Influence Of Radical Scavengers Research Articles

Mechanistic study of cefixime degradation with an atmospheric air dielectric barrier discharge – Influence of radical scavengers and metal ion catalyst

The ineffective removal of antibiotic residues and their metabolites by conventional wastewater treatment setups lead to their continuous discharge into the environment, causing risks to both aquatic life and human health. This study explored the use of a non-thermal plasma (NTP) generated by atmospheric air for the degradation of cefixime (CFX), a widely consumed and recalcitrant antibiotic. This study achieved a complete degradation of CFX using an NTP technology in 8 min treatment time at 6 kV and 20 kHz applied AC voltage and frequency, respectively using a high voltage alternating current power supply unit. An energy yield of 0.42 g/kWh was estimated. The degradation of the pollutant was influenced by solution flow rate, applied voltage and the solution characteristics. Five degradation by-products were identified based on quadrupole time-of-flight (Q-TOF) mass spectrum (MS) analysis and a possible degradation pathway for the pollutant was proposed. Also, radical scavenger experiments were set up to understand the specific chemical species facilitating CFX degradation. The effect of Fe2+ catalyst on the degradation of CFX was investigated in the aqueous solution. This low-cost metal ion catalyst has been known to improve the degradation of organic compounds by facilitating the oxidizing power of H2O2. Considering this, a new idea was examined in this study which was the degradation of the antibiotic in the presence of both Fe2+ catalyst and some radical scavengers (iso-propyl alcohol – IPA, tert-butyl alcohol – TBA, and sodium hydrogen carbonate – NaHCO3). When Fe2+ was introduced into CFX solutions containing TBA, IPA and NaHCO3, respectively, the degradation and kinetics increased by at least 33 %. In these mixed additives, the degradation of the pollutant was enhanced by the consumption of H2O2.

Influence of Radical Scavenger on Radiation Synthesis of Graphene Oxide/TiO2 Nanotubes/Ag Nanoparticles Nanocomposites and Their Dye Photodegradation Efficiency

Aqueous solutions of graphene oxide (GO), TiO2 nanotubes (TNTs), and silver nanoparticles (AgNPs) were synthesized through a facile, single-step radiolytic method at room temperature and ambient pressure. The resulting material, referred to as GO-TNTs-AgNPs (GTA), was investigated for its potential application in the photodegradation of Rhodamine-B (RhB) dye. This synthesis process relies on the interaction of high-energy gamma rays from a 60Co source with the water in the aqueous solutions. The main objective of this study was to evaluate the effect of irradiation dose and the presence of polyethylene glycol (PEG) solution on the combination within the nanocomposite materials. The inefficiency of GTA synthesis experimentally was in agreement with the hydroxyl radical (HO•) scavenger. Then, the irradiated materials were structurally characterized using various spectroscopic methods (Fourier transform infrared (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and ultraviolet-visible absorption (UV–Vis)). Scanning electron microscopy (SEM) studies reveal the variable morphology of nanocomposites. GTA samples in water exhibited significantly higher degradation efficiency on Rhodamine B dye under natural sunlight irradiation conditions.

Unraveling the sigmoidal profiles in Fenton catalysis: Toward mechanistic elucidation

Fenton reactions are widely known and have been employed to degrade different pollutants in various environmental matrices. However, some controversies related to the Fenton mechanism remain unresolved. Although not comprehensively understood, kinetic sigmoidal profiles with an initial induction period have frequently been reported for Fenton systems. A thorough kinetic study was carried out at different temperatures involving Fenton reactions promoted by Fe3+ and Fe2+ and under the influence of radical scavengers. Catalysis supported by Fe2+ displayed the usual pseudo-first-order profile, while Fe3+ catalysis showed a sigmoidal pattern. The sigmoidal profiles were correlated to a pseudo-elementary autocatalytic mechanism developed by Finke and Watzky (F–W). The use of the F–W equation indicates that a certain amount of oxidative species must be generated to promote the substrate degradation. This correlation is a breakthrough in the understanding of Fenton catalysis.

Decomposition of atrazine by ionizing radiation: Kinetics, degradation pathways and influence of radical scavengers

Abstract This study reports the radiation-induced degradation of an extensively used carcinogenic, endocrine disrupting and persistent herbicide, atrazine, in aqueous solution. The atrazine degradation rate was directly proportional whereas the dose constant was inversely proportional to the irradiation dose rate and initial atrazine concentration. The second-order rate constant of atrazine with eaq− and H were found to be 3.70 × 109 and 4.84 × 108 M−1 s−1, respectively. Humic acid has synergistic whereas hydrogen peroxide and chloroform have an inhibitory impact on atrazine degradation. Atrazine degradation was reduced in the presence of 1 mM of each of NO3−, NO2−, Br−, SO42−, HCO3− and CO32− due to their competition for reactive radicals with atrazine. The attack of eaq− and OH on atrazine successfully mineralized the organic chlorine and nitrogen to chloride, nitrate and ammonium ions, in addition to the formation of acetate ions from carbon atoms of side chains. Potential detoxification of atrazine solution could be revealed from 83% loss of chloride ion at an absorbed dose of 4000 Gy. The findings of this study suggested that atrazine can efficiently be removed from water by gamma-ray irradiation even in the presence of organic and inorganic radical scavengers commonly found in natural water.

Degradation of thiocyanate in aqueous solution by persulfate activated ferric ion

Thiocyanate formation from cyanidation of gold bearing ores is becoming a more common problem during gold processing. In this work, the application of an advanced oxidation process based on the use of persulfate (S2O82−) as an environmentally friendly oxidant in the presence of ferric ion for destruction of a persistent and non-volatile inorganic contaminant, such as thiocyanate, in aqueous solutions is reported for the first time. The influence of various reaction parameters like ferric ion and persulfate dosage, initial thiocyanate concentration and the influence of radical scavenger are examined. An accelerated reaction using S2O82− to destroy thiocyanate can be achieved via chemical activation with Fe3+ to generate highly reactive sulfate anion-radicals (SO4−). The results showed that degradation efficiency was negligible when persulfate was used alone, ferric ions significantly improved the degradation efficiency of thiocyanate at ambient temperature. Under the optimum molar ratios ([S2O82−]:[SCN−]=5:1 and [S2O82−]:[Fe3+]=1:0.2), 99% of thiocyanate present in aqueous solution at the initial concentration range of 1.72–17.2mM was degraded within 60min of reaction time. To evaluate the contribution of reactive free radicals generated through Fe(III)-mediated activation of persulfate to thiocyanate degradation, quenching experiments using methanol as the radical quenching agent were carried out. The obvious decrease in thiocyanate oxidation efficiency in the presence of methanol confirmed that the radical-based pathway was the dominant mechanism in Fe3+/S2O82− system. The degradation of thiocyanate was accompanied by the formation of cyanide as the main final product of the reaction. Thus the catalytic oxidation of thiocyanate makes it possible to return NaCN into the production process for leaching of precious metals. The work presents an efficient and environmentally acceptable wastewater treatment process applicable in mining facilities utilizing cyanidation of sulfide ores and/or concentrates.

Degradation of TAIC by water falling film dielectric barrier discharge – Influence of radical scavengers

This work describes the application of plasma generated by water falling film dielectric barrier discharge for the degradation of triallyl isocyanurate (TAIC). The results indicated that TAIC solution of 1000mg/L was effectively removed within 60min treatment at 120W output power. Six intermediates were identified and a possible evolution of the TAIC degradation process was continuously proposed basing on the results of mass spectrum analysis. The effects of metal ions and radical scavengers were investigated. Results showed that whatever hydrogen radical scavengers (carbon tetrachloride, perfluorooctane) or hydroxyl radical scavengers (iso-propyl alcohol, tert-butyl alcohol) all could further enhance the degradation processes, and both kings of radical scavengers could promote the generation of H2O2. In the present study, we employed a novel method by introducing the mixed additives of Fe2+ and radical scavengers into the plasma. It was found that the reaction rate constant and energy efficiency were improved by 309.2% and 387.8%, respectively. Among the mixed additives, Fe2+ could promote the decomposition and increase the oxidizing power of H2O2, which is generated from the plasma discharge and greatly enhanced by the radical scavengers.

The enhancing effect of weak magnetic field on degradation of Orange II by zero-valent iron

The effects of weak magnetic field (WMF) on degrading Orange II by zero-valent iron (ZVI) as functions of pHini, ZVI dosages, and Orange II concentrations were investigated. The pseudo-first-order rate constants of Orange II removal by ZVI decreased progressively from 0.0057 to 0.0006 min−1 without WMF and from 0.0419 to 0.0039 min−1 with WMF, respectively, as pHini increased from 3.3 to 5.5. The pseudo-first-order rate constants of Orange II sequestration by ZVI were increased by 2.6- to 21-folds due to the application of WMF under the reaction conditions investigated in this study. The WMF-induced improvement in Orange II removal by ZVI was attributed to the accelerated corrosion of ZVI in the presence of WMF. The application of WMF not only improved the decolorization efficiency, but also enhanced TOC removal dramatically. The influence of radical scavenger and oxygen on Orange II removal as well as the FTIR analysis revealed that Orange II was removed via reduction by ZVI as well as adsorption/co-precipitation by the corrosion products. The method of employing WMF to enhance contaminants removal by ZVI is considered to be a promising technique in future water treatment since it does not need extra energy and costly reagents.

Photo degradation of Methyl Orange an azo dye by Advanced Fenton Process using zero valent metallic iron: Influence of various reaction parameters and its degradation mechanism

Advanced Fenton process (AFP) using zero valent metallic iron (ZVMI) is studied as a potential technique to degrade the azo dye in the aqueous medium. The influence of various reaction parameters like effect of iron dosage, concentration of H 2O 2/ammonium per sulfate (APS), initial dye concentration, effect of pH and the influence of radical scavenger are studied and optimum conditions are reported. The degradation rate decreased at higher iron dosages and also at higher oxidant concentrations due to the surface precipitation which deactivates the iron surface. The rate constant for the processes Fe 0/UV and Fe 0/APS/UV is twice compared to their respective Fe 0/dark and Fe 0/APS/dark processes. The rate constant for Fe 0/H 2O 2/UV process is four times higher than Fe 0/H 2O 2/dark process. The increase in the efficiency of Fe 0/UV process is attributed to the cleavage of stable iron complexes which produces Fe 2+ ions that participates in cyclic Fenton mechanism for the generation of hydroxyl radicals. The increase in the efficiency of Fe 0/APS/UV or H 2O 2 compared to dark process is due to continuous generation of hydroxyl radicals and also due to the frequent photo reduction of Fe 3+ ions to Fe 2+ ions. Though H 2O 2 is a better oxidant than APS in all respects, but it is more susceptible to deactivation by hydroxyl radical scavengers. The decrease in the rate constant in the presence of hydroxyl radical scavenger is more for H 2O 2 than APS. Iron powder retains its recycling efficiency better in the presence of H 2O 2 than APS. The decrease in the degradation rate in the presence of APS as an oxidant is due to the fact that generation of free radicals on iron surface is slower compared to H 2O 2. Also, the excess acidity provided by APS retards the degradation rate as excess H + ions acts as hydroxyl radical scavenger. The degradation of Methyl Orange (MO) using Fe 0 is an acid driven process shows higher efficiency at pH 3. The efficiency of various processes for the de colorization of MO dye is of the following order: Fe 0/H 2O 2/UV > Fe 0/H 2O 2/dark >Fe 0/APS/UV > Fe 0/UV > Fe 0/APS/dark > H 2O 2/UV ≈ Fe 0/dark > APS/UV. Dye resisted to degradation in the presence of oxidizing agent in dark. The degradation process was followed by UV–vis and GC–MS spectroscopic techniques. Based on the intermediates obtained probable degradation mechanism has been proposed. The result suggests that complete degradation of the dye was achieved in the presence of oxidizing agent when the system was amended with iron powder under UV light illumination. The concentration of Fe 2+ ions leached at the end of the optimized degradation experiment is found to be 2.78 × 10 −3 M. With optimization, the degradation using Fe 0 can be effective way to treat azo dyes in aqueous solution.

Different pyrolytic cleavage mechanisms of β-ether bond depending on the side-chain structure of lignin dimers

Influence of C γ–OH on pyrolytic cleavage mechanism of β-ether-linkage in lignin dimer was studied in N 2 with C γ-deoxy-type dimers, which have various p-substituents (–H, –Cl, –OCH 3) at their C β-phenoxy groups. Reactivities at 400 °C and the influence of radical scavenger (tetralin) indicated that C γ-deoxy types, especially in phenolic forms, are degraded through radical chain mechanism. Furthermore, substituent effects on their reactivities under excess amount of tetralin as discussed with Hammett's substituent constant ( σ p) and bond dissociation energy (BDE)-reducing parameter (ΔBDE) revealed that this chain reaction is initiated with the radical species formed through C β–O bond homolysis. These chain reactions were only effective in a closed-type reactor and not effective in an open-type reactor. Contrary to this, C γ–OH type in phenolic form was degraded at 250 °C, which is much lower than that (400 °C) of the C γ-deoxy types, and the reactivity was not influenced by tetralin. These results indicate that introducing OH at C γ changes the β-ether cleavage mechanism in phenolic form from radical chain to quinone methide mechanism.

Free Radicals in Reperfusion Injury After Acute Aortic Occlusion

This investigation aims to evaluate the role of free radicals and the influence of radical scavengers in reperfusion injury of the skeletal muscle in male Wistar rats. Various parameters, including tissue blood flow, serum and calf muscle tissue levels of thiobarbituric acid (TBA) reactants, and the water content of calf muscles, were measured in the experimental setting, where infrarenal abdominal aorta was occluded for two hours followed by reperfusion with and without intraperitoneal administration of radical scavengers (superoxide dismutase or catalase). The rats were divided into four groups: group A: single laparotomy; group B: two-hour occlusion; group C: two-hour occlusion with superoxide dismutase; group D: two-hour occlusion with catalase. The increases in both serum and calf muscle tissue levels of TBA reactants following reperfusion were diminished in groups C and D as compared with those in group B. The water content of calf muscles showed a significant increase after reperfusion in group B, whereas it did not change in group D. The calf muscle tissue blood flow after reperfusion was significantly lower in group C than that in group B. These results indicate that oxygen-derived free radicals may be responsible for reperfusion injury in the lower extremity and that the attenuated blood flow during reperfusion produced by these scavengers seems to play an important role in reducing lipid peroxidation . In a clinical setting, limiting the rate of reperfusion blood flow may reduce the reperfusion injury in skeletal muscle.

Spectra and Decay Kinetics of Diadamantyl-Dioxetane Chemiluminescence

Abstract The thermal decomposition of 1,2-diadamantyldioxetane was studied by kinetic and spectroscopic methods. Spectra of the chemiluminescence emitted during the thermally induced decomposition of 1,2-diadamantyldioxetane, tetramethyldioxetane and trimethyldioxetane were obtained and the influence of quenchers and radical-scavengers, and the presence of "heavy atoms" in the surrounding of the emitting species was investigated. The kinetics of the decay mechanism was followed by measuring the time dependence of the chemiluminescence. The influence of radical-scavengers, quenchers and "external heavy atoms" on the kinetics was assessed. Experimental results were discussed in terms of a biradical decay mechanism.

?-Radiolysis of liquid t-butyl hydroperoxide

The 60Co γ-radiolysis of liquid t-butyl hydroperoxide gives O2 as the principal gaseous product together with small amounts of H2, CH4, C2H6, C2H4(CH3)2CCH2 and CO. The liquid products are t-butanol, water, di-t-butyl peroxide, acetone and traces of t-butyl methyl ether and t-butyl methyl peroxide. A satisfactory material balance was obtained between the disappearance of the hydroperoxide (G–ButOOH= 33.7 at 20°C) and the yields of the products detected. G values have been measured over a range of radiation doses, dose rates and temperatures and the influence of radical scavengers has been examined. Nitrous oxide and benzene did not cause any changes in the product yields. The results indicate that radiolytic decomposition occurs predominantly in the hydroperoxy group, and they are discussed in terms of a mechanism which leads to a G value of 14.2 for direct radiolysis of the liquid hydroperoxide.