Citrate Precursor Research Articles

Synthesis and Characterization of Core–Shell NiFe2O4@MgFe2O4 and ZnFe2O4@MgFe2O4 Nanoferrites

Two magnetic nanocomposites were prepared from spinel ferrite magnetic nanoparticles NiFe2O4 (NF) and ZnFe2O4 (ZF) with MgFe2O4 (MF) using citrate precursor method. The X-ray diffraction confirmed that the structure of all the samples was a single phase of spinel ferrites with space group Fd-3m. The determined lattice parameter (a) is within the expected values of MF, NF, and ZF. The grain size of all the nanocomposites obtained from the high resolution transmission electron microscope images showed that all the samples are in the nanoscale. The vibrating sample magnetometer was used to investigate the magnetic properties. An unexpected value of saturation magnetization (MS) was obtained for both NF@MF and ZF@MF where NF@MF is less than NF and ZF@MF is higher than of ZF. Self-heating characteristics under an alternating current magnetic field of 9.27 km−1 and a frequency of 198 kHz were investigated for hyperthermia applications. The results show an upward trend for the samples in the temperature vs. time chart, as a result of increasing in MS of the samples where the NF@MF has the highest values of SAR.

Study of double perovskite La2B(II)MnO6 (B: Ni, Co, Cu) as electrode materials for energy storage

In this paper, the study of the potential capacity of energy storage in supercapacitors containing oxide La2B(II)MnO6 (with B = Cu, Co, Ni) as the electrode material is presented. The mixed oxides are prepared by route of citrate precursors, starting from the nitrates of the corresponding metallic cations. The samples were calcined at 800 °C. The material was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The electrochemical characterization was performed through cyclic voltammetry (CV), galvanostatic charge/discharge measurements (GCD) and electrochemical impedance spectroscopy (EIS) in a three-electrode cell at room temperature, using a platinum electrode and a hydrogen electrode as counter and reference electrodes, respectively. The working electrode was prepared by a dispersion of the nanocomposite and carbon black in an isopropanol solution added on glassy carbon and covered by a Nafion® thin film. Runs were carried out in 0.05-–0.95-V range in 0.5 M KOH solution. The cyclic voltamperograms were obtained at varying the scan rates from 10 to 100 mV s−1. The galvanostatic charge/discharge curves were realize at current density values in the 0.625–31.25 A g−1 range. The higher capacitance values were obtained for La2CuMnO6. Thus, a specific capacitance of 781.25 F g−1at a current density of 3.12 A g−1, and a power and an energy specific of 72.6 kW kg−1 and 113.4 Wh kg−1, were obtained.

Impact of phosphorus structural position on the electrochemical enhancement of phosphorus doped LiMn2O4

Nanostructures of phosphorus doped and undoped LiMn2O4 have been obtained through the thermal decomposition of different citrate precursors. The oxides have been characterized by XRD, XPS, 7Li-NMR-MAS, STEM and electrochemical tests in aqueous electrolyte. XPS showed that no pyrophosphate species were formed during the doping process. The position of the phosphorus in the LiMn2O4 nanostructure were elucidated on both samples through analyses of STEM images and structural refinement using the Rietveld method. These analyses allowed to set the P in a 48f position with coordinates (1/8, 1/8, 0.338) at the crystalline structure of the LiMn2O4 spinel. Electrochemical tests corroborated the improvement of electrochemical properties of the oxide when phosphorus is used as dopant. XRD measurements on cycled electrodes showed the inhibition of segregated collateral phases during the cycling process. That allows to propose an explanation of the achieved advantages of doping the lithium manganese oxide spinel structure on the ground of the phosphorous position in the LiMn2O4 crystalline cell.

Low temperature synthesis and influence of rare earth Nd3+ substitution on the structural, magnetic behaviour of M-type barium hexa ferrite nanomaterials

The (Nd3+) substituted M-type Barium hexaferrite (BaFe12-x NdxO19) with (Nd3+) concentration (x = 0, 0.25, 0.50, 0.75, 1.00) is prepared using citrate precursor based sol gel process. The X-ray intensity pattern confirms that synthesized nanomaterials were in the pure phase and they possess hexagonal crystal structure having P63/mmc space group. Crystallite size and lattice strain values decreased with increment in concentration of Nd3+ in Barium Hexaferrite lattice. The Williamson-Hall plot is utilized for calculating these structural parameters. The Saturation Magnetization and Anisotropy values are highest for (0.25) mole (Nd3+) in Barium Hexaferrite lattice. All the prepared nanomaterials shows pure phase with good magnetization (43.11 emu/g–56.90 emu/g), retentivity (21.41 emu/g–29.02 emu/g) at room temperature. Curie temperature was found to be shifted to 429 °C from 446 °C with respect to increasing molar concentration of Neodymium.

Production of Li1.5Al0.5Ge1.5(PO4)3 ionic conductor from liquid-phase precursors

The synthesis of lithium-conducting solid electrolyte Li1.5Al0.5Ge1.5(PO4)3 (LAGP) from liquid-phase precursors using available water-soluble salts (LiNO3·3H2O, Al(NO3)3·9H2O, (NH4)2HPO4) and a stable citrate [Ge(C6H5O7)3]5– or oxalate [Gе(С2О4)3]2– germanium complex was studied. Germanium complexes were obtained by dissolving the hexagonal modification of GeO2 in citric or oxalic acid. As a result of the transfer of all initial components to the solution with the formation of a true collective solution, the subsequent interaction proceeded with the formation of a single-phase LAGP product in one stage from an oxalate precursor at 650°C, from a citrate precursor — at 800°C. The synthesized LAGP was studied by XRD, TG-DSC, IR spectroscopy, chemical analysis and impedance spectroscopy. The total ionic conductivity at room temperature was 8·10–4 S/cm and 2.5·10–4 S/cm for LAGP synthesized from oxalate and citrate precursor respectively. LAGP synthesis from oxalate precursor is preferred over synthesis from citrate precursor.

Composition Dependence of Elastic Moduli of Mixed Cobalt-Zinc Ferrites Prepared by Citrate Precursor Method

CoxZn1-xFe2O4 nanoparticles were prepared by chemical citrate precursor synthesis method. The Young’s modulus ‘E’ and the rigidity modulus ‘n’ of mixed cobalt-zinc ferrites have been determined by the ultrasonic pulse transmission technique at 1 MHz. The elastic modules of the ferrites were corrected to zero porosity using the formulae of Harselman and Fulrath. The observed variation of the elastic module with composition has been interpreted on the basis of binding forces between the atoms of the spinal lattice. A linear relationship between Debye temperature ØD and average sound velocity Vm has also been observed.

High-Surface-Area Sodium Tantalate Nanoparticles with Enhanced Photocatalytic and Electrical Properties Prepared through Polymeric Citrate Precursor Route.

NaTaO3 nanoparticles with a high surface area of 46.2 m2/g have been successfully synthesized using a polymeric citrate precursor route. As-prepared nanoparticles were extensively characterized by X-ray diffraction, Fourier transform infrared, transmission emission microscopy, and scanning electron microscopy studies for the analysis of phase purity, crystallinity, and morphology. NaTaO3 nanoparticles show efficient photo-induced removal of the methylene blue dye under sunlight, which were confirmed by using liquid chromatography–mass spectroscopy. 86% dye has been degraded in 200 min at neutral pH, whereas the same amount of dye was decolorized in only 80 min at alkaline pH. Also, the dielectric behavior of the as-prepared nanoparticles at different annealing temperatures was explained by the Maxwell–Wagner polarization mechanism. At 500, 600, and 700 °C annealing temperatures, the dielectric constant and dielectric loss at 500 kHz for the samples were found to be 21.5, 18, and 16 and 0.012, 0.022, and 0.029, respectively. The unsaturated hysteresis loop shows weak ferroelectric behavior of NaTaO3 nanoparticles with remanent and saturation polarizations of 0.0013 and 0.21 μC/cm2, respectively, and S-E hysteresis shows a bipolar strain of 0.10%.

Facile Synthesis of a Tin Oxide-Carbon Composite Lithium-Ion Battery Anode with High Capacity Retention

A tin oxide-carbon composite (SnOx-C) was fabricated as a candidate for use as an anode in lithium-ion batteries through the pyrolysis of a ditin citrate precursor. The simultaneous formation of ti...

Influence of Calcination Conditions on Structural and Solid-State Kinetic Properties of Iron Oxidic Species Supported on SBA-15.

Iron oxidic species supported on silica SBA‐15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid‐state kinetic properties of FexOy/SBA‐15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the FeIII nitrate precursor compared to the FeIII citrate precursor. Temperature‐programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from FeIII nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from FeIII citrate precursor. TPR traces were analyzed by model‐dependent Coats‐Redfern method and model‐independent Kissinger method. Differences in solid‐state kinetic properties of FexOy/SBA‐15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.

Probing the local atomic structure in CoLa0.15Fe1.85O4 as a function of the synthesis method by multi edge XAFS

We combined x-ray powder diffraction (XRD) and x-ray absorption fine structure spectroscopy (XAFS) to characterize the crystallographic and local atomic structure of nanosized La3+ substituted CoFe2O4 spinel ferrite of composition CoLa0.15Fe1.85O4 synthesized by different synthesis routes: standard ceramic technique, citric acid (citrate) precursor and urea assisted flash auto-combustion process. Rietveld refinement of XRD patterns allowed to describe the long-range atomic structure that was used as structural model for quantitative analysis of XAFS spectra collected at the Fe–K, Co–K and La–L3 and refined via a multi-edge approach, which provided details about local atomic structure and coordination chemistry around the absorbers. Combining the complementary information from XRD and XAFS it was possible to reliably describe the cation distribution over the two spinel sublattices (tetrahedral and octahedral) as a function of the synthesis routes. We demonstrated that the inversion parameter, the cation distribution, and the local atomic structure depend strongly on the synthesis method which in particular affects the La3+ lattice-site and vacancies. In particular the citrate synthesis appears to provide a pure single pure phase with highest coordination number of La and lowest inversion parameter.

Direct solid-state synthesis of maghemite as a magnetically recoverable adsorbent for the abatement of methylene blue

Solid phase extraction of dyes using a magnetically recoverable and reusable adsorbent is highly desirable from a sustainable environmental perspective. A simple, direct and highly scalable solid-state thermal decomposition of ferric citrate in an oxygen deprived environment has been shown to yield magnetic maghemite phase in the temperature range of 300–350 °C. By increasing the calcination temperature, the formation of less-magnetic hematite phase has been found to be predominant. The synthesized iron oxides have been thoroughly characterized using various techniques. SAXS analyses have revealed that the less-magnetic hematite phase has been formed through the surface oxidation of maghemite domains, and thus transitioning from γ-Fe2O3 to α-Fe2O3 passing through γ-Fe2O3@α-Fe2O3 core-shell architecture. The thermal decomposition temperature and duration of the ferric citrate precursor have been optimized towards maximizing the saturation magnetization value and adsorption capacity of MB. The adsorption of MB over iron oxides has been thoroughly studied for its vital sorption parameters such as pH, adsorbent amount, isotherms, adsorption capacity, kinetics, and thermodynamics. The surface area of the adsorbent synthesized at 300 °C and 2 h heating duration is determined to be 163.1 m2/g. Under the optimal pH of 10 and 1 g/L loading of the adsorbent, the adsorption maximum was found to be in the range of 34 to 38 mg/g. With the magnetic iron oxide adsorbent synthesized at 350 °C and 2 h heating duration, we have demonstrated 100 times pre-concentration of MB in a magnetically recoverable and recyclable manner.

Partial substitution of cobalt by rare-earths (Gd or Sm) in cobalt ferrite: Effect on its microstructure and magnetic properties

Microstructure and magnetic properties of partially substituted cobalt ferrite, with small amounts of gadolinium or samarium, were investigated. Co1-xGdxFe2O4+δ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, and 0.15) and Co1-xSmxFe2O4+δ (x = 0.04, and 0.08) were obtained through the citrate precursors route. X-ray powder diffraction patterns, of samples treated at temperatures between 400 and 1000 °C, are consistent with a cubic spinel-type structure. Substituted ferrites, with x = 0.04 and 0.08 (600 °C/2 h), show the combination of maximum enhancement of crystallinity and minimum change of the lattice parameters. At this temperature and composition range the crystallite size decreases up to a 41%. Rietveld analyses of Co1-x(Gd/Sm)xFe2O4+δ (x = 0, 0.04, and 0.08), carried out considering that Gd3+ (or Sm3+) occupies Co2+ positions, give rise to a good quality of refinement and cell parameters which are slightly smaller than those provided in the crystallographic database of CoFe2O4. Raman spectra of Gd3+ or Sm3+ substituted ferrites show the characteristic Raman modes expected in inverse spinel ferrites without additional signals. TEM micrographs reveal the presence of small agglomerates of nanoparticles. SAED patterns and HRTEM micrographs, are characteristic of polycrystalline powders while the interplanar distances well correspond to those of CoFe2O4. EDS analyses confirm the presence of Gd or Sm in substituted ferrites. Magnetic hysteresis loops of samples suggest a ferrimagnetic behavior and their squareness ratio values decrease up to 36% in Co1-xSmxFe2O4+δ (x = 0.04). Mössbauer studies reveal the presence of only Fe3+ ions, distributed in a proportion of 60 and 40% through octahedral and tetrahedral sites, respectively and a canted ferrimagnetic structure. Although the formation of the mixed spinel, rather than different substances (Sm or Gd oxide), fall in the sensitivity limits of the XRD technique all the results demonstrate that the replacement of Co2+ by Gd3+ or Sm3+ ions, in CoFe2O4, can tailor the crystal structure, microstructure, and magnetic properties of cobalt ferrite.

Effect of pH, Surfactant, and Temperature on Mixed-Phase Structure and Band Gap Properties of BiNbO4 Nanoparticles Prepared Using Different Routes

α- and β-BiNbO4 nanoparticles were successfully prepared using three different routes, namely co-precipitation, hydrothermal, and citrate precursor methods. Structural characterization has been analyzed using powder X-ray diffraction where results confirmed the mixed-phase nature of the prepared powders. When co-precipitation method is applied, BiNbO4 prepared at pH 2 and calcined at 750 °C shows predominately the α-BiNbO4 owning the narrowest band gap of 2.86 eV, whereas an increase in the pH value resulted in the β-BiNbO4 phase being the predominant phase. On the other hand, samples prepared using citrate precursor method show co-existence of both α- and β-BiNbO4 at all pH values under study; however, at pH 10 the β-BiNbO4 was the dominant phase exhibiting a higher bandgap energy value of 3.16 eV. When applying the hydrothermal approach, BiNbO4 prepared at all pH ranges of the present study show a band gap >3.2 eV indicating their activity in the ultraviolet region of the spectrum. Moreover, increasing calcination temperature to 900 °C, a gradual transformation of α- to β was observed. Lastly, it was noticed that as the lattice volume increases, the band gap of prepared BiNbO4 decreases.

Structure and Enhanced Dielectric Properties of B and Sr Modified CaCu3Ti4O12 Ceramics

B doped CaCu3Ti4O12 (CCTO), Sr doped CCTO and (B + Sr) co-doped CCTO ceramics were synthesized using the citrate precursor process and were sintered at 1080°C for 3 h. The effects of B and/or Sr doping on dielectric properties, Raman spectra and resistance were studied. Raman results corroborate with the results of x-ray diffraction, and Raman spectra show a multiphonon phenomenon. The pure CCTO phase can be obtained by citrate precursor processing and a short sintering time. The micrographs reveal that B and Sr additions can speed the grain growth, and a dense and homogenous microstructure was obtained for B and Sr co-doped ceramic. The addition of B and Sr can increase the grain boundary resistance and enhance dielectric properties with dielectric constant of 12108 and dielectric loss of 0.044 at 10 kHz. Moreover, B and Sr additions can enhance the frequency stability (between 100 Hz and 50 kHz) and temperature stability (between 20°C and 100°C) of dielectric loss. The present results show that the microstructure characteristics and grain boundary response are the primary factors in improving the dielectric properties of CCTO ceramics.

Synthesis and properties of SrFe12O19 obtained by solid waste recycling of oily cold rolling mill sludge

The aim of this study was to develop a new approach for the preparation of environmentally friendly, high-value products from oily cold rolling mill (CRM) sludge. Utilizing oily CRM sludge as a source of iron, strontium hexaferrite (SrFe12O19) powders were prepared by multi-step processes involving acid leaching, chemical conversion treatment, and synthesis by a citrate precursor. The influences of citric acid dosage and the pH of the sol system on the formation, crystallite size, and magnetic properties of the obtained SrFe12O19 powders were investigated. High saturation magnetization (74.8 mA-m(2)g(-1)) and intrinsic coercivities (614.46 mT) were achieved for pH 7.0 of the sol system, for which the molar ratio of citric acid dosage to the total dosage of Fe-3+ and Sr2+ was 1.5. This study presents a new approach to utilizing oily CRM sludge, and even refractory iron-containing solid waste.

Controlling the Composition and Magnetic Properties of Nano-SrFe12O19 Powder Synthesized from Oily Cold Mill Sludge by the Citrate Precursor Method.

This paper proposes a new method for producing nano-SrFe12O19 powder by the citrate precursor route using solid waste as a source of iron. This solid iron-containing waste, which exists in the form of an oily sludge, is produced by a cold rolling mill. This sludge was first subjected to a process, including sulfuric acid leaching, oxidation, precipitation, and nitric acid leaching, to obtain an iron nitrate (Fe(NO3)3) solution. Next, the Fe(NO3)3 solution was mixed with a strontium nitrate (Sr(NO3)2) solution obtained by subjecting strontium carbonate to nitric acid leaching. Subsequently, citric acid, as chelating agent, and ammonia water, as precipitating agent, were added to the mixed solution to form a gel. The gel was dried and spontaneously combusted, then annealed at different temperatures for 2 h in flowing air. The effects of the Fe3+/Sr2+ molar ratio and annealing temperature on the formation, morphology, and magnetic properties of SrFe12O19 were investigated. The results showed that single-phase SrFe12O19 powder was obtained by decreasing the Fe3+/Sr2+ molar ratio from the stoichiometric value of 12 to 11.6 and increasing the annealing temperature to 1000 °C for 2 h. Adjustment of the Fe/Sr molar ratio to 12 and the annealing temperature to 900 °C enabled the magnetic properties to be optimized, including saturation magnetization (Ms) 80.2 emu/g, remanence magnetization (Mr) 39.8 emu/g, and coercive force (Hc) 6318 Oe.

Electrocatalytic and Enhanced Photocatalytic Applications of Sodium Niobate Nanoparticles Developed by Citrate Precursor Route

Development of cost effective and efficient electrocatalysts is crucial to generate H2 as an alternative source of energy. However, expensive noble metal based electrocatalysts show best electrocatalytic performances which acts as main bottle-neck for commercial application. Therefore, non-precious electrocatalysts have become important for hydrogen and oxygen evolution reactions. Herein, we report the synthesis of high surface area (35 m2/g) sodium niobate nanoparticles by citrate precursor method. These nanoparticles were characterized by different techniques like X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic properties of cost-effective sodium niobate nanoparticles were investigated for HER and OER in 0.5 M KOH electrolyte using Ag/AgCl as reference electrode. The sodium niobate electrode showed significant current density for both OER (≈2.7 mA/cm2) and HER (≈0.7 mA/cm2) with onset potential of 0.9 V for OER and 0.6 V for HER. As-prepared sodium niobate nanoparticles show enhanced photocatalytic property (86% removal) towards the degradation of rose Bengal dye. Dielectric behaviour at different sintering temperatures was explained by Koop’s theory and Maxwell-Wagner mechanism. The dielectric constants of 41 and 38.5 and the dielectric losses of 0.04 and 0.025 were observed for the samples sintered at 500 °C and 700 °C, respectively at 500 kHz. Conductivity of the samples was understood by using power law fit.

A green recycling process of the spent lead paste from discarded lead-acid battery by a hydrometallurgical process.

In this study, a green recycling process of discarded lead-acid battery paste, which could avoid both the smelting and electro-winning route has been developed. Leaching reagents containing sodium citrate, acetic acid and hydrogen peroxide were reacted with spent lead paste in aqueous media at the pH of 5-6. Lead paste was leached and formed into lead citrate precursor, which was recrystallized and separated from the solution. The optimal conditions for the leaching process at room temperature were found to be the: concentration of acetic acid solution of 0.92 mol L-1; concentration of sodium citrate solution of 0.478 mol L-1; initial mass ratio of solid spent lead paste to liquid (solid/liquid ratio) of 1/5 g/mL; and reaction time of 2 hours. The results showed that the desulphurization efficiency of lead paste was up to 99.9%. The optimal conditions for lead citrate re-crystallization from the leaching mixed solution were found to be the re-crystallization temperature of 55oC for 5 hours in a water bath. The lead citrate precursor synthesized from discarded lead-acid battery pastes was the chemical formula of Pb3(C6H5O7)2·3H2O with columnar shape in the length of 30-50 μm, which was easily separated from the leaching solution. The results of kilogram-scale experiments made progress easier for obtaining the ultrafine lead oxide product (PbO and Pb) from discarded lead-acid battery paste.

Induced effects of Zn+2 on the transport and complex impedance properties of Gadolinium substituted nickel-zinc nano ferrites

Abstract We report on the preparation and transport properties of Gadolinium substituted Ni ( 1 - x ) Zn x Gd y Fe ( 2 - y ) O 4 ( 0 ⩽ x ⩽ 1 , y = 0.1 ) nano particles using low temperature citrate precursor combustion method. The Rietveld refinement of PXRD data suggests the crystal structure of sample belongs to Fd-3m space group with an octahedral occupation of Gd+3 ions. FESEM micrographs show the existence of porosity in the samples. The dielectric studies reveal the good dielectric behaviour with high dielectric constant in Zn+2 substituted sample (x = 0.4). An increase in a . c conductivity observed in the Zn+2 substituted sample due to the hopping mechanism. The impedance spectroscopy of the samples shows the existence of high grain boundary resistance and an alternate switching of dielectric relaxation from non-Debye to Debye type. The activation energies and Curie temperature estimated using D. C. conductivity measurements drop linearly with an increase in Zn+2 concentration. We attribute the observed transport properties mainly to the hopping of Fe+2 ↔ Fe+3 ions.

Superior electrical and magnetic properties of microwave-sintered NiMgCuZn nanoferrites in comparison to their conventionally sintered counterparts

Microwave technique was employed for sintering a series of Ni0.5−xMgxCu0.3Zn0.2Fe2O4 nanoferrites (x = 0.05, 0.10, 0.15, 0.20) synthesized by citrate precursor method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), LCR meter, and Fourier-transform infrared spectroscopy (FTIR). A comparative analysis was performed for the microwave-sintered specimens and conventionally sintered specimens. This work highlights the significant reduction in sintering duration for microwave technique and remarkable improvement in electromagnetic properties like higher dc resistivity and higher initial permeability for microwave-sintered samples as compared to conventionally sintered ones, thereby making microwave-sintered samples more suitable for high frequency and multilayer chip inductor (MLCI) applications.