Nanostructured ZnFe2O4: An Exotic Energy Material

Waxberry-like hydrophilic Co-doped ZnFe2O4 as bifunctional electrocatalysts for water splitting

Water splitting is a promising technique for clean hydrogen production. To improve the sluggish hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the development of efficient bifunctional electrocatalysts for both HER and OER is urgent to approach the scale-up applications of water splitting. Nowadays transition metal oxides (TMOs) are considered as the promising electrocatalysts due to their low cost, structural flexibility and stability, however, their electrocatalytic activities are eager to be improved. Here, we synthesized waxberry-like hydrophilic Co-doped ZnFe2O4 electrocatalysts as bifunctional electrocatalysts for water splitting. Due to the enhanced active sites by electronic structure tuning and modified super-hydrophilic characteristics, the spinel ZFO-Co0.5 electrocatalyst exhibits excellent catalytic activities for both OER and HER. It exhibits a remarkable low OER overpotential of 220 mV at a current density of 10 mA cm-2 and a Tafel slope of 28.2 mV dec-1. Meanwhile, it achieves a low overpotential of 73 mV at a current density of 10 mA cm-2 with the Tafel slope of 87 mV dec-1 for HER. In addition, for water electrolysis device, the electrocatalytic performance of ZFO-Co0.5||ZFO-Co0.5 surpasses that of commercial IrO2||Pt/C. Our work reveals that the hydrophilic morphology regulation combined with metallic doping strategy is a facile and effective approach to synthesize spinel TMOs as excellent bifunctional electrocatalyst for water splitting.

Tuning the Magnetic Behavior of Zinc Ferrite via Cobalt Substitution: A Structural Analysis

Cobalt-doped zinc ferrite is a contemporary material with significant structural and magnetic characteristics. Our study explores the magnetic properties of cobalt-substituted zinc ferrite (ZnxCo1-xFe2O4), synthesized via a simple sol-gel method. By varying the cobalt ratio from 0 to 0.5, we found that zinc substitution impacts both the magnetization and lattice parameters. FTIR analysis suggested the presence of functional groups, particularly depicting an M-O stretching band, within octahedral and tetrahedral clusters. X-ray diffraction analysis confirmed the phase purity and cubic structure. The synthesized materials exhibited an average particle size of 24-75 nm. Scanning electron microscopy revealed the morphological properties, confirming the formation of truncated octahedral particles. In order to determine the stability, mass loss (%), and thermal behavior, a thermal analysis (thermogravimetric analysis (TGA)/differential thermal analysis (DTA)) was performed. The magnetic properties of the synthesized ferrites were confirmed via a vibrating sample magnetometer (VSM). Finally, the highest saturated magnetization and lowest coercivity values were observed with higher concentrations of the cobalt dopant substituting zinc. The synthesized nanomaterials have good stability as compared to other such materials and can be used for magnetization in the near future.

Ceramics and Nanostructures for Energy Harvesting and Storage

In recent years, the worldwide research in the field of energy harvesting and storage has focused on the development of clean and sustainable methods that can respond to the rising energy demands of humankind [...].

Investigations of Structural, Magnetic, and Electrochemical Properties of NiFe2O4 Nanoparticles as Electrode Materials for Supercapacitor Applications

Magnetic nanoparticles of NiFe₂O₄ were successfully prepared by utilizing the sol-gel techniques. The prepared samples were investigated through various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), dielectric spectroscopy, DC magnetization and electrochemical measurements. XRD data analysed using Rietveld refinement procedure inferred that NiFe₂O₄ nanoparticles displayed a single-phase nature with face-centred cubic crystallinity with space group Fd-3m. Average crystallite size estimated using the XRD patterns was observed to be ~10 nm. The ring pattern observed in the selected area electron diffraction pattern (SAED) also confirmed the single-phase formation in NiFe₂O₄ nanoparticles. TEM micrographs confirmed the uniformly distributed nanoparticles with spherical shape and an average particle size of 9.7 nm. Raman spectroscopy showed characteristic bands corresponding to NiFe₂O₄ with a shift of the A_1g mode, which may be due to possible development of oxygen vacancies. Dielectric constant, measured at different temperatures, increased with temperature and decreased with increase in frequency at all temperatures. The Havrilliak-Negami model used to study the dielectric spectroscopy indicated that a NiFe₂O₄ nanoparticles display non-Debye type relaxation. Jonscher's power law was utilized for the calculation of the exponent and DC conductivity. The exponent values clearly demonstrated the non-ohmic behaviour of NiFe₂O₄ nanoparticles. The dielectric constant of the nanoparticles was found to be >300, showing a normal dispersive behaviour. AC conductivity showed an increase with the rise in temperature with the highest value of 3.4 × 10^-9 S/cm at 323 K. The M-H curves revealed the ferromagnetic behaviour of a NiFe₂O₄ nanoparticle. The ZFC and FC studies suggested a blocking temperature of ~64 K. The saturation of magnetization determined using the law of approach to saturation was ~61.4 emu/g at 10 K, corresponding to the magnetic anisotropy ~2.9 × 10⁴ erg/cm³. Electrochemical studies showed that a specific capacitance of ~600 F g^-1 was observed from the cyclic voltammetry and galvanostatic charge-discharge, which suggested its utilization as a potential electrode for supercapacitor applications.

Establishment of a novel system for photothermal removal of ampicillin under near-infrared irradiation: Persulfate activation, mechanism, pathways and bio-toxicology

One of the most effective ways to address the problems of low solar spectrum utilization in photocatalysis and the high cost of persulfate activation technology is to create a cost-effective synergistic photothermal persulfate system. In this work, a brand-new composite catalyst called ZnFe₂O₄/Fe₃O₄@MWCNTs (ZFC) was developed to activate PDS (K₂S₂O₈) from the aforementioned basis. ZFC's surface temperature could unbelievably reach 120.6 °C in 150 s together with the degrading synergistic system solution temperature could reach 48 °C under near-infrared light (NIR) in 30 min, thus accelerating the ZFC/PDS decolorization rate for reactive blue KN-R (150 mg/L) to 95% in 60 min. Furthermore, the ZFC's ferromagnetism bore it with good cycling performance, allowing it to maintain an 85% decolorization rate even after 5 cycles with OH·, SO₄^-·, ¹O₂, and O₂^-· dominating the degrading process. In the meantime, the DFT calculations of the kinetic constants for the entire process of S₂O₈^2- adsorption on Fe₃O₄ in dye degradation solution were in agreement with the outcomes of the experimental pseudo-first-order kinetic fitting. By analyzing the particular degradation route of ampicillin (50 mg/L) and the possible environmental impact of the intermediate using LC-MS and the toxicological analysis software (T.E.S.T.), respectively, it was shown that this system might function as an environmentally friendly method for removing antibiotics. This work may provide some productive research lines for the creation of a photothermal persulfate synergistic system and suggest fresh approaches to water treatment technology.

Investigation of the Structural and Optical Properties of Zinc Ferrite Nanoparticles Synthesized via a Green Route

We report herein the synthesis of ZnFe₂O₄ (ZF) nanoparticles via a simple and eco-friendly green route using lemon juice as a reducing agent and fuel. The effect of different calcination temperatures on the particle size and bandgap of grown ZF nanoparticles was investigated. The structural, morphological and optical properties of the synthesized nanoparticles were evaluated using synchrotron x-ray diffraction (S-XRD), field emission scanning electron microscopy (FE-SEM) and UV-visible diffuse reflectance spectroscopy (UV-Vis-DRS), respectively. S-XRD confirmed a spinel F-d3m phase in all four samples calcined at 350°C, 550°C, 750°C and 1000°C. The crystallite size calculated from the Debye-Scherrer equation showed an increase from 14 nm to 20 nm with the increase in calcination temperature. Williamson-Hall (W-H) analysis revealed an increase in the particle size from 16 nm to 21 nm and a decrease in the lattice microstrain from 0.913 × 10^-3 to 0.154 × 10^-4 with the increase in calcination temperature. The optical bandgap of the ZF nanoparticles obtained from UV-Vis-DRS decreased from 2.265 eV to 2.225 eV with the increase in calcination temperature. The ZF nanoparticles with tunable particle size, lattice microstrain and optical bandgap have potential application in ferrofluid, electromagnetic shielding, photocatalysis, hyperthermia, dye degradation and other areas.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11664-022-09813-2.

Ferrimagnetic Clusters as the Origin of Anomalous Curie-Weiss Behavior in ZnFe2O4 Antiferromagnetic Susceptibility

Different studies carried out in the last three decades on the magnetic susceptibility of the spinel ZnFe₂O₄ ferrite have revealed the positive character of its Curie–Weiss temperature, contradicting its observed antiferromagnetic behavior which is characterized by a well-defined susceptibility peak centered around the Neel temperature (10 K). Some approaches based on ab initio calculations and mixture of interactions have been attempted to explain this anomaly. This work shows how for very low values of the inversion parameter, the small percentage of Fe atoms located in tetrahedral sites gives rise to the appearance of ferrimagnetic clusters around them. Superparamagnetism of these clusters is the main cause of the anomalous Curie–Weiss behavior. This finding is supported experimentally from the thermal dependence of the inverse susceptibility and its evolution with the degree of inversion.

Unveiling the Hidden Entropy in ZnFe2O4

The antiferromagnetic (AFM) transition of the normal ZnFe₂O₄ has been intensively investigated with results showing a lack of long-range order, spin frustrations, and a “hidden” entropy in the calorimetric properties for inversion degrees δ ≈ 0 or δ = 0. As δ drastically impacts the magnetic properties, it is logical to question how a δ value slightly different from zero can affect the magnetic properties. In this work, (Zn_1-δFe_δ)[Zn_δFe_2-δ]O₄ with δ = 0.05 and δ = 0.27 have been investigated with calorimetry at different applied fields. It is shown that a δ value as small as 0.05 may affect 40% of the unit cells, which become locally ferrimagnetic (FiM) and coexists with AFM and spin disordered regions. The spin disorder disappears under an applied field of 1 T. Mossbauer spectroscopy confirms the presence of a volume fraction with a low hyperfine field that can be ascribed to these spin disordered regions. The volume fractions of the three magnetic phases estimated from entropy and hyperfine measurements are roughly coincident and correspond to approximately 1/3 for each of them. The “hidden” entropy is the zero point entropy different from 0. Consequently, the so-called “hidden” entropy can be ascribed to the frustrations of the spins at the interphase between the AFM-FiM phases due to having δ ≈ 0 instead of ideal δ = 0.