Effect of reactive oxygen species generated with ultraviolet lamp and plasma on polyimide surface modification

Understanding the effect of reactive oxygen species (ROS), such as singlet oxygen molecule and atomic oxygen, on polyimide (PI) film properties, such as wettability, morphology, and chemical bonding state, is essential for further development of PI‐based surfaces. We investigated the effect of different ROS generated during ultraviolet (UV) and plasma treatment in oxygen gas on surface modification of Kapton PI. Different surface modification techniques, UV and plasma treatment, are known to generate different ROS. In this work, we demonstrate the effect of different ROS on PI surface modification. From the diagnostics of ROS by means of electron spin resonance and optical emission spectroscopy, we confirmed that during UV treatment, excited singlet oxygen molecules are the main ROS, while plasma treatment mainly generated atomic oxygen. The wettability of PI surface treated by UV and plasma resulted in hydrophilic PI surfaces. XPS results show that the wettability of PI samples is mainly determined by their surface O/C ratio. However, chemical bonding states were different: while UV treatment tended to generate C=O bonds, while plasma treatment tended to generate both C―O and C=O bonds. Singlet oxygen molecules are concluded to be the main oxidant during UV treatment, and their main reaction with PI was concluded to be of the addition type, leading to an increase of C=O groups on the surface of PI film. Meanwhile, atomic oxygen species were the main oxidant during plasma treatment, reacting with the PI surface through both etching and addition reaction, resulting in a wider variety of bonds, including both C―O and C=O groups.     

HREELS investigation of the surfaces of nanocrystalline diamond films oxidized by different processes

This article reports on the use of high-resolution electron energy loss spectroscopy (HREELS) for the investigation of as-grown (hydrogen-terminated) and oxidized nanocrystalline diamond films (NCD) using chemical, physical, and electrochemical approaches. The results indicate that the nature and number of oxygen-related chemical groups generated on the NCD surface depend strongly on the oxidation process. A high concentration of C-O functions has been obtained on the NCD surface oxidized by rf (radio frequency) oxygen plasma, whereas the highest C═O/C-O ratio has been achieved by electrochemical oxidation. The NCD surface oxidized by rf plasma was totally free of C═O groups. Traces of surface hydroxyl groups (C-OH) have been detected upon annealing in air or through UV/ozone oxidation.     

氧气常压介质阻挡放电的发射光谱及能量传递机理

为研究氧气常压介质阻挡放电中的物理化学行为, 以纯氧作为放电体系, 用发射光谱(optical emission spectroscopy)诊断技术分析了等离子体中可能存在的化学活性物种. 利用在500-950 nm范围的氧原子发射光谱计算出等离子体中的电子温度为(1.02±0.03) eV; 观测了760 nm处的具有清晰转动结构的氧气A带(atmospheric band)O2(b1∑+g-X3∑-g), 并用其转动结构计算了转动温度(气体温度)为(650±20) K; 在500-700 nm范围观测了氧气的第一负带系(first negative system) O+2(b4∑-g-a4∏u), 在190-240 nm范围观测了微弱但特征清晰的氧气的Hopfield带系O+2(c4∑+u-b4∑-g). 研究发现, 在氧气常压介质阻挡放电等离子体中存在多种激发态氧原子、激发态氧气分子、基态和激发态氧气分子离子等反应活性物种, 这些活性物种的形成涉及氧气分子的激发、解离和电离等多种过程, 每个过程都包含多个能量传递步骤, 氧分子解离产生的氧原子是导致一系列高激发态氧原子生成和氧气电离激发的主要因素.     

Synthesis of Ozone at Atmospheric Pressure by a Quenched Induction-Coupled Plasma Torch

The technical feasibility of using an induction-coupled plasma (ICP) torch to synthesize ozone at atmospheric pressure is explored. Ozone concentrations up to ~250 ppm were achieved using a thermal plasma reactor system based on an ICP torch operating at 2.5 MHz and ~11 kVA with an argon/oxygen mixture as the plasma-forming gas. The corresponding production rate and yield were ~20 g ozone/hr and ~2g ozone/kWh, respectively. A gaseous oxygen quench formed ozone by rapid mixing of molecular oxygen with atomic oxygen produced by the torch. The ozone concentration in the reaction chamber was measured by Fourier Transform infrared (FTIR) spectroscopy over a wide range of experimental conditions and configurations. The geometry of the quench gas flow, the quench flow velocity, and the quench flow rate played important roles in determining the ozone concentration. The ozone concentration was sensitive to the torch RF power, but was insensitive to the torch gas flow rates. These observations are interpreted within the framework of a simple model of ozone synthesis.     

大气压射频等离子体化学气相沉积TiO2体系的发射光谱诊断

开展了大气压射频(RF)等离子体化学气相沉积(PCVD)TiO₂放电体系的发射光谱诊断研究, 分别考察了氧气分压、钛酸四异丙酯(TTIP)分压和输入功率对氧原子谱线相对强度、氩原子激发温度、OH振动温度以及转动温度的影响. 结果表明: 随着氧气分压的增加, 氧原子谱线相对强度先迅速增加至峰值后缓慢下降, OH振动温度缓慢增加, 而氩原子激发温度和OH转动温度基本不变. 随着TTIP 分压的增加, 氧原子谱线相对强度下降, 氩原子激发温度没有明显变化, 而OH振动温度和转动温度增加. 随着输入功率的增加, 氧原子谱线相对强度下降, 氩原子激发温度、OH振动温度和转动温度升高.     

Plasma chemistry of NO in complex gas mixtures excited with a surfatron launcher

The plasma chemistry of NO has been investigated in gas mixtures with oxygen and/or hydrocarbon and Ar as carrier gas. Surface wave discharges operating at microwave frequencies have been used for this study. The different plasma reactions have been analyzed for a pressure range between 30 and 75 Torr. Differences in product concentration and/or reaction yields smaller than 10% were found as a function of this parameter. The following gas mixtures have been considered for investigation: Ar/NO, Ar/NO/O2, Ar/NO/CH4, Ar/CH4/O2, Ar/NO/CH4/O2. It is found that NO decomposes into N2 and O2, whereas other products such as CO, H2, and H2O are also formed when CH4 and O2 are present in the reaction mixture. Depending on the working conditions, other minority products such as HCN, CO2, and C2 or higher hydrocarbons have been also detected. The reaction of an Ar/NO plasma with deposits of solid carbon has also been studied. The experiments have provided useful information with respect to the possible removal of soot particles by this type of plasma. It has been shown that carbon deposits are progressively burned off by interaction with the plasma, and practically 100% decomposition of NO was found. Plasma intermediate species have been studied by optical emission spectroscopy (OES). Bands and/or peaks due to N2*, NO*, OH*, C2*, CN*, CH*, or H* were detected with different relative intensities depending on the gas mixture. From the analysis of both the reaction products and efficiency and the type of intermediate species detected by OES, different plasma reactions and processes are proposed to describe the plasma chemistry of NO in each particular mixture of gases. The results obtained provide interesting insights about the plasma removal of NO in real gas exhausts.     

Reaction CH(3) + OH Studied over the 294-714 K Temperature and 1-100 bar Pressure Ranges

Reaction of methyl radicals with hydroxyl radicals, CH(3) + OH → products (1) was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 294-714 K temperature and 1-100 bar pressure ranges (bath gas He). Methyl radicals were produced by photolysis of acetone at 193.3 nm. Hydroxyl radicals were generated in reaction of electronically excited oxygen atoms O((1)D), produced in the photolysis of N(2)O at 193.3 nm, with H(2)O. Temporal profiles of CH(3) were recorded via absorption at 216.4 nm using xenon arc lamp and a spectrograph; OH radicals were monitored via transient absorption of light from a dc discharge H(2)O/Ar low pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light inside the reactor was determined by an accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study indicate that the rate constant of reaction 1 is pressure independent within the studied pressure and temperature ranges and has slight negative temperature dependence, k(1) = (1.20 ± 0.20) × 10(-10)(T/300)(-0.49) cm(3) molecule(-1) s(-1).     

Surface Modification of Poly-ε-Caprolactone with an Atmospheric Pressure Plasma Jet

In this work, poly-ε-caprolactone samples are modified by an atmospheric pressure plasma jet in pure argon and argon/water vapour mixtures. In a first part of the paper, the chemical species present in the plasma jet are identified by optical emission spectroscopy and it was found that plasmas generated in argon/0.05 % water vapour mixtures show the highest emission intensity of OH (A–X) at 308 nm. In a subsequent section, plasma jet surface treatments in argon and argon/water vapour mixtures have been investigated using contact angle measurements and X-ray photoelectron spectroscopy. The polymer samples modified with the plasma jet show a significant decrease in water contact angle due to the incorporation of oxygen-containing groups, such as C–O, C=O and O–C=O. The most efficient oxygen inclusion was however found when 0.05 % of water vapour is added to the argon feeding gas, which correlates with the highest intensity of OH (X) radicals. By optimizing the OH (X) radical yield in the plasma jet, the highest polymer modification efficiency can thus be obtained.     

Kinetics of Active Oxygen Species with Implications for Atmospheric Ozone Chemistry

Photochemical processes involving singlet oxygen (O₂(a¹Δ)), oxygen atoms_, and ozone are critical in determining atmospheric ozone concentrations. Here we report on kinetic measurements and modeling that examine the importance of the reactions of vibrationally excited ozone. Oxygen atoms and O₂(a¹Δ) were produced by UV laser photolysis of ozone. Time‐resolved absorption spectroscopy was used for O₃ concentration measurements. It was found that vibrationally excited ozone formed by O + O₂ + M → O₃(ν) + M recombination reacts effectively with O₂(a¹Δ) and O atoms. The reaction O₃(υ) + O₂(a¹Δ) → O + 2O₂ results in a reduction of the ozone recovery rate due to O atom regeneration, whereas the reaction O₃(υ) + O → 2O₂ removes two odd oxygen species, resulting in incomplete ozone recovery. The possible impact of these reactions on the atmospheric O₂(a¹Δ) and O₃ budgets at altitudes in the range of 80–100 km is considered.     

Molecular Species Generated by Surface Dielectric Barrier Discharge Micro-plasma in Small Chambers Enclosing Atmospheric Air and Water Samples

In many applications of the atmospheric pressure plasmas, the plasma is generated in chambers that enclose samples to be treated. In the case of plasma treatments of water or water-containing materials, the humidity in gaseous medium rises during the treatment, and this affects considerably the plasma generation of reactive oxygen and nitrogen species (RONS). In this study, Fourier transform infrared absorption spectroscopy is used to investigate the kinetics of reactive species generated by surface dielectric barrier (SDBD) micro-plasma in a small volume of atmospheric air (0.5 L) enclosed in a discharge chamber. The investigations were made for dry air (in absence of liquid water) and for humid air in presence of liquid water. The SDBD plasma contributes to desorption of water from the inner wall of the discharge chamber and enhances evaporation of liquid water, which increases air humidity and decreases the generation rates of reactive species. Kinetics of RONS generated in small samples of liquid water in contact with discharge medium is investigated by ex situ UV absorption spectroscopy measurements of plasma treated water.

     

Performance of an Ozone Decomposition Catalyst in Hybrid Plasma Reactors for Volatile Organic Compound Removal

In order to enhance the energy efficiency of nonthermal plasma methods for volatile organic compound decomposition in a catalyst-hybrid plasma reactor, we used a Cu–Cr catalyst to dissociate ozone into active atomic oxygen species at low temperatures. We investigated the conditions necessary to obtain the synergetic effect in single-stage and two-stage combinations. The ozone decomposition catalyst was not effective for the reaction under plasma discharge in the single-stage combination. In the two-stage combination, the efficiency increased by increasing the amount of catalyst. Although the propensity of catalysts for active oxygen species formation from ozone decomposition is important for optimizing the reaction efficiency, the surface area is even more important. We conclude that ozone decomposition catalysts are more effective in the two-stage combination compared to the single-stage.     

磷酸根修饰的Mn掺杂介孔TiO2在VUV-PCO体系高效催化氧化甲苯性能

Vacuum ultraviolet irradiation coupled with photocatalytic oxidation (VUV-PCO) is an efficient and promising method for eliminating pollutants at room temperature; it involves three processes: vacuum ultraviolet (VUV) photolysis, photocatalytic oxidation (PCO), and ozone catalytic oxidation. Herein, toluene was chosen as the representative volatile organic compound (VOC), which is one of the most important precursors to form fine particulate matter and photochemical smog, because of its high toxicity and extensive existence in industries. All experiments were performed in a fixed-bed continuous-flow reactor that contained units for VUV photolysis and PCO. Mesoporous P-Mn-TiO₂ was prepared by one-step hydrolysis and used as a catalyst for the oxidation of gaseous toluene under VUV irradiation through the VUV-PCO process. The as-prepared P-Mn-TiO₂ samples were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible light (UV-Vis) spectroscopy, and X-ray diffraction (XRD) analysis to determine the physicochemical properties of the catalysts and to determine the mechanisms of Mn doping and phosphoric acid modification and the effects of these processes on photocatalytic activity, ozone catalytic activity, and adsorption performance. The results indicated that the synergistic effect of phosphoric acid modification and Mn doping can improve the ozone catalytic activity and photocatalytic performance by increasing the number of oxygen active sites, completely eliminating the outlet ozone, and simultaneously promoting the efficient degradation of toluene. Moreover, doping TiO₂ with Mn³⁺ significantly enhanced light harvesting, and numerous oxygen vacancies can be generated on the catalyst surface because of the presence of doped Mn³⁺ in the lattice, which adsorbs and transforms the oxygen species for toluene degradation. In addition, modification with an appropriate amount of phosphate groups can facilitate O₂ and O₃ adsorption on the TiO₂ surface that can favor photo-induced charge carrier separation, thereby significantly improving the photocatalytic and ozone catalytic activities. The excellent catalytic performance of mesoporous P-Mn-TiO₂ for toluene degradation and outlet ozone elimination was ascribed to the formation of highly reactive oxidizing species such as O(1D), O(3P), and ·OH via the catalytic decomposition of O₃ adsorbed on the oxygen vacancy sites containing Mn and phosphate groups on the catalyst surface. In the VUV-PCO process, toluene was first destructed via VUV photolysis and oxidized by residual O₃ generated from VUV photolysis and the active oxygen species formed in the presence of the catalyst. Finally, toluene and the generated intermediate products were oxidized and degraded to CO₂ and H₂O through VUV-PCO. In addition, the outlet ozone byproduct was simultaneously eliminated by the multifunctional catalyst.      

Reaction OH + OH studied over the 298-834 K temperature and 1-100 bar pressure ranges

Self-reaction of hydroxyl radicals, OH + OH → H(2)O + O (1a) and OH + OH → H(2)O(2) (1b), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy over the 298-834 K temperature and 1-100 bar pressure ranges (bath gas He). A heatable high-pressure flow reactor was employed. Hydroxyl radicals were prepared using reaction of electronically excited oxygen atoms, O((1)D), produced in photolysis of N(2)O at 193 nm, with H(2)O. The temporal behavior of OH radicals was monitored via transient absorption of light from a dc discharge in H(2)O/Ar low-pressure resonance lamp at ca. 308 nm. The absolute intensity of the photolysis light was determined by accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The results of this study combined with the literature data indicate that the rate constant of reaction 1a, associated with the pressure independent component, decreases with temperature within the temperature range 298-414 K and increases above 555 K. The pressure dependent rate constant for (1b) was parametrized using the Troe expression as k(1b,inf) = (2.4 ± 0.6) × 10(-11)(T/300)(-0.5) cm(3) molecule(-1) s(-1), k(1b,0) = [He] (9.0 ± 2.2) × 10(-31)(T/300)(-3.5±0.5) cm(3) molecule(-1) s(-1), F(c) = 0.37.     

What are the Implications of Nonequilibrium in the O+OH and O+HO2 Reactions?

Vibrationally excited O2, OH, and HO2 species have been suggested (J. Phys. Chem. A 2004, 108, 758) to provide clues for explaining the "ozone deficit problem" and "HOx dilemma" in the middle atmosphere under conditions of local thermodynamic disequilibrium (LTD), but the question arises of how much LTD will affect the title ozone sink reactions. Besides providing novel kinetic results, it is shown that LTD tends to disfavor ozone depletion relative to traditional atmospheric modeling under Boltzmann equilibration, which is partly due to competition between the various reactive channels. The calculations also suggest that the title LTD processes can be important sources of highly vibrationally excited O2 in the middle atmosphere. Moreover, LTD is shown to offer an explanation for the fact that some down revision of the O + HO2 rate constant, or the ratio of the O + HO2 to O + OH rate constants, is required to improve agreement between the predictions of traditional modeling and observation. This, in turn, provides significant evidence supporting LTD at such altitudes.     

Oxidation of polyethylene surfaces by remote plasma discharge: A comparison study with alternative oxidation methods

The reaction rates and products of remote oxygen plasma treatment, corona discharge, and ozone treatment of high and low density polyethylenes have been examined using x-ray photoelectron spectroscopy. The oxygen uptake by remote plasma treatment was faster than that of other surface treatments using excited oxygen species. A steady state concentration of 18 ± 1% oxygen can be attained within 1 s of exposure in the remote plasma.     

GaAs(100)表面氧化的XPS研究

X-ray photoelectron spectroscopy（XPS）was used to study two different oxidation treatments on the GaAs（100）surface———the thermal oxidation in the air,and the ultraviolet-light oxidation in the UV-ozone. A series of properties including the oxide composition,chemical states,the surface Ga/As atomic ratio and the thickness of the oxide layer grown on GaAs surface were compared. The results indicate that the oxide composition,the surface Ga / As atomic ratio and the thickness of the oxide layer oxide on GaAs surface are different for different oxidation methods. The oxides on GaAs surface grown by thermal oxidation in the air are composed of Ga2O3,As2O5,As2O3 and elemental As;and the Ga/As atomic ratio is drifted off the stoichiometry far away. The Ga/As atomic ratio of oxide layer on GaAs surface is increases with the thickness of oxide. However,the oxides on GaAs surface grown by UV-ozone are made up of only Ga2O3 and As2O3,As2O5 and elemental As are not detected,the Ga/As atomic ratio is close to unity. The thickness of oxide layer on GaAs can be controlled by the UV exposing time. The mechanism of oxidation of GaAs is also discussed. The UV-light radiation not only causes the oxygen molecular excited forming atomic oxygen,but also induces the valence electrons of the GaAs excited from the valence band,and then the reactivity of Ga and As atom increase,and they can easily react with the excited atomic oxygen at the same reactive velocity.     

The OH(v = 9) + O3 reaction pathway

The oxygen-hydrogen system, including the reactive species H, O, H₂, O₂, O₃, OH, and HO₂, is very complex, and contains numerous reactions whose kinetics and branches have been insufficiently explored. In the present study we use computer modeling to simulate observations made in a 300-K ozone-hydrogen mixture, in which a critical H₂ pressure leads to rapid ozone decomposition, and generation of high concentrations of atomic oxygen. Initiation of the reaction chain involves heterogeneous O and/or H atom production, and the chain branching step is the reaction OH(v) + O₃ → OH + O + O₂, which is shown to be the predominant pathway for these reactants. The critical H₂ pressure (ca. 3 torr) sets important constraints upon the system kinetics.     

Oxygen discharge and post-discharge kinetics experiments and modeling for the electric oxygen-iodine laser system

Laser oscillation at 1315 nm on the I(2P1/2)-->I(2P3/2) transition of atomic iodine has been obtained by a near resonant energy transfer from O2(a1Delta) produced using a low-pressure oxygen/helium/nitric oxide discharge. In the electric discharge oxygen-iodine laser (ElectricOIL) the discharge production of atomic oxygen, ozone, and other excited species adds levels of complexity to the singlet oxygen generator (SOG) kinetics which are not encountered in a classic purely chemical O2(a1Delta) generation system. The advanced model BLAZE-IV has been introduced to study the energy-transfer laser system dynamics and kinetics. Levels of singlet oxygen, oxygen atoms, and ozone are measured experimentally and compared with calculations. The new BLAZE-IV model is in reasonable agreement with O3, O atom, and gas temperature measurements but is under-predicting the increase in O2(a1Delta) concentration resulting from the presence of NO in the discharge and under-predicting the O2(b1Sigma) concentrations. A key conclusion is that the removal of oxygen atoms by NOX species leads to a significant increase in O2(a1Delta) concentrations downstream of the discharge in part via a recycling process; however, there are still some important processes related to the NOX discharge kinetics that are missing from the present modeling. Further, the removal of oxygen atoms dramatically inhibits the production of ozone in the downstream kinetics.     

Water formation by surface O3 hydrogenation

Three solid state formation routes have been proposed in the past to explain the observed abundance of water in space: the hydrogenation reaction channels of atomic oxygen (O + H), molecular oxygen (O(2) + H), and ozone (O(3) + H). New data are presented here for the third scheme with a focus on the reactions O(3) + H, OH + H and OH + H(2), which were difficult to quantify in previous studies. A comprehensive set of H/D-atom addition experiments is presented for astronomically relevant temperatures. Starting from the hydrogenation/deuteration of solid O(3) ice, we find experimental evidence for H(2)O/D(2)O (and H(2)O(2)/D(2)O(2)) ice formation using reflection absorption infrared spectroscopy. The temperature and H/D-atom flux dependence are studied and this provides information on the mobility of ozone within the ice and possible isotope effects in the reaction scheme. The experiments show that the O(3) + H channel takes place through stages that interact with the O and O(2) hydrogenation reaction schemes. It is also found that the reaction OH + H(2) (OH + H), as an intermediate step, plays a prominent (less efficient) role. The main conclusion is that solid O(3) hydrogenation offers a potential reaction channel for the formation of water in space. Moreover, the nondetection of solid ozone in dense molecular clouds is consistent with the astrophysical picture in which O(3) + H is an efficient process under interstellar conditions.     

Hydrogen/argon plasma jet with methane addition

Spatial distributions of plasma parameters are presented for a H₂/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred do arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral ernissivity values have been evaluated using a routine Abel inversion procedure. Half- width and emissivity of H spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to fund rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.