Evaluation of preliminary causes for vitamin D series degradation via DSC and HPLC analyses

Scientific evidence suggests that 25-(OH) vitamin D serum levels should be above 75 nmol L^?1, which is the level required for the beneficial effects of vitamin D on long-latency diseases. Supplementing vitamin D in a daily diet is advantageous for the health of elderly individuals. The focus of this study was on the causes of vitamin D₂ and D₃ degradation, such as vitamin D₂ being left in the open for days. The differences in the analysis results for fresh vitamin D and vitamin D stored in air for several days were compared. Comparisons were also made of the differences in vitamins D₂ and D₃ and their origins, i.e., oxidation, thermal decomposition, and photolysis, using high-performance liquid chromatography analyses and differential scanning calorimetry tests. We also developed a novel approach to examine the effect of heat on vitamin D, including the heat reactivity properties of vitamins D₂ and D₃, such as the kinetics of endothermic and exothermic reactions, the natural logarithm of the pre-exponential factor (lnk ₀), reaction order (n), activation energy (E _a), enthalpy of melting (?H), heat of decomposition (?H _d), isothermal conditions for the time to maximum rate, total energy release, and time until 10% conversion limited. Overall, the parameters, the reactivity properties, and the degradation results can be applied to determine the optimal conditions for vitamins D₂ and D₃ during cooking, storage, heat treatment, and food processing that will be beneficial to human health.     

氨能源作为清洁能源的应用前景

合成氨是一种成本低廉的化工原料,具有较高能量密度和辛烷值、易于压缩储运、燃烧不产生CO2等优点,是一种应用前景广泛的新型清洁能源。氨既可替代汽油、柴油等化石燃料,为汽车发动机直接提供清洁燃料,也可以经催化分解制取氢气,为车载燃料电池提供安全氢气。作为传统石油燃料的理想替代品,氨为解决环境污染和能源短缺问题提供了新的燃料选择。本文主要从发动机燃料和燃料电池原料两方面,介绍氨用于汽车动力源的优越性和可操作性,以及国内外相关研究进展;集中分析了氨分解制氢的催化剂体系的研究进展和局限性,以及合成氨的研究现状。     

Photochemical reduction of carbonate to formaldehyde on TiO2 powder

Photochemical reactions at semiconductor particle surfaces have been used to drive energy uphill reactions to store light energy. Carbonate radical anion was found to be intermediate when carbonate was used to intercept the photogenerated hole on TiO₂ by exciting with light energy of more than 3.2 eV. The carbonate anion radical undergoes secondary reactions on the surface to give formaldehyde. The chemical energy stored in this reaction is 580 kj/mole. The quantum yield for the formation of HCHO is 4 × 10^?3, but extended irradiation leads to loss of formaldehyde.     

Reactions in Tirapazamine Induced by the Attachment of Low‐Energy Electrons: Dissociation Versus Roaming of OH

Tirapazamine (TPZ) has been tested in clinical trials on radio‐chemotherapy due to its potential highly selective toxicity towards hypoxic tumor cells. It was suggested that either the hydroxyl radical or benzotriazinyl radical may form as bioactive radical after the initial reduction of TPZ in solution. In the present work, we studied low‐energy electron attachment to TPZ in the gas phase and investigated the decomposition of the formed TPZ^? anion by mass spectrometry. We observed the formation of the (TPZ–OH)^? anion accompanied by the dissociation of the hydroxyl radical as by far the most abundant reaction pathway upon attachment of a low‐energy electron. Quantum chemical calculations suggest that NH₂ pyramidalization is the key reaction coordinate for the reaction dynamics upon electron attachment. We propose an OH roaming mechanism for other reaction channels observed, in competition with the OH dissociation.     

Active MgH2?Mg Systems for Reversible Chemical Energy Storage

An overview of the importance of and methods available for heat storage in the form of sensible and latent heat is followed by a discussion of the advantages and disadvantages of reversible thermochemical energy storage compared to conventional energy sources such as fuels, i.e. irreversible chemical energy carriers. Of the reversible metal-hydride–metal systems, the MgH₂? Mg system is particularly attractive as a hydrogen and a high-temperature heat storage material because of its high hydrogen content and the high energy content of the Mg–H bond. The advances made in this area over the past few years, namely in catalytic hydrogenation and the doping of magnesium powders, have led to the development of “active MgH₂? Mg systems” for energy storage. The first experimental results on high-temperature heat storage (also with cooling) by coupling a MgH₂? Mg storage system with a low-temperature metal hydride storage system are presented.     

The thermal decomposition of NaHCO3 powders and single crystals

The thermal decomposition of four commercial powders and of differently stored single crystals of sodium hydrogen carbonate is studied by power compensation DSC and by optical and FT-IR microscopy. Independently of manufacturer, specified purity and price, the thermal curves of all the commercial powders show a more or less pronounced low temperature peak preceding the one due to the main decomposition. Such small peak is not observed when samples of laboratory recrystallized material are used. However the thermal behaviour of the latter preparation differs remarkably depending on storage conditions: the material kept in closed glass containers decomposes at temperatures higher than those of the material stored in a dessiccator in the presence of concentrated H₂SO₄. The observation by optical microscopy of the behaviour of the surfaces of single crystals coming from different storage conditions when the temperature is raised in a Kofler heater helps the interpretation of the data collected. The mechanism of the decomposition is discussed and the relevant kinetic parameters reported.     

Electricity Storage With High Roundtrip Effciency in a Reversible Solid Oxide Cell Stack

We theoretically investigate the electricity storage/generation in a reversible solid oxide cell stack. The system heat is for the first time tentatively stored in a phase-change metal when the stack is operated to generate electricity in a fuel cell mode and then reused to store electricity in an electrolysis mode. The state of charge (H₂ frication in cathode) effectively enhances the open circuit voltages (OCVs) while the system gas pressure in electrodes also increases the OCVs. On the other hand, a higher system pressure facilitates the species diffusion in electrodes that therefore accordingly improve electrode polarizations. With the aid of recycled system heat, the roundtrip efficiency reaches as high as 92% for the repeated electricity storage and generation.     

Fragmentations of Hydroxymethyl Radical Cation: An Ab Initio Study

The probable fragmentation channels of hydroxymethyl radical cation were studied through the H‐and H₂‐abstraction and C‐O bond breaking reactions including their related isomerization reactions. The energy barriers for hydroxymethyl cation undergoing isomerization reactions are generally higher than those undergoing the concerted 1,2‐elimination reactions to generate CHO⁺ and H₂. The fragmentation reaction to form CHO⁺ and H₂ through the 1,2‐elimination pathways is the major fragmentation channel for hydroxymethyl cation, consistent with the experimental observation. H abstraction from the hydroxyl group of CH₂OH⁺ is more difficult than that from the methylene group. The feasible path to lose H is to generate CHOH₂⁺ through hydrogen transfer reaction as the first step and then to undergo H‐elimination to generate trans‐CHOH⁺. Among all the reactions found in this study, the OH‐elimination to generate CH₂⁺ has the highest energy barrier. Our calculation results indicate that the major signals contributed from the related species of hydroxymethyl cation found in the mass spectrum should be m/e 29, m/e 30.     

非等温反应过程中新的动力学方程

对于非等温过程中的动力学方程，正确的Arrhenius方程的温度积分应该是从T₂到T₁，但是许多动力学方程中的温度积分是从T到0 K，例如Ozawa等方程。我们的研究指出对于某些反应，这些方程中的活化能存在较大的误差，因此我们提出了一个新的动力学方程。凭借等转化率法，应用新的方程可以精确求解线性或非线性加热过程中化学反应的活化能。用新方程对2个经典反应（聚酰胺的热裂解和一水草酸钙的热分解）的研究表明：Ozawa方程的活化能有时是精确的，有时偏差太大。     

Reactions of hydroxyl radicals with polystyrene

The reaction of polystyrene with hydroxyl radicals, generated by the photolysis (λ > 300 nm) of H₂O₂, has been studied at 25° in dichloromethane solution, both under vacuum conditions and in presence of O₂. Spectroscopic analyses suggest the presence of phenols and hydroxymucondialdehydes (when O₂ is present) among the reaction products, indicating that OH addition occurs at the phenyl groups of the polymer. By comparison with initiated oxidation reactions under the same conditions, it is concluded that the OH radicals undergo mainly addition reactions. A mechanism has been produced to account for the products. The significance of OH addition reactions in the oxidation of polystyrene is considered, the OH radicals being produced by hydroperoxide decomposition during oxidation, and the products having been previously identified as containing mucondialdehydes.     

Bulk Nanostructuring of Janus-Type Metal Electrodes

The stable deposition of reactive nanostructures on metal electrodes is a key process for modern technologies including energy conversion/ storage, electrocatalysis or sensing. Here a facile, scalable route is reported, which allows the bulk nanostructuring of copper foam electrodes with metal, metal oxide or metal hydroxide nanostructures. A concentration-gradient driven synthetic approach enables the fabrication of Janus-type electrodes where one face features Cu(OH)₂ nanowires, while the other face features CuO nanoflowers. Thermal or chemical conversion of the nanostructured surfaces into copper oxide or copper metal is possible whilst retaining the respective nanostructure morphologies. As proof of concept, the functionalized electrodes are promising in electrocatalytic water oxidation and water reduction reactions.     

Thermal decomposition of model compound of algal biomass

This contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self-condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO₂ and –OH, respectively, from the –COOH group attached to the α-carbon. The molecular channel for deamination involves cleavage of NH₂ from α-carbon of leucine. The activation energies for direct elimination of CO₂, NH₃, and H₂O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical-prompted pathways, systematically require lower energy barriers, in reference to closed-shell reaction corridors. Detailed computations at the CBS-QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas-phase reactions, within the context of a plug-flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed-phase leucine. Among notable N-containing species, the model predicts the prevailing of NH₃ over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self-condensation reactions of leucine in the gas phase.     

Elucidating the Thermal Decomposition of Dimethyl Methylphosphonate by Vacuum Ultraviolet (VUV) Photoionization: Pathways to the PO Radical,a Key Species in Flame‐Retardant Mechanisms

The production of phosphoryl species (PO, PO₂, HOPO) is believed to be of great importance for efficient flame‐retardant action in the gas phase. We present a detailed investigation of the thermal decomposition of dimethyl methylphosphonate (DMMP) probed by vacuum ultraviolet (VUV) synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. This technique provides a snapshot of the thermolysis process and direct evidence of how the reactive phosphoryl species are generated during heat exposure. One of the key findings of this work is that only PO is formed in high concentration upon DMMP decomposition, whereas PO₂ is absent. It can be concluded that the formation of PO₂ needs an oxidative environment, which is typically the case in a real flame. Based on the identification of products such as methanol, formaldehyde, and PO, as well as the intermediates O?P?CH₃, H₂C?P?OH, and H₂C?P(?O)H, supported by quantum chemical calculations, we were able to describe the predominant pathways that lead to active phosphoryl species during the thermal decomposition of DMMP.     

Application of heat conduction calorimetry to high explosives

This paper describes some thermal analysis experiments conducted on high explosive samples. These employ differential scanning calorimetry to monitor thermal effects at elevated temperatures (around 200 °C) and heat conduction calorimetry to record thermal effects at much lower temperatures (below 100 °C).The work shows that, due to the generally high thermal stability of many high explosive compositions, heat generation rates are very low, if detectable at all, at normal storage temperatures, even when using a very sensitive instrument. The sensitivity and reproducibility of this technique has been investigated in detail by Wilker et al. [S. Wilker, U. Ticmanis, G. Pantel, Detailed investigation of sensitivity and reproducibility of heat flow calorimetry, in: Proceedings of the 11th Symposium on Chemical Problems Connected with the Stability of Explosives, Sweden, 1998] and shown to be capable of recording heat generation rates of less than a microwatt. This allows continuous measurement of decomposition processes in nitrate ester based propellants at temperatures as low as 40 °C. However, the measurement of very low levels of heat generation is difficult, time consuming and therefore expensive. If the assumption is made that the life limiting process is invariably the slow decomposition of the energetic component, this will frequently lead to very long service lifetime predictions.A number of possible complications are identified. Firstly, due to its low detection threshold, a heat conduction calorimeter may detect other reactions which will not lead to failure, but which may still dominate the heat flow signal. Secondly, the true failure process may generate little energy and be overlooked. In view of these considerations, at present it seems unwise to rely on heat conduction microcalorimetry as the only tool for the assessment of the life of high explosive energetic systems.Based on examples of life terminating processes in high explosives during storage and use, it is clear that decomposition of the energetic material is not invariably the cause of system failure. It is also by no means the only reaction that may take place in, and be observed by, a heat conduction calorimeter.     

Sulfur‐Based Electrodes that Function via Multielectron Reactions for Room‐Temperature Sodium‐Ion Storage

Emerging rechargeable sodium‐ion storage systems—sodium‐ion and room‐temperature sodium–sulfur (RT‐NaS) batteries—are gaining extensive research interest as low‐cost options for large‐scale energy‐storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur‐based materials, in particular metal sulfides (MS_x) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na‐storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na‐storage mechanisms of the S‐based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MS_x anodes in Na‐ion batteries are reviewed. In addition, current advances on S cathodes in RT‐NaS batteries are presented. We outline a novel emerging concept of integrating MS_x electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT‐NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S‐based materials for the future Na‐storage techniques.     

An experimental and modeling study of ethanol oxidation kinetics in an atmospheric pressure flow reactor

Experimental profiles of stable species concentrations and temperature are reported for the flow reactor oxidation of ethanol at atmospheric pressure, initial temperatures near 1100 K and equivalence ratios of 0.61–1.24. Acetaldehyde, ethene, and methane appear in roughly equal concentrations as major intermediate species under these conditions. A detailed chemical mechanism is validated by comparison with the experimental species profiles. The importance of including all three isomeric forms of the C₂H₅O radical in such a mechanism is demonstrated. The primary source of ethene in ethanol oxidation is verified to be the decomposition of the C₂H₄OH radical. The agreement between the model and experiment at 1100 K is optimized when the branching ratio of the reactions of C₂H₅OH with OH and H is defined by (30% C₂H₄OH + 50% CH₃CHOH + 20% CH₃CH₂O) + XH. As in methanol oxidation, HO₂ chemistry is very important, while the H + O₂ chain branching reaction plays only a minor role until late in fuel decay, even at temperatures above 1100 K.     

Achilles’ Heel of Lithium–Air Batteries: Lithium Carbonate

The lithium–air battery (LAB) is envisaged as an ultimate energy storage device because of its highest theoretical specific energy among all known batteries. However, parasitic reactions bring about vexing issues on the efficiency and longevity of the LAB, among which the formation and decomposition of lithium carbonate Li₂CO₃ is of paramount importance. The discovery of Li₂CO₃ as the main discharge product in carbonate‐based electrolytes once brought researchers to “the end of the idyll“ in the early 2010s. In the past few years, tremendous efforts have been made to understand the formation and decomposition mechanisms of Li₂CO₃, as well as to conceive novel chemical/material strategies to suppress the Li₂CO₃ formation and to facilitate the Li₂CO₃ decomposition. Moreover, the study on Li₂CO₃ in LABs is opening up a new research field in energy technology. Considering the rapid development and innumerous emerging issues, it is timely to recapitulate the current understandings, define the ambiguities and the scientific gaps, and discuss topics of high priority for future research, which is the aim of this Minireview.     

Combustion synthesized crystalline La-Mn perovskite catalysts: Role of fuel molecule on thermal and chemical events

Solution combustion synthesis (SCS) technique was applied to produce LaMnO_3+δ with the aim to investigate the effect of the chemical nature of a series of six fuel molecules (glycine, maleic acid, succinic acid, citric acid, acetic acid, urea) on the combustion reaction mechanism and physicochemical properties of the as-prepared powders. The whole SCS process was found to involve two types of combustion reactions depending on the used sacrificial molecules. Type I (with glycine, maleic acid and succinic acid) was characterized by a one-step exothermic reaction implying a semi-decomposed mixed nitrate-fuel complex and NO₂ arising from manganese nitrate decomposition. The heat emission allows reaching the temperature suitable for well crystallized as-prepared perovskite powders. Type II (with citric acid, acetic acid and urea) was typified by a multi stage process in which intermediate decomposition reactions occurred before the formation of a mixed nitrate-fuel complex. In this case, the heat emission became lower than that expected from stoichiometric reaction, thus limiting the completion of the direct reaction for perovskite production. Consequently, part (with citric acid and acetic acid) or totally (with urea) of lanthanum and manganese remained distinctly combined in two amorphous phases (La(OH)₂NO₃, MnO_x) that were intimately mixed. With respect to other fuels, combustion synthesis, using glycine, produced better crystallized, more defective and performant catalytic perovskite phase toward deep ethanol oxidation.     

Ultrasonic Decomposition of Ammonia‐Nitrogen and Organic Compounds in Coke Plant Wastewater

The investigations of the ultrasonic decomposition of NH₃‐N and organic compounds (i.e., COD_Cr) in coke plant wastewater are presented in this work. The process parameters were controlled with respect to the presence (or absence) of air atmosphere, initial pH value, initial concentration, and ultrasonic power density in the process of ultrasonic decomposition. It is noted that the ultrasonic removal efficiencies for both the NH₃‐N and the COD_Cr were increased in the presence of the air atmosphere and significantly affected by the initial pH value. The removal efficiencies increased with increasing the ultrasonic power density while they decreased with increasing the initial concentration. The effects of n‐butyl alcohol as an effective OH radical scavenger on the removal efficiencies indicates that the ultrasonic decomposition of the NH₃‐N was carried out mainly via the mechanism of thermal decomposition in cavitation bubbles or in the interfacial region, whereas the ultrasonic decomposition of the COD_Cr mainly resulted from the reactions with OH radicals in the bulk solution. The GC/MS analysis indicates that most of the organic compounds in the wastewater were effectively destroyed by ultrasound.