Structural, magnetic and electrochemical properties of LiNi0.5Mn0.5O2 as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.5O₂ was synthesized by wet-chemical method and characterized by X-ray diffraction and SQUID magnetometry. The powders adopted the α-NaFeO₂ structure. The ferromagnetism observed below Tc = 140 K is attributed to the linear Ni²⁺(3a)-O-Mn⁴⁺(3b)-O-Ni²⁺(3a) magnetic paths, from which we derive that 7% of the nickel occupies the (3a) Wyckoff position in place of Li, constituting a Ni²⁺(3a) defect. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie-Weiss law agrees well with the combination of Ni²⁺ (S = 1) and Mn⁴⁺ (S = 3/2) spin-only values. Results of structural and magnetic properties of chemically delithiated sample are consistent with the electronic state Mn⁴⁺/Ni⁴⁺ and the high-spin configuration for Ni⁴⁺ ions. The LiNi_0.5Mn_0.5O₂ electrode sintered at 900 °C delivers a capacity 166 mAh/g at 0.1C rate which is capacity retention of 95%.     

Conducting IPN Based on Polyaniline and Crosslinked Cellulose

Polyaniline/crosslinked cellulose conductive interpenetrating polymer networks (IPNs) were prepared by oxidative polymerization of aniline within the self-synthesized cellulose network using ammonium persulphate as oxidant. The conductivity of the IPN increases and then decreases with decrease in the aniline/(NH₄)₂S₂O₈ ratio, with increase in the HCl/aniline ratio, with increase in aniline content, as well as with increase in reaction time. In addition, the conductivity of the films strongly depends on the amount of tetraethyl orthosilicate crosslinker. In comparison with polyaniline/cellulose acetate composites, the conductivity increases by an order of one to two magnitudes in spite of the lower polyaniline content in this work. © of SCI.     

Metal Chelates with Some Cellulose Derivatives: V. Synthesis and Characterization of Some Iron(III) Complexes with Cellulose Ethers

Two types of monoligand complexes of FeCl₃, Fe(NO₃)₃ and Fe₂(SO₄)₃ with hydroxyethyl cellulose (HEC) and carboxymethyl cellulose (CMC) were prepared and characterized. Elemental analysis, UV and IR spectro-scopies, conductance and magnetic measurements were used to assign the mode of coordination in the isolated species. The investigation revealed that Fe(III ) exhibits tetrahedral coordination with HEC and CMC. These ligands act as a bidentate chelating agent via the two oxygen atoms of the vicinal hydroxyl and ether groups (ethoxyl or carboxymethyl groups). The prepared complexes have the formula [(HEC) FeCl]Cl, [(HEC) FeNO₃]NO₃, [(HEC)FeSO₄·H₂O]H₂O, [(CMC)FeCl·H₂O]Cl·2H₂O, [(CMC)Fe·2NO₃]3H₂O and [(CMC)-FeSO₄·H₂O]H₂O. The results also showed that the type of cellulose ether (functional group) and the anion of the metal salts used have an effect on the conductivity, structure and absorptivity of Fe(III ) complexes. © of SCI.     

Sorption of phenol from aqueous solution by novel magnetic polysulfone microcapsules containing Cyanex 923

This paper describes the sorption of phenol from aqueous solution by using novel magnetic polysulfone (PSF) microcapsules containing Fe₃O₄ nanoparticles and mixture of trialkyl-phosphine oxides (Cyanex 923) (Cyanex 923/Fe₃O₄@PSF microcapsules). The preparation of the Cyanex 923/Fe₃O₄@PSF microcapsules was based on the phase-inversion technique. The prepared microcapsules were characterized by using Fourier Transform Infrared Spectroscopy (FT-IR), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Vibrating Sample Magnetometer (VSM). Fe₃O₄ nanoparticles in the microcapsules provided easier separation via application of external magnetic field. The experiments indicated that phenol could be removed from aqueous solution at a pH range between 3 and 9. The Cyanex 923/Fe₃O₄@PSF microcapsules prepared with dispersed phase containing 3.35% of Cyanex 923 (by wt.) provided the highest removal. The sorption reached an equilibrium in 120 min and it obeyed the pseudo-second order kinetic model. The non-linear Chi-square (χ²) statistical test showed that Langmuir isotherm model better represented the sorption data in comparison to Freundlich and Redlich–Peterson models. The Langmuir sorption capacity (Q_o) and sorption constant (b) were 0.664 mmol/g and 0.855 L/mmol, respectively. The regenerated microcapsules could be used five times with no change in their sorption capacity and magnetic separability.     

Gelation behaviors of cellulose solution dissolved in aqueous NaOH/thiourea at low temperature

Cellulose was dissolved rapidly in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution pre-cooled to −5 °C, as a result of the formation of an inclusion complex (IC) associated with cellulose, NaOH and thiourea, which could bring cellulose to the aqueous system. To clarify the rheological behaviors of the system dissolved at low temperature, this cellulose solution was investigated by dynamic viscoelastic measurement. The shear storage modulus (G′) and loss modulus (G″) as a function of the angular frequency (ω), concentration (c), temperature (T) and weight-average molecular weight (M_w) were analyzed and discussed. The results revealed that gels could form in the cellulose solution at either high temperature or low temperature, or for longer time. Interestingly, 4 wt% cellulose solution having cellulose M_w of 12.0 × 10⁴ remained at liquid state for longer time (12 days) at the temperature ranging from 0 to 5 °C. The gels already formed at elevated temperature were irreversible, i.e., after cooling to lower temperature including the temperature of cellulose dissolution (−5 °C), they could not be dissolved to become liquid. The Arrhenius analysis of the temperature dependence of viscosity in the cellulose solution indicated that a high apparent activation energy (E_a) occurred at 0 to −5 °C, suggesting the relatively stable IC structure. However, the viscosity of the cellulose solution increased slowly with an increase in the temperature at 0-40 °C, leading to the negative E_a values. The results suggested that the cellulose solution in NaOH/thiourea system is complex to differ from normal polymer systems.     

Synthesis and characterization of a novel iron (III) silsesquioxane compound

A new iron (III) containing silsesquioxane compound, [Bu₄N][((CH₃)₂CHCH₂)₇Si₇O₁₂FeCl] (4) was prepared by reacting [Bu₄N][FeCl₄] (3) with the isobutyl substituted silsesquioxane trisilanol, ((CH₃)₂CHCH₂)₇Si₇O₁₂H₃, (1) in the presence of three equivalents of triethylamine, Et₃N (2). The magnetic susceptibility of 4 was measured by Evans method, and the effective magnetic moment, μ_eff, is consistent with a high spin Fe (III) center. The composition and molecular structure of 4 was fully determined by IR, elemental analysis, APCI mass spec, and X-ray crystal analyses, and its potential as a precursor to a model of the structure and chemistry of the Fe-ZSM-5 catalyst is discussed.     

Electric relaxation of superparamagnetic Gd-doped lead molybdato-tungstates

Tetragonal, scheelite-type Pb_1–3x□_xGd_2x(MoO₄)_1–3x(WO₄)_3x materials (x?=?0.0455, 0.0839, 0.1154, 0.1430, 0.1667 and 0.1774, where □ denotes vacancies) synthesized via solid state reaction route were magnetically and electrically examined. The ac and dc magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and a spin-only contribution to the paramagnetic moment. Broadband dielectric spectroscopy studies exhibited existence in the loss spectra the faster and slower relaxation processes with various time scales for the gadolinium-poorer samples with the x vacancy parameter up to 0.1154. For samples with higher Gd content, i.e. when x?>?0.1154, no signs of any relaxation processes was observed. This phenomenon has been explained by a smaller number of structural and spin defects as opposed to the samples poorer in gadolinium ions.     

Synthesis of pH-sensitive hollow polymer microspheres with movable magnetic core

The pH-sensitive hollow poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres with movable magnetic/silica (Fe₃O₄/SiO₂) cores were prepared by the selective removal of poly(methacrylic acid) (PMAA) layer in ethanol/water from the corresponding Fe₃O₄/SiO₂/PMAA/P(MBAAm-co-MAA) tetra-layer microspheres, which were synthesized by the distillation precipitation copolymerization of N,N′-methylenebisacrylamide (MBAAm) and methacrylic acid (MAA) in the presence of Fe₃O₄/SiO₂/PMAA tri-layer microspheres as seeds in acetonitrile with 2,2′-azobisisobutyronitrile (AIBN) as the initiator. The Fe₃O₄/SiO₂/PMAA tri-layer microspheres were afforded by the distillation precipitation polymerization of MAA with 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified Fe₃O₄/SiO₂ core-shell particles as the seeds. The functional multi-layer inorganic/polymer microspheres and the corresponding hollow polymer microspheres with movable magnetic cores were characterized with transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectra, dynamic light scattering (DLS), and vibrating sample magnetometer (VSM).     

Preparation and magnetoelectric properties of NiFe2O4–PZT composites obtained in-situ by gel-combustion method

Magnetoelectric composites of xNiFe₂O₄–(1 ? x)Pb(Zr,Ti)O₃ with x = 2, 5, 10, 20, 30% were prepared by citrate–nitrate combustion using PZT-based template powders. In order to ensure a better connectivity of dissimilar phases, we have used chemical methods for preparation in situ composites, followed by adequate sintering procedure. The structural, microstructural and functional properties of di-phase magnetoelectric composites of NiFe₂O₄–PZT are reported. The XRD analysis is demonstrating the synthesis of pure ferrite phase directly on the ferroelectric templates. An excellent mixing was obtained in the composite powders, as proved by a detailed SEM analysis.The magnetic and dielectric behaviors of the ceramic composites vary with the ratio of the two phases. The dielectric behavior is greatly influenced by the magnetic phase. The magnetoelectric (ME) coefficient was measured as a function of applied DC magnetic field. The maximum ME coefficient (dE/dH) varies from 0.0011 mV/(cm Oe) to 0.5 mV/(cm Oe) with increasing of NF addition.     

Systematic study of H_2 production from catalytic photoreforming of cellulose over Pt catalysts supported on TiO_2

Hydrogen(H_2) production from photocatalytic reforming of cellulose is a promising way for sustainable H_2 to be generated. Herein, we report a systematic study of the photocatalytic reforming of cellulose over Pt/m-TiO_2(i.e.mixed TiO_2, 80% of anatase and 20% of rutile) catalysts in water. The optimum operation condition was established by studying the effect of Pt loading, catalyst concentration, cellulose concentration and reaction temperature on the gas production rate of H_2(r_(H_2)) and CO_2(r_(CO_2)), suggesting an optimum operation condition at 40°C with 1.0 g·L~(-1) of cellulose and 0.75 g·L~(-1) of 0.16-Pt/m-TiO_2 catalyst(with 0.16 wt% Pt loadting) to achieve a relatively sound photocatalytic performance with rH_2= 9.95 μmol·h~(-1). It is also shown that although the photoreforming of cellulose was operated at a relatively mild condition(i.e. with an UV-A lamp irradiation at40 °C in the aqueous system), a low loading of Pt at ～0.16 wt% on m-TiO_2 could promote the H_2 production effectively. Additionally, by comparing the reaction order expressed from both r_(H_2)(a_1) and r_(CO_2)(a_2) with respect to cellulose and water, the possible mechanism of H_2 production was proposed.     

Effect of oxygen vacancies on the microstructure and multiferroic behavior of Bi4.25La0.75Fe0.5Co0.5Ti3O15 ceramics

In order to reveal the solid relationship between oxygen vacancies and multiferroic properties, polycrystalline Bi_4.25La_0.75Fe_0.5Co_0.5Ti₃O₁₅ (BLFCT) ceramics were sintered in argon (BLFCT-Ar), air (BLFCT-air) and oxygen (BLFCT-O₂) by conventional solid state reaction, respectively. Their microstructures, ferroelectric, magnetic properties and valence states of magnetic ions were investigated and compared. X-ray diffraction patterns confirmed a single phase crystal structure in all samples. The lattice constants were calculated and the minor variation of the lattice constants is attributed to the different oxygen vacancy concentration. Furthermore, different oxygen vacancy concentration may be responsible for the different values of RT-recorded remanant magnetization (2M_r), remanent polarization (2P_r) as well as magnetic phase transition temperatures (T_CM). The magnetic response of sample sintered in argon (2M_r =0.52 emu/g, T_CM=392 K) is significantly superior to that of the others, while the sample sintered in oxygen exhibits a better remnant polarization (2P_r =11.6 µC/cm²) at an applied electric field of 160 kV/cm. The BLFCT-Ar sample was then annealed in oxygen to further justified the dependence of 2P_r and 2M_r on oxygen vacancies. Finally, outcome of the XPS measurement manifested the ratios of Fe²⁺/Fe³⁺ and Co²⁺/Co³⁺, and reconfirmed the different oxygen vacancy concentration in three samples.     

Synthesis and characterization of the new cellulose derivative films based on the hydroxyethyl cellulose prepared from esparto “stipa tenacissima” cellulose of Eastern Morocco. II. Esterification with acyl chlorides in a homogeneous medium

Esparto “Stipa tenacissima” cellulose esters derivatives: HECA‐COO? C₄H₈? COOC₂H₅, HECA‐COO? C₈H₁₆? COOC₂H₅, and HECA‐COO? C₆H₄? COOC₂H₅ were successfully prepared in Tetrahydrofuran (THF)/triethylamine system with a degree of substitution (DS), respectively, DS_AD‐Et=0.32, DS_SB‐Et=0.22, and DS_TRP‐Et=0.50 using hydroxyethyl cellulose acetate (HECA; DS_AC=0.50) as intermediate product, and we avoided the drawbacks of cellulose solubility. The structural modifications were investigated using Fourier transform infrared spectroscopy (FTIR), Proton nuclear magnetic resonance (¹H‐NMR), Carbon‐13 nuclear magnetic resonance (¹³C‐NMR), and Distortionless Enhancement by Polarization Transfer 135° (DEPT‐135). The results from these analyses revealed the presence of the characteristic groups indicating that the grafting reaction was successful. The crystallinity and the structure order changes during the esterification reactions were recorded by X‐ray diffraction (XRD), it is found that the crystallinity degree decrease from 63.1% for Esparto “Stipa tenacissima” cellulose to 27.74% for HECA. The thermal stability of the esterified and unmodified cellulose samples was studied by thermogravimetric analysis (TGA)‐differential thermal analysis (DTA); the modified HECA exhibits a decrease in thermal stability relatively to the unmodified HECA, and this may be related to the groups grafted. The resulted cellulose esters HECA‐P_x (x = 1, 2, or 3) were soluble in THF and present an amorphous structure justified by XRD spectra. It was noted by TGA‐DTA analysis that the cellulose esters with low melting range were proved as thermoplastic polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Neutron diffraction study and temperature variation of magnetic anisotropy in Bi substituted nickel ferrite

Bismuth doped NiFe₂O₄ (NFO) polycrystalline samples: Ni_1-xBi_xFe₂O₄ with x = 0.00, 0.05 and 0.10, were synthesized using solid-state reaction method. The crystal structural, magnetic structure and magnetic properties of parent NFO and Bi-doped NFO samples were characterized using X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization (M) versus magnetic field (H) isotherms, respectively. Rietveld refinement of XRD and NPD patterns confirms the formation of a single-phase cubic spinel crystal structure. No observable change in the lattice parameter was found (within the error limits) with the 5 at % Bi doping to NFO, whereas ≈0.15% change in the lattice parameter was observed in case of 10 at % Bi-doped NFO. Room temperature magnetic structure studies using NPD reveal a net magnetic moment of 1.55(3) μ_B/f. u., in the case of NiFe₂O₄. The net magnetic moment at room temperature changes to 1.61(4) μ_B/f.u. and 1.47(5) μ_B/f.u. for Ni_0.95Bi_0.05Fe₂O₄ and Ni_0.90Bi_0.10Fe₂O₄, respectively. The same observation was also inferred from the spontaneous magnetization (M_sp) obtained from approach-to-saturation (ATS) analysis of M-H isotherms. Temperature (T) dependence of M_sp follows a T² decline. Approximately 14% increase in magnetic anisotropy was observed in Ni_0.95Bi_0.05Fe₂O₄ compared to NiFe₂O₄ in the temperature range 5 K -300 K.     

Synthesis and analysis of structural,compositional, morphological,magnetic, electrical and surface charge properties of Zn-doped nickel ferrite nanoparticles

Zn-doped nickel ferrite nanoparticles (Zn_xNi_(1-x)Fe₂O₄) were synthesized using the co-precipitation technique. The structural and compositional studies of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles, and the maximum magnetization of 30 emu/g for the Zn_0.2N_0.8Fe₂O₄ sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of Zn_xNi_(1-x)Fe₂O₄ nanoparticles. The electrical conduction in Zn_xNi_(1-x)Fe₂O₄ nanoparticles was explained through the Verway hopping mechanism. The Zn_0.2N_0.8Fe₂O₄ nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe³⁺ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.     

Solution combustion synthesis of new metal borophosphates (Fe1-xCrx)2B(PO4)3: Structural,thermal, surface,and magnetic properties

The new borophosphates were successfully synthesized by solution combustion synthesis assisted with glycine. The obtained materials were systematically characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, UV–visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, Brauner-Emmett-Teller surface area, and magnetometry. The Rietveld refinements indicated that Fe₂B(PO₄)₃ is a hexagonal, space group P63/m with a = b = 8.029 and c = 7.408. As Cr substitutes the Fe atoms, there is a significant decrease in the lattice parameters. When all Fe atoms are replaced by Cr, Cr₂B(PO₄)₃ is formed and the structure turns out to be a trigonal, space group P3 with a = b = 7.950 and c = 7.360. The materials are thermally stable and demonstrate paramagnetic behavior at room temperature. The magnetization increases as the iron content increases because of the high magnetic moment of the iron ion. Temperature-dependent magnetic measurements reveal that Fe₂B(PO₄)₃ has a Néel transition at 30 K and the Néel temperature decreases with Cr substitution.     

Structure and magnetic properties of regenerated cellulose/Fe3O4 nanocomposite films

Cellulose nanocomposites containing high contents of Fe₃O₄ nanoparticles were successfully prepared with regenerated cellulose films as a matrix and mixture solutions of Fe²⁺/Fe³⁺ as precursors. The structure and properties of the magnetic nanocomposite films were investigated with X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and vibrating sample magnetometry. Fe₃O₄ nanoparticles as prepared were irregular spheres and were homogeneously dispersed in the cellulose matrix. With an increase in the concentration of precursors from 0.2 to 1.0 mol/L, the content of Fe₃O₄ nanoparticles in the dried nanocomposites increased from 12 to 39 wt %, and the particle diameter increased from 32 to 64 nm. The cellulose nanocomposite films demonstrated superparamagnetic behavior, and their saturation magnetizations were in the range 4.2–21.2 emu/g, which were related to the increase in Fe₃O₄ nanoparticle content. With increasing nanophase content, the nanocomposite films displayed significantly anisotropic magnetic properties in the parallel and perpendicular directions. This study provided a green and facile method for the preparation of biobased nanocomposite films with high nanophase content and excellent magnetic properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Spin-orbit coupling in manganese doped calcium molybdato-tungstates

The manganese doped calcium molybdato-tungstates with the formula of Ca_1-xMn_x(MoO₄)_0.50(WO₄)_0.50 (x = 0.01, 0.03, 0.05, 0.10, 0.125, and 0.15) were successfully obtained by two-step synthesis using in both steps a solid state reaction route. All ceramics show scheelite-type tetragonal structure with space group I4₁/a. The electrical and magnetic studies within the temperature range of 2–300 K showed a weak p-type electrical conductivity and the paramagnetic state of Mn-doped ceramic materials. With increasing Mn content in samples under study, a change in the short-range interactions from ferromagnetic to antiferromagnetic as well as an increase in the orbital contribution to the magnetic moment, resulting in a strong spin-orbit coupling, were observed. The Brillouin procedure was used to estimate the Landé factor.     

Synthesis,structure and magnetic properties of a tetranuclear Mn(II) complex with carbohydrazone based ligand

A new tetranuclear complex of Mn(II), [Mn₄(L)₂(CH₃OH)₂(μ-N₃)₄(N₃)₂] ∙ 2(CH₃OH) (1), was synthesized and characterized by spectroscopic methods, single-crystal X-ray diffraction analysis and TGA analysis where HL is bis-[(E)-N′-(phenyl(pyridin-2-yl)methylene)]carbohydrazide. Single crystal X-ray analysis reveals that 1 has a Mn₄ core in which Mn(II) ions are connected by azide and enolate oxygen atoms. IR spectroscopy and X-ray analysis indicate that the carbohydrazone is coordinated to the metal cores as a mononegative ligand in the enol form. The magnetic behavior of 1 was investigated between 2 and 295 K and indicated that the magnetic coupling mediated via azide bridge is ferromagnetic whereas the enolate oxygen mediates antiferromagnetic coupling that leads to overall antiferromagnetic behavior.     

Characterization of SrBiMn2−xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response

Two new phases in the (SrTiO₃)-(BiMnO₃) perovskite type system were studied. These SrBiMn_2−xTi_xO₆ (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal I4/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with T_m in the 140–240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed.     

A new type of copper coordination polymer based on γ-aminobutyric acid: Syntheses,structures and magnetic properties

A copper coordination polymer with γ-aminobutyric acid (GABA), {[Cu₃(GABA)₂(NO₃)₂(OH)₂(H₂O)₂] (NO₃)₂·2H₂O}_n (1), has been synthesized and characterized by single-crystal X-ray diffraction, IR, PXRD, TGA and elemental analysis. It exhibits a 1D chain structure including μ₃-OH-Cu₃ cluster as a building block. The strong H-bonding links these chains to form 2D sheet structure and the main intermolecular interaction between the 2D sheets is electrostatic interaction. According to the crystal structure of complex 1, the magnetic properties of complex 1 have been investigated by the cluster and cycle magnetic coupling models. There are three different magnetic coupling pathways of Cu(II) (J₁, J₂, J₃) from each method and the resulting fitted curves based on the magnetic parameters of both methods compare well with the experiment values.