibited excellent, continuous, and stable interface bonding. The addition of Mn reduced the interface mismatch between TiC particles and the matrix. As the Mn content increased, the tensile strength and elongation of the composites first increased and then decreased, while the hardness of the composites increased. The addition of 1.2 wt% Mn resulted in an increase in the tensile strength, elongation, and hardness of the composite by 1160 MPa, 7.3%, and 43 HRC, respectively. These values were 109.8%, 151.7%, and 31.1% higher than those of the composite without Mn addition. However, an excess of Mn led to severe distortion of the Fe lattice and clustering at the interface, resulting in the degradation of the mechanical properties in the composites.

First principles and molecular dynamics simulations of effect of dopants on properties of high strength steel for hydrogen storage vessels

High-pressure gaseous hydrogen storage is an important way of hydrogen energy storage and transport at present, while high-strength steel material is one of the main materials used for hydrogen storage vessels. However, their internal doping elements and inherent defects often lead their mechanical properties to decrease, thus reducing the pressure-bearing capability and storage life of the vessel. At present, the mechanism of doping elements influencing the mechanical properties of high-strength steels is still unclear. In this work, a first-principles approach is used to study the influence of elemental doping (Cr, Mn, Mo, As, Sb, Bi, Sn, Pb) on the mechanical properties of Fe single crystals and Fe-C systems. The results show that among the above elements, Mn doping can increase the elastic modulus, bulk modulus, and shear modulus compared with those of pure Fe, while the doping by remaining elements will reduce the three moduli above, with the non-transition metal elements having a greater effect on the three moduli than the transition metal elements. Electronic structure analysis shows that the transition metal elements have better compatibility with the Fe lattice. Molecular dynamics results further show that the injection of H atoms significantly disrupts the lattice ordering of the Fe polycrystalline doped by C, Cr, and Mn elements, while the doping of Cr elements can significantly enhance the dislocation density of the system. The effects of doping elements on the mechanical properties of single-crystal and polycrystalline Fe, which are studied in this work, are of great significance in guiding the mechanistic study of the effects of doping and defects on the strength of Fe-based materials.

Lattice distortion SnS2 piezoelectric self-Fenton system for efficient degradation and detoxification of pollutants

Both piezoelectricity and self-Fenton catalysis are effective ways to degrade water pollution, but little research has combined them to construct a more efficient water pollution treatment method. Here, a Fe-doped SnS2 (Sn1-xFexS2) piezoelectric self-Fenton system was constructed, which shows superior water treatment performance. The best piezoelectric properties of the Sn0.97Fe0.03S2 system were verified by degrading rhodamine B (RhB). The toxicity analysis of degradation intermediates and solutions confirmed that the toxicity of RhB decreased after degradation. In addition, Kelvin probe force microscopy and photoelectrochemical analysis confirmed the better piezoelectric properties of Sn0.97Fe0.03S2. It has demonstrated the enhancement of systematic piezoelectricity by Fe lattice defects and the formation of self-Fenton by Fe as an active center in the degradation of RhB. In this work, an efficient piezoelectric and self-Fenton technology is constructed to remove organic pollutants from water, which is significant for developing water treatment technology.

Revealing the atomic mechanism of diamond–iron interfacial reaction

AbstractDiamond, with ultrahigh hardness, high wear resistance, high thermal conductivity, and so forth, has attracted worldwide attention. However, researchers found emergent reactions at the interfaces between diamond and ferrous materials, which significantly affects the performance of diamond‐based devices. Herein, combing experiments and theoretical calculations, taking diamond–iron (Fe) interface as a prototype, the counter‐diffusion mechanism of Fe/carbon atoms has been established. Surprisingly, it is identified that Fe and diamond first form a coherent interface, and then Fe atoms diffuse into diamond and prefer the carbon vacancies sites. Meanwhile, the relaxed carbon atoms diffuse into the Fe lattice, forming Fe3C. Moreover, graphite is observed at the Fe3C surface when Fe3C is over‐saturated by carbon atoms. The present findings are expected to offer new insights into the atomic mechanism for diamond‐ferrous material's interfacial reactions, benefiting diamond‐based device applications.

Elucidating the Geometric Active Sites for Oxygen Evolution Reaction on Crystalline Iron-Substituted Cobalt Hydroxide Nanoplates.

Transition-metal (oxy)hydroxides are among the most active and studied catalysts for the oxygen evolution reaction in alkaline electrolytes. However, the geometric distribution of active sites is still elusive. Here, using the well-defined crystalline iron-substituted cobalt hydroxide as a model catalyst, we reported the scanning electrochemical cell microscopy (SECCM) study of single-crystalline nanoplates, where the oxygen evolution reaction at individual nanoplates was isolated and evaluated independently. With integrated prior- and post-SECCM scanning electron microscopy of the catalyst morphology, correlated structure-activity information of individual electrocatalysts was obtained. Our result reveals that while the active sites are largely located at the edges of the pristine Co(OH)2 nanoplates, the Fe lattice incorporation significantly promotes the basal plane activities. Our approach of correlative imaging provides new insights into the effect of iron incorporation on active site distribution across nano-electrocatalysts.

Superionic effect and anisotropic texture in Earth’s inner core driven by geomagnetic field

Seismological observations suggest that Earth’s inner core (IC) is heterogeneous and anisotropic. Increasing seismological observations make the understanding of the mineralogy and mechanism for the complex IC texture extremely challenging, and the driving force for the anisotropic texture remains unclear. Under IC conditions, hydrogen becomes highly diffusive like liquid in the hexagonal-close-packed (hcp) solid Fe lattice, which is known as the superionic state. Here, we reveal that H-ion diffusion in superionic Fe-H alloy is anisotropic with the lowest barrier energy along the c-axis. In the presence of an external electric field, the alignment of the Fe-H lattice with the c-axis pointing to the field direction is energetically favorable. Due to this effect, Fe-H alloys are aligned with the c-axis parallel to the equatorial plane by the diffusion of the north–south dipole geomagnetic field into the inner core. The aligned texture driven by the geomagnetic field presents significant seismic anisotropy, which explains the anisotropic seismic velocities in the IC, suggesting a strong coupling between the IC structure and geomagnetic field.

A first principles study on H-atom interaction with bcc metals

Solute hydrogen trapping has long been proposed as one of the mechanisms for hydrogen embrittlement in steel. It has been reported that the maximum hydrogen trapping energy of metallic solutes ranged from −0.7 eV to −0.9 eV. In this work, the mechanism of metal-H interaction in Cr-Mo steels was investigated with first principles calculations by modelling the binary alloy Fe-X (X = C, Si, Mn, Cr, Mo) system with reference to the chemical composition of Cr-Mo steels. The formation of hydrogen bonds in the case of H atoms located at different sites in Fe-X crystals was analyzed. Results indicated that various atomic doping had different roles in hydrogen effect in the steel, with C, Si and Mo doping making the solid solution of hydrogen in Fe crystals easier, while Mn and Cr doping was rather more difficult. In Fe-Mn and Fe-Cr crystals, the repulsion between Fe lattices was insignificant when H atoms were located in tetrahedral sites, which considerably reduced the binding energy in the crystal. When H atoms were dissolved into the crystal, the interatomic bonding interactions in Fe-X crystals were weakened, resulting in higher charge density fluctuations. The current work extends the understanding of H-atom diffusion and migration in steel from the microscopic scale to the atomic and electronic scales, which underpins the physics for tailoring chemical elements of bcc metals towards higher resistance to hydrogen embrittlement.

Fundamental insights on ductile to brittle transition phenomenon in ferritic steel

Ductile to brittle transition (DBT) is a well-known phenomenon responsible for deteriorating the low temperature fracture toughness of ferritic steels. It is unambiguous to state that the transition phenomenon is a direct consequence of the strong temperature and strain rate sensitivity of flow stress, which in turn is regulated by the thermally activated motion of screw dislocation at the atomic scale. Due to very high Peierls stress, screw dislocation motion is accompanied by the nucleation and propagation of kink-pairs along the dislocation line. Thus, the activation energy required for kink-pair nucleation is an essential ingredient for correctly predicting the flow stress sensitivity and hence the ductile to brittle transition temperature (DBTT) of ferritic steel. However, experimental determination of kink-pair activation energy is rather tedious and there exists a strong discrepancy between atomistic simulation results (using Density Functional Theory and empirical potentials). Therefore, the present review is aimed at understanding the mechanism of screw dislocation motion in BCC Fe lattice and comparing the results obtained for kink-pair activation energy through experiments and simulations. The effect of different alloying elements on the overall flow stress sensitivity of Fe is also discussed with reference to the interaction of screw dislocation with solute atoms or clusters. Finally, the importance of screw dislocation on predicting the DBTT is explored to identify the present knowledge gaps and the future research directions.

Iron Hydride in the Earth's Inner Core and Its Geophysical Implications

AbstractHydrogen is potentially a key light element in the Earth's core. Determining the stability of iron hydride is essential for Earth's core mineralogy applications. We investigated the thermal stabilities of a range of Fe‐H binaries at core P‐T conditions. It is concluded that face‐centered cubic phase FeH is stable in the Earth's inner core. The high mobility of hydrogen in the Fe lattice suggests that hydrogen is transferred to a superionic state under the inner core conditions, where the superionic state transfer temperature of H in Fe fcc lattice is ∼500 K higher than that in hcp Fe system. The H concentration in the inner core is estimated to be ∼0.92 wt% to explain its density deficit, this value was further constrained to ∼0.21 wt% by matching the density jump at the inner‐core boundary. H alongside other light elements are required to account for the geophysical observations of the Earth's inner core.

(Corrosion Division Morris Cohen Graduate Student Award) Microscopic Electrochemical Properties of Carbon Steels and Metallurgical Approach for High Corrosion Resistance

Carbon steels are widely used in the production of automobiles, bridges, plates, and so on because of their superior mechanical properties and low cost. Carbon steels contain various types of microstructures such as ferrite, pearlite, and martensite, and desired mechanical properties can be obtained by combining these microstructures. While carbon steels exhibit excellent mechanical properties, their pitting corrosion resistance is relatively low in chloride-containing environments. Although the steels are successfully protected from corrosion by coating and/or painting, localized corrosion is readily initiated at cut edges and in coating defect areas in atmospheric environments. To prolong their service life and improve their reliability, it is necessary to elucidate the initiation mechanism of pitting corrosion on carbon steels. While it is widely known that the microstructures of carbon steels affect their corrosion resistance, the detailed mechanism is still unclear. The objective of this research is to clarify the relationship between the microstructure and pitting corrosion resistance of carbon steels in chloride-containing near-neutral pH environments.The pitting corrosion resistance of the typical microstructures of carbon steels was investigated using a micro-electrochemical polarization technique. Various microstructures (ferrite, pearlite, tempered martensite, decarburized martensite, as-quenched martensite etc.) were obtained by conducting different heat-treatments, and micro-scale electrodes (ca. 100 μm × 100 μm) were prepared with only one microstructure included. Small areas without any non-metallic inclusions were chosen as the micro-scale electrodes to eliminate the effect of pit initiation at the inclusion and evaluate the intrinsic corrosion behavior of the microstructure itself. Then, potentiodynamic anodic polarization measurements were carried out in NaCl-containing boric-borate buffers at pH 8.0. It was determined that the pitting corrosion resistance depends on the type of microstructure, with the as-quenched martensite showing the highest pitting corrosion resistance. The as-quenched martensite includes a high amount of interstitial C in the Fe lattice, and it was also clarified that the anodic dissolution of steels was clearly suppressed with increasing interstitial C content. During pitting corrosion, the local breakdown of the passive film is induced by chloride ions, which results in the initiation of active dissolution. It was considered that the low dissolution rate provided by interstitial C results in the superior pitting corrosion resistance of as-quenched martensite.To clarify the reason for the superior active dissolution resistance obtained by interstitial C, first-principles calculations were conducted. At first, the electronic structure of martensite was analyzed using bulk-model supercells with bct Fe crystal structures which included interstitial C. According to first-principles calculations, the electronic density of states (DOS) at and around the Fermi level decreased due to the presence of interstitial C. In addition, a valence electron transfer occurred from Fe to C atoms, resulting in a decrease in the number of valence electrons of Fe. Because the presence of valence electrons at and around the Fermi level affects the kinetics of electron (charge) transfer in oxidation/reduction reactions, including the active dissolution reaction, it was considered possible that the presence of interstitial C suppressed the electronic reactivity of Fe. Furthermore, first-principles calculations were also carried out for slab-model supercells consisting of a metal/vacuum interface, and the effect of interstitial C on the work function of martensite was analyzed. The result of the calculations indicated the work function of martensite linearly increased with increasing interstitial C content. Since the work function and ionization energy of metals are the same, the electrochemical properties of metals, such as dissolution resistance, are considered to be principally associated with their work function. In other words, it is understood that metals with a high work function are associated with a higher dissolution resistance. According to the above calculation results, the change in the electronic structure of Fe and the increase in the work function provided by interstitial C are key factors contributing to the superior dissolution resistance of martensite.

Thermal diffusion behavior of Fe/Cu/Ni multilayer coatings: a molecular dynamics study

In this paper, the thermal diffusion behavior of Fe/Cu/Ni multilayer coatings was investigated by molecular dynamics. The results show that the Fe, Cu, and Ni elements can diffuse each other at 1250 K. Meanwhile, the intrinsic diffusion coefficients and interdiffusion coefficients of the Fe, Cu, and Ni were calculated. Besides, the diffusion mechanism for high melting-point elements of Fe and Ni at 1250 K was analyzed in the paper. According to the simulation result, the Fe and Ni lattices were disturbed by the active Cu particles. Fe and Ni particles at higher energies may move out of their original positions and migrate into the Cu lattice randomly. Thus, the Fe and Ni elements were involved in the thermal diffusion. This can be confirmed by the decrease of the peak and the disappearance of the secondary peak in the radial distribution function curves. However, the position of the curve peaks did not change. Thus, the lattice structure was still maintained during the whole diffusion process. The thermal diffusion of the three elements was carried out by particle substitution at the lattice positions. It was a solid phase diffusion process. Furthermore, there was a clear particle diffusion asymmetry at the original interface of the element. It was consistent with the diffusion asymmetry of diffusion-couple experiments. The primary reason for this diffusion asymmetry was the difference in the interaction potential of the three elements. This asymmetry was ultimately reflected in the intrinsic diffusion coefficient and the interdiffusion coefficient of each element. For the Fe–Cu–Ni ternary system, the largest diffusion coefficient was copper and the smallest was iron at 1250 K.

Regulating the electro-deposition behavior of Fe metal anode and the applications in rechargeable aqueous iron-iodine batteries

The iron metal electrode based on the Fe2+/Fe redox reaction is a promising anode candidate for aqueous batteries. It possesses high capacity, large abundance, low price, as well as a little higher redox potential than Zn2+/Zn which corresponds to suppressed hydrogen evolution reaction. However, the reversibility and stability of Fe electrodes require improvement. Herein, we regulate the Fe deposition behavior with Zn doping. The positively charged [ZnI]+ complex is introduced into FeCl2 electrolytes by adding ZnI2, which is adsorbed on the negatively charged surface of Fe metal and realizes the doping of Zn into Fe lattice during deposition. In comparison to the large chunks with sole Fe deposition, the Zn doped Fe forms homogeneous small particles with the (110) plane preferred to grow parallel to the substrate. Enhanced coulombic efficiencies of 98% are achieved for over 1200 cycles. Stable Fe plating/stripping is accomplished for over 2500 h at the current density of 1 mA cm−2 and capacity of 1 mAh cm−2, as well as for over 300 h under ultra-high current density and capacity of 10 mA cm−2 and 10 mAh cm−2. Benefiting from the iodine species in electrolyte, an iron-iodine full cell is demonstrated. The battery exhibits excellent capacity retention of 99.8% with average coulombic efficiency of 96.7% for over 1200 cycles. The work provides a potential path for high-performance aqueous Fe-metal batteries.

The effect of Ni and Ti additions on the glass forming ability and magnetic properties of Al-Fe-Y alloy prepared by mechanical alloying

Amorphous Al82Fe14Ni2Y2 and Al82Fe14Ti2Y2 alloys were synthesized by mechanical alloying. Morphological and structural characterizations of the powders, milled for different periods of time, were investigated by scanning electron microscopy and X-ray diffraction methods. The dissolution of Ni and Al into the Fe lattice led to the formation of Fe(Ni,Al) solid solutions in Al82Fe14Ni2Y2 alloy after 20 h of milling. A slower dissolution of Ti and Al into the Fe lattice can be observed for Al82Fe14Ti2Y2 after milling 40 h. The fully amorphous structure can be obtained for Al82Fe14Ni2Y2 after 60 h of milling. The amorphization of the Al82Fe14Ti2Y2 sample milled for 100 h was not complete, and a partially nanocrystal phase of Ti was still present. Coercivity (Hc) and the saturation magnetization (Ms) of as-milled powders decreased markedly with increasing milling time. The magnetic properties of the alloys were consistent with the structural changing during milling process. The amorphous phase transforms into fcc-Al and metallic compounds after annealed DSC treatment.

Research on the Lattice Matching of Different Solute Atoms in BCC Fe: A Molecular Dynamics Simulation

AbstractIn this article, molecular dynamics simulation is used to primarily explore the lattice matching problem of solute atoms in different configurations after entering the Fe lattice at 0 K temperature. It reveals that by changing the initial configurations, metal solute atoms (Cr, Cu, Ti, Al) are more stable in the <110> configuration while C atom tends to stay in the octahedral gap of the BCC lattice. In addition, the matching mechanisms of different solute atoms in BCC Fe lattice in different configurations are elaborated in detail. The relaxation of metal solute atoms in different configurations eventually forms different stable structures while C atoms only exist in the nearest‐neighbor octahedral gap of the BCC Fe lattice in each configuration.

Effect of Magnesium Addition and High Energy Processing on the Degradation Behavior of Iron Powder in Modified Hanks’ Solution for Bioabsorbable Implant Applications

This paper shows the results of applying a combination of high energy processing and magnesium (Mg) as an alloying element in a strategy for enhancing the degradation rate of iron (Fe) for applications in the field of non-permanent medical implants. For this purpose, Fe powder was milled with 5 wt% of Mg (Fe5Mg) and its microstructure and characterized degradation behavior. As-received Fe powder was also milled in order to distinguish between the effects due to high energy processing from those due to the presence of Mg. The powders were prepared by high energy planetary ball milling for 16 h. The results show that the initial crystallite size diminishes from >150 nm to 16 nm for Fe and 46 nm for Fe5Mg. Static degradation tests of loose powder particles were performed in Hanks’ solution. Visual inspection of the immersed powders and the X-ray diffraction (XRD) phase quantification indicate that Fe5Mg exhibited the highest degradation rate followed by milled Fe and as received Fe, in this order. The analysis of degradation products of Fe5Mg showed that they consist on magnesium ferrite and pyroaurite, which are known to present good biocompatibility and low toxicity. Differences in structural features and degradation behaviors of milled Fe and milled Fe5Mg suggest the effective dissolution of Mg in the Fe lattice. Based on the obtained results, it can be said that Fe5Mg powder would be a suitable candidate for non-permanent medical implants with a higher degradation rate than Fe.

Atomistic simulation of the diffusion behavior in Al-Fe

• As Al block was attached to Fe block, Al atoms penetrated Fe block and vice versa on simulation. • Al atoms diffused massively into the Fe lattice, whereas Fe atoms moved deeper inside Al block. • The diffusion coefficient of Al was 2 times the diffusion coefficient of Fe. • Activation energy is 0.83 and 0.72 eV for Al and Fe, respectively. • Pre-exponentials is 1.03 × 10 −6 m 2 /s for Al and 5.83 × 10 −8 m 2 /s for Fe. The diffusion behavior of the Al-Fe system was investigated by a classical molecular dynamics simulation for simulating the Al coating process on Fe. Two bulks were built as the model: one bulk contained Al atoms and the other was made from Fe atoms. The diffusion was studied at four different temperatures for 6 ns by utilizing a MEAM potential. The mean square displacement (MSD) and potential energy of Al and Fe atoms were recorded during the simulation. Fe atoms penetrated inside the Al lattice in low quantities and at a slower rate compared with the fast and large number of diffusing Al atoms that did not penetrate inside the Fe lattice. The diffusion coefficient was estimated by the fitting of the linear region from the MSD and time curves. The Arrhenius equation was used to find the activation energy and the frequency of attempts. The activation energy of Al was 0.83 eV, whereas that of Fe was 0.72 eV. The frequency of attempts for the Al and Fe atoms were 1.03 × 10 - 6 and 5.83 × 10 - 8 m 2 /s, respectively. The diffusing mechanisms were studied, and it was found that the Fe atoms diffused into the Al lattice by the first-neighbor hopping mechanism. The potential energy of the Fe atoms increased as the Fe atoms penetrated the Al lattice.

Removal of Sb(V) from wastewater via siliceous ferrihydrite: Interactions among ferrihydrite, coprecipitated Si, and adsorbed Sb(V)

Although ferrihydrite (Fh) exhibits good Sb(V) adsorption behavior, the instability of its amorphous structure limits its engineering applications. In this study, siliceous ferrihydrite (SiFh) was prepared via coprecipitation to resolve these limitations. X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and SiFh aging tests revealed that the growth of Fh particles covered with Fe–O–Si links was inhibited while maintaining their amorphous structure. Meanwhile, the XRD patterns indicated that SiFh maintained excellent stability after five adsorption–desorption cycles. During the aging process, the added Si decreased the electrostatic interaction between SiFh and Sb(V), which weakened the affinity between Sb(V) and Fh; however, most of the Sb(V) still entered the Fe lattice after seven days of aging, which was favorable for Sb(V) recovery during reutilization. Furthermore, Sb(V) adsorbed from the simulated textile wastewater onto SiFh had the highest adsorption energy (Eads), which meant its unstable inner-sphere complexation on the surface of SiFh. Meanwhile, the presence of SO42−, NO3−, Ca2+, and Mg2+ contributed to Sb(V) outer-sphere adsorption. Both of these factors were conducive to Sb(V) desorption. Hence, SiFh is a promising adsorbent owing to its facile preparation process, stability, and optimal regeneration properties.