Increased OH Radicals Research Articles

Enhanced photocatalytic degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) by the addition of H2O2

Photocatalytic remediation technology has been shown to be a favorable approach for the removal of a range of environmental pollutants in water treatment. While this approach can often achieve complete degradation, often overlooked are reaction intermediates that are potentially as harmful as the original parent compound. In the case of photocatalytic oxidation of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA), we have recently shown that 4-chloro-2-methylphenol (CMP) is formed as the primary intermediate. To ensure the continued development of the technology, it is crucial to ensure the removal of both MCPA and CMP can be achieved by photocatalysis. Reported here is the enhanced photocatalytic removal and subsequent suppression of MCPA and CMP respectively, by the addition of small quantities of H2O2. While the addition of H2O2 often accelerates degradation rates (via increased OH radical production), it was found to restrict the formation of CMP in this study through competitive adsorption at the surface of TiO2. Based on the combination of MCPA removal coupled with supressed CMP formation, 0.5% H2O2 was determined to be an optimal loading for the process. Under these conditions 100% MCPA removal was achieved (to the limit of HPLC detection) after 45 min irradiation at a degradation rate of ∼1 mg L−1 min−1 (ƞphoton = 4.4), which also resulted in a ∼83% reduction in CMP formation when compared to a system with no H2O2 present.

Photocatalytic degradation of aniline blue, brilliant green and direct red 80 using NiO/CuO, CuO/ZnO and ZnO/NiO nanocomposites

Photocatalytic degradation of three dyes, aniline blue (AB), brilliant green (BG) and direct red 80 (DR 80) by transition metal oxide nanocomposites having p-p isotype heterojunction, NiO/CuO and p-n type heterojunction, CuO/ZnO and ZnO/NiO has been explored under sun light and UV light. The effect of reaction conditions such as initial dye concentration, catalyst dosage, pH, contact time and presence of electron acceptor on photocatalytic degradation of these dyes was investigated. A suitable mechanism has been proposed for the photocatalytic degradation of dyes by the nanocomposites with illustration. The results show that NiO/CuO has higher degradation ability on AB dye (91 %) than BG (82 %) and DR 80 dyes (67 %). Among the three nanocomposites, the enhanced degradation ability shown by NiO/CuO are due to its lowest particle size, reduced electron/hole pair recombination, high BET surface area and increased OH radical generation during the photocatalytic reaction. The percentage degradation of all the dyes was carried out under sun light and UV light. It has been found that the rate of dye degradation under sun light is slightly higher than in UV light due to the existence of all type of radiations in sun light.

Enhanced photo-induced catalytic activity of Cu ion doped ZnO - Graphene ternary nanocomposite for degrading organic dyes

A ternary photocatalyst Cu doped (0 to 10 wt%) ZnO-hybridized Graphene nanocomposite (GZCu) was prepared by hydrothermal method. A detailed analysis by XRD, RAMAN, FTIR and FESEM showed a formation of ZnO nanorods with hexagonal wurtzite structure on graphene sheets. Optical band gap has been decreased from 3.12 eV for GZnO (undoped ZnO) to 2.89 eV for GZCu. Subsequently, intensity of PL emission and PL lifetime have also been decreased with increasing Cu ion content in ZnO. Photocatalytic studies under UV and Sunlight irradiations were done on the photodegradation of organic dyes such as methyl orange (MO). The GZCu with 0.5 wt % Cu showed the highest photodegradation of MO. The maximum MO degradation was 85.7 and 89.1% under UV and Sunlight irradiation respectively for GZCu and this was 12% and 11% higher than the same shown by undoped GZnO. The enhanced degradation observed at lower Cu doping (0.5 wt %) in ZnO was attributed to the optimum doping concentration which is responsible for reduced charge recombination, increased PL lifetime and increased OH radical generation during the photocatalytic reaction. Photocatalytic experiments under different pH conditions showed that the photocatalyst could effectively degrade cationic dye in basic medium, because under basic conditions the catalyst’s surface become negatively charged, whereby more adsorption of the cationic dye took place on its surface and resulted in enhanced degradation.

Formation and reduction of NO from the oxidation of NH3/CH4 with high concentration of H2O

This study investigated the homogeneous formation and reduction of NO from the oxidation of CH4/NH3 to understand the effect of the high concentrations of H2O on NO emissions. The experimental results about the effects of excess oxygen ratio, gas compositions including H2O, CO2, NH3 and recycled NO, on NO formation and reduction were presented. The mechanism about the effects of high concentration of H2O and combined effect of H2O/CO2 on NO formation and reduction has been discussed. The results indicates that NO formation was markedly enhanced at high concentrations of H2O, which were mainly attributed to the increased OH radicals with steam addition at oxygen-rich conditions. By contrast, the radicals were consumed by reduction radicals, such as CO, H, and CHi radicals, under oxygen-lean conditions. NO concentrations followed the sequence of H2O/Ar > H2O/CO2 > CO2/Ar under both the oxygen-rich and oxygen-lean conditions, which meant that the highest and lowest NO emissions were recorded in Ar/H2O and CO2/Ar respectively. The combined H2O/CO2 concentration accordingly exerted an effective impact on NO reduction. The results about the effect of NH3 concentration in fuel on NO emission showed that NO emission increased with increasing NH3 concentration. Furthermore, NO reburning results implied that with increasing NO concentration, the total NO reduction increased, whereas the reduction ratio decreased.

Effects of hydrogen addition on nanostructure and reactivity of carbon particles in flame–wall interactions

An experimental study was performed to investigate the influence of hydrogen addition on carbon particles (soot) characteristics in flame–wall interactions through the ethylene jet diffusion impinging flames. Different soot rings were formed on the plate surface when the impinging flames propagated along the plate surface. The nanostructure, oxidation reactivity and other internal properties of inner and outer ring soot were comparably analyzed with the help of high-resolution transmission electron spectroscopy (HRTEM), thermogravimetric analyzer (TGA) and X-ray diffraction (XRD). The results showed that the inner ring soot was the liquid-like material with the amorphous structure. The outer ring soot was composed of primary spherical particles with classic core-shell structures. The increasing addition of hydrogen promoted the disordered extent of inner ring soot with the decrease of fringe length and the increase of fringe tortuosity. It was potentially attributed to the reduction of nucleation rates and the less condensation of PAHs on the particle surface. The degree of graphitization for outer ring soot increased and the opposite trends of fringe length and tortuosity variations were observed when part of ethylene was substituted by hydrogen. It might be due to the higher flame temperature of the post-impingement region which led by the decrease of flame domain contacted to the plate and the enhancement of soot oxidation by increased OH radicals. The oxidation reactivity increased for the inner ring soot and decreased for the outer ring soot with the increasing addition of hydrogen. It also verified the correlation between soot nanostructure and oxidation reactivity that soot with the higher graphitization degree of nanostructure presented the lower oxidation reactivity.

Understanding in-cylinder soot reduction in the use of high pressure fuel injection in a small-bore diesel engine

This study shows how soot particles inside the cylinder of the engine are reduced due to high pressure fuel injection used in a light-duty single-cylinder optical diesel engine fuelled with methyl decanoate, a selected surrogate fuel for the diagnostics. For various injection pressures, planar laser induced incandescence (PLII) imaging and planar laser-induced fluorescence of hydroxyl (OH-PLIF) imaging were performed to understand the temporal and spatial development of soot and high-temperature flames. In addition, a thermophoresis-based particle sampling technique was used to obtain transmission electron microscope (TEM) images of soot aggregates and primary particles for detailed morphology analysis. The OH-PLIF images suggest that an increase in the injection pressure leads to wider distribution of high-temperature flames likely due to better mixing. The enhanced high-temperature reaction can promote soot formation evidenced by both a faster increase of LII signals and larger soot aggregates on the TEM images. However, the increased OH radicals at higher injection pressure accelerates the soot oxidation as shown in a higher decreasing rate of LII signals as well as dramatic reduction of the sampled soot aggregates at later crank angles. The analysis of nanoscale carbon layer fringe structures also shows a consistent trend that, at higher injection pressure, the soot particles are more oxidized to form more graphitic carbon layer structures. Therefore, it is concluded that the in-cylinder soot reduction at higher injection pressure conditions is due to enhanced soot oxidation despite increased soot formation.

Effect of after injections on late cycle soot oxidation in a small-bore diesel engine

After injection, for which a short fuel injection follows the main injection, is proved to be effective in reducing soot emissions in diesel engines. The present study aims to better understand this in-cylinder soot reduction mechanism of after injection with a particular emphasis on its efficacy in a small-bore diesel engine in which more significant flame-wall interactions could cause different behaviour compared with extensively studied heavy-duty diesel engines in the literature. With the main injection only case as a baseline, two after-injection cases of close-coupled and long-dwell timings have been investigated in a single-cylinder common-rail optical engine. Various optical/laser-based imaging diagnostics have been performed including line-of-sight integrated chemiluminescence imaging of OH*, planar laser-induced florescence of hydroxyl (OH-PLIF), planar laser-induced incandescence of soot (PLII) and transmission electron microscope (TEM) imaging of thermophoretically sampled in-flame soot particles to visualise the spatial and temporal evolution of high temperature reaction and soot as well as particle structure. The results indicate that both after-injection strategies introduce a secondary heat release that leads to additional bulk gas temperature rise and thereby promoting the late-cycle soot oxidation. However, the efficacy is found to be dependent upon the after-injection timing. The OH-PLIF and PLII images show that the close-coupled after-injection induces additional high-temperature reaction and soot formation due to high ambient gas temperature. The new reaction occurs near the jet–wall impingement point, which is well separated from the main combustion zone as the main fuel jet travelled along the bowl wall due to significant jet–wall interactions. Although the main and after-injection soot are decoupled, soot morphology analysis based on TEM images suggests that the close-coupled after-injection does enhance the oxidation of main combustion-generated soot particles through the breakdown of large soot aggregates at elevated temperatures and with increased OH radicals. In comparison, both OH-PLIF and PLII images show no visual evidences of decoupled after-injection combustion for the long-dwell case due to insufficient temperature as the additional reaction occurs later in the expansion stroke. However, the increased OH radicals and breakdown of soot aggregates in the main combustion region are evident in OH-PLIF and TEM images. Overall, the close-coupled after-injection adds more soot but induces a higher degree of oxidation for the main combustion-generated soot particles. By contrast, the promotion of soot oxidation is less significant for the long-dwell after-injection but it produces no extra soot.

Fructan dynamics and antioxidant capacity of 4-day-old seedlings of wheat (Triticum aestivum) cultivars during drought stress and recovery.

One of the inevitable consequences of drought stress is enhanced production of reactive oxygen species (ROS). Fructan might function as effective candidate for capturing ROS in a wide range of stresses. Herein, 4-day-old seedlings of drought-tolerant and -sensitive wheat cultivars were exposed to drought stress for 7 days by water cessation, followed by further 7 days re-watering. The content, metabolism, related enzymes activity, degree of polymerisation (DP) and antioxidant capacity of fructan were compared in the two cultivars. High resolution HPAEC-PAD analysis of fructan showed an increase in the activities of fructan: fructan 1-fructosyltransferase (1-FFT) in the tolerant cultivar and sucrose: sucrose 1-fructosyltransferase (1-SST) and 1-FFT in the sensitive cultivar under drought condition. The activity of fructan exohydrolase (FEH) did not show any significant change in tolerant cultivar, but decreased in a sensitive one. In comparison with the sensitive cultivar, the tolerant one accumulated fructan (0.9% of dry matter) with higher degree of polymerisation (10.67±1.1), accompanied by increased OH radical scavenging activity, during drought condition. In regard to the fact that OH radical is the most prevalent ROS in damaging membrane lipids, the results suggest that fructans play a crucial role in the tolerance of wheat seedlings against drought stress.

The Effects of Fuel Mixtures in Nonpremixed Combustion for a Bluff-Body Flame

A numerical investigation is presented assessing the effects of hydrogen compositions and nonflammable diluent mixtures on the combustion and NO emission characteristics of syngas nonpremixed flames for a bluff-body burner. An assessment of turbulent nonpremixed modeling techniques is presented and is compared with the experiments of Correa and Gulati (1992, “Measurements and Modeling of a Bluff Body Stabilized Flame,” Combust. Flame, 89(2), pp. 195–213). The realizable k–ε and the Reynolds stress (RSM) turbulence models were found to perform the best. As a result, increased hydrogen content caused the radial velocity and strain rate to decrease, which was important for mixing whereby NO production decreased. Also, the effectiveness of nonflammable diluent mixtures of N2, CO2, and H2O was characterized in terms of the ability to reduce NO emission in syngas nonpremixed flames. Results indicated that CO2 was the most effective diluent to reduce NO emission and H2O was more effective than N2. CO2 produced low levels of OH radical, which made CO2 the most effective diluent. Although H2O increased OH radicals, it was still effective to reduce thermal NO because of its high specific heat. It will be numerically shown that hydrogen concentration in the H2/CO/N2 flame does not significantly affect temperature but dramatically decreases NO emission, which is important for industrial applications that can use hydrogen in syngas flames.

Increased Sterility by Fenton Reaction and Increased OH Radicals upon UV Irradiation-Comparison of Sterility between Fenton Reaction and UV Irradiation to Hydrogen Peroxide

Copyright: © 2015 Shintani H. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Fenton reaction produces OH radicals from hydrogen peroxide with the catalyst of Fe2+ or Cu+. The sterilization mechanism of hydrogen peroxide can be explained from OH radicals. If so using Fenton reaction, OH radical from hydrogen peroxide may increase and increased result of sterilization can be attained. Fe2+ was inoculated onto the sterilization pack and by contacting hydrogen peroxide with Fe2+, Fenton reaction occurred. Production of OH radicals from hydrogen peroxide was increased and increased sterility efficiency can be confirmed from the comparison of D value to the control. The D values of hydrogen peroxide with Fe2+ and without Fe2+ were 5 s and 30 s, respectively, indicating OH radical formed greater by Fenton reaction. In addition, we studied the production of OH radicals from the UV exposure at 254 nm to hydrogen peroxide. The result of D values was compared with UV254 nm exposure and without UV 254 nm exposure, the D value of the former was 1.7 s and the latter was 3.3 s, respectively, indicating UV exposure supplied increased OH radicals. Furthermore sterility efficiency of Fenton reaction and UV 254 nm exposure was compared. Fenton reaction was inferior to UV 254 nm exposure due to the greater D value. The former was 5-10 s and the latter was 1.7 s. However, this comparison has a problem that primary package was absence and presence. UV exposure was absence and Fenton reaction was presence. Primary package present an obstacle to penetrate OH radicals into the interior of BI. As a conclusion, Fenton reaction was not always inferior to UV 254 nm exposure.

Increased Sterility Efficiency by Fenton Reaction and Increased Sterility by Increased OH Radicals upon UV Irradiation to Hydrogen Peroxide

Increased Sterility Efficiency by Fenton Reaction and Increased Sterility by Increased OH Radicals upon UV Irradiation to Hydrogen Peroxide

In vitro antioxidant properties of Musa paradisiacal Peel aqueous extract

Plants and plants products are the major sources of natural antioxidant which can be used to ameliorate oxidative stress caused by reactive oxygen species in biological systems. In vitro antioxidant activity of Musa paradisiacapeel aqueous extract was evaluated. Sodium nitroprusside was used to induce lipid perioxidation in rat pancreas. The total phenol, flavonoid and vitamin C contents were determined using standard methods of analysis. OH radical scavenging ability, Fe2+ chelating ability and lipid peroxidation were also analyzed using standard methods. The result revealed substantial amount of total phenol (0.76 ±0.04 mg/g), total flavonoid (0.53 ±0.04 mg/g) and vitamin C contents (24.11 ±0.41 mg/100 g). The result also revealed increased OH radical scavenging ability, Fe2+ chelating ability and MDA inhibition with increase in concentration of the extract used. The present study therefore, revealed that Musa paradisiacapeel aqueous extract could serve as source of natural antioxidant which can be used to ameliorate some disease associated with oxidative stress.

Evaluation of extra- and intracellular OH radical generation, cancer cell injury, and apoptosis induced by a non-thermal atmospheric-pressure plasma jet

In this study, we investigated the effects of a non-thermal atmospheric-pressure plasma jet inducing extracellular and intracellular OH radical generation as well as cell injury and apoptosis for the cultured human breast cancer cells. Increased OH radical generation in the extracellular culture medium (liquid phase) was observed with increased irradiation time, distance to the liquid surface, and voltage. From the voltage–response relationships for two breast cancer cell lines (invasive MDA-MB-231 cells and non-invasive MCF-7 cells) and normal breast cells (HMEC), the half-maximal effective peak-to-peak voltage (EV50) values were 16.7 ± 0.3 kV, 15.0 ± 0.4 kV and 11.2 ± 0.7 kV for MDA-MB-231, MCF-7 and HMEC cells, respectively. This indicated that there was almost no selective cancer cell injury induced by plasma jet irradiation under these conditions. Compared with control condition without a plasma jet, intracellular OH radical accumulation and apoptotic cells were observed with a plasma jet using conditions that induced injury to 50% of cells irrespective of the cancer cell line.

Ultrasonic degradation of reactive brilliant red K-2BP in water with CCl 4 enhancement: Performance optimization and degradation mechanism

The ultrasonic degradation of reactive brilliant red K-2BP (K-2BP) in water with CCl 4 enhancement was investigated. The effects of operating parameters, such as CCl 4 dosage, ultrasonic power, media temperature, dye initial concentration, and initial media pH on K-2BP degradation were discussed. The ultrasonic degradation of K-2BP was obviously enhanced by CCl 4 addition – an effect attributed to the increased OH radical concentration in the presence of CCl 4 as a hydrogen atom scavenger, and the formation of chlorine-containing radicals. The main degradation products of K-2BP were tentatively identified by GC–MS and ion chromatography. A possible degradation pathway for K-2BP was also proposed.

Hydrogen addition to acetylene–air laminar diffusion flames: Studies on soot formation under different flow arrangements

Axisymmetric co-flowing acetylene/air laminar diffusion flames have been experimentally investigated to study the effect of hydrogen addition on soot formation and soot morphology. An acetylene–hydrogen jet burning in co-flowing air at atmospheric pressure has been studied under different flow arrangements, i.e., premixed and with separate addition of acetylene and hydrogen. Thermophoretic sampling and analysis by transmission electron microscopy are employed for soot diagnostics. Soot microstructure, primary particle size, soot volume fraction, and fractal geometry results are reported. The effect of hydrogen addition on the temperature field is moderate (maximum increase ∼ 100 K ), the effect being greater when hydrogen is premixed with acetylene. Soot volume fraction decreases with hydrogen addition. A shift was noted in the soot volume fraction peak with change in the Reynolds and Froude numbers at the burner exit. The primary soot particle diameter is in the range of 20–35 nm. Soot particles are larger in size close to the burner for the pure acetylene flame. A reverse trend is observed with hydrogen addition. The fractal dimension of the soot aggregates is about 1.7–1.8. It is unaffected by hydrogen addition and location in the flame. Soot aggregate size tends to decrease with hydrogen addition. The results of the present study on the effect of hydrogen addition on soot volume fraction and mean primary particle size are in good correlation with the results of other investigators for ethylene–, propane–, and butane–air flames, which have been described with regard to the HACA mechanism of soot nucleation and growth and enhanced soot oxidation in fuel-rich flames by increased OH radical concentration.