Preparation and properties of two-dimensional Ti2CTxMXene based on electroetching method.

The continuous advancements in wearable electronics have drawn significant attention toward 2D MXenes materials for energy storage owing to their abundant availability, adaptability, and distinctive physicochemical properties. Two unresolved concerns currently revolve around environmental pollution by F-containing etching and finite kinetics caused because of re-stacking of nanosheets. In this study, Al was electrochemically etched from porous Ti2AlC electrodes without the use of fluorine, through a selective electrochemical etching process in dilute hydrochloric acid. Subsequently, Ti2CTxMXene was vertically grown on carbon fiber (CF) substrates. The resulting Ti2CTx@CF electrodes are lightweight, thin, and flexible, exhibiting a surface capacitance of 330 mF cm-2at a constant current density of 1 mA cm-2after 2000 cycles. They display a surface capacitance retention of 96.16% and a high energy density of 45.3µWh cm-2at a power density of 0.497 mW cm-2. These metrics underscore the Ti2CTx@CF electrode's commendable multifunctionality, electrochemical performance, ion transport efficiency, and charge storage capacity. Moreover, a flexible energy storage electrode material with a high area capacity was developed by combining Ti2CTxMXene nanosheets, possessing a large specific surface area, with a flexible carbon fabric substrate.

Loading of Single Atoms of Iron, Cobalt, or Nickel to Enhance the Electrocatalytic Hydrogen Evolution Reaction of Two-Dimensional Titanium Carbide.

The rational design of advanced electrocatalysts at the molecular or atomic level is important for improving the performance of hydrogen evolution reactions (HERs) and replacing precious metal catalysts. In this study, we describe the fabrication of electrocatalysts based on Fe, Co, or Ni single atoms supported on titanium carbide (TiC) using the molten salt method, i.e., TiC-FeSA, TiC-CoSA, or TiC-NiSA, to enhance HER performance. The introduction of uniformly distributed transition-metal single atoms successfully reduces the overpotential of HERs. Overpotentials of TiC-FeSA at 10 mA cm-2 are 123.4 mV with 61.1 mV dec-1 Tafel slope under acidic conditions and 184.2 mV with 85.1 mV dec-1 Tafel slope under alkaline conditions, which are superior to TiC-NiSA and TiC-CoSA. TiC samples loaded with transition-metal single atoms exhibit high catalytic activity and long stability under acidic and basic conditions. Density functional theory calculations indicate that the introduction of transition-metal single atoms effectively reduces the HER barrier of TiC-based electrocatalysts.

Dopant Site Engineering on 2D Co3O4 Enables Enhanced Toluene Oxidation in a Wide Temperature Range.

Development of cost-effective oxide catalysts holds the key to the removal of toluene, one of the most important volatile organic compounds. However, the catalysts follow varied working mechanisms at different reaction temperatures, posing a challenge to achieving efficient toluene removal over a wide temperature range. Here we report an agitation-assisted molten salt method, which achieves the rational doping on a two-dimensional Co3O4 catalyst and forms two different structures of active sites to enhance catalytic oxidation of toluene in specific temperature intervals, enabling a facile tandem design for working in a wide temperature range. Specifically, Co3O4 is doped with Cu at the octahedral site (Cu-Co3O4) and Zn at the tetrahedral site (Zn-Co3O4) to form CuOh-O-CoTe and ZnTe-O-CoOh structures on the surface, respectively. Mechanistic studies reveal the different working mechanisms of these two active sites toward remarkable performance enhancement at specific temperature intervals, and the improved performance derived from accelerated consumption of intermediates adsorbed on the catalyst surface. Taken together, Cu-Co3O4 and Zn-Co3O4 achieve excellent toluene purification performance over a wide temperature range. This work provides insights into the mechanism-oriented design of active sites at the atomic level.

Controllable sites and high-capacity immobilization of uranium in Nd2Zr2O7 pyrochlore.

As potential nuclear waste host matrices, two series of uranium-doped Nd2Zr2O7 nanoparticles were successfully synthesized using an optimized molten salt method in an air atmosphere. Our combined X-ray diffraction, Raman and X-ray absorption fine-structure (XAFS) spectroscopy studies reveal that uranium ions can precisely substitute the Nd site to form an Nd2-xUxZr2O7+δ (0 ≤ x ≤ 0.2) system and the Zr site to form an Nd2Zr2-yUyO7+δ (0 ≤ y ≤ 0.4) system without any impurity phase. With increasing U concentration, there is a phase transition from pyrochlore (Fd3m) to defect fluorite (Fm3m) structures in both series of U-doped Nd2Zr2O7. The XAFS analysis indicates that uranium exists in the form of high-valent U6+ in all samples. To balance the extra charge for substituting Nd3+ or Zr4+ by U6+, additional oxygen is introduced accompanied by a large structural distortion; however, the Nd2Zr1.6U0.4O7+δ sample with high U loading (20 mol%) still maintains a regular fluorite structure, indicating the good solubility of the Nd2Zr2O7 host for uranium. This study is, to the best of our knowledge, the first systematic study on U-incorporated Nd2Zr2O7 synthesized via the molten salt method and provides convincing evidence for the feasibility of accurately immobilizing U at specific sites.

Coal-based ultrathin N-doped carbon nanosheets synthesized by molten-salt method for high-performance lithium-ion batteries.

Coal is a typical fossil fuel and it is also a natural carbon material, therefore, converting it to functional carbon materials is an effective way to enhance the economic advantages of coal. Here, ultrathin N-doped carbon nanosheets were prepared from low-cost coal via a handy and green molten-salt method, which shown excellent performance for lithium-ion batteries (LIBs). The formation mechanism of ultrathin nanosheets was studied in detail. The eutectic molten salts possess low melting points and become a strong polar solvent at the calcined temperature, making the acidified coal miscible with them in very homogeneously state. Therefore, they can play a gigantic role inin situpore-forming during the carbonization and induce the formation of ultrathin nanosheets due to the salt ions. Simultaneously, the ultrathin N-doped carbon nanosheets with rich defects and controllable surface area was smoothly prepared without any more complex process while revealing brilliant electrochemical performance due to rich ion diffusion pathways. It delivers reversible capacity of 727.0 mAh g-1at 0.2 A g-1after 150 cycles. Thus, the molten-salt method broadens the avenue to construct porous carbon materials with tailor-made morphologies. Equally important, this approach provides a step toward the sustainable materials design and chemical science in the future.

One-pot molten salt method for constructing CdS/C3N4 nanojunctions with highly enhanced photocatalytic performance for hydrogen evolution reaction.

The construction of heterojunction photocatalysts for efficiently utilizing solar energy has attracted considerable attention to solve the energy crisis and reduce environmental pollution. In this study, we use the energy released from an easily-occurred exothermic chemical reaction to serve as the drive force to trigger the formation of CdS and C3N4 nanocomposites which are successfully fabricated with cadmium nitrate and thiourea without addition of any solvents and protection of inert gas at initial temperature, a little higher than the melting point of thiourea. The as-prepared CdS/C3N4 materials exhibit high efficiency for photocatalytic hydrogen evolution reaction (HER) with the HER rate as high as 15,866 µmol/(g∙hr) under visible light irradiation (λ > 420 nm), which is 89 and 9 times those of pristine C3N4 and CdS, respectively. Also, the apparent quantum efficiency (AQE) of CdS/C3N4-1:2-200-2 (CdS/C3N4-1:2-200-2 means the ratio of Cd to S is 1:2 and the reaction temperature is set at 200°C for two hours) reaches 3.25% at λ = 420 ± 15 nm. After irradiated for more than 24 hr, the HER efficiencies of CdS/C3N4 do not exhibit any attenuation. The DFT calculation suggests that the charge difference causes an internal electric field from C3N4 pointing to CdS, which can more effectively promote the transfer of photogenerated electrons from CdS to C3N4. Therefore, most HER should occur on C3N4 surface where photogenerated electrons accumulate, which largely protects CdS from photo-corrosion.

V2O5/NaV6O15nanocomposites synthesized by molten salt method as a high-performances cathode material for aqueous zinc-ion batteries.

Aqueous zinc-ion batteries (ZIBs) is a potential energy storage system due to its advantages of low cost, good safety, and high theoretical capacity (820 mAh g-1). However, the lack of cathode materials with long cycle stability severely restricts the development of ZIBs. In this paper, V2O5/ NaV6O15nanocomposites are synthesized by molten salt method in one step and used as cathode material for ZIBs, which have good electrochemical performances. The specific capacity of the materials remain 160 mAh g-1when the current density is 0.5 A g-1after 1000 cycles, and the capacity retention rate is 102.03% when the current density is 5 A g-1for 1000 cycles. This is mainly due to the large number of active sites generated by crystal defects and the synergistic interaction between the dual-phase materials, which reduces the stress of ions inserted/extracted during the Zn2+storage process and improves the electrochemical performance.

Molten-Salt-Mediated Synthesis of an Atomic Nickel Co-catalyst on TiO2 for Improved Photocatalytic H2 Evolution.

Atomic co-catalysts offer high potential to improve the photocatalytic performance, of which the preparation with earth-abundant elements is challenging. Here, a new molten salt method (MSM) is designed to prepare atomic Ni co-catalyst on widely studied TiO2 nanoparticles. The liquid environment and space confinement effect of the molten salt leads to atomic dispersion of Ni ions on TiO2 , while the strong polarizing force provided by the molten salt promotes formation of strong Ni-O bonds. Interestingly, Ni atoms are found to facilitate the formation of oxygen vacancies (OV) on TiO2 during the MSM process, which benefits the charge transfer and hydrogen evolution reaction. The synergy of atomic Ni co-catalyst and OV results in 4-time increase in H2 evolution rate compared to that of the Ni co-catalyst on TiO2 prepared by an impregnation method. This work provides a new strategy of controlling atomic co-catalyst together with defects for efficient photocatalytic water splitting.

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.

Molten salt synthesis of MXene-derived hierarchical titanate for effective strontium removal.

The removal and recovery of radioactive Sr(II) from wastewater and seawater has been of great concern due to the negative environmental impacts of nuclear energy development and the potential risk of nuclear accidents. Herein, a facile molten salt synthesis strategy was developed to systematically investigated the reaction of different types of MXenes with nitrates. Among the products, K+ intercalated hierarchical titanate nanostructures (K-HTNs) obtained from the direct chemical transformation of multilayered Ti3C2Tx exhibited unique layered structures, good physicochemical properties, and outstanding adsorption performance for Sr(II). The maximum adsorption capacity of Sr(II) by K-HTNs reached 204 mg·g-1 at ambient temperature, and the good regeneration and reusability of the titanate was also demonstrated. K-HTNs showed preferential selectivity for Sr(II) in different environmental media containing competing ions, and the removal efficiency of Sr(II) in real seawater was as high as 93.3 %. The removal mechanism was elaborated to be the exchange of Sr2+ with K+/H+ in the interlayers of K-HTNs, and the adsorbed Sr(II) had a strong interaction with Ti-O- termination on the titanate surface. Benefiting from the merits of rapid and scalable synthesis and excellent adsorption performance, MXene-derived K-HTNs have broad application prospects for the purification of 90Sr-contaminated wastewater and seawater.

Semiconducting Properties of Delaminated Titanium Nitride Ti4N3Tx MXene with Gate-Tunable Electrical Conductivity.

MXenes have garnered significant attention due to their atomically thin two-dimensional structure with metallic electronic properties. However, it has not yet been fully achieved to discover semiconducting MXenes to implement them into gate-tunable electronics such as field-effect transistors and phototransistors. Here, a semiconducting Ti4N3Tx MXene synthesized by using a modified oxygen-assisted molten salt etching method under ambient conditions, is reported. The oxygen-rich synthesis environment significantly enhances the etching reaction rate and selectivity of Al from a Ti4AlN3 MAX phase, resulting in well-delaminated and highly crystalline Ti4N3Tx MXene with minimal defects and high content of F and O, which led to its improved hydrophobicity and thermal stability. Notably, the synthesized Ti4N3Tx MXene exhibited p-type semiconducting characteristics, including gate-tunable electrical conductivity, with a current on-off ratio of 5 × 103 and a hole mobility of ∼0.008 cm2 V-1 s-1 at 243 K. The semiconducting property crucial for thin-film transistor applications is evidently associated with the surface terminations and the partial substitution of oxygen in the nitrogen lattice, as corroborated by density functional theory (DFT) calculations. Furthermore, the synthesized Ti4N3Tx exhibits strong light absorption characteristics and photocurrent generation. These findings highlight the delaminated Ti4N3Tx as an emerging two-dimensional semiconducting material for potential electronic and optoelectronic applications.

In Situ Grown 1D/2D Structure of Dy3Si2C2 on SiCw for Enhanced Electromagnetic Wave Absorption.

To improve electromagnetic wave (EMW) absorption performance, a novel nano-laminated Dy3Si2C2 coating was successfully in situ coated on the surface of SiC whisker (SiCw/Dy3Si2C2) using a molten salt approach. A labyrinthine three-dimensional (3D) net was constructed by the one-dimensional (1D) SiCw coated with the two-dimensional (2D) Dy3Si2C2 layer with a thickness of ~100 nm, which significantly improved the EMW absorption properties of SiCw. Compared to pure SiCw with the minimum reflection loss (RLmin) value of -10.64 dB and the effective absorption bandwidth (EAB) of 1.04 GHz for the sample with a thickness of 4.5 mm, SiCw/Dy3Si2C2 showed a significantly better EMW absorption performance with RLmin of -32.09 dB and wider EAB of 3.76 GHz for thinner samples with a thickness of 1.76 mm. The enhancement of the EMW absorption performance could be ascribed to the improvement of impedance matching, enhanced conductance loss, interfacial polarization as well as multiple scattering. The SiCw/Dy3Si2C2 can be a candidate for EMW absorber applications due to its excellent EMW absorption performance and wide EAB for relatively thin samples, light weight, as well as potential oxidation and corrosion resistance at high temperatures.

Improvement of Mechanical Properties of Composites with Surface Modified B4C for Precision Machining.

In order to solve the problem of difficult sintering and high brittleness of B4C-based ceramics, B4C@ZrB2-TiB2 composite powder was synthesized by molten salt method, and B4C-(Zr, Ti)B2 composite ceramics were successfully prepared by spark plasma sintering. The effects of different raw material ratios on the composition, microstructure, and mechanical properties of the prepared composite ceramics were characterized by XRD, XPS, SEM, and TEM. The results show that ZrB2 and TiB2 were grown on the surface of B4C by template mechanism to form a dense nanocrystalline coating, and the original surface of B4C was exposed gradually with the decrease of the ratio of metal powder. When the composite powders were sintered at 1700 °C, ZrB2 and TiB2 formed a solid solution, which can refine grains and improve strength. When the raw material ratio is n(B4C): n(Zr): n(Ti) = 12:1:1, the composite ceramics have excellent comprehensive properties, the Vickers hardness reaches 41.2 GPa.

Effects of Synthesis Conditions of Na0.44MnO2 Precursor on the Electrochemical Performance of Reduced Li2MnO3 Cathode Materials for Lithium-Ion Batteries.

Li2MnO3 nanobelts have been synthesized via the molten salt method that used the Na0.44MnO2 nanobelts as both the manganese source and precursor template in LiNO3-LiCl eutectic molten salt. The electrochemical properties of Li2MnO3 reduced via a low-temperature reduction process as cathode materials for lithium-ion batteries have been measured and compared. Particularly investigated in this work are the effects of the synthesis conditions, such as reaction temperature, molten salt contents, and reaction time on the morphology and particle size of the synthesized Na0.44MnO2 precursor. Through repeated synthesis characterizations of the Na0.44MnO2 precursor, and comparing the electrochemical properties of the reduced Li2MnO3 nanobelts, the optimum conditions for the best electrochemical performance of the reduced Li2MnO3 are determined to be a molten salt reaction temperature of 850 °C and a molten salt amount of 25 g. When charge-discharged at 0.1 C (1 C = 200 mAh g-1) with a voltage window between 2.0 and 4.8 V, the reduced Li2MnO3 synthesized with reaction temperature of Na0.44MnO2 precursor at 850 °C and molten salt amounts of 25 g exhibits the best rate performance and cycling performance. This work develops a new strategy to prepare manganese-based cathode materials with special morphology.

In-situ electrochemical conversion of Na5V12O32@graphene for enhanced cycle stability in aqueous zinc ion batteries.

HYPOTHESIS: Na5V12O32 (NVO) is a potential cathode for aqueous zinc ion batteries (AZIBs). However, it suffers severe capacity decay due to the dissolution of the active material. The structural design may be an effective solution to the problem. EXPERIMENTS: Herein, we construct a typical two-dimensional hierarchical structure of Na5V12O32@graphene (NVO@G) via a facile molten salt method. FINDINGS: The capacity fading problem is solved by the in-situ conversion of NVO@G to a more stable hierarchical system during cycling. The in-situ formed zinc pyrovanadate (Zn3V2O7(OH)2·2H2O, ZVO) nanosheets on the surface of graphene exhibits excellent zinc-ion storage stability. The presence of graphene induces the growth of NVO nanobelts to construct the typical two-dimensional hierarchical structure. Additionally, the in-situ conversion makes the formed ZVO nanosheets contact with graphene better. Benefitting from the hierarchical nanostructure and in-situ phase conversion, the NVO@G electrode shows excellent long-term stability (96.4% retention after 340 cycles at 0.3 A g-1, 85.7% retention after 4400 cycles at 5 A g-1) and high zinc ion storage capacity (220 mAh g-1 at 0.3 A g-1), which is superior to those of most electrode materials previously reported.

Synthesis of Uniform Size Rutile TiO2 Microrods by Simple Molten-Salt Method and Its Photoluminescence Activity.

Uniform-size rutile TiO2 microrods were synthesized by simple molten-salt method with sodium chloride as reacting medium and different kinds of sodium phosphate salts as growth control additives to control the one-dimensional (1-D) crystal growth of particles. The effect of rutile and anatase ratios as a precursor was monitored for rod growth formation. Apart from uniform rod growth study, optical properties of rutile microrods were observed by UV-visible and photoluminescence (PL) spectroscopy. TiO2 materials with anatase and rutile phase show PL emission due to self-trapped exciton. It has been observed that synthesized rutile TiO2 rods show various PL emission peaks in the range of 400 to 900 nm for 355 nm excitation wavelengths. All PL emission appeared due to the oxygen vacancy present inside rutile TiO2 rods. The observed PL near the IR range (785 and 825 nm) was due to the formation of a self-trapped hole near to the surface of (110) which is the preferred orientation plane of synthesized rutile TiO2 microrods.

Carbon nanofibers derived from cellulose via molten-salt method as supercapacitor electrode.

Carbon nanofibers (CNFs) have been paid much attention as supercapacitor electrode due to outstanding chemical stability, high electron transfer rate and large specific surface area. However, the preparation process of CNFs is always stalemated in electrospinning, heat stabilization and carbonization. The problems of solvent pollution in the electrospinning process, complex process and high energy consumption in conventional carbonization process can't be solved. Herein, CNFs have been innovatively prepared from nanofibrillated cellulose by the molten-salt method (NaCl/NaOH). Molten salt penetrates between the fibers, separates and activates the fibers. The obtained carbon nanofibers remain developed branching structures and have a large specific surface area (899 m2 g-1). The electrical properties are tested in a symmetrical two-electrode system. The specific capacitance is 150 F g-1 at the current density of 1 A g-1. Low equivalent series resistance (1.13 Ω) indicates that it has high electrode conductivity. This study has taken into account energy conservation, environmental protection, recyclability and simplified preparation process, which has a very far-reaching significance for the industrial production of CNFs.

N, S Co-Doped Carbons Derived from Enteromorpha prolifera by a Molten Salt Approach: Antibiotics Removal Performance and Techno-Economic Analysis.

N, S co-doped bio-carbons with a hierarchical porous structure and high surface area were prepared using a molten salt method and by adopting Entermorpha prolifera (EP) as a precursor. The structure and composition of the bio-carbons could be manipulated by the salt types adopted in the molten salt assisted pyrolysis. When the carbons were used as an activating agent for peroxydisulfate (PDS) in SMX degradation in the advanced oxidation process (AOP), the removal performance in the case of KCl derived bio-carbon (EPB-K) was significantly enhanced compared with that derived from NaCl (EPB-Na). In addition, the optimized EPB-K also demonstrated a high removal rate of 99.6% in the system that used local running water in the background, which proved its excellent application potential in real water treatment. The degradation mechanism study indicated that the N, S doping sites could enhance the surface affinity with the PDS, which could then facilitate 1O2 generation and the oxidation of the SMX. Moreover, a detailed techno-economic assessment suggested that the price of the salt reaction medium was of great significance as it influenced the cost of the bio-carbons. In addition, although the cost of EPB-K was higher (USD 2.34 kg-1) compared with that of EPB-Na (USD 1.72 kg-1), it was still economically competitive with the commercial active carbons for AOP water treatment.

Exfoliation and Delamination of Ti3C2Tx MXene Prepared via Molten Salt Etching Route.

MXenes are two-dimensional metal carbides or nitrides that are currently proposed in many applications thanks to their unique attributes including high conductivity and accessible surface. Recently, a synthetic route was proposed to prepare MXenes from the molten salt etching of precursors allowing for the preparation of MXene (denoted as MS-MXenes, for molten salt MXene) with tuned surface termination groups, resulting in improved electrochemical properties. However, further delamination of as-prepared multilayer MS-MXenes still remains a major challenge. Here, we report on the successful exfoliation of MS-Ti3C2Tx via the intercalation of the organic molecule TBAOH (tetrabutylammonium hydroxide), followed by sonication to separate the layers. The treatment time could be adapted to tune the wetting behavior of the MS-Ti3C2Tx. As a result, a self-supported Cl-terminated MXene film could be prepared by filtration. Finally, MS-Ti3C2Tx used as a Li-ion battery anode could achieve a high specific capacity of 225 mAh g-1 at a 1C rate together with an excellent rate capability of 95 mAh g-1 at 167C. These results also show that tuning of the surface chemistry of MXene is of key importance to this field with the likely result being increased electrochemical performance.

Motivating borate doped FeNi layered double hydroxides by molten salt method toward efficient oxygen evolution.

The incorporation of borate is a beneficial strategy to improve the catalytic activity of transition metal-based electrocatalyts for oxygen evolution reaction (OER). However, how to efficiently introduce borate has always been a challenge. Here, a facile and scalable molten salt method is developed to successfully dope borate into FeNi layered double hydroxides (FeBi@FeNi LDH) for efficient OER. The molten salt method can not only promote the formation of evenly dispersed nano-pompous FeBi precursor, thus providing the possibility to realize the direct doping of borate and the increase of mass, charge transfer and oxygen evolution active sites in FeNi LDH, but also promote the in-situ growth of FeBi@FeNi LDH on the conductive iron foam, improvingconductivity and stability of the material. The results indicate that the synthesized FeBi@FeNi LDH shows enhanced OER activity by delivering current densities of 10 and 100 mA cm-2 at low overpotentials of 246 and 295 mV and showing a small Tafel slope of 56.48 mV dec-1, benefiting from the optimization of geometric structure of active sites as well as the adjustment of electron density by borate doping especially in the case of molten salt. In addition, the sample can maintain durability at an industrial current density of 100 mA cm-1 for 90 h. This work provides a new way for the construction of efficient catalysts using boron doping assisted by molten salt.