Thermal properties analysis and thermal cycling of HITEC molten salt with h-BN nanoparticles for CSP thermal energy storage applications

Molten salts are the operational fluid for most concentrated solar power (CSP) systems, which has attracted more attention among the scientific community due to the augmentation of their properties with the doping of nanoparticles. Hexagonal boron nitride (h-BN) nanoparticles were dispersed in HITEC molten salt to create a novel nanofluid and evaluate the h-BN nanoparticles' influence on HITEC thermophysical properties. The influence of nanoparticle concentration (0.1, 0.5, and 1wt.%) of h-BN and HITEC was studied in this research. HITEC and nano-enhanced HITEC molten salt (NEHMS) were characterized using energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FT-IR). Specific heat capacity, latent heat, and melting temperature were assessed using differential scanning calorimetry (DSC). The maximum working temperature was evaluated with thermogravimetric analysis (TGA). The ideal nanoparticle concentration is 0.1 wt.% h-BN, which results in a 27% increase in heat capacity, a 72% increase in latent heat, and a 7% enhancement in thermal stability. The thermal cycling stability test proved the stability of the enhanced thermophysical properties. The material characterization revealed that the samples with improved thermophysical properties have a homogeneous dispersion of nanoparticles with minor nanoparticle agglomeration. The system advisor model (SAM) simulation comparison of the optimum sample with solar salt and HITEC salt revealed that using the optimum sample increases CSP plant efficiency by 0.4% and reduces power costs by 0.13¢/kWh.

Molten salt synthesis of 1T/2H mixed phase MoS2 for boosting photocatalytic H2 evolution via Schottky junction under EY-sensitized system

Clean H2 fuel obtained from the photocatalytic water splitting to hydrogen reaction could efficiently alleviate current energy crisis and the concomitant environmental pollution problems. Therefore, it is desirable to search for a highly efficient photocatalytic system to decrease the energy barrier of water splitting reaction. Herein, the 1T/2H mixed phase MoS2 sample with Schottky junction between contact interfaces is developed through molten salt synthesis for photocatalytic hydrogen production under a dye-sensitized system (Eosin Y-TEOA-MoS2) driven by the visible light. In mixed phase MoS2 sample, the photogenerated electrons of 2H-phase MoS2 migrated to the 1T-phase MoS2 are difficult to jump back because of the existence of Schottky barrier, which greatly suppresses the quenching of EY and therefore results in an enhanced hydrogen evolution performance. Therefore, the optimized MoS2 sample (MoS2-350) has an initial hydrogen evolution rate of 213 μmol h-1 and corresponding apparent quantum yield of 36.1 % at 420 nm, far higher than those of pure Eosin Y. It is strongly confirmed by the steady-state/time-resolved photoluminescence (PL) spectra and transient photocurrent response experiments. With the assistance of Density functional theory (DFT) calculation, the function of Schottky junction in photocatalytic hydrogen evolution reaction is well explained. In addition, a new and universal method (SVM curve) of judging oxidation or reduction quenching for photosensitizers is proposed.

Synthesis of sewage sludge biochar in molten salt environment for advanced wastewater treatment: Performance enhancement, carbon footprint and environmental impact reduction

Sewage sludge (SS) pyrolysis to produce biochar is a vital approach for treating and utilizing SS, while reducing the carbon footprint of SS disposal. However, the high inorganic content in SS results in low carbon content and underdeveloped pore structure of biochar prepared under inert atmospheres. There is a significant risk of secondary pollutant emissions, including CO2, SO2, and NOx. In this study, we propose an innovative approach that utilizes excess molten salts, specifically a Li-Na-K molten carbonate (MC) and a Li-Na-K molten chloride (MCH), to create a medium-temperature liquid phase reaction environment (500 °C) for SS pyrolysis. This environment promotes the functional enhancement of biochar (SSB-MC and SSB-MCH) and in-situ absorption of secondary pollutants. The pore structure of SSB-MC and SSB-MCH are greatly optimized. Thanks to the dissolution of calcium-silicon-aluminum-based minerals by molten salt, the carbon content is also significantly increased. The increased specific surface area and surface-enriched functional groups (O, N, P, etc.) of SSB-MC result in greatly enhanced adsorption performance for Rhodamine B (27.9 to 89.1 mg g-1). SSB-MCH, due to the increased iron and phosphorus doping, also exhibits enhanced Fenton oxidation capability. Life cycle assessments demonstrate that the molten salt processes effectively reduce the carbon footprint, energy consumption, and environmental impact.

Quantification of lithium in molten chlorides by optical emission spectrometry using a novel molten-salt-electrode microplasma source

A new molten-salt-electrode microplasma (MSEMP) source for optical emission spectrometry (OES) was constructed, equipped with a molten salt electrode and a metal hollow tube (fed with helium) counter electrode. The use of the MSEMP-OES for constituent analysis of molten salt was primarily evaluated. The acquirement of characteristic spectral lines of some elements in several molten chloride samples verified the good qualitative ability of the proposed MSEMP-OES. Solid copper was dissolved via charge transfer and excited in glow discharge, indicating its potential application in solid sample analysis. The temperature and composition of molten salt were found to have no influence on the lithium response and the accurate quantification of lithium in molten salt was achieved. This work provides new insights for promoting the application of microplasma technology in the in-situ analysis of elements, even in special samples.

Molten salts for efficient removal of radioactive contaminants from stainless steel surface: Mechanisms and applications

Here, we have demonstrated an innovative decontamination strategy using molten salts as a solvent to clean stubborn uranium contaminants on stainless steel surfaces. The aim of this work was to investigate the evolutionary path of contaminants in molten salts to reveal the decontamination mechanism, thus providing a basis for the practical application of the method. Thermodynamic analysis revealed that alkali metal hydroxides, carbonates, chlorides and nitrates can react with uranium oxides (UO3 and U3O8) to form various uranates. Notably, the decontamination mechanism was elucidated by analyzing the chemical composition of the contaminants in the molten salts and the surface morphology of the specimens considering NaOH-Na2CO3-NaCl melt as the decontaminant. The decontamination process involved two stages: a rapid decontamination stage dominated by the thermal effect of molten salt, and a stable decontamination stage governed by the chemical reactions and diffusion of molten salt. Subsequently, a multiple decontamination strategy was implemented to achieve high decontamination rates and low residual radioactivity. Within the actual cleaning time of 30 min, the decontamination efficiency (DE) of UO3-contaminated specimens reached 97.8% and 93.0% for U3O8-contaminated specimens. Simultaneously, the radioactivity levels of all specimens were reduced to below the control level for reuse in the nuclear domain. Particularly, the actual radioactive waste from the nuclear industry reached a reusable level of radioactivity after decontamination. The NaOH-Na2CO3-NaCl melt outperforms conventional chemical solvents and may be one of the most rapid and efficient decontaminants for stubborn uranium contamination of metal surfaces, which provides insights in regard to handling nuclear waste.

Molten salt strategy to activate biochar for enhancing biohydrogen production

Generally, dark fermentation (DF) of hydrogen (H₂) synthesis has low H₂ production from industrial-scale plant. In this study, campus greening wastes-ginkgo leaves were used to produce molten salt-modified biochar (MSBC) and nitrogen (N₂)-atmosphere BC (NBC) in molten salt and N₂ environment at 800 °C, respectively. MSBC showed excellent properties including high specific surface area and electron transfer ability. After supplementation with MSBC, H₂ yield rose by 32.4% compared to the control group without carbon material. Electrochemical analysis revealed MSBC improved the electrochemical properties of sludge. Furthermore, MSBC optimized the microbial community structure and increased the relative abundance of dominant microbes, thus promoting H₂ production. This work is provide the deep understanding of two carbons that play vital roles in increasing microbial biomass, supplementing trace element and favoring electron transfer in DF reactions. Salt recovery achieved 93.57% in molten salt carbonization, which has sustainability compared with N₂-atmosphere pyrolysis.

Prediction of ionic conductivity from adiabatic heating in non-equilibrium molecular dynamics on various test systems

CONTEXT

The evaluation of ionic conductivity through atomistic modeling typically involves calculating diffusion coefficients, which often necessitates simulations spanning several hundreds of nanoseconds. This study introduces a less computationally demanding approach based on non-equilibrium molecular dynamics applicable to a wide range of systems.

METHOD

Ionic conductivity is determined by evaluating the Joule heating effect recorded during non-equilibrium molecular dynamics (NEMD) simulations. These simulations which involve applying a uniform electric field using classical force fields in LAMMPS are conducted within the MedeA software environment. The conductivity value for a specific temperature can thus be obtained from a single simulation together with an estimation of the associated uncertainty. Guidelines for selecting NEMD parameters such as electric field intensity and initial temperature are proposed to satisfy linear irreversible transport.

RESULTS

The protocol presented in this study is applied to four different types of systems, namely, (i) molten NaCl, (ii) NaCl and LiCl aqueous solutions, (iii) solution of ionic liquid with two solvents, and (iv) NaX zeolites in the anhydrous and hydrated states. The main advantages of the proposed protocol are simplicity of implementation (eliminating the need to store individual ion trajectories), reliability (low electric field, linear response, no perturbation of the equations of motion by a thermostat), and a wide range of applications. The estimated contribution of field-induced drift motion of ions to kinetic energy appears very low, justifying the use of standard kinetic energy in the method. For each system, the reported influence of temperature, ion concentration, solvent nature, or hydration is correctly predicted.

Decontamination of uranium-containing radioactive waste from stainless steel surfaces using NaOH-based molten salts

Herein, we report a new strategy for the rapid removal of uranium-containing contaminants from metal surfaces, and it relies on decontaminants made of NaOH-based molten salts. The addition of Na₂CO₃ and NaCl to NaOH exhibited superior decontamination performance, with a decontamination rate of 93.8% within 12 min, outdoing the performance of the single NaOH molten salt. The experimental results demonstrated that the synergistic effects between CO₃^2- and Cl^- promoted the corrosion efficiency of the molten salt on the substrate, which accelerated the decontamination rate. Additionally, benefiting from the optimization of the experimental conditions by the response surface method (RSM), the decontamination efficiency was improved to 94.9%. Notably, it also showed remarkable results in the decontamination of specimens containing different uranium oxides at low and high levels of radioactivity. This technology is promising for broadening the path in rapid decontamination of radioactive contaminants on metal surfaces.

Molten salt synthesis of NiCo-NiCo(2)O(4)@C nanotubes as anode materials for Li-ion batteries

The construction of carbon-encapsulated transition metal nanotube structures is a preferred method that can effectively slow down volume expansion, improve cycling stability and enhance the electrical conductivity of the reactive sites of lithium-ion batteries. In this study, nanotubes of carbon-coated NiCo-NiCo₂O₄ nanoparticles (NC-NCO@C) were prepared by a one-step molten salt method at high temperature using Ni and Co as catalytic centers and sodium acetate as carbon source. We used NC-NCO@C-2 nanotubes as anode materials for lithium-ion batteries(LIBs), which exhibited excellent lithium storage performance and good stability, with a specific capacity of 616.26 mAh g^-1 after 1000 cycles at a high current density of 1 A g^-1. In addition, NC-NCO@C-2 were used as anodes in lithium-ion full cells and LiFePO₄ (LFP) was used as the cathode. The NC-NCO@C-2//LFP full-cell exhibits high capacity and good cycling stability, with a capacity of 100.7 mAh g^-1 after 100 cycles and a capacity retention rate of 92%. The construction of NC, NCO, and carbon ternary complexes was found to activate and promote the reversible conversion of certain inorganic components at the solid electrolyte interfaces (SEI), which effectively reduced the volume change during cycling, increased the electrical conductivity, and improved the cycling stability of the electrode. The proposed one-step molten salt synthesis of Carbon-coated metals complexes with excellent compatibility characteristics, is expected to solve the problem of volume change in transition metals, which is encountered in LIBs applications.

Molten salt-confined pyrolysis towards heteroatom-doped porous carbon nanosheets for high-energy-density Zn-ion hybrid supercapacitors

Carbon nanosheets with heteroatom doping and well-developed porosity exhibit broad application foreground for Zn-ion hybrid supercapacitors (ZHSCs), but the simple and controllable preparation is still of great challenge. In this study, by using LiCl-KCl as in-built templates, histidine as carbon and nitrogen sources, and KNO₃, K₂SO₄, KOH or Na₂S₂O₃ as active agent, a series of N and NS doped porous carbon nanosheets are developed. Results indicate that, with the activator introduction, pore structures of the carbonized products are notably boosted, showing an astounding 30-244 % increase in BET specific surface area, and meanwhile, heteroatom with a content of ca. 12 % can be doped into the resultant carbon skeletons. Specifically, the NSPCN-800 (activated by Na₂S₂O₃) with a large specific surface area of 1297 m²/g, a hierarchically porous structure composed of abundant micropores and mesopores, and a suitable heteroatom content (N: 11.9 wt%; S: 0.6 wt%) presents an impressive energy storage behavior as cathode for ZHSCs, including a specific capacitance of 165.8F/g, a specific capacity of 95.2 mAh/g, an energy density of 59.0 Wh kg^-1 and a cyclic stability with a 82.6 % capacity retention after 5000 cycles. These performance parameters surpass numerous reported ZHSCs, making NSPCN-800 a very promising cathode for practical use.

Catalytic pyrolysis of lotus leaves for producing nitrogen self-doping layered graphitic biochar: Performance and mechanism for peroxydisulfate activation

In this study, nitrogen self-doping layered graphitic biochar (Na-BC900) was prepared by catalytic pyrolysis of lotus leaves at 900 ^°C, in the presence of NaCl catalyst, for peroxydisulfate (PDS) activation and sulfamethoxazole (SMX) degradation. NaCl as catalyst played a crucial part in the preparation of Na-BC900 and could be reused. The SMX degradation rate in Na-BC900/PDS system was 12 times higher than that in un-modified biochar (BC900)/PDS system. The excellent performance of Na-BC900 for PDS activation was attributed to its large specific surface areas (SSAs), the enhanced graphitization structure and the high graphitic N content. The quenching and electrochemical experiments, electron paramagnetic resonance (EPR) studies inferred that the radicals included SO₄^•-, ^•OH, O₂^•- and the non-radical processes were driven by ¹O₂ and biochar mediated electron migration. Both radical and non-radical mechanisms contributed to the removal of SMX. Additionally, this catalytic pyrolysis strategy was clarified to be scalable, which can be applied to produce multiple biomass-based biochar catalysts for restoration of polluted water bodies.

Potential and current practices of recycling waste printed circuit boards: A review of the recent progress in pyrometallurgy

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated.

Molten salt synthesis of WS2 and MoS2 nanosheets toward efficient gaseous elemental mercury capture

The development of high-efficient adsorbents for Hg⁰ capture in a broad temperature window remains a big challenge. Transition-metal dichalcogenides (TMDs) present great prospects owing to their two-dimensional layered structures and abundant active sulfur species. Here, tungsten disulfide (WS₂) and molybdenum disulfide (MoS₂) nanosheets are easily synthesized via a molten salt route and employed for Hg⁰ sequestration. With the elevation of the annealing temperature, the Hg⁰ capture ability of WS₂ nanosheet gradually enhances, while MoS₂ nanosheet first increases and then decreases. They both display good mercury removal performances in an enlarged temperature range of 60-260 °C. Acidic flue gas components (i.e., SO₂ and NO) subtly interfere the mercury removal process, indicating the prospective application potentials of WS₂ and MoS₂ nanosheets in thermal plants.

Removal of flue gas mercury by porous carbons derived from one-pot carbonization and activation of wood sawdust in a molten salt medium

Porous carbons derived from one-pot carbonization and activation of wood sawdust in a molten salt (LiCl-KCl) medium were employed for Hg⁰ removal. The carbons derived from molten salt carbonization (MSC) displayed much superior Hg⁰ removal performance comparing with the carbons derived from N₂ pyrolysis method (NC). The best molar ratio of LiCl-KCl was 59:41, the optimal molten salt temperature was 700 °C, and the best mass ratio of wood sawdust to molten salt was 1:10. The MSC displayed good applicability at 50-125 °C. The saturation Hg⁰ adsorption capacity of MSC was about 7828.39 μg·g^-1, far exceeding those for carbonaceous adsorbents reported in literatures. A Hg⁰ removal mechanism over MSC was proposed, i.e., the hierarchical porous structure accelerated mass transfer of Hg⁰, and the CO groups served as electron acceptors from Hg⁰ atoms to form organic matter bonded mercury (Hg-OM). The molten salt could be easily separated from the mixture of MSC for recycling multiple times. Thus, molten salt carbonization method appears to be promising in one-pot carbonization and activation of biomass as efficient adsorbents for gaseous Hg⁰.

Recovery of porous silicon from waste crystalline silicon solar panels for high-performance lithium-ion battery anodes

A low-cost and easy-available silicon (Si) feedstock is of great significance for developing high-performance lithium-ion battery (LIB) anode materials. Herein, we employ waste crystalline Si solar panels as silicon raw materials, and transform micro-sized Si (m-Si) into porous Si (p-Si) by an alloying/dealloying approach in molten salt where Li⁺ was first reduced and simultaneously alloyed with m-Si to generate Li-Si alloy at the cathode. Subsequently, the as-prepared Li-Si alloy served as the anode in the same molten salt to release Li⁺ into the molten salt, resulting in the production of p-Si by taking advantage of the volume expansion/contraction effect. In the whole process, Li⁺ was shuttled between the electrodes in molten LiCl-KCl, without consuming Li salt. The obtained p-Si was applied as an anode in a half-type LIBs that delivered a capacity of 2427.7 mAh g^-1 at 1 A g^-1 after 200 cycles with a capacity retention rate of 91.5% (1383.3 mAh g^-1 after 500 cycles). Overall, this work offers a straightforward way to convent waste Si panels to high-performance Si anodes for LIBs, giving retired Si a second life and alleviating greenhouse gas emissions caused by Si production.

Molten-salt-assisted synthesis of onion-like Co/CoO@FeNC materials with boosting reversible oxygen electrocatalysis for rechargeable Zn-air battery

A melt-salt-assisted method is utilized to construct an onion-like hybrid with Co/CoO nanoparticles embedded in graphitic Fe-N-doped carbon shells (Co/CoO@FeNC) as a bifunctional electrocatalyst. The iron-polypyrrole (Fe-PPy) is firstly prepared with a reverse emulsion. Direct pyrolysis of Fe-PPy yields turbostratic Fe-N-doped carbon (FeNC) with excellent oxygen reduction reaction (ORR) electrocatalysis, while the melt salt (CoCl₂) mediated pyrolysis of Fe-PPy obtains onion-like Co/CoO@FeNC with a reversible overvoltage value of 0.695 V, largely superior to Pt/C and IrO₂ (0.771 V) and other Co-based catalysts reported so far. The ORR activity is mainly due to the graphitic FeNC and further enhanced by CoN_x bonds, whereas the oxygen evolution reaction (OER) activity is principally due to the Co/CoO composite. Concurrently, Co/CoO@FeNC as cathode catalyst enables Zn-air battery with a high open circuit voltage of 1.42 V, a peak power density of 132.8 mW cm^-2, a specific capacity of 813 mAh g_Zn^-1, and long-term stability.

Electrochemical Lithium Storage Performance of Molten Salt Derived V2SnC MAX Phase

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of V₂SnC MAX phase by the molten salt method. V₂SnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g^-1 and volumetric capacity of 570 mAh cm^-3 as well as superior rate performance of 95 mAh g^-1 (110 mAh cm^-3) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn-Li (de)alloying reaction that occurs at the edge sites of V₂SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V₂C layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.

Red mud-molten salt composites for medium-high temperature thermal energy storage and waste heat recovery applications

Red mud (RM) is an industrial waste of the aluminum industry with presently estimated worldwide legacy-site stockpiles of 4 billion tones. RM is typically disposed in the sea, dams or dykes, posing a significant environmental hazard due to its high alkalinity and traces of heavy metals. Despite recent valorization efforts, only 15% of RM deposits are currently utilized. In this work, a novel use of RM to formulate composite phase change materials (CPCMs) is proposed. The CPCM is formulated by milling nitrate salts with RM, compressing and subsequent sintering of the two. Overall good performance over the temperature range of 25-400 ℃ is observed. Maximum latent heat of the CPCMs is 58 J/g, while average thermal conductivity and C_p are in the range of 0.77-0.83 W/mK and 1.03-1.31 J/g ℃, respectively. No variations in the melting point or latent heat are observed after 48 cycles. Energy storage density is calculated to be up to 1396 MJ/m³. The working temperature of this novel CPCM make it ideal for waste heat recovery of medium-high temperature waste heat streams providing a valorization pathway and valorization for RM as a by-product for energy-related applications.

Raman and density functional theory studies of lutecium fluoride and oxyfluoride structures in molten FLiNaK

Combined with Raman spectroscopy and density functional theory (DFT) calculations, the micro-structures in molten FLiNaK-LuF₃ and FLiNaK-LuF₃-Li₂O systems were studied. Both LuF₅^2- (D_3h) and LuF₆^3- (O_h) anions were identified in molten FLiNaK, and their relative content varied with the concentration of LuF₃. For regarding the affection of oxygen anion, Li₂O was added into the molten FLiNaK-LuF₃ (20 mol%) sample. The lutecium oxyfluoride anion Lu₂OF₈^4- was firstly formed which possesses a linear LuOLu geometry with two LuF₄ moieties bridged by one single oxygen atom. Further increasing the Li₂O content to 10 mol% resulted in the formation of two species, which belonged to the Lu₂O₂F₄^2- and Lu₂O₂F₆^4- anions. When increased the concentration of Li₂O to 20 mol%, a new species appeared which was approximate to the oxide structure.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g^-1 at 0.5 A g^-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm^-2), specific capacity (767 mAh g_Zn^-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

Molten salt induced nitrogen-doped biochar nanosheets as highly efficient peroxymonosulfate catalyst for organic pollutant degradation

Advanced oxidation processes based on carbon catalysis is a promising strategy possessing great potential for environmental pollution degradation. Herein, nitrogen-doped biochar nanosheets (NCS-x) were synthesized using a nitrogen-rich biomass (Candida utilis) as sole precursor. The involvement of environmental-friendly molten salt (NaCl and KCl) in pyrolysis process not only facilitated the exfoliation of biochar, but also favored the retention of N element in biochar. When applying as catalyst for peroxymonosulfate activation, the as-obtained NCS-6 exhibited outstanding performance in catalytic degradation of bisphenol A (BPA). A 100% removal efficiency was observed in 6 min with fast reaction kinetic (k = 1.36 min^-1). Based on quenching test and in-situ electron paramagnetic resonance analysis, both radical pathway and non-radical pathway were suggested to be involved in BPA degradation, while singlet oxygen was identified as the dominant reactive oxygen species. Furthermore, the ecotoxicity evaluation using Chlorella vulgaris as ecological indicator indicated that BPA solution after degradation was less toxic than the original solution. It is expected that this green and facile strategy holds great promise for value-added conversion of nitrogen-rich biomass to highly efficient biochar nanosheets for environment remediation.

Extraction of Co and Li2CO3 from cathode materials of spent lithium-ion batteries through a combined acid-leaching and electro-deoxidation approach

Recycling of the spent LIBs to extract Li and Co not only offers raw materials for batteries but also lays a sustainable way for battery development. Herein, we adopt a route combining hydrometallurgical and pyro-electrochemical routes to extract Li₂CO₃ and Co powder from the spent LIBs of cell phones. The LiCoO₂-based cathode materials were firstly dissolved in H₂SO₄ solution containing H₂O₂ as the reductant, and the optimal conditions for attaining a high extraction rate of 99% were studied. After that, the precipitated Co(OH)₂ was calcinated in air under 500 °C to generate Co₃O₄ which was thereafter electrochemically converted into Co powder and oxygen in molten Na₂CO₃-K₂CO₃. Overall, the hybrid method employing both hydro- and pyro-route provides an effective pathway to recover both Li₂CO₃ and Co powder from spent LIBs.

Molten hydroxide for detoxification of chlorine-containing waste: Unraveling chlorine retention efficiency and chlorine salt enrichment

Hazardous waste dechlorination reduces the potential of creating dioxins during the incineration process. To investigate the salt effect on waste dechlorination, molten hydroxides with a low melting temperature were utilized for the pre-dechlorination and decomposition of chlorine-containing organic wastes (COWs) including trichlorobenzene (TCB), perchloroethylene, hexachlorobenzene and chlordane. The results showed that a eutectic mixture of caustic sodium and potassium hydroxides (41 wt.% NaOH and 59 wt.% KOH) led to a low melting point below 300°C and a relatively high chlorine retention efficiency (CRE) with TCB as a representative COWs. The amounts of hydroxides, reaction time, and temperature all had notable influence on CRE. When the mass ratio of hydroxides to TCB reached 30:1, approximately 98.1% of the TCB was destroyed within 2.5 hr at 300°C with CRE of 71.6%. According to the residue analysis, the shapes of reaction residues were irregular with particles becoming swollen and porous. The benzene ring and C-Cl bonds disappeared, while carboxyl groups formed in the residues. The stripped chlorine was retained and condensed to form chloride salts, and the relative abundance of the chloride ions associated with the mass of TCB in residues increased from 0 to 75.0% within the 2.5 hr reaction time. The observed concentration of dioxins in residues was 5.6 ngTEQ/kg. A reaction pathway and possible additional reactions that occur in this dechlorination system were proposed. Oxidizing agents may attack TCB and facilitate hydrogenation/dechlorination reactions, making this process a promising and environmentally friendly approach for chlorine-containing organic waste treatment.

Fabrication of Al and Al-Si alloy microspheres by ultrasonic irradiating the molten salt-aluminum immiscible system

Microspheres of pure aluminum and Al-7wt%Si alloy were successfully fabricated by ultrasonic irradiating the molten NaCl-KCl-Al and NaCl-KCl-(Al-Si) systems respectively. Ultrasonic cavitation is mainly responsible for the formation of metal microspheres. A minimum diameter of ∼15 μm of the microspheres can be achieved. The final morphology and size of the metal spheres are determined by both the irradiation process and the subsequent solidification condition. Under the protection of molten salt, this process provides a novel way to fabricate spherical metal powder that has relative high activity and melting point.

High oxygen reduction reaction performance nitrogen-doped biochar cathode: A strategy for comprehensive utilizing nitrogen and carbon in water hyacinth

In this study, a novel nitrogen-doped biochar oxygen reduction reaction cathode-water hyacinth carbon, was prepared by ZnCl₂ molten salt carbonization without additional nitrogen source, which displayed a high performance in electro-Fenton (E-Fenton) process. The BET result shows that water hyacinth carbon achieved a much larger specific surface area (829 m²·g^-1) than non-melt salt carbonized one (323 m²·g^-1) and graphite powder (28 m²·g^-1). Furthermore, characterization by XPS and EIS shows that both pyridinic-N (43.24%) and graphitic-N (56.75%) existed in water hyacinth carbon and Warburg constant was only 0.051. Because of a high H₂O₂ producing yield 1.7 mmol·L^-1 and corresponding current efficiency 81.2 ± 2.5% in molten salt carbonized water hyacinth biochar, a high kinetic constant 0.318 min^-1 in DMP degradation was achieved, which was 4 times higher than graphite powder (0.076 min^-1). The TOC removal achieved 86.8% in 30 min and the corresponding energy consumption reached a low level 60.15 kW·h·kgTOC^-1.

In situ production of titanium dioxide nanoparticles in molten salt phase for thermal energy storage and heat-transfer fluid applications

In this study, TiO₂ nanoparticles (average particle size 16 nm) were successfully produced in molten salt phase and were showed to significantly enhance the specific heat capacity of a binary eutectic mixture of sodium and potassium nitrate (60/40) by 5.4 % at 390 °C and 7.5 % at 445 °C for 3.0 wt% of precursors used. The objective of this research was to develop a cost-effective alternate method of production which is potentially scalable, as current techniques utilized are not economically viable for large quantities. Enhancing the specific heat capacity of molten salt would promote more competitive pricing for electricity production by concentrating solar power plant. Here, a simple precursor (TiOSO₄) was added to a binary eutectic mixture of potassium and sodium nitrate, heated to 450 °C, and cooled to witness the production of nanoparticles.

Absorption and desorption of SO2 in aqueous solutions of diamine-based molten salts

SO2 absorption and desorption behaviors were investigated in aqueous solutions of diamine-derived molten salts with a tertiary amine group on the cation and a chloride anion, including butyl-(2-dimethylaminoethyl)-dimethylammonium chloride ([BTMEDA]Cl, pKb=8.2), 1-butyl-1,4-dimethylpiperazinium chloride ([BDMP]Cl, pKb=9.8), and 1-butyl-4-aza-1-azoniabicyclo[2,2,2]octane chloride ([BDABCO]Cl, pKb=11.1). The SO2 absorption and desorption performance of the molten salt were greatly affected by the basicity of the molten salt. Spectroscopic, X-ray crystallographic, and computational results for the interactions of SO2 with molten salts suggest that two types of SO2-containg species could be generated depending on the basicity of the unquaternized amino group: a dicationic species comprising two different anions, HSO3(-) and Cl(-), and a monocationic species bearing Cl(-) interacting with neutral H2SO3.

Molten salt-supported polycondensation of optically active diacid monomers with an aromatic thiazole-bearing diamine using microwave irradiation

Microwave heating was used to prepare optically active thiazole-bearing poly(amide-imide)s. Polymerization reactions were carried out in the molten tetrabutylammonium bromide as a green molten salt medium and triphenyl phosphite as the homogenizer. Structural elucidation of the compounds was performed by Fourier transform infrared and NMR spectroscopic data and elemental analysis results. The polymeric samples were readily soluble in various organic solvents, forming low-colored and flexible thin films via solution casting. They showed high thermal stability with decomposition temperature being above 360 °C. They were assembled randomly in a nanoscale size.

Glassy state lead tellurite nanobelts: synthesis and properties

The lead tellurite nanobelts have been first synthesized in the composite molten salts (KNO3/LiNO3) method, which is cost-effective, one-step, easy to control, and performed at low-temperature and in ambient atmosphere. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectrum, energy dispersive X-ray spectroscopy and FT-IR spectrum are used to characterize the structure, morphology, and composition of the samples. The results show that the as-synthesized products are amorphous and glassy nanobelts with widths of 200-300 nm and lengths up to tens of microns and the atomic ratio of Pb:Te:O is close to 1:1.5:4. Thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) and investigations of the corresponding structure and morphology change confirm that the nanobelts have low glass transition temperature and thermal stability. Optical diffuse reflectance spectrum indicates that the lead tellurite nanobelts have two optical gaps at ca. 3.72 eV and 4.12 eV. Photoluminescence (PL) spectrum and fluorescence imaging of the products exhibit a blue emission (round 480 nm).