(Mg,Mn,Fe,Co,Ni)O: A rocksalt high-entropy oxide containing divalent Mn and Fe

High-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating to their structure formation, phase stability, and the interplay between configurational disorder and physical and chemical properties. Introducing Fe(II) and Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this structure under ambient conditions. Here, we develop a bottom-up method for synthesizing Mn- and Fe-containing rocksalt HEO (FeO-HEO). We present a comprehensive investigation of its crystal structure and the random cation-site occupancy. We show the improved structural robustness of this FeO-HEO and verify the viability of an oxygen sublattice as a buffer layer. Compositional analysis reveals the valence and spin state of the iron species. We further report the antiferromagnetic order of this FeO-HEO below the transition temperature ~218 K and predict the conditions of phase stability of Mn- and Fe-containing HEOs. Our results provide fresh insights into the design and property tailoring of emerging classes of HEOs.

{Nano-gold, iron(III)-1,3,5-benzene tricarboxylate metal organic framework (MOF)} nano-composite as precursor for laser ablation generation of gold-iron Aum Fen +/- (m = 1-35, n = 1-5) clusters. Mass spectrometric study

RATIONALE

Gold-iron bimetallic materials have applications in many fields, especially in nanotechnology and biomedicine. The chemistry of iron-doped gold clusters is still not fully understood but opens up the possibility of developing new materials, e.g. of gold cages doped with iron atoms. There have been several theoretical studies on these clusters but only a few experimental studies.

METHODS

Laser desorption ionisation (LDI) was used for the generation of Au-Fe bimetallic clusters via laser ablation (337 nm nitrogen laser) of the synthesised nano-composite {nano-gold; Fe(III) 1,3,5-benzene tricarboxylate}, i.e. {AuNPs, Fe-MOF}, while a quadrupole ion trap time-of-flight mass spectrometer, equipped with a reflectron, was used to acquire mass spectra.

RESULTS

A {AuNPs, Fe-MOF} nano-composite was prepared and found suitable for the LDI generation of Au_m Fe_n clusters. In addition to Au_m ^+/- (m = 1-35) clusters, a series of positively and negatively charged gold-iron Au_m Fe_n ^+/- clusters were generated. The mass spectra exhibited evidence for the clusters containing up to five iron atoms. In total, 113 binary Au_m Fe_n ^+/- clusters (m = 1-35, n = 1-5) were identified in the gas phase.

CONCLUSIONS

A synthesised {AuNPs, iron(III)-1,3,5-benzene tricarboxylate MOF} nano-composite was found suitable for the generation of many new gold-iron clusters and mass spectrometry was shown to be an efficient technique for the determination of the cluster stoichiometry. A broad series of over 100 bimetallic Au_m Fe_n clusters, some of them suggested to be gold cages doped with iron atoms (for m = 12 and higher), not only demonstrate a rich and complex chemistry, but also open wide possibilities of biomedical applications.

Microwave-assisted hydrometallurgical extraction of Li4Ti5O12 and LiFePO4 from ilmenite: effect of PPy-Br2 derived C-coating with N, Br, and Nb5+ Co-doping on electrodes for high-rate energy storage performance

Microwave-driven hydrometallurgical (MW-HM) method has been adopted to extract spinel-type Li4Ti5O12 (LTO) and orthorhombic-type LiFePO4 (LFP) from naturally occurring Ilmenite (FeTiO3) within 2 h unlike the conventional process that requires >30 h. We have successfully demonstrated aliovalent-Nb5+ doping and carbon coating with N, Br co-doping upon the pyrolysis of a polypyrrole-(PPy)-Br2 charge-transfer-(CT)-complex via MW-hydrothermal and MW-solid state heating within 30 min. Further, we also investigated the effect of carbon coating and co-doping of LTO and LFP electrodes at high C-rate performance of the lithium battery. XRD, XPS, FTIR, and Raman spectroscopy results confirmed the co-existence of dual-phase Li4Ti5O12/rutile-TiO2 (LTO-RTO) with substitution-induced transition of Ti4+ → Ti3+ in spinel-LTO due to Nb5+ and N, Br co-doping, which facilitates fast Li+ ion and electron transfer at the electrode-electrolyte interface. Conversely, in situ Nb5+ doped LiFePO4 combined with ex situ carbon-coating with N, Br co-doping improved the overall electronic conductive behavior. The UV-Visible absorption spectra and Tauc plots further support the decrease in the band gap upon co-doping, thus promoting n-type electronic behavior of the electrodes. A significant enhancement in the discharge-capacities of the carbon-coated N, Br co-doped Li4Ti4.97 Nb0.03O12/rutile-TiO2 (NBC-LTNO-RTO) and pristine anode in the range of 174-148 mA h g-1 and 167-125 mA h g-1 was exhibited at different rates in the range of 0.2 C-20 C with 97% and 94% capacity retention, respectively. Instead, the carbon-coated N, Br co-doped LiFe0.99 Nb0.01PO4 (NBC-LFNP) and pristine cathode exhibited discharge capacities in the range of 169-73 mA h g-1 and 136-65 mA h g-1 at different rates in the range of 0.2 C-20 C with 92% and 40% capacity retention for 500 cycles, respectively. Hence, this innovative, rapid, and sustainable chemical process for the fabrication of the modified cathode and anode from the earth abundant ilmenite ore as the single source with high-rate capability and ultra-stability can be used for high-power and safer lithium-ion energy storage.

Electrorheological behavior of iron(ii) oxalate micro-rods

Electrorheological (ER) fluids represent smart materials with extensive application potential due to their rheological properties which can be readily changed under an external electric field. In this study, the iron(ii) oxalate particles with rod-like morphology were successfully synthesized by the co-precipitation method using sulphate heptahydrate and oxalic acid dihydrate. The characterization of particles was performed via X-ray diffractometry and scanning electron microscopy. Subsequently, the ER fluids were prepared by dispersing the synthesized particles in silicone oil. The optical microscopy demonstrated the formation of chain-like particle structures upon the application of an electric field. Rheological properties were determined by means of rotational rheometry including creep-recovery experiments. The viscoelastic behavior of systems under investigation in the presence of the electric field was confirmed by the presence of recoverable strain of the system.

The application of rod-like iron(ii) oxalates particles led to significant electrorheological effect as proved e.g. via the creep-recovery experiments under the application of an external electric field.

Efficient removal of amoxicillin and paracetamol from aqueous solutions using magnetic activated carbon

Activated carbon (AC)/CoFe₂O₄ nanocomposites, MAC-1 and MAC-2, were prepared by a simple pyrolytic method using a mixture of iron(III)/cobalt(II) benzoates and iron(III)/cobalt(II) oxalates, respectively, and were used as efficient adsorbents for the removal of amoxicillin (AMX) and paracetamol (PCT) of aqueous effluents. The synthesized nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The sizes of cobalt ferrite nanoparticles formed from benzoates of iron(III)/cobalt(II) and oxalates of iron(III)/cobalt(II) precursors were in the ranges of 5-80 and 6-27 nm, respectively. The saturation magnetization (M _s), remanence (M _r) and coercivity (H _c) of the MAC-2 nanocomposites were found to be 3.07 emu g^-1, 1.36 emu g^-1 and 762.49 Oe; for MAC-1, they were 0.2989 emu g^-1, 0.0466 emu g^-1 and 456.82 Oe. The adsorption kinetics and isotherm studies were investigated, and the results showed that the as-prepared nanocomposites MAC-1 and MAC-2 could be utilized as an efficient, magnetically separable adsorbent for environmental cleanup. The maximum sorption capacities obtained were 280.9 and 444.2 mg g^-1 of AMX for MAC-1 and MAC-2, respectively, and 215.1 and 399.9 mg g^-1 of PCT using MAC-1 and MAC-2, respectively. Both adsorbents were successfully used for simulated hospital effluents, removing at least 93.00 and 96.77% for MAC-1 and MAC-2, respectively, of a mixture of nine pharmaceuticals with high concentrations of sugars, organic components and saline concentrations.

One-step synthesis of Fe3O4/carboxylate-rich carbon composite and its application for Cu(ii) removal

A magnetically separable adsorbent, Fe₃O₄/carboxylate-rich carbon composite was synthesized via a facile one-step low temperature carbonization process.

A new synthesis of carbon encapsulated Fe5C2 nanoparticles for high-temperature Fischer-Tropsch synthesis

Using a simple thermal treatment under a CO flow, uniform micrometer-sized iron oxalate dihydrate cubes prepared by hydrothermal reaction were transformed into Fe5C2@C nanoparticles to form a mesoporous framework; the final structure was successfully applied to the high-temperature Fischer-Tropsch reaction and it showed high activity (CO conversion = 96%, FTY = 1.5 × 10(-4) molCO gFe(-1) s(-1)) and stability.

The glassy behaviour of poorly crystalline Fe2O3 nanorods obtained by thermal decomposition of ferrous oxalate

Nanorod ferrous oxalate dihydrate (FeC2O4 × 2H2O) which had been synthesized by the microemulsion method, was used as a precursor in the thermal decomposition process performed in air atmosphere. The formation of nanocrystalline hematite as the final product was preceded by the appearence of an intermediate product. Comprehensive study comprising several complementary techniques (x-ray diffraction, transmission electron microscopy, selected area electron diffraction, thermogravimetric/differential thermal analyses and SQUID magnetometry) confirmed that the intermediate product corresponds to the poorly crystalline Fe2O3. Due to the specific nanorod shape and poorly crystalline structure, the investigated Fe2O3 showed high coercive field value of ~0.5 T at 5 K. Special attention in this study was devoted to the peculiar magnetic properties of poorly crystalline Fe2O3, which were thoroughly investigated by employing sophisticated experimental procedures such as relaxation of thermoremanent magnetization for different cooling fields, zero field and field cooled memory effects as well as aging experiments for different waiting times. At low temperatures and weak applied magnetic fields, the investigated system behaves similarly to spin glasses, manifesting slow, collective relaxation dynamics of magnetic moments through memory, rejuvenation and aging effects.

Creation of hollow microtubular iron oxalate dihydrate induced by a metallo-supramolecular micelle based on the self-assembly of potassium ferrioxalate and sodium dodecyl sulphate

A novel metallo-supramolecular micelle PF–SDS–SM was formed at room temperature through the self-assembly of potassium ferrioxalate and sodium dodecyl sulphate.

Kinetic modeling for thermal dehydration of ferrous oxalate dihydrate polymorphs: a combined model for induction period-surface reaction-phase boundary reaction

In this study, ferrous oxalate dihydrate polymorph particles, α- and β-phases, with square bipyramidal and quadratic prismatic shapes, respectively, were synthesized. Thermal dehydration of the samples was subjected to kinetic study as a typical reaction that indicates a significant induction period and a sigmoidal mass-loss behavior. On the basis of the formal kinetic analysis of the mass-loss traces recorded under isothermal, nonisothermal, and constant transformation rate conditions and the morphological observations of the surface textures of the partially reacted sample particles, a combined kinetic model for the induction period-surface reaction-phase boundary reaction was developed. The sigmoidal mass-loss behavior after the significant induction period under isothermal conditions was satisfactorily simulated by the combined kinetic model. The kinetic parameters for the component processes of induction period, surface reaction, and phase boundary reaction were separately determined from the kinetic simulation. The differences in the kinetic behaviors of the induction period and the phase boundary reaction between α- and β-phase samples were well described by the kinetic parameters. The applicability of the combined kinetic model to practical systems was demonstrated through characterizing the physicogeometrical kinetics of the thermal dehydration of ferrous oxalate dihydrate polymorphs.

Oxalate capped iron nanomaterial: from methylene blue degradation to bis(indolyl)methane synthesis

An efficient, sustainable and green procedure for the synthesis of selective orthorhombic iron(oxalate) capped Fe(0) [Fe(ox)–Fe(0)] nanomaterial is developed using sodium borohydride (NaBH₄) reduction of iron(ii) salt in the presence of oxalic acid at room temperature in water.

Mechanism studies of LiFePO4cathode material: lithiation/delithiation process, electrochemical modification and synthetic reaction

Olivine-structured lithium ion phosphate (LiFePO₄) is one of the most competitive candidates for fabricating energy-driven cathode material for sustainable lithium ion battery (LIB) systems.

One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240 °C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20 nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature Mössbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.

A preliminary investigation into the new class of lithium intercalating LiNiSiO(4) cathode material

A unique attempt to exploit silicate chemistry for a possible enhancement of the electrochemical properties of a lithium ion system via exploration of the novel category lithium intercalating LiNiSiO(4) cathode has been made through the present study. A novel citric acid assisted modified sol-gel method (CAM sol-gel) has been adopted to synthesize the title compound with a formation temperature positioned well below 500 °C, as derived from thermal studies. A powder x-ray diffraction (PXRD) pattern evidenced the absence of undesirable peaks and confirmed the formation of a hexagonal lattice structure with enhanced crystallinity and phase purity, and the presence of uniformly distributed particles of ∼200 nm size with well defined grain boundaries is obvious from the scanning electron microscopy (SEM) image of LiNiSiO(4) material. Further, magic angle spinning (MAS) (7)Li nuclear magnetic resonance (NMR) results from LiNiSiO(4) confirmed the presence of a layered type of crystal arrangement. A cyclic voltammetry (CV) study performed on a LiNiSiO(4) cathode revealed an excellent reversibility without any change in the peak position upon extended cycling, thus substantiating the structural stability upon progressive cycling.

Magnetically modified bentonite as a possible contrast agent in MRI of gastrointestinal tract

A composite of iron oxide nanoparticles and mineral matrix has been studied by XRD, Mössbauer spectroscopy, and TEM. Magnetite and superparamagnetic magnetite have been identified by Mössbauer spectroscopy in the nanocomposite. A relationship between the hyperfine parameters and iron oxide particle size has been confirmed by TEM. The optimal concentration of “magnetite—bentonite” composite, when the MRI signal is fully reduced, was found for using this composite as a negative contrast agent.