Oxygen-related Radicals Research Articles

Photocatalytic oxidation of SO2 on TiO2 and the catalyst deactivation: A kinetic study

Kinetics for the photocatalytic oxidation (PCO) of SO2 on TiO2 surface considering catalyst deactivation were investigated in this study. Different deactivation rate models as a function of SO2 concentration and the catalyst residual activity were studied. The kinetic parameters of the overall reactions were obtained and discussed for different water contents, oxygen contents, and reaction temperatures. The addition of water and oxygen into the flue gas both benefited the PCO performance of TiO2. According to the model, however, the water-related radicals appeared to be more reactive than the oxygen-related radicals on UV-irradiated TiO2 surface. In addition, the presence of water significantly reduced the residual activity of the deactivated catalyst from ∼7% to ∼1%, while the influences of oxygen and temperature can be negligible. The model prediction in the temperature range of 60–100 °C reveals that the apparent activation energy of the photocatalytic reaction was about 29.0 kJ/mol under the UV intensity of 3 mW/cm2. This indicates that SO2 can be oxidized by photocatalysis much easier when compared with other oxidation approaches. The thermodynamic analysis of the kinetic parameters shows that the adsorption of SO2 on TiO2 surface was spontaneous physisorption with the adsorption enthalpy of −17.5 kJ/mol.

Implantation of Iron(III) in porphyrinic metal organic frameworks for highly improved photocatalytic performance

Herein a simple approach is proposed to greatly improve the photocatalytic performance of a porphyrinic metal organic framework (PCN-224) by implantation of coordinatively unsaturated Fe(III) sites into the porphyrin unit. Taking the photooxidation of isopropanol (IPA) as a model reaction, the newly developed Fe@PCN-224 exhibits significantly enhanced photocatalytic activity, which is equivalent to an 8.9-fold improvement in acetone evolution rate and 9.3-fold enhancements in CO2 generation rate compared with the PCN-224. Mechanism investigation reveals that the presence of Fe(III) sites in the PCN-224 can not only greatly boost the electron–hole separation efficiency, but also effectively convert the in-situ photogenerated inactive H2O2 into reactive oxygen-related radicals via Fenton reactions to participate in the photocatalytic IPA oxidation. The enhanced photocatalytic activity for IPA oxidation is also observed over another Fe(III) implanted porphyrinic metal organic framework (Fe@PCN-222), suggesting the generality of this strategy.

Impact on the Gas Barrier Property of Silicon Oxide Films Prepared by Tetramethylsilane-Based PECVD Incorporating with Ammonia

The gas barrier property of a silicon oxide (SiOx) film synthesized from plasma-enhanced chemical vapor deposition using the tetramethysilane (TMS)-oxygen gas mixture was modified by introducing ammonia gas in the glow discharge. The change in the glow discharge with the ammonia gas incorporation was monitored by an optical emission spectrometer (OES). Structures, chemical bond configurations, and material properties of the resulting films were investigated. The introduced ammonia gas in the TMS-oxygen plasma resulted in emission lines dominated by the N2 and CN species with the suppression of the OH and oxygen-related radicals, thereby introducing nitrogen and carbon atoms in the deposited film. A silicon oxynitride (SiOxNy) film had the best surface morphology and the lowest residual internal stress was achievable by controlling the reactant gas flow ratio of the ammonia and oxygen. The barrier property to the water vapor permeation of the silicon oxide film (~1.65 g/m2/day) deposited onto the polyethylene terephthalate (PET) substrate was thus greatly improved to 0.06 g/m2/day for the film synthesized from an adequate TMS-oxygen-ammonia gas mixture.

Incorporation of graphene nanodots and oxygen defects triggers robust coupling between solar energy and reactive oxygen

Efficient coupling between solar energy and active oxygen-related radicals plays a very important role in promoting photocatalytic oxidation processes; however, the poor solar energy harvesting, serious carrier recombination and especially sluggish interfacial reaction kinetics always make this process very inefficient.

Constructing Solid–Gas-Interfacial Fenton Reaction over Alkalinized-C3N4 Photocatalyst To Achieve Apparent Quantum Yield of 49% at 420 nm

Efficient generation of active oxygen-related radicals plays an essential role in boosting advanced oxidation process. To promote photocatalytic oxidation for gaseous pollutant over g-C3N4, a solid-gas interfacial Fenton reaction is coupled into alkalinized g-C3N4-based photocatalyst to effectively convert photocatalytic generation of H2O2 into oxygen-related radicals. This system includes light energy as power, alkalinized g-C3N4-based photocatalyst as an in situ and robust H2O2 generator, and surface-decorated Fe3+ as a trigger of H2O2 conversion, which attains highly efficient and universal activity for photodegradation of volatile organic compounds (VOCs). Taking the photooxidation of isopropanol as model reaction, this system achieves a photoactivity of 2-3 orders of magnitude higher than that of pristine g-C3N4, which corresponds to a high apparent quantum yield of 49% at around 420 nm. In-situ electron spin resonance (ESR) spectroscopy and sacrificial-reagent incorporated photocatalytic characterizations indicate that the notable photoactivity promotion could be ascribed to the collaboration between photocarriers (electrons and holes) and Fenton process to produce abundant and reactive oxygen-related radicals. The strategy of coupling solid-gas interfacial Fenton process into semiconductor-based photocatalysis provides a facile and promising solution to the remediation of air pollution via solar energy.

Controlled oxygen-doped diamond-like carbon film synthesized by photoemission-assisted plasma

Controlled oxygen doping into a diamond-like carbon (DLC) film was succeeded under a current regulation by the photoemission-assisted Townsend (PAT) discharge plasma with the aid of UV-excited photoelectrons. An oxygen-doped DLC layer was formed on a non-doped DLC underlayer in the methane/argon plasma containing a certain amount of carbon dioxide as an oxygen dopant source. Oxygen-related radicals generated in the doped layer synthesis did not etch and penetrate the underlayer. However, such controlled doping failed in the photoemission-assisted glow (PAG) discharge where high-energy oxygen-related radicals etched the underlayer. A non-doped DLC layer finally capped the doped layer to build an oxygen box-doped DLC film. The dielectric constant of the film was unchanged irrespective of the amount of oxygen incorporated in the doped layer. However, very high breakdown strength was obtained, especially, over 10MV/cm in negative electrical polarization when the doped layer contained large amount of oxygen. This result suggested that the interfaces between the doped layer and the non-doped side layers exhibited an n-type barrier. The voltage characteristics in the layer syntheses under the same current regulation suggested that the UV photons passed through the doped layer and excited photoelectrons in the non-doped underlayer. The photoelectrons went back through the doped layer and emitted from the surface to cause reactions.

Hierarchical regrowth of flowerlike nanographene sheets on oxygen-plasma-treated carbon nanowalls

Cauliflorous nanographene sheets were hierarchically regrown on the spearlike structures of carbon nanowalls (CNWs) produced by O2-plasma etching. The spears on the CNWs acted as a stem for the growth of flowerlike flaky nanographene sheets, where the root of the nanoflower was located at a defect or disordered site. The defects on the graphitic structures were induced by irradiation with oxygen-related radicals and ions in the O2-based plasmas and acted as sites for the nucleation of flowerlike nanographene. The porous carbon nanostructures regrown after O2-plasma treatment have a relatively higher surface area and are thus promising materials for electrochemical applications.

Effect of N2O on high-rate homoepitaxial growth of CVD single crystal diamonds

Various gases such as N2, O2, and CO2 have been introduced in the typical reaction atmosphere of CH4/H2 and proposed to improve the growth of chemical vapor deposited (CVD) single-crystal diamonds (SCDs). In this paper, we study the influence of a new adding gas nitrous oxide (N2O) on the growth rate, morphology, and optical properties of homoepitaxy (100) CVD SCDs. The reaction pressure (H2/CH4 flow rates) was fixed at 300Torr (750/90 in sccm) with the addition of a small amount of N2O gas varied at flow rates of 0, 2, 5, 8 and 10sccm. With the appropriate addition of N2O, the growth rate was increased up to 135μm/h and the surface roughness was decreased to around 2nm. Furthermore, adding N2O is favorable for inhibiting the generation of large anti-pyramidal pits on the top surface of SCDs, which generally appeared in the products synthesized in CH4/H2 ambient. The combined effect of the nitrogen- and oxygen-related radicals decomposed from N2O on the growth and properties of the CVD SCDs is discussed. As a result, the addition of N2O provides a new route to realize high-rate growth CVD SCDs instead of the traditional nitrogen.

Determination of nitrofurans in feeds based on silver nanoparticle-catalyzed chemiluminescence

A highly sensitive chemiluminescence (CL) method for the determination of nitrofurans (NFs) was developed based on the enhancement of CL intensity of luminol–H 2O 2–NFs system by silver nanoparticles (AgNPs). It was supposed that the oxygen-related radicals of OH and superoxide radical (O 2 − ) could be produced when NFs reacted with H 2O 2. Furthermore, the enhancement mechanism was originated from the reinforcer of AgNPs, which could catalyze the generation of the OH radical. Then OH radicals reacted with luminol anion and HO 2 − to form luminol radical (L − ) and O 2 − . The excited state 3-aminophthalate anion was obtained in the reaction of L − and O 2 − , which was the emitter (luminophor) in the luminol–H 2O 2 CL reaction system and the maximal emission of the CL spectrum was at 425 nm. The experiments of scavenging oxygen-related radicals were done to confirm these reactive oxygen species participated in the CL reaction. The limits of detection (LOD) ( S/ N=3) were 8×10 −7 g mL −1 for furacilin, 8×10 −8 g mL −1 for furantoin, 4×10 −8 g mL −1 for furazolidone and 2×10 −7 g mL −1 for furaltadone. The proposed method was successfully applied to the determination of NFs in feeds and pharmaceutical samples.

The new approach for captopril detection employing triangular gold nanoparticles-catalyzed luminol chemiluminescence

In this work, we utilize the triangular gold nanoparticles (AuNPs) prepared by trisodium citrate reduction of HAuCl4 in presence of nonionic fluorosurfactant (FSN) as a novel chemiluminescence (CL) probe for the determination of captopril. Captopril can induce a sharp decrease in CL intensity from the triangular AuNPs-catalyzed luminol system. Under the selected experimental conditions, a linear relationship was obtained between the logarithm of CL intensity and the logarithm of concentration of captopril in the range of 23.0–920nM, and the detection limit at a signal-to-noise ratio of 3 for captopril was 4.6nM. The as-prepared triangular AuNPs were easier to synthesize, stable at a wider pH range and high ionic strength, and exhibited a high selectivity and an excellent sensitivity toward captopril. The applicability of the proposed method has been validated by determining captopril in commercial pharmaceutical formulations and human urine samples with satisfactory results. The recoveries for captopril in spiked samples were found to be between 95.0% and 103.5%. The method shows promise for routine control analysis of pharmaceutical preparations and human urine samples. Moreover, based on the CL spectra, UV–vis spectra and transmission electron microscope (TEM) measurements, a possible CL mechanism was proposed. The mechanism of high selectivity toward captopril is supposed to originate from the tight binding of the sulphydryl groups of captopril to the active site of the as-prepared triangular AuNPs, leading to oxygen-related radicals cannot easily be generated from H2O2 on the surface of triangular AuNPs.

Flow injection chemiluminescence determination of isoniazid using luminol and silver nanoparticles

Abstract The effect of silver colloidal nanoparticles (AgNPs) on the luminol–isoniazid system was investigated. It was found that AgNPs could act as a nanocatalyst on the luminol–isoniazid system to generate chemiluminescence (CL). The CL emission spectrum of the luminol–isoniazid–AgNPs system showed a peak with a maximum at 425 nm. It was suggested that the luminophor species was the excited state 3-aminophthalate. The reduction of dissolved O 2 to H 2 O 2 by isoniazid and decomposition of H 2 O 2 to the oxygen-related radicals were attributed to the catalytic effect of AgNPs. Under optimized conditions, the CL signal intensity was linear with the isoniazid concentration in the range of 10–1000 ng mL − 1 , with the correlation coefficient of 0.9996. The limit of detection was 2.7 ng mL − 1 isoniazid. The relative standard deviations for seven repeated measurements of 60 and 200 ng mL − 1 isoniazid were 1.4 and 2.4%, respectively. The effect of potent interfering compounds on the CL signal intensity of the proposed luminol–isoniazid–AgNPs system was investigated. The proposed method was successfully applied to the determination of isoniazid in a pharmaceutical sample.

Effect of hot filament on preparation of YBCO superconducting films by pulsed laser ablation in nitrous oxide gas

YBa2Cu3Ox (YBCO) films were prepared in nitrous oxide (N2O) gas by pulsed laser ablation (PLA) using Kanthal hot filament of approximately 1000°C for cracking the N2O gas. The crystal orientation was changed from the a-axis to c-axis by turning on the filament. The possible origin of this result is a rise of surface temperature of the substrate by thermal radiation from the hot filament and/or generation of oxygen-related radicals produced by cracking of N2O. Temperature measurements revealed that the change of crystal orientation caused by the hot filament could be partly explained by the substrate heating effect. Mass-analysis revealed that N2O gas was really cracked by the hot filament, supporting the possible change of the crystal orientation by the cracking effect of N2O.

有磁場マイクロ波プラズマ気相合成装置内に付着した炭素薄膜の酸素プラズマによるエッチング

Carbon films deposited unintentionally on substrate holder and reactor walls significantly influenced on diamond nucleation and growth using magneto-active microwave plasma chemical vapor deposition method (MPCVD). In this study, the etching process of such carbon films for a reproducible cleaning process has been investigated. In order to clarify the effect of magneto-active microwave pure-oxygen plasma, CO2 and CO products were mainly measured as functions of treatment time, plasma pressure, microwave power and substrate bias voltage. The results obtained show that there are three time regions in the etching process which may depend on the spatial distributions of the oxygen-related radicals and the carbon films in the chamber. It is found that relatively inefficient etching proceeded in the third stage, the origin of which is discussed.

Alkylperoxyl radical-scavenging activity of various flavonoids and other phenolic compounds: implications for the anti-tumor-promoter effect of vegetables.

We recently reported that alkylperoxyl radical (ROO(*)) enhanced carcinogenesis in rats treated with carcinogen (Sawa et al. Cancer Epidemiol. Biomarkers Prev. 1998, 7, 1007-1012), and the tumor promoting action of ROO(*) could be reduced by addition of hot-water extracts of vegetables (Maeda et al. Jpn. J. Cancer Res. 1992, 83, 923-928). Here we described the ROO(*)-scavenging activity of flavonoids and nonflavonoid phenolics and their role in anti-tumor-promoter effects. A model molecular species, ROO(*), was generated from tert-butyl hydroperoxide (t-BuOOH) and heme iron, and the scavenging of t-BuOO(*) was determined by (a) bioassay based on the bactericidal action of ROO(*), (b) luminol-enhanced chemiluminescence, and (c) electron spin resonance. Of 17 authentic plant phenolics tested, 9 compounds (including rutin, chlorogenic acid, vanillin, vanillic acid, neohesperidin, gallic acid, shikimic acid, rhamnetin, and kaempferol) showed remarkably high ROO(*)-scavenging activity. Some of them were detected and quantified in hot-water extracts of mung bean sprouts, used as the model vegetable, and their contents increased after germination, which paralleled very well to the ROO(*)-scavenging capacity of the vegetable extracts. Thus, a diet rich in these radical scavengers would reduce the cancer-promoting action of ROO(*). Consequently, the carcinogenic potentials of oxygen-related radicals may be suppressed.