O2 Molecules Research Articles

Tropospheric Fate of Methylhydroxycarbene and the Ability of a Single Water Molecule to Efficiently Promote Its Isomerization into Acetaldehyde.

The ultraviolet (UV) photodissociation of pyruvic acid through the absorption of solar actinic flux generates methylhydroxycarbene (MHC) in the atmosphere. It is recognized that isolated MHC can undergo unimolecular isomerization to form acetaldehyde and vinyl alcohol. However, the rates and mechanism for its possible bimolecular reactions with atmospheric constituents, which can occur in parallel with its unimolecular reaction, is not well understood. Here we investigate the energetics, kinetics, and mechanism of the reaction of MHC with three ubiquitous atmospheric molecules N2, O2, and H2O over the 160 K-380 K temperature range. Our study, at the CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd) level, reveals that the MHC + N2 encounter is nonreactive, while the MHC + O2 reaction, which leads to CH3CO + HO2 formation, has a rate that is significantly different from previous estimates. For the MHC + H2O reaction, we find that a single H2O molecule is very effective in catalyzing the isomerization of MHC to form predominantly acetaldehyde. An analysis of the computed rate for this reaction indicates that it will be an important source of tropospheric acetaldehyde ̵ a major pollutant and precursor for atmospheric reactive intermediates. Our findings are in sharp contrast to current assessments in the literature that the MHC + H2O reaction is minor. Furthermore, in the MHC + H2O reaction system, we find that due to the presence of the OH group on MHC, the concerted insertion mechanism, which is typically dominant in reactions involving singlet carbenes, is suppressed relative to a hydrogen bond mediated double hydrogen atom transfer mechanism.

Highly selective adsorption of MoS2/ZnO heterojunctions for SO2 and H2S gas molecules: A DFT study

Highly selective adsorption of MoS2/ZnO heterojunctions for SO2 and H2S gas molecules: A DFT study

Monte Carlo Calculation of Electron Energy Degradation in a Pure O2 Atmosphere

Electron degradation serves as a significant energy source in planetary upper atmospheres. In this study, a Monte Carlo model is constructed to investigate the degradation of electrons in a pure O2 atmosphere under the local approximation. Both elastic and inelastic collision processes between electrons and O2 molecules are considered in the model. The yield spectra, characterizing the occurrence of various inelastic collisions for a specified pair of incident and post-collision energies, are obtained from the model. When combined with the information of e-O2 collision cross sections, the yields of each inelastic process are then determined. Furthermore, we derive the mean energy per ion pair and the efficiencies of various inelastic processes, along with the yields of secondary (and higher-order) electrons. The calculations presented here are beneficial for understanding the ionization and heating budgets in planetary atmospheres containing a significant amount of O2 such as Earth and Jovian icy satellites (Europa, Ganymede, and Callisto).

ЕЛЕКТРОСТАТИЧНЕ ПОЛЕ В КАМЕРІ БАР’ЄРНОГО РОЗРЯДУ ДЛЯ ОЧИЩЕННЯ ВОДИ З УРАХУВАННЯМ ОКРЕМИХ ВОДНИХ КРАПЕЛЬ

The use of pulsed dielectric barrier discharge (DBD) for water purification via low-temperature plasma (LTP) is a promising technology. DBD enables the purification of water in a droplet-film state from organic contaminants by generating highly reactive molecules (OH radicals, O, H2O2, and O3 molecules) produced in LTP upon contact with water. A two-dimensional model was developed to calculate the electrostatic field in the DBD discharge chamber (DC), which includes two electrodes, a dielectric barrier, two water droplets or streams in the air gap, and water films. The model employs Laplace’s equation for the electrostatic field with periodic boundary conditions. Expressions were proposed for determining the length of the symmetric part of the DC and setting the voltage on the electrodes with a constant droplet surface area and a constant average electric field intensity in the air gap, independent of droplet radius. The study investigates the dependence of the electrostatic field energy and DC capacitance on the droplet radius and their mutual positioning along the DC length. Changes in electrode voltage and droplet density per unit DC length relative to droplet radius are demonstrated. An analysis of the electric field distribution, DC capacitance, and stored energy was conducted. The average electric field intensity on the surfaces of droplets and water films was examined. The electric forces acting on the droplets were determined using Maxwell's stress tensor. An expression was derived for calculating the recommended amount of water in the form of droplets or streams per unit dimensions of the DC to achieve a more uniform distribution of the electric field intensity within the DC and to minimize the impact of electric forces on the droplets. Ref. 18, fig. 7.

DFT study of the adsorption properties and sensitivity of a B2N monolayer toward harmful gases

In this study, we investigate the adsorption of harmful gases - CO, NO, NO2, SO2, and O3 molecules - on a B2N monolayer using periodic density functional theory. The adsorption energy values for the CO/B2N, NO/B2N, NO2/B2N, SO2/B2N, and O3/B2N complexes are determined to be -1.96, -1.39, -1.80, -0.70, and − 2.36 eV, respectively. The B2N monolayer has the ability to adsorb harmful gas molecules, even in humid air, and displays favorable adsorption energy and standard recovery time when exposed to SO2 gas. Consequently, the impact of SO2 gases on the transmission characteristics of the B2N monolayer has been assessed through current-voltage analysis. These findings are of great importance as they serve to demonstrate the remarkable sensing capabilities of a B2N monolayer in efficiently detecting SO2 gas. The desorption time for CO, NO, NO2, and O3 molecules is quite long, thereby indicating the remarkable stability of the B2N sheet for adsorption of these gases. The current study offer valuable insights for further research into the potential utilization of B2N monolayers in long-term monitoring and gas purification applications, specifically in relation to four toxic gases: CO, NO, NO2, and O3.

Solvate Complex LiAlCl4·SO2: Synthesis and Physical-Chemical Properties.

This work describes the synthesis of the LiAlCl4·SO2 solvate complex and its properties. Its composition was determined using thermogravimetric analysis, Raman spectroscopy, and UV-vis spectroscopy. The specific ionic conductivity of LiAlCl4·SO2 is 4.7 × 10-2 S·cm-1. The dynamic viscosity is 19 cP at 25 °C, and the lithium transference number is 0.78. The melting point (+2.5 °C) and decomposition temperature (+60 °C) of LiAlCl4·SO2 were determined by simultaneous thermogravimetric analysis and differential scanning calorimetry. The structure of the solvate complex LiAlCl4·SO2 has been studied using a molecular dynamics method. A lithium cation is coordinated by one atom of Cl of the anion AlCl4- and one oxygen atom of SO2. The coordination number of lithium ions of LiAlCl4·SO2 is 4. The lithium cation is coordinated by three anions of AlCl4- and one molecule of SO2. Anion AlCl4- acts as a bridging ligand and binds different lithium cations.

Measurements and kinetic modeling of O2 vibrational Kknetics in O2-Ar mixtures partially dissociated by a Ns pulse discharge

Abstract Vibrational kinetics of O2 is studied during the O atom recombination in an O2-Ar mixture, partially dissociated by a burst of ns discharge pulses in a heated plasma flow reactor. The time-resolved temperature in the discharge afterglow is determined by Rayleigh scattering. Time-resolved O atom number density is measured by ps Two-Photon absorption Laser Induced Fluorescence (TALIF), calibrated in xenon. Time-resolved vibrational level populations of molecular oxygen, O2(v=8-20), are measured by ps Laser Induced Fluorescence (LIF), with the absolute calibration by NO LIF. Time-resolved ozone number density is monitored by broadband UV absorption. The results are compared with the predictions of a state-specific kinetic model. The experimental data indicate a rapid initial decay of O2(v) populations generated by electron impact in the discharge, due to the vibration-translation (V-T) relaxation by O atoms. This is followed by a slower population reduction, on the time scale much longer compared to that for V-T relaxation or vibration-vibration (V-V) exchange. Both O atoms and the O2(v) populations decay on the same time scale, indicating that chemical reactions initiated by the O atom recombination result in the generation of vibrationally excited O2 molecules. These trends are reproduced by the kinetic model, which shows that the reaction of O atoms with ozone is the dominant pathway of O2(v) generation at the present conditions. The predicted relative O2(v) populations are close to the experimental results, but absolute number densities differ from the experimental data. This is likely due to uncertainties in the absolute calibration of LIF measurements and in the spectroscopic model used in the data reduction. The present work demonstrates the capability for the absolute, time-resolved measurements of vibrationally excited O2 in recombining gas flows, to quantify the energy partition in the recombination reactions.

Recent Advances in Perovskite Nanomaterials for Sensing Applications

Abstract Perovskite-structured materials have been extensively studied for sensing applications on account of their good thermal stability and 3-4 eV bandgap. They have been utilized to detect traces of O2, NO, CO, NO2, CO2, H2O, CH4, H2 and similar smaller gas molecules such as C2H5OH etc. In addition, other sensing applications are optical sensing, I-V fluctuations, strain sensors, electromechanical sensors, sensing of metal ions, etc. Perovskite-structured halides are reported for sensing of metal ions, toxic gases, Volatile Organic Compounds (VOCs), detection of fungicides, pesticides, explosives, cellular imaging, radiation detection and humidity and temperature sensing.

The gas-sensing mechanism of Nb2C monolayer for SF6 decomposition based on the DFT study

Abstract During fault analysis of gas-insulated switchgear (GIS), continuous monitoring of the gases produced by the decomposition of SF6 is critical to the safe operation of the equipment. Although a variety of gas detection technologies are currently available on the market, low-power gas detection devices for SF6 decomposition products are still in the development stage, and technological advances in this area are of great significance for improving the reliability of GIS systems. Based on the density functional theory (DFT), the Nb2C crystal surface structure was established and six adsorption structures of SO2, H2S, SOF2, SO2F2, HF and CO gas molecules on Nb2C crystal surface were constructed by geometrical optimization in this paper. The gas-sensitive properties of each adsorption system were explored in terms of adsorption energy, charge transfer, electron density, density of states and recovery time. The results showed that the Nb2C crystal surface was unfit HF and CO gases detection, both of which showed weak physical adsorption; the adsorption energies of SO2, H2S, SOF2, and SO2F2 on the Nb2C crystal surface were −1.846 eV, −1.081 eV, −5.270 eV, and −10.582 eV, respectively, and all of them were strong chemical adsorption. It was further shown by theoretical recovery time calculations that the Nb2C crystal surface can act as SOF2 and SO2F2 gas scavengers, and are able to desorb H2S (4.69 s) and SO2 (2.26 s) gases by appropriately increasing the temperature, but the Nb2C crystal surface is more suitable for use as a low-power gas-sensitive material for H2S gas detection. Therefore, Nb2C is anticipated to be a promising material for high response, low-power consumption and fast recovery for H2S gas detection in SF6 decomposition gas.

Influence of species kinetics on discharge characteristics in oxygen helicon plasma

Abstract Oxygen (O2) helicon plasmas in multiple wave modes were excited by a right-helical antenna with an upper metal endplate at low pressure. Mode transitions were observed at increasing input power or magnetic field, characterized by obvious jumps of plasma parameters. Blue Core appears at high magnetic fields (~700 G) and input powers (~1700 W), with a large radial gradient of plasma density, ion line intensity, and electron temperature. Emission spectra demonstrate that the blue lights originate from O II lines. We found that the intensity ratio of O II to O I of Blue Core in O2 is lower by one order than that in N2 or Ar despite their similar ionization rates and plasma densities in Blue Core area. A high-temperature B-dot probe together with a waveform fitting procedure was used to present the measured oscillating waveforms of m =+1 helicon waves, showing distinct wave structures of different eigenmodes. Cavity mode resonance is suggested to be responsible for the formation of standing waves of discrete eigenmodes. A pressure balance model was developed to estimate the species densities around the central area in different modes, showing massive dissociation of O2 molecules and high density of O atoms locally, so that O2 helicon plasma behaves a species feature of monatomic gas discharge. The obviously low intensity of O II lines compared to O I lines of Blue Core in O2 is related to the quite high excitation threshold of O+ ions (~30 eV) although electron density and temperature are relatively high. The combined effects of dispersed reaction energy distribution, massive molecule dissociation and negative ion creation are considered to be the main causes for requirement of much higher RF power and magnetic field for Blue Core formation in O2 helicon plasma than that in Ar. The calculated radial profile of power deposition and the captured plasma morphology confirm that the dominant central electron heating is the essential reason for the large radial gradients of plasma density and electron temperature which contributes to the serious neutral depletion and Blue Core formation.

Tailoring ORR Activity in Fe-N-C Catalysts through Phosphorus Incorporation.

Atomically dispersed iron and nitrogen co-doped carbon materials (Fe-N-C) represent promising non-precious metal catalysts for the oxygen reduction reaction (ORR), offering potential alternatives to noble metal-based benchmarks. In our study, we investigated the influence of phosphorus doping on the catalytic activity of Fe-N-C. The experimental research demonstrate that the doping of phosphorus significantly enhances the ORR activity. Specifically, the resulting Fe-NPC exhibits high metal loading and excellent ORR activity in 0.1 M KOH with an onset potential of 1.00 V and a half-wave potential of 0.864 V. Density functional theory (DFT) simulations reveal that phosphorus improves the electrocatalytic activity by activating O2 molecules and reducing the energy barrier (the hydrogenation reaction *OH→H2O) of the rate-determining step. Furthermore, Fe-NPC exhibits promising application prospects as an air cathode in Zn-air batteries, delivering a high maximum discharge power density of 180.3 mW cm-2 and outstanding discharge specific capacity (758.8 mAh g-1Zn) at a discharge current density of 10 mA cm-2.

Electrical and work function-based chemical gas sensors utilizing NC3 and graphene combination

Research has been conducted on the potential practical uses of heterostructures made of graphene and carbon nitride (NC3) following their successful synthesis. The remarkable gas sensing properties of these 2D nanosheets have captured significant interest, attributed to distinctive electronic characteristics and exceptional surface-to-volume ratio that are resulted from combination of NC3 and graphene. In this study, we present a detailed analysis of electronic and structural features of pristine NC3 and graphene (PG), and their in-plane heterostructures using first-principles density functional theory. Our investigation utilizes the B3LYP and dispersion-corrected van der Waals (vdW) functional WB97XD, along with 6-311G (d, p) basis set. Our findings indicate that the nanosheets we anticipated exhibit robust structural stability, characterized by a desirable cohesive energy. Furthermore, we observed a gradual increase in the bandgap as the concentration of N–C in the nanosheets increases. Additionally, we investigated the adsorption characteristics of these heterostructures towards toxic gas molecules such as SO2 and CO. Among the studied heterostructures, GNC3I demonstrated higher adsorption energy (Eads), with values of approximately −0.283 and −0.491 eV when exposed to SO2 and carbon monoxide gas molecules respectively. Electronic characteristics, including LUMO and HOMO energy values, energy gap (Eg) between HOMO and LUMO, work function, Fermi level, and conductivity, underwent notable modifications upon SO2 gas adsorption over nanosheets, except for PG. However, these parameters remained relatively unchanged following carbon monoxide adsorption. Natural bond orbital (NBO) and Mulliken charge analysis demonstrates that there is a transfer of charge from gas molecules to nanosheets. Although nanosheets exhibit slightly higher adsorption energy (Eads) values for CO gas compared to SO2 gas, various assessments, including molecular electrostatic potential (MEP) mapping, electronic properties, and charge transfer (CT) analysis, suggest that these nanosheets are superior sensors for detecting SO2 gas rather than carbon monoxide gas molecules.

Modulator-Directed Counterintuitive Catenation Control for Crafting Highly Porous and Robust Metal-Organic Frameworks with Record High SO2 Uptake Capacity.

Sulfur dioxide (SO2) is an important industrial feedstock that can be directly utilized or catalytically transformed to value-added chemicals such as sulfuric acid. The development of regenerable porous sorbents for the highly efficient storage and energy-minimal release of toxic SO2 operating under ambient conditions has attracted growing interest. Herein, we report the topology-guided construction of highly porous acs-type metal-organic frameworks (MOFs) through a counterintuitive modulator-directed catenation control approach. In contrast to the conventional modulator facilitated coordination competition that favors the thermodynamic catenated phase, we show that the elevation of modulator concentration can promote the formation of the noncatenated phase probably through a sublattice dissolution pathway. The assembly of a custom-designed trigonal prismatic triptycene-quinoxaline linker and trinuclear Fe3O cluster affords either the threefold catenated SJTU-219 or noncatenated SJTU-220 with desired acs net. Impressively, the synthetic approach is applicable to various metal ions, including Al3+, V3+, and even Ti4+. The noncatenated SJTU-220 exhibits an extraordinary SO2 sorption capacity of 29.6 mmol g-1 at 298 K and 1 bar, surpassing all reported solid sorbents. The uptake capacity can be further raised to 35.6 mmol g-1 via the replacement of Fe3+ with kinetically more inert Cr3+, resulting in a staggering ∼329-fold volume reduction compared with free ideal SO2 gas. Computational simulations suggest that unique Fe3+···S(SO2) interactions dominate the SO2 seeding process, facilitating the efficient packing of SO2 molecules in the large channels. Besides, the exceptionally low uptake at the low pressure region implies global weak framework-SO2 interactions, which offer great potential for practically implementing an "easy-on/easy-off" SO2 delivery system.

Mn-Fe Dual-Metal Assemblages on Carbon-Coated Al2O3 Spheres for Catalytic Ozonation Oxidation: Structure, Performance, and Reaction Mechanism.

Catalysts with high catalytic activity and low production cost are important for industrial application of heterogeneous catalytic ozonation (HCO). In this study, we designed a carbon-coated aluminum oxide carrier (C-Al2O3) and reinforced it with Mn-Fe bimetal assemblages to prepare a high-performance catalyst Mn-Fe/C-Al2O3. The results showed that the carbon embedding significantly improved the abundance of surface oxygen functional groups, conductivity, and adsorption capacity of γ-Al2O3, while preserving its exceptional mechanical strength as a carrier. The prepared Mn-Fe/C-Al2O3 catalyst exhibited satisfactory catalytic ozonation activity and stability in the degradation of p-nitrophenol (PNP). Electron paramagnetic resonance (EPR) and quenching experiments reveal that radical ( ⋅ OH and ⋅ O2 ⋅ ) and nonradical oxidation (1O2) dominated the PNP degradation process. Theoretical calculations corroborated that the anchored atomic Fe and Mn sites regulated the local electronic structure of the catalyst. This modulation effectively promoted the activation of O3 molecules, resulting in the generation of atomic oxygen species (AOS) and reactive oxygen species (ROS). The economic analysis on Mn-Fe/C-Al2O3 revealed that it was a cost-competitive catalyst for HCO. This study not only deepens the understanding on the reaction mechanism of HCO with transition metal/carbon composite catalysts, also provides a high-performance and cost-competitive ozone catalyst for prospective application.

Gas Phase Reactions of Pristine and Single-Atom-Doped Copper and Silver Clusters: Probing Size-Dependent Stability and Novel Superatoms.

Gas phase reactions have been a subject of research interest, enabling reliable strategies to explore the stability and reactivity of metal clusters as well as to probe novel superatoms that form the building blocks to assemble new materials with tailored properties. Coinage metal clusters have attracted great research attention due to their simple electronic shell structures and rich photochemical and catalytic properties at relatively low cost. This perspective focuses on the recent progress made in studying the gas phase reactions of undamaged and single-atom-doped Cun±,0 and Agn±,0 clusters with O2, CO, and NO molecules. It covers various aspects, such as reaction mechanisms, relationships between structure and activity, control of reactivity by changing cluster size and composition, and the identification of novel superatoms (Cu18-, Ag13-, Ag17-, and Ag15O+). Lastly, we provide a detailed account of the obstacles and prospective avenues for future research in order to establish a connection between these findings and nanocluster systems that have practical applications.

Achieving Sub-ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework.

We report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine-functionalized COF (SonoCOF-9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g-1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g-1 with excellent reversibility for at least 50 adsorption-desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled -42.3 kJ mol-1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller-Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF-9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub-ppm level (0.0064 ppm of SO2).

Achieving Sub‐ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework

AbstractWe report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine‐functionalized COF (SonoCOF‐9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g−1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g−1 with excellent reversibility for at least 50 adsorption‐desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled −42.3 kJ mol−1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller–Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF‐9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub‐ppm level (0.0064 ppm of SO2).

Atomistic insight into the interfacial reaction and evolution between FeCr alloys and supercritical CO2 with impurities

The supercritical CO2 cycle offers high thermal efficiency and flexibility, enhancing energy conversion efficiency and utilization. As the commercialization of supercritical CO2 cycles advances, the stability of the metal-CO2 interface is the key to ensure the safety of this power cycle. In this paper the interfacial reactions between FeCr alloys and CO2 with impurities were investigated using the oxidation thermodynamics and molecular dynamics. With the increase of Cr content in FeCr alloy, the adsorption stability of SO2 and CO2 molecules on the surface of FeCr alloy became stronger, in which CO2 molecules were adsorbed and decomposed in two ways. When the C-O bond was broken, the detached O atom was in a free state or reorganized into O2 molecule, while the CO molecule would be separated from the CO2 molecule. In the initial oxidation stage, adding appropriate amount of H2S in CO2 environment could reduce the diffusion of O atoms from the CO2 molecule to Fe20Cr alloy, and the stress in the oxide film would not increase. The early oxidation behavior of Fe20Cr alloy in CO2 with H2S impurity gas may prove to be an effective method for enhancing its oxidation resistance of Fe20Cr alloy.

Reaction mechanism of pyridine radicals with molecular oxygen: A theoretical study

Pyridine is a suitable surrogate of the fuel-nitrogen in flame studies. The goal of the present work was to extend the analysis of reactions of pyridyl radicals with O2. All reactions proceed following similar mechanisms, through the barrier-free addition of an O2 molecule and further development along two main paths: through barrier-free abstraction of an oxygen atom and through the formation of a seven-membered ring. The energies of the main intermediates of all three reactions, calculated relative to the pyridyl + O2 system, have similar values. All three reactions are characterized by the formation of 1λ2-pyrrole, as well as HCO, HCN, C2H2 and CO.

Spin-Polarized PdCu-Fe3O4 In-Plane Heterostructures with Tandem Catalytic Mechanism for Oxygen Reduction Catalysis.

Alloying has significantly upgraded the oxygen reduction reaction (ORR) of Pd-based catalysts through regulating the thermodynamics of oxygenated intermediates. However, the unsatisfactory activation ability of Pd-based alloys toward O2 molecules limits further improvement of ORR kinetics. Herein, the precise synthesis of nanosheet assemblies of spin-polarized PdCu-Fe3O4 in-plane heterostructures for drastically activating O2 molecules and boosting ORR kinetics is reported. It is demonstrated that the deliberate-engineered in-plane heterostructures not only tailor the d-band center of Pd sites with weakened adsorption of oxygenated intermediates but also endow electrophilic Fe sites with strong ability to activate O2 molecules, which make PdCu-Fe3O4 in-plane heterostructures exhibit the highest ORR specific activity among the state-of-art Pd-based catalysts so far. In situ electrochemical spectroscopy and theoretical investigations reveal a tandem catalytic mechanism on PdCu-Fe3O4─Fe sites that initially activate molecular O2 and generate oxygenated intermediates being transferred to Pd sites to finish the subsequent proton-coupled electron transfer steps.