Search Results (142)

In the present study, we synthesized fluorocarbon-coated cobalt ferrite (CoFe₂O₄) magnetic nanoparticles using alkoxysilanes such as trimethoxy(3,3,3-trifluoropropyl)silane (TFPTMS), trimethoxy(1H,1H,2H,2H-nonafluorohexyl)silane (NFHTMS), and triethoxy(1H,1H,2H,2H-perfluorodecyl)silane (PFDTES). The synthesized nanoparticles were characterized by various techniques, including X-ray diffractometry (XRD), transmission electron microscopy (TEM/HRTEM/EDXS), Fourier transform infrared spectroscopy (FTIR), specific surface area measurements (BET), and magnetometry (VSM). To understand their surface characteristics, contact angle (CA) measurements were carried out, providing valuable insights into their hydrophobic properties. Among the samples of CoFe₂O₄ coated with fluoroalkoxysilanes, those with PFDTES surface coating had the highest water contact angle of 159.2°, indicating their superhydrophobic character. The potential of the prepared fluoroalkoxysilane-coated CoFe₂O₄ nanoparticles for the removal of waste low-SAPS synthetic engine oil from a model aqueous solution was evaluated based on three key parameters: adsorption efficiency (%), adsorption capacity (mg/g), and desorption efficiency (%). All synthesized CoFe₂O₄ samples coated with fluoroalkoxysilane showed high oil adsorption efficiency, ranging from 87% to 98%. The average oil adsorption capacity for the samples was as follows: F₃-SiO₂@CoFe₂O₄ (3.1 g of oil/g of adsorbent) > F₉-SiO₂@CoFe₂O₄ (2.7 g of oil/g of adsorbent) > F₁₇-SiO₂@CoFe₂O₄ (1.5 g of oil/g of adsorbent) as a result of increasing oleophobicity with increasing fluorocarbon chain length. The desorption results, which showed 77–97% oil recovery, highlighted the possibility of reusing the adsorbents in multiple adsorption/desorption cycles. Full article

Spinel-structured hausmannite (Mn(II)Mn(III)₂O₄) is a vital intermediate in Mn mineralogy and a key player in redox chemistry in the environment. Its transformation into other Mn oxides is a critical factor in controlling its environmental occurrence and reactivity. Yet structural impurities and solution pH, as well as the fate of impurities during transformation, which influence hausmannite transformation processes and products, remain largely unknown. In the present work, we address this knowledge gap by investigating pristine and metal-substituted hausmannite, specifically nickel (Ni) or cobalt (Co), equilibrated at two time periods (8 h and 30 days) and three different pH levels (4, 5, and 7). Solution chemistry data revealed that both the equilibration period and pH had a significant impact on hausmannite dissolution rates and the concomitant repartitioning of Ni or Co. Hausmannite with Ni or Co substitution exhibited lower dissolution rates than pristine mineral under acidic conditions. Mineralogy and crystal chemistry data indicated that hausmannite was the major host phase after 30-day equilibration, followed by minor transformed products, including birnessite and manganite. Although minor, birnessite became more abundant than manganite at low pHs. Analytical high-resolution transmission electron microscopy (HRTEM) analyses revealed a poorly crystalline, nano-scaled MnO₂ formed from hausmannite and the majority of metal impurities remaining in the host hausmannite. Yet Co was associated with both hausmannite and the newly formed birnessite, whereas Ni was only found with hausmannite, indicating the strong sequestration of Co by Mn(II/III) and Mn(IV) mineral phases. This study highlights the significant impacts of metal impurities and pH on the stability of hausmannite and its transformation into birnessite, as well as the control of Mn-oxide minerals on the solubility and sequestration of transition metals in the environment. Full article

Composites of ferromagnetic and ferroelectric phases are of interest for studies on mechanical strain-mediated coupling between the two phases and for a variety of applications in sensors, energy harvesting, and high-frequency devices. Nanocomposites are of particular importance since their surface area-to-volume ratio, a key factor that determines the strength of magneto-electric (ME) coupling, is much higher than for bulk or thin-film composites. Core–shell nano- and microcomposites of the ferroic phases are the preferred structures, since they are free of any clamping due to substrates that are present in nanobilayers or nanopillars on a substrate. This review concerns recent efforts on ME coupling in coaxial fibers of spinel or hexagonal ferrites for the magnetic phase and PZT or barium titanate for the ferroelectric phase. Several recent studies on the synthesis and ME measurements of fibers with nickel ferrite, nickel zinc ferrite, or cobalt ferrite for the spinel ferrite and M-, Y-, and W-types for the hexagonal ferrites were considered. Fibers synthesized by electrospinning were found to be free of impurity phases and had uniform core and shell structures. Piezo force microscopy (PFM) and scanning microwave microscopy (SMM) measurements of strengths of direct and converse ME effects on individual fibers showed evidence for strong coupling. Results of low-frequency ME voltage coefficient and magneto-dielectric effects on 2D and 3D films of the fibers assembled in a magnetic field, however, were indicative of ME couplings that were weaker than in bulk or thick-film composites. A strong ME interaction was only evident from data on magnetic field-induced variations in the remnant ferroelectric polarization in the discs of the fibers. Follow-up efforts aimed at further enhancement in the strengths of ME coupling in core–shell composites are also discussed in this review. Full article

Abundant valuable metals such as manganese and cobalt are present in cobalt-rich slags from the hydrometallurgical zinc industry. However, due to the high cost of traditional hydrometallurgical separation methods, these metals cannot be effectively recovered. In this paper, a novel recycling strategy based on mineral phase recovery was proposed, utilizing cobalt-rich slags as raw materials to fabricate microwave-absorbing composite materials. A feasible solid-phase thermochemical method has been developed to recover the mineral phase from cobalt-rich slags, with calcination temperature 800 °C and duration 90 min, yielding MnCo₂O₄ spinel. The results demonstrated that under the conditions of a ball-to-material ratio of 20:1 and ball milling time of 4 h, the MnCo₂O₄ powder and graphene materials, after being ball-milled and compounded, exhibited appropriate electromagnetic parameters and impedance matching. At 5.2 GHz, the minimum reflection loss of the composite material reached −40 dB. This study provides a new approach for the value-added utilization of valuable metal resources in cobalt-rich slags. Full article

Nanomaterials have attracted significant attention in recent decades for their diverse applications, including energy storage devices like supercapacitors. Among these, cobalt oxide (Co₃O₄) nanostructures stand out due to their high theoretical capacitance, unique electrical properties, and tunable morphology. This study explores the hydrothermal synthesis of Co₃O₄, revealing that the molar ratio of cobalt nitrate to potassium hydroxide significantly influences the morphology, crystal structure, and electrochemical performance. An optimized 1:1 molar ratio (COK 11) yielded well-defined cubic nanostructures with uniform elemental distribution, as confirmed by SEM, TEM, and EDS analyses. Structural characterization through XRD, XPS, and FTIR validated the formation of the Co₃O₄ spinel phase with distinctive lattice and surface oxygen features. Electrochemical property analysis demonstrated the superior performance of the COK 11 electrode, achieving a high specific capacity of 825 ± 3 F/g at a current density of 1 A/g, a rate capability of 56.88%, and excellent cycle stability of 88% at 3 A/g after 10,000 cycles. These properties are attributed to the nano-cubic morphology and interconnected porosity, which enhanced ion transport and active surface area. This study highlights the importance of synthesis parameters in tailoring nanomaterials for energy storage, establishing COK 11 as a promising candidate for next-generation high-performance supercapacitor applications. Full article

With the increasing demand for air pollution control, the development of efficient and stable catalysts to degrade hazardous VOCs such as toluene has become particularly important. Herein, various copper-doped attapulgite-supported cobalt oxide spinel composites (Cu_xCo_3−xO₄/ATP) were synthesized using an ultrasonic-assisted precipitation method. The results showed that the abundant Si-OH groups on the surface of ATP played a crucial role in anchoring Co, and the instantaneous high-energy input of ultrasonication facilitated the formation of Si-O-Co bonds in Co₃O₄/ATP. The doping of Cu ions induced the expansion of the Co₃O₄ lattice, resulting in a significant number of oxygen vacancies. The ultrasound-induced synthesized Cu_0.1Co_2.9O₄/ATP catalyst exhibited the best catalytic oxidation performance, achieving a 99% toluene degradation rate at 300 °C under a weight hourly space velocity (WHSV) of 10,000 mL·g⁻¹ h⁻¹ and initial toluene concentration of 1000 ppm, along with high stability during 12 h of continuous running. This work presents a new strategy for the cost-effective catalytic elimination of VOCs. Full article

Zinc cobaltite (ZnCo₂O₄) is a ternary metal oxide found in spinel with promising properties for various applications. Optimizing its catalytic activity requires an understanding of its electrochemical behavior. The electrochemical properties of ZnCo₂O₄ have significantly improved due to recent developments in nanostructuring, doping, surface modification, hybridization, structural engineering, and electrochemical activation. These improvements have inspired and motivated researchers by presenting the latest developments in the field. The spinel structure, coupled with the redox properties of cobalt ions, semiconducting characteristics, and electrocatalytic potential, positions ZnCo₂O₄ as a versatile material for several electrochemical energy storage and conversion systems. This review explores these advancements; the notable properties of ZnCo₂O₄; and its applications in sensors, batteries, photovoltaics, and supercapacitors. Full article

The purpose of this work was to consider the decolorization efficiency of reactive yellow 160 (Ry-160) dye utilizing cobalt aluminum oxide (AlCo₂O₄)-anchored Multi-Walled Carbon Nanotubes (AlCo₂O₄/MWCNTs) nanocomposites as catalysts for the first time in a photocatalytic process under natural sunlight irradiation. The compositional, morphological, and functional group analyses of AlCo₂O₄ and AlCo₂O₄/MWCNTs were performed by utilizing Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FE-SEM), and Fourier Transform Infrared (FTIR) Spectroscopy, respectively. A UV-Vis (UV-Vis) spectrophotometer was used to investigate degradation efficiency. The results exhibited a reduction in the optical bandgap for AlCo₂O₄/MWCNTs nanocomposites as catalysts from 1.5 to 1.3 eV compared with pure spinel AlCo₂O₄ nanocomposites. AlCo₂O₄/MWCNTs nanocomposites showed excellent photocatalytic behavior, and around 96% degradation of Ry-160 dye was observed in just 20 min under natural sunlight, showing first-order kinetics with rate constant of 0.151 min⁻¹. The results exhibited outstanding stability and reusability for AlCo₂O₄/MWCNTs by maintaining more than 90% photocatalytic efficiency even after seven successive operational cycles. The betterment of the photocatalytic behavior of AlCo₂O₄/MWCNTs nanocomposites as compared to AlCo₂O₄ nanocomposites owes to the first-rate storage capacity of electrons in MWCNTs, due to which the catalyst became an excellent electron acceptor. Furthermore, the permeable structure of MWCNTs results in a greater surface area leading to the onset of more active sites, and, in turn, it also boosts conductivity and reduces the formation of agglomerates on the surface of catalysts, which inhibits e−/h⁺ pair recombination. Concisely, the synthesis of a novel AlCo₂O₄/MWCNTs catalyst with excellent and fast photocatalytic activity was the aim of this study. Full article

Mīnā’ī wares, crafted during the 12th–13th centuries, represent some of the earliest examples of sophisticated painted enamel decoration by potters. Due to the thinness of these enamel layers, their detailed characterization remains challenging, even with the use of advanced techniques, such as Proton-Induced X-ray Emission (PIXE) analysis and Rutherford Backscattering Spectrometry (RBS). This study provides the first combined non-invasive analysis, using X-ray fluorescence (XRF) and Raman spectroscopy, of five shards attributed to mīnā’ī wares. For comparison, two İznik shards from the 17th century, which feature similarly styled but thicker enamel decorations, were also analyzed. Interestingly, the mīnā’ī paste was found to contain lead and tin, suggesting the use of a lead-rich frit in its composition. This finding was confirmed through micro-destructive analysis, using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM–EDS). Elements, such as rubidium (Rb), strontium (Sr), yttrium (Y), and zirconium (Zr), produced significant XRF signals and effectively distinguished mīnā’ī wares from İznik wares. A uniform tin-rich glaze, measuring 300–500 µm in thickness, was used as a base layer for the much thinner painted mīnā’ī enamels. The colored areas (blue, turquoise, red, green, black, white, eggplant) revealed the presence of various coloring agents and phases, such as spinels, chromite, and ions like Cu²⁺ and Co²⁺, as well as opacifiers like cassiterite and lead–calcium/potassium arsenates. Two distinct cobalt sources were identified: one associated with arsenic and the other with manganese and nickel. These cobalt sources are comparable to those used in İznik pottery. For the first time, boron was detected in the blue enamel of mīnā’ī wares. Full article

The cobalt manganese oxides, especially the spinels and related (multiphase) materials described with the formula Co_xMn_3−xO₄ (0 < x < 3), are widely used catalysts in a range of processes in significant industrial and environmental areas. The great diversity in the phase relations, composition, and metal ion valences, together with ion and vacancy site distribution variations, results in great variety and activity as catalysts in various industrially important redox processes such as the removal of CO or volatile organic substances (VOCs) from the air and oxidative destruction of pollutants such as dyes and pharmaceuticals from wastewater using peroxides. These mixed oxides can gain application in the selective oxidation of organic molecules like 5-hydroxyfurfural or aromatic alcohols such as vanillyl alcohol or in the production of fuels and other valuable chemicals (alcohols, esters) with the Fischer–Tropsch method. In this review, we summarize these redox-based reactions in light of the chemical and phase composition of the catalysts with the formula Co_xMn_3−xO₄ with 0 < x < 3. Full article

Zinc-substituted cobalt ferrites were obtained by a green method using a black grape extract as a reductant and fuel. XRD analysis confirmed the spinel structure of the synthesized ferrites. An increase in the lattice constant is explained by increased Zn content. SEM analysis confirmed changes in surface morphology, whereas FTIR spectra demonstrated the presence of organic species in the samples, which originated from grape extract. The content of Co(II) ions in octahedral sites as a function of the ratio between Fe(III) ions in A- and B-sites was calculated from Mössbauer data. pH_PZC rose from 7.85 to 8.13 with an increase in zinc content, indicating a positive charge of the adsorbent surface at natural pH. The adsorption–catalytic properties of the spinel samples were investigated in terms of Congo Red (CR) dye removal. The mechanism of CR adsorption on the ferrite surface includes electrostatic and donor–acceptor interactions with the adsorbent surface. Furthermore, the sample with x(Zn) = 0.4 exhibited the highest degradation rate constant k = 0.102 min⁻¹ in the peroxide oxidation of CR, whereas the sample with x(Zn) = 1.0 exhibited the highest adsorption capacity. The electron transfer between ferrite samples and hydrogen peroxide was evidenced using electrochemical tests. The green-synthesized Co-Zn ferrites demonstrate a big potential as adsorbents/catalysts for water treatment. Full article

In this work, the origin of the synergetic effect in mixed Mn_xCo_3-xO₄ oxides with the spinel structure in the CO oxidation reaction was tested. A series of Mn_xCo_3-x oxide catalysts were synthesized by the coprecipitation method with further calcination at 600 °C and varying manganese content from x = 0 to x = 3. The catalysts were characterized using XRD, TEM, N₂ adsorption, TPR, EXAFS, and XPS. The catalytic activity of Mn_xCo_3-x oxide catalysts was tested in CO oxidation reactions. The addition of manganese to cobalt oxide results in the formation of mixed Mn-Co oxides based on a cubic or tetragonal spinel structure, a change in microstructural properties, such as surface area and crystal size, as well as local distortions and a decrease in the surface concentration of Co ions and Co in the octahedral sites in spinel structure; it also decreases catalyst reducibility. For all catalysts, the activity of CO oxidation decreases as follows: Mn_0.1Co_2.9 > Co₃O₄~Mn_0.3Co_2.7 > Mn_0.5Co_2.5 > MnO_x > Mn_0.7Co_2.3 > Mn_0.9Co_2.1~Mn_1.1Co_1.9~Mn_2.5Co_0.5 > Mn_2.9Co_0.1 > Mn_1.7Co_1.3 > Mn_2.1Co_0.9 > Mn_1.3Co_1.7~Mn_1.5Co_1.5~Mn_2.3Co_0.7. The Mn_0.1Co_2.9 catalyst displays the best catalytic activity, which is attributed to its small crystal size and the maximum surface ratio between Co³⁺ and Co²⁺. A further increase in the manganese content (x > 0.3) provokes drastic changes in the catalytic properties due to a decrease in the cobalt content on the surface and in the volume of mixed oxide, changes in the oxidation states of cations, and structure transformation. Full article

Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals and critical raw materials. The historical slags associated with the smelting of polymetallic ores originating from Mississippi Valley-type (MVT) deposits consisted primarily of gypsum. The contemporary slags, obtained from industrial waste rich in zinc and lead, were predominantly spinels (magnesium-aluminate and ferric) that exhibited higher iron content (up to 46.6 wt% of Fe₂O₃) compared to the historical slags (up to 26.1 wt% of Fe₂O₃). The zinc content was similar for both the slag types (3.5 wt% Zn). The average titanium and arsenic contents in the old and contemporary slags were at the same level as well, with 0.21 wt% (Ti) and 0.13 wt% (As), respectively. The contemporary slags contained higher levels of critical raw materials, such as cobalt, nickel, copper, and manganese, compared to the historical slags. Rare earth elements (REEs) were also more abundant in the contemporary slags, with an average content of 212 ppm, while the historical slags averaged 124 ppm. These findings underscore the potential for recovering valuable metals and critical raw materials from such slags, presenting opportunities for resource optimisation and environmental management. Full article

Ananas comosus leaves were converted to a porous graphitized carbon (GPLC) material via a high-temperature pyrolysis method by employing iron salt as a catalyst. A cobalt molybdate (CoMoO₄)-and-GPLC composite (CoMoO₄/GPLC) was then prepared by engineering CoMoO₄ nanorods in situ, grown on GPLC. N₂ adsorption–desorption isothermal curves and a pore size distribution curve verify that the proposed composite possesses a porous structure and a large specific surface area, which are favorable for charge and reactant transport and the rapid escape of O₂ bubbles. Consequently, the as-synthesized CoMoO₄/GPLC shows low overpotentials of 289 mV and 399 mV to afford the current densities of 10 mA cm⁻² and 100 mA cm⁻² towards the oxygen evolution reaction (OER), which is superior to many CoMoO₄-based catalysts in previous studies. In addition, the decrease in current density is particularly small, with a reduction rate of 3.2% after a continuous OER procedure for 30 h, indicating its good stability. The excellent performance of the CoMoO₄/GPLC composite proves that the GPLC carrier can obviously impel the catalytic activity of CoMoO₄ by improving electrical conductivity, enhancing mass transport and exposing more active sites of the composite. This work provides an effective strategy for the efficient conversion of waste ananas comosus leaves to a biomass-derived-carbon-supported Co-Mo-based OER electrocatalyst with good performance, which may represent a potential approach to the development of new catalysts for OER, as well as the treatment of waste biomass. Full article

Spinel ferrites demonstrate extensive applications in different areas, like electrodes for electrochemical devices, gas sensors, catalysts, and magnetic adsorbents for environmentally important processes. However, defects in the real spinel structure can change the many physical and chemical properties of spinel ferrites. Although the number of defects in a crystal spinel lattice is small, their influence on the vast majority of physical properties could be really decisive. This review provides an overview of the structural characteristics of spinel compounds (e.g., CoFe₂O₄, NiFe₂O₄, ZnFe₂O₄, Fe₃O₄, γ–Fe₂O₃, Co₃O₄, Mn₃O₄, NiCo₂O₄, ZnCo₂O₄, Co₂MnO₄, etc.) and examines the influence of defects on their properties. Attention was paid to the classification (0D, 1D, 2D, and 3D defects), nomenclature, and the formation of point and surface defects in ferrites. An in-depth description of the defects responsible for the physicochemical properties and the methodologies employed for their determination are presented. DFT as the most common simulation approach is described in relation to modeling the point defects in spinel compounds. The significant influence of defect distribution on the magnetic interactions between cations, enhancing magnetic properties, is highlighted. The main defect-engineering strategies (direct synthesis and post-treatment) are described. An antistructural notation of active centers in spinel cobalt ferrite is presented. It is shown that the introduction of cations with different charges (e.g., Cu(I), Mn(II), Ce(III), or Ce(IV)) into the cobalt ferrite spinel matrix results in the formation of various point defects. The ability to predict the type of defects and their impact on material properties is the basis of defect engineering, which is currently an extremely promising direction in modern materials science. Full article