Octahedral Structure Research Articles

Synthesis, Characterisation and Microbial Activity of 2-(1H-benzothiazol-2-yl) Thioacetic acid with some Bivalent Metal Ions

The complexes of the potassium salt of 2-mercaptobenzthiazole with potassium salt of 2-chloroacetic acid in aqueous dioxane at reflux temperatures result in the formation of potassium salt of 2-(1H- benzolthiazol-2-yl) thioacetic acid (K C9 H6 NO2 S2 =KL). The Ligand KL forms stable complexes with bivalent metal chloride in aqueous ethanol to form bisligated complexes [ML2 ]nH2 O [(M=Co(II), Ni(II), Mn(II), Cu(I), Zn(II), or Cd(II) and n=o, 2 or 4)]. The Magnetic susceptibility and electronic spectral studies of Co(II), Mn(II), Ni(II), and Cu(II) complexes resemble their octahedral or distorted octahedral structure of these metal ions. The i. r spectral bands positions of complexes indicated that benzothiazole part of the ligand is not involved in coordination. The antifungal activity of ligand and its complexes were examined by cup and disc method. The results do not show appreciable antifungal activity examined by cup and disc method. The results do not show appreciable antifungal activity examined on fungi. The thermal stability of complexes indicated that two water molecules in Co(II), Ni(II) Cu (II) and Mn(II) Complexes [ML2 (H2 O)2]2H2 O are present in coordination sphere.

Exploration of AB3Si3 (A = Na/K/Rb/Cs) compounds under moderate pressure.

We discovered the composition of ternary AB3Si3 (A = Na/K/Rb/Cs) compounds in the moderate pressure range of 0-100 GPa using first-principles structural prediction and systematically analyzed their structures, stability, electronic and optical properties within the framework of density functional theory. The AB3Si3 compounds exhibit a diverse phase diagram, including nine structures that are selected based on formation energies, along with a known clathrate RbB3Si3 structure with Pm3̄n symmetry. All predicted phases are thermodynamically and dynamically stable within the studied pressure range. In particular, the KB3Si3 compound with a direct band gap of 1.0 eV is identified as a promising candidate for photovoltaic materials beyond silicon-based materials, among which boron atoms form a unique regular octahedral structure; in contrast, NaB3Si3 and RbB3Si3 compounds are shown to have metallicity. Our findings enrich crystal structures of alkali-metal borosilicides and provide valuable insights into their potential applications.

Effects of tungsten on vacancy aggregation behavior and its induction for interstitial and vacancy migration in tantalum–tungsten alloys: A first-principles study

Tantalum–tungsten (Ta–W) alloys have been considered candidates for plasma-facing materials (PFMs) in advanced nuclear fusion design due to their excellent thermal and mechanical properties. Herein, the effects of tungsten (W) on the clustering and migration of vacancies and interstitials in Ta are studied using first-principles calculations. We find that W can attract vacancies at the second nearest neighbor position, causing the original non-clustered W to gather around the vacancies, forming an octahedral cluster structure. However, as the number of W atoms increases, W exerts a progressive inhibitory effect on the formation of vacancy clusters. Furthermore, this work confirms that W induces the migration of vacancies, thus significantly improving the mobility and recombination ability of vacancies. Similarly, W also induces the migration of interstitial atoms in addition to reducing the interstitial rotation threshold energy, leading to an evolution of Ta–Ta interstitial to Ta–W interstitial. Therefore, it can be speculated that W not only plays a vital positive role in the combination between interstitials and vacancies, but also can effectively inhibit the formation of voids by adding W, and then improving the anti-irradiation ability of Ta–W alloy material under neutron irradiation.

Synthesis of GO/Fe–Ni MOF octahedral structure as an effective magnetic adsorbent in the removal of sulfur compounds from liquid fuel

An effective composite of bimetallic metal-organic frameworks (MOFs) GO/Fe–Ni in the presence of a specified quantity of graphene oxide (1, 5, 10, 25, and 50 wt%) was synthesized via a solvothermal method for removal of thiophene (TP) from a model of oil. The efficiency of adsorption desulfurization was evaluated by removing TP from the n-heptane-TP as a model oil. XRD, FTIR, FESEM, EDS, BET, VSM, and TGA techniques were used to investigate and confirm the structural characteristics of the GO/Fe–Ni MOF composite. The composite material of GO to Fe–Ni MOF = 5 wt% with adsorption capacity of 18.54 mg. g−1 displayed the best performance in TP at the optimal experimental conditions, which was ascribed to its high porosity and suitable pore size. GO/Fe–Ni MOF adsorption has a surface area of (431 m2. g−1) higher than Fe–Ni MOF (352 m2. g−1), based on the BET technique, there would be more opportunity for TP to be adsorbed on the GO/Fe–Ni MOF. The reused tests prove that GO/Fe–Ni MOF can be recycled for at least four runs with negligible losses in its capacity performance (11%). More significantly, the magnetic properties of GO/Fe–Ni MOF (5 wt%) can be used to facilitate the separating of oils in harsh conditions.

(E)-2-((1,7,7-Trimethylbicyclo [2.2.1]Heptan-2-Ylidene) Amino) Acetic Acid Compound and their Metal Complexes: Synthesis and Characterization

The reaction of camphor with glycine under the showing conditions yielded (E)-2-((1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)amino)acetic acid ligand . The complexes of Cu(II), Ni(II), Co(II), Zn(II) and Fe(II) with ligand have been obtained by the reaction between copper bromide, hydrate nickel chloride, hydrate cobalt chloride, zinc chloride, and iron bromide with ligand in 1:2 mole ratio. The free ligands and their metal complexes have been separated in the solid state. The spectroscopic data of the complexes recommend their 1:2 structures which are researched by elemental analysis (CHN) 1H NMR and FT-IR spectroscopy. From the spectroscopic data proposed the octahedral structure for the all complexes.

Interactions of novel pyrazole ligand and its transition metal complexes with CT-DNA and BSA: A combination of experimental and computational studies

A novel pyrazole acylhydrazone (C11H11N5O, HL) and its four transition metal complexes [Co(HL)L]NO3(C1), [Ni(HL)L]NO3(C2), [Cu(HL)L]NO3(C3), [Zn(HL)L]NO3(C4) have been synthesized and characterized. The crystal structures of the above five compounds were studied by single-crystal X-ray diffraction analysis. HL was a triclinic crystal system, crystallized in the P-1 space group, and C1-C4 were all six-coordinated octahedral mononuclear structures with two ligands providing the NNO donor atoms, and the C2/c space group. The kinetic interactions of HL and C1-C4 with CT-DNA and BSA were determined by UV–vis absorption spectra, fluorescence spectroscopy and microcalorimetry. Furthermore, possible interactions were calculated by molecular docking simulation using available software. The UV–vis absorption spectra measurements indicated that HL and C1-C4 could bind to CT-DNA by intercalations. Fluorescence spectroscopy suggested that HL and C1-C4 could bind to BSA through a static mechanism. The microcalorimetric studies showed that the durations of interactions of HL and C1-C4 with CT-DNA/BSA were all<60 min. The calculated enthalpy, entropy and Gibbs free energy changes were ΔH < 0, ΔS < 0 and ΔG < 0, presenting that all interaction processes were exothermic with spontaneous entropic reduction reactions. The order of binding abilities of the HL and C1-C4 to CT-DNA was C4 > C1 > C2 > C3 > HL, and the order of binding capacities to BSA was C2 > C3 > C1 > C4 > HL. The molecular docking simulations further verified the “semi-insertion” binding modes of HL and C1-C4 to CT-DNA and the fluorescence quenching of tryptophan in BSA in the presence of five compounds, which indicated that the interactions of HL and C1-C4 with DNA/BSA included hydrogen bonding, hydrophobic interactions and electrostatic interactions. In addition, by comparing the antibacterial activities of HL and C1-C4 against B. subtilis (A), S. aureus (B), P. aeruginosa (C), E. coli (D) and C. albicans (E), it was found the antibacterial activities of C1-C4 were all higher than that of HL, and the inhibitory effects of C1-C4 on fungi were better than that of four bacteria. At the maximum concentration of 2 mg/mL, C2 exhibited excellent antibacterial activities against B. subtilis, S. aureus, E. coli and C. albicans.

Octahedral Hexapalladium Pseudo-Td Pd6(μ3-CO)4(PEt3)6 with 80 Electron-Deficient Cluster Valence Electrons (CVEs) and a Comparison with Octahedral Hexapalladium Pseudo-C2v Pd6(μ3-CO)4(PMe3)7 with 82 CVEs: Computational Analysis and Resulting Implications.

The elusive octahedral hexapalladium Pd6(μ3-CO)4(PEt3)6 (1) was obtained by the reaction of Pd10(CO)12(PEt3)6 with TlCo(CO)4 in tetrahydrofuran under N2 at 55 °C. Its pseudo-Td octahedral structure, established from a CCD X-ray diffractometry study at 100 K, has the highest ideal symmetry of any of the characterized octahedral-based CO/PR3-ligated homopalladium Pdn clusters (n = 6, 7, 8, 10). Each Pd atom in 1 is coordinated to a PEt3 ligand, and each nonadjacent triangular Pd3 face is capped by a triply bridging μ3-CO ligand. The 31P{1H} NMR and IR spectra of 1 are in accordance with its solid-state molecular structure. Cluster 1 has a total of 80 cluster valence electrons (CVEs), the lowest reported for octahedral-based metal polyhedra that normally conform to the Wade-Mingos bonding rule with an 86 CVE count. Comparative density functional theory calculations involving natural population analysis are presented for trimethylphosphine analogues of the triethylphosphine (1-Me) and the previously reported octahedral hexapalladium trimethylphosphine Pd6(μ3-CO)4(PMe3)7 (2), which has pseudo-C2v symmetry with 82 total CVEs.

SYNTHESIS AND LUMINESCENCE OF CERIUM DOPED KSrY(BO3)2

The rare-earth borate compounds are widely used in various fields of science and technology as solid-state lasers, LEDs, and plasma panels. Development of blue emitting phosphors typically involves doping with cerium ions various matrices, exhibiting high photoluminescence quantum yields for LEDs. However, the main problem of such compounds, in addition to the concentration quenching, is the presence in the matrix of both the trivalent Ce3+ and tetravalent Ce4+ states of cerium ions. The goal. Study of the luminescent properties of the new KSrY0.95(BO3)2:0.05Ce3+ compound. Experimental. New phosphors based on complex borate KSrY(BO3)2 doped with cerium ions have been obtained by the solid-phase synthesis. The mixture of the starting materials after grinding in an agate mortar has been calcined at 700°C in a platinum crucible for 12 hours. The calcination temperature has been increased in steps of 50°C with re-ground of the mixture at each stage. The KSrY0.95(BO3)2:0.05Ce3+sample has been annealed in hydrogen at 900°C for 8 hours. Results and discussion. The X-ray phase analysis has shown that the new compound crystallizes in the monoclinic space group P21/m. The calculated unit cell parameters for KSrY0.95(BO3)2:0.05Ce3+are: a = 9.2861(23) Å, b = 5.3654(6) Å, c = 6.5854(14) Å, V = 289.7(1) Å3. In the crystal structure of KSrY(BO3)2, each B atom is connected to three O atoms, forming a BO3 triangle. The planar groups (BO3)3 are distributed layer by layer in the plane. The Y atoms are surrounded by six oxygen atoms, forming an octahedral structure and occupying interlayer positions.Ce3+ ions in the crystal lattice mainly replace the Y+3positions based on the similarity of the ionic radius and valency of Y+3 (r = 0.90 Å, CN = VI), Ce3+ (r = 1.01 Å, CN = VI). Conclusion. At a wavelength of 440 nm, the excitation spectrum exhibits one absorption band with the 2F7/2 → 5D1 energy transition, which corresponds to the excitation of the cerium ion from the ground state to the excited state. A decrease in the luminescence intensity of the KSrY0.95(BO3)2:0.05Ce3+ sample has been found for 3 hours after its annealing.

Synthesis, characterization, theoretical study and biological evaluation of Schiff base and their La(III), Ce(IV) and UO2(II) complexes

ABSTRACT. A new three metal complexes of La(III), Ce(IV) and UO2(II) ions have been synthesized based on a Schiff base derived from the condensation of L-histidine and anisaldehyde. All prepared compounds were characterized by different spectroscopic techniques and Density-functional theory (DFT) calculations. The complexes were proposed to have an octahedral structure based on the investigated results. The optimized shape, numbering system, and dipole moment vector of Ligand and La, Ce, and UO2 (1:1) chelates were investigated. The Schiff base ligand and complexes exhibit moderate action against all of the bacteria tested, with P. aeruginosa, Klebsiella sp., and E. faecalis respectively being the order of inhibition.&#x0D; &#x0D; KEY WORDS: 2-Anisaldehyde, Biological activity, DFT, L-Histidine, Metal complexes, Schiff base&#x0D; &#x0D; Bull. Chem. Soc. Ethiop. 2023, 37(2), 335-346. &#x0D; DOI: https://dx.doi.org/10.4314/bcse.v37i2.7

Octahedral Distortion Co-Regulation via Dual Strategies toward Luminescence Enhancement for the MA4InBr7 Perovskite Single Crystal.

A series of novel perovskite single crystals are innovatively grown. Aiming to enhance the luminescence performance, octahedral distortion co-regulation via dual strategies for the as-prepared perovskite single crystals is performed. The distortion of the octahedral structure strengthens the electron-phonon coupling and electron localization, resulting in a more stable self-trapped state, which thereby increases the potential for radiative recombination, accompanied by the self-trapped exciton emission. Accordingly, the luminescence spectra of the as-prepared MA4In0.975Sb0.025Br7 single crystal can cover the 450-800 nm range, and the photoluminescence quantum yield is up to 81.25%.

Oxygen vacancy and facet engineering of cuprous oxide by doping transition metal oxides for boosting alcohols selectivity in electrochemical CO2 reduction

Nanostructured Cu-based catalysts have gained much attention for electrochemical CO2 reduction (ECR) to value-added alcohols, while they are facing the challenges of unsatisfactory catalytic activity and selectivity. Herein, oxygen vacancy and facet engineering strategies are employed to modulate the ECR performance of Cu2O by doping transition metal oxides (TMOs). TMOs doping improves CO2 conversion by suppressing hydrogen evolution reaction (HER). The catalyst doped with 0.001 mol% ZnO exhibits a high alcohols Faradaic efficiency of 63.67% at −0.3 V vs. RHE, which exceeds that of the bare Cu2O (35.4%). The enhanced activity and alcohols selectivity is ascribed to the enriched oxygen vacancy defects (57.26%) for enhanced CO2 adsorption and activation and the synergistic effect between Cu and Zn sites for facilitated CO* protonation and C–C coupling. Alcohols selectivity increases from 56.87% to 64.27% and then declines to 63.67% with the increasing ZnO molar ratio from 0.00025 to 0.001. The Cu2O–ZnO-0.0005 catalyst features the octahedral structure (enclosed by the (111) and (100) facets) exhibits favorable ECR performance with the highest alcohols selectivity of 64.27% at −0.3 V vs. RHE. The enhanced alcohols selectivity is associated with the facet-dependent effect, as the exposed (111) facet favors CO2 adsorption and activation in ECR.

Мобильный спелеологический параллельный робот с пространственной тактильной системой распознавания контактной поверхности

The paper considers the problem of conducting speleological studies of natural and artificial caves, including channels of the underground rivers, as well as various mine workings in dangerous or inaccessible conditions for a speleologist. In this case, external environment of the objects under study could turn out to be opaque for optical, radio, ultrasonic and other physical methods of monitoring the inner surface, for example, due to partial or complete flooding of the object with water with inhomogeneous suspensions. A solution to the problem is proposed by robotizing the research using a mobile speleological parallel robot (MSPR) with a spatial tactile system for identification of the contact surface. MSPR is created in the form of an active octahedral structure, which edges are rods with linear drives. The rod ends are pivotally connected to the corresponding vertices of the active octahedral structure ensuring its geometric invariability when the linear drives are turned off. As a result, MSPR is able to carry out contact (tactile) mapping of the inner surface under study regardless of the external environment transparency and its geodetic binding to the base coordinate system with visualization in the form of histograms. At the same time, MSPR is able to self-move along the internal surfaces regardless of their spatial orientation. MSPR and its functionalities are described, one of which is the ability to build the 3D histograms of the surrounding space bind to the base (inertial) coordinate system through the mechanical contact. The tactile system of identifying the contact surface makes it possible not only to move the MSPR, but also to tactilely monitor in the external environment that is opaque for optical, radio, ultrasonic and other physical control methods. MSPR allows robotizing speleological research in dangerous, hard-to-reach and inaccessible places for a speleologist, as well as to carry out rescue operations and ensure delivery of the required cargo.

Bimetal Synergetic Strategy of Nickel Iron Selenides to Improve the Catalytic Activity and Cyclic Stability in Dye‐Sensitized Solar Cells

Due to the shortage of freshwater resources and uneven distribution, the dye‐sensitized solar cell has become an effective strategy to obtain green electric energy. However, the counter electrode (CE) is the bottleneck that restricts the development of this technology. Herein, a novel ternary nickel iron selenide with octahedral structure using a simple solvothermal strategy assisted by d‐(+)‐glucose (Ni0.5Fe0.5Se2/C) has been designed and applied as CE catalyst for the first time. Profiting from the synergistic effect between Ni and Fe, the simulative cell with the Ni0.5Fe0.5Se2/C CE yields a superior efficiency of 9.37% to corresponding pure selenides, notably outperforming that of conventional Pt CE (8.79%).

Synthesis, structural characterization and in vitro antibacterial activity studies of ternary metal complexes of anti-inflammatory bromhexine drug

A novel d-block metal complexes of M(II)/(III) ions using bromhexine (BHX) as primary ligand and glycine (GLY) as secondary ligand were synthesized and characterized. The structures of these complexes were confirmed by different spectroscopic tools. From the molar conductivity, elemental analyses and thermal analysis data of the synthesized complexes, general formula of [M(BHX)(Gly)(H2O)2]XCl·yH2O, (where M = Cr(III), x = y = 2; Mn(II), Co(II), Ni(II), Cu(II) and Zn(II), x = 1, y = 0; Cd(II), x = 1, y = 2) and [Fe(BHX)(Gly)(H2O)Cl]Cl with an octahedral structure were proposed. The octahedral geometry was supported by the magnetic moment and diffuse solid reflectance spectra measurements. The IR spectra pointed out that BHX ligand coordinated in neutral bidentate mode to the metal ions while Gly coordinated in mono negative bidentate mode. Conductivity measurements revealed that the ternary complexes were electrolytes. The complexes were tested against a variety of pathogenic bacterial strains and shown to have effective antibacterial capabilities when compared to bromhexine, suggesting that they could be useful models for the development of effective antibiotic drug molecules. In addition, the ligands were tested for anticancer activity against the MCF-7 breast cancer cell line, and the results revealed that the metal complexes were more active than the parent BHX free ligand. The BHX ligand and Co(II) complex were molecular docked to a variety of potential biological targets, including the receptors of Staphylococcus aureus crystal structure (PDB ID: 4K3V) and the receptors of breast cancer mutant oxidoreductase (PDB ID: 3HB5).

Preparation and characterization of electromagnetic wave absorbing material from polymetallic vanadium titano-magnetite (VTM): Oriented phase transformation underlying formation mechanism

Polymetallic vanadium titano-magnetite (VTM) is recognized as one of the most refractory mineral resources because of its multiple-element composite symbiosis feature. Conventional carbothermic reduction and smelting separation treatment are characterized by high energy consumption and large greenhouse gas emissions. Considering the material attribute, an alternative and clean utilization of refractory VTM via the pyrometallurgically oriented phase transformation in air atmosphere to prepare the composite electromagnetic wave absorbing material was proposed for the first time in this work. The theoretical foundation of the oriented composite material design, phase transformation, microstructure and interfacial element migration, magnetism, electromagnetic properties, and wave absorbing properties were investigated via thermodynamic calculations, XRD, XPS, optical microscope, SEM‒EDS, VSM, and VNA analyses. Theoretical calculations indicated that the formation of composite ferrites was thermodynamically feasible over 1085 °C. In the oriented phase reconstruction, the symbiotic structure of the VTM was reconstructed via MnO2 addition at 1150 °C, and almost all the Fe, Mn, Ti, and V were concentrated in the composite ferrites, in which the Ti and V were doped in the octahedral structure (B site) of spinel-type crystalline structure. The as-purified composite ferrite material from the VTM+80%MnO2 mixture roasted at 1150 °C for 2 h showed good electromagnetism performance. A minimum RL peak of −50 dB was obtained at a veneer thickness of 11 mm, and the RL value less than −20 dB had a big frequency bandwidth of 9 GHz (frequency range of 8 GHz–17 GHz). It's inferred that this low-cost and abundant composite ferrite material can be economically applied in the construction industry. This work provided a clean and higher-value application of abundant refractory polymetallic VTM resources.

Different atomic contrasts in HAADF images and EELS maps of rutile TiO2.

High-angle annular dark-field (HAADF) imaging and elemental mapping at the atomic scale by scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) are widely used for material characterization, in which quantitative understanding of the contrast of the image is required. Here, we report an unexpected image contrast in the elemental mapping of rutile TiO2, where the Ti L2,3 map shows an anisotropic elliptical shape that extends along the long axis in the octahedral structure, while the atomic contrast of Ti columns in the HAADF image is almost circular. Multi-slice simulation reveals that unique electron channeling related to the rutile structure and the difference of the potentials between HAADF and EELS cause the different atomic contrasts in the two images.

A robust octahedral NiCoOxSy core-shell structure decorated with NiWO4 nanoparticles for enhanced electrocatalytic hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction by water splitting is deemed to a clean and efficient approach for greener energy. The intensive pursuit of cost-effective and stable electrocatalysts for HER is quite imperative and challenging. Herein, a typical core-shell NiWO4@NiCoOxSy/NCF nano-architecture consisted of NiCoOxSy/NCF octahedrons and NiWO4 nanoparticles on nickel-cobalt foam is synthesized, and the NiWO4@NiCoOxSy/NCF requires quite small overpotential of 85 mV to afford current density of 10 mA cm−2 for HER in 1 M KOH, respectively, while NiCoOxSy/NCF shows the overpotential of 132 mV at the current density of 10 mA cm−2 in 0.5 M H2SO4. Moreover, they still present good durability with continuous operation of 72 h in alkaline and acidic electrolytes, outperforming most of the non-noble bimetallic oxides or sulfides electrocatalysts. The prominent performance benefits from NiWO4@NiCoOxSy/NCF takes advantages of component respective strengths such as interfacial cooperative effect, strong electrical connection and fast electron transfer, the highly exposed surface area, in situ surface reconstruction. The work provides a new prospect toward the controlled design and rational fabrication of multicomponent hierarchical core-shell structure electrocatalyst in high-performance flexible electrochemical hydrogen production.

Synthesis, physicochemical properties, biological, molecular docking and DFT investigation of Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes of the 4-[(5-oxo-4,5-dihydro-1,3-thiazol-2-yl)hydrazono]methyl}phenyl 4-methylbenzenesulfonate Schiff-base ligand

A new Schiff-base ligand, 4-[(4-oxo-4,5-dihydro-1,3-thiazol-2-yl)hydrazono]methylphenyl 4-methylbenzenesulfonate (L), and its Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes were synthesized and characterized. Elemental analysis, NMR spectroscopy, mass spectra, FT-IR analysis, molar conductivity, magnetic susceptibility tests and electronic spectra (UV-vis.) were all used to describe the ligand and its metal complexes. The complexes of Ni(II) and Zn(II) were found to have a tetrahedral structure, whereas those of Fe(III), Co(II) and Cu(II) exhibited an octahedral structure. The geometry of the ligand and its metal complexes was investigated by density functional theory (DFT) calculations at the B3LYP/6-311G(d, p) and LanL2dz levels of theory, respectively. To round out the picture, we evaluated not only the overall energy but also the HOMO and LUMO molecular orbitals and the molecular electrostatic potential (MEP). The synthetic analogues were tested for their in vitro antibacterial and antifungal efficacy against various pathogens using the disc diffusion method. The research shows that the metal complexes are more effective against these diseases than the free ligand. In addition, the DPPH method was used to measure the antioxidant activity in vitro. The antioxidant activity of each complex was higher than that of its free corresponding ligand. Molecular docking was carried out to determine the interactions between the complexes and the probable binding sites of Human Peroxiredoxin 2 Oxidized (PDB ID: 5IJT) and Escherichia coli (PDB ID: 3t88) receptors.

Reductive dehalogenation in groundwater by Si-Fe(II) co-precipitates enhanced by internal electric field and low vacancy concentrations

Fe(II) and silicate can form Si-Fe(II) co-precipitates in anoxic groundwater and sediments, but their phase composition and reactivity towards subsurface pollutants are largely unknown. Three types of Si-Fe(II) co-precipitations with the same chemical composition, namely Si-Fe(II)-I, Si-Fe(II)-II, and Si-Fe(II)-III, have been synthesized by different hydroxylation sequences in this work. It was found that Si-Fe(II)-III reduce carbon tetrachloride (CT) much faster (k1=0.04419 min−1) than Si-Fe(II)-I (0 min−1) and Si-Fe(II)-II (7.860 × 10−4 min−1). XRD results show that the main component of Si-Fe(II)-III is ferrous silicate (FeSiO3), which is quite different from that of Si-Fe(II)-I and Si-Fe(II)-II. The unique arrangement of hydroxyl coordination, the less distorted octahedral structure, the polyhedral morphology and the absence of Si-A center vacancies in Si-Fe(II)-III are responsible for its high reductive dehalogenation reactivity. The highest redox activity of Si-Fe(II)-III was shown by electrochemical characterization. The [FeII-O-Si]+ in Si-Fe(II)-III may stabilize the dichlorocarbene anion (˸CCl2−), which favors the transformation of CT to methane (9.2%). The Si-Fe(II) co-precipitates consist of countless internal electric fields, and the transformation of hydroxyl and CT both consumed electrons. The coexistence of hydroxyl and CT increases the electron density in the electron-rich region due to their electronegativity, enhancing their electron-accepting capabilities. This study deepens our understanding of the phase composition and electronic structure of Si-Fe(II) co-precipitates, which fills the gap in the reductive dehalogenation of halides by Si-Fe(II) co-precipitates.

Complete Description of the LaCl3-NaCl Melt Structure and the Concept of a Spacer Salt That Causes Structural Heterogeneity.

Lanthanides are important fission products in molten salt reactors, and understanding their structure and that of their mixtures is relevant to many scientific and technological problems including the recovery and separation of rare earth elements using molten salt electrolysis. The literature on molten salts and specifically on LaCl3 and LaCl3-NaCl mixtures is often fragmented, with different experiments and simulations coinciding in their explanation for certain structural results but contradicting or questioning for others. Given the very practical importance that actinide and lanthanide salts have for energy applications, it is imperative to arrive at a clear unified picture of their local and intermediate-range structure in the neat molten state and when mixed with other salts. This article aims to unequivocally answer a set of specific questions: is it correct to think of long-lived octahedral coordination structures for La3+? What is the nature as a function of temperature of networks and intermediate-range order particularly upon dilution of the trivalent ion salt? Is the so-called scattering first sharp diffraction peak (FSDP) for neat LaCl3 truly indicative of intermediate-range order? If so, why is there a new lower-q peak when mixed with NaCl? Are X-ray scattering and Raman spectroscopy results fully consistent and easily described by simulation results? We will show that answers to these questions require that we abandon the idea of a most prominent coordination state for M3+ ions and instead think of multiple competing coordination states in exchange due to significant thermal energy in the molten state.