Structure Of NiFe2O4 Research Articles

High-Performance and Sensitive Humidity Sensors Based on Reduced Graphene Oxide/Nickel Ferrite Nanocomposites

This work reports the fabrication of highly sensitive humidity sensors using reduced graphene oxide (rGO), nickel ferrite nanoparticles (NiFe2O4 NPs), and their nanocomposites. rGO and NiFe2O4 NPs, obtained by the modified Hummers method and the wet chemical coprecipitation method, respectively, were used to synthesize rGO/NiFe2O4 nanocomposites at two different compositions. XRD analysis confirmed both the spinel structure of NiFe2O4 and the reinstatement of π-conjugated structure of graphene. Average crystallite sizes, calculated by XRD, were 17.80 nm, 13.60 nm, and 8.22 nm for NiFe2O4 NPs, rGO/NiFe2O4 (70/30), and rGO/NiFe2O4 (90/10), respectively. FTIR affirmed the successful reduction of graphene oxide to rGO. Optical bandgaps of 1.83 eV and 2.18 eV were obtained for rGO and NiFe2O4 respectively using Tauc plot. SEM confirmed the films’ porosity, providing more active sites for the adsorption of water molecules. Our results demonstrate that NiFe2O4 NPs show the highest response and sensitivity within the 35–90 RH% range. Additionally, the rGO/NiFe2O4 (70/30) nanocomposite achieved the fastest response/recovery time of 8/4 s at 100 Hz, with good repeatability and stability. These findings suggest that rGO/NiFe2O4 NCs are promising candidates for advanced humidity sensing applications due to their rapid response, sensitivity, and long-term reliability.

Enhancing redox stability through metal substitution in nickel ferrite for chemical looping hydrogen production via water splitting

NiFe2O4 oxygen carrier has tremendous potential for application in chemical looping hydrogen production via water splitting. However, it exhibits poor high-temperature cycling stability. The current study investigates the impact of substituting other elements (Cu, Ce, La or K) for Fe in NiFe2O4 on the hydrogen production performance during the chemical looping water splitting process. No crystalline phase of oxides for Fe, La or Ni has been detected in the XRD patterns, indicating that substituting element has been successfully doped into the spinel structure of NiFe2O4. After the substitution with the other elements such as K, La, and Ce, the hydrogen yield of the oxygen carrier has been improved, with the highest hydrogen yield observed for the NiLa0.02Fe1.98O4 oxygen carrier. Through optimized experiments, the optimum substitution amount of La is 10%, resulting in the formation of NiLa0.2Fe1.8O4. With the substitution of 10% Fe by La, the hydrogen production performance of the fresh oxygen carrier is increased from 170 mL/kg to 297 mL/kg, which can be explained by various characterization results. Lattice distortion and an obvious increase in oxygen vacancy content are observed in NiLa0.2Fe1.8O4, with the reduction peak shifting to the low-temperature region. In addition, compared to NiFe2O4, NiLa0.2Fe1.8O4 exhibits better cycling stability in 30 cycles. Finally, the changes of structure and morphology for NiFe2O4, NiLa0.2Fe1.8O4 before and after 30 cycles have been comparatively analyzed using XRD, XPS, SEM, BET, and H2-TPR.

Investigating morphological, optical and magnetic properties of blended novel ZnO-Ag/NiFe2O4 nanocomposite

Metal oxide nanoparticles and magnetic nanoparticles are combined to create magnetic nanocomposites (MNCs) with unique physical, chemical, and biological properties. A new ZnO-Ag/NiFe2O4 ternary magnetic nanocomposite was created in the current study using a simple and straightforward solid-phase mixing process with subsequent thermal treatment. The structural, optical, and magnetic properties of the ZnO-Ag/NiFe2O4 nanocomposite were studied using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDAX), vibrating sample magnetometry (VSM), and Raman spectroscopy. Brunauer–Emmett–Teller (BET) analysis was performed to analyze the surface area and average pore diameter of the nanocomposite. Cyclic voltammetry and photoelectrochemical analysis were performed to study the electrical behavior and charge carrier concentrations. According to XRD studies, the ZnO-Ag/NiFe2O4 nanocomposite is composed of the hexagonal wurtzite of ZnO and the spinel cubic structure of NiFe2O4. FESEM analysis revealed that the crystals of the nanocomposite were nearly spherical, and EDAX elemental mapping indicated that the elements were evenly dispersed across the sample without any impurities. The average diameter of the ZnO-Ag/NiFe2O4 nanocomposite obtained from the TEM images was nearly 50.65 nm. The specific surface area and average pore diameter of the ZnO-Ag/NiFe2O4 nanocomposite were 13.58 m2/g and 4.33 nm, respectively, according to BET analysis. CV analysis revealed a sharp increase in the specific capacitance of the ZnO-Ag/NiFe2O4 nanocomposite. The specific capacitances of the 1 M NaOH electrolyte, ZnO nanoparticles and ZnO-Ag/NiFe2O4 nanocomposite were 55.7302 F/g, 53.947 F/g, and 87.229 F/g, respectively, at a 0.05 V/s scan rate. With a coercive field (Hc) of 167 Oe, remnant magnetization (Mr) of 0.73 emu/g, and saturation magnetization (Ms) of 6.58 emu/g, the blended magnetic nanocomposite ZnO-Ag/NiFe2O4 exhibited superparamagnetic behavior at ambient temperature. Using an external permanent magnet, the ZnO-Ag/NiFe2O4 nanocomposite may be extracted from the reaction mixture, indicating its probable environmental and biomedical application.

NiFe2O4 nanoparticles as highly efficient catalyst for oxygen reduction reaction and energy storage in supercapacitor

Nickel ferrite (NiFe2O4) nanostructures (NSs) were synthesized via a low-cost and reproducible co-precipitation method. The as-synthesized material was annealed at different temperatures to investigate electrochemical performances for oxygen reduction reaction (ORR) and energy storage capacity. The X-ray diffraction (XRD) pattern confirmed the cubic structure of NiFe2O4 (NF) NSs. The decreased agglomeration and increased particle size were observed by field effect scanning electron microscopy (FE-SEM) with annealing temperature. The presence of Ni–O and Fe–O bonds at tetrahedral and octahedral sites was confirmed by Fourier transform infrared (FTIR) spectroscopy. The electrochemical analysis studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) demonstrated that the NF NSs annealed at 900 °C exhibited impressive electrochemical activity with a specific capacitance of ∼136 F/g, outperforming samples synthesized at lower temperatures. Moreover, the electrode material displayed excellent long-term stability over 3000 cycles for ORR activity. The remarkable electrochemical performance of NF NSs at higher annealing temperatures highlights their potential for future energy storage and conversion devices.

NiFe2O4/Ti3C2 nanocomposite as an efficient catalyst for methanol electro-oxidation reaction: Investigating annealing temperature and synergetic effect

In the present work, NiO/Ti3C2, γ-Fe2O3/Ti3C2, and NiFe2O4/Ti3C2 nanocomposites were prepared via hydrothermal method. The influence of annealing temperature on the crystalline structure and subsequently, on the electrocatalytic performance was investigated by characterization and electrochemical processes. The presence of Ti3C2 Mxene substrate improved the electron transfer kinetics of NiFe2O4 spinel nanoparticles. In addition, due to the synergistic effect of nickel and iron elements in the structure of NiFe2O4, the NiFe2O4/Ti3C2 nanocomposite showed better electrochemical activity and stability compared to the single metal oxides (NiO and γ-Fe2O3). Based on the results, NiFe2O4/Ti3C2 nanocomposite annealed at 200 °C, showed the highest current density (24 mA cm−2) and the most stable catalytic performance (90.6%) compared to other temperatures. This nanocatalyst can be proposed as a promising catalyst for methanol oxidation reactions in direct alcohol fuel cells.

Chemical looping reforming of toluene as bio-oil model compound via NiFe2O4@SBA-15 for hydrogen-rich syngas production

Hydrogen-rich syngas was a clean energy and an important industrial material. Based on the decoupling strategy of biomass chemical looping gasification process, this paper proposed a strategy of metal oxides embedded into molecular sieves to prepare highly dispersed and nanosized oxygen carriers for producing hydrogen-rich syngas. NiO@SBA-15, Fe2O3@SBA-15, and NiFe2O4@SBA-15 were prepared by the impregnation method, and the reaction conditions on the chemical looping reforming of toluene were investigated. The results showed that NiFe2O4@SBA-15 had the highest toluene conversion rate of 93.4% and a relatively high CO selectivity rate of 80.7%. It was confirmed that the embedding strategy can effectively enhance the nanocrystallization and dispersion of metal oxides in oxygen carriers, which could effectively reduce sintering. The inverse spinel structure of NiFe2O4 made the oxygen carrier have more metal adsorption sites and a closer reaction distance, which were beneficial to the adsorption and reaction of the fuel. After testing, the optimum reaction temperature was 750 °C, and the optimum weight hourly space velocity was 1.168 h−1. In the 10 cycles of testing of 20 NiFe2O4@SBA-15, the average conversion rate of toluene was 95.34%, the moderate selectivity of CO in the gaseous product was 94.83%, the average H/C ratio was 1.97, which indicated that the cycle stability is good. It provided a reference for developing and designing future oxygen carriers of biomass chemical looping reforming.

NiFe2O4/ZnO nanocomposites for degradation of MB dye with their local electrical behavior

In the present work NiFe2O4/ZnO nanocomposites were successfully prepared by in-situ wet chemical co-precipitation process. XRD study reveals the presence of the cubic structure of NiFe2O4 and wurtzite hexagonal structure of ZnO. FTIR reveals the distribution of cations and anions at different interstitials sites. Further, the morphology of synthesized sample is analyzed by use of TEM. The oxidation state was explained from X-ray photoelectron spectroscopy (XPS). Dielectric constant is calculated from impedance spectroscopy. UV–vis spectroscopy was used to evaluate the band gap (1.68eV-3.2 eV) of the materials by Tauc's plot. As a model contaminant methylene blue (MB) dye used to check the performance and (0.5) NiFe2O4 - (0.5) ZnO sample shows the maximum degradation efficiency which is 91.36%. The photocatalytic activity of composites is found to be better than bare materials.

Solar light induced photocatalytic degradation of tetracycline in the presence of ZnO/NiFe2O4/Co3O4 as a new and highly efficient magnetically separable photocatalyst.

In this study, a new solar light-driven magnetic heterogeneous photocatalyst, denoted as ZnO/NiFe2O4/Co3O4, is successfully prepared. FT-IR, XPS, XRD, VSM, DRS, FESEM, TEM, EDS, elemental mapping, and ICP analysis are accomplished for full characterization of this catalyst. FESEM and TEM analyses of the photocatalyt clearly affirm the formation of a hexagonal structure of ZnO (25–40 nm) and the cubic structure of NiFe2O4 and Co3O4 (10–25 nm). Furthermore, the HRTEM images of the photocatalyst verify some key lattice fringes related to the photocatalyt structure. These data are in very good agreement with XRD analysis results. According to the ICP analysis, the molar ratio of ZnO/NiFe2O4/Co3O4 composite is obtained to be 1:0.75:0.5. Moreover, magnetization measurements reveals that the ZnO/NiFe2O4/Co3O4 has a superparamagnetic behavior with saturation magnetization of 32.38 emu/g. UV-vis DRS analysis indicates that the photocatalyst has a boosted and strong light response. ZnO/NiFe2O4/Co3O4, with band gap energy of about 2.65 eV [estimated according to the Tauc plot of (αhν)2 vs. hν], exhibits strong potential towards the efficacious degradation of tetracycline (TC) by natural solar light. It is supposed that the synergistic optical effects between ZnO, NiFe2O4, and Co3O4 species is responsible for the increased photocatalytic performance of this photocatalyst under the optimal conditions (photocatalyst dosage = 0.02 g L−1, TC concentration = 30 mg L−1, pH = 9, irradiation time = 20 min, and TC degradation efficiency = 98%). The kinetic study of this degradation process is evaluated and it is well-matched with the pseudo-first-order kinetics. Based on the radical quenching tests, it can be perceived that •O2 − species and holes are the major contributors in such a process, whereas the •OH radicals identify to have no major participation. The application of this methodology is implemented in a facile and low-cost photocatalytic approach to easily degrade TC by using a very low amount of the photocatalyst under natural sunlight source in an air atmosphere. The convenient magnetic isolation and reuse of the photocatalyst, and almost complete mineralization of TC (based on TOC analysis), are surveyed too, which further highlights the operational application of the current method. Notably, this method has the preferred performance among the very few methods reported for the photocatalytic degradation of TC under natural sunlight. It is assumed that the achievements of this photocatalytic method have opened an avenue for sustainable environmental remediation of a broad range of contaminants.

High current flux electrochemical sensor based on nickel-iron bimetal pyrolytic carbon material of paper waste pulp for clenbuterol detection

As a β-stimulant, clenbuterol (CLB) is abused to varying degrees by athletes worldwide. It is also used in the meat and dairy industries. CLB inadvertently enters the human body through the food chain, endangering human health. Therefore, a rapid and convenient method for detecting CLB is needed. In this study, nanocarbon-supported NiFe2O4 electrode materials (NiFe2O4–NPCs) were synthesized, and an electrochemical sensor (NiFe2O4–NPCs/GCE) for CLB detection was fabricated. NiFe2O4–NPCs have good electrical conductivity, electrocatalytic activity, and high electrical flux, owing to their large specific surface area and the anti-spinel structure of NiFe2O4. The fabricated sensor is an effective detector of CLB. The sensor exhibits linear ranges of 10−7–10−5 M and 7 × 10−11–10−7 M and a limit of detection (LOD) of 3.03 × 10−12 M (S/N = 3). The sensor also exhibits good sensitivities of 3.264 μA μM−1 cm−2 and 0.751 μA μM−1 cm−2 (S/N = 3). Additionally, NiFe2O4–NPCs/GCE successfully detected CLB in real samples of human urine. Thus, this study highlights the potential of the NiFe2O4–NPCs/GCE sensor for the detection of CLB in biological samples.

Construction of highly efficient separable p-n junction based light driven composite (NiFe2O4/MnWO4) for improved solar light utilisation

Magnetic separable p-NiFe2O4/n-MnWO4(NFMW) composites were synthesised by combined co-precipitation and hydrothermal process with varied stoichiometry ratio of p-NiFe2O4. The best composite having 20 mg of p-NiFe2O4(NFMW-2) demonstrated excellent band gap, work function, durability, photo stability, ferromagnetism properties etc. XRD shows wolframite MnWO4 and spinel structure of NiFe2O4. Elemental mapping confirms the uniform dispersion of composites. The optimized loading of p-NiFe2O4 results in enhanced Light-harvesting capability. Photoluminescence analysis shows the prolonged decay time of the composite (8.769 µs) with reduced recombination rate. Transient photocurrent and Nyquist plot reveals the excellent separation efficiency and mobility of the charge carriers. Although NFMW-2 has shown ~56% reduction in the coercivity but withstands its ferromagnetic nature. Further, its edge potentials were evaluated through MS plot suggests Z-scheme mode of electron transfer. The solar photocatalysis process was dominated by superoxide and hydroxyl radicals and thus resulted in complete removal of Congo red and 92% for phenol within 240 min and 360 min.

Role of Mg2+ and In3+ substitution on magnetic, magnetostrictive and dielectric properties of NiFe2O4 ceramics derived from nanopowders.

The effect of Mg2+ and In3+ substitution on the structural, magnetic, magnetostrictive and dielectric properties of NiFe2O4 samples derived through sintering of nanocrystalline ceramic powders is investigated. Namely, NiFe2O4, NiMg0.2Fe1.8O4 and NiIn0.2Fe1.8O4 nanopowders were synthesized by a tartrate-gel route followed by calcination at 500 °C, pelletization and sintering at 1200 °C for 2 h. The average particle size was found to decrease from ∼13 nm (for NiFe2O4) to ∼9 nm and ∼7 nm for as-synthesized Mg2+ and In3+ substituted NiFe2O4 samples (after calcination), respectively. However, after sintering a better grain growth occurs for the In3+ substituted sample, as confirmed through the microscopy and dielectric results. Due to the replacement of smaller Fe3+ cations by larger In3+ and Mg2+ cations at the tetrahedral (Td) and octahedral (Oh) interstitial positions, respectively, in the spinel structure of NiFe2O4, the lattice parameters increase in both the cases. The Td site occupation of In3+ leads to higher magnetization for the NiIn0.2Fe1.8O4 sample, but Oh site occupation of Mg2+ leads to lower magnetization for the NiMg0.2Fe1.8O4 sample, in comparison to the pure NiFe2O4 sample. Furthermore, the Curie temperatures (TC) and magnetocrystalline anisotropy constants (K1) for both the samples are considerably lower than the parent compound, with all the parameters being the lowest for the In3+ substituted sample because the Td occupation of non-magnetic In3+ drastically decreases the A-O-B magnetic superexchange interactions. The above alteration to the magnetic interactions alters the magnitude of maximum magnetostriction (λmax), which is explained based on the occupation of the Mg2+ and In3+ cations in our samples. The obtained magnetostriction properties of our samples are very useful for magnetostriction based sensor application.

Physical study on nife2o4/ α- Fe2O3 composite-thin films for potential applications

This work highlights some physical investigations on NiFe2O4/ α- Fe2O3 composite deposited on glass substrates as thin films at T = 460 °C by the spray pyrolysis technique. First, X-ray diffraction analysis approved the polycrystalline nature of such films with a mixture of NiFe2O4 and α- Fe2O3 materials. The majority phase based on NiFe2O4 compound indicated the achievement of a cubic structure and the preferred orientation of the crystallites are along (311) direction while α- Fe2O3 is a minority phase crystallizing in rhombohedra structure. Raman spectroscopy measurement depicts the presence of cubic structure of NiFe2O4. Moreover, the reflectance and the transmittance optical coefficients increase with wavelength and do not exceed 45% which reveals an absorbent character of these films. Second, we evaluated the electrical properties of such films at various temperatures (430–490 °C) by using the impedance spectroscopy technique in frequency range of 5 Hz–13 MHz. Both the DC conductivity and relaxation frequency were thermally activated with an activation energy around 0.67 eV. Also, AC conductivity was estimated and deeply discussed through Jonscher law. Nonetheless, the electropyroelectric study of these films has been made and discussed. Also, the wettability experiments have been carried out regarding the contact angle CA which reveals a hydrophilic nature of NiFe2O4/ α- Fe2O3 sprayed thin films. Finally, the photocatalytic activity of these films were carried out regarding the photodegradation of methylene bleu (MB) under sunlight during 120 min.

Electronic structure, magnetic and optic properties of spinel compound NiFe2O4

We report ab initio investigation of structural, electronic, magnetic and optical properties of the NiFe2O4 compound. Hubbard parameters are computed for both Ni and Fe atoms. Employing generalized gradient approximation (GGA) and GGA + U approximations and taking into consideration four possible types of atomic arrangements, we identify the most stable structural–magnetic configuration of the system. Interestingly, the inverse spinel NiFe2O4 compound is found to exhibit a ferrimagnetic structure. The ground state structural lattice parameters and the interatomic distances of spinel NiFe2O4 compound are computed. Furthermore, band structure calculations demonstrate that NiFe2O4 compound exhibits large band gaps in both spin configurations with a large magnetic moment. Energetically, ferrite nickel favors the inverse spinel phase in which Fe and Ni cations in either octahedral or tetrahedral sites adopt the high-spin configuration. We found that the energy of the normal spinel is higher than that of the inverse spinel, confirming that inverse spinel is the most stable structure of the NiFe2O4 compound. The optical behavior of the NiFe2O4 compound is characterized by calculating the real and imaginary part of the dielectric function, the absorption coefficients, the refractive index, the optical conductivity and the energy loss. Optimizing structural, electronic, magnetic and optical properties of this novel compound is crucial for exploring and utilizing it for modern device applications.

Incremental substitution of Ni with Mn in NiFe2O4 to largely enhance its supercapacitance properties

By using a facile hydrothermal method, we synthesized Ni1−xMnxFe2O4 nanoparticles as supercapacitor electrode materials and studied how the incremental substitution of Ni with Mn would affect their structural, electronic, and electrochemical properties. X-ray diffractometry confirmed the single-phase spinel structure of the nanoparticles. Raman spectroscopy showed the conversion of the inverse structure of NiFe2O4 to the almost normal structure of MnFe2O4. Field-emission scanning electron microscopy showed the spherical shape of the obtained nanoparticles with a size in the range of 20–30 nm. Optical bandgaps were found to decrease as the content of Mn increased. Electrochemical characterizations of the samples indicated the excellent performance and the desirable cycling stability of the prepared nanoparticles for supercapacitors. In particular, the specific capacitance of the prepared Ni1−xMnxFe2O4 nanoparticles was found to increase as the content of Mn increased, reaching the highest specific capacitance of 1,221 F/g for MnFe2O4 nanoparticles at the current density of 0.5 A/g with the corresponding power density of 473.96 W/kg and the energy density of 88.16 Wh/kg. We also demonstrated the real-world application of the prepared MnFe2O4 nanoparticles. We performed also a DFT study to verify the changes in the geometrical and electronic properties that could affect the electrochemical performance.

Biosynthesis of NiFe2 O4 @Ag Nanocomposite and Assessment of Its Effect on Expression of norA Gene in Staphylococcus aureus.

Activity of norA efflux pump has been known as a resistance mechanism to antibiotics like ciprofloxacin in Staphylococcus aureus. This study was carried out to assess the effect of biosynthesized NiFe2 O4 @Ag nanocomposite on expression of norA gene in Staphylococcus aureus. In this experimental study, 30 clinical samples were collected from patients hospitalized at different hospitals in Guilan Province, Iran. Then, clinical isolates of S. aureus were identified by standard microbiological tests. Antimicrobial susceptibility tests of clinical and standard strains of S. aureus were done by disk diffusion method according to CLSI guideline. Fourier transform infrared spectroscopy (FT-IR) was used to analyze the various functional groups present in the biosynthesized NiFe2 O4 @Ag nanocomposite. This analysis confirmed the formation of alga proteins coated on magnetite nanocomposite. X-ray diffraction (XRD) verified the crystalline structure of NiFe2 O4 @Ag and the deposition of silver on the surface of NiFe2 O4 . Energy dispersive X-ray mapping (EDX-map) analysis confirmed the existence of Ag, Ni, Fe and O in the final product. Scanning electron microscopy (SEM) confirmed that the nanocomposites were spherical in shape and Transmission electron microscopy (TEM) results revealed that the NiFe2 O4 @Ag had the particle size about 100 nm. Antibacterial activity of NiFe2 O4 @Ag alone and combined with ciprofloxacin was evaluated using the disk assay method, and minimum inhibitory concentration (MIC) by broth dilution method. Afterwards, the expression of norA efflux pump gene with and without of NiFe2 O4 @Ag nanocomposite and ciprofloxacin was evaluated by Real-Time PCR. Real-Time PCR results demonstrated that the expression of norA gene in the strains exposed to both NiFe2 O4 @Ag nanocomposite (1/4 MIC) and ciprofloxacin (1/8 MIC) significantly reduced in comparison to untreated strains. This study reveals that, when NiFe2 O4 @Ag nanocomposite is combined with ciprofloxacin, the inhibitory effect of ciprofloxacin increases against growth of S. aureus. Therefore, NiFe2 O4 @Ag nanocomposite can be considered as an effective factor to decrease the growth of S. aureus along with ciprofloxacin.

Highly Active Ternary Nickel–Iron oxide as Bifunctional Catalyst for Electrochemical Water Splitting

AbstractThe development of noble metal free, robust catalyst is highly sought for commercialization of clean, renewable energy technology and to replace the fossil fuel‐based energy equipments. Herein, we report a highly efficient and stable ternary Nickel Iron oxide (NiFe2O4) electrocatalyst for bifunctional oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline medium. The as‐synthesized NiFe2O4 has been confirmed by techniques like FESEM, HR‐TEM, powder X‐ray diffraction (XRD), and X‐ray photoelectron spectra analysis. NiFe2O4 demonstrate nanoparticle morphology with an average size of ∼10 nm. The synthesized NiFe2O4 electrocatalyst exhibit superior electrocatalytic efficiency for OER, and achieves a current density of 10 mA cm−2 at an overpotential of 290 mV, with smaller Tafel slope of 42 mV/dec. A stable performance of OER is obtained at 10 mA cm−2 for more than 8 h. The electrocatalytic activity of NiFe2O4 is comparable with benchmark electrocatalyst IrO2/C. Similarly, NiFe2O4 also shows superior HER activity in 1 M KOH. The enhanced bi‐functional activity of NiFe2O4 is thought to be the synergy between the multicomponent structure of NiFe2O4, high surface area, and stability leading to high electrical conductivity.

New method to calculate Mössbauer recoilless f-factors in NiFe2O4. Magnetic, morphological and structural properties

Mössbauer spectroscopy has long been used to calculate the degree of inversion (λ) in ferrites. To perform this calculation in NiFe2O4, it is assumed that the recoilless f-factors ratio of the Fe3+ cations at octahedral [B] and tetrahedral (A) sites of the spinel structure, fFeB3+fFeA3+, is equal to 1 at very low temperatures and equal to 0.94 at room temperature (RT). However, these values were reported for ideal Fe3O4 but not for NiFe2O4, and the physical properties of both materials are very different. In this work, we use a simple method and propose equations for directly determining the fFeA3+ and fFeB3+ values at RT relative to the recoilless f-factor of standard metallic iron powder (fFe). NiFe2O4 was synthesized from a stoichiometric mixture of nickel oxide and hematite by combining milling processes and heat treatments. The sample was characterized using X-ray diffraction, Mössbauer spectroscopy, infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and magnetic measurements. The results of all the characterization techniques confirm the synthesis of NiFe2O4 and the formation of the spinel structure. The lattice parameter of the cubic unit cell of NiFe2O4 was calculated using a crystallographic model and the Rietveld refinement. By comparing the lattice parameters, it was possible to determine the degree of inversion (λ = 0.96) of the spinel structure of NiFe2O4, and it could be established that the sample obtained has a mixed spinel structure of the type Ni0.042+Fe0.963+ANi0.962+Fe1.043+BO42-. Finally, a value of fFeB3+fFeA3+ = 1.09 ± 0.01 was calculated for NiFe2O4 at RT.

Green synthesis and characterization of magnetic NiFe2O4@ZnO nanocomposite and its application for photocatalytic degradation of organic dyes

In this work, for the first time, magnetic NiFe2O4@ZnO nanocomposite was synthesized using tragacanth gel by the novel sol–gel method. NiFe2O4@ZnO magnetic nanocomposite was investigated using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). The NiFe2O4@ZnO MNCs exhibit ferromagnetic behavior at room temperature, with a saturation magnetization of 15.22 emu/g and a coercivity of 150 Oe. XRD results show that NiFe2O4@ZnO nanocomposite corresponds to the hexagonal wurtzite of ZnO and the spinel cubic structure of NiFe2O4. The present magnetic nanocomposite displays high photocatalytic activity for the removal of direct blue 129 dye and reactive blue 21 dye under irradiation with visible light. The results demonstrated that the catalyst can degrade ca. 98% of the direct blue 129 and ca. 96% of the reactive blue 21 dyes. The current nanocomposite can be separated from the reaction mixture using an external permanent magnet and its high performance saved even after recycling fifth times.

Characterization of NixFe3-xO4 dispersed particles obtained by the plasma method

ABSTRACTThe highly dispersed nickel ferrites NixFe3-xO4 (x = 0.25, 0.5, 0.75, 1.0, 1.5) were obtained by a two-step method involving coprecipitation and treatment with contact low-temperature nonequilibrium plasma (CNP). The synthesized nanoparticles were studied using an X-ray diffractometer, a scanning electron microscope and a vibrational magnetometer. X-ray diffraction confirmed the formation of nanoparticles of the single-phase spinel cubic structure of NiFe2O4 of different inversion degree. The morphology of the surface showed that the particles had a spherical shape with some agglomeration. The magnetic measurements showed that coercivity, anisotropy and saturation magnetization decreased with increasing nickel content.With an increase in nickel content, an anomalous increase in the lattice parameter associated with the formation of a mixed spinel was observed. The average crystallite size in the series varied from 30 to 50 nm.The results showed that the particle size, the deviation from the inverse spinel structure, and the magnetization of nickel ferrite samples increased inversely with the value of x.

Facile synthesis of mesoporous NiFe 2 O 4 /CNTs nanocomposite cathode material for high performance asymmetric pseudocapacitors

Abstract Morphology and synergistic effect of constituents are the two very important factors that greatly influence the physical, chemical and electrochemical properties of a composite material. In the present work, we report the enhanced electrochemical performance of mesoporous NiFe2O4 and multiwall carbon nanotubes (MWCNTs) nanocomposites synthesized via hexamethylene tetramine (HMT) assisted one-pot hydrothermal approach. The synthesized cubic phase spinel NiFe2O4 nanomaterial possesses high specific surface area (148 m2g−1) with narrow mesopore size distribution. The effect of MWCNTs addition on the electrochemical performance of nanocomposite has been probed thoroughly in a normal three electrode configuration using 2 M KOH electrolyte at room temperature. Experimental results show that the addition of mere 5 mg MWCNTs into fixed NiFe2O4 precursors amount enhances the specific capacitance up to 1291 F g−1 at 1 A g−1, which is the highest reported value for NiFe2O4 nanocomposites so far. NiFe2O4/CNT nanocomposite exhibits small relaxation time constant (1.5 ms), good rate capability and capacitance retention of 81% over 500 charge-discharge cycles. This excellent performance can be assigned to high surface area, mesoporous structure of NiFe2O4 and conducting network formed by MWCNTs in the composite. Further, to evaluate the device performance of the composite, an asymmetric pseudocapacitor has been designed using NiFe2O4/CNT nanocomposite as a positive and N-doped graphene as a negative electrode material, respectively. Our designed asymmetric pseudocapacitor gives maximum energy density of 23 W h kg−1 at power density of 872 W kg−1. These promising results assert the potential of synthesized nanocomposite in the development of efficient practical high-capacitive energy storage devices.