Impact of high energy photons on physical, structural and magnetic properties of Mn0.65Zn0.35Fe2-xNdxO4 nanoparticles.

Ultrafine powders of Nd+3 doped Mn-Zn ferrite powders with composition Mn0.65Zn0.35Fe2-xNdxO4 (x = 0.04, 0.06, 0.08) were prepared using the combustion method of preparation. Monophasic nanoparticle formation was confirmed by X-ray diffraction. The particle size was determined using a Transmission electron microscope (TEM). The nanopowders were investigated for their physical, structural, and magnetic properties and then radiated with gamma photons obtained from Co60 source with a dose of 500Gy, 750Gy and 1000Gy. The characterization of radiated powders showed preservation of spinel structure with breaking down of crystallites into finer crystals with increment in amorphous content. Structural and physical parameters were drastically altered due to high-energy photon exposure. The breaking down of larger particles was observed as a result of photon energy impact on the samples. The Saturation magnetization of ferrite nanoparticles was observed to increase with increasing gamma radiation dose. Mössbaure spectra showed the dominance of Fe+3 in the high spin state.

Iron-based fluorophosphate Na2FePO4F as a cathode for aqueous zinc-ion batteries.

Aqueous zinc-ion batteries form a key post-Li-ion batteries to cater the rising demand for grid storage. Fe-based compounds can be used as economical cathodes for zinc-ion batteries. Herein, we explored iron-based flourophosphate as a potential polyanionic cathode. Involving the Fe3+/2+ redox process, it can reversibly intercalate Zn2+ yielding a capacity of ∼80 mA h g-1, involving a solid-solution mechanism. Polyanionic Fe-based phosphate frameworks can be harnessed as potential low-cost cathodes for secondary zinc-ion batteries.

Plasma polymerized functional supermagnetic Fe3O4 nanostructured templates for laccase immobilization: A robust catalytic system for bio-inspired dye degradation.

Fe3O4 magnetic nanoparticles, synthesized using co-precipitation method, were epoxy functionalized via plasma polymerization of 2,3-epoxypropylmethacrylate (EPMA) precursor. The EPMA-functionalized Fe3O4 nanoparticles (EPMA-f-MN) were employed as templates for facile, one-step covalent immobilization of laccase enzyme at room temperature. Samples were rigorously characterized by FTIR, TGA, SEM, TEM, XRD techniques, while Mössbauer spectroscopy (MöS) and vibrating sample magnetometry (VSM) confirmed the supermagnetic nature of Fe3O4 nanoparticles. Activities of free and immobilized laccase (ImLac) were assayed by spectrophotometrically monitoring the enzymatic reduction of substrate 2,2-azino-bis(3-ethylthiazoline-6-sulfonate) (ABTS) at 420 nm, corresponding to the λmax of ABTS.+. In addition to possessing higher thermal stability and a broader pH tolerance window compared to free laccase, the supermagnetic property of the Fe3O4 renders the ImLac system conveniently recoverable and recyclable. Practical applicability of ImLac towards catalytic degradation of industrial dyes was also ably demonstrated using Acid Blue 193 (AB 193) as a commercially used model textile dye, which belongs to the family of azo dyes. Over 95% degradation of the dye was achieved within a period of 4 hours. ImLac could be used for more than 10 dye degradation cycles with >90 % of retention in enzyme activity.

Size dependent electronic structure of LiFePO4 probed using X-ray absorption and Mössbauer spectroscopy.

We present the combined Mössbauer and X-ray absorption spectroscopy investigation of the electronic structure and local site symmetry of Fe in olivine structured LiFePO4 (LFP) with crystallite size (CS). The lattice parameters are found to contract with a decrease in CS, monotonously, whereas the electronic structural parameters exhibit two different regions with a threshold anomaly of around ≈30 nm. 57Fe Mössbauer studies reveal the coexistence of Fe2+ and Fe3+ sites and their relative concentrations are mainly determined by CS, which provides a comprehensive insight into the electronic structure of LFP at the mesoscopic level. The soft X-ray absorption unequivocally unravels the valence states of Fe 3d electrons in proximity to the Fermi level, which are prone to the local lattice distortion. The obtained spectra fingerprint the effect of CS supplying rich information on valency, lithium-ion vacancy concentration, covalency and crystal field. By comparing the spectra with the results of charge-transfer multiplet calculations, which include the full-atomic multiplet theory, we have found that the local symmetry of Fe ions is well described by the D4h point group with intermixing between eg and t2g orbitals. The unique structural and electronic properties of LFP are closely interlinked with changes in the bonding character, which shows the strong dependency on CS. The evolution of 3d states is in overall agreement with the local lattice distortion and provides the origin of the size effects on the electronic structure of olivine phosphate and other transition metal ion-containing materials.

TiO2-Doped Ni0.4Cu0.3Zn0.3Fe2O4 Nanoparticles for Enhanced Structural and Magnetic Properties.

TiO2 (0-10 wt %)-doped nanocrystalline Ni0.4Cu0.3Zn0.3Fe2O4 (Ni-Cu-Zn) ferrites were synthesized using the sol-gel route of synthesis. The cubic spinel structure of the ferrites having the Fd3m space group was revealed from the analysis of Rietveld refined X-ray diffraction (XRD) data. The secondary phase of TiO2 with a space group of I41/amd was observed within the ferrites with doping, x > 3 wt %. The values of lattice parameter were enhanced with the addition of TiO2 up to 5 wt % and reduced further for the highest experimental doping of 10 wt %. Field emission scanning electron microscopy (FESEM) images exhibit the spherical shape of the synthesized particles with some agglomeration, while the compositional purity of prepared ferrite samples was confirmed by energy-dispersive X-ray spectroscopy (EDX) and elemental mapping. The cubic spinel structure of the prepared ferrite sample was confirmed by the Raman and Fourier transform infrared (FTIR) spectra. UV-visible diffuse reflectance spectroscopy was utilized to study the optical properties of the ferrites. The value of band gap energy for the pristine sample was less than those of the doped samples, and there was a decrement in band gap energy values with an increase in TiO2 doping, which specifies the semiconducting nature of prepared ferrite samples. A magnetic study performed by means of a vibrating sample magnetometer (VSM) demonstrates that the values of saturation magnetization of the ferrites decrease with the addition of TiO2 content, and all investigated ferrites show the characteristics of soft magnetic materials at room temperature. The Mössbauer study confirms the decrease in the magnetic behavior of the doped ferrites due to the nonmagnetic secondary phase of TiO2.

Effect of crystallite size on the phase transition behavior of heterosite FePO4.

For advanced lithium-ion battery technology, olivine-based cathodes are considered to be the most dominant and technologically recognized materials. The extraction of lithium ions from olivine LiFePO4 results in the two-phase mixture with heterosite FePO4 exhibiting a deintercalation potential of 3.45 V vs. Li+/Li over a wide range of lithium content. Here, we report the synthesis and characterization of chemically deintercalated heterosite FePO4 with varying crystallite sizes using different analytical techniques. The decrease in the crystallite size of heterosite FePO4 leads to an increase in the lattice parameters including the unit cell volume. The characteristic behavior in the structural properties of heterosite FePO4 shows a strong dependency on the crystallite size which is correlated with the change in the chemical bonding. The volume expansion of the nano-sized heterosite FePO4 with respect to the bulk counterpart is suggested to be a direct consequence of reduced hybridization between the Fe3d and O2p states. Furthermore, the combined X-ray diffraction and Mössbauer spectroscopic studies reveal the appearance of a new phase namely trigonal FePO4 at the lower crystallite sizes due to the enhanced surface energy kinetics. We also find that the observed trigonal FePO4 phase is more magnetically active than the paramagnetic olivine FePO4. For the unique structural advantage of the heterosite phase as an electrode material, the change in bonding characteristics is very useful and can have strong implications on the electronic properties of heterosite FePO4 at the nanoscale level.

Sustainable preparation of sunlight active α-Fe2O3 nanoparticles using iron containing ionic liquids for photocatalytic applications.

Inspired by the nano-segregation of ionic liquids (ILs) into bi-continuous structures constituting of arrays of ionic and non-ionic components, herein, a new and sustainable strategy for preparation of mesh-like nano-sheet α-Fe2O3 nanoparticles and their photo-catalytic activity under sunlight, is presented. For the purpose, metal (iron) containing ionic liquids (MILs), 1-alkyl-3-methylimidazolium tetrachloroferrates, [C n mim][FeCl4], (n = 4, 8 and 16), which not only act as precursors and solvents but also as structure directing agents have been used. Thus prepared NPs show MIL dependent structural, photophysical and magnetic properties. The catalytic efficiency of NPs has been tested for the photo-degradation of organic dyes (Rhodamine B) in aqueous solution under sunlight. The NPs are found to exhibit comparable catalytic efficiency under sunlight as compared to that observed under high intensity visible lamplight, without showing a decline in their catalytic efficiency even after 4 catalytic cycles. It is anticipated that the present work will provide a new platform for preparation of sunlight active nanomaterials for photo-catalytic applications with control over the structural and physical properties via varying the molecular structure of MILs.

Optimization of lithium content in LiFePO4 for superior electrochemical performance: the role of impurities.

Carbon coated Li x FePO4 samples with systematically varying Li-content (x = 1, 1.02, 1.05, 1.10) have been synthesized via a sol-gel route. The Li : Fe ratios for the as-synthesized samples is found to vary from ∼0.96 : 1 to 1.16 : 1 as determined by the proton induced gamma emission (PIGE) technique (for Li) and ICP-OES (for Fe). According to Mössbauer spectroscopy, sample Li1.05FePO4 has the highest content (i.e., ∼91.5%) of the actual electroactive phase (viz., crystalline LiFePO4), followed by samples Li1.02FePO4, Li1.1FePO4 and LiFePO4; with the remaining content being primarily Fe-containing impurities, including a conducting FeP phase in samples Li1.02FePO4 and Li1.05FePO4. Electrodes based on sample Li1.05FePO4 show the best electrochemical performance in all aspects, retaining ∼150 mA h g-1 after 100 charge/discharge cycles at C/2, followed by sample Li1.02FePO4 (∼140 mA h g-1), LiFePO4 (∼120 mA h g-1) and Li1.10FePO4 (∼115 mA h g-1). Furthermore, the electrodes based on sample Li1.05FePO4 retain ∼107 mA h g-1 even at a high current density of 5C. Impedance spectra indicate that electrodes based on sample Li1.05FePO4 possess the least charge transfer resistance, plausibly having influence from the compositional aspects. This low charge transfer resistance is partially responsible for the superior electrochemical behavior of that specific composition.

Enabling the Electrochemical Activity in Sodium Iron Metaphosphate [NaFe(PO3)3] Sodium Battery Insertion Material: Structural and Electrochemical Insights.

Sodium-ion batteries are widely pursued as an economic alternative to lithium-ion battery technology, where Fe- and Mn-based compounds are particularly attractive owing to their elemental abundance. Pursuing phosphate-based polyanionic chemistry, recently solid-state prepared NaFe(PO3)3 metaphosphate was unveiled as a novel potential sodium insertion material, although it was found to be electrochemically inactive. In the current work, employing energy-savvy solution combustion synthesis, NaFe2+(PO3)3 was produced from low-cost Fe3+ precursors. Owing to the formation of nanoscale carbon-coated product, electrochemical activity was enabled in NaFe(PO3)3 for the first time. In congruence with the first principles density functional theory (DFT) calculations, an Fe3+/Fe2+ redox activity centered at 2.8 V (vs Na/Na+) was observed. Further, the solid-solution metaphosphate family Na(Fe1-xMnx)(PO3)3 (x = 0-1) was prepared for the first time. Their structure and distribution of transition metals (TM = Fe/Mn) was analyzed with synchrotron diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. Synergizing experimental and computational tools, NaFe(PO3)3 metaphosphate is presented as an electrochemically active sodium insertion host material.

Zinc oxide functionalized human hair: A potential water decontaminating agent.

HYPOTHESIS: Nano-ZnO is an efficient photocatalyst that can be employed for water purification but its separation from water is difficult. Immobilization of nano-ZnO on a fibrous material is expected to add practicality to its application. EXPERIMENTS: We synthesized ZnO nanostructures on a natural waste, human hair, via a cost-effective process, characterized the system and tested the efficacy of the composite for photo-decomposition of a few toxic materials in water. FINDINGS: Layers of well crystalline ZnO nanostructures grew homogeneously on hair strands, initially as thin plates that slowly turned with time into nanorods (length 400-600nm, width 28-30nm), converting the mildly hydrophobic hair (water contact angle 104°) surface into superhydrophobic (water contact angle 149°). The composite was found to effectively photodecompose toxic dyes like methylene blue, direct red, alizarin red S and aromatics (toluene), for multiple cycles without losing much efficacy.

Core-shell Prussian blue analogue molecular magnet Mn(1.5)[Cr(CN)6]·mH2O@Ni(1.5)[Cr(CN)6]·nH2O for hydrogen storage.

Core-shell Prussian blue analogue molecular magnet Mn1.5[Cr(CN)6]·mH2O@Ni1.5[Cr(CN)6]·nH2O has been synthesized using a core of Mn1.5[Cr(CN)6]·7.5H2O, surrounded by a shell of Ni1.5[Cr(CN)6]·7.5H2O compound. A transmission electron microscopy (TEM) study confirms the core-shell nature of the nanoparticles with an average size of ∼25 nm. The core-shell nanoparticles are investigated by using x-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and elemental mapping, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. The Rietveld refinement of the XRD pattern reveals that the core-shell compound has a face-centered cubic crystal structure with space group Fm3m. The observation of characteristic absorption bands in the range of 2000-2300 cm(-1) in IR spectra corresponds to the CN stretching frequency of Mn(II)/Ni(II)-N≡C-Cr(III) sequence, confirming the formation of Prussian blue analogues. Hydrogen absorption isotherm measurements have been used to investigate the kinetics of molecular hydrogen adsorption into core-shell compounds of the Prussian blue analogue at low temperature conditions. Interestingly, the core-shell compound shows an enhancement in the hydrogen capacity (2.0 wt % at 123 K) as compared to bare-core and bare-shell compounds. The hydrogen adsorption capacity has been correlated with the specific surface area and TGA analysis of the core-shell compound. To the best of our knowledge, this is the first report on the hydrogen storage properties of core-shell Prussian blue analogue molecular magnet that could be useful for hydrogen storage applications.