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Spinel ferrite compounds continue to receive a lot of attention due to their unique properties. Among the numerous synthesis routes existing, the solid-state method was applied for the production of nickel ferrite, by introducing the use of a quartz vial. A mixture of nickel oxide (NiO) and hematite (Fe2O3) was ground and vacuum-sealed in the vial and different thermal treatment programs were tested. The resulting particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. For temperatures, below 1000 °C, the solid-state reaction is not complete as nickel oxide (NiO) and hematite (Fe2O3) are still present. The reaction time is a decisive parameter for the morphology of the particles obtained. If, for different reaction times, the particle size distribution is always between 0.3 and 1.7 µm, a longer reaction time leads to the formation of dense, interconnected clusters of particles. Optimal parameters to synthesize a pure phase of spherical nickel ferrite were sought and found to be a reaction temperature of 1000 °C for 72 h.

Nickel ferrites have served as electrode materials in energy storage applications such as batteries and supercapacitors in comparison to other metal oxides, they have a higher theoretical capacitance range. Pristine metal oxides are poor candidates as electrode components in electrochemical applications because of their tendency to aggregate and their less specific surface areas. Herein, we reported wet impregnation method to incorporate Nickel Ferrite (NiFe 2 O 4 ) to multiwalled carbon nanotubes (MWCNTs) for improved electrochemical performance of nickel ferrites (NiFe 2 O 4 ). The synthesized materials attained good crystallinity confirmed by X-ray diffraction (XRD). NiFe 2 O 4 nanoparticle adhesions on multiwalled carbon nanotubes have been confirmed by scanning electron microscopy (SEM). UV-DRS was used to measure the bandgap for optical studies. Cyclic Voltammetry (CV), Galvanostatic Charge/Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) investigations for supercapacitor applications revealed that synthesized materials demonstrated good electrochemical potential, but MWCNTs supported NiFe 2 O 4 composite attained exceptionally high specific capacitance (CV: 830 F g −1 at 5 mV s −1 , GCD:343 F g −1 at current density of 0.1 A g −1 ) with capacitance retention of 98% at the current density of 0.8 A g −1 after 3500 stability cycles. Graphical abstract

Abstract In the present work, a nickel-ferrite/reduced-graphene-oxide composite was synthesized by a hydrothermal co-precipitation approach. The obtained materials were characterized by using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray microscopy (mapping energy dispersive X-Ray), adsorption/desorption isotherms of nitrogen, vibrating sample magnetometer, X-ray photoelectron microscopy, and Raman spectroscopy. The obtained composite with a large surface area consists of highly dispersed nickel-ferrite nanoparticles (7–10 nm) over reduced-graphene-oxide layers. In addition, this composite possesses high magnetization saturation with a soft magnetic property. A sensitive electrochemical sensor for the determination of clenbuterol was manufactured by modifying a glassy-carbon electrode with nickel ferrite/reduced graphene oxide composite film. The peak current measured with differential pulse voltammetry for clenbuterol solutions is linearly proportional to its concentration ranging from 0.99 to 18.03 µM with a limit of detection of 0.17 µM and a limit of quantification of 0.52 µM. Furthermore, the reproducibility, precision, and accuracy of the proposed method were also investigated. This proposed method was applied to detect clenbuterol in pig urine samples with satisfactory results.

This investigation involves the development and implementation of NiFe 2 O 4 /g-C 3 N 4 (NFCN) heterogeneous structures for the photocatalytic elimination of crystal violet (CV) using sol-gel assisted ultrasonication method. The synthesized sample was characterized by XRD, UV–vis spectroscopy, FTIR, HR-SEM, EDX, and XPS. An effective combination of pure nickel ferrite (NF), g-C 3 N 4 (CN), and their composite NFCN with minimal Fe 2 O 3 phases was verified by XRD analysis. Optical studies revealed that the NFCN composite’s outermost region is red shifted towards the visible light range associated with pure NF, which proved highly beneficial for photocatalytic applications. FTIR spectra confirmed that the nanocomposite exhibits the absorbing bands of both CN and NF. According to HR-SEM, the NF nanoparticles have been embedded onto the CN surface, which indicates the creation of NF–CN heterogeneous structures. CV was degraded by the analysed nanocomposite NFCN (30 mg/litre) in 180 min, at a rate of 65%. This result indicated that h + , ∙OH, and ∙O 2 − play a role in the breakdown of dyes. The primary objective of this investigation is to get more insight into the process of creating beneficial photocatalysts for the breakdown of naturally occurring contaminants. Graphical Abstract

Nickel ferrite (NiFe₂O₄) nanoparticles have gained significant attention for their magnetic, optical, and photocatalytic properties, ideal for environmental and energy applications. This study presents a green, sustainable, and cost-effective method for synthesizing NiFe₂O₄ nanoparticles via a honey-mediated combustion technique, where the natural sugars and organic compounds in honey act as fuel and stabilizing agents. The NiFe₂O₄ nanoparticles were characterized using XRD, FTIR, DRS-UV and FE-SEM. XRD confirmed a cubic spinel structure with a lattice constant of 8.3554 Å and an average crystallite size of 3-5 nm, further analyzed using Scherrer, Modified Scherrer, and Williamson - Hall methods. FTIR demonstrated the characteristic ferrite functional groups, while DRS-UV revealed an optical band gap of 2.02 eV. SEM images showed predominantly spherical nanoparticles with sizes ranging from 10 to 20 nm. Photocatalytic performance was evaluated for Crystal Violet dye under UV light, demonstrating effective degradation of 75.5%. The influence of pH, dye concentration, and contact time was investigated, along with catalyst reusability. Addition of AgNO 3 enhanced the degradation efficiency to 88.58%. However, the catalyst showed limited activity against the anionic dye Alizarin Red S, with only 22.3% degradation. These honey-synthesized NiFe₂O₄ nanoparticles show strong potential as eco-friendly photocatalysts for organic dye removal.

A promising nickel ferrite (NiFe 2 O 4 ) NPs with excellent magnetic characteristics was synthesized using an aqueous-based reflux approach that eliminates the need for calcination temperature. The magnetic nanoparticles obtained were analysed using X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM). The analysis showed that synthesized nickel ferrite had a spherical shape with an average size ranging from 18 to 29 nm. The synthesized nickel ferrite is utilized for the removal of hexavalent chromium (Cr (VI)) and pentavalent arsenic (As (V)) ions from aqueous solution through adsorption method. The removal of Cr (VI) ions achieved a maximum efficiency of 65% after 120 minutes at a pH of 5, with a ferrite dose of 2 g/L and a concentration of Cr (VI) ions of 25 mg/L. while the removal of As (V) at a pH of 5, with a dose of 1 g/L of ferrite and an initial concentration of 25 mg/L of As (V) ions was 77% after 120 minutes. In addition, the data obtained from the isotherms of Langmuir (R 2  = 0.99, 0.98), Freundlich (R 2  = 0.86, 0.97) and Temkin (R 2  = 0.83, 0.97). The adsorption of Cr (VI) ions is governed by a pseudo first-order kinetics process, whereas the adsorption of As (V) ions is governed by a pseudo second-order kinetics reaction. After five adsorption–desorption cycles at the same optimal operating condition, Cr (VI) and As (V) removal efficiency dropped from 65%, 77% to 25%, 30%, respectively.

The accurate and precise monitoring of epirubicin (EPR), one of the most widely used anticancer drugs, is significant for human and environmental health. In this context, we developed a highly sensitive electrochemical electrode for EPR detection based on nickel ferrite decorated with gold nanoparticles (Au@NiFe2O4) on the screen-printed electrode (SPE). Various spectral characteristic methods such as Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), energy-dispersive X-ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS) were used to investigate the surface morphology and structure of the synthesized Au@NiFe2O4 nanocomposite. The novel decorated electrode exhibited a high electrocatalytic activity toward the electrooxidation of EPR, and a nanomolar limit of detection (5.3 nM) was estimated using differential pulse voltammetry (DPV) with linear concentration ranges from 0.01 to 0.7 and 0.7 to 3.6 µM. The stability, selectivity, repeatability reproducibility and reusability, with a very low electrode response detection limit, make it very appropriate for determining trace amounts of EPR in pharmaceutical and clinical preparations.

Low volumetric energy density is a bottleneck for the application of lithium-sulfur (Li-S) battery. The low-density sulfur cooperated with the light-weight carbon substrate realizes electrochemical cycle stability, but leads to worse volumetric energy density. Here, nickel ferrite (NiFe2O4)nanofibers as novel substrate for sulfur not only anchor lithium polysulfides to enhance the cycle stability of sulfur cathode, but also contribute to the high volumetric capacity of the S/nickel ferrite composite. Specifically, the S/nickel ferrite composite presents an initial volumetric capacity of 1,281.7 mA h cm−3-composite at 0.1 C rate, 1.9 times higher than that of S/carbon nanotubes, due to the high tap density of the S/nickel ferrite composite.

Nickel ferrite nanoparticles of very small size were prepared by sol-gel combustion and co-precipitation techniques. At the same annealing temperature sol-gel derived particles had bigger crystallite size. In both methods, crystallite size of the particles increased with annealing temperature. Sol-gel derived nickel ferrite particles were found to be of almost spherical shape and moderate particle size with a narrow size distribution; while co-precipitation derived particles had irregular shape and very small particle size with a wide size distribution. Nickel ferrite particles produced by sol-gel method exhibited more purity. Sol-gel synthesized nanoparticles were found to be of high saturation magnetization and hysteresis. Co-precipitation derived nickel ferrite particles, annealed at 400°C exhibited superparamagnetic nature with small saturation magnetization. Saturation magnetization increased with annealing temperature in both the methods. At the annealing temperature of 600°C, co-precipitation derived particles also became ferrimagnetic.

In the present work, Nickel ferrite and graphene nanocomposite has been synthesized and investigated as flexible electrodes for supercapacitor application in an aqueous electrolyte with sodium sulfate (Na 2 SO 4 ). The structural properties of the as-prepared nanocomposite electrode were analyzed by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy was used to study the surface morphology and particles size in the nanocomposite. Elemental analysis of the electrode was performed using Energy dispersive spectroscopy. Supercapacitor performance of the nickel ferrite/graphene nanocomposite was evaluated using cyclic voltammetry. We have observed that specific capacitance depends significantly on the charging/discharging voltage window of the device. A maximum specific capacitance of 22 mF/cm 2 (73 F/gm) was achieved between voltage range of − 0.5 to + 0.5 V. Nanocomposite electrodes showed the power density in the range of 200–900 W/kg.