Dielectric Properties of Nd-Doped Yttrium Iron Garnet and Cu Or Co-Doped Nickel Zinc Ferrites

In this work, three series of soft ferrites were synthesized via solid state route. These are Nio.3-xCu,Zno.7Fe20(4x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30), Ni0.S- .C&Zno.~Fe204 (x=O.O, 0.1, 0.2, 0.3, 0.4, and 0.5) and Y3..NdxFes0~2 (x=O.O, 0.4, 0.8, 1.2 and 1.6). The X-ray diffraction patterns showing single phases for these three samples series, confirmed that the spinel and garnet structure had been formed in the Ni-Zn ferrites and YIG respectively. Ni-Zn ferrites substituted with copper oxide showed exaggerated grain growth whereas the other series substituted with cobalt oxide had no massive changes in the microstructure. For the YIG substituted with neodymium oxide, the first sample exhibited a porous microstructure and developed to become a more compact and poreless microstructure as neodymium increased. Measurement of the electrical properties was carried out in the temperature range from 28°C to 300°C in the low frequency region of 10 Hz to 1 MHz. Impedance analyzer was employed in the ac data acquisition whereas a pico-ammeter and a dc voltage source were used to measure electric current at different voltages. The results obtained from dielectric measurements indicate that microstructure of the samples plays an important role in the dielectric dispersion. A sample with higher porosity is associated with a low value of dielectric permittivity due to its high resistivity. Meanwhile a sample with a more compact structure exhibits higher dielectric permittivity due to its higher conductivity. Hence, electron hopping between ~ ean~d ~+e w~ou'ld increase in the conductive sample and give higher dielectric permittivity if compared with the resistive one. The dielectric response for every sample in the three series of soft ferrites displayed different mechanisms throughout the investigated temperature range. Therefore, dielectric behaviour of a sample can be modeled into at least two equivalent circuits. The complex impedance plots of both samples Ni-Zn ferrites and YIG showed overlapping semicircles. However, at high temperature the high frequency arc disappeared and there remained just one semicircle. The center of the semicircle for all samples was depressed below the real impedance axis and described by the parameter a. The results indicate that all these three series of soft ferrites can be represented by two parallel RC circuits connected in series that correspond to the contributions of grain and grain boundary. The ac conductivity for the three series of soft ferrites showed almost similar behaviour. At lower temperature, the ac curves can be divided into two region. The low frequency region showed that the ac conductivity was weakly dependent on frequency whereas at high frequency region, it was strongly dependent on frequency. As the temperature increased, the ac conductivity seemed independent of frequency. Extrinsic and intrinsic conductions had been inferred to occur in these samples. It is also found that microstructural entities such as grains and porosity play an important role in the dc resistivity. The two activation energies obtained indicated that there were probably two parallel conduction mechanisms or spin reorientation phase transition occurred

Role And Correlation Of Synthesis, Size And Morphology To The Magnetic Properties Of Cobalt And Cobalt/Gold Bimetallic Hierarchical Nanostructures

Cobalt is a ferromagnetic material while cobalt-gold bimetallic particles are expected to have modulated magnetic properties. Besides, gold nanostructure is also a good plasmonic material. However, cobalt is susceptible to oxidation in aqueous environment. The oxidised layer can harm the magnetic properties. Therefore, in order to avoid oxidation of cobalt, this work was devoted to the synthesis of cobalt and cobalt-gold bimetallic hierarchical particles using polyol method cum galvanic replacement reaction. A number of synthesis conditions were experimented in order to investigate their impacts on the morphologies of the cobalt particles produced. The parameters studied including reaction time, sodium hydroxide, concentration of cobalt salt, reaction temperature, reducing agent and surfactants. Various morphologies were successfully prepared such as hierarchical microspheres, hierarchical polyhedral shape, hierarchical raspberry like, truncated hexagonal bipyramid, flower-like, elongated and quasi cubic-like particles. All of these hierarchical cobalt particles exhibited their own unique magnetic properties. Sample prepared from 1mmol cobalt chloride, 2 mmol of sodium hydroxide, 5 mmol of hydrazine hydrate and 3.0% (w/v) of sodium dodecyl sulfate has a mixture of quasi cubic and elongated particles. It has the highest coercivity of about 290 Oe. Cobaltgold bimetallic hierarchical particles were prepared by galvanic replacement reaction where cobalt acted as sacrificial template. Bimetallic particles with hollow hierarchical structure and arbitrary shapes were produced under different synthesis conditions

Synthesis Of Cobalt/Gold Bimetallic Hollow Microspheres And Its Optical Properties

Galvanic replacement reaction is a very simple and effective method to prepare the particles with hollow interior [1]

Synthesis of MRGO nanocomposites as a potential photocatalytic demulsifier for crude oil-in-water emulsion

Oil-in-water (O/W) emulsion has been a major concern for the petroleum industry. A cost-effective magnetite-reduced graphene oxide (MRGO) nanocomposite was synthesized to study the demulsification process of emulsion using said nanocomposite under solar illumination. Characterization data show that the magnetite was successfully deposited on reduced graphene oxide through redox reaction at varying loading amounts of magnetite. Demulsification of the O/W emulsion using MRGO nanocomposite shows that in general the demulsification efficiency was dependent on the loading amount of Fe3 O4 on the RGO sheet. It was proposed that the surfactant hydroxyl groups have an affinity towards Fe3 O4, which the loading amount was directly proportionate to available active site in Fe3 O4. As the loading amount increases, charge recombination centers on the RGO sheet would increase, effectively affecting the charge distribution within MRGO structure

Layered construction of integrated sulfur-bridged CoNi-S/rGO architecture for enhanced electrochemical energy storage

Transition metals chalcogenides (TMCs) have been recognised so far with their high Faradic activity, making them promising candidates for efficient charge transfer electrodes. However, their tendency to aggregate hindered their potential applications in supercapacitors. This study introduces a novel cathode material composed of CoNi-sulfides (CoNi-S) nanostructured flakes and reduced graphene oxide (rGO) sheets designed to be connected through additional sulfur atoms to enhance their conductivity and electroactive surface area for hybrid supercapacitors. Remarkable results were realised by forming a layered structure of CoNi-S/rGO in which rGO sheets wrap CoNi-S flakes. Interestingly, the CoNi-S/rGO composite exhibited a specific capacitance of 3308F g−1 (1654C g−1) at 1 A g−1, outperforming the performance of a single CoNi-S component, which recorded 2155F g−1 (1077.5C g−1) at identical conditions. Both materials demonstrated exceptional high-rate capabilities, retaining about 70 % of their capacitance even at an elevated current density of 10 A g−1. In a two-electrode coin cell system, the device showcased a high energy density of 50.2 Wh kg−1 at a power density of 750 W kg−1. It maintained an impressive 84 % capacitance retention after enduring 35,000 cycles. These remarkable findings hold significant promise for advanced energy storage applications, marking substantial progress forward in hybrid supercapacitor technology

Enhancing capacitive performance of magnetite-reduced graphene oxide nanocomposites through magnetic field-assisted ion migration

The transition towards renewable energy sources necessitates efficient energy storage systems to meet growing demands. Electrochemical capacitors, particularly electric double-layer capacitors (EDLCs), show promising performance due to their superior properties. However, the presence of resistance limits their performance. This study explores using an external magnetic field to mitigate ion transfer resistance and enhance capacitance in magnetite-reduced graphene oxide (M-rGO) nanocomposites. M-rGO nanocomposites with varying weight ratios of magnetite were synthesized and comprehensively characterized. Characterization highlighted the difference in certain parameters such as C/O ratio, the Id/Ig ratio, surface area and particle size that contribute towards alteration of M-rGO’s capacitive behaviour. Electrochemical studies demonstrated that applying a magnetic field increased specific capacitance by approximately 20% and reduced resistance by 33%. Notably, a maximum specific capacitance of 16.36 F/g (at a scan rate of 0.1 V/s) and 27.24 F/g (at a current density of 0.25 A/g) was achieved. These improvements were attributed to enhanced ion transportation and migration at the electrode/electrolyte interface, lowering overall resistance. However, it was also observed that the aforementioned parameters can also limit the M-rGO’s performance, resulting in saturated capacitive state despite a reduced resistance. The integration of magnetic fields enhances energy storage in nanocomposite systems, necessitating further investigation into underlying mechanisms and practical applications

Dependence of the optical constant parameters of p-toluene sulfonic acid-doped polyaniline and its composites on dispersion solvents

The optical constants of Para-Toluene sulfonic acid-doped polyaniline (PANI), PANIchitosan composites, PANI-reduced graphene-oxide composites and a ternary composite comprising of PANI, chitosan and reduced graphene-oxide dispersed in diluted p-toluene sulfonic acid (PTSA) solution and N-Methyl-2-Pyrrolidone (NMP) solvent have been evaluated and compared. The optical constant values were extracted from the absorbance spectra of thin layers of the respective samples. The potential utilization of the materials as the active sensing materials of surface plasmon resonance biosensors has also been assessed in terms of the estimated value of the penetration depth through a dielectric medium. The results show a reasonable dependence of the optical constant parameters on the solvent type. Higher real part refractive index (n) and real part complex dielectric permittivity (ε’) values were observed for the samples prepared using PTSA solution, while higher optical conductivity values were observed for the NMP-based samples due to their relatively higher imaginary part refractive index (k) and imaginary part complex dielectric permittivity (ε″) values. In addition, NMP-based samples show improvement in terms of the penetration depth through a dielectric medium by around 9.5, 1.6, 4.4 and 2.9 times compared to PTSA-based samples for the PANI, PANI-chitosan, PANI-RGO and the ternary composites, respectively. Based on these, it is concluded that preparation of these materials using different dispersion solvents could produce materials of different optical properties. Thus, the variation of the dispersion solvent will allow the flexible utilization of the PANI and the composites for diverse applications

Effect on the Formation of Magnetite Reduced Graphene Oxide with Controlled Stirring Duration

Graphene is a promising material due to its fascinating properties, such as mechanical, electronic and thermal properties. Graphene based hybrids materials also have been widely studied due to its wide applications, such as sensors, energy storage and conversion, electronic device and others. The current study presents the synthesis of magnetite-reduced graphene oxide (M-rGO) nanocomposites through in situ chemical synthesis at different stirring durations. This synthesis process involves the redox reaction between the iron(II) salts and graphene oxide (GO) sheets. Various techniques were employed to characterize the synthesized M-rGO nanocomposites. From X-ray diffraction (XRD) results, the crystal structure of M-rGO was found to be independent on the stirring duration. Three magnetite vibrations, D band and G band were observed in Raman spectrum of M-rGO with 24 hours stirring duration. From Fourier transform infrared (FTIR) analysis, M-rGO with 24 hours stirring duration showed the strong intensity of Fe-O vibration. Thus, this indicated that a large amount of magnetite nanoparticles were covered on the surface of rGO sheets. This result is further supported by the morphology of nanocomposites from scanning electron microscopy (SEM) and the elemental analysis (EDX). A monolayer of rGO sheet (C= 33.79 atomic %) with full coverage of magnetite nanoparticles (Fe= 30.20 atomic %) was found for the M-rGO with 24 hours stirring duration. Overall, M-rGO require 24 hours of continuous stirring to ensure full coverage of magnetite nanoparticles on the surface of rGO sheets

Removal of methylene blue dye by solvothermally reduced graphene oxide: a metal-free adsorption and photodegradation method

In this work, reduced graphene oxide (rGO) was fabricated at different reduction temperatures via an environmentally friendly solvothermal approach. The rGO formed at 160 °C clearly showed the partial restoration of the sp2 hybridization brought about by the elimination of oxygenated functionalities from the surface. Owing to the augmented surface area and the band gap reduction, rGO-160 exhibited the best adsorption (29.26%) and photocatalytic activity (32.68%) towards the removal of MB dye. The effects of catalyst loading, initial concentration of dye, light intensity, and initial pH of solution were evaluated. It was demonstrated that rGO-160 could achieve a higher adsorptive removal (87.39%) and photocatalytic degradation (98.57%) of MB dye when 60 mg of catalyst, 50 ppm of dye at pH 11, and 60 W m-2 of UV-C light source were used. The MB photodegradation activity of rGO-160 displayed no obvious decrease after five successive cycles. This study provides a potential metal-free adsorbent-cum-photocatalyst for the decontamination of dyes from wastewater. This journal is © The Royal Society of Chemistry

Correction: Magnetically recoverable magnetite-reduced graphene oxide as a demulsifier for surfactant stabilized crude oil-in-water emulsion.

[This corrects the article DOI: 10.1371/journal.pone.0232490.]