Molten Salt Method Research Articles

Influence of (Ta Nb Ti V) C powders synthesized by molten salt at low temperature on densification and properties of high entropy carbide ceramics

AbstractPowder synthesis is crucial for achieving the densification and facilitating widespread applications of high entropy carbide (HEC). Specifically, the production of fine particle‐size powders is essential to enhance the densification of HECs. Consequently, this paper proposes the molten salt method for synthesizing HEC powders. The synthesis process successfully yielded (Ta Nb Ti V) C powders with a particle size of only 0.44 µm at 1400°C, exhibiting a uniform distribution of each element. Subsequent densification of (Ta Nb Ti V) C within the 1700–1900°C temperature range was carried out using spark plasma sintering. It was observed that as the densification temperature increased, the densification and mechanical properties of HEC significantly improved. This study presents innovative ideas for the preparation of HEC at lower temperatures.

Crystal structural, morphological and Raman spectroscopy characterizations of Ba0.97La0.02Ti1-xNb4x/5O3 (0.00 < x < 0.10) ceramics

In our present study, we have synthesized polycrystalline ceramics with the chemical composition Ba0.97La0.02Ti(1-x)Nb4x/5O3, denoted as BLTi1-xNb4x/5, where x takes on various values, including 0.00, 0.02, 0.05, 0.07, and 0.10. The materials were prepared through a molten salt method, followed by the formation of powders into pellets, and subsequent sintering at 800 °C for 24 h in the air. Through X-ray diffractometer (XRD), we confirmed that the synthesized ceramics exhibited a tetragonal perovskite structure, and they were found to be in a single phase. Surface characteristics were determined using Scanning Electron Microscopy (SEM). Raman spectroscopic investigations further verified the tetragonal perovskite structure of our materials. Additionally, this analysis revealed the successful incorporation of La3+ ions in place of Ba2+ ions within the A-site and Nb5+ ions substituting for Ti4+ ions within the B-site of the BT lattice. Notably, our study demonstrated the capability to adjust the Raman shifts of essential optical modes. While the majority of Raman shifts remained unchanged, La and Nb doping had a significant impact specifically on the A1[TO3] mode. This mode is associated with the deformation of the oxygen octahedron centered on the central Ti ion, indicating that the influence of these dopant ions primarily pertains to the B-site of the material.

Structure, dielectric, and energy storage properties of perovskite CaTiO3 ceramic synthesized using the natural calcium from Pensi shell (Corbicula moltkiana) waste

Recently, dielectric capacitors have attracted immense interest as energy storage materials. In this work, we prepare the dielectric material CaTiO3 by the molten-salt method, utilizing Pensi shell waste as a natural calcium source, aligning with principles of green chemistry. Pensi shell contains 53.1 % calcium oxide, as revealed by TGA analysis, suggesting its potential use as a natural precursor in CaTiO3 synthesis. The phase formation, structure, and electrical properties of the resulting CaTiO3 phase are investigated. XRD data revealed the formation of single-phase CaTiO3 and a distortion of the TiO6 octahedra, accompanied by displacement of the A-site cations resulting in an orthorhombic Pbnm structure. CaTiO3 exhibits good linear dielectric characteristics with an energy storage efficiency of 84.8 %.

Rapid and high-throughput synthesis of rare earth molybdate materials via molten salt method

The exceptional electronic structure of rare earth molybdates renders them highly suitable for applications in photocatalysis and photoluminescence. However, currently available methods for preparing rare earth molybdates suffer from drawbacks such as inefficient yields, prolonged synthesis duration and high sintering temperatures. Here we present a novel molten salt method that facilitates rapid and high-throughput preparation of rare earth molybdate materials. This method achieved a yield of 99% for the synthesis of rare earth molybdate within a 5 h duration. An investigation into the structural and morphological characteristics of synthetic rare earth molybdate was conducted. The photocatalytic activity of Nd6MoO12 and Ln2MoO6 (Ln = La, Nd, Sm, Eu, and Gd) for Methylene blue degradation demonstrates their effective functional applications in the field of photocatalysis. The fluorescence properties of Sm3+/Eu3+-doped Gd2MoO6 demonstrate their potential applications in white light emitting diodes. These studies provide a new path to realize the synthesis of rare earth molybdate functional materials in a rapid and high-throughput manner.

Constructing the facet junction on solid solution BiOBr1-xClx for efficient photocatalytic CO2 reduction with H2O

Photocatalytic conversion of CO2 to renewable clean fuels was a promising way to alleviate the energy crisis and solve environmental issues. However, it remained significantly challenging for designing highly efficient photocatalysts. Herein, the solid solution BiOBr1-xClx (0 ≤ x ≤ 1, BOBC-n, n represented the amount of molten salt) with (001)/(102) facet junction was constructed through a molten salt method. In situ photochemical probing demonstrated that distinct exposed facets allowed photogenerated holes and electrons to migrate to the dominantly exposed and co-exposed facets and thus exhibited different reactivity. Benefiting from facet junction, the optimized BOBC-0.5 exhibited the superior performance of photocatalytic CO2 to CH3OH (5.52 μmol·g−1·h−1) to that of BiOBr with (001)/(110) facet junction (1.78 μmol·g−1·h−1). The density functional theory (DFT) calculations further confirmed the separation path of photogenerated carriers between distinct facets, which realized the effective spatial separation of electrons and holes. Moreover, the (102) facet revealed superior adsorption energy of CO2 molecules to that of (110) facet. This work highlighted a molten-salt strategy to build facet junction for boosting photocatalytic CO2 performance.

Ti2CTx MXene Cathode Host for Enhanced Zinc‐Bromine Battery Performance

AbstractAqueous zinc‐bromine batteries represent a promising large‐scale energy storage system, yet generally suffer from the dissolution of polybromides in the cathode. Currently, various nonpolar carbon materials are employed as hosts for the bromine cathode. Still, they typically exhibit weak adsorption capabilities toward polybromides. Here, a highly conductive Ti2CTx MXene synthesized through an eco‐friendly molten salt method is reported, serving as an ideal bromine cathode host material for the first time. Ti2CTx MXene shows strong chemisorptive capability to soluble polybromide species and can effectively immobilize them for enhanced coulombic efficiency and prolong cycling life of zinc‐bromine batteries. Additionally, Ti2CTx MXene enhances the reaction kinetics of the bromine cathode. Benefiting from the synergistic polybromide adsorption and catalysis effects of Ti2CTx, the dual‐plating zinc‐bromine batteries exhibit good cycle stability, with a capacity retention of 87% after 3000 cycles, outperforming traditional carbon host which fail after 2300 cycles. Meanwhile, Ti2CTx achieves a much lower polarization voltage of only 84 mV, significantly less than 240 mV observed with carbon hosts. This research highlights the potential of developing host materials with polybromide chemisorptive properties to advance the performance of zinc‐bromine batteries.

High temperature synthesis, surface characterization, and photoluminescence property of boron carbon nitride

The present study demonstrates the synthesis of boron carbon nitride (BCN) by molten salt method which utilizes melamine (source of carbon and nitrogen), boric acid (source of boron) and potassium chloride as the salt. The synthesis is performed at 915 °C for 4 h under N2-atmosphere. The synthesized material is further acid-treated. The physicochemical characterization data for as-synthesized and acid-treated materials confirm successful synthesis of BCN. SEM and AFM data display that synthesized BCN pre and post acid-treatment exhibit sheet-type morphology. Thermogravimetric analysis data confirm that the acid-treated material is thermally stable up to 800 °C, with only 2 % mass-loss is observed till 800 °C. Water contact angle measurement study demonstrates that acid-treatment significantly improves the surface hydrophilicity. Additionally, the low photoluminescence peak intensity of the acid-treated material indicates low electron-hole pair recombination rate. The synthesized material may be useful for the photocatalytic degradation of potentially toxic chemicals from water.

Crystal Structure and Molten Salt Environment Cooperatively Controlling the Morphology of the Plate-like CaMnO3 Template through Topochemical Conversion.

In the field of oxide thermoelectrics, perovskite CaMnO3 ceramics have drawn plenty of attention due to their chemical stability, low cost, and environmental friendliness. By employing Ruddlesden-Poppe phase Ca3Mn2O7 as a precursor, the plate-like CaMnO3 microcrystals were successfully synthesized by the molten salt method combined with topochemical microcrystal conversion (TMC). The plate-like morphology of CaMnO3 was coordinately optimized by modulating the crystal structure of MnO2 and the molten salt environment. Plate-like microcrystals with an average size of ∼14.55 μm and a thickness of ∼2.89 μm were obtained by TMC reaction, demonstrating an obvious anisotropy. When β-MnO2 was used as the raw material, a length-thickness ratio of 4.77 was obtained, which was attributed to the fact that CaMnO3 inherited the plate-like morphology of the Ca3Mn2O7 precursor during the TMC. The results confirm that the plate-like CaMnO3 microcrystals with obvious anisotropy can provide excellent template seeds for high-quality CaMnO3-based textured ceramics.

Nano-laminated BN modified graphite reinforced unfired MgO–C refractories: Preparation, properties and strengthening mechanism

To solve the problem of deterioration of oxidation resistance and thermal shock resistance caused by low carbonization of MgO–C refractories, nano-laminated BN modified graphite was prepared by the molten salt method to reinforce unfired MgO–C refractories. The findings revealed that the introduction of nano-laminated BN modified graphite significantly improved the mechanical properties. Moreover, the oxidation index of MgO–C refractories with 4 wt% nano-laminated BN modified graphite was 34% lower than that of the unadded sample, and the residual strength after thermal shock was significantly increased by 224%. Furthermore, incorporating nano-laminated BN modified graphite facilitated the formation of columnar Mg2SiO4, octagonal columnar MgAl2O4, and MgO–Mg2SiO4–MgAl2O4–Mg3B2O6 dense layers, thereby contribute to overall performance improvements.

Partially oxidized mackinawite/biochar for photo-Fenton organic contaminant removal: Synergistically improve interfacial electron transfer and H2O2 activation

Immobilizing Fe-based nanoparticles on electron-rich biochar has becoming an attractive heterogeneous Fenton-like catalysts (Fe/BC) for wastewater decontamination. However, the insufficient graphitization of biochar causing low electron transfer and by slow H2O2 activation limited its application. Herein, we firstly constructed FeS/biochar composite through all-solid molten salt method (Fe/MSBCs), which can provide strong polarization force and liquid reaction environment to improve carbonization. As expected, the obtained Fe/MSBCs exhibits high surface area and fast interfacial electron transfer between FeS and biochar. More importantly, the partially oxidized FeS (001) facet facilitate H2O2 adsorption and thermodynamically easily decomposition into •OH. Such a synergistic effect endowed them excellent photo-Fenton degradation performance for methyl orange (MO) with large kinetic rate constants (0.079 min−1) and high H2O2 utilization efficiency (95.9%). This study first demonstrated the critical regulatory role of molten salt method in iron-based biochar composites, which provide an alternative for H2O2 activator in water pollutant control.

One-step synthesis of BiOCl/Bi4NbO8Cl heterostructures with high-purity and enhanced photocatalytic activities via in-situ room-temperature acid-etching

In this study, BiOCl/Bi4NbO8Cl heterojunctions with improved photocatalytic performance were designed and synthesized by in-situ room-temperature acid-etching. Bi4NbO8Cl prepared by the solid-phase method was often accompanied by certain impurities, such as Bi24O31Cl10 and Bi3NbO7. With the assistance of glacial acetic acid, the impurities could be eliminated. At the same time, BiOCl nanosheets were formed in situ at room temperature, and BiOCl/Bi4NbO8Cl (BBN) heterostructures were obtained. For comparison, pure Bi4NbO8Cl was prepared using the molten salt method (S-BNC). Compared to S-BNC, BBN exhibited better performance in degrading rhodamine B (RhB) and ciprofloxacin (CIP). The mechanism of the improved photocatalytic activities was studied by analyzing photoluminescence spectra, UV–vis diffuse reflection absorption spectra, and cyclic voltammetry curves.

Structural and resistivity properties of Fe1-xCoxSe single crystals grown by the molten salt method

A series of tetragonal Fe1-xCoxSe single crystals with a complete Co doping range (0 ≤ x ≤ 0.52) up to its solid solubility limit in FeSe have been grown by an eutectic AlCl3/KCl molten salt method. The typical lateral size of as-grown Fe1-xCoxSe single crystals is 1–5 mm. The chemical composition and homogeneity of the crystals was examined by both inductively coupled plasma atomic emission spectroscopy and energy dispersive spectrometer. X-ray diffraction analysis demonstrates that the crystal lattice parameters a and c are both linearly decreased with increasing Co doping level x. In the whole doping range, all the samples show metallic behaviour in contrast to a metal insulator transition of Cu-doped FeSe according to the resistivity measurements.

One-step molten salt synthesis of high entropy oxides

High-entropy oxides (HEOs) have received widespread attention owing to their tunable properties and vast composition spaces. However, the universal synthesis of HEOs with high purity still faces challenge. In this work, a one-step molten salt method is reported for the synthesis of phase-pure rock salt-type (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O. When used as an anode material for lithium-ion batteries, (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O exhibits high specific capacity and cycling stability, maintaining a capacity retention of 94% after 220 cycles (0.2 A g−1). The superior performance can be attributed to accelerated electron and ion transport as well as enhanced Li adsorption/coupling induced by internal defects. To further demonstrate the wide applicability of the molten salt method, single-phase spinel and pyrochlore HEOs are also successfully synthesized. The presented molten salt method, with its ease of operation, homogeneous reaction environment and low synthesis temperatures, makes it an ideal synthesis technique for the development of novel HEO powders, especially for electrode materials.

P-Ni co-doped Mo2C embedded in carbon-fiber paper as a highly efficient electrocatalyst for hydrogen evolution in alkaline media

The development of noble-metal-free electrocatalysts with high electrocatalytic performance and stability by adopting a scalable route is key to solving the energy crisis. We report a PNi co-doped Mo2C-based electrocatalyst with high hydrogen evolution reaction (HER) catalytic activity prepared by a molten-salt method. Using phosphating times of 2 h and 4 h yielded P-Ni-Mo2C-2h and P-Ni-Mo2C-4h, respectively, both of which exhibited nanoflower-like structures that provided abundant active sites for the reaction. P-Ni-Mo2C-2h possessed good electrocatalytic properties with a low overpotential of only 140.5 mV at j = 10 mA cm−2 and a small Tafel slope of 50.7 mV dec−1 in an alkaline environment. P-Ni-Mo2C-2h exhibited excellent stability after 20 h of continuous hydrogen production. The use of an excessively long phosphating time caused a narrow down of spaces formed by nanoflakes, thereby reducing the HER performance of the electrocatalyst. The results of this study provide guidelines for the preparation of high-efficiency PNi co-doped electrocatalysts.

Luminescence properties of (Gd, M)2O2S: Tb3+, Dy3+ (M = Lu, Y, Zn, Ti) phosphors

(Gd, M)2O2S: 3.5 %Tb3+, 0.75 %Dy3+ (M = Lu, Y, Zn, Ti) phosphors were prepared using a molten salt method. The samples were characterized using XRD, SEM, UV–visible absorption spectroscopy, photoluminescence and cathodoluminescence. The XRD results showed that the phosphors introduced by different cations were still hexagonal crystal system although the unit cell shrinks. SEM showed particle sizes between 150∼1000 nm. The doping of Dy3+ can effectively improve the luminescence of Tb3+. The photo- and cathodo-luminescence spectra of (Gd, M)2O2S: 3.5 %Tb3+, 0.75 %Dy3+ indicated the luminescence intensity of Gd2O2S: 3.5 %Tb3+, 0.75 %Dy3+ can be effectively improved that when adding M = Lu, Y, Zn. The same energy transfer mechanism was followed. (Gd, Ti)2O2S: 3.5 %Tb3+, 0.75 %Dy3+ possessed favorable thermal stability. When the temperature rose to 425 K, the luminescence intensity was 74.6 % of that at 300 K. The charge-transfer process of Tb3++Ti4+↔ Tb4++Ti3+ provides new ideas for obtaining high thermal stability sulfur oxide phosphors.

Study on the pathway of performance improvement and mechanism of Gd2O2S:Tb3+ green phosphor

To improve the luminescence performance of Gd2O2S:Tb3+, Gd2O2S:Tb3+, Tm3+, Gd2O2S:Tb3+, Dy3+, Tm3+ and Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 phosphors have been prepared by molten salt method. The samples are characterized using XRD, SEM, TEM, FT-IR, UV-Vis absorption spectroscopy, photoluminescence, cathodoluminescence and thermal stabilization tests. XRD tests and refinement results show that the crystal structure of the phosphor is still the hexagonal Gd2O2S crystalline phase and the lattice parameter decrease due to Dy3+/Tm3+ occupying the Gd3+ sites. SEM images and mapping of each element show that the particle grain and all expected elements distribute uniformly. TEM results illustrate that SiO2 coating is in an amorphous form on the surface of the powder grains. FT-IR tests indicate that SiO2 is present on the powder surface through Si-O-Gd bonding. The results of photoluminescence and cathodoluminescence show that the luminescence intensity increase 50% while adding Tm3+ into Gd2O2S:Tb3+, Gd2O2S:Tb3+, Dy3+ phosphors caused mainly by the energy transfer from Dy3+/Tm3+ to Tb3+. The core-shell structure of Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 has better photoluminescence and cathodoluminescence and the fluorescence lifetime remains unchanged while SiO2 coats phosphor. And it has good thermal stability. Its luminescence intensity at 425 K reaches 71.4% of that at room temperature, which is better than the corresponding value (46.4%) for the uncoated sample.

Chloride molten salt derived attapulgite with ground-breaking electrochemical performance

The existence of adsorbed water and structural water in the crystal structure of attapulgite (ATP) endows it with poor capability to store lithium ions. Herein, the chloride molten salt method was developed to function ATP materials based on theoretical calculations, which exhibit ground-breaking electrochemical performance. After the modification process, the metal ions in chloride molten salt occupy the vertices of the Mg-O octahedral structure from the liberation of structural water and hydroxyl groups in ATP, forming MaMgbAlcSixOy (M = Li, Na, or K). Using LiCl molten salt-modified ATP (Li-ATP) as a proof-of-concept, the detailed phase transition, physicochemical properties, and lithium storage capacity were investigated. Compared to the original ATP, Li-ATP achieves a nearly 7-fold increase in lithium storage capacity (498 mAh/g), featuring a promising low-cost polyanionic type anode material.

Regulation of Photogenerated Redox Species through High Crystallinity Carbon Nitride for Improved C-S Coupling Reactions.

A novel and efficient approach for the synthesis of α, β-unsaturated sulfones through heterogeneous photocatalyzed C-S coupling reactions have been developed. The use of molten-salt method derived carbon nitride (MCN), a transition metal-free polymeric photocatalyst, combined with enhanced crystallinity and potassium iodide as an additive, effectively modulates photogenerated reactive redox species, markedly increasing the overall reaction selectivity. This method achieves the shortest reaction time (2 h) with high yield (up to 95 %) among the reported heterogeneous catalytic C-S bond formation reactions, matching the efficiency of the homogeneous photocatalysts. Furthermore, the application to challenging alkyne substrates has been demonstrated, underscoring the potential for a broad range of applications in pharmaceutical research and synthetic chemistry.

Stabilizing Highly Active Ru Sites by Electron Reservoir in Acidic Oxygen Evolution.

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO2 is regarded as a promising alternative to IrO2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO2. However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO2 with large specific surface areas. The experimental results revealed that a high content of surface Ru4+ species promoted the OER intrinsic activity of high-valence doped RuO2. It was found that there was a linear relationship between the ratio of surface Ru4+/Ru3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru4+/Ru3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re0.1Ru0.9O2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm-2. More importantly, Re0.1Ru0.9O2 demonstrated outstanding stability at both 10 mA cm-2 (over 300 h) and 100 mA cm-2 (over 25 h). The characterization of post-stability Re0.1Ru0.9O2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER.

A facile eutectic mixed molten salt method for synthesizing LiNi0.5Co0.2Mn0.3O2 cathode material for lithium-ion batteries

LiNi0.5Co0.2Mn0.3O2 as a kind of layered oxide, has garnered significant interest due to its low cost and facile preparation method. Nevertheless, fast discharge capacity attenuation, poor cycle stability restricts it further application. To optimize its properties, in this paper, a novel eutectic mixed molten salt method is proposed to synthesize LiNi0.5Co0.2Mn0.3O2. The results demonstrate that the LiNi0.5Co0.2Mn0.3O2 obtained through LiOH-LiNO3 as eutectic mixed molten salt exhibited exceptional electrochemical properties. It had a reversible capacity of 151.7 mAh·g−1 after 100 cycles at 0.2 C, with a capacity retention of 89.3%, the discharge capacities of 165.6, 135.8, 121.8 and 111.2 mAh·g−1 at 0.5, 1.0, 2.0 and 5.0 C, respectively. This study highlights a convenient method for preparing LiNi0.5Co0.2Mn0.3O2 and demonstrates the effectiveness of the eutectic mixed molten salt approach in enhancing electrochemical properties.