Search Results (706)

Fe^II-doped zinc ferrite nanocrystals (Fe^II_xZn_1-xFe^III₂O₄) were prepared via a sol–gel approach in the presence of polyvinyl alcohol as a stabilizer and assessed for their capability to eliminate crystal violet (CV) dye from water-based solutions. The structural and surface characteristics of the prepared materials were examined by XRD, HRTEM, FESEM, ATR–FTIR, XPS, UV–visible spectrophotometer and BET analyses. XRD patterns confirmed the formation of a cubic spinel ferrite structure (Fd-3m), indicating successful incorporation of Fe^II into the ZnFe₂O₄ lattice. ATR–FTIR spectra showed characteristic metal–oxygen vibrations at the tetrahedral and octahedral sites. XPS analysis confirmed the coexistence of Fe^II and Fe^III species, which may promote interfacial charge transfer and redox reactions. HRTEM and FESEM images showed particle agglomeration and grain growth after calcination at 700 °C. Fe^II_0.2Zn_0.8Fe^III₂O₄ exhibited the highest photocatalytic performance, achieving 97.2% degradation of CV under optimized conditions. The effects of contact time, catalyst dosage, initial dye concentration, and pH were systematically studied. The maximum removal efficiency was obtained at pH 10 using 0.075 g catalyst for 20 mg L⁻¹ CV solution within 40 min. Freundlich isotherm models exhibited the strongest correlation (R² = 0.918), pointing to multilayer adsorption occurring across a non-uniform nanoparticle surface. The Dubinin–Radushkevich analysis returned an adsorption energy of 3.01 kJ mol⁻¹, implying that physical forces predominantly control the adsorption mechanism. Kinetic investigations revealed a two-stage CV uptake pathway: fast initial binding at exterior surface sites, succeeded by a slower migration of dye molecules into the internal pores of the adsorbent. Full article

Biomass-templated spinel ferrite/carbon nanocomposites are promising electrode materials; however, dense carbon shells formed during low-temperature carbonization can block electrolyte access to active sites and impair electrochemical performance. The role of this carbon-shell passivation in biomass-derived ferrite/carbon composites remains largely unexplored. Here, we identify this limitation in a stepwise-synthesized NiFe₂O₄/rGO@C composite (NFC-S, BET surface area = 5.23 m² g⁻¹, ΔEp = 113.3 mV) and resolve it through a rationally designed one-pot optimization strategy in which urea simultaneously serves as a pore-forming agent and nitrogen precursor. The optimized composite (N-NFC-O) achieves a BET surface area of 186.39 m² g⁻¹—a 35.6-fold enhancement—with 70.1% micropore contribution and 3.13 at.% in-situ nitrogen doping. Electrochemically, ΔEp narrows to 72.3 mV and enables efficient NO₂⁻ oxidation with a ~70 mV cathodic shift, whereas NFC-S shows negligible catalytic response under identical conditions. As a proof of concept, differential pulse voltammetry (DPV) yields a nitrite sensitivity of 9.17 µA cm⁻² mM⁻¹ and a detection limit of 92.5 µM. Overall, this work identifies carbon pore accessibility as a key structural descriptor governing electrocatalytic performance in biomass-derived ferrite/carbon composites and provides a general design strategy for developing high-performance biomass-derived carbon/oxide hybrid electrodes. Full article

In this work, nanocrystalline high-entropy spinels with the nominal composition (Co,Mn,Ni,Cr,Fe)₃O₄ and different Fe contents were synthesized by a facile solution combustion method and evaluated as catalysts for the complete oxidation of light hydrocarbons and methanol decomposition. Structural characterization by XRD, SEM, TEM, XPS, Mössbauer spectroscopy, and N₂ physisorption confirmed the formation of single-phase cubic spinels and mesoporous morphology. Increasing the Fe content resulted in changes in surface elemental distribution without altering the oxidation states of the cations. Among the investigated catalysts, HES-Fe 1:1 exhibited the highest specific surface area, favorable surface enrichment in Co and Mn, and the best catalytic performance for the complete oxidation of light hydrocarbons. In methanol decomposition, HES-Fe 1:1 showed the highest methanol conversion at lower temperatures, whereas HES-Fe 1:2 exhibited the highest CO selectivity, making it the most efficient catalyst for syngas production. The results establish a relationship between Fe content, surface composition, redox properties, and catalytic performance, revealing high-entropy spinels as promising catalysts for environmental catalysis and syngas production. Full article

Limonitic nickel laterite is difficult to sinter because of its high loss on ignition, high combined-water content, and complex refractory mineral composition, which often result in poor sinter strength and high solid fuel consumption. In this study, a pellet-sintering process was adopted to improve the sintering performance of limonitic nickel laterite. Pot sintering tests were carried out to investigate the effects of key process parameters—including moisture content, solid fuel dosage, return fines dosage, and drying–holding regime—on yield, tumble index, productivity index, and solid fuel consumption. The selected conditions were determined as follows: moisture content of 21%, solid fuel dosage of 5.8%, return fines dosage of 25%, drying at 450 °C for 5 min, and holding at 1000 °C for 10 min, under a fixed basicity of 1.5 and a bed height of 850 mm. Under these conditions, the yield, tumble index, productivity index, and solid fuel consumption reached 70.19%, 57.87%, 1.37 t·m⁻²·h⁻¹, and 95.86 kg·t⁻¹, respectively. Compared with conventional sintering, pellet sintering increased the yield, tumble index, and productivity index by 24.05%, 35.56%, and 31.73%, respectively, while reducing solid fuel consumption by 22.87%. XRD, OM, quantitative image analysis, and SEM–EDS analyses showed that pellet sintering reduced the average two-dimensional pore area fraction from 33.29% to 18.05% and the large-pore area fraction from 22.25% to 11.61%, while promoting a more continuous bonding structure characterized by a spinel-rich mineral framework, spinel–olivine eutectic-type composite bonding phases, and SFCA-type bonding phases. These results demonstrate that pellet sintering is a feasible route for improving the sintering performance and consolidation behavior of limonitic nickel laterite. Full article

Glass-ceramics are inorganic, non-metallic materials obtained by controlled crystallization of glasses through different processing routes; they contain at least one functional crystalline phase together with a residual glass, and the crystallized fraction may range from trace levels to nearly complete crystallization. Transparent glass-ceramics (TGCs) constitute the optically transparent subset of this class and combine a controlled crystalline microstructure with a residual amorphous matrix. Their transparency distinguishes them from conventional opaque glass-ceramics and is achieved by minimizing light scattering through careful control of crystallite size, volume fraction, spatial distribution, and refractive-index mismatch between the crystalline and glassy phases. Unlike conventional sintered ceramics, TGCs retain many of the processing advantages of glass while incorporating crystalline phases that can enhance mechanical, thermal, optical, or functional properties. Depending on their composition and microstructure, TGCs may exhibit improved hardness, fracture toughness, thermal stability, chemical durability, luminescence, nonlinear optical response, or ion-exchange strengthening capability. These features make TGCs attractive for applications requiring both optical clarity and advanced performance, including protective cover glass, transparent armour, precision optical substrates, laser and photonic components, optical sensors, and multifunctional host materials for rare-earth ions and nanoparticles. Full article

High-voltage spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode for next-generation lithium-ion batteries, yet its application is limited by structural instability and poor high-temperature/high-rate performance. Here, spherical secondary polycrystalline aggregate (LNMO-PC), micron-sized primary particle (single-crystal morphology) (LNMO-SC-L), and submicron primary particle (single-crystal morphology) (LNMO-SC-S) LNMO were synthesized. Their structures, morphologies, and surface properties were characterized and electrochemical performance evaluated at room (25 °C)/high (55 °C) temperature and high rates. LNMO-SC-S exhibited the highest crystallinity, lowest Mn³⁺ content, and minimal charge-transfer resistance. It showed superior cycling stability (93.3% retention at 1 C over 500 cycles), excellent rate capability (~20 mAh g⁻¹ at 20 C), and enhanced high-temperature performance. The submicron primary particles suppress grain-boundary degradation and Mn³⁺ disproportionation, shortens Li⁺ paths, and improves reaction kinetics. Full article

A mass action concentration model of FeO-Fe₂O₃-SiO₂-CaO-MgO-Al₂O₃-ZnO multi-component slag was established to address the problems of high viscosity and high copper content in oxygen-enriched top-blown copper smelting slag. Theoretical calculations, combined with experimental investigations, were performed to evaluate the effects of ZnO additions (0–25 wt.%) on phase transformation, Fe₃O₄ reduction and copper content in the slag at temperatures ranging from 1200 to 1400 °C. The results indicate that ZnO addition decreases the mass concentrations of Fe₂O₃, Fe₃O₄, Fe₂SiO₄ and SiO₂, while increasing the proportions of zinc-bearing structural units and enhancing the reducing capability of the slag. In the copper slag system, Zn²⁺ substitutes for Fe in Fe₃O₄ and Fe₂SiO₄ through isomorphous substitution, forming Fe-Zn spinel and Fe-Zn olivine. As the addition of ZnO gradually increases to 25 wt.%, the liquid slag fraction increases and the slag viscosity decreases, resulting in a reduction in copper content from 5.64 wt.% to 2.04 wt.%. Furthermore, ZnO promotes the transformation of Fe₃O₄ into zinc–iron spinel, which is more readily reducible by carbothermic reaction than Fe₃O₄ itself, thereby facilitating the overall reduction of iron oxides in the copper slag. These findings provide a theoretical basis for slag-type regulation and the efficient separation of copper from slag via high-temperature gravity settling of matte. Full article

The formation of W-type hexaferrite magnets was investigated using in situ synchrotron X-ray powder diffraction. Both the holding time and precursor composition were investigated to evaluate the effect on phase purity and crystallite size using Rietveld refinements. Based on the refinements, it was found that the formation of W-type hexaferrites initiates shortly after reaching 1200 °C and happens within a few seconds. M-type hexaferrite was formed at a lower temperature before being transformed into W-type hexaferrite. Despite the short holding times, at elevated temperatures, the crystallite sizes along the a,b-axis exceeded the detection limit of the powder diffraction data, as the peak widths associated with the a,b-planes became too narrow to resolve changes as function of time. Magnetization data recorded from the in situ prepared samples revealed a higher saturation magnetization in the W-type hexaferrites relative to conventional M-type hexaferrites. No appreciable coercivity was found, which can be attributed to different effects: (1) reduced anisotropy constant, (2) large crystallite growth resulting in multi-domain crystallites, or (3) exchange-coupling with soft spinel ferrite found in the sample. Based on this study, we conclude that W-type hexaferrites can be formed after a few seconds at 1200 °C and that crystallite growth happens subsequently after the formation of the W-type hexaferrite structure. Full article

High-performance energy sources for electric vehicles and portable electronic devices require state-of-the-art lithium-ion batteries (LIBs) characterized by high energy density, superior power output, and excellent long-term cycling stability. Among the various components of LIBs, the cathode material plays a decisive role in determining the electrochemical performance, safety, and commercial viability of the battery. To meet the growing demands of modern applications, these materials must combine high capacity with structural stability, thermal safety, cost-effectiveness, and excellent rate capability. This article reviews the most widely used cathode materials with layered, spinel, and olivine structures. Their key advantages and intrinsic limitations are analyzed in detail, alongside strategies to enhance performance through elemental doping and surface coating approaches. Furthermore, the review presents simple, cost-effective, and industrially scalable synthesis methods, and highlights advanced characterization techniques that provide a deeper understanding of their nanostructured features and electrochemical behavior. Full article

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at air cathodes severely restrict the practical application of rechargeable zinc–air batteries (ZABs). Herein, equimolar lanthanide-doped spinel Co₃O₄ bifunctional electrocatalysts were synthesized via a citric acid-assisted sol–gel method. Among Ce-, Pr-, La-, and Sm-doped catalysts, Sm-Co₃O₄ exhibits the optimal electrocatalytic performance with a high ORR half-wave potential of 0.72 V and superior OER activity with an overpotential of 1.65 V at 10 mA cm⁻², achieving a minimal potential gap ΔE of 0.93 V. Rotating ring-disk electrode (RRDE) measurements and Koutecky–Levich (K–L) analyses confirm the exclusive 4e⁻ ORR pathway. Characterizations reveal that Sm doping modulates the electronic structure and lattice distortion of Co₃O₄, raises the Co²⁺/Co³⁺ ratio (0.59) and creates abundant oxygen vacancies, thereby significantly lowering the overpotentials for both ORR and OER. This study provides new insights for designing high-performance spinel-based bifunctional electrocatalysts for ZABs. Full article

The particle size refinement of hercynite (FeAl₂O₄) powders during wet high-energy mechanical milling was investigated through an integrated experimental and kinetic modeling approach. Hercynite powders were milled for different durations, and their microstructural, chemical, and particle size evolution was characterized using scanning electron microscopy, X-ray diffraction, semi-quantitative X-ray fluorescence analysis, and SEM–ImageJ-based particle size reconstruction. Particle size distributions were reconstructed from large particle populations, and the characteristic descriptors $D_{10}$, $D_{50}$, and $D_{90}$ were determined from empirical cumulative distributions. The results revealed a pronounced reduction in median particle size from approximately 83.1 $\mathrm{\mu }$m in the as-received powder to 0.422 $\mathrm{\mu }$m after 8 h of milling. X-ray diffraction analysis showed progressive peak broadening and intensity reduction with increasing milling time, suggesting milling-induced structural disorder and possible crystallite refinement and/or lattice strain accumulation, while no additional crystalline phases associated with milling-induced decomposition were detected within the detection limit of XRD. Semi-quantitative chemical analysis indicated limited metallic transfer from the stainless-steel milling media under the applied wet milling conditions. The evolution of $D_{50}$ with milling time exhibited a non-linear behavior characterized by rapid particle fragmentation at early stages, followed by a gradual transition toward a refinement-limited regime. This behavior was described using a first-order kinetic model with saturation behavior, yielding an asymptotic particle size of 0.443 $\mathrm{\mu }$m and an effective milling rate constant of 1.539 h⁻¹. Overall, the proposed kinetic framework provides a descriptive and condition-specific quantitative basis for interpreting the competing fracture and agglomeration mechanisms governing particle size evolution during wet mechanical milling of refractory spinel powders. Full article

The co-contamination of manganese ions (Mn²⁺) and ammonia nitrogen (NH₄⁺) caused by the stockpiling of manganese residue poses a serious threat to the ecological environment. In this study, a series of the composite was prepared from red mud, bentonite, and corn straw via oxygen-limited pyrolysis. The effects of pyrolysis temperature and raw material ratio on the material properties were investigated, and the synergistic remediation performance of the composites for Mn²⁺ and NH₄⁺ in manganese residue-contaminated soil was evaluated through a 180-day soil column experiment. The results showed that the composite prepared with a raw material ratio of 1:1:1 at a pyrolysis temperature of 700 °C exhibited the largest specific surface area and the most developed pore structure, achieving a Mn²⁺ removal rate of 92.72% ± 0.85% in aqueous solution. In the soil column experiment, the material prepared at 700 °C gave the highest immobilization rate for soil Mn²⁺ (96.22% ± 0.5%), whereas the combined addition of materials prepared at 700 °C and 500 °C achieved the best removal efficiency for NH₄⁺ (99.33% ± 0.23%). Mechanistic studies revealed that the stabilization of Mn²⁺ is primarily attributable to alkaline precipitation and mineral lattice solid solution induced by the composite, leading to the formation of stable spinel phases (e.g., (Fe,Mn)₃O₄) and insoluble manganese phosphate-carbonate salts. The removal of NH₄⁺ is proposed to proceed via adsorptive enrichment by the porous structure and Fe⁰-mediated Fenton-like catalytic oxidation, ultimately converting NH₄⁺ to N₂ gas. The 180-day monitoring results demonstrated that the remediation effect continuously increased over time, indicating good long-term stability of the composite. This study provides an efficient, low-cost functional material derived from solid waste for the remediation of manganese residue-contaminated soil and offers a theoretical basis for the synergistic resource utilization of multiple solid wastes. Full article

The firing of traditional gray pottery relies on complex physicochemical reactions governing its color, dimensional accuracy, and structural stability. Unclear kiln-transformation mechanisms restrict standardized and digital production of this Chinese intangible cultural heritage. Herein, direct ink writing (DIW) was used to fabricate Hejin gray pottery green bodies from local ternary raw materials. Thermodynamic calculations, TG–DTG/DSC, XRD, XRF, and atmosphere-controlled firing tests were combined to reveal coupled phase evolution and reduction color-forming mechanisms during sintering. Two interrelated kiln-transformation processes were identified. First, sequential mineral reconstruction occurs at four critical temperatures: free water loss at 119.8 °C, two-stage dehydroxylation of hydrous silicates at 270.5 °C and 767.9 °C, and CaCO₃ decomposition at 547.9 °C. Uneven shrinkage and gas release at these temperatures induce cracking, blistering, and deformation of printed bodies. Micron-sized CaCO₃ (equivalent radius ≈ 1.31 μm) exhibits high surface energy and significantly reduces its decomposition temperature, consistent with experimental observations. Second, reducing atmospheres trigger competitive phase formation. Distinct from the conventional Fe₂O₃ → Fe₃O₄ → FeO reduction pathway, Fe oxides preferentially react with abundant Al₂O₃ to form thermodynamically stable FeAl₂O₄ spinel, yielding uniform celadon-gray tones. The final color is nearly independent of 20–90 vol% CO, and air-isolated cooling below 600 °C is mandatory to prevent secondary oxidation and reddening. This work establishes a thermodynamic framework for DIW-printed Hejin gray pottery kiln transformation, clarifies microscale defect and color-evolution mechanisms, and offers theoretical guidance for atmosphere-controlled firing and digital mass production of heritage ceramics. Full article

In material research, heteroatom doping in a host lattice is regarded as an effective method to modify the structural and electronic properties of the materials, consequently enhancing their electrochemical performance. This study represents the microstructural and electrochemical properties of lanthanum-doped Li₄Ti₅O₁₂ (Li₄Ti_5−xLa_xO₁₂, x = 0.02, 0.04, and 0.06) using a hydrothermal method. The findings indicate that all three compositions demonstrate a comparable crystallite phase, free from discernible impurities, and exhibit a flake-like morphology. The Li₄Ti_4.96La_0.04O₁₂ sample exhibited a cubic spinel structure with flake-like morphology, a low crystallite size of 9.7 nm and a reasonably good electrical conductivity of 3.56 × 10⁻⁶ S cm⁻¹. In order to delve deeper into the supercapacitive behavior, the electrochemical characteristics of the electrodes were assessed through cycling voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Notably, the Li₄Ti_4.96La_0.04O₁₂ electrode demonstrated exceptional electrochemical performance, achieving a specific capacitance of 461 F g⁻¹ at 1 A g⁻¹. Furthermore, it exhibited commendable cycling stability with approximately 80% capacitance retention after 5000 cycles and around 89% Coulombic efficiency, highlighting its potential as a noteworthy electrode material for energy storage applications. Full article