Adding Radical Scavengers Research Articles

Preparation of a novel BiVO4-Ni(Ⅱ)/g-C3N4 bifunctional photo electrocatalyst for oxidative and absorptive desulfurization of model fuel

This investigation aims to remove sulfur-based compounds (SBCs) by a combination of absorptive and oxidative desulfurization processes. Accordingly, a series of novel Bi-based bifunctional photo electrocatalysts is prepared by thermal method and used to remove dibenzothiophene (DBT) as a source of SBC from n-heptane as model fuel. The catalysts are used in photo electrocatalytic, photocatalytic, and electrocatalytic desulfurization systems and their effect on oxidative and absorptive processes is compared. The catalysts showed higher efficiency in absorptive desulfurization (ADS) by electrocatalytic desulfurization (EDS) and better results in oxidative desulfurization (ODS) by photocatalytic desulfurization (PDS). Among the results, photoelectrocatalytic desulfurization (POEDS) performed best in DBT removal (94%). The catalyst characterization was carried out with various analyses such as XPS, Raman, FTIR, DRS, TGA, FESEM, TEM, and chronoamperometry. The effect of adding radical scavengers on desulfurization was studied to determine the reaction mechanism. The stability of the selected catalyst is examined by repeating the reaction under optimum reaction conditions.

Carbon nanotube-based electrocatalytic filtration membrane for continuous degradation of flow-through Bisphenol A

Endocrine disruptors (EDCs) are a group of persistent and toxic organic pollutants which can pose a significant threat to human endocrine system. Developing novel technique for contaminants removal or degradation is urgently needed. In this study, a three-dimensional porous membrane was fabricated based on the self-assembly of carbon nanotubes coated with bismuth-doped tin dioxide (Bi-SnO2) nanoparticles. The prepared Bi-SnO2/CNTM was evaluated for treatment of aqueous EDCs using Bisphenol A (BPA) as a model compound. The effect of Bi-SnO2 coating was proved with respect to enhanced BPA removal performance compared with pure CNTM. Furthermore, through in-depth investigation of generated intermediates during degradation process, the BPA degradation pathways were identified. The electrochemical degradation mechanism was also explored by adding radical scavengers and ·OH was determined to be prominent active radical for electrocatalytic degradation. These results indicate the potential of Bi-SnO2/CNTM to continuously and effectively treat EDCs residue in aquatic environment by a flow-through system.

Behaviour of magnesium phosphate cement-based materials under gamma and alpha irradiation

Stabilization and solidification of low- and intermediate-level radioactive waste using Portland cement, possibly blended with fly ash or blastfurnace slag, is a well-established practice. However, when the waste contains high amounts of alpha emitters, this solution can be restricted by the strong release of radiolytic gases, wherein H2 is the most abundant. This work investigates the interest of using magnesium potassium phosphate cement (MPC), a binder with a high chemical water demand, as a possible substitute to Portland cement (PC). The radiolytic gas production of PC and MPC pastes and mortars is determined under external gamma and internal alpha irradiation. The H2 radiolytic yield of MPC materials is found to be 2 to 3 times smaller than that of PC references, provided that the main part of the mixing water is consumed by K-struvite formation. Moreover, gamma irradiation of a MPC mortar up to an integrated dose of 10 MGy has no significant influence on its mechanical strength (flexural, compressive) nor on its mineralogy. MPC materials are thus potential candidates for the conditioning of high amounts of radioactivity with limited H2 release. The H2 production of MPC materials can be reduced further by adding radical scavengers or H2 getters within the matrix. However, other radiolytic gases such as O2 are often produced, making these solutions potentially less attractive considering the concern of pressure build-up within the cemented waste package.

Screening of heterogeneous catalysts for the activated persulfate oxidation of sulfamethoxazole in aqueous matrices. Does the matrix affect the selection of catalyst?

AbstractBACKGROUNDThe contribution of persulfate oxidation to water treatment technologies based on advanced oxidation processes is nowadays widely accepted. However, the importance of the water matrix on the removal of micropollutants has been neglected during early screening of heterogeneous catalysts, which can hinder further developments in the field.RESULTSThree magnetic graphitic nanocomposites (MGNCs), obtained by carbon encapsulation of magnetite (Fe3O4), nickel ferrite (NiFe2O4) and cobalt ferrite (CoFe2O4), were prepared and employed as heterogeneous catalysts in the activation of persulfate for the degradation of antibiotic sulfamethoxazole (SMX). The importance of the water matrix and its constituents on the performance of the MGNC materials was assessed. It was found that their relative performance in terms of oxidation of SMX in pure water decreases in the order: NiFe2O4/MGNC > Fe3O4/MGNC > CoFe2O4/MGNC. However, the order changed (Fe3O4/MGNC > NiFe2O4/MGNC > CoFe2O4/MGNC) when drinking water or secondary treated wastewater were employed. The individual effects of the water matrix constituents, such as bicarbonate, chloride, pH, and humic acid, or the use of added radical scavengers, on the catalyst performance were investigated, while the heterogeneous nature of the process was confirmed through leaching tests.CONCLUSIONA realistic water matrix should be considered throughout all the steps involved in the evaluation of new heterogeneous catalysts for the activated persulfate oxidation of SMX. Otherwise, misleading conclusions may be drawn, limiting potential improvements of this treatment technology. © 2019 Society of Chemical Industry

Degradation of glucocorticoids in aqueous solution by dielectric barrier discharge: Kinetics, mechanisms, and degradation pathways

Performance and mechanism of non-thermal plasma (NTP) technology in removing glucocorticoids (GCs) was investigated using a dielectric barrier discharge (DBD) reactor with fluocinolone acetonide (FA), triamcinolone acetonide (TA) and clobetasol propionate (CP) as representative compounds. Effects of discharge power, plasma-working gases, initial pH, coexistence of ions, and various water matrices (ultrapure water, lake water, drinking water, wastewater effluent) on GC removal and energy yield were evaluated. The results confirm that DBD treatment could efficiently remove FA, TA, and CP, achieving efficiency of 72% (k = 0.0126 min−1), 71% (k = 0.0096 min−1), and 74% (k = 0.0116 min−1), respectively in air-DBD system at 45.2 W, with the process following the first order kinetics and energy yield of 6 mg kW−1h−1. The removal efficiency decreased when adding radical scavengers, indicating that hydroxyl radicals played an important role in GC degradation, while other active species (such as solvated electrons (eaq−), ozone (O3), hydrogen peroxide (H2O2) and ultraviolet photolysis (UV)) also contribute to GC degradation. The intermediates generated during the process were analyzed using quadrupole time-of-flight mass spectrometry (QTOF-MS). A total of 23 transformation products of FA, TA and CP were identified, and it was noted that substitution of halogen atoms with OH, oxidation of hydroxyl group to keto acid, decarboxylation of the keto acid, addition of OH, intramolecular cyclization, and hydrolysis of esters occurred during GC degradation by DBD treatment.

Visible-light-driven photocatalytic degradation of 4-CP and the synergistic reduction of Cr(VI) on one-pot synthesized amorphous Nb2O5 nanorods/graphene heterostructured composites

In this study, Nb2O5 nanorods/graphene composites (NbO NRs/GR) are prepared by one-pot alkaline hydrothermal process, utilizing the new roles of graphene oxide (GO) as the structure-directing and morphology-controlling agent for the growth of NbO NRs. Compared to blank NbO, NbO/GR composites exhibit significantly improved photocatalytic activity for 4-CP degradation under visible-light irradiation, although 4-CP and NbO do not absorb visible light themselves. The in-situ formation of surface complexes between 4-CP and NbO and the subsequent charge transfer based on LMCT mechanism can be responsible for the visible photocatalytic activity. And meanwhile, the photoelectrons transferred to GR surface from in-situ formed complex (NbO/4-CP) via NbO NRs can initiate the synergistic Cr(VI) reduction. The GR contents and NbO crystalline phase have great effects on the photocatalytic activity of NbO/GR composites toward simultaneous 4-CP degradation and Cr(VI) reduction. The amorphous NbO/GR composite with 4.0 wt% GR (NbO-400/GR-4.0%) shows the highest photocatalytic activity. The influences of various experimental conditions (including the surface fluorination of NbO/GR, the initial concentrations of 4-CP and Cr(VI), pH, reaction atmosphere, and adding radical scavengers) on the visible photocatalytic activities are investigated in detail. According to the catalytic activity, UV-vis DRS and FT-IR spectra of NbO/4-CP or NbO/GR/4-CP, and photocurrent response in aqueous 4-CP solution, the formation of the surface complex is evidenced and the visible-light catalytic mechanism based on LMCT process is proposed.

Bromate formation during the oxidation of bromide-containing water by ozone/peroxymonosulfate process: Influencing factors and mechanisms

Previously, we proposed a novel advanced oxidation process combining ozone (O3) with peroxymonosulfate (PMS), which simultaneously produces sulfate radical (SO4−) and hydroxyl radical (OH) and significantly enhances the removal of organic matter. However, bromate formation is poorly understood during the oxidative treatment of bromide-containing water by O3/PMS process. In this study, factors influencing bromate formation were explored during the O3/PMS process, including the influences of solution pH, PMS dosage, and bromide concentration in distilled water and in actual water samples. Furthermore, the bromate formation mechanism was also clarified by monitoring the intermediate hypobromous acid (HOBr/OBr−), calculating the change of bromide species at different pH levels, and was further confirmed by adding radical scavengers. Generally, the O3/PMS process significantly promotes bromate formation compared with ozone treatment alone. During the O3/PMS process, increasing the PMS dosage and bromide concentrations promoted bromate formation, which was also significantly improved by raising the pH from 4.0 to 10.0. Bromate formation was a result of the combined effect of molecular ozone, OH, and SO4−, and the HOBr/OBr− was the essential intermediate species. Bromate formation was inhibited in the actual water sample due to the competitive effect of natural organic matter, bicarbonate, and reaction of HOBr/OBr− with ammonia. Therefore, the bromate formation should be evaluated as applying the O3/PMS process for organic matters abatement in bromide-containing actual water.

Detection and scavenging of hydroxyl radical via D-phenylalanine hydroxylation in human fluids

Hydroxyl radical (.OH) is highly reactive, and therefore very short-lived. Finding new means to accurately detect .OH, and testing the ability of known .OH scavengers to neutralize them in human biological fluids would leverage our ability to more effectively counter oxidative (.OH) stress-mediated damage in human diseases. To achieve this, we pursued the evaluation of secondary products resulting from .OH attack, using a detection system based on Fenton reaction-mediated D-phenylalanine (D-Phe) hydroxylation. This reaction in turn generates o-tyrosine (o-tyr), m-tyrosine (m-tyr) and p-tyrosine (p-tyr). Here, these isomers were separated by HPLC, equipped with fluorescence detectors due to the natural fluorescence of these hydrotyrosines. By extension, we found that, adding radical scavengers competed with D-Phe on .OH attack, thus allowing to determine the .OH quenching capacity of a given compound expressed as inhibition ratio percent (IR%). Using a kinetic approach, we then tested the .OH scavenging capacity (OHSC) of well-known antioxidant molecules. In a test tube, N,N′-dimethylthiourea (DMTU) was the most efficient scavenger as compared to Trolox and N-Acethyl-L-cysteine, with NAC being the less effective. OHSC assay was then applied to biological fluid samples as seminal plasma, human serum from normal subjects and patients undergoing hemodialysis (HD), colostrum and human breast milk from mothers that received daily doses of 30g of chocolate (70% cocoa) during pregnancy. We found that a daily administration of dark chocolate during pregnancy almost doubled OHSC levels in breast milk (1.88 ± 0.12 times, p < 0.01). Furthermore, HD treatment determined a significant reduction of serum OHSC concentration (54.63 ± 2.82%, p < 0.001). Our results provide evidence that Fenton reaction-mediated D-Phe hydroxylation is a suitable method for routine and non-invasive evaluation of .OH detection and its scavenging in human biological fluids.

Hydrogen peroxide kinetics in water radiolysis

The kinetics of the formation and reaction of hydrogen peroxide in the long time γ- radiolysis of water is examined using a combination of experiment with model calculations. Escape yields of hydrogen peroxide on the microsecond time scale are easily measured with added radical scavengers even with substantial amounts of initial added hydrogen peroxide. The γ-radiolysis of aqueous hydrogen peroxide solutions without added radical scavengers reach a steady state limiting concentration of hydrogen peroxide with increasing dose, and that limit is directly proportional to the initial concentration of added hydrogen peroxide. The dose necessary to reach that limiting hydrogen peroxide concentration is also proportional to the initial concentration, but dose rate has a very small effect. The addition of molecular hydrogen to aqueous solutions of hydrogen peroxide leads to a decrease in the high dose limiting hydrogen peroxide concentration that is linear with the initial hydrogen concentration, but the amount of decrease is not stoichiometric. Proton irradiations of solutions with added hydrogen peroxide and hydrogen are more difficult to predict because of the decreased yields of radicals; however, with a substantial increase in dose rate there is a sufficient decrease in radical yields that hydrogen addition has little effect on hydrogen peroxide decay.

Efficient and recyclable Cu2(BPDC)2(DABCO)-catalyzed direct amination of activated sp3 C[sbnd]H bonds by N–H heterocycles

A metal-organic framework Cu2(BPDC)2(DABCO) was successfully synthesized and employed as an efficient heterogeneous catalyst for the direct CN cross-coupling reaction via sp3 CN bond activation between N–H heterocycles and amides. Kinetic investigation was thoroughly conducted. The optimal conditions involve the use of Cu2(BPDC)2(DABCO) catalyst (3%), di-tert-butyl peroxide oxidant (2 equivalents) in chlorobenzene solvent at 120°C in 2h. The Cu2(BPDC)2(DABCO) offered higher catalytic activity than that of other Cu-MOFs such as Cu2(BPDC)2(BPY), Cu3(BTC)2 and Cu2(BDC)2(DABCO), and that of several common copper salts such as CuCl, CuBr, CuI, Cu(NO3)2, and CuSO4. To investigate the mechanism, catalyst poisoning experiments and reactions with added radical scavengers were conducted. Furthermore, the catalyst could be recovered and reused several times without much decline in the reaction yield.

Syntheses, characterization and biological activities of rare earth metal complexes with curcumin and 1,10-phenanthroline-5,6-dione

Three new solid complexes have been synthesized by the reaction of rare earth(III) nitrate with the first ligand curcumin (HL) and the second ligand 1,10-phenanthroline-5,6-dione (L') in alcohol solution (pH=6.5-7.0). The composition of the complexes has been characterized by elemental analysis, molar conductivity, thermogravimetric analysis, IR, UV-vis methods. The results reveal that beta-diketone group of the first ligand to coordinates with rare earth ions in bidentate mode after deprotonated. But the second ligand uses its two N atoms coordinates with rare earth ions in bidentate mode. The general formula of the complexes is REL(3)L' (RE=Sm, Eu, Dy). The results of antibacterial activity indicated that the complexes have excellent antibacterial ability for the testing bacterium than that of curcumin. The result of agarose gel electrophoresis suggested that the complex of SmL(3)L' can cleave the plasmid DNA at physiological pH and temperature. And it was found that the cleavage process of plasmid DNA was sensitive to pH, however, adding radical scavengers almost had no effect on the DNA cleavage reaction, therefore, the cleavage of DNA by SmL(3)L' does not produce diffusible hydroxyl radicals via the Fenton reaction.

Hydroxyl radical scavenging assay of phenolics and flavonoids with a modified cupric reducing antioxidant capacity (CUPRAC) method using catalase for hydrogen peroxide degradation

Hydroxyl radicals ( OH) generated in the human body may play an important role in tissue injury at sites of inflammation in oxidative stress-originated diseases. As a more convenient, efficient, and less costly alternative to HPLC/electrochemical detection techniques and to the nonspecific, low-yield deoxyribose (TBARS) test, we used a salicylate probe for detecting OH generated by the reaction of iron(II)–EDTA complex with H 2O 2. The produced hydroxyl radicals attack both the salicylate probe and the hydroxyl radical scavengers that are incubated in solution for 10 min. Added radical scavengers compete with salicylate for the OH produced, and diminish chromophore formation from Cu(II)–neocuproine. At the end of the incubation period, the reaction was stopped by adding catalase. With the aid of this reaction, a kinetic approach was adopted to assess the hydroxyl radical scavenging properties of polyphenolics, flavonoids and other compounds (e.g., ascorbic acid, glucose, mannitol). A second-order rate constant for the reaction of the scavenger with OH could be deduced from the inhibition of colour formation due to the salicylate probe. In addition to phenolics and flavonoids, five kinds of herbs were evaluated for their OH scavenging activity using the developed method. The modified CUPRAC (cupric ion reducing antioxidant capacity) assay proved to be efficient for ascorbic acid, gallic acid and chlorogenic acid, for which the deoxyribose assay test is basically nonresponsive. An important contribution of this developed assay is the inhibition of the Fenton reaction with catalase degradation of hydrogen peroxide so that the remaining H 2O 2 would neither give a CUPRAC absorbance nor involve in redox cycling of phenolic antioxidants, enabling the rapid assay of polyphenolics.

DNA-Binding and Cleavage Studies of Zinc(II) Mixed-polypyridyl Complex

The complex of Zn[(phen)(dione)Cl]ClO4·H2O (where phen is 1,10-phenanthroline and dione is 1,10-phenanthroline-5,6-dione) has been synthesized and characterized. The interaction of the complex with DNA was investigated using UV absorption, fluorescence spectroscopy and electrophoresis measurements. The results show that the complex mainly binds to the double helix of DNA with intercalation mode and the binding constant K is 2.4×104 mol−1·L. Moreover, the complex can efficiently cleave plasmid DNA at physiological pH and temperature. The cleavage occurs via a hydrolysis mechanism, which is showed by adding radical scavengers, rigorously anaerobic experiments, analysis for malondialdehyde-like products, and the hydrolysis experiment of BDNPP with a rate constant kobs of 5.3×10−6 s−1.

A simple copper(II)-L-histidine system for efficient hydrolytic cleavage of DNA.

Copper(II)-L-histidine complexes effectively promote the cleavage of plasmid DNA and dideoxynucleotide dApdA at physiological pH and temperature. Studies of the mechanism of plasmid DNA cleavage by added radical scavengers, using rigorously anaerobic experiments, analyses for malondialdehyde-like products, religation assays, and HPLC analyses, indicate that DNA cleavage mediated by Cu(L-His) occurs via a hydrolytic path. The hydrolytic cleavage rate constants at 37 degrees C are estimated to be 0.76 h-1 for the decrease of form I and 0.25 h-1 for the increase of form III. The phosphoimager picture reveals that Cu(L-His) cleaves DNA with a certain sequence specificity (preferentially at 5'-GT-3'). The dinucleotide hydrolysis shows, with [Cu(L-His)] = 0.8 mM, rate enhancement factors of > 10(8). Interestingly, histidine-metal ion interactions (with Cu(II), Ni(II), Zn(II), etc.) have been used for various applications, e.g., protein purification, cross-linking, and targeting proteins to lipid bilayers. Our findings may provide the basis for developing new applications and new ways to design more effective and useful catalysts for DNA cleavage. Cu(L-His) is one of only a few well-defined metal complexes demonstrated to hydrolytically cleave dideoxynucleotides and DNA.

Hematoporphyrin-sensitized degradation of deoxyribose and DNA in high intensity near-UV picosecond pulsed laser photolysis

The photosensitized degradation of deoxyribose and DNA, using hematoporphyrin (HP) and picosecond laser pulses at high intensities (pulse duration 30 ps, λ exc = 355 nm, light intensity range 10 8–10 10W/cm 2) was studied. Aldehyde formation from 2-deoxy- d-ribose and long-chain double-stranded DNA, when analyzed as a function of light intensity, followed a non-linear dependence, suggesting the involvement of multiphoton light absorption by HP. The degradation mechanism was studied by analysis of the yield dependence on excitation intensity and the effect of added radical scavengers. The participation of OH radicals in the degradation process was confirmed by spin trapping techniques. At low light intensities added N 2O largely increased product formation, suggesting that HP photoionization predominates under these conditions. At higher intensities (I ≥ 3 GW/cm 2) the product yield was not affected by N 2O which, combined with spin trapping data, suggested that OH radical formation occurred, but that neither HP photoionization nor peroxy radical formation was involved. Single and double strand breaks in supercoiled plasmid DNA (pBR 322) confirmed the generation of OH or OH-like radicals during high-intensity excitation of HP. A mechanism involving a multistep excitation of HP, followed by resonance energy transfer to H 2O resulting in dissociation to yield OH and H atoms, is proposed.

Radiolysis of water vapor and a surface-catalyzed isotope-exchange reaction

The steady-state radiolysis of deuterium oxide vapor has been examined using protium, perprotiopropane, or mixtures of these two as free-radical scavengers. Tritiated water was used as an internal radiation source, and glass irradiation vessels were employed. D atoms are produced in the radiolytic decomposition of D/sub 2/O, and HD is formed by reaction of this species with the added radical scavengers. It was assumed previously that the yield of HD molecules could be equated with the yield of radiolytically produced D atoms. However, the experimental results of the present investigation demonstrate conclusively that when H/sub 2/ is used as a radical scavenger there are two pathways for HD formation: (1) homogeneous scavenging of the radiolytically produced D atoms by H/sub 2/, as expected, and (2) heterogeneous combination of H atoms produced in the scavenging reaction (D + H/sub 2/ ..-->.. HD + H) with D atoms absorbed on the vessel surface, where the adsorbed D atoms are generated by a surface-catalyzed isotope-exchange reaction between H atoms adsorbed from the volume and D/sub 2/O. From the results of this investigation, it appears that the yield of D atoms produced in the radiolysis of D/sub 2/O is G/sub D/ = 7.0 atoms/100more » eV absorbed energy, i.e., the G(HD) found in experiments using propane as the radical scavenger. G/sub D/sub 2// is shown to be 0.65 molecules/100 eV.« less