Role Of Active Oxygen Species Research Articles

Synthesis and application of ZSM-5/Graphene composite for photocatalytic degradation of industrial dyes

Various materials and technologies are being employed to address the concern of increased wastewater generation. In this work, the synthesis of ZSM-5 (Zeolite Socony Mobil-5) and graphene (GR) composite, their characterisation, and application for the removal of dyes are presented. Two composites of ZSM-5 and GR composites were prepared via the hydrothermal method by varying the loading amount of GR, i.e. 1% and 5%, and labelled as GZ1 and GZ5. The parent and composite materials were characterised using field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), x-ray photoelectrons spectroscopy (XPS), Raman, and Fourier transform infrared (FTIR). The materials were then employed for the photodegradation of methyl orange (MO) dye. The adsorption efficiencies for ZSM-5, GR, GZ1, and GZ5 were found as 0%, 17.8%, 0%, and 16% respectively. According to photodegradation results, the GZ1 composite exhibits the maximum degradation efficiency of 75.3% for 20 ppm of MO, within 180 min of light exposure. The scavenger studies were performed to evaluate the role of active oxygen species (AOS) in the photocatalysis mechanism. All studies were performed with the catalyst dosage of 0.5 mg ml−1. The degradation efficiencies for GR, GZ5, and Z5 were reported as 34.2%, 20.8%, and 17.5%, respectively. On increasing the irradiation time to 240 min, the degradation efficiency of GZ1 reached 92%. The removal efficiencies for MO (7 ppm) and methyl blue (5 ppm) in a 12-ppm dye mixture were observed to be 98% and 97.2% respectively within 180 min of light exposure with GZ1 composite.

Elucidating the role of active oxygen species and hydroxyl groups in the furfural base-free oxidation to furoic acid over δ-MnO2

δ-MnO2 shows potential application in furfural base-free oxidation to furoic acid. While, its catalytic mechanism was unclear, which limited the further improvement of the catalytic activity. Therefore, three δ crystal MnO2 with different hydroxyl and active oxygen species concentrations were prepared and applied in the furfural oxidation reaction. IR, Furfural-IR, O2-TPD, H2O-18O2-TPD, and XPS techniques characterized the hydroxyl and active oxygen species. The results show that the hydroxyl group on δ-MnO2 is important in absorbing and attacking furfural to form geminal diol intermediate. Moreover, two types of oxygen species O-OH and Oads originating from the surface hydroxyl and the strongly adsorbed gas-phase O2, respectively, play an essential role in defhydrogenating geminal diol to furoic acid. Most importantly, the hydroxyl, O-OH, and Oads consumed on δ-MnO2 can be reconstructed under reaction conditions. Among the three δ crystal MnO2, δ-MnO2, with the most abundant hydroxyl and active oxygen species, exhibited the best catalytic performance with 99.53% furfural conversion and nearly 100% furoic acid selectivity. This work identifies the function of hydroxyl and active oxygen species on δ-MnO2 in furfural oxidation reaction, guiding the design of a non-noble metal catalyst for furoic acid synthesis under base-free conditions.

Role of active oxygen species in Fe-doped ZrO2 catalyst during CO2 assisted ethane dehydrogenation reaction

CO2 assisted ethane dehydrogenation provides a promising route for the utilization of shale gas and greenhouse gas. This study investigates the role and evolution of active oxygen species over Fe-doped ZrO2 catalysts in distinct dehydrogenation reactions via Mars-van Krevelen mechanism. Fe doping led to an increase in active oxygen species (from 12.9% to 23.4%) benefitted from the phase transformation of ZrO2. This enhancement significantly boosted ethane dehydrogenation activity from 5.0 to 16.1 mmolEthene/gCat/h. In the absence of CO2, the ethane conversions rapidly decreased with a deactivation rate constant (kd) of 0.930 h−1 due to the irreversible oxygen species loss and coke deposition. Although the catalytic stability of the optimal catalyst was greatly improved (kd = 0.006 h−1) after CO2 introduction, a decrease in ethane conversion occurred when CO2 could not supplement oxygen species due to the formation of coke layers. A simple O2 oxidation can effectively restore stable activity during 5 reaction-regeneration cycles for 3600 mins.

Modulating active oxygen species on α-MnO2 with K and Pb for SCR of NO at low temperatures

In this study, a completely new mechanism for the effect of K and Pb on α-MnO2 was proposed. The findings provide valuable insights on the roles of active oxygen species and oxygen vacancies in the low-temperature SCR process.

Graphene oxide supported sulfidated nano zero-valent iron (S-nZVI@GO) for antimony removal: The role of active oxygen species and reaction mechanism

Sulfidated nano zero-valent iron (S-nZVI) was used to remove various pollutants from wastewater. However, the instability, poor dispersibility, and low electron transfer efficiency of S-nZVI limit its application. Herein, graphene oxide supported sulfidated nano zero-valent iron (S-nZVI@GO) was successfully synthesized using graphene oxide (GO) as a carrier. The properties of S-nZVI@GO were characterized by scanning electron microscopy coupled to X-ray photoelectron spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) concerning the surface morphology, crystalline structure, and elemental components. S-nZVI@GO displayed an excellent capacity for antimony (Sb) removal under aerobic conditions (96.7%), with a high adsorption capacity (Qmax = 311.75 mg/g). It maintained a high removal rate (over 90%) during a wide pH range (3–9). More importantly, S-nZVI@GO activated the molecular oxygen in water via a single-electron pathway to produce •O2－ and H2O2, and then oxidized trivalent antimony (Sb(III)) to pentavalent antimony (Sb(V)) and further separated it by synergistic adsorption and co-precipitation. Therefore, S-nZVI@GO shows excellent potential for Sb contamination remediation.

Unveiling the Role of Active Oxygen Species in Oxidative Dehydrogenation of Ethane with CO2 over NiFe/CeO2

AbstractThe oxidative dehydrogenation of ethane (ODH) assisted by CO2 to produce ethylene is inevitably accompanied by the side reaction of dry reforming (DRE) to produce carbon monoxide. However, the key factor determining the dehydrogenation selectivity is still ambiguous. In this paper, four different NiFe/CeO2 catalysts were synthesized via an impregnation method over four types of CeO2. The dehydrogenation selectivity of the four catalysts ranged from 40 % to 83 %. Temperature‐programmed surface reaction and transient response experiments reveal the existence of two types of oxygen species over NiFe/CeO2 catalysts. FeOx layers exist as an oxygen species supply buffer over CeO2 supports. Weakly electrophilic oxygen species supplied by FeOx overlayers could participate in producing C2H4 while strong electrophilic oxygen species supplied by CeO2 supports could participate in producing CO. The content of weakly electrophilic oxygen species is identified to be a rational descriptor of C2H4 selectivity.

Theoretical insights into the roles of active oxygen species in heterogeneous oxidation of CO over Mn/TiO2 catalyst

Quantum chemistry calculations were performed to reveal the roles of the active oxygen species in the CO oxidation and the interactions between the gaseous molecules (CO, O2, CO2, etc.) and the active sites to design a highly active and low-temperature Mn/TiO2 catalyst. The results show that the Ti5a-O2b-Mn5c (TOM) coordination structure is the active center for the chemisorption of CO and O2. The dominant cycles were proposed over the TOM structure, which consist of three reaction stages, i.e., first CO oxidation → surface re-oxidation → second CO oxidation. Two kinds of active oxygen species, i.e., the lattice oxygen of TOM and the two atomic oxygen formed during the surface re-oxidation process, play critical roles in the dominant CO oxidation cycles. The energy barriers of the dominant oxidation cycles are lower than 50 kJ/mol, which explain well the high low-temperature activity of Mn/TiO2 catalyst for CO abatement.

Diesel Soot Combustion over Mn2O3 Catalysts with Different Morphologies: Elucidating the Role of Active Oxygen Species in Soot Combustion

Catalytic diesel soot combustion was examined using a series of Mn2 O3 catalysts with different morphologies, including plate, prism, hollow spheres and powders. The plate-shaped Mn2 O3 (Mn2 O3 -plate) exhibited superior carbon soot combustion activity compared to the prism-shaped, hollow-structured and powdery Mn2 O3 under both tight and loose contact modes at soot combustion temperatures (T50 ) of 327 °C and 457 °C, respectively. Comprehensive characterization studies using scanning electron microscopy, scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction and oxygen release measurements, revealed that the improved activity of Mn2 O3 -plate was mainly attributed to the high oxygen release rate of surface-adsorbed active oxygen species, which originated from oxygen vacancy sites introduced during the catalyst preparation, rather than specific surface-exposed planes. The study provides new insights for the design and synthesis of efficient oxidation catalysts for carbon soot combustion as well as for other oxidation reactions of harmful hydrocarbon compounds.

Formation of active oxygen species on single-atom Pt catalyst and promoted catalytic oxidation of toluene

Catalytic oxidation of toluene over noble metal catalysts is a representative reaction for elimination of volatile organic compounds (VOCs). However, to fully understand the activation of molecular oxygen and the role of active oxygen species generated in this reaction is still a challenging target. Herein, MgO nanosheets and single-atom Pt loaded MgO (Pt SA/MgO) nanosheets were synthesized and used as catalysts in toluene oxidation. The activation process of molecular oxygen and oxidation performance on the two catalysts were contrastively investigated. The Pt SA/MgO exhibited significantly enhanced catalytic activity compared to MgO. The oxygen vacancies can be easily generated on the Pt SA/MgO surface, which facilitate the activation of molecular oxygen and the formation of active oxygen species. Based on the experimental data and theoretical calculations, an active oxygen species promoted oxidation mechanism for toluene was proposed. In the presence of H2O, the molecular oxygen is more favorable to be dissociated to generate •OH on the oxygen vacancies of the Pt SA/MgO surface, which is the dominant active oxygen species. We anticipate that this work may shed light on further investigation of the oxidation mechanism of toluene and other VOCs over noble metal catalysts.

Selective removal of CO from hydrocarbon-rich industrial off-gases over CeO2-supported metal oxides

For the selective removal of CO in the off-gas streams from real-life chemical processes, the interfacial interaction between the support and the active metal oxides and the role of active oxygen species are two fascinating problems. Herein, a series of CeO2-supported metal oxide catalysts were synthesized by co-precipitation method and employed for the selective removal of CO from the off-gas stream of propane oxidation process. CuO/CeO2 catalyst exhibits full CO conversion and 100% selectivity for CO removal in off-gas stream within a rather wide temperature window of 140–190 °C, being relatively stable in 200-h long-term time-on-stream experiment. Raman spectra, H2-TPR, CO-TPD and XPS spectra studies revealed that the redox properties and the concentration of active oxygen species varied with supported metal oxide compositions, for which CuO/CeO2 catalyst exhibited the highest surface oxygen vacancy concentration, good low-temperature reduction behavior and the highest adsorption capacity of CO, thus resulting in advanced CO removal performance. This study presents a strategy to design a promising CeO2-supported catalyst for oxidation removal of CO from off-gas of alkane oxidation process.

Photo-assisted activation of H2O2 over Nb2O5 – The role of active oxygen species on niobia surface in photocatalytic discoloration of Rhodamine B

The influence of hydrogen peroxide on the efficiency of Rhodamine B (RhB) photooxidation over Nb2O5, which exhibits unique ability to generate strongly oxidative species both upon irradiation with UV light and upon treatment with hydrogen peroxide, was investigated. According to the results, niobia displays low activity in RhB discoloration by photocatalytic and Fenton-like processes, but the efficiency of the reaction is greatly improved when both advanced oxidation processes are combined. The tests with the use of various reactive oxygen species scavengers revealed that the crucial species responsible for the improved efficiency of RhB discoloration in the hybrid process were superoxide radical anions (O2•−) and singlet oxygen (1O2). It was documented that the former species exhibited low activity in RhB discoloration, but they were the precursors of the latter species, which played the key role in the dye discoloration.

The effects of estradiol and testosterone on renal tissues oxidative after central injection of angiotensin II in female doca - salt treated rats.

Background Although numerous studies have proven that estrogen (Est) has a protective effect on the development of hypertension, more research needs to be done to show its detailed mechanism in a variety of hypertension. The important role of active oxygen species in blood pressure is well defined. We examined whether or not sex hormones change the growth of reactive oxygen species (ROS) ‎in kidneys after central microinjection of angiotensin II (Ang II).‎ Materials and methods Female Wistar rats, 8 weeks old (200 ± 10 g) were used in this study. The animal groups were (1) Sham, (2) Ovariectomy (OVX), (3) Sham-Hypertension (Sham-Hyper), (4) OVX-Hypertension (OVX-Hyper), (5) Sham-Hyper-Est, (6) OVX-Hyper-Est‎;‎ (7) Sham-Hyper-Testosterone (Tst) and (8) OVX-Hyper-Tst. Solutions of 1% NaCl and 0.1 KCl ‎were used and desoxycorticostrone (doca-salt) was injected (45 mg/kg) 3 times a week in Hypertension groups. Estradiol and Tst (2 mg/kg and ‎5 mg/kg‎; daily; subcutaneously) for 4 weeks. Ang II (50 μM, 5 μL) was microinjected by intracerebroventricular ( i.c.v.) infusion and malondialdehyde (MDA) and thiol in the kidneys were measured. Results MDA in the kidneys was increased by Ang II and doca-salt treatments. Both estradiol and Tst decreased the kidney's MDA. The level of thiol was higher in Hyper ‎groups and reversed after treatment with estradiol and Tst. Conclusions Our findings suggest that central effect of Ang II on blood pressure and kidney ‎disease is accompanied with increased levels of oxidative stress in the kidneys. Indeed sex hormones change the ROS level in the kidneys after central ‎microinjection of Ang II.‎‎.

Insights on germinability and desiccation tolerance in developing neem seeds (Azadirachta indica): Role of AOS, antioxidative enzymes and dehydrin-like protein

The germinability and desiccation tolerance (DT) in developing seed are regulated by cellular metabolism involving active oxygen species (AOS) and protective proteins during maturation drying. The aim of the present investigation was to unravel the functions of AOS (superoxide, H2O2 and OH-radical), antioxidative enzymes (SOD, CAT and APX) and dehydrin-like proteins in regulating the germinability and DT in undried and artificially desiccated developing neem seeds. Germination was first observed in seeds of 8 weeks after anthesis (waa) whereas DT was noticed from 9 waa. High levels of superoxide in undried and artificially desiccated seeds of 9 waa were rapidly declined up to 15 waa with simultaneous increase in levels of SOD (quantitative and isoenzymes) that dismutates superoxide with corresponding formation and accumulation of H2O2. Activities and isoenzymes of APX and CAT were promoted in seeds from 9 to 12 waa. Intensity of dehydrin-like proteins increased as development progressed in seeds with higher intensities in slow dried (SD) seeds. Desiccation modulated the metabolism for the acquisition of germinability and DT in the developing neem seeds from 8 to 15 waa by altering the levels of superoxide, H2O2 and OH-radical those possibly act as signalling molecules for reprogramming protective proteins. Desiccation mediated the expression of new bands of SOD and APX in undried as well as SD seeds during 9–12 waa but the bands were more intense in SD seeds. The superoxide and H2O2-regulated intensity of dehydrin-like protein in SD seeds further validated our conclusion.

Involvement of H2O2 in fluazifop-P-butyl-induced cell death in bristly starbur seedlings

In order to understand the action mechanism of fluazifop-P-butyl (FB) in bristly starbur (Acanthospermum hispidum D.C.), a susceptible plant, the role of active oxygen species (ROS) in herbicide-induced cell death in shoots was investigated. FB-induced phytotoxicity was not reduced by the antioxidants, 1,4-diazabicyclooctane (dabaco), sodium azide, l-tryptophan, d-tryptophan, hydroquinone and dimethyl pyridine N-oxide (DMPO). The activities of superoxide dismutase (SOD) and catalase (CAT), in bristly starbur seedlings were significantly increased by FB at 12 HAT and 24 HAT, while ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased only at 12 HAT. The contents of H2O2 in FB-treated bristly starbur seedlings were significantly higher to that of control between 8 and 24 HAT. According to the analysis of potassium iodide – starch or 3,3-diaminobenzidine, the accumulation of hydrogen peroxide was observed in the apical growing point, stem, petiole and veins of FB-treated bristly starbur seedlings at 24 HAT. The cell viability of bristly starbur seedlings treated by 10μM FB decreased at 18 HAT. These results suggested that FB-induced cell death in bristly starbur shoots may be caused by ROS (O2– and H2O2) generation and lipid peroxidation.

Role of active oxygen species in the liquid-phase photocatalytic degradation of RhB using BiVO4/TiO2 heterostructure under visible light irradiation

The systematic clarification of the photocatalytic process is an indispensable basis for the in-depth understanding of the photocatalytic mechanism. Various types of active oxygen species involved into the photocatalytic process have been investigated extensively, including OH and O2−, but still remain obscure and controversial. Herein, the roles of the active oxygen species generated in the liquid-phase photocatalytic degradation of RhB using BiVO4/TiO2 heterostructure under visible light irradiation are discussed in detail. The results revealed that the liquid-phase photocatalytic degradation behavior was greatly affected by the amount of BiVO4. When the loading BiVO4 was less than 9wt%, the de-ethylation of RhB on BiVO4/TiO2 was observed. While, the direct oxidative degradation of RhB took place in the BiVO4/TiO2/RhB system loaded with more BiVO4 (>9wt%). Particularly, 9% BiVO4/TiO2 enhanced the photosensitized degradation of RhB, and the degradation efficiency was 80% which was 1.14 times than that of pure TiO2. Combined with different surface analysis techniques (EPR, photoluminescence technique, etc.), it was found that O2− and OH were the key active species when the loading BiVO4 was less than 9wt%, while in the 50% BiVO4/TiO2/RhB system, O2− and holes played much more roles. Our findings provide certain theoretical guidance in understanding the functional mechanism of heterostructured photocatalysts, which can pave the way to further improve the concentration of the active species and design novel efficient photocatalysts.

Role of reactive oxygen species in the bactericidal action of quinolones as inhibitors of DNA gyrase

Quinolone antibiotics inhibit DNA gyrase, but the induced degradation of chromosomal DNA is determined by a complex process of joint action quinolones and hydroxyl radical OH'. To quantify the level of stress responses and their time dependence in bacterial cells the induced specific lux-biosensors--the bacterium Escherichia coli, containing hybrid plasmids pColD'::lux; pSoxS'::lux; pKatG'::lux were used in this study. It is shown that quinolones (nalidixic acid, norfloxacin) induce SOS-response and oxidative stress with the formation of superoxide anion O2(-) in E. coli cells. The main parameters of SOS-response and oxidative stress, which depend on the quinolone concentration, are determined. Formation of superoxide anion O2(-) occurs almost simultaneously with the SOS-response. The mutant strain of E. coli sodA sodB, which do not contain active forms of superoxide dismutases SodA and SodB, is characterized by an increased resistance to quinolones as compared to the wild type cells. At high concentrations of quinolones (nalidixic acid-->20 μg/mL; norfloxacin-->500 ng/mL) their bactericidal effect is partially caused by conversion of the superoxide anion to hydrogen peroxide H2O2, conducted by superoxide dismutases SodA and SodB, which is followed by the Fenton reaction and the formation of toxic hydroxyl radical OH'. At low concentrations of quinolones (nalidixic acid--<20 μg/mL; norfloxacin--<500 ng/mL), the role of active oxygen species in the antimicrobial effect is practically nonexistent.

Advances in quantitative structure–activity relationship models of antioxidants

Background: During the past decade a large number of reports described the roles of active oxygen species in the development or exacerbation of various kinds of diseases. The systemic antioxidant defense system often fails to control the excess free radicals. Such a condition necessitates external antioxidant supplementation either in the form of drugs or vitamins. Quantitative structure–activity relationship (QSAR) serves as an effective computational tool for search and design of active molecules that may eventually be synthesized and assayed. Objective/method: This review presents the current knowledge about QSAR studies of diverse groups of molecules with free radical scavenging activity. The QSAR studies summarized here would help to understand the proper mechanism underlying the interaction between the free radicals and antioxidant molecules. Conclusion: The primary determinant factors for potent antioxidant activity include the electronic distribution of the molecules together with their lipophilicity and size and orientation of the substituents attached to the parent molecules. The potency of the antioxidants depends on the degree of reactivity of these molecules with the nearby free radicals and the stability of the oxidized antioxidant molecules thus obtained. The nature of substitution at the parent moiety plays a key role in the design of antioxidant molecules.

Some recent developments concerning the mechanisms of tumor promotion

Recent developments in tumor promotion are reviewed, particularly the biochemical effects of phorbol esters and new tumor promoters such as the teleocidins. The role of active oxygen species, and the nature and properties of the phorboid receptor, protein kinase C, are discussed. Finally, the relevance of gene expression to promotion, and of promotion to human cancer are explored.

Investigation of the roles of active oxygen species in photodegradation of azo dye AO7 in TiO 2 photocatalysis illuminated by microwave electrodeless lamp

A novel microwave electrodeless lamp (MWL) was used as the light source for microwave assisted TiO 2 photocatalysis to degrade azo dye Acid Orange 7 (AO7). This technique aims to provide a new way to study the synergetic effect of both UV–vis light and microwave irradiations on aqueous solution of catalysts. The roles of active oxygen species in the photodegradation of AO7, such as hydroxyl radical (HO ), positive holes (h +) and hydrogen peroxide (H 2O 2), were investigated to understand the photodegradation mechanism. The presence and roles of these oxidative species were examined using appropriate quenchers. It was found that the degradation of AO7 proceeded via three pathways, namely, UV-induced photocatalytic degradation, visible light-induced dye self-photosensitized degradation and direct photolytic degradation. The percentages of dye degradation by the three pathways were about 31.1%, 39.0% and 19.5%, respectively.

A Review on Quantitative Structure-Activity Relationships (QSARs) of Natural and Synthetic Antioxidants Compounds

During the last decade an increasing number of reports describe the roles of active oxygen species in the development or exacerbation of various kinds of diseases. Antioxidants are of great interest because of their involvement in important biological and industrial processes. They have been found to possess anticancer, anti-cardiovascular, anti-inflammatory and many other activities. Many attempts have been made to elucidate the QSAR of antioxidants by using different physicochemical parameters. Unfortunately the limited number of antioxidants and the unavailable sigma Hammett values of complex substituents did not lead to significant results in regression analysis. The redox potentials are well correlated to the antioxidant activities. In this report we will attempt to collect and discuss all the published results concerning the QSAR research on natural and synthetic antioxidants compounds.