Green preparation of vanadium carbide through one-step molten salt electrolysis

Vanadium carbide (VC) as excellent ceramic and functional material is usually prepared by carbothermal reduction of V₂O₅ which must be extracted from a typical V slag by complex processes. Pollutants, such as ammonia-nitrogen wastewater, NH₃ and CO₂ are inevitably discharged. A novel and green method for VC preparation was proposed by one-step co-electrolysis of soluble NaVO₃ and CO₂ in molten salt. It was found that VC with high purity was easily obtained by reducing electrolysis temperature and CO₂ flow rate to 600 °C and 10 mL min⁻¹ at 3.0 V. Besides VC with particles and layered stacking structure in products, a small amount of carbon and oxygen elements existed. The atomic percentage contents of C, V, and O elements in VC were about 50.0%, 44.5% and 3.8%, respectively. During electrolysis, CO₃²⁻ and VO₃⁻ was reduced at about −0.55 V (vs. Ag/AgCl) and −1.38 V (vs. Ag/AgCl), respectively. CO₃²⁻ ions were more easily reduced than VO₃⁻, and was firstly reduced to CO₂²⁻ and then converted to C. Then, VC was prepared by two routes from CO₂ and NaVO₃. One route is that VO₃⁻ ions are firstly electroreduced to VO₂⁻ ions and then are further electroreduced to VC with C. Another route is that VO₃⁻ ions are electroreduced to V which in-situ reacted with C to VC. Both VO₃⁻ and CO₃²⁻ ions are electroreduced by two-step process. In final, VC is in-situ deposited on cathode. It provides a novel and green way to prepare VC and also achieves the high value-added utilization of vanadium slag and CO₂.     

不同盐沼湿地类型脱氮除磷效能及影响因素分析

采用沉水植物表面流湿地(沉水组)、挺水植物表面流湿地(挺水组)和浮床湿地(浮床组)3种盐沼湿地对长江口近岸低污染水体进行脱氮除磷效能的研究。结果表明,HRT为3 d时,水组、挺水组、浮床组对NO3^--N的去除率在高温时段分别为79.9%±13.2%、71.8%±15.2%、77.2%±13.2%,中温时段分别为39.4%±13.7%、31.5%±8.5%、18.4%±16.6%,低温时段分别为15.6%±14.6%、19.7%±8.6%、2.%5±8.6%。沉水组和挺水组对TP的去除率受温度影响较小,分别为66.4%±32.4%、55.5%±29.4%;而浮床组除磷效果受温度影响较大。当HRT缩短为1.5 d时,3组湿地系统在高温时段仍可达到相近的脱氮除磷效果,在中低温时段脱氮除磷效果都有不同程度的下降。     

Stem Photosynthesis—A Key Element of Grass Pea (Lathyrus sativus L.) Acclimatisation to Salinity

Grass pea (Lathyrus sativus) is a leguminous plant of outstanding tolerance to abiotic stress. The aim of the presented study was to describe the mechanism of grass pea (Lathyrus sativus L.) photosynthetic apparatus acclimatisation strategies to salinity stress. The seedlings were cultivated in a hydroponic system in media containing various concentrations of NaCl (0, 50, and 100 mM), imitating none, moderate, and severe salinity, respectively, for three weeks. In order to characterise the function and structure of the photosynthetic apparatus, Chl a fluorescence, gas exchange measurements, proteome analysis, and Fourier-transform infrared spectroscopy (FT-IR) analysis were done inter alia. Significant differences in the response of the leaf and stem photosynthetic apparatus to severe salt stress were observed. Leaves became the place of harmful ion (Na⁺) accumulation, and the efficiency of their carboxylation decreased sharply. In turn, in stems, the reconstruction of the photosynthetic apparatus (antenna and photosystem complexes) activated alternative electron transport pathways, leading to effective ATP synthesis, which is required for the efficient translocation of Na⁺ to leaves. These changes enabled efficient stem carboxylation and made them the main source of assimilates. The observed changes indicate the high plasticity of grass pea photosynthetic apparatus, providing an effective mechanism of tolerance to salinity stress.     

Synthesis and Properties of New Cleavable Cationic Surfactants Containing Carbonate Groups

A novel series of cleavable alkyltrimethylammonium surfactants with different hydrocarbon chain lengths (C8–16) were synthesized. A carbonate break site inserted between the polar head and the hydrocarbon chain makes these compounds hydrolyzable. The reagents used are renewable, (bio)degradable, or reusable. The hydrolysis of these cleavable surfactants will lead to the generation of fatty alcohols and choline, which is an essential biological nutrient. The surface activities in aqueous solution of the synthesized carbonates fulfill the requirement of being good surfactants. In addition, the cleavable compounds containing n-decyl and n-dodecyl chains showed similar or higher antimicrobial activities when compared to a non-cleavable analog.     

Potassium titanate whiskers on the walls of cordierite honeycomb ceramics for soot catalytic combustion

In this paper, potassium titanate whiskers was prepared via the Molten salt synthesis on the surface of cordierite ceramics for the regeneration of diesel particulate filters (DPFs). SEM, EDS, XRD, FT-IR, TG-DSC and TPO were carried out to characterize the morphology, microstructure, growth mechanism and catalytic performance of the samples. Potassium titanate whiskers with diameter (100–500 nm) and length (about 3 μm) is tightly combined with the cordierite ceramic substrate. The catalyst performance investigation demonstrates that potassium titanate whiskers decrease the soot combustion temperature apparently. The soot combustion process was studied by thermal analysis tests, and the activation energy of the combustion reaction can be calculated using Freeman-Carroll method. The carbon oxidation activation energy is 14.009 kcal/mol, and the activation energy for the catalytic reaction with potassium titanate whiskers is 6.287 kcal/mol, it can be illustrated that potassium titanate whiskers/cordierite catalyst possess excellence performance for carbon catalytic combustion. The coarseness of the interface increased because potassium titanate whiskers grew on the cordierite substrate, and the trapping ability could improve. This unique microstructure has potential application in the DPF field.     

In-situ synthesis of zirconium oxycarbide by electroreduction of ZrO2/C in molten salt

Homogenous ZrC_xO_y powders have been successfully synthesized by in-situ electro-reduction of solid ZrO₂–C composite precursors in molten CaCl₂. The effect of applied cell voltage and molar ratio of ZrO₂ to C on preparation of ZrC_xO_y were investigated. The reduction pathway of the composite electrode was studied based on the analysis of intermediate products using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that ZrO₂ is firstly converted to CaZrO₃. The resulting CaZrO₃ is then reduced to ZrC_xO_y. The ZrC_xO_y formation is dramatically influenced by electrolysis voltage and molar ratio of ZrO₂ to C: a higher cell voltage and lower molar ratio of the ZrO₂ to C are more preferable for the formation of ZrC_xO_y powder. Homogenous ZrC_xO_y powders with particle size of ~100 nm are synthesized by ZrO₂/C starting elemental powders in CaCl₂ molten salt at 1123 K for more than 3 h, when the cell voltage is 3.0 V and the molar ratio of the ZrO₂ to carbon starting materials is 1:1.0.     

Manganese oxides treated with organic compounds as catalysts for water oxidation reaction

Manganese oxides of different crystalline structures: α-MnO₂, δ-MnO₂, α,γ-MnO₂ and Mn₂O₃; were treated with the organic compounds picolinic acid, ethylenediamine and pyridine; and were applied as catalysts in the chemical water oxidation reaction using Ce(IV) ammonium nitrate as sacrificial oxidant. The treatment led to modifications in the oxides properties, such as reduction of the particle size, increase of surface area and partial reduction of Mn⁴⁺ to Mn³⁺ for the Mn(IV) oxides, or of Mn³⁺ to Mn²⁺ for Mn₂O₃, because of favored interactions of the organic molecules with the lattice planes with higher d spacing. Oxygen evolution reaction (OER) tests showed the superior catalytic activity of the treated Mn(IV) oxides, for instance α,γ-MnO₂-en presented TOF five times higher than pure α,γ-MnO₂. The increase in surface area as well as the higher Mn³⁺ content caused by the treatment of the Mn(IV) oxides were correlated with the improvement in the OER catalytic activity.     

Generation-IV reactors and nuclear hydrogen production

There are dozens of hydrogen production methods and techniques from many sources such as fossil fuels, renewable energy sources and nuclear energy in the literature. Thermo-chemical methods are more efficient at higher temperatures to produce large quantities of hydrogen. In this study, a comparative overview of Generation VI nuclear reactor types for major hydrogen production methods have been researched in the literature and suggestions have been carried out.This research work is addressing that both electric power cycle and hydrogen production based on nuclear technologies need to be developed. Generation IV nuclear reactors can provide hydrogen for a worldwide hydrogen economy. Both thermo-chemical and electrolysis (hybrid) processes in hydrogen production have a promising future, especially when integrated with Generation IV nuclear power plants. Efficient heat transfer is required for both high temperature thermodynamic cycles and the high temperature steam electrolysis. Hence, highly efficient heat exchanger designs are one of the key technologies for that purpose.     

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al₂O₃–SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al₂O₃–SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.     

Effects of corrosion in liquid fluoride salt on the tensile strength of domestic SiC fibers

The relationship between the tensile strength of corroded domestic second-generation (2ed-gen) SiC fibers at various temperatures for 500 h in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt and the typical microstructure was studied. Weibull theory was used to analyze the critical defects that caused the tensile fracture, and the microstructure of fibers before and after corrosion was characterized. It is concluded that the decrease of tensile strength after corrosion at 800 °C is caused by the surface injury of fibers, which led to the shift of critical defects from the internal defects of virgin fibers to surface defects. Moreover, corrosion at higher temperature accelerates the corrosion process and dissolve the surface O-contained layer thoroughly. This shifts the critical defects back to the internal defects and will be helpful for the recovery of tensile strength of corroded fibers at the higher temperature.