Primary Oxidant Research Articles

Triple reaction centers Vo-Ce-CuO nanosheets with single Ce atom for the Fenton-like degradation of niflumic acid

Vo (oxygen vacancy)-Ce-CuO nanosheet catalysts were studied for degrading niflumic acid (NFA) by the heterogeneous Fenton-like process (HFLP). NFA removal percentage of optimal Vo-Ce0.05-CuO reached 92% after 60 min of Fenton-like reactions and dropped only 0.28% after five times of recycles. Synergetic effects of triple reaction centers with electron-rich Vo centers, single Ce atom centers, and electron-deficient Cu centers have been demonstrated for generating hydroxyl radicals (OH) by H2O2 decomposition. The electrons from the organic pollutants adsorbed at the electron-deficient Cu centers could be transferred to Vo and Ce via the internal bridge bond to balance the electron transfer. H2O2 could directly obtain electrons from electron-rich Vo and single Ce atom centers to produce OH with a high H2O2 utilization efficiency instead of reducing metal ions by consuming H2O2. For the first time, we demonstrate that triple reaction centers with single Ce atom could improve the conversion percentage of H2O2 to OH with 71.1%. OH, HO2/O2− and 1O2 were the primary oxidants in the HFLP, in which OH played the dominant role.

Protecting the Eye Lens from Oxidative Stress through Oxygen Regulation.

Molecular oxygen is a primary oxidant that is involved in the formation of active oxygen species and in the oxidation of lipids and proteins. Thus, controlling oxygen partial pressure (concentration) in the human organism, tissues, and organs can be the first step in protecting them against oxidative stress. However, it is not an easy task because oxygen is necessary for ATP synthesis by mitochondria and in many biochemical reactions taking place in all cells in the human body. Moreover, the blood circulatory system delivers oxygen to all parts of the body. The eye lens seems to be the only organ that is protected from the oxidative stress through the regulation of oxygen partial pressure. The basic mechanism that developed during evolution to protect the eye lens against oxidative damage is based on the maintenance of a very low concentration of oxygen within the lens. This antioxidant mechanism is supported by the resistance of both the lipid components of the lens membrane and cytosolic proteins to oxidation. Any disturbance, continuous or acute, in the working of this mechanism increases the oxygen concentration, in effect causing cataract development. Here, we describe the biophysical basis of the mechanism and its correlation with lens transparency.

Investigation of the Cytotoxicity of Mars-Relevant Minerals upon Abrasion.

Since the Viking Labeled Release experiments were carried out on Mars in the 1970s, it has been evident that the martian surface regolith has a strong oxidizing capacity that can convert organic compounds into CO2 and probably water. While H2O2 was suggested originally for being the oxidizing agent responsible for the outcome of the Viking experiments, recent analyses of the martian regolith by the Phoenix lander and by consecutive missions point toward radiation-mediated decomposition products of perchlorate salts as the primary oxidant. In a series of experiments, we have shown that abrasion and triboelectric charging of basalt by simulated saltation could be an additional way of activating regolith. We have also shown that abraded basalt with a chemical composition close to that of martian regolith is toxic to several bacterial species and thus may affect the habitability of the martian surface. In the present study, we investigated the effect of the quantitatively most important minerals (olivine, augite, and plagioclase) and iron oxides (hematite, magnetite, and maghemite) on the survival of bacterial cells to elucidate whether a specific mineral that constitutes basalt is responsible for our observations. We observed that suspensions of iron-containing minerals olivine and augite in phosphate-buffered saline (1 × PBS) significantly reduce the number of surviving cells of our model organism Pseudomonas putida after 24 h of incubation. In contrast, the iron-free mineral plagioclase showed no effect. We also observed that suspending abraded olivine and augite in 1 × PBS led to a dramatic increase in pH compared to the pH of 1 × PBS alone. The sudden increase in pH caused by the presence of these minerals may partly explain the observed cytotoxicity. The cytotoxic effect of augite could be relieved when a strong buffer (20 × PBS) was used. In contrast, olivine, despite the stronger buffer, maintained its cytotoxicity. Iron oxides per se have no negative effect on the survival of our test organism. Overall, our experiments confirm the cytotoxicity of basalt and show that no single constituent mineral of the basalt can account for its toxicity. We could show that abraded iron-containing minerals (olivine and augite) change the pH of water when brought into suspension and thereby could affect the habitability of martian regolith.

Blue‐LED Synthesis of Pummerer's Ketones by Peroxidase‐Lignin‐Catalyzed Oxidative Coupling of Substituted Phenols

AbstractPummerer's ketones resembling the tricyclic scaffold of bioactive natural substances were synthesized by blue‐LED driven Horseradish Peroxidase oxidative coupling of substituted phenols in 2‐methyltetrahydrofuran by using meso‐tetraphenylporphyrin as photosensitizer and dioxygen as primary oxidant. The application of functionalized lignin nanoparticles as a renewable and efficient platform for the immobilization of the enzyme extended the effectiveness of the overall process to heterogeneous catalysis under buffer limiting conditions.

The ferryl generation by fenton reaction driven by catechol

The Fenton and Fenton-like reactions are based on the decomposition of hydrogen peroxide catalyzed by Fe(II), primarily producing highly oxidizing hydroxyl radicals (HO∙). While HO∙ is the main oxidizing species in these reactions, Fe(IV) (FeO2+) generation has been reported as one of the primary oxidants. FeO2+ has a longer lifetime than HO∙ and can remove two electrons from a substrate, making it a critical oxidant that may be more efficient than HO∙. It is widely accepted that the preferential generation of HO∙ or FeO2+ in the Fenton reaction depends on factors such as pH and Fe: H2O2 ratio. Reaction mechanisms have been proposed to generate FeO2+, which mainly depend on the radicals generated in the coordination sphere and the HO∙ radicals that diffuse out of the coordination sphere and react with Fe(III). As a result, some mechanisms are dependent on prior HO∙ radical production. Catechol-type ligands can induce and amplify the Fenton reaction by increasing the generation of oxidizing species. Previous studies have focused on the generation of HO∙ radicals in these systems, whereas this study investigates the generation of FeO2+ (using xylidine as a selective substrate). The findings revealed that FeO2+ production is increased compared to the classical Fenton reaction and that FeO2+ generation is mainly due to the reactivity of Fe(III) with HO∙ from outside the coordination sphere. It is proposed that the inhibition of FeO2+ generation via HO∙ generated from inside the coordination sphere is caused by the preferential reaction of HO∙ with semiquinone in the coordination sphere, favoring the formation of quinone and Fe(III) and inhibiting the generation of FeO2+ through this pathway.

Substrate Conformation Regulates Aromatic C-H Vs C-F Bond Activation in Heme-Dependent Tyrosine Hydroxylase.

A recently discovered heme-dependent enzyme tyrosine hydroxylase (TyrH) offers a green approach for functionalizing the high-strength C-H and C-F bonds in aromatic compounds. However, there is ambiguity regarding the nature of the oxidant (compound 0 or compound I) involved in activating these bonds. Herein, using comprehensive molecular dynamics (MD) simulations and hybrid quantum mechanical/molecular mechanical calculations, we reveal that it is compound I (Cpd I) that acts as the primary oxidant involved in the functionalization of both C-F and C-H bonds. The energy barrier for C-H and C-F activation using compound 0 (Cpd 0) as an oxidant was very high, indicating that Cpd 0 cannot be an oxidant. Consistent with the previous experimental finding, our simulation shows two different conformations of the substrate, where one orientation favors the C-H activation, while the other conformation prefers the C-F activation. As such, our mechanistic study shows that nature utilizes just one oxidant, that is, Cpd I, but it is the active site conformation that decides whether it selects C-F or C-H functionalization which may resemble involvement of two different oxidants.

Hierarchical nano-reactor with core-shell structure for efficient removal of atrazine via heterogeneous catalytic ozonation: Experimental parameters, kinetics and performance analysis

The engineering application of the heterogeneous catalytic ozonation process (HCOP) is severely hampered by inefficient heterogeneous catalysts. Herein, a novel hierarchical core-shell MnO2@mSiO2 nano-reactor was prepared using hydrothermal and sol-gel methods. Its catalytic performance was systematically evaluated through the degradation and mineralization of atrazine (ATZ) in HCOP under various reaction parameters. At optimal parameters (O3/7.5 mg/L, ATZ/15 uM, catalyst/30 mg/L, pH = 7), 96.5 % and 36.1 % of ATZ and total organic carbon (TOC) removal efficiencies could be obtained after 30 min, respectively. After five cycles, the ATZ removal efficiency of MnO2@mSiO2 only decreased by approximately 10 %. The synergy effects between the core and mesoporous shell played a vital role in its efficient catalytic activity. The large specific surface area and confined environment favored ozone adsorption, mass transfer and enhanced the enrichment of ATZ, intermediate products, and oxidants. Quenching experiments and the chemical kinetic model indicated that hydroxyl radical (·OH) was the primary oxidant. The Mn3+/ Mn4+ and oxygen vacancies (OVs) acted as active sites to promote ozone decomposition via electron transfer facilitated by the shell. This work provides new advancements for the development of high-efficiency catalysts for the engineering application of HCOP.

Electrochemical Properties of Ru Polypyridyl Phosphonates

Abstract[Ru(bpyPO3H2)(bpy)Cl]Cl (bpyPO3H2=6,6’‐bipyridin‐2‐yl)phosphonic acid) and [Ru(tpy)(MepyPO3H2)Cl]Cl (MepyPO3H2=(pyridin‐2‐ylmethyl)phosphonic acid) were synthesized and characterized spectroscopically and electrochemically. Each compound was found to exhibit proton‐coupled electron transfer (PCET). In the case of [Ru(bpyPO3H2)(bpy)Cl]Cl, a Ru(V/IV) couple was detected at 1.4 V vs. NHE. Each complex was tested for its ability to catalyze C−H bond oxidation using a variety of sacrificial oxidants, and it was found that under aqueous conditions [Ru(bpyPO3H2)(bpy)Cl]Cl oxidizes secondary C−H bonds using sodium periodate (NaIO4) as the primary oxidant.

Vanadyl heterosubstituted 1,3-β-diketonate complexes: Synthesis, characterization and catalytic applications for the selective oxidation and detoxification of sulfur compounds

Six novel Vanadyl heterocyclic/aromatic substituted 1,3-β-diketonates complexes containing bidentate ligands have been synthetized and their structures full characterized by single crystals X-ray analyses (complexes 1–3), EPR spectroscopy either in a glassy state (100 K) or as powder, FT-IR and UV-Vis analyses. The coordination environment of the complexes (a distorted octahedron) is formed by two chelate dianions in the equatorial plane in a cis-planar configuration. The catalytic activity of these new oxidovanadium(IV) complexes has been studied in the selective oxidation of a series of sulfur-containing substrates toward their corresponding sulfides and/or sulfones, using tert-butyl hydroperoxide as primary oxidant. The effects of oxidant to substrate molar ratio, catalyst amount, solvent and temperature have been studied. The high activity and selectivity showed by the complexes, prompted us to apply, successfully, the catalyst 4 in the challenging decontamination of the mustard gas simulants CEES and CEPS, towards their corresponding sulfoxide derivatives, under mild conditions. A rationale analysis on the main observed results in terms of substrate conversion yields and sulfoxides (or sulfones) selectivities, has been addressed.

Formaldehyde and hydroperoxide distribution around the Arabian Peninsula – evaluation of EMAC model results with ship-based measurements

Abstract. Formaldehyde (HCHO), hydrogen peroxide (H2O2) and organic hydroperoxides (ROOH) play a key role in atmospheric oxidation processes. They act as sources and sinks for HOx radicals (OH + HO2), with OH as the primary oxidant that governs the atmospheric self-cleaning capacity. Measurements of these species allow for evaluation of chemistry-transport models which need to account for multifarious source distributions, transport, complex photochemical reaction pathways and deposition processes of these species. HCHO is an intermediate during the oxidation of volatile organic compounds (VOCs) and is an indicator of photochemical activity and combustion-related emissions. In this study, we use in situ observations of HCHO, H2O2 and ROOH in the marine boundary layer (MBL) to evaluate results of the general circulation model EMAC (ECHAM5/MESSy2 Atmospheric Chemistry; European Center HAMburg, Modular Earth Submodel System). The dataset was obtained during the Air Quality and Climate Change in the Arabian Basin (AQABA) ship campaign around the Arabian Peninsula in summer 2017. This region is characterized by high levels of photochemical air pollution, humidity and solar irradiation, especially in the areas around the Suez Canal and the Arabian Gulf. High levels of air pollution with up to 12 ppbv HCHO, 2.3 ppbv ROOH and relatively low levels of H2O2 (≤0.5 ppbv) were detected over the Arabian Gulf. We find that EMAC failed to predict absolute mixing ratios of HCHO and ROOH during high-pollution events over the Arabian Gulf, while it reproduced HCHO on average within a factor of 2. Dry deposition velocities were determined for HCHO and H2O2 at night with 0.77±0.29 cm s−1 for HCHO and 1.03±0.52 cm s−1 for H2O2 over the Arabian Sea, which were matched by EMAC. The photochemical budget of H2O2 revealed elevated HOx radical concentrations in EMAC, which resulted in an overestimation of H2O2 by more than a factor of 5 for the AQABA dataset. The underestimated air pollution over the Arabian Gulf was related to EMAC's coarse spatial resolution and missing anthropogenic emissions in the model.

Ice-templated synthesis of tungsten oxide nanosheets and their application in arsenite oxidation

Tungsten oxide (WO3) nanosheets were prepared as catalysts to activate hydrogen peroxide (H2O2) in arsenite (As(III)) oxidation. Ice particles were employed as templates to synthesize the WO3 nanosheets, enabling easy template removal via melting. Transmission electron microscopy and atomic force microscopy revealed that the obtained WO3 nanosheets were plate-like, with lateral sizes ranging from dozens of nanometers to hundreds of nanometers and thicknesses of <10 nm. Compared to that of the WO3 nanoparticle/H2O2 system, a higher efficiency of As(III) oxidation was observed in the WO3 nanosheet/H2O2 system. Electron spin resonance spectroscopy, radical quenching studies, and As(III) oxidation experiments under anoxic conditions suggested that the hydroperoxyl radical (HO2●) acted as the primary oxidant. The WO3 nanosheets possessed numerous surface hydroxyl groups and electrophilic metal centers, enhancing the production of HO2● via H2O2 activation. Various anions commonly present in As(III)-contaminated water exhibited little effect on As(III) oxidation in the WO3 nanosheet/H2O2 system. The high oxidation efficiency was maintained by adding H2O2 when it was depleted, suggesting that the catalytic activity of the WO3 nanosheets did not deteriorate after multiple catalytic cycles.

Transformation of hydroxylamine to nitrosated and nitrated products during advanced oxidation process

Recently, hydroxylamine (HAm) was introduced to drive advanced oxidation processes (AOPs) for removing organic contaminants. However, we found that HAm-driven Cu(II)/peroxymonosulfate oxidation of phenol produced p-nitrosophenol, 2-nitrophenol and 4-nitrophenol. The total nitro(so) products accounted for approximately 25.0 % of the phenol transformation at certain condition. SO4•− and •OH were identified as the primary and second significant oxidants, respectively. Reactive nitrogen species (RNS) were involved in phenol transformation. The pathway and mechanism of HAm transformation in HAm-driven transition metal ion-catalyzed AOPs were proposed for the first time in this study. The product of HAm via twice single-electron oxidation by Cu(II) is nitroxyl (HNO/NO−), which is a critical oxidation intermediate of HAm. Further oxidation of HNO by SO4•− or •OH is the initial step in propagating radical chain reactions, leading to nitric oxide radical (•NO) and nitrogen dioxide radical (•NO2) as the primary RNS. HAm is a critical intermediate in natural nitrogen cycle, suggesting that HAm can drive the oxidation processes of pollutants in natural environments. Nitro(so) products will be readily produced when AOPs are applied for ecological remediation. This study highlights the formation of toxic nitrosated and nitrated products in HAm-driven AOPs, and the requirement of risk assessments to evaluate the possible health and ecological impacts.

Degradation of surrogate and real naphthenic acids from simulated and real oil sands process water using electrochemically activated peroxymonosulfate (EO-PMS) process

The remediation of dissolved organics in oil sands process water (OSPW), specifically, naphthenic acids (NAs) is considered a major challenge facing the oil sands industry due to recalcitrant and persistent nature of this class of organics in the environment. Herein, the degradation of 5-Phenylvaleric Acid (PVA) as a NA surrogate compound and real NAs in a simulated OSPW and real OSPW was investigated by coupling electro-oxidation and electrochemically activated peroxymonosulfate (EO-PMS) process. The combined EO-PMS process showed high removal efficiency of PVA, in which EO was enhanced by the successful electrochemical activation of PMS at different electrode surfaces. The effects of different cathode and anode materials, initial PMS concentration, and applied current intensity on the PVA degradation were investigated. The PVA degradation efficiencies increased with the increase in the PMS concentration and applied current, however, decreased at higher levels. Carbon felt cathode and BDD anode showed the highest improvement during EO-PMS process. Both sulfate radicals (SO4•‾) and hydroxyl radicals (•OH) were found to be the primary reactive oxidants identified for the PVA degradation by both radical scavenger and spin-trapped techniques. A complete degradation of 50 mg/L PVA solution and significant reduction of the classical and oxidized NAs as well as aromatics in real OSPW were achieved by EO-PMS compared to EO alone. The results confirmed that the combination of electrochemical oxidation and electro-activated PMS process (EO-PMS) could be a promising and efficient technology for the treatment of recalcitrant NA compounds in OSPW.

Fe-Ti bimetals catalyst derived from biowaste for highly efficient persulfate activation: Performance and mechanisms

Sludge based catalysts (SBCs) has been considered as a promising and viable approach to sludge reclamation. Herein, we fabricated bimetallic Fe-Ti doped SBCs via a facile synthesis with sludge containing polyacrylamide (PAM) as N-precursor. The adsorption capacity and degradation efficiency of as-synthesized SBCs were assessed using tetracycline (TC) as a target pollutant, in which PAM in sludge played a dual role by promoting porosity, active sites, and structural defects beneficial for persulfate (PS) activation. Fe-Ti doping induced the activation of PS by a fast redox cycle of Fe3+/Fe2+ associated with the coexistence of Ti4+/Ti3+, which enabled an efficient electron transfer between the catalyst and PS. The synergistic effect of PAM-derived N doping and Fe-Ti bimetals resulted in prevention of iron leaching and enhanced catalyst stability over a wide pH range. The surface SO4•− was the primary oxidant in the TC degradation process based on free-radical quenching experiments, and degradation pathways of TC were proposed given the intermediate evidence from UPLC-HRMS analysis. This study promotes the reclamation of PAM-containing sludge providing an eco-friendly and efficient process to activate PS for wastewater treatments.

Extreme hydroxyl amounts generated by thunderstorm-induced corona on grounded metal objects

Atmospheric electrical discharges are now known to generate unexpectedly large amounts of the atmosphere's primary oxidant, hydroxyl (OH), in thunderstorm anvils, where electrical discharges are caused by atmospheric charge separation. The question is "Do other electrical discharges also generate large amounts of oxidants?" In this paper, we demonstrate that corona formed on grounded metal objects under thunderstorms produce extreme amounts of OH, hydroperoxyl (HO2), and ozone (O3). Hundreds of parts per trillion to parts per billion of OH and HO2 were measured during seven thunderstorms that passed over the rooftop site during an air quality study in Houston, TX in summer 2006. A combination of analysis of these field results and laboratory experiments shows that these extreme oxidant amounts were generated by corona on the inlet of the OH-measuring instrument and that corona are easier to generate on lightning rods than on the inlet. In the laboratory, increasing the electric field increased OH, HO2, and O3, with 14 times more O3 generated than OH and HO2, which were equal. Calculations show that corona on lightning rods can annually generate OH that is 10-100 times ambient amounts within centimeters of the lightning rod and on high-voltage electrical power lines can generate OH that is 500 times ambient a meter away from the corona. Contrary to current thinking, previously unrecognized corona-generated OH, not corona-generated UV radiation, mostly likely initiates premature degradation of high-voltage polymer insulators.

Pollution-Derived Br2 Boosts Oxidation Power of the Coastal Atmosphere.

The bromine atom (Br•) has been known to destroy ozone (O3) and accelerate the deposition of toxic mercury (Hg). However, its abundance and sources outside the polar regions are not well-known. Here, we report significant levels of molecular bromine (Br2)─a producer of Br•─observed at a coastal site in Hong Kong, with an average noontime mixing ratio of 5 ppt. Given the short lifetime of Br2 (∼1 min at noon), this finding reveals a large Br2 daytime source. On the basis of laboratory and field evidence, we show that the observed daytime Br2 is generated by the photodissociation of particulate nitrate (NO3-) and that the reactive uptake of dinitrogen pentoxide (N2O5) on aerosols is an important nighttime source. Model-calculated Br• concentrations are comparable with that of the OH radical─the primary oxidant in the troposphere, accounting for 24% of the oxidation of isoprene, a 13% increase in net O3 production, and a nearly 10-fold increase in the production rate of toxic HgII. Our findings reveal that reactive bromines play a larger role in the atmospheric chemistry and air quality of polluted coastal and maritime areas than previously thought. Our results also suggest that tightening the control of emissions of two conventional pollutants (NOx and SO2)─thereby decreasing the levels of nitrate and aerosol acidity─would alleviate halogen radical production and its adverse impact on air quality.

Simultaneous reduction of nitrogen oxides and sulfur dioxide in circulating fluidized bed combustor during oxy-coal combustion

For stable carbon capture utilization and storage, highly-pure CO2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N2O) and sulfur dioxide (SO2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N2O, and SO2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N2O, and SO2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO2 content and low pollutant emissions.

Generation of interfacial high-spin manganese intermediates as reactive oxidant during peroxymonosulfate activation mediated by amorphous MnOx supported on polymeric substrate

The preparation of transition metal oxides based on traditional hydrothermal and calcination processes for heterogeneous PMS activation in contaminants' abatement has been widely reported. A satisfactory PMS activation efficiency often demands the transition metal oxides with crystallographic structure; however, the preparation processes of crystalline metal oxides require more energy input. Besides, achieving the targeted electron transfer between pollutants and reactive oxygen species (ROS) to overcome the disturbance of the actual water matrix is still challenging. Herein, we immobilized manganese oxides onto polymeric substrates under room temperature by a novel redox method with lower energy consumption. The obtained composite was applied for PMS activation to degrade multiple phenolic pollutants mainly through non-radical pathways. Combining the results of multiple characterizations and 18O isotope-tracer experiments, we proposed that the interfacial high-spin MnIII-peroxy complex was the primary reactive oxidant. Besides, a small portion of MnIII-peroxy complex could further undergo interspecies oxygen-transfer to form MnV-oxo species as the secondary reactive oxidant, resulting in the different manganese reduction products (MnIII/MnIV). The proposed mechanism could explain the average oxidation state of Mn changed after PMS activation. Comparing with the radical-based systems, interfacial reactive manganese intermediates exhibited satisfactory resistance against complex water matrices, such as chloride, bicarbonate, natural organic matter (NOM), and effluent organic matter (EfOM). We believe that this study could inspire novel methods with lower energy consumption to prepare active manganese oxides and provide intriguing mechanistic insights into PMS activation mediated by amorphous manganese oxides.

Polymeric Nanocapsule Enhances the Peroxidase-like Activity of Fe3O4 Nanozyme for Removing Organic Dyes

Peroxidase-like nanozymes are nanoscale materials that can closely mimic the activity of natural peroxidase for a range of oxidation reactions. Surface coating with polymer nanogels has been considered to prevent the aggregation of nanozymes. For a long time, the understanding of polymer coating has been largely limited to its stabilization effect on the nanozyme in aqueous media, while little is known about how polymer coating plays a role in interaction with substrates and primary oxidants to dictate the catalytic process. This work reported a facile sequential modification of Fe3O4 nanoparticles to polyacrylamide coated nanozymes, and as low as 112 mg/L samples with only 5 mg/L Fe3O4 could nearly quantitatively (99%) remove a library of organic dyes with either H2O2 or Na2S2O8 as primary oxidants. The catalytic results and molecular simulation provide both experimental and computational evidence that the hydrogen bonding interaction between the reactant and nanozymes is key for the high local concentration hence catalytic efficiency. We envision that this work, for the first time, provides some insights into the role of polymer coating in enhancing the catalytic activity of nanozyme apart from the well-known water dispersity effect.

Atomically dispersed cobalt on carbon nitride for peroxymonosulfate activation: Switchable catalysis enabled by light irradiation

Herein, we present atomically dispersed cobalt anchored carbon nitride (Co-CN) as a highly efficient peroxymonosulfate (PMS)-activation catalyst. Different from the traditional catalytic pathways, in which hydroxyl radical, sulfate radical, singlet oxygen, or surface-bound PMS engaged as primary oxidants, high-valent cobalt-oxo [Co(IV)] species generated from a unique two-electron transfer pathway are confirmed as primary oxidants. Hydroxyl radical triggered by Co(IV) serves as secondary intermediate oxidant. In addition, it is interesting to find that such Co(IV)-based nonradical pathway can be switched to a radical-dominated pathway under light irradiation, suggesting the Co-CN can not only act as a PMS activator but also as a photoswitch to regulate the PMS oxidation pathways. On the basis of experiment and DFT calculations, the switchable catalysis can be attributed to the formation of photoinduced hole-trapping sites on the single Co atoms, which result in the primary PMS activation sites convert from single Co atoms to melem units. More importantly, considering the distinctive oxidation feature of Co(IV) and radical species, our finding provides a novel strategy to expand the application possibilities of Co-based Fenton-like process in dealing with different environmental issues by flexibly controlling the PMS catalytic pathways.