Molten Salt Method Research Articles

Functionalized MXenes for Enhanced Visible-Light Photocatalysis: A Focus on Surface Termination Engineering and Composite Design

MXenes, a groundbreaking class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have emerged as highly promising materials for photocatalytic applications due to their unique structural, electrical, and surface properties. These materials are synthesized by selectively etching the A layer from MAX phases, yielding compositions with the general formula Mn+1XnTx, where M is a transition metal, X represents carbon or nitrogen, and Tx refers to surface terminations such as –OH, –O, or –F. This review delves into the advanced synthesis techniques of MXenes, including fluoride-free etching and molten salt methods, and explores their potential in photocatalysis for environmental remediation. MXenes exhibit remarkable light absorption capabilities and efficient charge carrier separation, making them highly effective for the photocatalytic degradation of organic pollutants under visible light. Modulating their surface chemistry and bandgap via functional group modifications further enhances their photocatalytic performance. These attributes position MXenes as next-generation materials for sustainable photocatalytic applications, offering significant potential in addressing global environmental challenges.

Enhanced properties of (TaNbTiV)C high‐entropy carbide ceramics through controlled structure and morphology of high‐entropy carbide powders

AbstractSubmicron high‐entropy carbide (HEC) (TaNbTiV)C powders with various morphologies and properties were prepared using the molten salt method by adjusting structures and graphitization of carbon sources. Subsequently, the HEC ceramics were sintered at 1900°C using spark plasma sintering. Compared to traditional carbon sources (carbon black and flake graphite), powders synthesized using graphitic carbon microspheres with a spherical shape exhibited a smaller particle size of 0.45 µm, a larger specific surface area of 14.46 m2/g, and a larger lattice constant of 0.4451 nm. Moreover, the HEC powders prepared using graphitic carbon microspheres enhanced the sintering of the HEC matrix, leading to improved mechanical properties and oxidation resistance of the HEC ceramics compared to those prepared using other carbon sources. Unlike the precursor method used to adjust the HEC powder structure, the molten salt method is a low‐cost and straightforward approach to regulating the HEC powder structure by controlling the structure of raw material.

Upcycling Spent Selective-Catalytic-Reduction Catalyst to Produce Titanium Carbide Through Molten-Salt Electrolysis

The molten-salt electrolytic method was employed to recycle spent SCR catalyst to prepare TiC compound. A systematic investigation has been carried out through thermodynamic calculation and experimental analysis. The effects of graphite content, cell voltage, electrolyzing temperature, and electrolyzing time on electrolytic products were explored. The results show that a suitable amount of graphite content, high cell voltage, and a high electrolyzing temperature are beneficial to promote the formation of TiC compounds. It has also been found that the electroreduction of spent SCR catalyst/graphite can completely transform it into TiC compound in a relatively short time. The final electrolytic product is confirmed to be a solid solution of (Ti, W, Si, V)C. Meanwhile, the electrolytic process and reaction mechanism were investigated through the analysis of intermediates and the thermodynamic calculation. The electrolytic product has a potential application as reinforcement in metal matrix, which is a high additional-value utilization for spent SCR catalysts.

Li+ Quasi‐Grotthuss Topochemistry Transport Enables Direct Regeneration of Spent Lithium‐Ion Battery Cathodes

Direct regeneration of spent lithium‐ion batteries offers economic benefits and a reduced CO2 footprint. Surface prelithiation, particularly through the molten salt method, is critical in enhancing spent cathode repair during high‐temperature annealing. However, the sluggish Li+ transport kinetics, which relies on thermally driven processes in the traditional molten salt methods, limit the prelithiation efficiency and regeneration of spent cathodes. Here, we introduce a special molecular configuration (benzoate) into molten salts that facilitates rapid Li+ transport to the surface of LiNi0.5Co0.2Mn0.3O2 (NCM) via a quasi‐Grotthuss topochemistry mechanism, effectively avoiding the phase transitions that could adversely degrade the electrochemical performance due to insufficient lithiation during the repair process. Computational and experimental analyses reveal that the system enables fast Li+ migration through the topological hopping of benzoate in organic lithium salt, rather than relying solely on thermally driven diffusion, thereby significantly improving the prelithiation and repair efficiency of spent NCM cathodes. Benefiting from the quasi‐Grotthuss Li+ topochemistry transport, the degraded structure and Li vacancies in the spent cathode are effectively eliminated, and the regenerated cathode exhibits good cycling stability comparable to commercial counterparts. The proposed Li+ transport mechanism presents a promising route for the efficient regeneration of spent cathodes.

Li+ Quasi-Grotthuss Topochemistry Transport Enables Direct Regeneration of Spent Lithium-Ion Battery Cathodes.

Direct regeneration of spent lithium-ion batteries offers economic benefits and a reduced CO2 footprint. Surface prelithiation, particularly through the molten salt method, is critical in enhancing spent cathode repair during high-temperature annealing. However, the sluggish Li+ transport kinetics, which predominantly relies on thermally driven processes in the traditional molten salt methods, limit the prelithiation efficiency and regeneration of spent cathodes. Here, we introduce a special molecular configuration (benzoate) into molten salts that facilitates rapid Li+ transport to the surface of LiNi0.5Co0.2Mn0.3O2 (NCM) via a quasi-Grotthuss topochemistry mechanism. This approach effectively avoids the phase transitions that could adversely degrade the electrochemical performance due to insufficient lithiation during the repair process. Computational and experimental analyses reveal that the system enables fast Li+ migration through the topological hopping of benzoate in organic lithium salt, rather than relying solely on thermally driven diffusion, thereby significantly improving the prelithiation and repair efficiency of spent NCM cathodes. Benefiting from the quasi-Grotthuss Li+ topochemistry transport, the degraded structure and Li vacancies in the spent cathode are effectively eliminated, yieding the regenerated cathode with good cycling stability comparable to commercial counterparts. The proposed Li+ transport mechanism presents a promising route for the efficient and sustainable regeneration of spent cathodes.

Controlled A-site stoichiometric ratio and enhanced piezo-catalysis of K1−xNaxNbO3 powders prepared using a molten salt method

Controlled A-site stoichiometric ratio and enhanced piezo-catalysis of K1−xNaxNbO3 powders prepared using a molten salt method

A two-dimensional amorphous iridium-cobalt oxide for an acidic oxygen evolution reaction.

A two-dimensional (2D) amorphous iridium cobalt oxide (Am-IrCoyOx) was prepared using the molten salt method. The optimal catalyst shows a low overpotential of 230 mV at 10 mA cm-2 in 0.5 M H2SO4. DFT calculations show that the unsaturated Ir active sites on the surface are responsible for the excellent electrocatalytic performance. This work exhibits the advantages of 2D oxides and might find potential applications in other fields.

Recent Advances in Salt-Assisted Synthesis of 2D Materials.

Two-dimensional (2D) materials have been attracting extensive interest due to their remarkable chemical, optical, electrical, and magnetic properties, making them ideal candidates for a broad range of applications. Developing facile synthesis methods that can fabricate high-quality 2D materials in an efficient, scalable, and cost-effective way is essential. Among the emerging techniques, salt-assisted methods to synthesize 2D materials, including molten salt method, salt-assisted chemical vapor deposition, and salt-template method, has demonstrated significant potential in fulfilling these requirements. This review highlights recent advancements in the synthesis of 2D materials through salt-assisted methods, focusing on their preparation processes and wide-ranging applications. It also explores the role of salts, in various forms, in directing the formation of 2D structures, providing insights for strategic synthesis design. Finally, challenges and future directions in salt-assisted synthesis are discussed, emphasizing strategies to enable controllable, high-yield production of 2D materials.

Interfacial Engineering to Fabricate Nanoporous FeMo Bimetallic Nitride for Enhanced Electrochemical Ammonia Synthesis.

The electrochemical N2 reduction reaction (NRR) currently represents a green and sustainable approach to ammonia production. However, the further progress of NRR is significantly hampered by poor catalytic activity and selectivity, necessitating the development of efficient and stable electrocatalysts. Herein, a nanoporous Fe-Mo bimetallic nitride (Fe3N-MoN) is synthesized using a molten-salt preparation method. This catalyst demonstrates notable NRR performance, achieving a high NH3 yield rate of 45.1µgh-1mg-1 and a Faradaic efficiency (FE) of 26.5% at -0.2V (vs RHE) under ambient conditions. Detailed experimental studies and density functional theory (DFT) calculations reveal that the fabricated interface between Fe3N and MoN effectively modulates the surface electronic structure of the catalyst. The interface induces an increase in the degree of electron deficiency at the nitrogen-vacancy sites on the catalyst surface, allowing N2 molecules to occupy the nitrogen vacancies more easily, thereby promoting N2 adsorption/activation during the NRR process. Consequently, the Fe3N-MoN catalyst exhibits outstanding NRR activity. The insights gained from fabricating the Fe3N-MoN interface in this work pave the way for further development of interfacial engineering to prepare high-efficient electrocatalyst.

Research on the Adsorption Mechanism and Performance of Cotton Stalk-Based Biochar.

In this research, we produced two types of biochar (BC) using cotton stalks as raw material and KOH as an activator, and compared their performance and adsorption mechanisms in the removal of tetracycline (TC) and methylene blue (MB) from wastewater. The results showed that the biochar generated using both procedures formed pores that connected to the interior of the biochar and had extensive microporous and mesoporous structures. The molten salt approach produces biochar with a higher specific surface area, larger pore size, and higher pore volume than the impregnation method, with a maximum specific surface area of 3095 m2/g. KBCM-900 (the BC produced using the molten salt method at 900 °C) had a better adsorption effect on TC, with a clearance rate of more than 95% in 180 min and a maximum adsorption amount of 912.212 mg/g. The adsorption rates of the two BCs for MB did not differ significantly at low concentrations, but as the concentration increased, KBCI-900 (the BC generated by the impregnation method at 900 °C) exhibited better adsorption, with a maximum adsorption of 723.726 mg/g. The pseudo-second-order kinetic model and the Langmuir isotherm model may accurately describe the TC and MB adsorption processes of KBCI-900 and KBCM-900. The KBCI/KBCM-900 adsorption process combines physical and chemical adsorption, with the primary mechanisms being pore filling, π-π interactions, hydrogen bonding, and electrostatic interactions. As a result, biochar generated using the molten salt method is suitable for the removal of large-molecule pollutants such as TC, whereas biochar prepared using the impregnation method is suitable for the removal of small-molecule dyes such as MB.

Utilization of Novel (KNbO3)1−x(Ba2FeNbO6)x (x = 0.1, 0.2, 0.3) Solid Solutions for Efficient Photo‐Assisted Fenton Degradation of Methylene Blue Dye

Novel (KNbO3)1−x(Ba2FeNbO6)x (x = 0.1, 0.2, 0.3) solid solutions corresponding to K0.82Ba0.18Fe0.09Nb0.91O3, K0.64Ba0.36Fe0.18Nb0.82O3, and K0.46Ba0.54Fe0.27Nb0.73O3 compounds have been synthesized via molten salt method. X‐ray diffraction confirms the formation of solid solutions, while transmission electron microscopy combined with energy‐dispersive spectroscopy results demonstrates a homogeneous distribution of elements. The obtained solid solutions crystallized in a cubic crystal structure, whereas the parent KNbO3 possesses an orthorhombic structure. The wide bandgap semiconductor KNbO3 transformed into a visible‐light‐active material, with its bandgap energy reduced from 3.56 eV to ≈2.4 eV. The substitution of K in KNbO3 with Ba is responsible for structural modification from orthorhombic to cubic symmetry, whereas both structural modification and the substitution of Nb with Fe correlated with optical properties. The photocatalytic activities of all obtained solid solutions are improved compared with the parent KNbO3 and Ba2FeNbO6 compounds for photocatalytic degradation of methylene blue (MB) dye. Among the series of solid solutions, K0.82Ba0.18Fe0.09Nb0.91O3 photocatalysts show the highest MB removal efficiency owing to its relatively higher surface area, suppressed charge carrier recombination, and more negative conduction band edge. Moreover, K0.82Ba0.18Fe0.09Nb0.91O3 photocatalyst (0.1 g) combined with hydrogen peroxide (H2O2) to form a novel photo‐Fenton system, achieving almost complete degradation of 100 mL of 10 mg L−1 MB dye in 30 min.

Multi-enzyme simulation activity of MXene-based metal composites and the application for detection and degradation of phenolic pollutants

Phenolic pollutants are commonly employed in industries such as petrochemicals, dyeing, textiles, and pesticides, which cause great harm to our living environment and food safety. In this paper, the MXenes-based metal composites (M/MXenes, M = Cu, Co, Ni, Zn, Fe, Mn) with multi-enzyme mimic activity were prepared by a facile molten salt method. The M/MXenes have mimic catalytic activity of peroxidase (POD), ascorbic acid oxidase (AAO), catalase (CAT), superoxide dismutase (SOD) and laccase. The catalytic properties of M/MXenes were analyzed and discussed in detail. In addition, M/MXenes still have excellent catalytic performance and stability in harsh pH and high temperature environments, making them very suitable for practical applications. Due to the excellent laccase mimic activity of M/MXenes, a simple colorimetric sensor was constructed for the detection and degradation of phenolic pollutants. Because obvious color changes can be observed during the catalytic process of phenolic pollutants by M/MXenes, M/MXenes were fixed into sodium alginate (SA) to form a simple hydrogel-based sensing platform for 2, 4-chlorophenol, methoxyphenol, 4-bromophenol, 3-bromo-4-methoxyphenol, 3-bromo-4-methylphenol, hydroquinone and 1,8-naphthol. By introducing different concentrations of phenolic compounds, a series of color changes on the gel carrier can be observed by naked eyes. Then, the red (R), green (G) and blue (B) values matching with the color change of the hydrogel were read out by the color recognition application in the smartphone, and the RGB value was converted into the concentration of phenolic compounds, which offered a convenient and reliable method for the rapid detection of phenolic compounds. Thus, the strategy offers the potential in rational design of nanozymes with the advantages of multi-enzyme mimic activity, simple preparation, low cost and good stability.

N-doped hierarchical porous carbon derived from corncobs by molten salt method for high-performance supercapacitors

The use of biomass-derived carbon in supercapacitors is widespread due to the advantages of low price and environmentally friendly. However, these materials often exhibit limitations regarding specific capacity and cycle characteristics. Therefore, in this study, N-doped hierarchical porous carbon (NPC) was obtained by one-step LiCl/KCl molten salt carbonization activation using biomass waste corncobs as the carbon precursor and urea as an N doping medium. By modifying the ratio of molten salt to precursor, NPC-10 exhibits an optimal microstructure including specific surface area and pore characteristics. Furthermore, the suitable degree and type of N doping provide additional reactive active sites for energy storage. The combination of N doping and hierarchical porous improves the energy storage capacity of the NPC. The NPC-10 has a specific capacity of 278.2Fg-1 at 1Ag-1 and maintains 169.5Fg-1 at 100Ag-1. This study offers a novel approach to the synthesis of hierarchical porous carbon materials derived from biomass for the storing energy in supercapacitors.

Facilitating Oriented Electron Transfer from Cu to Mo2C MXene for Weakened Mo─H Bond Toward Enhanced Photocatalytic H2 Generation.

Mo2C MXene (Mo2CTx) is recognized as an excellent cocatalyst due to unique physicochemical properties and platinum-like d-band of Mo active sites. However, Mo sites of Mo2CTx with high-density empty d-orbitals exhibit strong Mo─Hads bonds during photocatalytic hydrogen evolution, leading to easy adsorption of hydrogen ions from solution and unfavorable desorption of H2 from Mo sites. To weaken the Mo─Hads bond, a strategy of oriented electron transfer from Cu to Mo2CTx to increase the antibonding orbital occupancy of Mo─Hads hybrid orbitals is implemented by introducing Cu into Mo2CTx interlayers to form Cu-Mo2CTx. The Cu-Mo2CTx is synthesized from Mo2Ga2C and CuCl2 via a one-step molten salt method and combined with TiO2 to form Cu-Mo2CTx/TiO2 photocatalyst through an ultrasound-assisted approach. Hydrogen production tests reveal that an exceptional performance of Cu-Mo2CTx/TiO2 (6446µmol h-1 g-1, AQE=18.3%) is 8.4 fold higher than that of Mo2CF2/TiO2 (Mo2CF2 by the conventional etchant NH4F+HCl). Density functional theory (DFT) calculations and characterization results corroborate that the oriented electron transfer from Cu to Mo2CTx increases the Mo─Hads antibonding occupancy in Cu-Mo2CTx, thereby weakening Mo─Hads bonds and accelerating the hydrogen evolution rate of TiO2. This research offers valuable insights into optimizing H-adsorption capabilities at active sites on MXene materials.

From Ba2Bi2Zn(PO4)4 to Ba2Bi2Cu(PO4)4: Rational design of an ultraviolet phosphate with enhanced birefringence

Despite its inherent challenges, the exploration of UV phosphates with enhanced birefringence holds immense importance. In this study, a unique Ba2Bi2Zn(PO4)4-type phosphate, Ba2Bi2Cu(PO4)4, was successfully obtained through a judicious combination of a substitution design strategy and a molten salt method. In comparison to Ba2Bi2Zn(PO4)4, Ba2Bi2Cu(PO4)4 was characterized by a distinctive ∞[Cu(PO4)4]10- chain, which not only enhanced its birefringence (reaching 0.057@546.1 nm) but also maintained a comparable ultraviolet cut-off edge (296 nm) and a similar thermal behavior.

La0.8Sr0.2Cr0.5Fe0.5O3-δ (LSCF) synthesized by molten salt method

La0.8Sr0.2Cr0.5Fe0.5O3-δ was synthesized by the molten salt method using NaCl and KCl as the molten salt medium. The specimens were analyzed by XRD, SEM, TG, and DSC. The results are listed as follows: Firstly, all of them have orthorhombic crystalline perovskite structure under the conditions of 1000–1200 °C; the optimum temperature and holding time for the synthesis of La0.8Sr0.2Cr0.5Fe0.5O3-δ by the molten salt method is 1100 °C for 3 h. Secondly, the thermal and kinetic analysis allow the synthesis of La0.8Sr0.2Cr0.5Fe0.5O3-δ to be divided into three stages, with the first phase being the decomposition of La(OH)3, the second phase being the synthesis of La2CrO6 and SrCrO4, and the third phase being the synthesis of La0.8Sr0.2Cr0.5Fe0.5O3-δ, with the activation energies of 0.4408 (KJ·mol−1), 0.1188 (KJ·mol−1), and 0.3631 (KJ·mol−1). Finally, the synthesis mechanism of La0.8Sr0.2Cr0.5Fe0.5O3-δ powder synthesized by the molten salt method is "dissolution-precipitation."

Developing Catalysts for Proton and Anion Exchange Membrane Water Electrolyzers

To achieve carbon neutrality, extensive research is ongoing to produce green hydrogen via water electrolysis combined with renewable energy sources. Understanding and developing catalysts for membrane electrode assembly (MEA) type water electrolysis systems, such as proton exchange membrane water electrolysis (PEMWE) and anion exchange membrane water electrolysis (AEMWE), are critical steps toward this goal. Therefore, this presentation will focus on catalyst development for PEMWE and AEMWE, with emphasis on cost-effective catalysts.For oxygen evolution reaction (OER) catalysis in PEMWE, the primary challenge is to minimize iridium (Ir) usage for sustainable green hydrogen production. Layered monoclinic iridium nickel oxide (IrNiOx) platelets were synthesized using a molten salt method and employed for the OER. These platelets exhibited high OER activity with reduced Ni dissolution in acidic conditions. When applied in MEA, they demonstrated enhanced interconnectivity within the catalyst layer, promoting electron transfer. Even at low Ir loading (0.2 mgIr cm-2), the platelets showed good performance with an initial cell voltage of 1.70 V at 1 A cm-2 and minimal degradation over 100 hours. This highlights the effectiveness of incorporating transition metals into Ir oxide to reduce Ir usage in PEMWE.For oxygen evolution reaction (OER) catalysis in AEMWE, attention is focused on nickel iron (NiFe) hydroxide catalysts for their high activity and stability in alkaline conditions. However, the lack of initial electrical conductivity of as-prepared NiFe LDH limits its potential as an electrocatalyst. To address this issue, a monolayer structuring approach was proposed. This method improved mass transport to allow a high energy conversion efficiency of 72.6% with exceptional stability over 50 hours at 1 A cm-2. Additionally, lack of initial electrical conductivity hinders determination of electrochemically active surface area (ECSA) of NiFe LDH using conventional double layer capacitance method. Use of electrochemical impedance spectroscopy (EIS) at reactive OER potentials to extract the capacitance that is hypothesized to arise due to reactive OER intermediates (O*, OH*, OOH*) adsorbed on the catalyst surface was thus investigated. This allowed the estimation of ECSA and intrinsic activity of NiFe LDH, validating the methodology through rigorous catalyst loading and support studies.For hydrogen evolution reaction (HER) catalysis in AEMWE, replacing platinum (Pt) with Ni-based alloys containing molybdenum (Mo) species has shown promise. Dynamic active sites of Ni catalysts with Mo species require innovative approaches to maintain initial performance, warranting material innovation or careful manipulation of operating protocol. The approaches in which this is made possible is shortly presented, together with the innovations that allows probing of such phenomenon.

Optimized Cycling Stability of Single-Crystalline Na0.67Ni0.33Mn0.67O2 Cathode Material via Molten Salt Synthesis for Advanced Sodium-Ion Battery Applications

Recent advancements have highlighted the P2-layered Na0.67Ni0.33Mn0.67O2 (NNMO) cathode material as a leading candidate for next-generation sodium-ion batteries due to its superior specific capacity. Traditional solid-state synthesis methods, while straightforward and scalable, struggle with challenges such as achieving homogeneous atomic-level elemental distribution and mitigating the formation of intermediate phases during powder mixing. In contrast, the molten salt synthesis method offers a controllable and efficient alternative for producing uniform materials with varied chemical compositions and structures. In this study, we utilize sodium chloride as the molten salt flux, with Na2CO3, NiO, and Mn2O3 as reactants, to synthesize single-crystal MS-NNMO. This method yields an NNMO with an initial reversible capacity of 90.6 mAh g−1 at 0.1C across a voltage range of 2.0-4.2 V, demonstrating 88.5% capacity retention after 100 cycles. Long-term stability is further evidenced by an 83.9% capacity retention after 300 cycles at 1C. In full cell tests, MS-NNMO paired with a hard carbon anode shows 90.3% capacity retention after 200 cycles at 1C. Additionally, MS-NNMO exhibits exceptional bulk stability, with no impurity peaks detected after 1 hour of water exposure, underscoring its superior air stability. This work validates the molten salt method as an effective and scalable process for producing high-performance sodium-ion battery cathodes.

Tailoring Particle Size/Morphology for the Stable Cathode Performance of Polygonal-Shaped Li(Ni,Mn)2O4 Single Crystals

We regulate the particle size and surface facet of single-crystal (SC) Li(Ni,Mn)2O4 cathode materials to give guidance without compromising electrochemical performance. Adjusting the molten salt method with selecting sintering aids , we synthesized size controlled SC particles, both small and large, and evaluated their electrochemical characteristics focusing on differences in the lithiation/delithiation reactivity depending on size with crystal facet conditions. While the initial charge capacity is similar to each other, the given cathode using an small SC particle with ordered crystalline and uniform particle sizes (≤5 um) exhibits outstanding rate capability with stable capacity retention irrespective of loading density and current density, which indicates the stable lithium transport during the repetitive electrochemical reactions. The dependency of the impedance response with change in the electrode resistances as well as the stability during the cycle reactions in conjunction with the post-mortem the Li distribution by using laser-induced breakdown spectroscopy as function of porosity change and cell degradation are thoroughly discussed from the standpoint of regulated particle property.

Enhanced Electromagnetic Wave Absorption in W-Type Ba-Hexaferrites: Role of Composition and Grain Growth

W-type Ba-hexaferrite, BaZn2−xCoxFe16O27, was synthesized via both conventional solid-state (x = 0.4, 0.5, 0.6, 0.75, 1.0, 1.25, 1.5) and molten-salt methods (x = 0.75, 1.0, 1.25). The structure, electromagnetic (EM) properties, and EM wave absorption characteristics were examined across a frequency range of 0.1–18 GHz, focusing on the influence of varying x. As x increased from 0.4 to 0.75, the magnetic anisotropy field (Hani) decreased, reaching its minimum at x = 0.75, before rising again as x continued to increase up to 1.5. Hani was found to be proportional to the ferromagnetic resonance (FMR) frequency, allowing for the tuning of the EM wave absorption frequency range. W-type hexaferrite–epoxy composites (10 wt%) with x values between 0.6 and 1.5 exhibited outstanding wideband EM wave absorption, with a maximum absorption (RLmin < −50 dB) and a wide absorption bandwidth where RL < −10 dB extended beyond 10 GHz (Δfwb > 10 GHz). The x = 1.25 sample with a thickness of 2.37 mm achieved RLmin = −69 dB at 7.8 GHz, while the x = 1.0 sample with a thickness of 2.33 mm delivered Δfwb = 12.5 GHz (5.1–17.6 GHz). Samples synthesized via the molten-salt method showed larger plate-like grain growth compared to those produced by the solid-state method, with permeability spectra shifting to lower frequencies, consequently lowering the EM wave absorption band.