Generation Of Reactive Radical Species Research Articles

Peroxymonosulfate-activated photocatalytic degradation of norfloxacin via a dual Z-scheme g-C3N5/BiVO4/CoFe − LDH heterojunction: Operation and mechanistic insights

The design of novel dual Z-scheme heterojunction plays a significant path in eradicating organic contaminants via enriched charge carrier separation. Herein, a wet chemical method was used to synthesize ternary g-C3N5/BiVO4/CoFe–LDH (CBCF) nanocomposites, and their corresponding abilities were characterized as follows: crystal phases, optical properties, surface morphologies, and compositions. The g-C3N5/BiVO4/CoFe–LDH-30% (CBCF-3) sample optimized the removal efficiency of norfloxacin (NOR) by up to 95.3% through peroxymonosulfate (PMS) activation in a visible light medium. The combined effects from the Vis/PMS/CBCF-3 catalytic system led to 7-times higher degradation efficiency than visible light only system. This improved performance was attributed to the generation of reactive radical species because of higher PMS utilization and an effective Z-charge transfer process from well-oriented band structures. Moreover, scavenging tests and electron spin resonance analysis revealed the production of active radical and non-radical species, namely •OH, SO4•−, •O2−, and 1O2. Based on the appropriate experimental analysis, the expected NOR degradation mechanism and possible pathways were proposed. Then, the toxicity evaluation results revealed that the intermediate products may not have an adverse effect on the aquatic ecosystems. This research study provides a positive outcome for wastewater remediation using enriched dual Z-scheme mechanism.

Bifunctional photocatalytic nanofiltration membranes with immobilized BaTiO3/Ti3C2Tx catalysts for the simultaneous separation and degradation of azo compounds

Bifunctional photocatalytic nanofiltration (NF) membranes are becoming increasingly popular because of their ability to separate and degrade azo compounds (azos) in water. However, several serious drawbacks limit their practical implementation. In this study, a polyamide (PA) layer formed by interfacial polymerization on the polyvinylidene fluoride membrane surface and polydopamine (PDA) were combined with BaTiO3/Ti3C2Tx (BT) nanoparticles to prepare photocatalytic BT@PDA (BTPP) membranes, which integrated physical separation and photocatalytic degradation into a single process. By optimizing synthesis conditions, a BTPP membrane with high water permeability (34.0 L·m–2·h–1·bar–1) and Na2SO4 rejection rate (94.7%) was produced. The photocatalytic activity of this membrane was examined by studying the photocatalytic degradation efficiency of several azos. After 180 min of irradiation with a 300 W Xe lamp (λ ≥ 420 nm), the degradation rate of methyl orange (MO) reached 95.3%, while the degradation rates of alizarin yellow GG and methyl red were 92.7% and 83.5%, respectively. The photocatalytic performance of the BTPP membranes for azos degradation was verified by studying the charge transfer process and generation of reactive radical species (·OH and·O2–), and possible structures of the main intermediates formed during MO degradation were identified. This work provides new insights into the synthesis and degradation properties of bifunctional photocatalytic NF membranes.

A photo- and redox actives mesoporous 3D covalent organic framework enables highly efficient metal-free photoredox catalysis

Visible-light photoredox catalysis has been emerged as prominent methodology for efficient chemical synthesis. However, the relying use of soluble noble-metal photoredox catalysts suffer from long-term supply, inefficient separation, and could pos serious threats to the environment. Development of recyclable metal-free photoredox catalyst is thus highly significance. Herein, suitable molecular chromophore and redox units are condensed into photo- and redox active mesoporous 3D COF (3D TAPPy-TFPA) that enable highly efficient photoredox catalysis. The 3D COF displayed high crystallinity, mesoporous channel, and excellent structural stability. Optical and electrochemical studies revealed the excellent light harvesting, redox activity and effective generation of reactive radical species to induce photoredox catalysis. As proof-of-concept, 3D TAPPy-TFPA efficiently catalyzed the visible-light induced photoredox thiol-ene cross coupling and thiol radical mediated acylation of amines with activities surpassing most of the reported soluble photoredox catalysts. Beside recoverable, 3D TAPPy-TFPA showcased the previously inaccessible diacylation of amine into di-amide with high selectivity. This report shows robust design of outstanding and low-cost photoredox catalyst and paves the development of functional 3D COFs.

Manganese impairs the QoxABCD terminal oxidase leading to respiration‐associated toxicity

Cell physiology relies on metalloenzymes and can be easily disrupted by imbalances in metal ion pools. Bacillus subtilis requires manganese for growth and has highly regulated mechanisms for import and efflux that help maintain homeostasis. Cells defective for manganese (Mn) efflux are highly sensitive to intoxication, but the processes impaired by Mn excess are often unknown. Here, we employed a forward genetics approach to identify pathways affected by manganese intoxication. Our results highlight a central role for the membrane-localized electron transport chain in metal intoxication during aerobic growth. In the presence of elevated manganese, there is an increased generation of reactive radical species associated with dysfunction of the major terminal oxidase, the cytochrome aa3 heme-copper menaquinol oxidase (QoxABCD). Intoxication is suppressed by diversion of menaquinol to alternative oxidases or by a mutation affecting heme A synthesis that is known to convert QoxABCD from an aa3 to a bo3 -type oxidase. Manganese sensitivity is also reduced by derepression of the MhqR regulon, which protects cells against reactive quinones. These results suggest that dysfunction of the cytochrome aa3 -type quinol oxidase contributes to metal-induced intoxication.

Light-induced variation in environmentally persistent free radicals and the generation of reactive radical species in humic substances

Environmentally persistent free radicals (EPFRs) in humic substances play an essential role in soil geochemical processes. Light is known to induce EPFRs formation for dissolved organic matter in aquatic environments; however, the impacts of light irradiation on the variation of EPFRs in soil humic substances remain unclear. In this study, humic acid, fulvic acid, and humin were extracted from peat soil and then in situ irradiated using simulated sunlight. Electron paramagnetic resonance spectroscopy results showed that with the increasing irradiation time, the spin densities and g-factors of humic substances rapidly increased during the initial 20 min and then gradually reached a plateau. After irradiation for 2h, the maximum spin density levels were up to 1.63 × 1017, 2.06 × 1017, and 1.77 × 1017 spins/g for the humic acid, fulvic acid, and humin, respectively. And the superoxide radicals increased to 1.05 × 1014–1.46 × 1014 spins/g while the alkyl radicals increased to 0.47 × 1014–1.76 × 1014 spins/g. The light-induced EPFRs were relatively unstable and readily returned back to their original state under dark and oxic conditions. Significant positive correlations were observed between the concentrations of EPFRs and reactive radical species (R2= 0.65–0.98, p < 0.05), which suggested that the newly produced EPFRs contributed to the formation of reactive radical species. Our findings indicate that under the irradiation humic substances are likely to be more toxic and reactive in soil due to the formation of EPFRs.

Perspective and status of polymeric graphitic carbon nitride based Z-scheme photocatalytic systems for sustainable photocatalytic water purification

• Exploration of basic principle of Z-scheme photocatalysis. • Selection of Z-scheme photocatalysts for photocatalytic environment applications. • Discussion on g-C 3 N 4 based Z-scheme photocatalysts for pollutant degradation. • Applicability of Z-scheme photocatalysts for photocatalytic antibacterial activity. • View point on scope and limitations in g-C 3 N 4 based Z-scheme photocatalysis. Developing bioinspired artificial Z-scheme heterojunction photocatalysts with exceedingly well performance of visible-light harnessing along with optimum band edge potentials is a robustly prominent avenue to combat the environmental and energy crisis. The current scenario in fixation of water shortages all over the world is utilisation of green and economical processes to maintain sustainability. In this regard, hybridizing fascinating metal-free polymeric conjugated graphitic carbon nitride (g-C 3 N 4 ) with other components to tailor an effectual visibly driven photocatalyst has triggered a superfluity in the field of photocatalysis. Considering the great adherence and eloquent progress in exploitation of g-C 3 N 4 goaded Z-scheme nanohybrids, we herein present an all-inclusive and updated study about photocatalytic wastewater treatment including pollutant degradation and bacterial inactivation. An in-depth overview comprising traditional photocatalysis along with Z-scheme photocatalytic systems have been exploited and discussed with respect to their facile synthesis techniques and application in environmental restoration. With revamp strategies, g-C 3 N 4 based Z-scheme photocatalytic systems provide broad range visible light absorption and efficient space separation of photo-generated charge carriers, resulting in efficacious photoactivity. The mechanistic insights inferring photocarriers migration and separation along with the generation of reactive radical species involved in the photodegradation process has also been highlighted and discussed. Finally, an all-embracing conclusive remark is presented regarding present studies and future perspectives for the development of g-C 3 N 4 goaded Z-scheme photocatalysis.

Assessment of tailor-made mesoporous metal doped TiO2 monolithic framework as fast responsive visible light photocatalysts for environmental remediation applications

The article reports on the facile one-pot synthesis of a structurally organized mesoporous crack-free monolithic network of Bi3+ doped TiO2, as a visible light workable photocatalyst materials for environmental remediation. The monolithic photocatalyst efficacy has been investigated using Acid Blue 113, an organic textile dye as the model organic pollutant, thereby rooting its decontamination potential towards dye effluents from textile and dye industries. The controlled stoichiometric surface doping of Bi3+ with the continuous framework of the TiO2 monolithic material not only ensures visible light-induced photocatalysis but also high quantum yield upon light impingement thereby leading a rapid generation of reactive radical species. The monolith structural properties and its morphology are characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDAX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PLS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm analysis. The anatase phase TiO2 monolith offers a high surface area that promotes the voluminous generation of photo-induced e−/h+ pairs that proceed towards the formation of reactive radical intermediates for the fast dissipation of pollutants. To valid the efficiency and effectiveness of the Bi3+ doped TiO2 monolith photocatalyst, a comprehensive study on the physicochemical parameters such as solution pH, dopant stoichiometry, photocatalyst quantity, light intensity, photosensitizers, and reusability, proves crucial. The results reveal that under optimized conditions, the photocatalyst has an ultra-fast response time of ≤0.2 h for complete mineralization, with 0.06 g of monolithic photocatalysts that are recoverable and reusable.

Easy access of dihydrofluoresceins as advanced fluorescence turn-on probes for oxidative stress

A mild NABH4/I2 strategy was designed to easily reduce fluoresceins to dihydrofluorescein alcohols and acids. Dihydrofluorescein alcohols exhibited surprisingly enhanced reactivity for oxidative stress sensing in comparison with the acid forms, using horseradish peroxidase/H2O2 as a model system for the generation of reactive radical species. Finally, two dual functional probes were then synthesized using our optimized reduction method, which showed great potentials for fluorescent imaging of subcellular oxidative stresses.

Photodeposition of gold nanoparticles on ZnS nanobelts for enhanced dye decomposition

Gold nanoparticles have been produced on the surfaces of ZnS nanobelts via direct reduction during a photodeposition process. Because the gold nanoparticles have been fabricated in the absence of any reducing agents or surfactants, charge-separating junctions between gold and ZnS have been effectively produced. As the wt% of surface-decorating gold nanoparticles increases, the photoexcited charges of ZnS nanobelts can be separated efficiently. This has been demonstrated by monitoring photoluminescence spectra and kinetics. The long-lived excited charges promote the generation of reactive radical species, increasing the photocatalytic degradation of 4-nitrophenol. Compared with commercial ZnS, the optimized photocatalyst of Au-ZnS nanobelts exhibits 5.2 times higher photocatalytic activity. Overall, via a simple and facile photodeposition process, charge separating junctions between gold and ZnS have been formed effectively to increase the photocatalytic efficiency of ZnS greatly, suggesting that the photodeposition of gold is an effective method to enhnace photocatalytic dye deomposition activity.

Mechanism and kinetics of catalytic ozonation for elimination of organic compounds with spinel-type CuAl2O4 and its precursor

CuAl2O4 based mixed oxides were used as heterogeneous catalysts for ozone activation to degrade organics in aqueous solution. The solids were thoroughly characterized by SEM/EDS, N2 physisorption, XRD, FTIR, Pyridine-FTIR, TEM and XPS. We demonstrated that the solid precursor calcined at 300 °C exhibited the best catalytic ozonation activity with respect to CuAl2O4 spinel phase obtained at higher temperatures. Such performance was attributed to the better textural properties and a higher density of active sites (hydroxyl groups and Lewis acidity). Specifically, the mixed oxide/O3 process allows to reach a near complete color removal of the dye solution (100 mg L−1) in 25 min at neutral pH. Corresponding reaction rate value was measured at 0.112 min−1 and was clearly higher compared with the single oxide ozonation process (0.071 min−1 for CuO/O3 and 0.074 min−1 for Al2O3/O3). Then, we proposed that such catalytic performance was related to a synergistic function between ≡Cu2+ and ≡Al3+, which took part of a mechanism of radical formation. In such mechanism, present ≡Al3+ could act as a reservoir for surface active sites such as hydroxyl groups and Lewis acid sites, while ≡Cu2+ could provide the possibility of electron transfer with ozone for the enhancement of radical generation. We suggested that the interaction between chemisorbed ozone and surface hydroxyl groups initially stabilized on ≡Al3+ initiated the generation of reactive radical species. This interaction led as well to the formation of surface adsorbed HO and few O2− on ≡Cu2+ Lewis acid sites. Besides, the interfacial redox reaction with ozone is favored by the presence of ≡Cu2+ following the sequence of ≡Cu2+/≡Cu+/≡Cu2+ redox cycle.

Recent Advances in Radical-Enabled Bicyclization and Annulation/1,n-Bifunctionalization Reactions.

Over the past few years, the development of new radical reactions has gained considerable momentum. Most such radical transformations heavily depend on the in situ generation of reactive radical species, initiated by oxidants, metal salts, visible-light photocatalysis, or electrocatalysis. In this context, numerous radical-enabled bicyclization and annulation/1,n-bifunctionalization reactions have been developed, thereby providing efficient synthetic strategies for the assembly of functionalized cyclic rings that contain both heterocyclic and isocyclic skeletons. In this Focus Review, we highlight recent progress in this rapidly growing area by presenting a series of catalytic oxidative reactions, along with their reaction mechanisms and applications.

Enhanced Photocatalytic Mineralization of Gaseous Toluene over SrTiO3 by Surface Hydroxylation

Perovskite structured SrTiO3 (STO) was synthesized by a hydrothermal method followed by a second hydrothermal treatment with H2O or NaOH (STO-H2O or STO-NaOH) for the photocatalytic mineralization of gaseous toluene. The second hydrothermal treatment enhances the light absorption and enriches the surface hydroxyl groups of STO. The surface hydroxyls’ enrichment of STO promotes the generation of hydroxyl radicals and the separation of photocarriers by the combination of hydroxyl with holes, induces a negative shift of its band edge, and benefits the reduction of adsorbed oxygen. The facile generation of reactive radical species, enhanced light absorption, and improved photocarrier separation together lead to greatly enhanced photocatalytic efficiency of STO-NaOH. Toluene was completely oxidized into CO2 under ultraviolet light illumination for 6 h at room temperature, demonstrating better performance than STO and commercial P25 catalysts. Such a surface hydroxylation promotion strategy may lead to new perc...

Study of natural anthraquinone colorants by EPR and UV/vis spectroscopy

The spectroscopic study was performed on 9,10-anthraquinone derivatives (purpurin, alizarin, carminic acid, and 2-(hydroxymethyl)-9,10-anthraquinone) in dimethylsulfoxide in the presence of triethylamine to bring information on their protonation/deprotonation equilibria in aprotic solvent. An interesting deprotonation effect of 5,5-dimethyl-1-pyrroline N-oxide (a spin trapping agent used in the EPR experiments) was revealed. The quantum chemical calculations enabled the identification of the individual protonated/deprotonated tautomeric forms present in the experimental systems. The UV photoexcitation of hydroxyanthraquinones (HAQ) led to the generation of reactive radical species and singlet oxygen, detected by in situ EPR spectroscopy (spin trapping, nitroxide radical elimination, oxidation of sterically hindered amines). The changes in the electronic absorption spectra upon photoexcitation, linked with the ability of the studied HAQ to generate reactive oxygen species upon exposure, confirm a substantial effect of the substituent character and position on the overall photochemical behavior of the HAQ, significantly influenced by the actual experimental conditions (solvent, pH).

Remediation HCHs POPs-contaminated soil by activated persulfate technologies: Feasibility, impact of activation methods and mechanistic implications

Hexachlorocyclohexanes (HCHs) waste stockpiles are the single largest source of POPs. Sites contaminated with high levels of HCHs pose serious threats to public health and environmental safety, but there remains a lack of proper environmentally sound solution. To provide guidance on this issue, the remediation of contaminated soil with high levels of γ-HCH (∼800mg/kg) by persulfate with three commonly applied field activation methods, namely heat activation at 40°C, high pH and Fe(III)-EDTA activation, was investigated. The effects of activation method and persulfate dosage on the degradation and dechlorination of γ-HCH were studied, and degradation pathways were proposed. The results show that heat-activated persulfate is highly effective for the remediation of γ-HCH, achieving complete degradation and dechlorination of γ-HCH in 14days. Under high pH conditions, γ-HCH rapidly dehydrochlorizes into trichlorobenzenes, which are further degraded by persulfate. On the other hand, persulfate alone at 20°C and Fe(III)-EDTA activated persulfate are not effective for the degradation of γ-HCH, due to limited generation of reactive radical species resulting from the inefficient activation of persulfate, and the competition of soil organic materials and Fe(III)-EDTA with γ-HCH for reactive radicals.

UVA generated free radicals in irinotecan (CPT-11) in the presence of copper ions

Abstract Irinotecan (CPT-11) is an efficient anticancer drug approved for clinical use in the treatment of advanced colorectal cancers. This work is focused on the study of photoinduced processes in irinotecan (CPT-11) both in the presence and absence of Cu(II) ions by means of UV/vis and EPR spectroscopy. Solid-state EPR revealed the solvent dependent coordination between CPT-11 and cupric ions. EPR spin trapping technique, using various spin trapping agents, was applied to monitor the generation of reactive radical species (oxygen- and carbon-centered radicals) in irradiated CPT-11 and CPT-11/CuCl 2 systems under the given experimental conditions. We confirmed that the presence of CPT-11 is necessary for the formation of reactive radicals and the photoinduced processes are influenced by the presence of cupric ions. ROS generated upon irradiation of CPT-11 in the presence/absence of copper ions can be regarded as complementary species to the original inhibitory action of the drug on the DNA topoisomerase I.

Effect of Chronic Hypoxia on Glutathione Status and Membrane Integrity in the Pancreas

Background: Our recent study has shown that chronic hypoxia could upregulate significantly a local renin-angiotensin system in the pancreas. The activation of such a local renin-angiotensin system may provide an alternate mechanism that leads to the generation of reactive radical species in the pancreas during chronically hypoxic exposure. The present study aims at elucidating the antioxidant status in the pancreas during varying degrees of chronic hypoxia. Methods: Sprague-Dawley rats were exposed to an isobaric hypoxic (10% oxygen) chamber for a period up to 28 days. The glutathione status and membrane integrity of the pancreas were studied with a time course of chronic hypoxia (3, 7, 14, 21 and 28 days). The effect of chronic hypoxia on changes of oxidative states in the pancreas was assessed based on the measurements of glutathione, malondialdehyde, α-amylase and DNA fragmentation using biochemical assays. Results: Pancreatic glutathione was decreased drastically after 3-day hypoxia and its level was almost completely recovered after 7-day hypoxia. Malondialdehyde was not affected while DNA fragmentation was increased significantly in a time-dependent manner during the course of chronic hypoxia. Membrane integrity of the pancreatic cells was improved, as evidenced by the decrease of plasma α-amylase during the time-course study of chronic hypoxia. Conclusion: Pancreatic glutathione was depleted only in the early period of chronic hypoxia followed by a rapid recovery, suggesting that adaptive response of the pancreas may occur during chronic hypoxia. The enhancement of glutathione-dependent antioxidant capacity during chronic hypoxia prevented oxidative damage to the membrane of the pancreatic cells.

Sonochemically induced radicals generated by pulsed high-energy ultrasound in vitro and in vivo

The aim of this study was to evaluate the role of radicals as a mechanism of tissue damage induced by pulsed high-energy ultrasound. Transient cavitation has proved to be an important mechanism for the generation of reactive radical species during pulsed high-energy ultrasound applications. The amount of radicals studied in in vitro experiments using a chemical dosimeter based on iodine release is proportional to the number of pulses. Sonications of the R3327-AT1 subline of the Dunning prostate rat tumor transplanted in the thigh of Copenhagen rats were performed applying 500 and 2000 pulses at a pulse repetition frequency of 1 Hz. Tumor growth after treatment was compared with sham-treated controls. We were able to assess a significant growth delay, but could not find a significant difference between the two groups treated. In conclusion, radical formation does not seem to be the major mechanism for tissue necrosis induced by pulsed high-energy ultrasound.