Evolution Of Reactive Oxygen Species Research Articles

Insights into the Formation Mechanism of Reactive Oxygen Species in the Interface Reaction of SO2 on Hematite.

The interplay between sulfur and iron holds significant importance in their atmospheric cycle, yet a complete understanding of their coupling mechanism remains elusive. This investigation delves comprehensively into the evolution of reactive oxygen species (ROS) during the interfacial reactions involving sulfur dioxide (SO2) and iron oxides under varying relative humidity conditions. Notably, the direct activation of water by iron oxide was observed to generate a surface hydroxyl radical (•OH). In comparison, the aging of SO2 was found to markedly augment the production of •OH radicals on the surface of α-Fe2O3 under humid conditions. This augmentation was ascribed to the generation of superoxide radicals (•O2-) stemming from the activation of O2 through the Fe(II)/Fe(III) cycle and its combination with the H+ ion to produce hydrogen peroxide (H2O2) on the acidic surface. Moreover, the identification of moderate relative humidity as a pivotal factor in sustaining the surface acidity of iron oxide during SO2 aging underscores its crucial role in the coupling of iron dissolution, ROS production, and SO2 oxidation. Consequently, the interfacial reactions between SO2 and iron oxides under humid conditions are elucidated as atmospheric processes that enhance oxidation capacity rather than deplete ROS. These revelations offer novel insights into the mechanisms underlying •OH radical generation and oxidative potential within atmospheric interfacial chemistry.

Unraveling the catalytic ozonation mechanisms with ZnO decorated rGO composite: Structural properties and reactive oxygen species evolution

In this study, a series of ZnO decorated rGO composites (x%ZnO@rGO) were successfully synthesized by the alkaline hydrothermal method. The crystal structure, surface morphology, and chemical property of x%ZnO@rGO were characterized by BET, XRD, FT-IR, SEM, TEM, and XPS, respectively. Amongst, 15%ZnO@rGO composite exhibited superior catalytic ozonation performance with an improvement of 68.4% on atrazine (ATZ) degradation efficiency (3 mins), more than 7.8 times of the pseudo-first-order rate constant compared with single O3. The roles of O3 and reactive oxygen species (ROSs) were confirmed and compared by the quenching and low-concentration probe experiments, suggesting that O3 and OH played an important role for ATZ degradation, while the function of 1O2 and O2− can be neglected both in single O3 and 15%ZnO@rGO/O3 system, which was contrary to that of the quenching experiments. Besides, the exposures of O3 and ROSs showed that 15%ZnO@rGO can facilitate the transformation process of 1O2 to OH in different conditions, and largely enhance the exposure of OH. The roles of electrons, Lewis acid sites, and oxygen vacancies of 15%ZnO@rGO in catalytic ozonation were identified as well, which offered us a new perspective to design a high-efficiency catalyst and may promote graphene-based metal oxides for practical pollutant elimination.

Singlet oxygen-dominated non-radical oxidation in biochar/peroxymonosulfate system for efficient degradation of tetracycline hydrochloride: Surface site and catalytic mechanism

BackgroundBiochar has attracted much attention in peroxymonosulfate (PMS) activation for the elimination of organic pollutants in water. However, the factor to determine the catalytic efficiency of biochar and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. Method & resultIn this study, Camellia oleifera shell-derived biochar (COSB) was prepared by one-step pyrolysis. The pyrolysis temperature could tune the catalytic performance of COSB. Owing to more C=O groups and defects, the COSB-1000 prepared at 1000 °C showed the optimal activity in PMS activation. In the presence of 0.4 g∙L−1 of COSB-1000 and 1.0 g∙L−1 PMS, 91.57% of tetracycline hydrochloride (TC, 20 mg·L−1) was degraded within 105 min. In addition, the COSB-1000/PMS system demonstrated good anti-interference ability and a wide pH applicability from 3.0 to 11.0. Quenching experiment and electron spin resonance (EPR) spectroscopy suggested that the non-radical oxidation process dominated by the generated 1O2, which was converted from O2•−, play the vital role in TC degradation by the COSB-1000/PMS system. Furthermore, four possible degradation pathways of TC in the COSB-1000/PMS system are proposed by the mass spectroscopy, and the growth-inhibition of Escherichia coli showed that the degradation intermediates were low toxicity. Significant findingsThe results here shed light on the generation of 1O2 by biochar and deepen the insight for the environmentally-friendly catalysts derived from biomass in activating PMS for wastewater treatment.

Efficient activation of peroxodisulfate by novel bionic iron-encapsulated biochar: The key roles of electron transfer pathway and reactive oxygen species evolution.

In this study, a novel iron-encapsulated biochar (Fe@BC) was prepared using the biomass cultivated with an iron-containing solution. The iron in Fe@BC showed the phase change from Fe3O4 to α-Fe, and to CFe15.1, with the increase of pyrolysis temperature (500-900°C), and a graphene shell formed on the surface of Fe@BC. In addition, the signals assigned to the π-π*shake up, pyridinic N, graphitic N, and defects of Fe@BC were found to be stronger as the pyrolysis temperature increased. The F4@B9 sample, which was prepared at 900°C, exhibited an excellent performance (98.01%) to activate peroxydisulfate (PDS) for the degradation of 2,4-dichlorophenol. Electron paramagnetic resonanceand chemical quenching experiments revealed that reactive oxygen radicals (ROS) including sulfate radical (•SO4-), hydroxyl radical (•OH), superoxide radical (•O2-), and singlet oxygen (1O2) existed in the F4@B9/PDS system. Furthermore, the micro-electrolysis process facilitated the generation of •O2- (12.35%) and 1O2 (6.49%) compared with the pure PDS system. Density functional theory revealed that, for the F4@B9-activated PDS process, the graphene shell of F4@B9 served as catalytic active sites as well. According to the correlation analysis, the iron specie of CFe15.1 was more favorable for the generation of ROS than α-Fe. Also, π-π*shake up, pyridinic N, graphitic N, and defects participated in the PDS activation. This study provides a new method for the preparation of high-performance catalysts from naturally grown biomass with high iron contents.

Efficient catalytic ozonation via Mn-loaded C-SiO2 Framework for advanced wastewater treatment: Reactive oxygen species evolution and catalytic mechanism

Heterogeneous catalytic ozonation (HCO) is attractive for water decontamination and catalyst is a core element. However, it is difficult to maintain high efficiency and stability of catalysts under stern conditions. In this study, we proposed Mn-loaded C-SiO2-Framework (Mn-CSF) which contained stable silica core and robust carbon shell for efficient catalytic ozonation. The pseudo-first-order kinetic rate constant for oxalic acid removal of Mn-CSF catalytic ozonation was 160 % and 875 % higher than those of Mn-SiO2 and pristine CSF, respectively. Mn-CSF was also proven effective in gasification wastewater treatment, where the COD was decreased to 46 mg·L−1, 37 % lower than that of Mn-SiO2. These results indicated that the graphitization carbon layer and Mn significantly enhanced the activity of the catalyst. Furthermore, a fulvic-like component and a protein-like component were recognized through 3D-EEM in coal gasification wastewater. It was proven that Mn-CSF catalytic ozonation exhibited higher fulvic-like component and protein-like component removal compared with ozonation. Moreover, O2− and 1O2 were identified to be responsible for organic degradation in this research. Sufficient external specific surface area and porous structure were important for complex wastewater treatment. Specifically, external specific surface area could enhance the degradation of macromolecular organics while porous structures were vital for smaller molecular pollutant removal. The results highlighted that Mn-CSF was a promising HCO catalyst for advanced wastewater treatment, and this study provided evidence of relationship between structure of catalysts and HCO efficiency.

Singlet oxygen-dominated activation of peroxymonosulfate by 3D hierarchical MnO2 nanostructures for degradation of organic pollutants in water: Surface defect and catalytic mechanism

Manganese dioxide (MnO2) is attracting significant attention in the activation of persulfate for the degradation of organic pollutants in water. But the factor determining the catalytic efficiency of MnO2, and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. Herein, three-dimensional (3D) hierarchical MnO2 nanostructures are synthesized via the calcination of hydrothermal product and used to active peroxymonosulfate (PMS) for degradation of acid orange 7 (AO7) in water. The results show that the calcination temperature can tune the morphology of 3D hierarchical MnO2 nanostructures from flower to urchin-like as well as phase transformation from δ-MnO2 to α-MnO2. Owing to the presence of more surface defects and surface adsorbed oxygen species, the urchin-like α-MnO2 nanostructures prepared at 500 °C (MnO2-500) deliver the best catalytic activity in activation of PMS, and 98.3 % of AO7 is degraded in 300 s. Additionally, the MnO2-500 shows wide pH applicability (3.5–9.6). Quenching tests and electron paramagnetic resonance spectra reveal that the catalytic oxidation of AO7 in the MnO2-500/PMS system is mainly mediated by the non-radical pathway, and the dominated ROS is 1O2. Besides, electrochemical experiment confirms the presence of electron transfer in the catalytic process. Density functional theory calculations indicate that the CN and CS groups of AO7 with high electron density are easily attacked by electrophilic ROS, which is further confirmed by liquid chromatography-mass spectrometry. Finally, MnO2-500 exhibits gradually enhanced catalytic activity with the increased cycle number due to the increased surface defects and the surface adsorbed oxygen. This study provides new insight into the PMS activation by MnO2-based catalyst for the remediation of organic pollutants in water.

Photocatalytic O2 activation and reactive oxygen species evolution by surface B-N bond for organic pollutants degradation

The efficiency of photocatalytic molecular oxygen (O2) activation is limited by the poor O2 adsorption and the obstruction of electron transfer. Herein, we designed a graphite carbon nitride with surface B-N bond (Bx-C3N4) to improve its efficiency. A series of characterizations and DFT calculations show that boron atom replaces carbon atom to form B-N bond, which increase the O2 adsorption energy from − 0.47 eV to − 1.17 eV. Moreover, the doped boron atom can be used as the electron capture center to transfer electrons to the N atom, then to the surface adsorbed O2 through the N-O bond, thus improving the photocatalytic generation of·O2- and 1O2. Finally, the photocatalytic degradation rates of RhB, tetracycline and o-nitrophenol by B0.05-C3N4 are 12.3, 4.8 and 18.5 times that of pure g-C3N4, respectively. Moreover, the degradation pathway and toxicity prediction of intermediates of RhB are proposed based on the results of HPLC-MS and DFT calculations.

Boron-doped diamond electrodes degrade short- and long-chain per- and polyfluorinated alkyl substances in real industrial wastewaters

Electrochemical oxidation (ECO) with boron-doped diamond (BDD) electrode of six legacy perfluoroalkyl substances (PFAS) present in semiconductor fabrication wastewaters was investigated in single-solutes, multi-solutes, and real wastewater matrices. ECO degradation kinetics decreased as carbon length decreased in single-solute systems. Because heterogeneous catalysis involves PFAS interacting at the electrode surface, the impact of PFAS in solution on altering the potential affinity for PFAS itself on the surface was quantified. The BDD electrode surface wettability, defined by the surface contact angle, increased with longer chain length and diminished with increasing PFAS concentration. PFASs with a sulfonated head group degraded 2–3x faster than their carboxylic counterparts. Industrial wastewaters can have high background organic concentrations and have a large pH range prior to discharge, offering different opportunities to treat for PFAS near the semiconductor manufacturing tool or prior to pH adjustment and discharge to sanitary sewers. Increasing pH (up to 12) decreased the evolution of reactive oxygen species on the electrode surface and therefore decreased removal kinetics compared to pH 3 and 7. The presence of surfactants (tetramethylammonium hydroxide [TMAH] and sodium dodecyl sulfonate [SDS]) in the wastewater significantly reduced the degradation efficiency of ECO. However, compared to single-solute PFAS systems, multi-solute solutions (mixture of 6 PFASs) had higher degradation rates during ECO. In a real wastewater (originated from RO concentrate), PFASs were efficiently removed in ~320 min reaction time. These results demonstrated the promise for ECO to treat PFAS contained in industrial manufacturing processes at both tool level and blended wastewater.

Geant4-DNA Modeling of Water Radiolysis beyond the Microsecond: An On-Lattice Stochastic Approach.

In this work, we use the next sub-volume method (NSM) to investigate the possibility of using the compartment-based (“on-lattice”) model to simulate water radiolysis. We, first, start with a brief description of the reaction-diffusion master equation (RDME) in a spatially discretized simulation volume (“mesh”), which is divided into sub-volumes (or “voxels”). We then discuss the choice of voxel size and merging technique of a given mesh, along with the evolution of the system using the hierarchical algorithm for the RDME (“hRDME”). Since the compartment-based model cannot describe high concentration species of early radiation-induced spurs, we propose a combination of the particle-based step-by-step (“SBS”) Brownian dynamics model and the compartment-based model (“SBS-RDME model”) for the simulation. We, finally, use the particle-based SBS Brownian dynamics model of Geant4-DNA as a reference to test the model implementation through several benchmarks. We find that the compartment-based model can efficiently simulate the system with a large number of species and for longer timescales, beyond the microsecond, with a reasonable computing time. Our aim in developing this model is to study the production and evolution of reactive oxygen species generated under irradiation with different dose rate conditions, such as in FLASH and conventional radiotherapy.

Mechanical agitation accelerated ultrasonication for wastewater treatment: Sustainable production of hydroxyl radicals

Low efficiency in energy conversion has long been the bottleneck in sonochemistry-based water treatment technologies. In this work, we reported a simple and efficient strategy by introducing mechanical agitation into a low powered ultrasonic system to facilitate the production of cavitation bubbles. The coupled system remarkably intensifies the evolution of reactive oxygen species (ROS) for degradation of refractory organic pollutants. We in-situ monitored the generation of hydroxyl radicals (•OH) by selective scavenging tests and chemical trapping experiments. The operational factors such as rotation speed, gas atmosphere, solution temperature and pH were carefully evaluated for their impacts on the degradation of a plastic microcontaminant, diethyl phthalate (DEP). It was found that the degradation efficiency is closely related to the population of cavitation bubbles in the solution, which was collaboratively governed by the aforementioned factors. A high mechanical agitation speed (600 rpm), great solubility of inert gas atmosphere (Argon), and low reaction temperature (15 ºC) are beneficial to the generation of cavitation bubbles and the associated production of ROS. This work shows a facile strategy to intensify the mechanical energy-to-chemical conversion and provides new mechanistic insights into the ultrasound-based advanced oxidation without external chemical inputs.

Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification.

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O3 molecules on the catalyst surface are regarded as the key clues for further elucidating the O3 activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

Oxygen vacancies induced heterogeneous catalysis of peroxymonosulfate by Ni-doped AgFeO2 materials: Evolution of reactive oxygen species and mechanism

Oxygen vacancies (OVs) modulation has emerged as a prevalent strategy to optimize the performance of Fenton-like catalysts. Nevertheless, the OVs-induced evolution of reactive oxygen species (ROSs) and associated mechanisms in the Fenton-like process remain insufficient. Herein, a series of oxygen-defective AgFe1−xNixO2 were synthesized to enhance peroxymonosulfate (PMS) decomposition and efficient degradation of bisphenol A (BPA) in water. The total amounts of OVs were regulated by varying the ratio of Ni dopant. Compared with original AgFeO2, the AgFe1−xNixO2 with rich OVs exhibited a better redox potential for PMS interaction and a lower reaction energy barrier of PMS decomposition. Superoxide radical (O2−) and singlet oxygen (1O2) worked as the dominant ROSs during the oxidation, rather than traditional sulfate radical (SO4−) or hydroxyl radical (OH). Notably, in situ electron spin resonance witnessed the evolution of growing O2− and 1O2, as well as lessened SO4− and OH with increasing OVs content. It was mainly attributed to the preferential dissociation of PMS into O2 on the OVs, additionally, OVs facilitated the superior surface oxygen mobility and electrical conductivity, which also gave rise to a significant enhancement in O2− and 1O2 generation. Consequently, an OVs-dependent PMS activation mechanism was proposed.

Two layered Bi-based borate photocatalysts MBi2B2O7 (M = Ca, Sr) for photocatalytic degradation and oxygen activation

Layered bismuth-based photocatalytic materials have great potential for environmental purification. In this work, we developed two novel layered bismuth-based borate photocatalysts CaBi2B2O7 (CBBO) and SrBi2B2O7 (SBBO) via solid-phase reaction. The crystal structure, microstructure and optical properties were investigated. The photocatalytic activities were studied by decomposition of tetracycline hydrochloride (TH) and evolution of reactive oxygen species (ROS) under UV light irradiation. The results revealed that CBBO and SBBO exhibit benign TH degradation activity with certain mineralization abilities. Within 4 min illumination, almost 70% and 58% of tetracycline hydrochloride was degraded by CBBO and SBBO, respectively. The quantitative capture experiment of radicals showed that the production rate of OH and O2− was determined to be 1.27 × 10-7 and 10.98 × 10-7 mol·L-1 min-1 for CBBO and 1.01 × 10-7 and 11.75 × 10-7 mol·L-1 min-1 for SBBO, respectively. Density functional theory (DFT) calculation results demonstrated that CBBO has smaller effective masses of electrons and holes than SBBO, which results in higher charge separation efficiency and photocatalytic activity. This work provides two new layered bismuth-based borate photocatalysts for photocatalytic environmental applications.

Establishing high-performance Au/cobalt oxide interfaces for low-temperature benzene combustion

A comprehensive strategy based on the facet control and elemental doping of Co3O4 support plus precise Au assembly was employed to develop the Au/h-MxCo3-xO4 (1 1 2) (h = hexagonal plates; M = Fe, Mn; x = 0.09–0.36) interfaces for low-temperature benzene combustion. The current route in synthesis of Co3O4 hexagonal plates with the most active (1 1 2) exposed facet is free of any organic solvent, surfactant, or coordinator, close to the nominal material yield. Well-controlled Au assembly onto the (1 1 2) facet of h-M0.18Co2.82O4 results in very efficient Au/h-M0.18Co2.82O4 for the target reaction. The processes developed for both controllable support fabrication and governable Au assembly are applicable to other systems and utilizations. N2 sorption, X-ray diffraction, scanning electron microscopy/(high-resolution)transmission electron microscopy, selected-area electron diffraction, energy-dispersive X-ray mapping, inductively coupled plasma mass spectrometry, H2 temperature-programmed reduction, O2 temperature-programmed desorption, and X-ray photoelectron spectroscopy were performed to understand the physicochemical properties of various interfaces. Turnover frequency calculation and activation energy determination were used to reveal distinct catalytic behaviors. The factors significantly determining the interface activity are as follows: (1) the critical support orientation and element constitution [h-MxCo3-xO4 (1 1 2) (M = Fe, Mn, x = 0.09–0.18)]; (2) the surface reconstruction [from (1 1 2) to (1 1 1)] owing to increasing dopant content; (3) the evolution of reactive oxygen species (OI− vs. OII−) and the oxidation state of Au entities.

Insights into Heteroatom-Doped Graphene for Catalytic Ozonation: Active Centers, Reactive Oxygen Species Evolution, and Catalytic Mechanism.

To guide the design of novel graphene-based catalysts in catalytic ozonation for micropollutant degradation, the mechanism of catalytic ozonation with heteroatom-doped graphene was clarified. Reduced graphene oxide doped with nitrogen, phosphorus, boron, and sulfur atoms (N-, P-, B-, and S-rGO) were synthesized, and their catalytic ozonation performances were evaluated in the degradation of refractory organics and bromate elimination simultaneously. Doping with heteroatoms, except sulfur, significantly improved the catalytic ozonation activity of graphene. Introducing sulfur atoms destroyed the stability of graphene during ozonation, with the observed partial performance improvement caused by surface adsorption. Degradation pathways for selected refractory organics were proposed based on the intermediates identified using high-resolution Orbitrap mass spectroscopy and gas chromatographic-mass spectroscopy. Three and six new unopened intermediates were identified in benzotriazole and p-chlorobenzoic acid degradation, respectively. Roles of chemical functional groups, doped atoms, free electron, and delocalized π electron of heteroatom-doped graphene in catalytic ozonation were identified, and contributions of these active centers to the formation of reactive oxygen species (ROS), including hydroxyl radicals, superoxide radicals, singlet oxygen, and H2O2, were evaluated. A mechanism for catalytic ozonation by heteroatom-doped graphene was proposed for the first time.

Efficient evolution of reactive oxygen species over the coordinated π-delocalization g-C3N4 with favorable charge transfer for sustainable pollutant elimination

Reactive oxygen species (ROS) as efficient and green oxidants can be generated through various catalytic methods, which is important for environmental chemistry and chemical engineering. Here we construct an efficient photocatalytic system to evolve ROS for environmental purification. In the work, the coordinated g-C3N4 photocatalysts (Cu/C3N4) are designed by interacting N 2p lone electrons at vacancy site of tri-s-triazine polymer with 3d orbits of Cu2+, resulting in the extended π-delocalization structure of g-C3N4. Experimental and theoretical calculations confirm that the extended π-delocalization structure of Cu/C3N4 strengthens the light capturing capability from ultraviolet to near infrared light, favors the charge transfer from N 2p of C3-N to the linked C, and Cu atoms. As a result, the efficient evolution of ROS including O2− (13 μmol L−1 h−1), and H2O2 (550 μmol L−1 h−1) can be completed over Cu/C3N4 photocatalysts. Cu/C3N4 photocatalysts results in a highly efficient generation of ROS and also exhibited a sustainable removal efficiency for NO, and HCHO, which demonstrates a promising application in the field of environmental purification.

Promoted peroxymonosulfate activation into singlet oxygen over perovskite for ofloxacin degradation by controlling the oxygen defect concentration

Recently, perovskite is becoming a promising alternative as peroxymonosulfate (PMS) activator for the remediation of organic pollutants in water. But the factor determining PMS activation efficiency of perovskite and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. In this study, we proposed an oxygen defect dependent PMS activation mechanism over perovskite with the singlet oxygen (1O2) as the dominant ROS. Among the tested four perovskites, ofloxacin (OFX) degradation efficiency increased with the following order: LaFeO3 < LaZnO3 < LaMnO3 < LaNiO3, which agreed well with their oxygen defect amounts based on X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis. The results clearly demonstrated a good relationship among oxygen defects in LaBO3, OFX degradation efficiency and 1O2 concentration. Moreover, 1O2 evolution mechanism over perovskite by decreasing the activation energy of PMS self-decomposition was proposed. The 1O2 mediated OFX degradation pathway was further studied by HPLC-MS technique and three-dimensional excitation–emission matrix fluorescence spectroscopy (3D EEMs). This work provides a new insight into PMS activation by perovskites and favors its application in actual water treatment.

Magnetic nitrogen-doped nanocarbons for enhanced metal-free catalytic oxidation: Integrated experimental and theoretical investigations for mechanism and application

Developing efficient, low-cost and environmental-friendly catalysts is of great significance for heterogeneous activation of persulfates toward strategic purification of wastewater with powerful sulfate radical based advanced oxidation processes (SR-AOPs). In this study, a three-dimensional and hierarchical nitrogen-doped magnetic carbon (Co@N-C) was developed via a facile one-pot carbonization of ZIF-67 with a green precursor of urea. Acid treatment was applied to remove the surface unstable cobalt nanoparticles (NPs) to avoid the potential leaching of toxic Co ions. Benefited from the rationally structural design of the carbon precursor and post-treatment with surface engineering, the derived Co@N-C can efficiently activate PMS for fast decomposition of bisphenol A (BPA) in aqueous solution, achieving high removal of total organic carbon (TOC) with trace cobalt leaching. The impacts of diverse reaction parameters on BPA degradation were systematically investigated. More importantly, density functional theory (DFT) calculations revealed that the entrapped Co NPs can impressively modulate the electronic states of the interacted carbon regions, giving rise to enhanced carbocatalysis with synergistic promotion of N-doping. The embedded Co NPs also afford the carbocatalysts to be magnetic for an easy recycling. Additionally, comprehensive investigations of the evolution of reactive oxygen species (ROS) on the carbonaceous materials by competitive radical scavenging tests and in situ radical trapping with advanced electron paramagnetic resonance (EPR) revealed the singlet oxygen (1O2) as the dominant ROS rather than sulfate radicals. This study proposed a facile strategy for fabricating novel hybrid nanocarbon catalysts with N-doping and magnetic property and enables new mechanistic insights into carbocatalysis in AOPs, providing a promising system for green wastewater remediation.

Construction of carbon nitride and MoS2 quantum dot 2D/0D hybrid photocatalyst: Direct Z-scheme mechanism for improved photocatalytic activity

Graphite-like carbon nitride (g-C3N4)-based compounds have attracted considerable attention because of their excellent photocatalytic performance. In this work, a novel direct Z-scheme system constructed from two-dimensional (2D) g-C3N4 nanoplates and zero-dimensional (0D) MoS2 quantum dots (QDs) was prepared through the combination of a hydrothermal process and microemulsion preparation. The morphologies, structures, and optical properties of the as-prepared photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy. In addition, the photocatalytic performances of the prepared 2D/0D hybrid composites were evaluated based on the photodegradation of rhodamine B under visible-light irradiation. The results demonstrated that the introduction of MoS2 QDs to g-C3N4 greatly enhanced the photocatalytic efficiency. For the optimum 7% MoS2 QD/g-C3N4 photocatalyst, the degradation rate constant was 8.8 times greater than that of pure g-C3N4 under visible-light irradiation. Photocurrent and electrochemical impedance spectroscopy results further demonstrated that the MoS2 QD/g-C3N4 composites exhibited higher photocurrent density and lower chargetransfer resistance than those of the pure g-C3N4 or MoS2 QDs. Active species trapping, terephthalic acid photoluminescence, and nitro blue tetrazolium transformation experiments were performed to investigate the evolution of reactive oxygen species, including hydroxyl radicals and superoxide radicals. The possible enhanced photocatalytic mechanism was attributed to a direct Z-scheme system, which not only can increase the separation efficiency of photogenerated electron-hole pairs but also possesses excellent oxidation and reduction ability for high photocatalytic performances. This work provides an effective synthesis approach and insight to help develop other C3N4-based direct Z-scheme photocatalytic systems for environmental purification and energy conversion.

Fast Electron Transfer and •OH Formation: Key Features for High Activity in Visible-Light-Driven Ozonation with C3N4 Catalysts

Photocatalytic ozonation of wastewater pollutants by sunlight is a highly attractive technology close to real application. Understanding this process on the atomic scale and under realistic working conditions is challenging but vital for the rational design of catalysts and photocatalytic decontamination systems. Here we study two highly active C3N4 photocatalysts (bulk C3N4 and a nanosheet-structured C3N4) under simultaneous visible-light irradiation and O3 bubbling in water by in situ EPR spectroscopy coupled with an online spin-trapping technique. The photoexcitation of electrons to the conduction band (CB-e–), their further trapping by dissolved O2 and O3, and the evolution of reactive oxygen species (ROS) have been semiquantitatively visualized. A dual role of O3 in boosting the CB-e– to •OH conversion is confirmed: (i) an inlet 2.1 mol % O3/O2 gas mixture can trap about 2–3 times more CB-e– upon aqueous C3N4 suspension than pure O2 and further produce •OH by a robust •O3–-mediated one-electron-reduc...