This review article presents a synthesis of nickel and cobalt ferrites, highlighting their structural, magnetic and electrical properties, as well as their technological applications. The text is organized into five main sections, covering everything from fundamental concepts of spinel ferrites to synthesis methods and recent advances obtained through doping and structural modifications. Initially, the magnetic behavior and classification of ferrites are discussed, focusing on the spinel-type crystal structure (Fd3m) and the distribution of cations between tetrahedral and octahedral sites. Then, nickel ferrites are analyzed, including their magnetic and structural properties and their applications in electronic and magnetic devices. The following section addresses cobalt ferrites, exploring their physical and chemical characteristics, in addition to their advantages in technological applications. The review emphasizes the influence of cation distribution and spin inclination on magnetic properties, especially in nanoparticles, where surface effects and structural defects affect magnetization. Furthermore, strategies to optimize these properties through metal ion substitution and heat treatments are discussed. By consolidating the most relevant findings on nickel and cobalt ferrites, this article aims to provide an updated overview of the field, serving as a reference for future research and development of new functional materials.
Cesium (Cs) is a critical strategic metal with rapidly escalating demand, yet its extraction from brines is severely challenged by ultra-low concentrations and intense interference from competing ions such as sodium and potassium. Herein, we report a facile phase-inversion strategy to fabricate millimeter-sized MIL-101-SO3H/polyacrylonitrile (PAN) composite beads, integrating the high selectivity of sulfonic acid-functionalized MOFs with the mechanical robustness and processability of a polymeric matrix. The optimal composite beads achieved rapid adsorption equilibrium within 30 min, delivering a high Cs+ capacity of 0.63 mmol g−1 (83.8 mg g−1) and prominent selectivity over Na+ and K+ with selectivity factors of 22.0 and 4.4, respectively, in ternary systems. This selectivity is attributed to lower dehydration energy of Cs+ and matched sulfonate-sulfonate distances of MIL-101-SO3H. Furthermore, the beads exhibited excellent regenerability, retaining 89.2% of the initial capacity after five consecutive cycles using 0.05 M HCl at 50 °C. Mechanistic investigations revealed that ion exchange at sulfonate sites and coordination on Cr-O-C/Cr-O-Cr governed the adsorption process. This work presents a practical and scalable adsorbent platform for the efficient and selective recovery of cesium from complex aqueous media.
Mullite-type compounds are of research attention because of their interesting crystal-chemical, physical, and thermal properties. While there are rare instances of connectivity between GeO5 and GaO6 polyhedra via oxygen vertices, GdGaGeO5 can serve for this purpose, highlighting the diverse structural flexibility of the mullite-type structures. The polycrystalline sample is prepared by solid-state synthesis method. The obtained phase crystallizes in the space group Pbam as characterized from X-ray powder diffraction data by Rietveld refinement. Structural bond valence sum leaves clear hints for a complete miscibility of Ga/Ge has been observed between the octahedral and pyramidal sites. Lattice thermal expansion of each metric parameter is simulated using Grüneisen first-order approximation, where a single Debye term describes the vibrational energy. Phonon decay modelling of the temperature-dependent Raman frequency shifts helps to isolate the isothermal (quasi-harmonic) and isochoric (intrinsic anharmonicity) contributions. For this purpose, the mode Grüneisen parameter is obtained from pressure-dependent Raman experiments carried out in a diamond anvil cell. Analysis of UV/Vis diffuse reflectance spectra using both derivation of absorption spectra fitting (DASF) and Tauc's methods demonstrate that GdGaGeO5 is a wide band gap oxide with a direct optical band gap of approximately 5.23(5) eV, consistent with its insulating optical behavior.
Praseodymium-doped zirconium silicate pigments (Pr0.05Zr0.95SiO4) were synthesized via a solid-state reaction, and the synergistic effects of Na2SiF6 mineralizer content (0.5–4.5 wt%) and heating rate (1–20 °C/min) on phase formation, microstructure, oxidation-state distribution, and color development were systematically investigated. XPS analysis confirmed the coexistence of Pr3+ and Pr4+ species, with the Pr3+/Pr4+ ratio being strongly dependent on synthesis conditions, thereby governing the chromatic response of the pigments. In particular, higher heating rates promoted improved crystallinity of the zircon-type phase, while also influencing lattice distortion and microstructural evolution. Moderate mineralizer content (2.5 wt%) combined with controlled heating rates (10–20 °C/min) resulted in well-developed crystalline morphology, homogeneous elemental distribution, and efficient Pr incorporation into the zircon lattice. Microstructural refinement and nucleation effects induced by increased mineralizer content and heating rate further contributed to particle size reduction and improved uniformity. The most intense yellow coloration (b* ≈ 83) was achieved under optimized conditions (2.5 wt% Na2SiF6 and 20 °C/min), corresponding to enhanced stabilization of Pr4+ within the zircon structure. These results demonstrate that the chromatic performance of Pr-doped zircon pigments is governed by the synergistic control of synthesis parameters through their effect on the Pr3+/Pr4+ equilibrium, providing a rational strategy for the design of high-performance ceramic pigments for high-temperature applications.
