Reactive Oxygen Species Transformation Research Articles

Transformation of reactive oxygen species caused by assembly of excitation modules into supramolecular organic frameworks for photocatalysis

Transformation of reactive oxygen species caused by assembly of excitation modules into supramolecular organic frameworks for photocatalysis

Enhancing Cu-EDTA decomplexation in a discharge plasma system coupled with nanospace confined iron oxide: Insights into electron transfer and high-valent iron species

Decomplexation of heavy metal-organic complexes dominated by reactive oxygen species (ROS) oxidation had attracted extensive attention. Nanospace confinement is a novel strategy to enhance pollutant removal due to its regulation on ROS transformation and local accelerated dynamics. Herein, nano-confined Fe2O3 catalyst supported by carbon nanotubes (Fe2O3-in-CNTs) was synthesized, and it displayed obvious synergistic effects on decomplexation of Cu-EDTA complex in a non-thermal plasma (NTP) process. Cu-EDTA decomplexation efficiency reached 98.8% within 20 min in the NTP/Fe2O3-in-CNTs system, and the corresponding kinetic constant was 4.5 and 2.5 times as that in single NTP and unconfined systems, respectively. Based on experimental and theoretical results, nanospace confinement induced electron localization around Fe and C atoms and rearrangement of orbital electrons, favoring strongly oxidative FeⅣ formation and catalytic decomposition of H2O2 and O3. Nanospace confinement made Cu-EDTA decomplexation process transform from radical pathway to non-radical pathway. Cu-EDTA decomplexation pathways in the NTP/Fe2O3-in-CNTs were proposed.

Effect of Interfacial Action on the Generation and Transformation of Reactive Oxygen Species in Tripolyphosphate-Enhanced Heterogeneous Fe3O4/O2 Systems.

It has been reported that tripolyphosphate (TPP) can enhance the oxygenation of natural Fe(II)-containing minerals to produce reactive oxygen species (ROS). However, the molecular structure of the TPP-Fe(II) mineral surface complex and the role of this complex in the generation and transformation of ROS have not been fully characterized. In the present study, a heterogeneous magnetite (Fe3O4)/O2/TPP system was developed for the degradation of p-nitrophenol (PNP). The results showed that the addition of TPP significantly accelerated the removal of PNP in the Fe3O4/O2 system and extended the range of effective pH to neutral. Experiments combined with density functional theory calculations revealed that the activation of O2 mainly occurs on the surface of Fe3O4 induced by a structural Fe(II)-TPP complex, where the generated O2•- (intermediate active species) can be rapidly converted into H2O2, and then the •OH generated by the Fenton reaction is released into the solution. This increases the concentration of •OH produced and the efficiency of •OH produced relative to Fe(II) consumed, compared with the homogeneous system. Furthermore, the binding of TPP to the surface of Fe3O4 led to stretching and even cleavage of the Fe-O bonds. Consequently, more Fe(II)/(III) atoms are exposed to the solvation environment and are available for the binding of active O2 and O2•-. This study demonstrates how common iron minerals and O2 in the natural environment can be combined to yield a green remediation technology.

Titanium Oxide Electrocatalytic Membrane Filtration: "Two Faces" of Oxygen Vacancies in Generation and Transformation of Reactive Oxygen Species.

Oxygen vacancies are crucial to the production of reactive oxygen species (ROS) in the metal oxide electrocatalytic membrane (MOx EM) process. Here, using cathodic TiOx EM as a model, we thoroughly reveal the roles of oxygen vacancies in ROS generation and transformation. Oxygen vacancies significantly promote H2O2 and •OH production at low concentrations (increment <35%) but inhibit their production at high concentrations (increment >35%). Electrochemical analysis discloses that the enhancement of ROS production profits from the acceleration of charge transfer kinetics by both bulk and surface oxygen vacancies, whereas we attribute the decline in ROS production to the strong adsorption of ROS by surface oxygen vacancies. It is strongly supported by theoretical calculations that reveal the promoted adsorption of *OOH and *OH by oxygen vacancies, which intensifies the capture and scavenging of H2O2 and •OH. Moreover, the gradual increase of interaction time between ROS and oxygen vacancies (from ∼1 to ∼5 s) notably reduces the generation and transformation efficiency of ROS, further highlighting the detrimental impact of oxygen vacancies. In summary, oxygen vacancies show "two faces" toward ROS generation and transformation, acting as ROS promoters at low concentrations but inhibitors at high concentrations. A medium oxygen vacancy concentration is preferred for ROS production, thus causing impressive pollutant removal (>95% removal of bisphenol A within 1.2-1.5 s at 360-440 LMH). This study provides guidance on regulating ROS generation and transformation by manipulating the oxygen vacancy concentration to enhance the decontamination efficiency of MOx EMs.

Vacancy pairs regulate BiOBr microstructure for efficient dimethyl phthalate removal under visible light irradiation

Developing new photocatalysts to achieve efficient removal of phthalate esters (PAEs) in water is an important research task in environmental science. However, existing modification strategies for photocatalysts often focus on enhancing the efficiency of material photogenerated charge separation, neglecting the degradation characteristics of PAEs. In this work, we proposed an effective strategy for the photodegradation process of PAEs: introducing vacancy pair defects. We developed a BiOBr photocatalyst containing “Bi-Br” vacancy pairs, and confirmed that it has an excellent photocatalytic activity in removing phthalate esters (PAEs). Through a combination of experimental and theoretical calculations, it is proved that “Bi-Br” vacancy pairs can not only improve the charge separation efficiency, but also alter the adsorption configuration of O2, thus accelerating the formation and transformation of reactive oxygen species. Moreover, “Bi-Br” vacancy pairs can effectively improve the adsorption and activation of PAEs on the surface of samples, surpassing the effect of O vacancies. This work enriches the design concept of constructing highly active photocatalysts based on defect engineering, and provides a new idea for the treatment of PAEs in water.

A novel design of Cu(I) active site on the metal–organic framework for exploring the structural transformation of Fenton-like catalysts through in situ “capturing” OH−

The mutual transformation of reactive oxygen species may affect the structural transformation of catalysts during the Fenton-like processes. Its in-depth understanding is essential to achieve high catalytic activity and stability. In this study, a novel design of Cu(I) active sites based on the metal–organic framework (MOF) is proposed to “capture” OH− produced via Fenton-like processes and re-coordinate the oxidized Cu sites. The Cu(I)-MOF presents an excellent removal efficiency for sulfamethoxazole (SMX), with a high removal kinetic constant of 7.146 min−1. Combing DFT calculations with experimental observations, we have revealed that the Cu of Cu(I)-MOF exhibits a lower d-band center, enabling efficient activation of H2O2 and spontaneous “capturing” of OH− to form Cu-MOF, which can be reorganized into the Cu(I)-MOF through molecular regulation for recycle. This research demonstrates a promising Fenton-like approach for solving the trade-off between catalytic activity and stability and provides new insights into the design and synthesis of efficient MOF-based catalysts for water treatment.

Regulating the concentration of dissolved oxygen to achieve the directional transformation of reactive oxygen species: A controllable oxidation process for ciprofloxacin degradation by calcined CuCoFe-LDH

Different reactive oxygen species (ROS) tend to attack specific sites on pollutants, leading to the formation of intermediates with different toxic effects. Therefore, regulating the directional transformation of ROS is a new effective approach for safe degradation of refractory organic compounds in wastewater. However, the regulation mechanism and transformation path of ROS remain unclear. In this work, the dissolved oxygen (DO) content was controlled by aeration to generate different ROS through the activation of O2 on the calcined CuCoFe-LDH (CuCoFe-300). ROS quantitative experiments and electron paramagnetic resonance proved that O2 was mainly activated to superoxide radical (•O2−) and singlet oxygen (1O2) under low DO concentration (0.231 mmol/L) (O2 → •O2− → 1O2). With the increasing of DO concentration (0.606 mmol/L), O2 was inclined to convert into hydroxyl radicals (•OH) (O2 → •O2− → H2O2 → •OH). The density functional theory and function model of active sites utilization and DO concentration built a solid proof for ROS conversion mechanism that increasing the DO concentration promotes the increase of active sites utilization on the CuCoFe-300 system. That is, the •O2− was more prone to convert to •OH, not 1O2 in thermodynamics under high active sites utilization condition. Hence, the ROS generation was controlled by regulating DO concentration, and the nontoxic degradation pathway of ciprofloxacin was well-designed. This work is dedicated to the in-depth exploration of the mechanism between DO concentration and ROS conversion, which provides an extremely flexible, low energy consumption, and environmentally friendly wastewater treatment method in a new perspective.

Adsorption-reduction of Fe(III) by different biochars and their co-activation of H2O2 for oxidation of refractory pollutants

Various biochar samples were used for exploring the Fe(III)/biochar interactions and transformation of reactive oxygen species during co-activation of H2O2. The enhanced •OH production is positively related to the biochars' capacity of reducing Fe(III) into Fe(II), which is then linked with their redox-active moieties and adsorption of Fe(III). Besides the •OH produced sustainably from Fenton reaction between H2O2 and regenerated Fe(II), a novel route involving dissolved O2 is proposed to enhance •OH production in the co-activated system. Consequently, faster and more efficient oxidation of refractory pollutants was achieved by co-activation of H2O2 with Fe(III) and biochar together.

Mineralization, characteristics variation, and removal mechanism of algal extracellular organic matter during vacuum ultraviolet/ozone process

Extracellular organic matter (EOM) produced by algal blooms in source water is detrimental to drinking water treatment processes and supplied water quality. Ozonation has been used to treat algal EOM, but it could not mineralize EOM effectively. In this study, mineralization and characteristics variation of EOM by vacuum ultraviolet/ozone (VUV/O3) and its sub-processes were comprehensively investigated. Results showed that EOM removal in different processes followed the order of VUV/O3 > UV/O3 > O3 > VUV > UV. For VUV/O3 process, removal efficiencies of dissolved organic carbon (DOC), UV254, protein, and polysaccharide at 50 min were 75.6%, 80.8%, 80.1%, and 78.0%, respectively, and fluorescence components received very high removal rates (≥92.8%, at 10 min). The yield of trichloromethane dropped from 102.0 to 30.1 μg/L after treating for 50 min by VUV/O3. Besides, effects of O3 dosage, initial pH, and water matrices on EOM removal in VUV/O3 process were investigated. Moreover, fluorescent molecular probe experiments confirmed that hydroxyl radical and superoxide radical were the main reactive oxygen species (ROS) in VUV/O3 process, and the transformation of ROS was proposed. The mechanism of EOM removal by VUV/O3 included VUV photolysis, direct O3 oxidation, and ROS oxidation. Furthermore, the removal of EOM in filtered water by VUV/O3 was satisfactory. All results indicated that VUV/O3 process had great application potential in treating EOM-rich filtered water.

Sonophotocatalytic degradation of 17β-estradiol by Er3+-CdS/MoS2: The role and transformation of reactive oxygen species

Reactive oxygen species (ROS) play a considerable role in the catalytic reaction for removing organic pollutants, however, the generation and transformation mechanism by catalyst with light and ultrasonic irradiation still requires intensive investigation. In this study, a novel Er3+-CdS/MoS2 (ECMS) composite was synthesized, and the synergetic degradation effects for 17β-estradiol (17β-E2) during the sonophotocatalytic (SPC) process were investigated. The contribution of ROSs for eliminating 17β-E2 during the SPC process through quenching experiments was generally ranked in the following order: superoxide radical (•O2−) ≈ hole (h+) > hydroxyl radical (•OH) > H2O2 > singlet oxygen (1O2). •OH plays a crucial role in 17β-E2 removal by ECMS under sonocatalysis and photocatalysis conditions. The transformation process among ROSs was further analyzed and elucidated in the light of the probe measurement results with positive or negative correlation among ROSs. Besides, we observed a phenomenon that the generated concentration of •O2− rises first and then falls during the SPC process, which might be attributed to the formation of 1O2 via the oxidation of h+ or recombination with •OH. This work clarifies the underlying mechanisms of sonophotocatalytic generation and transformation of ROSs in depth.

IMBALANCE OF ANTIOXIDANT ENZYMES AND CANCER

Oxidants are the substances which are produced in the body normally during a healthy and normal cellular metabolism. These chemical reactions are catalyzed by enzymes. Antioxidants refer to a substance that inhibits the oxidation process. Oxygen is a molecule which is highly reactive, and creates damage to living species by producing oxygen-based compounds that are reactive. The damage that is caused to the macromolecules at a cellular level is a main reason given for origin of many, life threatening illness including cancer. To protect itself, the body produces multiple antioxidant enzymes. Antioxidant enzymes refer to the proteins which are involved in the reactive oxygen species transformation which is a catalytic reaction along with their by -products into stable molecules which are non-toxic, and thereby representing a defense mechanism which is very important against the damage of cell because of the criteria oxidative stress-induced. The main Antioxidant enzymes are GPx (Glutathione Peroxidase), SOD (Superoxide Dismutase), CAT (Catalases), GST (Glutathione S- Transferase), and GR (Glutathione Reductase). An imbalance of any of these enzymes has serious repercussions. A study of cancer cells, showed an imbalance in the antioxidant enzyme level which is prevalent in almost all the types of Cancers. Low enzyme levels are commonly seen in human and animal cancer cells. It is significant to analyze and study the effects of these enzyme in case if unbalancing occur, as well as how and what type of reactions occur leading to the growth of cancer cells in the human body.

Unraveling the mechanisms for persulfate-based remediation of triphenyl phosphate-contaminated soils: Complicated soil constituent effects on the formation and propagation of reactive oxygen species

The continuous accumulation of triphenyl phosphate (TPHP) in soil poses a potential threat to human health. Persulfate-based advanced oxidation processes (SR-AOPs) are promising soil remediation technologies. Naturally occurring soil constituents could interact with persulfate (PS) during soil remediation by SR-AOPs. However, the production and transformation of reactive oxygen species (ROS) by synthetic reactions between PS and different soil constituents, as well as their roles in the pollutants degradation, are still largely unknown. This study systematically investigated the generation of ROS and their roles in degradation of TPHP in soil constituents activated PS process and in soil constituents-heat (50 °C) co-activated PS process. Comprehensive studies including ROS identification, electron paramagnetic resonance analysis, and ROS-generated model systems were carried out. An appreciable degradation rate of TPHP (~21.9%) in soil-PS system and the significant discrepancy in degradation rate (69.0–97.0%) in heat-soil-PS systems with three different soils suggested that soil constituents exhibited complex effects on the activation of PS. The Fe/Mn-minerals in soil effectively activated PS and facilitated TPHP degradation. Specially, the iron redox cycle (Fe(II) ↔ Fe(III)) plays a key role in ROS generation. Small molecular soil organic matter (SOM) rapidly consumed the produced ROS which led to their mineralization, while the remaining macromolecular SOM became more hydrophilic by interaction with ROS. SO4•−, •OH, and 1O2 played major roles directly in TPHP degradation, while O2•− could not degrade TPHP directly but might promote TPHP degradation by reducing Fe(III)- to Fe(II)-minerals or converting to other ROS. This study provides new and deeper insights into the interaction between PS and soil constituents and their roles in organic pollutant degradation in contaminated soil using SR-AOPs.

Carbonate doped Bi2MoO6 hierarchical nanostructure with enhanced transformation of active radicals for efficient photocatalytic removal of NO

Doping heteroatoms in photocatalyst is an effective strategy to signally enhance the photocatalytic activity. Herein, we have favorably fabricated the carbonate doped Bi2MoO6 via a facile one-pot solvothermal method, which was verified by structure and constituent characterization analysis. In addition, the NO removal efficiency of carbonate-intercalated Bi2MoO6 is ~34%, far-exceeding that of the pure Bi2MoO6 (~13%), whilst exhibits a good stability and durability, owing to that the dopants could modulate the electron states of the Bi2MoO6, thus stimulating charge separation and migration, incenting transformation of reactive oxygen species and facilitating reactants activation, which are synthetically investigated by experimental characterization coupled with DFT calculation. Significantly, the in situ DRIFTS measurement was employed to dynamic monitor the NO oxidation process and clarify the photocatalytic mechanism under visible light irradiation. This work provides an efficient strategy to design photocatalysts with tunable motivating charge conversion and reactants activation towards NO photooxidation.

Quantifying the activation energies of ROS-induced NOx conversion: Suppressed toxic intermediates generation and clarified reaction mechanism

The generation and transformation of reactive oxygen species (ROS) is a key parameter in catalyzing photocatalytic gas-phase oxidation reactions for environmental remediation. Thus the determination, quantification and kinetic tracking of ROS are conclusively required to realize complete pollutant conversion and intermediates suppression. By quantifying the activation energies (Ea) and ascertaining the rate-determining step (RDS), a panoramic understanding is established in ROS-induced NOx oxidation reactions. To be specific, the BiOCl photocatalyst with tailored facets were designed and fabricated as model catalysts. It is proposed that the ROS generation and transformation pathways are along the path of OH → H2O2 → O2−, in which the H2O2 dissociation is the RDS for O2− generation. Moreover, it is concluded that NO2 is the primary intermediate in NO oxidation reaction, and the further transformation of NO2 requires the highest Ea among all the elementary reactions. Significantly decreased Ea and suppressed NO2 accumulation are realized on the {010} facet of BiOCl to achieve efficient NOx conversion. A new perspective is stated in this research to establish a comprehensive understanding between ROS generation mechanism and intermediates suppression for efficient NOx removal, which provides new insights into the application of photocatalysis technology for air pollution control area.

The remediation of drought stress under VAM inoculation through proline chemical transformation action

This article discussed the enhanced drought tolerance under arbuscular mycorrhizal (AM) inoculation and normal growth of plants which linked with the activity of photoreceptors. The photoreceptor action in dual symbiosis under drought stress showed not only the high photosynthetic activity but also provide information about the broad range of physiological responses. The pot experiment conducted in a natural environment where drought condition was observed twice a week via regular irrigation with water up to twelve months. Plants analysis showed the high contents of water, hydrogen peroxide, carotenoids, proline, antioxidant enzymes like super dismutase (SOD) and catalase(CAT) in both leaves and roots with a large surface area of leaves over control. The elevated concentration of hydrogen peroxide (0.04 ± 0.0 μmol/g) coupled with singlet oxygen species was the main modified molecular mechanism which was operative in drought condition. The accretion of proline under drought stress in dual symbiosis (32.3 ± 0.3 μg/mL) was related to the highest branching pattern of young leaves and the chemical transformation of reactive oxygen species (ROS) including H2O2 and 3O2 into useful molecules like water and triplet molecular oxygen. The higher contents of carotenoids (5.0 ± 1.2 mg/g) in drought over control (4.8 ± 1.6 mg/g) and AM plant (4.9 ± 1.2 mg/g) was found to be supportive in the conversion of singlet oxygen into triplet one.

Generation and transformation of ROS on g-C3N4 for efficient photocatalytic NO removal: A combined in situ DRIFTS and DFT investigation

Understanding the performance of reactive oxygen species (ROS) in photocatalysis is pivotal for advancing their application in environmental remediation. However, techniques for investigating the generation and transformation mechanism of ROS have been largely overlooked. In this study, considering g-C3N4 to be a model photocatalyst, we have focused on the ROS generation and transformation for efficient photocatalytic NO removal. It was found that the key to improving the photocatalysis performance was to enhance the ROS transformation from •O2− to •OH, elevating the production of •OH. The ROS directly participate in the photocatalytic NO removal and tailor the rate-determining step, which is required to overcome the high activation energy of the intermediate conversion. Using a closely combined experimental and theoretical method, this work provides a new protocol to investigate the ROS behavior on g-C3N4 for effective NO removal and clarifies the reaction mechanism at the atomic level, which enriches the understanding of ROS in photocatalytic environmental remediation.

[Transformation of endogenous reactive oxygen species participates into bacterial antibiotic resistance].

A growing body of diversified antibiotic resistances raises a significant challenge to anti-infection clinical therapeutics. The emergence of superbugs carrying MCR-1/2 or NDM-1 determinants underlines the importance and urgency in elucidation of molecular mechanisms shared by antibiotic resistances. It is aware that different classes of bactericidal antibiotics consistently stimulate the production of deleterious reactive oxygen species (ROS), which are accompanied with metabolic disturbance. The different destinations of ROS determine its consequence on bacterial fate. Here, we review antibiotic-induced production, progression and transformation of ROS, as well as its role in the development of antibiotic resistance. Additionally, we anticipate that mesosome-like structures-aided exclusion of hydrogen peroxide might represent a previously-unknown mechanism for antibiotic resistance. This mini-review is aiming to present an update overview on antibiotic resistance and provide clues to the development of novel antibiotics.