Citrate Gel Technique Research Articles

Study of carboxymethyl cellulose (CMC) coated manganite as potential candidate for magnetic hyperthermia applications

The present study reports substantial coating of biocompatible polymer Carboxymethyl Cellulose (CMC) on magnetic nanoparticles (MNPs) of Lanthanum Strontium Manganese Oxide (LSMO) also called manganite, as a novel attempt, for magnetic Hyperthermia applications. Two series of manganite (La1-xSrxMnO3) were synthesized through Citrate-gel technique choosing “x” as (0.3) and (0.33). X-ray diffraction (XRD) study has shown satisfactory phase formation of MNPs in accordance with the standard patterns. High resolution transmission electron microscopy (HRTEM) was done to evaluate the effect of CMC on particles’ morphology after coating. The Fourier transform infrared spectroscopy (FTIR) has displayed successful attachment of CMC on the surface of MNPs and adsorbed coating amounts have been assessed through Thermogravimetric analysis and Differential Scanning Calorimetry (TGA/DSC). The coated LSMO were dispersed in Phosphate Buffer Saline (PBS, pH = 7) as an innovative try, to see the potential of these mediators towards effective Hyperthermia applications in fluid form at a suitable frequency of the applied magnetic field. The CMC coated MNPs have achieved quite appreciable specific absorption rate (SAR) up to 225 W/g and intrinsic loss power (ILP); showing a positive sign for their possible usage in Hyperthermia therapy.

Magnetization of Magnetically Inhomogeneous Sr2FeMoO6-δ Nanoparticles

In this work, we describe the magnetization of nanosized SFMO particles with a narrow size distribution around ca. 70 nm fabricated by the citrate-gel technique. The single-phase composition and superstructure ordering degree were proved by X-ray diffraction, the superparamagnetic behavior by magnetization measurements using zero-field cooled and field-cooled protocols, as well as by electron magnetic resonance. Different contributions to the magnetic anisotropy constant and the temperature dependence of the magnetocrystalline anisotropy are discussed.

Study of structural, magnetic and radio frequency heating aptitudes of pure and (Fe-III) doped manganite (La1-x SrxMnO3) and their incorporation with Sodium Poly-Styrene Sulfonate (PSS) for magnetic hyperthermia applications

The structural, magnetic and thermal features of Strontium (Sr) and iron doped (LaMnO3) have been studied to optimize their Hyperthermia efficiency. Citrate-gel technique was employed to synthesize (La1-xSrxMnO3) (x = 0.27, 0.3& 0.33) and a new composite (La1-x Srx Mn1-yFeyO3) (x = 0.27, y = 0.03). XRD patterns showed good polycrystalline structures with crystallite size up to 16 nm. HRTEM was employed to study the morphology of nanoparticles (NPs). Sodium Poly-Styrene Sulfonate (PSS) was opted to attach with (NPs), as a novel attempt, for coating purpose and FTIR showed existence of diversified peaks. Differential scanning calorimetric (DSC) studies were employed to assess the phase changes through respective heat flow mechanisms. The magnetic parameters using super quantum interface device (SQUID) showed good magnetization till 50 kȎe. Radio frequency (RF) induced field studies were employed at three different values (259.7, 327 & 518 kHz), to display comparative heating aptitudes of LSMO for hyperthermia efficacy.

Effect of sintering temperature on electronic properties of nanocrystalline La0.7Sr0.3MnO3

The effect of sintering temperature on the magnetic and electronic properties of La0.7Sr0.3MnO3 (LSMO) synthesized by the citrate gel technique is introduced. The single phase nature of all the sintered samples of La0.7Sr0.3MnO3 powder was confirmed by x-ray diffraction. Sintering temperature plays an important role in controlling the grain size. The morphology results show an increment in the average grain size of LSMO because of the grain growth as the sintering temperature increases. The chemical composition of La0.7Sr0.3MnO3 and oxidation states of the elements has been confirmed using x-ray photoelectron spectroscopy. The core level spectra of all elements were studied in detail. The study of valence band spectra revealed the effect of grain size on the degree of hybridization of Mn eg and O 2p orbitals. This effect of grain size is accountable for change in ferromagnetic to paramagnetic transition temperature (TC), resistivity, magnetic properties, and density of states at the Fermi level.

MAGNETORESISTANCE IN NANOSIZE STRONTIUM FERROMOLYBDATE WITH DIELECTRIC INTERLAYERS

Single phase strontium ferromolybdate nanopowder with a double perovskite structure has been synthesized using the citrate gel technique at pH = 4. A superstructural ordering degree of the iron and molybdenum cations of 88% has been obtained. X−ray diffraction of pressed Sr2FeMoO6−δ pellets subjected to annealing at T = 700 K and p(O2) = 10 Pa has revealed the formation of the SrMoO4 phase at grain boundaries. The temperature dependence of the electrical resistivity in the 4.2 to 300 K range changes from a metal type one in the single phase Sr2FeMoO6−δ to a semiconductor type one in the Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable charge hopping in the latter structure. In the applied magnetic fields the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistance of up to 41% at T = 10 K and B = 8 T is observed. The external field forms a collinear spin structure, thus increasing the spin−polarized current through the barriers in the granular Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ heterostructure.

Characteristic features of the magnetoresistance in the ferrimagnetic (Sr2FeMoO6-δ) – dielectric (SrMoO4) nanocomposite

Magnetic metal-oxide compounds with high values of magnetoresistance (MR) have attracted huge interest for spintronic applications, among which Sr2FeMoO6-δ (SFMO) has been relatively less known compared to the cobaltites and manganites, despite 100% electrons spin-polarization degree and a high Curie temperature. Here, stable fabrication and systematic analysis of nanocomposites based on SFMO with SrMoO4 dielectric sheaths are presented. SFMO-SrMoO4 nanocomposites were fabricated as follows: synthesis of the SFMO single-phase nanopowders by the modified citrate-gel technique; compaction under high pressure; thermal treatment for sheaths formation around grains. The nanocomposite is observed to exhibit a transitional behavior of conductivity from metallic, which is characteristic for the SFMO to semiconductor one in the temperature range 4 – 300K under magnetic fields up to 10T. A negative MR is observed due to the spin-polarized charge carriers tunneling through dielectric sheaths. MR value reaches 43% under 8T at 10κ. The dielectric sheaths thickness was determined to be about 10 nm by electric breakdown voltage value at current-voltage characteristics curves. The breakdown is found to be a reversible process determined by collisional ionization of dielectric atoms in strong electric field depending on knocked-out electrons from the SrMoO4. It was found that MR changes sign in electric breakdown region, revealing the giant magnetoresistive properties.

Silica-coated gadolinium-doped lanthanum strontium manganite nanoparticles for self-controlled hyperthermia applications

Gadolinium-doped lanthanum strontium manganite (LSM) nanoparticles were synthesized by using a citrate-gel technique. The particles were then annealed at 850 oC to remove defects for a good crystallinity, followed by coating with silica for possible biomedical application to magnetic hyperthermia. The chemical composition was determined to be La0.54Sr0.27Gd0.19MnO3 using an inductively coupled plasma mass spectrometer. The nanoparticles were characterized by X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectrometer to check the perovskite crystalline structure and to observe the particles size and coating status of silica on the surface of the particles. The Curie temperature of the particles was found to be about 280 K. The saturation temperature of the aqueous solution of the particles remained at the hyperthermia target temperature of 42 oC with increasing concentration of particles from 6 to 60 mg/mL in the dispersion. This saturation temperature for a highly concentrated 120-mg/mL-sample increased further, but less than the dangerous temperature of 47 oC for normal tissues. The saturation temperature of the powder sample reached only up to 53 oC. These results showed that the gadolinium-doped LSM nanoparticles can be used for the self-controlled hyperthermia in which the temperature does not exceed the target temperature of hyperthermia even at the tissue site of highly accumulated nanoparticles.

MgFe2O4/ZrO2 composite nanoparticles for hyperthermia applications

MgFe2O4/ZrO2 composites containing ZrO2 in different weight percentages from 0% to 80% were prepared via the citrate gel technique as potential candidate materials for magnetic hyperthermia. The biocompatible ceramic ZrO2 was introduced to prevent MgFe2O4 nanoparticles from aggregation and to reduce their dipolar interactions in order to enhance the specific absorption rate (SAR). Structural and magnetic properties of the samples were studied using powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and a vibrating sample magnetometer (VSM). Magnetically induced heating in radio frequency (RF) magnetic fields was observed in all samples. Most significantly, the sample with only 20wt% MgFe2O4 has been found to have a SAR that is larger than that of pure MgFe2O4. This is an important finding from the point of view of biomedical applications, because ZrO2 in known to have low toxicity and a higher biocompatibility as compared to ferrites.

Magnetoresistive effect in nanosized strontium ferromolybdate with dielectric interlayers

Monophasic iron ferromolybdate nanopowders with a double perovskite structure have been synthesized using the citrate-gel technique at pH=4. A superstructural ordering degree of the iron and molybdenum cations of 88% has been obtained. X-ray diffraction of pressed Sr2FeMoO6−δ pellets subjected to annealing at T=700K and p(O2)=10Pa has revealed the formation of the SrMoO4 phase at grain boundaries. The temperature dependence of the electrical resistivity in the range from 4.2 to 300K switches from a metal type one in the monophasic Sr2FeMoO6-δ to a semiconductor type one in the Sr2FeMoO6−δ–SrMoO4–Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable range hopping in the latter. In the applied magnetic fields the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistance of up to 41% at T=10K and B=8T is observed. The external field forms a collinear spin structure, thus increasing the spin-polarized current through the granular Sr2FeMoO6−δ–SrMoO4–Sr2FeMoO6−δ heterostructure.

Magnetocaloric effect in RMnO3 (R=Gd, Tb and Dy) multiferroics

Multiferroic materials with the compositional formula RMnO3 (where R=Gd, Tb and Dy), were prepared by the citrate gel technique. After characterizing the samples structurally, a systematic investigation of specific heat has been undertaken, over a temperature range 4–300K at different magnetic fields. All the samples display interesting specific heat behavior exhibiting transitions due to the long range ordering of Mn3+ and R3+ moments. Magnetic field change generates an entropy change of ~1J/molK when a magnetic field changes from 0 to 5T in the vicinity of antiferromagnetic ordering temperature of R3+. The value of adiabatic temperature change ~3K for a field of 5T is also appreciable to consider these materials as possible magnetic refrigerants at low temperatures.

Investigation of superparamagnetism in MgCr0.9Fe1.1O4 nano-ferrites synthesized by the Citrate-gel method

MgFe2O4 and MgCr0.9Fe1.1O4 nano-ferrites were synthesized using Citrate-gel technique and the magnetic properties were studied. The crystallite sizes of the prepared MgFe2O4 and MgCr0.9Fe1.1O4 nano-particles were estimated from X-ray diffraction patterns as 23nm and 7.6nm respectively. Magnetization as a function of field (±10T) and temperature was measured using a vibrating sample magnetometer for temperature ranging from 5K to 300K. From the temperature dependence of both the field cooled (FC) and the zero-field cooled (ZFC) magnetization measurements under a field of 100Oe, blocking temperature (Tb) for MgFe2O4 was obtained at above room temperature whereas for MgCr0.9Fe1.1O4 it was obtained at 94K. The M–H curves for MgCr0.9Fe1.1O4 nanoferrites indicated the presence of ferromagnetic behavior with hysteresis below the blocking temperature (Tb). A large coercive force of about 1100Oe was found at 5K. The phenomenon suggests that the synthesized Cr substituted Mg nano-ferrite with chemical composition MgCr0.9Fe1.1O4 shows superparamagnetic behavior above the blocking temperature 94K. This nature makes these materials to be used in biomedical applications like magnetically guided drug delivery and Magnetic Resonance Imaging (MRI).

Study of Magnetothermal Properties of Strontium Doped Lanthanum Manganite Nanoparticles for Hyperthermia Applications

Magnetic nanoparticles of strontium doped lanthanum manganite (LSMO) have been synthesized with Sr concentration x = 0.20 and 0.27 using the citrate gel technique. Magnetic and magnetothermal properties have been investigated with the objective of determining their specific absorption rates (SAR's) and comparing them with those obtained using the linear response theory. Adiabatic magnetothermia measurements were carried out in an RF magnetic field of 800 A/m and 214 kHz. Both magnetic and thermomagnetic behaviors of the LSMO nanoparticles are observed to be governed by the strontium content of the samples. The specific absorption rate has been determined using experimental data and good quantitative agreement has been observed between experimentally determined and theoretically derived values. Zero-field-cooled thermal demagnetization measurements were used to obtain the Curie temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> , which was found to be 320 K for x = 0.20 and 350 K for x = 0.27. The suitability of these materials for magnetic hyperthermia and self-controlled hyperthermia applications has been demonstrated.

Strontium hexaferrite (SrFe12O19) based composites for hyperthermia applications

Mixed phase composites of SrFe12O19/MgFe2O4/ZrO2 were prepared via the citrate gel technique as potential candidate materials for magnetic hyperthermia. Structural and magnetic properties of the samples were studied using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and a vibrating sample magnetometer. XRD and FE-SEM data confirm that magnesium ferrite and zirconium oxide phases increased with increasing Mg and Zr content in the precursors. Magnetization loops for the composites were measured at room temperature and showed significant variation of saturation magnetization, coercivity and remanence depending on the amount of the highly anisotropic Sr-hexaferrite phase. The sample with the highest Mg and Zr content had the lowest coercivity (80Oe) and saturation magnetization (41emu/g). The composite samples each were exposed to a 214kHz alternating magnetic field of amplitude 22Oe and a significant heating effect was observed in selected samples, which suggests potential for use in magnetic hyperthermia.

Synthesis and Characterization of Copper Substituted Nickel Nano-Ferrites by Citrate-Gel Technique

Mixed Copper substituted Nickel nano-ferrites having the chemical formula Ni1-xCuxFe2O4 (where x = 0, 0.2, 0.4, 0.6, 0.8, 0.9 and 1.0) were synthesized by citrate gel technique. The crystal structure characterization and morphology were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). An elemental composition of the samples were studied by energy dispersive X-ray Spectroscopy (EDS). Lattice parameter, X-ray density, Volume of the Unit Cell and The values of the hopping length for octahedral (dB) and tetrahedral (dA) sites were calculated. The observed results can be explained on the basis of composition.

Synthesis, XRD &amp;amp; SEM Studies of Zinc Substitution in Nickel Ferrites by Citrate Gel Technique

Ni-Zn ferrite with a nominal composition of Ni1–XZnXFe2O4 (X = 0, 0.2, 0.6, 0.8, 0.9 & 1.0) ferrite powders have been successfully prepared at a very low temperature (180℃) by a novel auto combustion process using citric acid as a coordinating agent. Phase purity of the solid solutions has been confirmed by X-ray diffraction. Morphological, elemental composition characterizations of the prepared samples were performed by high resolution scanning electron microscopy and energy dispersive spectroscopy (EDS). Magnetic properties of all samples are obtained by using VSM (Vibrating Sample Magnetometer) in the range of 10 K oe. The saturation magnetization values of the samples are carried out from the B-H loop. The effect of composition on saturation magnetization and magnetic moment are studied in this paper. The results showed that Saturation magnetization and magnetic moment values increases gradually as Zn2+ composition increases, it reaches maximum value 70.28 emu/gm for (X = 0.6) and decreases further with increasing Zn2+ composition.

Synthesis, magnetic and optical properties of core/shell Co1-x Zn x Fe2O4/SiO2 nanoparticles

The optical properties of multi-functionalized cobalt ferrite (CoFe2O4), cobalt zinc ferrite (Co0.5Zn0.5Fe2O4), and zinc ferrite (ZnFe2O4) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrites nanoparticles have been fired at temperatures: 400°C, 600°C and 800°C, respectively, for 2 h. The composition, phase, and morphology of the prepared core/shell ferrites nanoparticles were determined by X-ray diffraction and transmission electron microscopy, respectively. The diffuse reflectance and magnetic properties of the core/shell ferrites nanoparticles at room temperature were investigated using UV/VIS double-beam spectrophotometer and vibrating sample magnetometer, respectively. It was found that, by increasing the firing temperature from 400°C to 800°C, the average crystallite size of the core/shell ferrites nanoparticles increases. The cobalt ferrite nanoparticles fired at temperature 800°C; show the highest saturation magnetization while the zinc ferrite nanoparticles coated with silica shell shows the highest diffuse reflectance. On the other hand, core/shell zinc ferrite/silica nanoparticles fired at 400°C show a ferromagnetic behavior and high diffuse reflectance when compared with all the uncoated or coated ferrites nanoparticles. These characteristics of core/shell zinc ferrite/silica nanostructures make them promising candidates for magneto-optical nanodevice applications.

Specific heat and magnetization studies of RMnO3 (R=Sm, Eu, Gd, Tb and Dy) multiferroics

A series of multiferroic materials with the compositional formula RMnO3 (where R=Sm, Eu, Gd, Tb and Dy) were prepared by the well-known citrate gel technique. After characterizing the samples structurally, a systematic investigation of specific heat and magnetization studies were performed over the temperature range 4–300 K with different magnetic fields. Based on these studies, it was found that all the samples exhibit a transition in the temperature region 39–54 K and the transition is attributed to ordering of Mn3+ ions (TNMn3+). Further, the samples GdMnO3, TbMnO3 and DyMnO3 were found to exhibit another transition (Tlock) in the temperature range 20–29 K. Finally, yet another transition was exhibited by all the samples and it is attributed to the antiferromagnetic (AF) ordering of rare-earth ion moments (TNR3+). The entropy at the AF transition TNMn3+ was computed. Finally, using the specific heat data, the Debye temperature values were also calculated.

Electrical and gas sensing properties of Li and Ti codoped NiO/PVDF thin film

In this study the electrical and gas sensing properties of Li and Ti codoped NiO (LTNO)/polyvinylidenefluoride (PVDF) nanocomposites were investigated. LTNO with a composition of Li 0.1Ti 0.018Ni 0.882O was prepared using citrate-gel technique. Phase evolution of as-prepared and calcined powders were examined by XRD technique and single phase NiO was obtained at 500 °C. TEM investigation revealed that the size of particles ranged from 5 to 40 nm. Thin films of LTNO/PVDF nanocomposite were synthesized using spin coating method. The electrical properties of film were investigated as a function of temperature. It was observed that the ln σ dc–1/ T graph consists of two different linear regions. While room temperature impedance spectra of film consist of a curved line, a transformation into a full semicircle with increasing temperature was observed from the complex plane plots of impedance. From the analysis of frequency, f, dependence of electrical conductivity, σ ac, it was found that the σ ac obeys the power law given by σ ac = σ 0 ω s , in which the frequency exponent s decreases with temperature. The sensing properties of the film for NH 3 were also investigated. It was observed that the conductivity (dc and ac) strongly dependent on the presence of the NH 3 gas.

Preparation and characterization of Li and Ti codoped NiO nanocomposites for gas sensors applications

Abstract This work investigated the use of Li and Ti codoped NiO nanocomposites as a room temperature ( R T ) gas sensor. The nanocomposites were prepared using citrate–gel technique. In order to reduce agglomeration, the polyvinyl alcohol was added as a reducing agent. The thermal analysis of gel composition of Li 0.1 Ti 0.018 Ni 0.882 O (LTNO) was investigated by DTA/TG and phase evolution of as-burnt powder was examined by XRD technique. XRD showed single phase NiO at 500 °C. TEM investigation revealed that the size of particles ranged from 5 to 40 nm. To detect sensor response, final sample was dissolved with minimum amount of solvent and spin coated thin film onto glass substrate with interdigitated gold (Au) electrodes. The film was used to detect toluene, ethanol and chloroform at R T . The maximum sensitivity was obtained for toluene vapors at R T .

Electrochemical studies on LiFe 1− xCo xPO 4/carbon composite cathode materials synthesized by citrate gel technique for lithium-ion batteries

LiFePO 4/carbon and LiFe 1− x Co x PO 4/carbon ( x = 0.02, 0.04, 0.08 and 0.1) composite cathode materials were synthesized by citrate gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the phase and morphology of un-doped and Co doped lithium iron phosphate/carbon composites. The SEM images revealed that the particles were agglomerated and the particle sizes were almost homogeneously distributed. The particle size was found to be between 200 and 300 nm from transmission electron microscopy. Cyclic voltammetric studies were taken to investigate the electrochemical performance of the prepared composite materials. The high intensity of the anodic and cathodic peaks indicates that Li-ions and electrons were participating actively in redox reactions due to the carbon coating. Charge/discharge studies carried out on a CR2032 coin cell revealed that the carbon coated LiFePO 4/carbon composite exhibited an improved discharge capacity of 157 mAh/g at low rates. We found that cobalt doping does not have a favourable effect on the electrochemical performance of lithium iron phosphate cathode materials.