Pramod Bhatt

A fluoride ion selective Zr(IV)-poly(acrylamide) magnetic composite

A fluoride ion selective magnetic sorbent has been synthesized by the encapsulation of Fe3O4 nanoparticles in a network of Zr(IV) complexed poly(acrylamide) (Zr–PAM). This magnetic sorbent has been found to be efficient for the selective preconcentration of fluoride ions from natural waters. The Zr–PAM/Fe3O4 composite has been characterized using various physico-chemical techniques i.e. energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR) and a vibrating sample magnetometer (VSM). The Zr–PAM/Fe3O4 composite developed in the present work retains the super paramagnetic properties of Fe3O4 nanoparticles, and the results reveal that the sorption is rapid. The composite has a considerably higher fluoride sorption capacity (124.5 mg g−1) compared to other super-paramagnetic fluoride sorbents reported in the literature. Repeated sorption–regeneration cycles seem to suggest reusability of the sorbent for fluoride removal from natural waters, as well as other aqueous solutions having pH in the range 1–9.

Tuning the magnetocaloric properties of the Ni2+xMn1−xSn Heusler alloys

We report the effect of Ni substitution on the magnetic properties of polycrystalline Ni2+xMn1−xSn (x = 0, 0.05, and 0.1) Heusler alloys using the magnetization and neutron diffraction measurement techniques. The paramagnetic to ferromagnetic transition temperature (Curie temperature, TC) has been tuned with the substitution of Ni at the Mn sites (TC≈ 349, 337, and 317 K for x = 0, 0.05, and 0.1 samples, respectively) without a significant reduction in the magnetic entropy change −ΔSM. For a magnetic field change from 0 to 5 T, −ΔSM of 2.9, 2.5, and 2.2 J kg−1 K−1 have been observed for x = 0, 0.05, and 0.1 samples, respectively. From the neutron diffraction study, it has been found that with increasing x, the Mn site ordered moment decreases. −ΔSM as a function of changing magnetic field and Curie temperature follows the molecular mean field model. The studied Ni2+xMn1−xSn alloys, with their nontoxic constituent elements and low-cost, can be used for magnetic cooling over a wide temperature range of 278–...

Enhancement of Curie temperature in electrochemically prepared crystalline thin films of Prussian blue analogs KjFekII[CrIII(CN)6]l⋅mH2O

Structural and magnetic properties of electrochemically prepared crystalline films of Prussian blue analogs (PBAs) KjFekII[CrIII(CN)6]l⋅mH2O, with varying deposition time and electrode voltage, which result into change in film thickness and stoichiometry, respectively, have been investigated by using x-ray diffraction (XRD), infrared (IR) spectroscopy, and dc magnetization measurement techniques. An atomic force microscopy (AFM) and XRD study reveal uniform and crystalline nature of all films. As the film thickness increases from 1 μm to 5 μm, the Curie temperature (TC), coercive field, and maximum magnetization increase from 11 K to 21 K, 20 Oe to 160 Oe, and 5.7 μB to 6.5 μB, respectively. For the films prepared with variation in electrode voltage, it has been found that the alkali metal ions are introduced into the films just by using suitable electrode voltage, contrary to usual method where alkali metal ions are intentionally introduced into the lattice by using additional compounds of alkali metals ...

Correlation of structural, chemical, and magnetic properties in annealed Ti∕Ni multilayers

Ti/Ni multilayer samples have been synthesized on float glass substrates using an electron-beam evaporation technique under ultrahigh vacuum conditions at room temperature. Grazing incidence x-ray ...

Core–Shell Prussian Blue Analogue Molecular Magnet Mn1.5[Cr(CN)6]·mH2O@Ni1.5[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.

Enhanced Thermoelectric Properties of Selenium-Deficient Layered TiSe2–x: A Charge-Density-Wave Material

In the present work, we report on the investigation of low-temperature (300-5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10(-7) obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α(2)σ).

Hydrothermally synthesized oxalate and phenanthroline based ferrimagnetic one-dimensional spin chain molecular magnets [{Fe(Δ)Fe(Λ)}1−x{Cr(Δ)Cr(Λ)}x(ox)2(phen)2]n (x = 0, 0.1 and 0.5) with giant coercivity of 3.2 Tesla

Oxalate (ox) and phenanthroline (phen) ligands based one dimensional spin chain molecular magnets, [{Fe(Δ)Fe(Λ)}1−x{Cr(Δ)Cr(Λ)}x(ox)2(phen)2]n (x = 0, 0.1, and 0.5) have been designed, and synthesized using a hydrothermal synthesis method. The Rietveld refinement of the powder X-ray and neutron diffraction patterns at room temperature confirms the single-phase formation of the compounds in the monoclinic structure with a space group P21. The compounds consist of two ligands, the oxalate (C2O42−) as a coordination acceptor building block and the neutral phen (C12H8N2) as a coordination donor building block. Both ligands are connected to Fe ions of different symmetry {Fe(Δ) and Fe(Λ)}, thus forming an alternating zigzag chain like crystal structure having the repeating unit of [phen-Fe(Δ)-C2O4-Fe(Λ)-phen]n. The chain is infinite in length and lies in the crystallographic ac plane. The interchain is well separated with an intermetallic distance of ∼8.8 A and the absence of an interchain π–π overlap between the organic ligands, resulting in a magnetic isolation between the interchains. The Mossbauer spectroscopy reveals the presence of high spin states of the Fe2+ ions of the compound for x = 0 whereas, both high-spin Fe2+ (t2g4eg2, S = 2) as well as low spin Fe2+ (t2g6eg0, S = 0) states are present for the compounds x = 0.1 and 0.5. The dc magnetization measurements show that the compounds exhibit spontaneous magnetization below ∼9 K. The transition temperature is found to be ∼8.7, 8.2 and 4.0 K for x = 0, 0.1 and 0.5 compounds, respectively. Moreover, a short range antiferromagnetic spin–spin correlation around 18–45 K has been observed for the compounds x = 0 and 0.1. An application of the Ising chain model to the dc magnetization data reveals the presence of a one-dimensional magnetic nature of all compounds with alternately spaced magnetic Fe sites. It is observed that the different Lande g factors (3.4 and 2.8) and exchange coupling constant values (−86 and −54 K) for x = 0 at two alternating Fe sites give rise to a ferrimagnetic-like behavior of the chains. The ferrimagnetic chain like structure transforms toward antiferromagnetic with Cr doping i.e. for x = 0.1 and 0.5. A hysteresis loop with a giant coercivity (3.2 T for x = 0) has been observed at 1.6 K, indicating a hard magnet-type behavior. The frequency dependence of the peak temperature in ac susceptibility vs. temperature curves for the x = 0 compound has been fitted and analyzed using the Arrhenius law as well as the power law, which exclude the possibility of a spin glass behavior. The fitted parameters (Δ/kB = 208 K and τ0 = 2.9 × 10−14 s obtained from the Arrhenius law, and τ0 = 6.1 × 10−8 s, and zν = 2.6 from the power law) show that the compound obeys the Glauber dynamics and is a real ferrimagnetic one-dimensional single chain magnet. In addition, the high pressure magnetization measurements for the x = 0 compound show an enhancement in the transition temperature from ∼8.7 to 10.7 K with increasing pressure. The observation of both a one-dimensional spin chain nature and giant coercivity (3.2 Tesla) in such compounds opens up new opportunities to design and develop low dimensional molecular chain magnets through the appropriate choice of ligands using the hydrothermal synthesis method, because the observation of magnetic hysteresis of molecular origin in single-molecule magnets is considered one of the most relevant achievements in molecular magnetism.

Investigation of interface electronic structure of annealed Ti/Ni multilayers

The present paper deals with a systemic investigation of the interface electronic structure of as-deposited as well as annealed Ti/Ni multilayer (ML) samples up to 400??C using core level and valence band (VB) photoemission techniques. For this purpose [Ti(50??)/Ni(50??)] ? 10 ML samples have been prepared by employing an electron beam evaporation technique under ultrahigh vacuum conditions.The depth profile core level photoemission investigation carried out on annealed ML samples indicates a gradual change in the nature of the electronic bonding at the interface with temperature. In particular the ML samples annealed at 300 and 400??C clearly show shifts in the Ni?2p3/2 and Ti?2p3/2 core levels towards the higher binding energy side as compared to as-deposited samples, suggesting the formation of a TiNi alloy phase at the interface. The corresponding VB spectra also show appreciable changes and provide strong evidence for TiNi alloy formation. Further confirmation of this alloy phase formation is clearly reflected in the x-ray diffraction measurements carried out on these samples. The recorded x-ray diffraction patterns show a solid state reaction leading to amorphization when the ML sample is annealed at 300??C and recrystallization to a TiNi alloy phase at the annealing temperature of 400??C.In order to determine the charge transfer between Ti and Ni atoms in the formation of the TiNi alloy phase, the 2p3/2 core levels and the x-ray excited Auger regions of Ti and Ni were carefully investigated. The experimentally measured core level shifts for Ti and Ni were both found to be positive, leading to the conclusion that electronegativity criteria cannot be used to decide the direction of charge transfer in this case. The observed shifts in modified Auger parameters determined from recorded experimental data show a positive value for Ti and a negative one for Ni. This provides clear evidence that the direction of charge transfer is from Ni to Ti atoms during the formation of the TiNi alloy at the interface. The charge on ionized atoms calculated by using a simple electrostatic model indicates similar trends for the charge transfer deduced from Auger parameters and chemical shifts. In addition to this, areas under the core level peaks have been calculated by employing Shirley and Touggard background methods. The difference between the backgrounds, when normalized with respect to the elemental values, provides information about the density of states at the Fermi level (EF). The density of states at EF calculated in this way shows reductions in values for both Ti and Ni when the ML sample is annealed at different temperatures. This is in complete agreement with corresponding theoretically calculated densities of states.

Magnetic Exchange Interaction in Nitronyl Nitroxide Radical-Based Single Crystals of 3d Metal Complexes: A Combined Experimental and Theoretical Study

Two stable nitronyl nitroxide free radicals {R1 = 4′-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R2 = 2-(2′-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac)2 (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal–organic complexes Co(hfac)2(NNPhOMe)2, 1; Co(hfac)2(NNT)2·(H2O), 2; Mn(hfac)2(NNPhOMe)·x(C7H16), 3; and Mn(hfac)2(NNT)2, 4. The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C2/c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P21/c space group in which the N–O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions (J/KB) are derived using isotropic spin Hamiltonian H = −2J∑(SmetalSradical) for the model fitting to the magnetic susceptibility data for 1, 2, 3, and 4. The exchange interaction strengths are found to be −328, −1.25, −248, and −256 K, for the 1, 2, 3, and 4 metal–organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal–radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a more significant fraction {∼0.24 for Mn(II) and ∼0.13 for Co(II)} of delocalized spins from the metal ion is transferred to the coordinated oxygen atom(s) of nitronyl nitroxide.

Synthesis and spectral studies of metal complexes of a Schiff base derived from (2-amino-5-chlorophenyl)phenyl methanone

Some new complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Fe(III) with the Schiff base 5-chloro-2-(furan-2-yl methylamino)phenyl)phenyl methanone has been synthesized and characterized by elemental analysis, spectroscopic data including FT-IR, (1)H NMR, Electronic, ESI mass, Mössbauer & ESR. It has been found that the Schiff base behaves as a neutral bidentate N, O donor which chelates with the metal ions in 1:2 stoichiometry. Magnetic moment and electrolytic conductance data confirms this. The Schiff base and selected complexes were screened for antimicrobial activity. The complexes and the Schiff base were subjected to antioxidant study. The antitumor activity of Co(II) complex was tested by MTT assay. The result indicates the viability of the complex against tested cell lines.