Search Results (260)

M-type hexaferrites are widely used in magnetic applications, and tailoring their properties via aliovalent substitution requires a detailed understanding of charge compensation and cation distribution. In this work, Mg²⁺/M⁴⁺ (M = Zr, Hf) co-substituted BaFe₁₂O₁₉ was synthesized via Na₂CO₃ flux and comprehensively characterized by wavelength-dispersive X-ray spectroscopy, powder and single-crystal X-ray diffraction, Rietveld refinement, X-ray absorption near-edge structure, and magnetic measurements. Increasing substitution levels x, y in BaFe_12−x−yMg_xM_yO₁₉ result in increasing lattice parameters and decreasing the room-temperature magnetic parameters saturation magnetization, remanence, and coercivity, while remanence and coercivity increase at low temperatures. Secondary phases form for nominal substitution ≥ 1. Zr⁴⁺ and Hf⁴⁺ preferentially occupy the 4f₂ site, whereas Mg²⁺ is distributed over multiple sites, as indicated by polyhedral volume analysis. Wavelength-dispersive X-ray spectroscopy confirms homogeneous elemental distribution within individual crystals but reveals significant variation in substitution levels within batches. The maximum degree of substitution for the tetravalent metals was y ≈ 1.2–1.7, with lower Mg incorporation of x ≈ 0.9–1.1. Charge compensation was found to be partially achieved via vacancy formation, while minor Fe²⁺ contributions cannot be excluded. Full article

Nickel ferrite (NiFe₂O₄) is one of the most studied inverse-spinel ferrites because it combines moderate saturation magnetization, comparatively high electrical resistivity, chemical stability, and broad synthesis flexibility. Yet the literature shows that the measured structure and magnetism of NiFe₂O₄ are not intrinsic constants; they evolve strongly with dimensionality, size, thickness, strain state, cation distribution, surface spin disorder, and synthesis pathway. This review develops a unified theoretical and literature-based interpretation of how dimensionality reshapes the structural and magnetic behavior of NiFe₂O₄ across bulk ceramics, nanoparticles, one-dimensional nanostructures, polycrystalline thin films, and ultrathin epitaxial films. The review is anchored in the two uploaded nickel ferrite attachments and expanded using internet-sourced journal literature on spinel inversion, surface effects, mechanochemical synthesis, sputtered and pulsed laser deposited thin films, and epitaxial ultrathin-film anomalies. The central novelty of this article is the formulation of a dimensionality-dependent framework in which the observed magnetic response is governed by a competition among three coupled factors: (i) the cation-distribution function, which controls the A–B superexchange balance and therefore the net ferrimagnetic moment; (ii) the microstructural coherence function, which measures how crystallinity, strain, defects, and anti-phase boundaries preserve or degrade exchange continuity; and (iii) the surface/interface spin-order parameter, which quantifies the loss or reconfiguration of magnetic order at free surfaces and buried interfaces. Within this framework, bulk NiFe₂O₄ behaves as a near-equilibrium inverse spinel with relatively stable magnetization, whereas nanoscale NiFe₂O₄ experiences strong spin canting and finite-size suppression due to the growing fraction of disordered surface spins. Thin films introduce a distinct regime in which strain, texture, anti-phase boundaries, substrate mismatch, and growth kinetics determine both anisotropy and magnetization. In ultrathin epitaxial films, off-equilibrium cation redistribution and interface-controlled electronic reconstruction may even generate magnetization values far above bulk expectations. The review also compares major synthesis routes—solid-state reaction, sol–gel, co-precipitation, hydrothermal growth, reactive milling, combustion, pulsed laser deposition, and radio-frequency sputtering—and explains why each route biases the final dimensionality-dependent properties differently. A set of word-style equations is provided to formalize spinel inversion, finite-size suppression, anisotropy scaling, coercivity trends, and superparamagnetic crossover. Beyond summarizing the field, the review proposes a regime map linking dimensionality to characteristic structural defects and magnetic signatures, and it identifies unresolved questions concerning the true origin of enhanced magnetization in ultrathin NiFe₂O₄, the interplay between anti-phase boundaries and strain, and the distinction between intrinsic inversion changes and extrinsic substrate artifacts. The resulting article offers a submission-ready, originality-focused review that positions dimensionality as the master variable governing structure–magnetism correlations in nickel ferrite. Full article

Microwave-assisted polymerization is a transformative technique for synthesizing conductive polymers such as polypyrrole (PPy). Unlike conventional chemical or electrochemical methods that rely on external heating or electrode mediated oxidation, microwave irradiation induces volumetric and selective heating through dipole orientation and ionic conduction, which leads to faster reaction kinetics, improved uniformity and higher yields. This review highlights the fundamental mechanisms governing microwave polymer interactions, compares conventional and microwave-assisted polymerization routes and traces the evolution of pyrrole polymerization. Special emphasis is placed on the microwave-synthesized PPy composites and their superior electrochemical performance in energy storage, sensing and biomedical applications. Case studies of graphene/PPy, PPy–metal oxide (e.g., SnO₂@PPy nanotubes) and magnetic ferrite hybrids (e.g., BaFe₁₂O₁₉/PPy) nanocomposites demonstrate enhanced electrical conductivity, specific capacitance and more uniform nanostructures. Beyond energy storage, microwave polymerization techniques have led to the development of PPy composites that are used for sensing, antimicrobial activity and photothermal cancer therapy, highlighting the technique’s versatility across biomedical sciences. Reactor scale up, temperature and pressure control under sealed conditions, reproducibility and deeper mechanism understanding of how microwave radiation influences nucleation, chain growth, doping and charge transport were identified as the outstanding challenges that must be addressed to transform microwave-assisted synthesis from pilot to industrial scale. Overall, microwave-assisted polymerization is on its way to becoming a mainstream, energy efficient method for manufacturing high performance polymer composite materials. Full article

Imidacloprid (IMI), the commonly used neonicotinoid pesticide, has emerged as a persistent aquatic contaminant due to its high solubility and stability, posing risks to non-target organisms and ecosystem health. In this study, a MnZnFe₂O₄/SrWO₄ ferrite–tungstate nanocomposite was synthesized via a hydrothermal process and its ability to photocatalytically degrade IMI under UV light was assessed. SEM, XRD and FT-IR were used to characterize the composite to confirm its structural and morphological features. Photocatalytic performance was systematically investigated by examining the effects of operational factors, including initial pollutant concentration, catalyst dosage, pH, and irradiation time. The MnZnFe₂O₄/SrWO₄ nanocomposite exhibited significantly enhanced activity, achieving up to 87% degradation of IMI within 30 min at pH 9, outperforming individual components (SrWO₄: 37%; MnZnFe₂O₄: 75%) under identical conditions. The degradation kinetics followed a pseudo-first-order model consistent with the Langmuir–Hinshelwood mechanism. Effective interfacial charge transfer between the ferrite and tungstate phases, which suppresses electron-hole recombination and increases the production of reactive species, is responsible for the enhanced performance. Furthermore, the composite demonstrated good stability and reusability across several cycles, indicating its practical applicability. Overall, the results demonstrate the potential of MnZnFe₂O₄/SrWO₄ nanocomposites as efficient and sustainable photocatalysts for removing imidacloprid and similar organic contaminants from aqueous systems. Full article

Perovskite-type oxides are among the most promising cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their mixed ionic–electronic conductivity and compositional flexibility. Many high-performance cathodes rely on Sr substitution at the A-site, often associated with surface segregation and long-term degradation. In this work, we explore an alternative strategy based on defect engineering and phase interactions in Sr-free composites. Perovskite-fluorite composites based on LaFe_0.8Co_0.2O₃ were synthesized through a one-pot route designed to promote the formation of a perovskite phase and a limited amount of fluorite-type ceria. This approach allows the introduction of small fractions of Ce into the perovskite lattice, favoring the cooperative coexistence with La-doped CeO₂. Structural, microstructural and spectroscopic characterization indicates that Ce influences the crystallization pathway and composite defect chemistry. Variations in lattice parameters and Raman features suggest modifications of perovskite structure consistent with defect formation and lattice distortion. Reduction properties and electrical conductivity measurements indicate that Ce incorporation in the perovskite and oxide interaction affect charge transport and oxygen mobility. The electrochemical results demonstrate that the optimal trade-off between activation energy (Ea) and polarization resistance (Rp) is achieved for the sample, with a nominal cerium content, Ce/(La + Ce) of 0.16. Moreover, the electrochemical properties are found to correlate with the nominal cerium content, which regulates defect chemistry and the resulting composite composition. Overall, results suggest that the one-pot synthesis promotes beneficial interactions between the perovskite and ceria phases, allowing the development of Sr-free ferrite-based materials with enhanced functional properties, minimizing the amount of ceria in the composite. Full article

The quest for sustainable hydrogen production via water electrolysis requires the development of efficient, non-precious-metal electrocatalysts. This work presents the sonochemical-assisted synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles as a sustainable alternative to noble metal catalysts. Nanoparticles were synthesized by varying the ultrasonic tip power (40%, 50%, and 60%) to investigate the this effect on their structural and electrochemical properties. Comprehensive characterization using X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy confirmed the formation of phase-pure nanoscale spinel structures, with crystallite size increasing from 11.28 to 21.79 nm as the sonication power increased. Electrochemical analysis revealed that the sample synthesized at 60% power (CoFe₂O₄-60) exhibited the highest electrocatalytic performance among the synthesized samples for both the hydrogen and oxygen evolution reactions (HER and OER) in alkaline media. This superior performance is attributed to its largest electrochemically active surface area (ECSA = 6.95 cm²) and lowest overpotentials (${\eta }_{10}=-360$ mV for HER and 410 mV for OER). Despite the larger crystallite size, high-power sonication induced higher density of surface defects and roughness, as evidenced by Mössbauer spectroscopy and electrochemical capacitance measurements. Furthermore, all samples exhibited excellent operational stability during 120 h of chronopotentiometric testing. Moreover, the efficiency of the electrolizer for water splitting was calculated to be 64.7%. These findings demonstrate that ultrasonic power tuning can influence the structural and electrochemical properties of CoFe₂O₄ nanoparticles, contributing to improving durability and bifunctional efficient electrocatalytic activity for alkaline water electrolysis. Full article

Halloysite nanotubes (HNTs), composed of an aluminosilicate framework, are naturally abundant, biocompatible, and sustainable clay minerals with a tubular morphology and tunable surface chemistry, making them attractive platforms for targeted, multifunctional drug delivery systems. In this study, a zinc ferrite integrated halloysite nanocomposite (ZnFe₂O₄/HNT) was developed via a one-pot synthesis approach for sustained release of cisplatin (Cp), aiming to reduce systemic toxicity and enhance cell-specific activity. The nanocomposites were further functionalized by integrating Cp (Cp: ZnFe₂O₄/HNT ratio 0.05) and folic acid (ZnFe₂O₄/HNT/Cp: FA ratio 0.05), followed by PEGylation (0.17 µL/mg of ZnFe₂O₄/HNT/Cp/FA/PEG). The structural and surface characteristics, phase, interfacial interactions (FA and Cp), and colloidal stability of nanoformulations were systematically investigated using powder X-ray diffraction analysis (XRD), Fourier transformed infrared (FT-IR) spectroscopy, zeta potential analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), and diffuse reflectance UV–visible (DRS-UV-Vis) spectroscopy. The results confirmed that ZnFe₂O₄ integration preserved the clay’s tubular framework while inducing nanocrystallization of both ferrite and cisplatin, indicating molecular dispersion within the clay matrix. Functionalization with FA (ZnFe₂O₄/HNT/Cp/FA) promoted amide bond linkage, modulated Cp-FA interactions, and significantly enhanced cumulative Cp release compared to the non-functionalized system ZnFe₂O₄/HNT/Cp (10.3% at 72 h vs. 34.4% at 72 h) under tumor acidic conditions (pH 6.6). PEGylation maintained the controlled release profile while improving dispersion stability. In vitro cytotoxicity studies revealed that FA-conjugated nanocomposites exhibited enhanced, time-dependent anticancer activity against HeLa cervical cancer cells, with reduced toxicity toward normal fibroblasts, indicating preferential cellular uptake via folate receptor-mediated mechanism. Overall, this work demonstrates that FA-functionalized ZnFe₂O₄/HNT nanocomposite provides an effective clay-based platform for modulating Cp release and enhancing folate receptor protein-mediated targeted therapy for cervical cancer. Full article

CoFe₂O₄ nanoparticles were prepared using a hydrothermal method. All the studied samples were single-phase and were crystallized in a cubic Fd-3m structure. XRD and TEM analyses revealed that the particles had average sizes between 5 and 22 nm. It has been shown that, by using the PVP of different molecular masses, trends of growth and crystallization can be established, obtaining elongated 40 k, cubical 58 k, and rhomboidal 360 kg/mol nanoparticles. While using Ethylene glycol as solvent, the formation of separated “raspberry”-like nanostructures was revealed. The saturation magnetizations are somewhat smaller compared with crystalline CoFe₂O₄ saturation magnetization, but are high enough to have possible biomedical applications. FC and ZFC measurements show that the blocking temperature was around 100 K for the CF5 sample and around 20 K for the FC6 sample. The calculated anisotropy constants were between 7 and 10 kJ/m³, being close to previously reported values. The calculated blocking temperatures are in good agreement with experimental ones. The M_r/Ms ratio at room temperature was lower than 0.5, confirming the predominance of magnetostatic interactions. This paper serves as a good starting point for researchers seeking to synthesize a CoFe₂O₄ system with a desired size and growth tendency at the nanometer scale. Full article

Bismuth ferrite (BiFeO₃) is a promising material for developing the next generation of multifunctional electronic devices. However, the production of high-quality BiFeO₃ thin films is compromised by the tendency for structural and electronic defects to form during synthesis, which degrades their functional properties. In this work, BiFeO₃ thin films were prepared by chemical solution deposition to determine optimal conditions for minimizing oxygen vacancies and to evaluate the impact of these point defects on their physical properties. The films were pyrolyzed at 300 °C for 60 min and 360 °C for 10 min, and crystallized in air and in an O₂ atmosphere, at 600 °C and 640 °C for 40 min. High oxygen vacancies were observed in films prepared at low pyrolysis temperatures and crystallized in air, whereas oxygen vacancies were minimized in the film pyrolyzed and crystallized at high temperatures in an O₂ atmosphere. The oxygen vacancies markedly affected the films’ physical properties, leading to increased dielectric loss, dielectric dispersion, dc conductivity, and leakage current, with consequent degradation of photovoltaic and magnetic performance. These findings highlight the critical importance of controlling synthesis parameters to suppress oxygen vacancy formation and achieve high-quality BiFeO₃ thin films. Full article

As a ferrite material with excellent magnetic and dielectric properties, CoFe₂O₄ is in high demand for applications in areas such as wave absorption and magnetic storage. Effective regulation of its nanoscale morphology is central to improving application performance. Conventional synthesis methods often face challenges including poor particle dispersion and irregular morphology, which limit further optimization of material properties. In this study, a combined approach of microwave hydrothermal synthesis and annealing was employed to systematically investigate the effects of hydrothermal temperature, reaction time, and annealing parameters on the morphology and properties of CoFe₂O₄. The samples were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and other techniques. Experimental results show that process parameters exert a notable influence on the crystallinity, particle dispersibility, magnetic and wave-absorbing properties of CoFe₂O₄: the sample prepared by microwave hydrothermal treatment at 75 °C for 30 min exhibits relatively better wave-absorbing performance, with a minimum reflection loss of less than −30 dB and an effective absorption bandwidth covering 8~16 GHz; the sample treated at 100 °C for 15 min shows a more balanced magnetic performance, with the saturation magnetization approaching 60 emu/g. The quantitative structure–property relationships of pure-phase CoFe₂O₄ across microwave hydrothermal and post-annealing processes, and achieve stable, reproducible performance enhancements under optimized mild conditions. These results supplement key experimental data for the low-temperature preparation of CoFe₂O₄ and establish a practical, energy-efficient parameter framework for future structural design and process optimization of this important magnetic material. Full article

This paper investigates a ceramic material based on ferrite-doped zirconia intended for use as a solar absorber in systems designed for the conversion of solar energy into thermal energy. The experimental study details the synthesis procedure of the ferrite-doped zirconia ceramic and its structural, morphological, optical, and magnetic characterization using X-Ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy, electron paramagnetic resonance (EPR), and optical band gap energy determination. XRD analysis confirms the presence of the crystalline ferrite phase, which is responsible for the enhanced solar absorption properties. UV–Vis investigations reveal intense absorption bands across the ultraviolet, visible, and near-infrared regions, indicating high solar radiation absorptivity. These properties recommend the investigated ceramic as a promising solar receiver material for solar thermal power plants comparable to conventional materials such as carbides and nitrides. Full article

Traditional oxidative dehydrogenation of n-butene has typically required relatively high operating temperatures (400–500 °C), which has driven increasing interest in the development of catalysts capable of delivering high activity at lower temperatures. In this study, zinc ferrite (ZnFe₂O₄-ST) was successfully synthesized via hydrothermal hydrolysis of Zn–Fe oleate and demonstrated remarkable catalytic performance for the oxidative dehydrogenation of n-butene under mild conditions. At 300 °C, ZnFe₂O₄-ST achieved a conversion of 72.9% with 92.1% selectivity toward 1,3-butadiene, a result that, to the best of our knowledge, ranks among the best reported in the literature. By contrast, ZnFe₂O₄ prepared by conventional coprecipitation (17.2% conversion with 91.3% selectivity) and sol-gel (10.1% conversion with 86.4% selectivity) methods showed much lower activities, highlighting the critical influence of synthesis strategy on catalytic performance. To better understand the origin of these differences, a detailed structural and physicochemical characterization was undertaken using X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (H₂-TPR), temperature-programmed re-oxidation (TPRO), and NH₃-temperature-programmed desorption (NH₃-TPD). These analyses revealed that the as-synthesized ZnFe₂O₄-ST possessed a significantly smaller average particle size, a larger specific surface area, and superior reducibility compared with the other samples. These properties are believed to be the key factors underpinning its outstanding catalytic behavior and provide important insights into the design of efficient low-temperature catalysts for selective oxidative dehydrogenation. Full article

This study presents an in situ synthesis of a novel manganese ferrite/carbon (MF/C) composite material via a citrate sol–gel route followed by calcination in an inert argon (Ar) atmosphere. The structural and morphological and porosity properties were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), and N₂ gas physisorption analysis. Electrochemical evaluation of the MF/C in a 3 M KOH electrolyte in a three-electrode configuration showed a high specific capacity of 39.26 mAh g⁻¹ at 1 Ag⁻¹ and a rate capability of 69% at 5 Ag⁻¹ and an equivalent series resistance (ESR) of 0.798 Ω. Subsequently, an asymmetric hybrid supercapacitor device (MF/C//AC) was fabricated using MF/C as the positive electrode and human-derived activated carbon (AC) as the negative electrode. The assembled device exhibited remarkable performance, with a wide operating voltage window of 1.4 V, a high sweeping potential of 1 V s⁻¹, a specific capacity, energy, power and maximum power of 42.4 mAhg⁻¹, 16.35 Wh kg⁻¹, 1944 W kg⁻¹ and 236 kW kg⁻¹, respectively, and excellent capacitance retention of 92% after 15,000 charge–discharge cycles. The in situ preparation approach significantly reduced synthesis time and cost compared to conventional multi-step methods, as less equipment was required, while still achieving comparable or superior electrochemical performance to other supercapacitors in the literature. Full article

This review article provides a systematic analysis of synthesis methods, structural characteristics, and functional properties of spinel-structured ferrite nanoparticles (MFe₂O₄). The physicochemical principles, advantages, and limitations of various synthesis techniques—including co-precipitation, combustion, sol–gel, thermal decomposition, hydrothermal, solvothermal, microwave-assisted, sonochemical, electrochemical, and solid-state reaction methods—are comparatively discussed. The influence of synthesis parameters on crystal structure, morphology, and cation distribution between tetrahedral and octahedral sites, as well as on magnetic, dielectric, and optical properties, is critically analyzed. Furthermore, the capabilities of characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), Fourier-transform infrared spectroscopy (FTIR), FT-Raman spectroscopy, dielectric measurements, and magnetic measurements for investigating spinel ferrites are comprehensively summarized. Finally, the high potential of spinel ferrite nanoparticles for applications in electronics, microwave devices, water treatment, catalysis, sensors, and biomedical fields is highlighted. Full article

With increasing demands for controllable synthesis of nanomaterials, it has become particularly important to develop efficient and accurate methods for optimizing preparation processes. This study focuses on the nucleation and growth stages in the synthesis of ultra-small manganese ferrite nanoparticles, aiming to clarify the influence mechanisms of key parameters such as oleic acid dosage, precursor concentration, and aging temperature on the product size and properties and to optimize the preparation process accordingly. The probability-based multi-objective optimization method was adopted, using the above parameters as optimization variables to systematically design and screen the experimental conditions. The results show that this method can effectively achieve the optimization of multiple objectives in the preparation process, providing a reliable methodological framework for the controlled synthesis of ultra-small manganese ferrite nanoparticles. Full article