Selective fabrication of metastable greigite (Fe3S4) nanocrystallites and its magnetic properties through a simple solution-based route

Electronic structures of greigite (Fe3S4): A hybrid functional study and prediction for a Verwey transition

Greigite (Fe₃S₄) is a ferrimagnetic mineral with vital functions in both the bio-geochemical cycle and novel technological applications. However, the ground state electronic structure of this material has not been fully characterized by either experiment or theory. In the present study, ab initio calculations using the hybrid functional method have been performed to investigate the electronic structure and magnetic properties. It is found that the cubic structure observed under ambient temperature is a half metal and is metastable. A more stable monoclinic structure slightly distorted from the cubic form is found. The structural distortion is induced by charge ordering and associated with a metal-to-insulator transition, resulting in a semiconductive ground state with a bandgap of ~0.8 eV and a magnetic moment of 4 μB per formula unit. The results predict, similar to the magnetite (Fe₃O₄), a Verwey transition may exist in greigite, although it has not yet been observed experimentally.

Colloidal synthesis of greigite nanoplates with controlled lateral size for electrochemical applications

The excellent electrochemical performance of greigite (Fe3S4) coupled with its vast abundance and low toxicity make it a good prospect as an anode material for lithium ion batteries (LIBs). In this research, a simple and feasible approach for producing pure phase, small sized, shape-controllable, and stable Fe3S4 nanoplates (NPs) through hot injection of sulfur solution into Fe(iii) solution was demonstrated. The growth of Fe3S4 NPs involves the primary formation of a pyrite (FeS2) nucleus and subsequent Fe(iii) doping. The lateral size of the Fe3S4 NPs was controlled further by tuning the experimental variable-dependent reactivity of Fe sources in the nucleation and growth stage. The Fe3S4 NPs embedded in LIBs present a low electrochemical resistance and are highly active in lithiation/delithiation processes.

A comparative DFT study of the mechanical and electronic properties of greigite Fe3S4 and magnetite Fe3O4

Greigite (Fe3S4) and its analogue oxide, magnetite (Fe3O4), are natural minerals with an inverse spinel structure whose atomic-level properties may be difficult to investigate experimentally. Here, [D. Rickard and G. W. Luther, Chem. Rev. 107, 514 (2007)] we have calculated the elastic constants and other macroscopic mechanical properties by applying elastic strains on the unit cells. We also have carried out a systematic study of the electronic properties of Fe3S4 and Fe3O4, where we have used an ab initio method based on spin-polarized density functional theory with the on-site Coulomb repulsion approximation (Ueff is 1.0 and 3.8 eV for Fe3S4 and Fe3O4, respectively). Comparison of the properties of Fe3S4 and Fe3O4 shows that the sulfide is more covalent than the oxide, which explains the low magnetization of saturation of greigite cited in several experimental reports.

Assignment of Raman-active vibrational modes of tetragonal mackinawite: Raman investigations and ab initio calculations

We report on the first assignment of the Raman-active vibrational modes of mackinawite using Density Functional Perturbation Theory and direct methods with BLYP + dispersion correction. Based on experimental data and calculation results, the Raman bands were assigned as 236 cm⁻¹ (B_1g), 256 cm⁻¹ (E_g), 376 cm⁻¹ (A_1g) and 395 cm⁻¹ (E_g).

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing β-cyclodextrin (β-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe₃S₄) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. β-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8 mM⁻¹s⁻¹ which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs.

Hydrothermal fabrication and characterization of polycrystalline linneite (Co3S4) nanotubes based on the Kirkendall effect

In this study, polycrystalline linneite (Co(3)S(4)) nanotubes constructed with nanoparticles have been firstly fabricated using 1D Co(CO(3))(0.35)Cl(0.20)(OH)(1.10) nanowires as the sacrificial templates under hydrothermal conditions. The samples are characterized by means of XRD and TEM. The formation mechanism of the Co(3)S(4) nanotubes can be explained by the nanoscale Kirkendall effect, which results from the difference in diffusion rates between cobalt source and hydrogen sulfide. This simple synthetic route is expected to prepare other nanomaterials with the tubular structures.

Theoretical Electron Density Distributions for Fe- and Cu-Sulfide Earth Materials: A Connection between Bond Length, Bond Critical Point Properties, Local Energy Densities, and Bonded Interactions

Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, rho(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, rho(rc), the Laplacian, triangle down2rho(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of rho(rc) and triangle down2rho(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of rho(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the high-spin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the rho(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides.