Decomposition Of Molecules Research Articles

The multiple roles of a chemical tribofilm in hydrogen uptake from lubricated rubbing contacts

A newly developed in-situ technique has been employed to investigate the effect of lubricant additives and water contamination in oil on hydrogen intrusion into the steel. Hydrogen in oil-lubricated contacts is generated as a result of tribochemical reactions. The hydrogen uptake measurement results indicated that tribofilm formation can impede hydrogen ingress, in the substrate, by impeding the formation of fresh metal surfaces. This reduces the generation of hydrogen atoms by preventing the decomposition of hydrocarbon molecules. A uniform tribofilm across the wear track also acts as a physical barrier for hydrogen permeating through the tribo-contact. The water contamination in the oil negatively influenced tribofilm properties and therefore led to higher permeation of hydrogen into the steel.

Decomposition products of cylindrospermopsin – a cyanotoxin produced by Raphidiopsis raciborskii (Woloszynska)

Abstract Toxins produced by cyanobacteria (cyanotoxins) and released into water have become a serious problem worldwide due to the increasing morbidity and mortality of living organisms they have caused. The ability to synthesize the cytotoxic alkaloid cylindrospermopsin (CYN) has been demonstrated in several freshwater species of cyanobacteria. CYN is highly chemically stable under environmental factors and decomposes only under alkaline conditions, where it forms derivatives. The toxicity potential of the decomposition products formed at pH 10 combined with high temperature (100°C) or UV-B irradiation (36 μmol m−2 s−1) has been research based on the crustacean Thamnocephalus platyurus (Thamnotoxkit FTM) and bacteria Vibrio fischeri (Deltatox® II) bioassays. This paper is a continuation and completion of our previous experiments and the obtained results showed that the applied conditions contributed to the decomposition of the CYN molecule to non-toxic products and its structural modifications by separating the uracil ring or/and the sulfate group from the tricyclic guanidine moiety, leading to a reduction in its toxicity. To the best of our knowledge, this is the first report describing the toxicity of CYN decomposition products formed under alkaline conditions combined with boiling temperature or UV-B irradiation.

DFT, spectroscopic, DSC/TGA, electronic, biological and molecular docking investigation of 2,5-thiophenedicarboxylic acid: A promising anticancer agent

The molecular structural and various spectroscopic parameters (FT-IR, FT-Raman and UV–Visible) were determined by using quantum mechanical computation for 2,5-thiophenedicarboxylic acid (2,5-TDCA) molecule: a potential anticancer agent. The optimized geometrical parameters (monomer, dimer and trimer) were computed by B3LYP/6-311 + G(d,p) method and compared with related XRD data. The spectral studies of 2,5-TDCA molecule were adopted by recording FT-IR (4000-400 cm−1) and FT-Raman (3500-50 cm−1) spectroscopic techniques. The fundamental vibrational modes were computed for monomer and dimer, the vibrational assignments were done by finding Total Energy Distribution (TED) for each normal modes of vibrations by VEDA software. Mulliken charage analysis for monomer, dimer and trimer were analyzed by the same method. The UV–Vis absorption spectrum was recorded and correlated with electronic properties by TD-DFT method in gas and acetone phase by B3LYP/6-311 + G(d,p) method. The charge transfers happen within 2,5-TDCA molecule as well as in dimer form were investigated by using Natural Bond Orbital (NBO) approach. The MEP analysis was utilized for predicting the electrophilic and nucleophilic site in the 2,5-TDCA molecule. Total Density of State (TDOS) and Partial Density of State (PDOS) were also computed by Gauss Sum software. The non-covalent interaction of 2,5-TDCA was studied by adopting Reduced Density Gradient (RDG) and color filled electron density diagram. Thermodynamic properties have been performed by computing various thermodynamical parameters. The Electron density, Laplacian of electron density, Lagrangian Kinetic Energy, Hamiltonian Kinetic Energy and H-Bond energy at the bond critical point using Atoms in Molecule (AIM) theory reveal that there is a possibility of strong intermolecular hydrogen bonds. The DSC/TGA analysis was carried out to find the decomposition of molecule with respect to temperature. The biological activity of the 2,5-TDCA molecule were studied by using molecular docking analysis to identify hydrogen bond length and binding energies with different cancer protein. The 2,5-TDCA compound has been screened and found to exhibit anti-bacterial activity.

A first-principles investigation of double transition metal atoms embedded C2N monolayer as a promising SF6 gas adsorbent and scavenger

Greenhouse effect has become one of the most rigorous topics of environmental protection. The emission of one of the most typical greenhouse gas SF6 should be controlled and the waste gas treatment of SF6 has become a major topic to reduce the greenhouse effect. Two-dimensional porous materials have been widely used in gas adsorption and separation which may be useful for adsorbing waste SF6 gas. In this study, we report a promising adsorbent, transition metal dimer decorated C2N monolayer, for SF6 treatment by theoretical evaluation. The adsorption of SF6 molecule over the C2N surface are explored including the adsorption energy, electron transfer, magnetic moment and the electronic properties. Also, the decomposition process of SF6 molecule over the TM2-C2N monolayer is also considered. The results show that the SF6 can only be physical adsorption over the pristine C2N monolayer and experiences obvious decomposition over the Co2–C2N and Ni2–C2N monolayer. The adsorption with molecule decomposition can also significantly change the electronic properties of TM2-C2N. The low energy barrier of decomposition process over the TM2-C2N ensures good performance of adsorbent for SF6 in practical applications. This study provides theoretical foundation for TM2 dimer C2N monolayer as a promising adsorbent, scavenger and even catalytic material for degradation of greenhouse gas SF6 and waste gas treatment.

Fe2O3@FeP core-shell nanocubes/C composites supported irregular PtP nanocrystals for enhanced catalytic methanol oxidation

The construction of highly active Pt-based catalyst for methanol electrooxidation is still an ongoing challenge. Herein, irregular PtP nanocrystals with the length is around 7 nm supported on the Fe2O3@FeP/C composites consisting of Fe2O3@FeP core-shell nanocubes and carbon black particles are synthesized by an integrated hydrothermal, low temperature phosphidation and NaBH4 reduction process. TEM and EDS reveal that both the presence of phosphorus (P) and the mild Pt reduction method are play a critical role in constructing irregular PtP nanocrystals. Interestingly enough, the confinement effect of carbon particles on iron ions in the process of hydrothermal reaction leads to the generation of Fe-precursor nanocubes. Benefiting from the P can effectively modify the electronic state of the Pt surface, the strong interaction between special irregular PtP nanocrystals and the support surface as well as Fe2O3@FeP core-shell nanocubes for the enhanced activation and decomposition of H2O molecules, the as-prepared PtP-Fe2O3@FeP/C-8 h catalyst exhibits better anti-CO poisoning ability, stability and excellent catalytic activity for methanol oxidation. Specifically, the mass activity (831 mA mg−1Pt) of PtP-Fe2O3@FeP/C-8 h is 4.6- and 2.1-times greater than that of home-made Pt/C (Pt/C-H) (180 mA mg−1Pt) and commercial Pt/C (Pt/C-JM) (393 mA mg−1Pt) catalyst in acidic medium. At the same time, the mass activity of PtP-Fe2O3@FeP/C-8 h is as high as 3215 mA mg−1Pt, which is much higher than those of Pt/C-H (1298 mA mg−1Pt) and Pt/C-JM (1548 mA mg−1Pt) catalysts in alkaline medium. The present work provides a new entry points into the synthetic way for the irregular PtP nanocrystals and cheap co-catalytic species for methanol oxidation reaction (MOR).

Reactions of concerted decomposition of cyclic molecules, as studied by the quantum chemistry methods and parabolic model

Reactions of concerted decomposition of cyclic molecules (Diels—Alder retro-reactions) were studied using quantum chemical modeling and the method of intersecting parabolas (M3IP model). According to results of quantum chemical calculations and topological analysis of transition states (TSs) of five concerted decomposition reactions of cyclic molecules, all TSs represent six-membered rings in which the bonds being cleaved are weak covalent ones. The presence of ring heteroatoms (N, O, or S) has a strong impact on the TS geometry and on the energy characteristics of the reactions. The M3IP model was used to process the experimental results to develop an algorithm for calculating the activation energies (E) of the reactions in question and the classical potential barriers to thermally neutral reaction (Ee0). Factors influencing the energies E were determined and assessed. These include the enthalpy of reaction, substituents, ring heteroatoms, the force constants of bonds, and the bond dissociation energies. A comparison of the activation energies E and the enthalpies of reaction ΔH obtained from the M3IP and density functional B3LYP/6-311++G** calculations revealed good agreement between them.

High Density of End-Oxygens Induced by NO Adsorption on (2 × 1)Ni–O/Ni(110) Surfaces

The end-oxygens (end-O) of metal–oxygen chains on transition-metal (TM) surfaces play a vital role in the decomposition of H-contained molecules, such as H2O and alcohols. However, the achievement ...

Triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate

The triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex is detected during the mechanical grinding. The intense lines of N2 in the UV region and a band at 619 nm appeared due to luminescence of [Ru(bpy)3]2+ ion and coincided with the photoluminescence spectrum of the crystals are observed in the emission spectrum in air. The luminescence of N2 is due to electrification of the crystals during the destruction and subsequent discharges in the gas phase. We showed that the luminescence of [Ru(bpy)3]2+ does not occur due to absorption of UV luminescence of N2, because there is only luminescence of the crystal in O2 environment, whereas the luminescence of N2 is completely suppressed. The intense lines coincided with those of Ne and Ar atoms in the electric discharge are observed in the triboluminescence spectra of ruthenium(II) complex in neon and argon environments. In this case, there is an increase in intensity of N2 lines and of a band of [Ru (bpy)3]2+ due to more intense discharges than during the tribodestruction without inert gases. *OH radical is also detected in the triboluminescence spectrum due to mechanochemical decomposition of water molecules in the [Ru(bpy)3]Cl2·6H2O crystalline hydrate.

Overlooked electrolyte destabilization by manganese (II) in lithium-ion batteries

Transition-metal dissolution from cathode materials, manganese in particular, has been held responsible for severe capacity fading in lithium-ion batteries, with the deposition of the transition-metal cations on anode surface, in elemental form or as chelated-complexes, as the main contributor for such degradations. In this work we demonstrate with diverse experiments and calculations that, besides interfacial manganese species on anode, manganese(II) in bulk electrolyte also significantly destabilizes electrolyte components with its unique solvation-sheath structure, where the decompositions of carbonate molecules and hexafluorophosphate anion are catalyzed via their interactions with manganese(II). The manganese(II)-species eventually deposited on anode surface resists reduction to its elemental form because of its lower electrophilicity than carbonate molecule or anion, whose destabilization leads to sustained consumption. The reveal understanding of the once-overlooked role of manganese-dissolution in electrolytes provides fresh insight into the failure mechanism of manganese-based cathode chemistries, which serves as better guideline to electrolyte design for future batteries.

Reactive force field molecular dynamics (ReaxFF MD) simulation of coal oxy-fuel combustion

Understanding the reaction mechanism of oxy-coal combustion is fundamentally important to the CO2 capture and storage in coal-fired industrial processes. In this paper, the microscopic reactive behaviors of brown coal combustion in O2/CO2 atmosphere were simulated by combining the molecular dynamics (MD) simulations and the reactive force field (ReaxFF). With thoroughly tracing the motion trajectories of atoms, as well as the formation, transition and breaking of bonds between atoms, the generation pathways of CO2 and the effects of temperature (1600–2000 K) and oxygen concentration (21%~30%) on the coal oxy-fuel combustion process were studied. Results showed that the main process of CO2 generation consists of the decomposition, oxygenation, and dehydrogenation. The atmosphere with a high concentration of CO2 can accelerate the reaction rate of coal combustion and reduce the consumption of O2. The higher temperature will promote the production of major intermediates with more fragments being released earlier, and finally increase the generation of CO2. The increase of O2 concentration obviously hastens the decomposition of coal molecule and the generation of H2O, but shows very weak influence on the distributions of other major products and intermediates.

Activator-assisted pyrolysis of polypropylene

One of the most promising ways to recycle plastic is pyrolysis. Valuable fuels and chemicals can be obtained by pyrolysis of waste plastic. In this study, pyrolysis of polypropylene was conducted using a novel continuous two-stage process equipped with auger and fluidized bed reactors connected in series. The auger reactor played an important role as an activator to elevate the vibrational states of molecules fed into the fluidized bed reactor. Hence, the two-stage pyrolysis conducted herein was called activator-assisted pyrolysis. In this study, the effects of the temperatures of the auger reactor (or activator) and bubbling and freeboard zones of the fluidized bed reactor, the type of the fluidizing medium (product gas and N2), and the residence time of pyrolysis vapor on the product distribution and composition were investigated. In the experiments, the activator facilitated decomposition of polypropylene molecules, resulting in a high yield of the product gases (81 wt%) consisting mainly of H2 and CH4. The maximum olefin (ethene, propene, 1,3-butadiene, and butenes) yield was 52 wt%. The pyrolysis oil mainly consisted of aromatics (up to 92 wt%), particularly mono-aromatics. The activation energies of the activated and unactivated molecules were calculated using the Friedman and Flynn–Ozawa–Wall methods. The activation energy of the activated molecules was approximately 17 kJ/mol lower than that of unactivated molecules. Hence, it was clear that the degradation mechanism of polypropylene was different when activator-assisted pyrolysis was applied. The new activator-assisted pyrolysis proposed in the current work could be helpful to produce valuable chemicals from the pyrolysis of polyolefin waste.

Harvesting the Vibration Energy of BiFeO3 Nanosheets for Hydrogen Evolution

AbstractIn this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO3 (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 μmol g−1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration‐induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built‐in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H2/H2O redox potential (0 V) for hydrogen generation.

Harvesting the Vibration Energy of BiFeO3 Nanosheets for Hydrogen Evolution.

In this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO3 (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 μmol g-1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration-induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built-in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H2 /H2 O redox potential (0 V) for hydrogen generation.

Adsorption and decomposition of SF6 molecule on α-Al2O3 (0 0 0 1) surface: a DFT study

Based on the first principle, the interaction process between SF6 molecule and α-Al2O3 (0 0 0 1) surface was calculated. The results show that, under five adsorption sites, SF6 can form a relatively stable chemical adsorption at the O-3 site on α-Al2O3 (0 0 0 1) surface, while the other sites mainly showed physical adsorption processes. At O-3 site, 0.664 e electrons were transferred from α-Al2O3 to the SF6 molecule, and DOS analysis indicates that there was a strong electron orbital interaction between S and F atoms in SF6 and Al and O atoms on α-Al2O3 surface. After the adsorption, the molecule structure of SF6 changed significantly, the S–F bonds were elongated and partially broken, and the whole SF6 showed a tendency to be close to the surface of α-Al2O3. The energy barrier for SF6 decomposition was 0.147 eV. The results show the adsorption and decomposition process of SF6 molecules on the surface of α-Al2O3, which proves that α-Al2O3 has certain catalytic properties. The results indicate a simulation support for the efficient and harmless treatment of SF6 gas with Al2O3 catalysts.

Promising photocatalysts with high carrier mobility for water splitting in monolayer Ge2P4S2 and Ge2As4S2

Monolayer Ge2P4S2 and Ge2As4S2 are proposed as a new type of efficient photocatalyst for water splitting, based on first-principles calculations. Monolayer Ge2As4S2 exhibits a direct band gap of 1.89 eV (based on HSE06 calculation), while monolayer Ge2P4S2 is an indirect gap semiconductor that can turn into direct band gap by applying 3% compressive strain. Moreover, the band edge positions of monolayer Ge2P4S2 and Ge2As4S2 perfectly cover the redox potentials of water. Remarkably, the Ge2P4S2 and Ge2As4S2 monolayers possess rather high carrier mobilities (∼103–104 cm2 V−1 s−1), and have moderate optical absorption performance in the range of visible light. In addition, the adsorption and decomposition of water molecules on monolayer Ge2P4S2 and Ge2As4S2 are explored to illustrate the mechanism of photocatalytic hydrogen formation. These results demonstrate that the monolayer Ge2P4S2 and Ge2As4S2 hold great potential for photocatalytic water splitting.

Significantly Enhanced Electrical Performances of Eco-Friendly Dielectric Liquids for Harsh Conditions with Fullerene.

The eco-friendly vegetable liquid is increasingly used because of the growing demand for environmentally friendly dielectric liquid. A vegetable liquid/fullerene nanofluid was fabricated via ultrasonic processing with good dispersion of the fullerene nanoparticles. It was observed that a small amount of fullerene (~100 mg/L) can significantly improve the electrical properties of vegetable insulating liquid (dissipation factor decreased by 20.1%, volume resistivity increased by 23.3%, and Alternating Current (AC) dielectric breakdown strength increased by 8.6%). Meanwhile, the trace amount of fullerene is also able to improve the electrical performances (i.e., dissipation factor and electrical resistivity) of the vegetable nanofluid under harsh conditions of long-term thermal aging compared with the blank contrast. The reduced acid values (25%) and dissolved decomposition gases (58.2% for hydrogen) in the aged vegetable nanofluid indicate the inhibition of molecule decomposition of vegetable liquid with fullerene. The improved electrical performances and thermal resistance of the vegetable nanofluid contribute to the electron affinity of fullerene proved by calculation of electron density distribution on the surface. The thermogravimetric analysis of the nanofluid under different atmospheres interprets that the oxygen absorbed inevitably in the fullerene contributes to the performance deterioration of the nanofluids during the initial aging. This work provides a potential method towards eco-friendly dielectric liquid with great electrical performances for harsh environments.

A simple model for non-saturated reactive sputtering processes

Reactive sputtering processes are quite complex processes and therefore difficult to understand in detail. However, a number of attempts to clearify the behaviour of reactive sputtering of oxides and nitrides have been made. Several process modelling results for such processes have been published that reasonable well mirrors the actual experimental findings. All of these models indicate that the processes normally exhibit hysteresis effects and that the oxides/nitrides will saturate at the stoichiometric compound values. We therefore call these processes saturated reactive sputtering processes. Carrying out reactive sputtering in a hydrocarbon gas like CH4 instead of in oxygen or nitrogen cannot be described with the previously suggested models for oxide or nitride formations. Decomposition of the CH4 molecule in the plasma may result both in carbide formation with the target metal as well as plasma deposited carbon. Depending on the supply of the CH4 the deposited film composition may vary from 0 to 100% of carbon. In the extreme case of very high supply of CH4 a pure carbon film will be deposited. We expect that similar behaviour will be found when carrying out reactive sputtering in other solid material containing gases like e.g. silane or diborane. We have chosen to call such processes non-saturated reactive sputtering processes. In order to understand the behaviour of non-saturated reactive sputtering processes we have developed a new model that enables the user to find the response to individual processing parameters and thus obtain a tool for process optimization. In order to limit the number of parameters our model is outlined for reactive sputtering of Ti in a mixture of argon and CH4. In this article we report that the simulation results reasonable well correlate with our experimental findings.

A Field Electron Emitter in the Form of Iridium Tip with Carbon Coating

The properties of an field electron emitter, the surface of which is obtained by the decomposition of benzene molecules on the iridium tip, have been studied. As a result, a graphite crystal is formed at the top of the tip. Resistance of molecules of residual gases to adsorption, as well as the possibility of localizing emission by adsorption and intercalation of alkali metal atoms are shown.

The effects of U-232 on enrichment and material attractiveness over time

The effect of 232U on enrichment and material attractiveness provides a significant firewall against proliferation. Mixing 232U with natural uranium creates major obstacles to the weaponization process. The decay heat of 232U is significant and increases over time by a factor greater than 5 through the decay of 232U daughter products. The dose rate also becomes significant as 208Tl builds up and emits an energetic gamma ray of 2.615 MeV. These factors, along with the bare critical mass and spontaneous fission neutron rate are used to determine the material’s attractiveness through a Figure of Merit analysis. Considering 232U is lighter than 235U, attempting to enrich a mixture of natural uranium and 232U to weapons grade will also increase the concentration of 232U and thus increase the material’s unattractiveness. This study simulates natural uranium with a 232U concentration of 0.03 at.% being enriched to weapons grade and determines the attractiveness of the resulting uranium vector. The results show that the material becomes unattractive within a year of initial separation. In addition, the alpha decay of 232U in gaseous UF6 will result in the decomposition of UF6 molecules. The rate of this decomposition in the initial natural uranium mixture, the mixture enriched to 3 at.% 235U, and this mixture enriched to 90 at.% 235U is calculated. These rates are notable and may pose a significant firewall to obtaining weapons grade uranium.

Development and application of flexible integrated microsensor as real-time monitoring tool in proton exchange membrane water electrolyzer

The proton exchange membrane (PEM) water electrolyzer has such advantages as simple system, low operating temperature and small-scale hydrogen production according to real time requirement, and the hydrogen production process is clean, meeting the environmental requirements. The PEM water electrolysis hydrogen production is the reverse reaction of fuel cell, but the water electrolysis requires high operating voltage, the resistance is likely to generate a lot of waste heat, and the nonuniform current density results in hot spots, the internal temperature rises, accelerating the decomposition of hydrogen molecules, the water electrolyzer is likely to age and fail. In addition, four important physical parameters (temperature, flow, voltage and current) in the running water electrolyzer can influence its performance and life, but the present bottleneck is external, theoretical, simulated or single measurement, the authentic information in the water electrolyzer cannot be obtained accurately and instantly. This study uses micro-electro-mechanical systems (MEMS) technology to develop a flexible integrated (temperature, flow, voltage and current) microsensor applicable to the high voltage and electrochemical environment in water electrolyzer, which is integrated with a 20 μm thick polyimide (PI) film material. The real-time microscopic diagnosis and measurement in the PEM water electrolyzer can measure the internal local temperature, voltage, current and flow distribution uniformity instantly and accurately, so as to optimize the operating conditions and analysis.