Search Results (249)

Novel biogenic cobalt ferrite nanoparticles were prepared biologically using Adansonia digitata L. (Baobab) Fruit Pulp Extract, assisted by a microwave heating method. The utilization of Adansonia digitata L. (Baobab) Fruit Pulp Extract assisted by microwave heating is considered an eco-friendly method that is environmentally sustainable and inexpensive in terms of energy consumption and large-scale production. Different techniques were used to characterize plant extract-mediated nanoparticles, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption–desorption analysis. The XRD analysis revealed single-phase crystalline structures with a mean size of 31.5 nm. In SEM and TEM studies, the nanoparticles took different morphologies, such as regular and spherical shapes. The bio-synthesized nanoparticles showed high removal efficiency as adsorbent components in MO removal, for example, of organic dye. The influences of different factors on the adsorption process, such as MO concentration, solution pH, and doses used, were tested based on the amount of adsorbent used. The kinetic and isotherm study results revealed that pseudo-second-order kinetics models and the Freundlich sorption isotherm model fit the adsorption process of MO on nano adsorbents well. Additionally, the antimicrobial assessment of CoFe₂O₄ NPs was tested against five species of human pathogenic bacteria, as well as one fungal species. The results show that CoFe₂O₄ NPs exhibit higher inhibition activity against the examined microorganisms. Full article

Efficient removal of tetracycline (TC) from antibiotic-contaminated wastewater remains a significant challenge. In this study, a nitrogen-doped carbon modified cobalt ferrite (C@CoFe₂O₄, CF) composite was synthesized via a one-step hydrothermal method, and its adsorption–catalysis dual-function performance was systematically evaluated. Structural characterization revealed that CoFe₂O₄ nanoparticles were locally encapsulated by an N-doped carbonaceous layer, providing a high specific surface area and abundant nitrogen-containing active sites. Under optimized conditions, the CF-3/PMS system achieved 93.44% TC removal within 45 min, while CF-3 exhibited a maximum adsorption capacity of 486.5 mg·g⁻¹. Radical quenching experiments suggested that singlet oxygen (¹O₂) and superoxide radicals (O₂•⁻) played major roles in TC oxidation, while sulfate radicals (SO₄•⁻) and hydroxyl radicals (HO•) also contributed, indicating the coexistence of radical and non-radical oxidation pathways. TC adsorption was driven by surface complexation, π–π electron donor–acceptor interactions, and hydrogen bonding. The enhanced TC removal performance may arise from the cooperative contributions of N-containing carbon sites, accessible Co/Fe-containing regions, and interfacial electronic interactions, which promote TC enrichment and PMS-mediated oxidation. This work provides a promising strategy for designing bifunctional materials for antibiotic wastewater treatment. Full article

This study focuses on the synthesis of Co_0.5Cu_0.5Fe₂O₄ mixed ferrites supported on nanoporous carbon materials. The carbon supports were derived from two mixtures: a mixture of spent motor oil and pine wood chips (designated as AC-A), and a mixture of spent motor oil and crushed coal obtained from the Chukurovo mine (designated as AC-B). Additionally, two types of carbon components—nanodiamond and graphene oxide—were used for the synthesis of nanosized ceria-based hybrid nanocomposites. The results revealed that the active phase deposited on the carbon supports consists of a complex mixture of finely dispersed ferrite nanoparticles as well as small CeO₂ crystallites in the case of hybrid nanocomposites. The dispersion and phase composition of the deposited copper–cobalt ferrites depends on the textural properties of the carbon supports. Among the investigated materials, the graphene oxide-modified composites exhibited the highest catalytic activity at 670 K, achieving a methanol conversion of 90%. Full article

Co–Mg–Fe oxide systems are promising candidates for thermally stable deep oxidation catalysts because they potentially combine redox-active cobalt and iron components with stabilizing magnesium-containing phases. In this work, phase formation in a Co–Mg–Fe oxide system obtained by thermal decomposition of nitrate precursors with a Co:Mg:Fe ratio of 1:1:1 was studied over a wide range of heat-treatment temperatures from 400 to 1300 °C. The samples were characterized by X-ray diffraction, Mössbauer spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy mapping, and temperature-programmed oxygen desorption. The results show that the system undergoes staged phase evolution. At 400 °C, α-Fe₂O₃, including Mg-modified hematite-like states, cobalt-containing spinel phases, and a rocksalt oxide phase, is formed. Starting from 550 °C, a mixed ferrite spinel phase appears and its content increases with temperature. The transition through 800–900 °C is accompanied by decomposition of cobalt-containing spinels, a sharp change in the inversion parameter of the mixed ferrite, and formation of a stable high-temperature combination of ferrite spinel and rocksalt oxide solid solution. Oxygen desorption is most pronounced for the low- and medium-temperature samples and decreases strongly after high-temperature treatment. The obtained results provide the basis for the design of thermally stable Co–Mg–Fe oxide catalysts for deep oxidation processes. Full article

The study investigates Co²⁺/M⁴⁺ (Sn, Zr, Hf)-substituted M-type barium ferrites to understand phase formation, structural evolution and magnetic behavior. Ferrites with the general composition BaFe_12−x−yCo_xM_yO₁₉ were synthesized via sodium carbonate flux and analyzed using powder and single-crystal X-ray diffraction, wavelength dispersive X-ray spectroscopy, X-ray absorption spectroscopy and magnetic measurements. Structural analysis showed increasing lattice parameters with increasing degree of substitution, confirming incorporation of the substituting tetravalent metals. Differing maximum substitution levels were determined for the different systems, with wavelength dispersive X-ray spectroscopy providing the most reliable compositional data. A slight excess of the tetravalent metals Sn⁴⁺, Zr⁴⁺ and Hf⁴⁺ relative to Co²⁺ was frequently observed. X-ray absorption spectroscopy and wavelength dispersive X-ray spectroscopy analyses indicated negligible Fe²⁺ formation and no clear trends for formation of vacancies. Site occupancy analysis assigned tetravalent cations primarily to the Fe(4) site (4f₂), with evidence that cobalt partially occupies the Fe(3) site (4f₁). Magnetic measurements revealed decreasing saturation magnetization, remanence and coercivity at room temperature with increasing substitution level, while low-temperature measurements showed enhanced remanence and coercivity. Full article

Cobalt ferrite (CoFe₂O₄) magnetostrictive ultrasonic elliptical vibration cutting (UEVC) tools have recently emerged as a low-cost, low-eddy-loss alternative to piezoelectric and rare-earth-driven cutting heads. The structural design and resonance characterisation of such a dual-bending CoFe₂O₄ UEVC tool was reported in our previous work. The present paper builds directly on that platform and addresses a different objective: to determine how the four primary process variables—feed rate, cutting speed, cutting depth, and inter-channel phase difference—should be set to obtain the best surface quality on a representative ductile metal. Using H62 brass as the workpiece and a single-crystal diamond tool with a 0.2 mm nose radius and 60° included angle, single-factor experiments are run on a custom 5-axis precision lathe, and surface roughness is mapped in both the cutting and the feed direction with a Keyence VK-X1000 confocal microscope (Keyence, Osaka, Japan). The speed ratio K = Vc/(2πfA) is computed for every test point so that each result can be classified as belonging to the continuous-contact or to the intermittent-contact UEVC regime. The results show: (i) feed rate has a non-monotonic effect, with an optimum at 1 μm where ductile-mode separation is achieved without secondary tool-trajectory overlap, reducing the cutting direction roughness by up to 45% with respect to conventional cutting (CC); (ii) the UEVC advantage shrinks at high cutting speeds because the speed ratio approaches unity and the intermittent regime collapses, but is still 12.6%–38% over the 50–375 mm/s range tested; (iii) the relative improvement is largest at low depth and decreases as the depth grows, retaining 11.5%–49% gain over CC across 0.5–10 μm; (iv) the inter-channel phase difference, which controls the geometry of the tool-tip ellipse, is the strongest single lever—at 60°, the trajectory becomes an oblique ellipse whose major axis is tilted with respect to the cutting direction, bringing the cutting direction roughness down to 1.21 μm against 2.82 μm for CC, a 57% reduction. A simple kinematic argument links this optimum to a maximum effective separation duration per cycle and offers a design rule for analogous UEVC tools. 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

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

The development of interface-engineered, multifunctional nanostructured materials with controllable surface and magnetic properties remains a critical challenge in wastewater treatment and environmental remediation. In this work, a novel GO–CoFe₂O₄–Silicone Magnetic Sponge was successfully fabricated through the integration of graphene oxide and CoFe₂O₄ magnetic nanoparticles within a silicone-modified porous sponge matrix. The resulting material combines superhydrophobicity, oleophilicity, high adsorption capacity, and magnetic responsiveness in a single architecture. The prepared sponge exhibited a high water contact angle of 161.5°, confirming its superhydrophobic nature, while maintaining excellent structural integrity during repeated use. Vibrating sample magnetometry revealed clear ferrimagnetic behavior, enabling rapid magnetic manipulation and efficient recovery of the sponge from aqueous media. The GO–CoFe₂O₄–Silicone Magnetic Sponge demonstrated strong adsorption performance toward a wide range of oils and organic solvents, including chloroform, olive oil, toluene, ethanol, acetone, gasoline, and hexane, with adsorption capacities remaining stable over multiple cycles. Furthermore, the sponge showed outstanding separation efficiency exceeding 98.3% for various oil/water and organic solvent/water mixtures, both in batch and continuous vacuum-assisted separation systems. The adsorption capacity and separation efficiency were retained after repeated adsorption–desorption cycles, indicating excellent reusability and durability. Owing to its synergistic combination of surface chemistry, porous structure, and magnetic functionality, the GO–CoFe₂O₄–Silicone Magnetic Sponge represents a promising candidate for practical applications in oil spill cleanup and wastewater treatment. Full article

Recently, the demand for electric motors that can achieve high performance while ensuring stable magnet supply has continued to increase across various industrial sectors. Although rare-earth permanent magnets, such as neodymium and samarium cobalt, enable superior electromagnetic performance, their high cost and supply instability have motivated growing interest in motors employing non-rare-earth permanent magnets, such as ferrite magnets. Due to the relatively low remanent flux density and coercivity of non-rare-earth magnets, spoke-type rotor structures are commonly adopted to enhance flux concentration. However, spoke-type configurations inherently suffer from axial leakage flux, in which a portion of the magnetic flux generated by the permanent magnets fails to link with the stator and instead leaks along the axial direction. This axial leakage flux reduces the effective air-gap flux density, leading to a degradation of back electromotive force (back-EMF) and overall motor performance. In this study, a double-spoke-type motor employing asymmetric permanent magnet geometry is investigated. Finite element analysis (FEA) is performed to identify an effective rotor structure that reduces axial leakage flux without increasing magnet usage, demonstrating the feasibility of performance improvement in non-rare-earth permanent magnet motors. Full article

Magnetic-field-assisted electrocatalysis offers a powerful route to enhance the oxygen evolution reaction (OER) by coupling spin-dependent effects with magnetohydrodynamic phenomena. Here, we present a unified study of cobalt ferrite (CoFe₂O₄)-based nanofilms, elucidating the combined roles of rare-earth doping, nanoparticle size, film morphology, and electrode substrate magnetism on OER performance under external magnetic fields. The effect of UV-light irradiation is also investigated. CoFe₂O₄ and yttrium-doped CoFe₂O₄ nanoparticles were synthesized via thermal decomposition and self-combustion routes, yielding single-domain particles with distinct structural and magnetic properties, and assembled into homogeneous nanofilms using the Langmuir–Blodgett technique. Electrocatalytic measurements in alkaline media reveal that intrinsic OER activity is primarily governed by film compactness and charge-transfer efficiency, while the magnitude of magnetic-field-induced enhancement depends on the magnetic response of both the nanofilms and the supporting electrode. Ferromagnetic substrates promote enhanced catalytic activity under magnetic fields, whereas diamagnetic substrates can exhibit suppressed performance. Across all systems, the strongest enhancement is observed when the magnetic field is applied parallel to the electrode surface, reflecting the combined effects of spin polarization and Lorentz-force-driven mass transport. UV-light irradiation is also evaluated as an external stimulus to promote the reaction. Our findings establish a comprehensive framework for designing magnetically assisted OER electrocatalysts and demonstrate that magnetic-field effects can rival or complement rare-earth doping or UV-light irradiation, offering a sustainable pathway toward high-efficiency water oxidation. Full article

Fabrication of magnetic materials via a facile and environmentally favorable process with high self-heating performance is quite favored for biomedical applications. To tackle this challenge, magnetic ferrite nanoparticles were developed through an ultrasonic-assisted coprecipitation process. Magnetite (Fe₃O₄), magnetite doped with cobalt nanoparticles (Co_0.4Fe_2.6O₄), and magnetite doped with cobalt/zinc nanoparticles (Zn_0.15Co_0.25Fe_2.6O₄) were synthesized using ultrasonic-assisted coprecipitation techniques. Specific loss power (SLP) was estimated to optimize the heating influence under varied magnetic fields, coating agents, and dispersing solvents. Magnetite doped with cobalt/zinc nanoparticles demonstrated elevated SLP 110 W/g with preferable hyperthermic performance, where AMF conditions did not surpass the safety border for human exposure. The self-heating performance of magnetite doped with cobalt/zinc nanoparticles increased with increasing strength at a constant frequency. The self-heating performance of magnetite nanoparticles increased with increasing frequency at constant strength. Hence, the prepared magnetite doped with cobalt/zinc nanoparticles by the ultrasonic-assisted coprecipitation process can be appropriate for biomedical applications. Full article

This study developed multifunctional chitosan–hydroxyapatite (CH–HAp) scaffolds incorporating cobalt ferrite (CoFe₂O₄, CFO) nanoparticles and carvacrol to combine bone regeneration potential with magnetic responsiveness and antimicrobial activity. Scaffolds containing 5 wt% CFO and 10–30 wt% carvacrol (free or Tween 80-emulsified) were fabricated via freeze-drying. The inclusion of CFO provided ferrimagnetic behavior, while carvacrol reduced chitosan crystallinity and increased scaffold porosity. Formulations with 30 wt% carvacrol demonstrated the strongest antimicrobial effect, showing inhibition halos against Staphylococcus aureus, Escherichia coli, Candida albicans, and Candida glabrata. The scaffold combining emulsified carvacrol and CFO exhibited a highly porous (≈90%) structure, preserved magnetic response, and mild cytotoxicity toward L929 fibroblasts, indicating cytocompatibility. The synergistic integration of CFO and carvacrol in a CH–HAp matrix yielded a multifunctional platform that simultaneously provides structural support, magnetic responsiveness, and antimicrobial performance, showing great promise for advanced bone tissue engineering applications. Full article

The degradation of mercapto organic contaminants is highly important for safety and environmental protection since the specific chemical properties and the strong nature of S-containing bonds can make them less susceptible to traditional degradation mechanisms compared to other types of organic bonds. Thus, degradation of mercapto organic contaminants often requires catalysts with specific bandgap properties to ensure efficient generation of reactive species and appropriate redox potential alignment. Hence, in this work, we prepared bandgap-engineered semiconductor photocatalysts based on nanoparticles of different silica-doped spinel cobalt ferrite [SiO₂/CoFe₂O₄] (abbreviated as SiMCoF) [SiMCoF-1, SiMCoF-2, and SiMCoF-3] and characterized them by different analytical techniques. Since the dopant composition in a heterogeneous semiconductor material has important effects on its photocatalytic efficiency because adjusting the dopant profile can modulate impurity bands and enhance optical properties, which is crucial for the oxidative degradation of organic pollutants. Results from TEM, SEM, and their EDS analysis revealed that increased SiO₂ content showed improved surface area in the matrix, facilitating the increased absorption of oxygen impurities. This is further observed by the higher R_max values presented in AFM of SiMCoF-3 (139 nm) compared to SiMCoF-2 (116 nm) and SiMCoF-1 (8.78 nm), depicting its larger effective surface area (100 µm²), which in turn increases the active binding sites in the matrix. The Raman spectrum and XRD pattern of SiMCoF-3 showed various crystal planes with different atomic arrangements and a smaller crystallite size, leading to varying affinities for oxygen impurities. As a result, the optical bandgap decreased from 3.42 eV to 2.89 eV for SiMCoF-3, which is attributed to the quantum confinement effects caused by the smaller particle size and the dispersion of silica particles in the cobalt ferrite matrix. Thus, SiMCoF-3 showed elevated degradation performance without using any potential oxidants over the degradation of mercapto organic contaminants such as 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, and thiophenol under sunlight irradiation compared to other ferrites, and showed better results than Fenton’s reagent. Full article

Magneto-photoluminescent hybrid materials (MPHMs) were prepared by incorporating cobalt ferrite nanoparticles (CFNs) into the fluorescent polymer poly(terephthalaldehyde-undecan-2-one) (PT2U). The CFNs, with a mean size of 3.95 nm, formed aggregates within the PT2U matrix (650–1042 nm) due to surface and interfacial interactions, modulating aggregate morphology and interparticle coupling. Magnetization studies revealed non-monotonic variations in saturation magnetization (30.3–16.2 emu/g), mean blocking temperature (39.3–43.1 K) and effective magnetic anisotropy energy density (2.14 × 10⁶–1.31 × 10⁶ erg/cm³) with increasing CFN content, consistent with the presence of canted surface spins and enhanced magnetizing interparticle interactions. Photoluminescence exhibited progressive quenching, dominated by collisional mechanisms at low CFN content and by interfacial CFN–PT2U interactions at higher loadings. Under a magnetic field (800 Oe), additional quenching occurred, attributed to magnetically induced polymer-chain rearrangements that disrupted the molecular stacking required for efficient aggregation-induced emission. These results demonstrate tunable magneto-photoluminescent coupling in MPHMs governed by surface and interfacial phenomena, providing insights for the design of functional and responsive hybrid materials. Full article