H2O Reaction Research Articles

A-InGaZnO Thin-Film Transistors With Novel Atomic Layer-Deposited HfO2 Gate Insulator Using Two Types of Reactant Gases

Plasma-enhanced chemical vapor deposition is often utilized to fabricate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) with mobility of approximately 7 cm2/( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula> ) using a SiOx gate insulator. For use in high-resolution organic light-emitting diode displays, this value must be markedly improved. Therefore, we used various reactants to create a HfO2 bilayer via atomic layer deposition (ALD) and examined the electrical properties of IGZO TFTs, such as their mobility and subthreshold swing (SS). By adjusting the thickness of HfO2 with H2O reactant gas, the amount of hydrogen that diffused into the IGZO channel was controlled. The IGZO TFT with a specific HfO2 bilayer gate insulator exhibited high saturation mobility of 16.75 cm2/( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula> ) and an improved SS of 159 mV/dec compared to a conventional device with a HfO2 gate insulator formed using only O3 reactant gas. Furthermore, the fabricated HfO2 bilayer devices presented excellent reliability under positive bias stress and were more robust against the short-channel effect. Thus, based on the findings of this study, to improve the electrical properties of a-IGZO TFTs, the ALD process is suggested to be used to deposit a high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> gate insulator.

Heterogeneous and Combined Heterogeneous/Homogeneous Combustion Modeling of SOFC Off-Gases.

The heterogeneous (catalytic) and the hetero-/homogeneous (catalytic and gas-phase) combustion processes of solid oxide fuel cell (SOFC) off-gases with compositions typical of a high cell utilization rate are investigated with high-fidelity 2D simulations in a platinum-coated planar channel using detailed hetero-/homogeneous chemistry. The pressures are 1-8 bar; the reactant streams have volumetric H2 and CO contents 0.7-1.5 and 5.3-9.7%, respectively; H2O and CO2 dilutions are ∼40 and ∼50%, respectively; and the global fuel/air equivalence ratio is 0.90. Water inhibits chemically the catalytic oxidation of H2, as it leads to high H(s) surface coverage that favors the recombinative desorption of H(s) to H2. On the other hand, H2O promotes chemically the catalytic oxidation of CO by creating high OH(s) coverage that in turn accelerates the CO consumption. Strong flames are established at the highest H2 content cases and for pressures p ≥ 3 bar. For all cases with vigorous homogeneous combustion, the catalytic and gas-phase reaction pathways coexist and compete with each other for the consumption of H2 and CO. The large H2O content leads to gas-phase production of H2 via the reaction H2O + H = H2 + OH. However, the gas-phase produced H2 is subsequently consumed by the catalytic pathway, such that nearly complete H2 conversion is attained at the reactor outlet. Gaseous chemistry does not affect the reactor lengths required for complete H2 conversion but substantially reduces the corresponding lengths for CO conversion. The H2 emissions decrease with increasing pressure and are in the range 8-110 ppmv, while the CO emissions increase with rising pressure and span the range 0.3-52 ppmv, thus leading to corrected CO emissions (at 15% O2) of less than 15 ppmv. Finally, the peak wall temperatures are largely acceptable in terms of catalyst thermal stability.

Quantification of Key Peroxy and Hydroperoxide Intermediates in the Low-Temperature Oxidation of Dimethyl Ether

Dimethyl ether (DME) oxidation is a model chemical system with a small number of prototypical reaction intermediates that also has practical importance for low-carbon transportation. Although it has been studied experimentally and theoretically, ambiguity remains in the relative importance of competing DME oxidation pathways in the low-temperature autoignition regime. To focus on the primary reactions in DME autoignition, we measured the time-resolved concentration of five intermediates, CH3OCH2OO (ROO), OOCH2OCH2OOH (OOQOOH), HOOCH2OCHO (hydroperoxymethyl formate, HPMF), CH2O, and CH3OCHO (methyl formate, MF), from photolytically initiated experiments. We performed these studies at P = 10 bar and T = 450-575 K, using a high-pressure photolysis reactor coupled to a time-of-flight mass spectrometer with tunable vacuum-ultraviolet synchrotron ionization at the Advanced Light Source. Our measurements reveal that the timescale of ROO decay and product formation is much shorter than predicted by current DME combustion models. The models also strongly underpredict the observed yields of CH2O and MF and do not capture the temperature dependence of OOQOOH and HPMF yields. Adding the ROO + OH → RO + HO2 reaction to the chemical mechanism (with a rate coefficient approximated from similar reactions) improves the prediction of MF. Increasing the rate coefficients of ROO ↔ QOOH and QOOH + O2 ↔ OOQOOH reactions brings the model predictions closer to experimental observations for OOQOOH and HPMF, while increasing the rate coefficient for the QOOH → 2CH2O + OH reaction is needed to improve the predictions of formaldehyde. To aid future quantification of DME oxidation intermediates by photoionization mass spectrometry, we report experimentally determined ionization cross-sections for ROO, OOQOOH, and HPMF.

High-Pressure Laminar Flame Speeds and Markstein Lengths of Syngas Flames Diluted in Carbon Dioxide and Helium

Abstract New laminar flame speed and burned-gas Markstein length data for H2–CO–O2–CO2–He mixtures have been measured from spherically expanding flames. Experiments were conducted at 10 atm and room temperature for H2:CO ratios ranging from 2:1 to 1:4 and for overall CO2 mole fractions from 0% to 30%. CO2 dilution had little effect on Markstein length, but CO2 dilutions of 10%, 20%, and 30% caused average reductions in flame speed of 47%, 73%, and 89%, respectively, regardless of H2:CO ratio. The study was designed to isolate the dilution effect of CO2 on flame speed, and a detailed analysis using the FCO2 method was used to show that the chemical-kinetic participation of CO2 was responsible for up to 20% of the reduction in flame speed. Hence, the majority (80% or more) of the reduction in flame speed due to CO2 is from the thermal effect. Accurate flame speed predictions were produced by five different chemical kinetics mechanisms for most conditions, with the slight exception of high-CO, high-CO2 mixtures. A thorough sensitivity analysis highlighted the larger effect of CO2 dilution on the important kinetics reactions than the effect of changing H2:CO. Sensitivity analysis also showed that the chain branching reaction H2O + O ⇌ OH + OH could be modified (albeit beyond its uncertainty) to achieve more accurate flame speed predictions, but also indicated that further improvement of flame speed modeling would require changes to many lesser reactions.

Syntheses of Group 5 Amide Amidinates and Their Reactions with Water: Different Reactivities of Nb(V) and Ta(V) Complexes.

Chemistries of Nb(V) and Ta(V) compounds are essentially identical as a result of lanthanide contraction. Hydrolysis of M(NMe2)5 (M = Nb, Ta), for example, yields [M(μ3-O)(NMe2)3]4 (M = Nb, 1; Ta, 2) reported earlier. The similar reactivities of Nb(V) and Ta(V) compounds make it challenging, for example, to separate the two metals from their minerals. We have found that the reactions of H2O with amide amidinates M(NMe2)4[MeC(NiPr)2] (M = Nb, 3; Ta, 4) show that the niobium and tantalum analogues take different principal paths. For the Nb(V) complex 3, the amidinate and one amide ligand are liberated upon treatment with water, yielding [Nb(μ3-O)(NMe2)3]4 (1). For the Ta(V) complex 4, the amide ligands are released in the reaction with H2O, leaving the amidinate ligand intact. [Ta(μ3-O)(NMe2)3]4 (2), the analogue of 1, was not observed as a product in the reaction of 4 with H2O. To our knowledge, this is the first example of the formation of two different complexes that maintain the (V) oxidation state in both metals. The new complexes M(NMe2)4[MeC(NiPr)2] (M = Nb, 3; Ta, 4) have been prepared by the aminolysis of M(NMe2)5 (M = Nb, Ta) with iPrN(H)C(Me)=NiPr (5). The hydrolysis of 3 and 4 has been investigated by DFT electronic structure calculations. The first step in each hydrolysis reaction involves the formation of a hydrogen-bonded complex that facilitates a proton transfer to the amidinate ligand in 3 and protonation of an axial dimethylamide ligand in 4. Both proton transfers furnish an intermediate metal-hydroxide species. The atomic charges in 3 and 4 have been computed by Natural Population Analysis (NPA), and these data are discussed relative to which of the ancillary ligands is protonated initially in the hydrolysis sequence. Ligand exchanges in 3 and 4 as well as the exchange in iPrN(H)C(Me)=NiPr (5) were probed by EXSY NMR spectroscopy, giving rate constants of the exchanges: 0.430(13) s-1 (3), 0.033(6) s-1 (4), and 2.23(7) s-1 (5), showing that the rate of the Nb complex Nb(NMe2)4[MeC(NiPr)2] (3) is 13 times faster than that of its Ta analogue 4.

Molecular dynamic simulation of LiH–H2O reactions using the ReaxFF reactive force field

The hydrogen storage material Lithium hydride (LiH) has received wide attention due to its high hydrogen density. However, the reaction process of LiH with H2O is complex, and the microscopic mechanism has not been reported. This paper reveals the microscopic mechanism by the ReaxFF reaction force field module of the Amsterdam Modeling Suite (AMS). Combined with Gaussian09 software, the rate constants and energy changes are determined in the reaction course. As a result, LiH reacts with H2O preferentially, forming Li--O bonds and shedding H from Li--H, which collides randomly to generate H2 and H2LiO. As the reaction proceeds, there are by-products H4LiO2, HLiO, HLi2O, and H2Li2O generated. The reaction course of H4LiO2 is a spontaneous exothermic reaction, and the strong chemical bonding force of Li to H prompts the formation of HLiO, HLi2O, and H2Li2O. 100% of H2 comes from the H removed by LiH. Thus, LiH being fully involved in the reaction, the number of H2 produced remains the same.

One-step hydrothermal synthesis of hierarchically structured MoS2 nanorods via reaction intermediates as self-templates for chemoselective hydrogenation

Two-dimensional (2D) materials have unique planar structures and ultrathin thicknesses, but are prone to restacking and agglomerate due to the high surface energy. Building hierarchical structures is one of the effective ways to exploit their inherent properties and unique structural advantages. We unexpectedly found that the introduction of saturated NaCl solution to the hydrothermal synthesis of MoS2 could significantly change its structure, resulting in the hierarchically structured nanosheet-assembled MoS2 nanorods (R-MoS2) with intercalated alkali ions. The formation process and synthesis mechanism of R-MoS2 via NaNH4Mo3O10·H2O reaction intermediate are systematically revealed by morphology and spectroscopy. Benefiting from this interesting hierarchical structure, the catalytic conversion of R-MoS2 for p-chloronitrobenzene hydrogenation is significantly improved. Density functional theory calculation also demonstrates the intercalation of Na in MoS2 can downshift the d-band center of Mo and favors the key final desorption process.

Impact of a single water molecule on the atmospheric oxidation of thiophene by hydroperoxyl radical

Water as an important assistant can alter the reactivity of atmospheric species. This project is designed to investigate the impact of a single water molecule on the atmospheric reactions of aromatic compounds that have not been attended to comprehensively. In the first part, the atmospheric oxidation mechanisms of thiophene initiated by hydroperoxyl radical through a multiwell-multichannel potential energy surface were studied to have useful information about the chemistry of the considered reaction. It was verified that for the thiophene plus HO2 reaction, the addition mechanism is dominant the same as other aromatic compounds. Due to the importance of the subject and the presence of water molecules in the atmosphere with a high concentration that we know as relative humidity, and also the lack of insight into the influence of water on the reactions of aromatic compounds with active atmospheric species, herein, the effect of a single water molecule on the addition pathways of the title reaction is evaluated. In another word, this research explores how water can change the occurrence of reactions of aromatic compounds in the atmosphere. For this, the presence of one water molecule is simulated by higher-level calculations (BD(T) method) through the main interactions with the stationary points of the most probable pathways. The results show that the mechanism of the reaction with water is more complicated than the bare reaction due to the formation of the ring-like structures. Also, water molecule decreases the relative energies of all addition pathways. Moreover, atoms in molecule theory (AIM) along with the kinetic study by the transition state (TST) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theories demonstrate that the overall interactions of a path determine how the rate of that path changes. In this regard, our results establish that the interactions of water with HO2 (thiophene) in the initial complex 1WHA (1WTA or 1WTB) are stronger (weaker) than the sum of its interactions in transition states. Also, for the water-assisted pathways, the ratio of the partition function of the transition state to the partition functions of the reactants is similar to the respective bare reaction. Therefore, the reaction rates of the bare pathways are more than the water-assisted paths that include the 1WHA complex and are less than the paths that involve the 1WTA and 1WTB complexes.

Reaction mechanism of atomic layer deposition of zirconium oxide using zirconium precursors bearing amino ligands and water.

As a unique nanofabrication technology, atomic layer deposition (ALD) has been widely used for the preparation of various materials in the fields of microelectronics, energy and catalysis. As a high-κ gate dielectric to replace SiO2, zirconium oxide (ZrO2) has been prepared through the ALD method for microelectronic devices. In this work, through density functional theory calculations, the possible reaction pathways of ZrO2 ALD using tetrakis(dimethylamino)zirconium (TDMAZ) and water as the precursors were explored. The whole ZrO2 ALD reaction could be divided into two sequential reactions, TDMAZ and H2O reactions. In the TDMAZ reaction on the hydroxylated surface, the dimethylamino group of TDMAZ could be directly eliminated by substitution and ligand exchange reactions with the hydroxyl group on the surface to form dimethylamine (HN(CH3)2). In the H2O reaction with the aminated surface, the reaction process is much more complex than the TDMAZ reaction. These reactions mainly include ligand exchange reactions between the dimethylamino group of TDMAZ and H2O and coupling reactions for the formation of the bridged products and the by-product of H2O or HN(CH3)2. These insights into surface reaction mechanism of ZrO2 ALD can provide theoretical guidance for the precursor design and improving ALD preparation of other oxides and zirconium compounds, which are based ALD reaction mechanism.

Formation and consumption of HO2 radicals in ns pulse O2–He plasmas over a liquid water surface

Hydroperoxyl (HO2) radicals are an important precursor in the formation of hydrogen peroxide (H2O2), a key species in plasma-liquid interactions, such that their formation and consumption pathways need to be understood. In this work, the generation and decay of HO2 have been studied in a controlled environment, in ns pulse discharge O2–He plasmas in contact with a liquid water surface. For this, time-resolved, absolute number densities of HO2 in O2–He mixtures excited by a repetitive ns pulse discharge are measured in situ by cavity ring down spectroscopy (CRDS). The discharge cell with external electrodes to generate the plasma and a water reservoir are integrated into the CRDS cavity. The high-reflectivity cavity mirrors are purged with helium to protect them from water vapor condensation. The experimental results are obtained at near room temperature, both during the discharge pulse burst and in the afterglow. The HO2 number density is inferred from the CRDS data using a spectral model exhibiting good agreement with previous measurements of absolute HO2 absorption cross sections. HO2 is generated during the discharge burst and decays in the afterglow between the bursts. The HO2 number density is also measured vs. the O2 fraction in the mixture. Comparison with the kinetic modeling predictions demonstrates good agreement with the data and identifies the dominant HO2 generation and decay processes. HO2 in the plasma is formed predominantly by the recombination of H atoms, generated by the electron impact dissociation of water vapor, with O2 molecules. Reactions with O atoms and hydroxyl (OH) radicals are among the main HO2 decay processes in the afterglow. HO2 is also detected when O2 is not present in the mixture. In this case, it is generated primarily by the recombination of OH radicals, via the formation of H2O2. The results demonstrate that CRDS can also be used for HO2 and other plasma chemical reaction product measurements in atmospheric pressure plasma jets impinging on a liquid water surface in ambient air.

Quantitative Kinetics of HO2 Reactions with Aldehydes in the Atmosphere: High-Order Dynamic Correlation, Anharmonicity, and Falloff Effects Are All Important.

Kinetics provides the fundamental parameters for elucidating sources and sinks of key atmospheric species and for atmospheric modeling more generally. Obtaining quantitative kinetics in the laboratory for the full range of atmospheric temperatures and pressures is quite difficult. Here, we use computational chemistry to obtain quantitative rate constants for the reactions of HO2 with HCHO, CH3CHO, and CF3CHO. First, we calculate the high-pressure-limit rate constants by using a dual-level strategy that combines conventional transition state theory using a high level of electronic structure wave function theory with canonical variational transition state theory including small-curvature tunneling using density functional theory. The wave-function level is beyond-CCSD(T) for HCHO and CCSD(T)-F12a (Level-A) for XCHO (X = CH3, CF3), and the density functional (Level-B) is specifically validated for these reactions. Then, we calculate the pressure-dependent rate constants by using system-specific quantum RRK theory (SS-QRRK) and also by an energy-grained master equation. The two treatments of the pressure dependence agree well. We find that the Level-A//Level-B method gives good agreement with CCSDTQ(P)/CBS. We also find that anharmonicity is an important factor that increases the rate constants of all three reactions. We find that the HO2 + HCHO reaction has a significant dependence on pressure, but the HO2 + CF3CHO reaction is almost independent of pressure. Our findings show that the HO2 + HCHO reaction makes important contribution to the sink for HCHO, and the HO2 + CF3CHO reaction is the dominant sink for CF3CHO in the atmosphere.

Collaborative control of branching ratio in the O + HO2 → OH + O2 reaction via vibrational and rotational excitation

AbstractTo understand the effect of different vibrational and rotational modes of reactant to enhance the reactivity of the O + HO2 → OH + O2 reaction, we revisited this important atmospheric reaction. We report here a quasi‐classical trajectory (QCT) study of the reaction dynamics on a recently developed full‐dimensional potential energy surface (PES). Our previous work has indicated that this reaction has two pathways, the H abstraction (HA) channel and the O abstraction (OA) channel, which lead to totally different product energy distribution. In this work, we identified that the vibrational excitation of the OH stretching (v1) mode of HO2 is the switch of the HA channel at low collision energy; meanwhile, the rotational excitation can also greatly change the branching ratio of the two pathways. With the excitation of v1 mode, the original negligible HA channel controlled by the tight transition state becomes quite important. This work presents an approach to control the branching ratio via collaboration between vibrational and rotational excitation and will enrich the knowledge of the O + HO2 reaction in atmospheric chemistry and physics.

Low-temperature PECVD silicon-nitride passivation for perovskite solar cell

Low temperature PECVD Si-nitride was investigated as passivation layer for Ag electrode of perovskite solar cell, which is highly sensitive to H2O. FTIR analysis verified that, with H2O in aging ambient, hydrolysis and oxidation reaction occurred on Si-nitride films, which weakened and cracked Si-nitride film. Adding O2 in aging ambients, surface Si–N bonds could be passivated by adsorbed O and hydrolysis reaction of Si-nitride could be reduced. It is confirmed by FTIR spectrum of aged Si-nitirde films in O2/N2/H2O ambient. With further increasing O2 partial pressure (over 25% O2) in O2/N2/H2O ambient, surface-adsorbed O diffused into Si-nitride and accumulated at Si-nitride/Ag interface, which built-up pressure and cracking Si-nitride film. Thus, it is concluded that the pressure built-up from O2 accumulation and hydrolysis and oxidation reactions of Si-nitride are key factors for the reliability of Si-nitride passivation films.

HO2 + NO2: Kinetics, Thermochemistry, and Evidence for a Bimolecular Product Channel.

A master equation (ME) analysis of available experimental data has been carried out on the reaction HO2 + NO2 + M ⇋ HO2NO2 + M (1a)/(−1a). The analysis, based on the ME code MESMER, uses both the association and dissociation kinetic data from the literature, and provides improved thermochemistry on reaction 1a. Our preferred model assigns two low-frequency vibrations of HO2NO2 as hindered rotors and couples these to the external rotations. This model gives ΔrH°0(1a) = −93.9 ± 1.0 kJ mol–1, which implies that ΔfH°0 HO2NO2 = −42.0 ± 1.0 kJ mol–1 (uncertainties are 2σ). A significant contributor to the uncertainty derives from modeling the interaction between the internal and external rotors. Using this improved kinetics for reaction 1a/–1a, data at elevated temperatures, 353–423 K, which show no evidence of the expected equilibration, have been reanalyzed, indicating that an additional reaction is occurring that masks the equilibration. Based on a published ab initio study, this additional channel is assigned to the bimolecular reaction HO2 + NO2 → H–NO2 + O2 (1b); H–NO2 is nitryl hydride and has not previously been directly observed in experiments. The output of the master equation analysis has been parametrized and Troe expressions are provided for an improved description of k1a(p,T) and k–1a(p,T).

(Digital Presentation) H2o and CO2 Surface Contamination of the Lithium Garnet Li7La3Zr2O12 Solid Electrolyte

Garnet-type Li7La3Zr2O12 is a promising solid-state electrolyte for lithium (Li)-ion batteries, and it readily reacts with H2O and CO2 when exposed to ambient air. Such reactions form a contamination layer on Li7La3Zr2O12, which is detrimental to the battery operation. Here, using first-principles calculations, we investigate the adsorption and reactions of H2O and CO2 on a Li7La3Zr2O12 surface. We show that H2O reacts through the exchange of protons and Li+ and produces metal hydroxide species. At high H2O coverage, half of the H2O molecules dissociate, while the other half remain intact. CO2 reacts with the Li7La3Zr2O12 surface directly to produce carbonate species. We clarify that the individual reactions of H2O and CO2 with Li7La3Zr2O12 are thermodynamically more favorable than the co-adsorption of H2O and CO2. Finally, we demonstrate that low temperature and high partial pressure promote the reactions of H2O and CO2 with Li7La3Zr2O12. Our study provides guidance on processing conditions for the garnet Li7La3Zr2O12 solid electrolyte to minimize its surface contamination.

(Invited) Electrical, Thermal, and H2o and CO2 Poisoning Behaviors of PrNi0.5Co0.5O3-δ Cathode for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cell

PrNi0.5Co0.5O3-δ (PNC) cathode material demonstrates total electrical conductivity on the order of ~300 S/cm at 400-600oC in air, and the conductivity shows a slight increase as temperature increases with an activation energy (from ln(σT) vs 1/T plot) of 10.9 kJ/mol. The introduction of water vapor (H2O) leads to a small (~0.16%) increase in total resistivity, which is reversible upon water removal and explained, tentatively, by the defect reaction of H2O + 2Oo x + 2h• = 2(OH)O • + 0.5O2. The thermal expansion coefficient (TEC) of PNC is measured to be 17.6×10-6/K by dilatometry and 18.43×10-6/K by in situ XRD up to 800oC. On the other hand, despite bulk chemical stability for both PNC and BZCYYb4411 powders against low percentage H2O and CO2, a PNC cathode symmetrical cell over proton conducting BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolyte shows degradation (or increase) in interfacial resistance upon introduction of 3% moisture or 5% CO2 into simulated air at temperature in the range of 650 to 450oC. In comparison, oxygen ion conducting symmetrical cells with PNC cathode and Ce0.9Gd0.1O2-δ (GDC) electrolyte show no change upon H2O and CO2 introduction. The observed sensitivity of the PNC cathode proton conducting symmetrical cell to H2O and CO2 is attributed to the preferred adsorption of H2O and CO2 molecules onto the BZCYYb4411 proton conducting electrolyte surface than on the PNC cathode, and such an explanation is supported by temperature programmed desorption (TPD) measurements for H2O and CO2 on both PNC and BZCYYb4411 powders.

Hydrogen Absorption in Near Surface of Lithium-ion Conductive Glass Ceramics by Water Uptake at Room Temperature

The hydrogen isotope (H and D) concentrations in the two types of Li1+xAlxTi1−x/2Ge1−x/2P3−yO12 and Li1+x+yAlxTi2−xSiyP3−yO12 (LATP: AG-01 and SP-01, respectively) electrolytes, soaked in D2O for 19—22 days and subsequently exposed to air at room temperature and humidity of 80% for 11—21 days, were measured by combining elastic recoil detection with Rutherford backscattering spectrometry. The total numbers of H and D atoms in AG-01 and SP-01 were estimated to be approximately 5.0 and 0.66 atoms, respectively, after the absorption of H2O and D2O and the replacement of H by D. Field emission scanning electron microscopy and atomic force microscopy images revealed that many black substance formations with dimensions of approximately 0.5 × 3.0 μm2 in area and less than approximately 200 nm in thickness appeared on the surface of the D2O-soaked and air-exposed AG-01. These formations appeared because of the segregation of Li from the bulk to the surface by the reactions of H2O and D2O with the doped Ge, which might lead to H and D trapping at the Li substitutional sites.

Inefficient intramolecular vibrational energy redistribution for the H + HO2 reaction and negative internal energy dependence for its rate constant

Quasiclassical trajectories (QCT) and newly constructed global potential energy surfaces are used to compute thermal and nonthermal rate constants for the H + HO2 reaction. The thermal QCTs rate constants are up to 50% smaller than transition state theory (TST) rate constants based on the same level of electronic structure theory. This reduction is demonstrated to result from inefficient intramolecular vibrational energy redistribution (IVR) in the transient H2O2 well, with a significant fraction of trajectories that reach the H2O2 well promptly dissociating back to reactants instead of via the heavily statistically favored 2OH channel. The nonstatistical reduction factor, κIVR, that quantifies this effect is shown to increase in importance with temperature, with κIVR = 0.81 at 300 K and 0.47 at 2500 K. Finally, we show that inefficient IVR causes H + HO2 rate constants mediated by H2O2 to depend inversely on the initial vibrational excitation of HO2.

Optimized Removal of Azo Dyes from Simulated Wastewater through Advanced Plasma Technique with Novel Reactor

Increasing attention has been paid to removal of aqueous contaminations resulting from azo dyes in water by plasma technology. However, the influence factors and removal mechanism of plasma technology were still obscure, moreover, energy consumption and oxidized degradation efficiency of plasma reactor were also inferior. In the present study, a comparative analysis was performed using 100 mg/L of Methyl Orange (MO) in the simulated wastewater with a novel plasma reactor to achieve the ideal parameters involving voltage, discharge gap, and discharge needle numbers. Therefore, the optimal removal rate for MO could be up to 95.1% and the energy consumption was only 0.26 kWh/g after the plasma treatment for 60 min, when the voltage was set as 15 kV, the discharge gap was 20 mm, and the discharge needle numbers was 5. Based upon the response surface methodology (RSM), the removal rate of MO was predicted as 99.3% by massive optimization values in software, and the optimum conditions were confirmed with the plasma treatment period of 60 min, the voltage of 14.8 kV, the discharge gap of 20 mm, and the discharge needles of 5. Plasma associated with catalysts systems including plasma, plasma/Fe2+, plasma/PS, and plasma/PS/Fe2+ were further investigated, and the best removal rate for MO reached 99.2% at 60 min under the plasma/PS/Fe2+ system due to simultaneously synergistic reactions of HO• and SO4•−. Moreover, it was also revealed that –N=N– bond was attacked and broken by active species like HO•, and the oxidized by-products of benzenesulfonic acid and phenolsulfonic acid might be generated, via the analysis of the variation in the absorbances through UV-Vis spectrophotometry during the plasma treatment. As a result, the advanced plasma technique in this study presented excellent efficacy for MO removal from simulated wastewater with low energy consumption.

Yields of HONO2 and HOONO Products from the Reaction of HO2 and NO Using Pulsed Laser Photolysis and Mid-Infrared Cavity-Ringdown Spectroscopy.

The reaction of HO2 with NO is one of the most important steps in radical cycling throughout the stratosphere and troposphere. Previous literature experimental work revealed a small yield of nitric acid (HONO2) directly from HO2 + NO. Atmospheric models previously treated HO2 + NO as radical recycling, but inclusion of this terminating step had large effects on atmospheric oxidative capacity and the concentrations of HONO2 and ozone (O3), among others. Here, the yield of HONO2, φHONO2, from the reaction of HO2 + NO was investigated in a flow tube reactor using mid-IR pulsed-cavity ringdown spectroscopy. HO2, produced by pulsed laser photolysis of Cl2 in the presence of methanol, reacted with NO in a buffer gas mixture of N2 and CO between 300 and 700 Torr at 278 and 300 K. HONO2 and its weakly bound isomer HOONO were directly detected by their v1 absorption bands in the mid-IR region. CO was used to suppress HONO2 produced from OH + NO2 and exploit a chemical amplification scheme, converting OH back to HO2. Under the experimental conditions described here, no evidence for the formation of either HONO2 or HOONO was observed from HO2 + NO. Using a comprehensive chemical model, constrained by observed secondary reaction products, all HONO2 detected in the system could be accounted for by OH + NO2. At 700 ± 14 Torr and 300 ± 3 K, φHONO2 = 0.00 ± 0.11% (2σ) with an upper limit of 0.11%. If all of the observed HONO2 was attributed to the HO2 + NO reaction, φHONO2 = 0.13 ± 0.07% with an upper limit of 0.20%. At 278 ± 2 K and 718 ± 14 Torr, we determine an upper limit, φHONO2 ≤ 0.37%. Our measurements are significantly lower than those previously reported, lying outside of the uncertainty of the current experimental and recommended literature values.