Reaction Of Oxygen Atoms Research Articles

Oxidative Capacity and Radical Chemistry in a Semi-arid and Petrochemical-industrialized City, Northwest China

Heavy ozone (O-3) pollution is often observed in chemically industrialized Lanzhou and other capital cities located in the semi-arid and mountainous provinces of northwestern China. There are large knowledge gaps regarding the relationship between radical budgets and photochemistry in these cities. To gain insights into this relationship, a photochemical box model based on the Master Chemical Mechanism (MCM v3.3) was applied to investigate oxidative capacity and radical chemistry in the city of Lanzhou. The budgets of ROx (OH + HO2 + RO2) radicals were quantified, and the initiation, propagation, and termination process of the diurnal variation in the ozone chemistry were examined. The MCM model was constrained by in situ measurements at two sampling sites in the city, one located in the City downtown area (S1) and the other in the heavy petrochemical industrial area (S2) in the western suburb of the City, characterized by significant differences in volatile organic compounds (VOCs) and NOx concentrations between the two sites. Results showed that during the high O-3 episodes in summer, OH initiation was dominated by the reaction of excited oxygen atoms O(D-1) with water and the photolysis of nitrous acid (HONO) at the S1 site. At the S2 site, the most important production of OH was the reaction of O(D-1) + H2O, followed by the reaction of O-3 with VOCs. HONO photolysis was mostly identified at 7:00-13:00 local time at the S2 site, which is less important than that at the S1 site during the daytime. The photolysis of HCHO and OVOCs (except for HCHO) were the primary sources contributing to the initiation of HO2 and RO2 radicals at both sites. Results also revealed that the ROx termination could be attributed to the reactions of ROx with NO and NO2. The self-reactions between radicals also played an essential role at the S2 site. Overall OH was found to be the predominant oxidant, and NO3 was a major oxidant in the nighttime chemistry in the city.

Chemical kinetics in an atmospheric pressure helium plasma containing humidity.

Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H2O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 × 1014 cm-3 for OH and 3 × 1013 cm-3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH+ by proton transfer to H2O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H2O+ by proton transfer to H2O and by electron impact dissociation of H2O. It is lost by reactions with other OH molecules to form either H2O + O or H2O2. Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications.

Extremely flat metal films implemented by surface roughness transfer for flexible electronics.

We present an innovative approach to fabricate an extremely flat (EF) metal film which was done by depositing metal on an extremely flat mother substrate, then detaching the metal from the substrate. The detached flexible metal films had a roughness that was within 2% of the roughness of the mother substrate, so EFs with Ra < 1 nm could be fabricated using the surface roughness transfer method. With quantitative analysis using in situ synchrotron XPS, it was concluded that the chemical reaction of oxygen atoms with the metal film played a critical role in designing a peel-off system to get extremely flat metal films from the mother substrate. The OLED was successfully implemented on the metal film. The OLED's luminance could be increased from 15 142 to 17 100 cd m−2 at 25 mA m−2 by replacing the glass substrate with an EF copper (Cu) substrate, due to the enhanced heat dissipation during the operation. This novel method can be very useful for mass production of large scale, low-cost and high quality metal films using roll-to-roll process.

Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma

Radio-frequency driven atmospheric pressure plasmas are efficient sources for the production of reactive species at ambient pressure and close to room temperature. Pulsing the radio-frequency power input provides additional control over species production and gas temperature. Here, we demonstrate the controlled production of highly reactive atomic oxygen and nitrogen in a pulsed radio-frequency ( MHz) atmospheric-pressure plasma, operated with a small % air-like admixture (/ at ) through variations in the duty cycle. Absolute densities of atomic oxygen and nitrogen are determined through vacuum-ultraviolet absorption spectroscopy using the DESIRS beamline at the SOLEIL synchrotron coupled with a high resolution Fourier-transform spectrometer. The neutral-gas temperature is measured using nitrogen molecular optical emission spectroscopy. For a fixed applied-voltage amplitude (234 V), varying the pulse duty cycle from 10% to 100% at a fixed 10 kHz pulse frequency enables us to regulate the densities of atomic oxygen and nitrogen over the ranges of – and – , respectively. The corresponding 11 K increase in the neutral-gas temperature with increased duty cycle, up to a maximum of K, is relatively small. This additional degree of control, achieved through regulation of the pulse duty cycle and time-averaged power, could be of particular interest for prospective biomedical applications.

Oxygen defects formation and optical identification in monolayer borophene

Surface reactions with oxygen are a fundamental cause of the degradation of borophene, which has greatly limited the application in nanoelectronic and optoelectronic devices. Density functional theory calculations disclose that there is an energy release of about 3 eV for each oxygen atom adsorbed onto borophene. The hybridization between pz orbitals of oxygen and p orbitals of neighboring B atoms lead to minor distortions of the lattice and low energy metastable forms, finally to form different oxygen defects. The mechanism for oxidation involving reactive dangling oxygen atoms is proposed, and absorption spectra are suggested to identify the types of oxygen defects in borophene.

Kinetic Studies on the Reactions of Atomic Oxygen with Furan, 2-Methylfuran, and 2,5-Dimethylfuran at Elevated Temperatures

Abstract The reactions of O(3P) atoms with furan, 2-methylfuran (2-MF), and 2,5-dimethylfuran (2,5-DMF) were studied at elevated temperatures by using a shock tube technique coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients (k) determined from the time profiles of O(3P) atoms were expressed by the relation of kO+2,5-DMF &amp;gt; kO+2-MF &amp;gt; kO+FURAN. The molecular orbital calculations with CBS-QB3 level were also performed and the possible product channels of these reactions were discussed.

Iodine(III)-Catalyzed Formal [2 + 2 + 1] Cycloaddition Reaction for Metal-Free Construction of Oxazoles.

The iodine(III) catalyst, in situ generated from iodoarene as a precatalyst with m-CPBA and Tf2NH, promoted the metal-free [2 + 2 + 1] cycloaddition-type reactions of alkynes, nitriles, and oxygen atoms for the regioselective formations of 2,4-disubstituted and 2,4,5-trisubstituted oxazole. A first example of iodine catalysis for multicomponent reactions is represented.

Evaluation of the probability of reaction of fast oxygen atoms with polymers and graphite

On the basis of analysis of published data on the reaction efficiency of various polymer materials and graphite in their interaction with fast oxygen atoms (energy of about 4.5 eV) as obtained in flight tests of materials in low-Earth orbits of the International Space Station and ground tests, probability P r of chemical oxidation reactions accompanied by ablation has been evaluated. Estimates have been made for 33 polymers consisting of carbon, hydrogen, oxygen, and nitrogen and graphite for two extreme cases when the carboncontaining oxidation products are either CO or CO2 alone. The average probability values found are P r(CO)(av) = 0.184 and P r(CO2)(av) = 0.317. The probability values range from P r(CO) = 0.604 and P r(CO2) = 0.963 for allyl diglycol carbonate to P r(CO) = 0.038 and P r(CO2) = 0.075 for pyrolytic graphite.

Reaction of O(3P) with C3H6: Yield of the Reaction Products as a Function of Temperature.

Reaction of oxygen atoms with propene is an important step in combustion processes particularly affecting the profiles of intermediate species and flame speed. The relative importance of different pathways of this multichannel reaction at different temperatures represents significant theoretical interest and is essential for modeling combustion systems. In the present work, we report the first experimental investigation of the products of the O(3P) + C3H6 reaction over an extended temperature range (298-905 K). By using a low pressure flow reactor combined with a quadrupole mass spectrometer, the yields of the five reaction products, H atom, CH3, C2H5, CH2O and OH were determined as a function of temperature between 298 and 905 K: 0.0064 × (T/298)2.74 exp(765/T), 1.41 × (T/298)-1.0 exp(-335/T), 0.92 × (T/298)-1.41 exp(-381/T), 0.17 × (T/298)0.165 exp(-36/T), and 0.0034 × (T/298)2.34 exp(788/T), respectively (corresponding to the variation of the respective yields between 298 and 905 K in the ranges 0.08-0.31, 0.46-0.32, 0.26-0.12, 0.15-0.19, and 0.05-011), independent of pressure in the range 1-8 Torr of helium. For the yields of the minor reaction products, H2 and CH3CHO the upper limits were determined as 0.2 and 0.05, respectively. These results are compared with the experimental data and theoretical calculations available in the literature.

Computational Kinetics by Variational Transition-State Theory with Semiclassical Multidimensional Tunneling: Direct Dynamics Rate Constants for the Abstraction of H from CH3OH by Triplet Oxygen Atoms.

Rate constants and the product branching ratio for hydrogen abstraction from CH3OH by O(3P) were computed with multistructural variational transition-state theory including microcanonically optimized multidimensional tunneling. Benchmark calculations of the forward and reverse classical barrier heights and the reaction energetics have been carried out by using coupled cluster theory and multireference calculations to select the most reliable density functional method for direct dynamics computations of the rate constants. The dynamics calculations included the anharmonicity of the zero-point energies and partition functions, with specific-reaction-parameter scaling factors for reactants and transition states, and multistructural torsional anharmonicity was included for the torsion around the C-O bond in methanol and in the transition states. The resulting rate constants are presented over a wider range than they are available from experiment, but in the temperature range where experiments are available, they agree well with experimental values, which is encouraging for their reliability over the wider temperature range and for future computations of oxygen atom reaction rates. In contrast to a previous computational prediction, the branching ratio predicted by the present work shows that the formation of CH2OH + OH is the dominant channel over the whole range of temperature from 250 to 2000 K.

Preparation of high-content hexagonal boron nitride composite film and characterization of atomic oxygen erosion resistance

Space aircrafts circling in low earth orbit are suffered from highly reactive atomic oxygen (AO). To shield AO, a flexible thin film with 80wt.% hexagonal boron nitride (h-BN) and h-BN/epoxy film were fabricated through vacuum filtration and adding nanofibrillated cellulose fibers. H-BN nanosheets were hydroxylated for enhancing interaction in the films. Mass loss and erosion yield at accumulated AO fluence about 3.04×1020 atoms/cm2 were adopted to evaluate the AO resistance properties of the films. A carpet-like rough surface, chemical oxidations and change in crystal structure of h-BN were found after AO treatment, and the degrading mechanism was proposed. The mass loss and erosion yield under AO attack were compared between h-BN film and h-BN/epoxy film, and the comparison was also done for various types of shielding AO materials. Excellent AO resistance property of h-BN film is shown, and the reasons are analyzed.

A novel approach to the assessment of aerospace coatings degradation: The HyperTest

Protecting an aircraft from the extremes of environments during service begins at the interface between topcoat and environment. The topcoat considered here is an aliphatic polyurethane (PU) based matte coating. This paper examines the degradation of the PU topcoat through the use of a novel HyperTest which combines ultra-violet (UV) and ozone as the degradation method. To benchmark the technique against accepted accelerated testing methods, QUV was used and samples were tested between two and 56 days. For The HyperTest, samples were degraded at increments between one to 120 minutes. X-ray photoelectron spectroscopy (XPS) determined that 56 days of UV exposure was equivalent, in terms of the extent of the chemical degradation of the topcoat, to one to two minutes of UV/ozone (UV/O3) exposure. There was a significant increase in carbonyl component with increasing oxygen concentration for samples treated with The HyperTest, whereas no clear degradation trend was observed for the samples exposed to UV alone. After 60 minutes of UV/O3 exposure a steady-state mechanism is established as the oxidative decomposition of the PU coating. The proposed degradation mechanism of the PU topcoat, through UV/O3 exposure, is the reaction of atomic oxygen with the polymer matrix/binder through hydrogen abstraction producing a hydroxyl group. This further decomposes to produce a carbonyl component observed in the XPS analysis. The products of degradation are simple volatile molecules such as CO2 and H2O for both testing methods used here. However, the efficient nature of The HyperTest, requiring only minutes to degrade samples as shown here, proves it to be a viable complementary technique to established methods of laboratory accelerated testing.

Non-thermal production and escape of OH from the upper atmosphere of Mars

We present a theoretical analysis of formation and kinetics of hot OH molecules in the upper atmosphere of Mars produced in reactions of thermal molecular hydrogen and energetic oxygen atoms. Two major sources of energetic O considered are the photochemical production, via dissociative recombination of O2+ ions, and energizing collisions with fast atoms produced by the precipitating Solar Wind (SW) ions, mostly H+ and He2+, and energetic neutral atoms (ENAs) originating in the charge-exchange collisions between the SW ions and atmospheric gases. Energizing collisions of O with atmospheric secondary hot atoms, induced by precipitating SW ions and ENAs, are also included in our consideration. The non-thermal reaction O + H2(v, j) → H + OH(v′, j′) is described using recent quantum-mechanical state-to-state cross sections, which allow us to predict non-equilibrium distributions of excited rotational and vibrational states (v′, j′) of OH and expected emission spectra. A fraction of produced translationally hot OH is sufficiently energetic to overcome Mars’ gravitational potential and escape into space, contributing to the hot corona. We estimate its total escape flux from the dayside of Mars for low solar activity conditions at about 1.1 × 1023 s−1, or about 0.1% of the total escape rate of atomic O and H. The described non-thermal OH production mechanism is general and expected to contribute to the evolution of atmospheres of the planets, satellites, and exoplanets with similar atmospheric compositions.

Reaction of O(3P) with C2H4: Yield of the Reaction Products as a Function of Temperature.

Reaction of oxygen atoms with ethylene is an important step in the combustion process particularly affecting the profiles of intermediate species and flame speed. Currently, the relative importance of different pathways of this multichannel reaction at different temperatures is not fully established and determination of the branching ratios for different reaction channels as a function of temperature remains essential for modeling combustion systems. In the present work, the products of the O(3P) + C2H4 reaction have been studied over an extended temperature range (297-900 K) using a low pressure flow reactor (1-8 Torr) combined with a quadrupole mass spectrometer. The yields of the three main reaction products, H atom, CH3 radical, and CH2O, were determined to be 0.31 ± 0.05, 0.53 ± 0.09, and 0.17 ± 0.03, respectively, independent of pressure and temperature under experimental conditions of the study. For the yields of the minor reaction products, H2 and CH4, the upper limits were determined as 0.05 and 0.02, respectively. These results are compared with the experimental data and theoretical calculations available in the literature.

Experimental investigation on oxidation kinetics of germanium by ozone

Oxidation kinetics of germanium surface by ozone at low temperature (≤400°C) is experimentally investigated. The growth process contains two regions: initial linear growth region and following parabolic growth region. The GeOx thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. The linear growth region contains reaction of oxygen atoms with surface bond and back bonds of outmost Ge layer. And the activation energy is experimentally estimated to be 0.06eV. Such small activation energy indicates that the linear growth region is nearly barrier-less. The parabolic growth region starts when the oxygen atoms diffuse into back bonds of second outmost Ge layers. And the activation energy for this process is found to be 0.54eV. Furthermore, in the ozone oxidation it is not O3 molecules but O radicals that go through the GeOx film.

Ozonation in water treatment: the generation, basic properties of ozone and its practical application

AbstractThe widespread applications of ozone technologies are established on the basis of large-scale manufacture of ozone generator and chemical reactivity of ozone. It is hence necessary to summarize the principles of ozone generation and to analyze the physicochemical properties of ozone, which are of fundamental significance to indicate its technical developments and practical applications. This review presents a summary concerning ozone generation mechanisms, the physicochemical properties of ozone, as well as the applications of ozone in water treatment. Ozone can be produced by phosphorus contact, silent discharge, photochemical reactions, and electrochemical reactions, principally proceeding by the reaction of oxygen atom with oxygen molecule. There are side reactions to the generation of ozone, however, which are responsible for ozone depletion including thermal decomposition and quenching reactions by reactive species. The solubility of ozone in water is much higher than that of oxygen, suggesting that it may be reliably applied in water and wastewater treatment. Based on the resonance structures of ozone, one oxygen atom in ozone molecule is electron-deficient displaying electrophilic property, whereas one oxygen atom is electron-rich holding nucleophilic property. The superior chemical reactivity of ozone can also be indirectly revealed by radical-mediated reactions initiated from homogenous and heterogeneous catalytic decomposition of ozone. Owing to the reliable generation of ozone and its robust reactive properties, it is worthy to thoroughly elaborate the applications of ozone reaction in drinking water disinfection and pre- or post-treatment of industrial wastewater including cyanide wastewater, coking wastewater, dyeing wastewater, and municipal wastewater. The structural characteristics of ozone reactors and energy requirement of applied technologies are evaluated. In addition, future directions concerning the development of ozone generation, ozone reactivity, and industrial wastewater ozonation have been proposed.

Theoretical kinetics of O + C2H4

The reaction of atomic oxygen with ethylene is a fundamental oxidation step in combustion and is prototypical of reactions in which oxygen adds to double bonds. For 3O+C2H4 and for this class of reactions generally, decomposition of the initial adduct via spin-allowed reaction channels on the triplet surface competes with intersystem crossing (ISC) and a set of spin-forbidden reaction channels on the ground-state singlet surface. The two surfaces share some bimolecular products but feature different intermediates, pathways, and transition states. The overall product branching is therefore a sensitive function of the ISC rate. The 3O+C2H4 reaction has been extensively studied, but previous experimental work has not provided detailed branching information at elevated temperatures, while previous theoretical studies have employed empirical treatments of ISC. Here we predict the kinetics of 3O+C2H4 using an ab initio transition state theory based master equation (AITSTME) approach that includes an a priori description of ISC. Specifically, the ISC rate is calculated using Landau–Zener statistical theory, consideration of the four lowest-energy electronic states, and a direct classical trajectory study of the product branching immediately after ISC. The present theoretical results are largely in good agreement with existing low-temperature experimental kinetics and molecular beam studies. Good agreement is also found with past theoretical work, with the notable exception of the predicted product branching at elevated temperatures. Above ∼1000K, we predict CH2CHO+H and CH2+CH2O as the major products, which differs from the room temperature preference for CH3+HCO (which is assumed to remain at higher temperatures in some models) and from the prediction of a previous detailed master equation study.

Consecutive H2 Oxidation Mediated by Au2VO4+ Clusters

Laser-ablation generated gold–vanadium oxide cluster cations Au2VOx+ (x = 3, 4) were mass-selected by a quadrupole mass filter and interacted with H2 in an ion trap reactor. The reactions were characterized by mass spectrometry and density functional theory calculations. The Au2VO4+ cluster can oxidize two H2 molecules consecutively to produce Au2VO3+ and then Au2VO2+, the latter of which can react with one O2 molecule to regenerate Au2VO4+. Therefore, a catalytic cycle for H2 oxidation by O2 mediated with the Au2VO2+ clusters can be proposed. The theoretical studies predict that the gold atoms in both Au2VO4+ and Au2VO3+ are the active adsorption sites and facilitate the heterolytic cleavage of H2 in collaboration with the separate O2– ions of the vanadium oxide support. The consecutively oxidative reactivity of Au2VO4+ is attributed to the activation and dissociation of the superoxide or peroxide species (O2•– or O22–) into two reactive atomic oxygen species (O2–) with the promotional effect of gold ato...

Effects of irradiation distance on supply of reactive oxygen species to the bottom of a Petri dish filled with liquid by an atmospheric O2/He plasma jet

The impact of irradiation distances on plasma jet-induced specific effects on the supply of reactive oxygen species (ROS) to the bottom of a Petri dish filled with liquid was investigated using a KI-starch gel reagent that can be employed as a ROS indicator even in water. O3 exposure experiments without plasma irradiation were also performed to elucidate the specific effects of the plasma jet. Relative concentrations of ROS transported to the bottom were evaluated using absorbance measurements. The results indicated that ROS supply to the bottom is markedly enhanced by the plasma jet irradiation at shorter irradiation distances, whereas similar results could not be obtained for the O3 exposure. In these cases, the liquid mixing in the depth direction was also enhanced by the plasma jet irradiation only, and the supply of reactive atomic oxygen to the liquid surface was markedly increased as well.

Influence of oxygen plasma pre-treatment on the water repellency of cotton fibers coated with perfluoroalkyl-functionalized polysilsesquioxane

Oxygen plasma pre-treatment was applied to cotton fabric with the aim of improving the water repellency performance of an inorganic-organic hybrid sol-gel perfluoroalkyl-functionalized polysilsesquioxane coating. Cotton fabric was pre-treated with low-pressure oxygen plasma for different treatment times and operating powers. Afterward, 1H,1H,2H,2H-perfluorooctyltriethoxysilane (SiF) was applied to the cotton fabric samples using the pad-dry-cure method. The surfaces of the untreated and modified cotton fibers were characterised using Fourier transform infrared spectroscopy, Xray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The water repellency of the SiF-coated fabric samples was evaluated using static and sliding contact angle measurements with water. The results show that the plasma treatment with the shortest treatment time (10 s) and the lowest operating current (0.3 A) increased the atomic oxygen/carbon ratio of the cotton fiber surface from 0.6 to 0.8 and induced the formation of a nano-sized grainy surface. Increasing the plasma treatment time and/or operating current did not intensify the surface changes of the cotton fibers. Such saturation effects were explained by the large influence of reactive oxygen atoms during the plasma treatment. The measured static water contact angles on the surface of the untreated and plasma pre-treated and SiF-coated cotton fabrics showed that the oxygen plasma pre-treatment enabled the increase of the water contact angle from 135° to ≈150°, regardless of the applied plasma treatment time and discharge power. This improvement in the hydrophobicity of the SiF coating was followed by a decrease in the sliding angle of water droplets by more than 10° compared to the plasma untreated and SiF-coated sample characterized by a water sliding angle of 45°. Additionally, measurements of the water sliding angle revealed that the increase of the static contact angle from 149° to 150° corresponded to a drop of the water sliding angle from 33 to 24°, which suggests that the plasma pre-treatment of 20 s at an operating current of 0.3 A produced the best water-repellent performance of the SiF-coated cotton fabric.