Understanding of the Oxidation Behavior of Benzyl Alcohol by Peroxymonosulfate via Carbon Nanotubes Activation

Buffered Hydroxyl Radical for Photocatalytic Non-Oxidative Methane Coupling

Hydroxy radical (⋅OH) is a prestigious oxidant that allows the cleavage of strong chemical bonds of methane but is untamed, leading to over-oxidation of methane and waste of oxidants, especially at high methane conversion. Here, we managed to buffer ⋅OH in an aqueous solution of photo-irradiated Fe3+, where ⋅OH almost participates in methane oxidation. Due to the interaction between Fe3+ and SO4 2-, the electron transfer from OH- to excited-state Fe3+ for ⋅OH generation is retarded, while excessive ⋅OH is consumed by generated Fe2+ to restore Fe3+. When combined with a Ru/SrTiO3:Rh photocatalyst, the buffered ⋅OH converts methane to C2+ hydrocarbons and H2 with formation rates of 246 and 418 μmol h-1, respectively. The apparent quantum efficiency reaches 13.0±0.2 %, along with 10.2 % methane conversion and 81 % C2+ selectivity after 80 hours of reaction. Overall, this work presents a strategy for controlling active radicals for selective and efficient photocatalysis.

Sustainable production of 2,5-diformylfuran via peroxymonosulfate-triggered mild catalytic oxidation of lignocellulosic biomass

The relentless depletion of fossil fuels accentuates the urgent necessity for the sustainable synthesis of chemicals from renewable biomass. 5-Hydroxymethylfurfural (HMF), extracted from lignocellulosic biomass, emerges as a beacon of hope for conversion into value-added chemicals. However, the inherent susceptibility of its unsaturated aldehyde groups to excessive oxidation often culminates in undesired reactions, compromising both the yield and specificity of the desired products. Here, we introduce a holistic methodology for the cost-effective and ecologically responsible generation of 2,5-diformylfuran (DFF), through the heterogeneously catalyzed oxidation of HMF utilizing peroxymonosulfate (PMS) under benign conditions. This strategy, characterized by the meticulous enhancement of surface ketone groups via a mixed-salt-assisted co-pyrolysis technique, achieves an unparalleled selective activation of PMS, engendering singlet oxygen to catalyze the oxidation of HMF into DFF with a selectivity surpassing 80%. Life-cycle assessments underscore a negligible impact on human health, ecosystems, and natural resources, endorsing the holistic utilization of biomass. This integration of pyrolysis for the creation of functional carbonaceous materials within biomass conversion processes significantly enhances sustainability and economic viability, while paving green pathways for selective biomass oxidation and the production of high-value chemicals.

Hydroxyl Defects-Mediated Hydrolytic Activation of Peroxydisulfate Under Nanoconfinement: Role of Lewis Basic Sites for Altering the Photosensitized Species and Pathways

Herein, the pivotal mechanism of defect engineering-mediated triazine-based conjugated polymers (TCPs) is comprehensively elucidated for photosensitized activation of peroxydisulfate (PDS) under nanoconfinement by encapsulating the defective polymer framework into the nanochannel of SBA-15 (d-TCPs@SBA-15). The incorporated hydroxyl defects (-OH defects) substantially accelerate the accumulation of electrons at -OH defects, forming the Lewis basic sites. Due to the facilitated elongation of the S─O bond and reduced energy barrier of SO5* generation, the captured PDS undergo prehydrolysis process, oxidized into O2 - and 1O2 by surrounding h+, thereby setting apart from the conventional reductive activation of SO4 -/•OH generation occurred in pristine TCPs (p-TCPs). Crucially, this work represents a pioneering effort in exploring the PDS activation pathway upon the defective polymer under the nanoconfinement to leverage kinetic merits of slow photon effect and reactive oxygen species (ROSs) enrichment, and the novel prehydrolysis activation mechanism involved may catalyze the rational design of photocatalysts featuring Lewis-acid/base centers.

Beneficial utilization of ball-milled carbon sand to activate peroxymonosulfate oxidation: Quantitation of ROS using probe-based kinetic models and mechanism insights

In this study, the oil sand was treated with an integrated process of pyrolysis and ball milling, and the obtained ball-milled carbon sand (BMCS) was utilized as peroxymonosulfate (PMS) activator to treat wastewater containing aniline (AN). Quenching experiments and electron paramagnetic resonance (EPR) confirmed the existence of sulfate radical (SO4∙-), hydroxyl radical (·OH) and singlet oxygen (O12) in the BMCS/PMS system. A probe-based kinetic model was constructed to describe the degradation process of pollutants in the BMCS/PMS system, quantified the exposure of each reactive oxygen species and their contributions to AN degradation. BMCS activated PMS to quickly produce SO4∙- and gradually generate ·OH. The O12 exposure showed a rapid increasing trend and the largest total exposure, while its contribution to AN degradation was small. Ball milling time and BMCS dosage demonstrated significant effect on the exposure of ·OH and O12. The main active sites for BMCS to activate PMS were iron oxides, defective carbon and oxygen-containing functional groups. This study provides a green and low-cost process for value-added transformation of pyrolytic residue of oil sand (PROS), so as to promote PROS treatment mode from harmless disposal to resource utilization.

Biocompatible bismuth-based biochar material for degrading environmental endocrine disrupting compounds: Performance study and enhanced electron transfer radical process

Environmental endocrine disrupting compounds (EDCs) present a significant environmental threat and represent a major challenge in water pollution management. Photocatalysis is a promising method for the treatment of EDCs. Among them, bismuth-based photocatalysts have attracted attention due to their excellent visible light response, narrow band gap, and high efficiency. However, challenges such as easy recombination of photogenerated electrons and holes, low reaction rates, and difficulty in recycling powdered catalysts hinder their practical application. In this investigation, a swift microwave-assisted hydrothermal technique was utilized to fabricate a composite material comprising bismuth-based biochar (BC): BiVO4/AgI/BC. Using 17α-ethynylestradiol (EE2) and estradiol (E2) as model EDCs, the photocatalytic degradation efficiency of BiVO4/AgI/BC was evaluated, alongside an examination of its degradation mechanism and pathways. Remarkably, the incorporation of BiVO4/AgI onto BC significantly augmented the electron transfer rate, fostering the production of •O2-, resulting in a removal efficiency of 99.68% for EE2 and 99.44% for E2, surpassing that of other materials. Furthermore, BiVO4/AgI/BC demonstrated nos3reusability, stability, and low biotoxicity. Thus, BiVO4/AgI/BC exhibits substantial potential for the efficient and environmentally benign elimination of endocrine-disrupting compounds under realistic water conditions.

Revealing the Synergistic Effect of Cation and Anion Vacancies on Enhanced Fenton-Like Reaction: The Electron Density Modulation of O 2p-Co 3d Bands

Defect engineering is considered as a flexible and effective mean to improve the performance of Fenton-like reactions. Herein, a simple method is employed to synthesize Co3O4 catalysts with Co-O vacancy pairs (VP) for peroxymonosulfate (PMS) activation. Multi-scaled characterization, experimental, and simulation results jointly revealed that the cation vacancies-VCo contributed to enhanced conductivity and anion vacancies-VO provided a new active center for the 1O2 generation. Co3O4-VP can optimize the O 2p and Co 3d bands with the strong assistance of synergistic double vacancies to reduce the reaction energy barrier of the "PMS → Co(IV) = O → 1O2" pathway, ultimately triggering the stable transition of mechanism. Co3O4-VP catalysts with radical-nonradical collaborative mechanism achieve the synchronous improvement of activity and stability, and have good environmental robustness to favor water decontamination applications. This result highlights the possibility of utilizing anion and cation vacancy engineering strategies to rational design Co3O4-based materials widely used in catalytic reactions.

Enhancing colorimetric efficiency: nanozyme-activated peroxymonosulfate for in situ 3-aminophenol detection

A novel colorimetric approach specifically designed to effectively identify the presence of 3-aminophenol (3-AP) in environmental water is introduced. Briefly, a nitrogen-doped carbon-supported cobalt nanozyme (Co@CN-1) was synthesized and utilized to improve the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of peroxymonosulfate (PMS). Comparative catalytic reactions confirmed that the performance of PMS as an activator exceeds that of hydrogen peroxide catalytically by a factor of 3.5. The catalytic reaction parameters underwent optimization, further resulting in the derivation of a linear detection equation for 3-AP, expressed as inhibition rate (IR%) = 3.35[3-AP]-4.36 (0-20 μM, R2 = 0.994) and IR% = 1.43[3-AP] + 31.87 (20-36 μM, R2 = 0.992), with the limit of detection (LOD) of 2.84 μM. The linear relationship between 3-AP concentration and the conversion of color to grayscale value (GSV) was established by smartphones, expressed as GSV = 1.28[3-AP] + 147.10 (R2 = 0.972). Density functional theory calculations revealed that Co acts as the preferred active site for donating electrons in PMS activation. This work provides a rapid and accurate approach for monitoring 3-AP concentration, enabling real-time analysis and potentially contributing to environmental and ecological studies.

Progress of metal-loaded biochar-activated persulfate for degradation of emerging organic contaminants

In recent years, studies on the degradation of emerging organic contaminants by sulfate radical (SO4-·) based advanced oxidation processes (SR-AOPs) have triggered increasing attention. Metal-loaded biochar (Me-BC) can effectively prevent the agglomeration and leaching of transition metals, and its good physicochemical properties and abundant active sites induce outstanding in activating persulfate (PS) for pollutant degradation, which is of great significance in the field of advanced oxidation. In this paper, we reviewed the preparation method and stability of Me-BC, the effect of metal loading on the physicochemical properties of biochar, the pathways of pollutant degradation by Me-BC-activated PS (including free radical pathways: SO4-·, hydroxyl radical (·OH), superoxide radicals (O2-·); non-free radical pathways: singlet oxygen (1O2), direct electron transfer), and discussed the activation of different active sites (including metal ions, persistent free radicals, oxygen-containing functional groups, defective structures, etc.) in the SR-AOPs system. Finally, the prospect was presented for the current research progress of Me-BC in SR-AOPs technology.

N-doped lignin-based activated carbon aerogel derived from bamboo black pulp liquor for efficient removal of malachite green in wastewater

In this study, a lignin-based aerogel (LA) was prepared through acid precipitation of BPBL, followed by sol-gel method and freeze-drying. Additionally, a one-step activation-carbonization method was used to acquire nitrogen-doped lignin-based activated carbon aerogel (NLACA). The adsorption and catalytic degradation performance for malachite green (MG) were examined. The specific surface area of NLACA after N-doping was 2644.5 m2/g. The adsorption capacity for MG was increased to 3433 mg/g with the presence of nitrogenous functional groups on surface of NLACA compared without N-doping. Meanwhile, non-radical singlet oxygen is the primary active substance and degradation efficiency arrives at 91.8% after the catalytic degradation within 20 min and it has good stability and reuse. Three possible degradation pathways during degradation were analyzed by LC-MS technique. The adsorption isotherm and kinetic data demonstrated conformity with both the Langmuir model and the pseudo-second-order kinetic model. The primary mechanisms of the adsorption for MG dyes on NLACA include hydrogen bonding, π-π interactions, attraction of electrostatic and pore filling. Hence, NLACA derived from BPBL acts as a cost-effective and high-performance adsorbent and catalyst for removal of MG in dye wastewater. This concept introduces an innovative approach of "treatment of waste with waste" for developing a low-consumption, high-efficiency dye wastewater treatment and provides significant reference to treatment dye wastewater.

La(FeCuMnMgTi)O3 High-Entropy Oxide Nanoparticles as Highly Efficient Catalysts for Solvent-Free Aerobic Oxidation of Benzyl Alcohol

In this work, a solid-state method for the synthesis of perovskite La(FeCuMnMgTi)O3 high-entropy oxide (HEO) nanoparticles is detailed. Additionally, the high performance of these nanoparticles as catalysts in the aerobic and solvent-free oxidation of benzyl alcohol is demonstrated. The structural features of HEO nanoparticles are studied by X-ray diffraction and high-resolution transmission electron microscopy. The La(FeCuMnMgTi)O3 nanoparticles demonstrate excellent benzyl alcohol conversion rates and selectivity for benzaldehyde, reaching 10.6% conversion and 52.8% selectivity after reaction for only 4 h and ≤75.6% conversion after 24 h. In addition, the as-prepared HEO catalyst displays robust stability in benzyl alcohol oxidation. Density functional theory calculations demonstrate that the adsorption energy of benzaldehyde on the HEO surface is lower than that of the benzoic acid. This, in turn, hinders the gradual conversion of benzaldehyde to benzoic acid on the surface of HEO and retains benzaldehyde as the main product.

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

Eosin Y Post-Decorated Metal-Organic Framework as a Selectivity Regulator for the Alcohols Oxidation

The selective oxidation of alcohols into aldehydes is a basic and significant procedure, with great potential for scientific research and industrial applications. However, as an important factor in the C(sp3)-H activation process, high selectivity is generally difficult to achieve due to the fact that the more easily activated properties of aldehydes are compared to alcohols. Herein, by the ingenious decoration of eosin Y into a Zr-based metal-organic framework (MOF-808), EY@MOF-808 was prepared as a selectivity regulator for the aerobic oxidation of the benzyl alcohols into corresponding aldehydes, possessing applicability for the benzylic alcohols with various substituents. By anchoring eosin Y on Zr6O4(OH)4 clusters of MOF-808 and maintaining open metal nodes with selective binding effects, the benzyl alcohol substrates were selectively coordinated to the unsaturated metal clusters adjacent to eosin Y, which ensured that the excited eosin Y rapidly activated substrates to generate carbon radicals by the hydrogen atom transfer (HAT) process. The rapid electron transfer (ET) simultaneously produced reactive oxygen species (O2•-) and then a combination of both to further promote the generation of benzaldehydes. The weak interaction of benzaldehydes with the skeleton allowed it to dissociate rapidly, thus preventing overoxidation. Under the catalysis of EY@MOF-808, the selectivity of various benzaldehydes was more than 99%. In contrast, eosin Y gave only benzoic acid products under the same conditions, which demonstrated the superiority of regulatory selectivity of EY@MOF-808. Taking advantage of the heterogeneity of the MOF, EY@MOF-808 was recycled four times without a decrease in its selectivity and avoided the quenching effect of eosin Y. The organic functional units postdecorated MOF-based photocatalyst strategy exhibits a promising new perspective approach to sustainably regulating the selectivity of inert oxidation.

Ball Milling of La2O3 Tailors the Crystal Structure, Reactive Oxygen Species, and Free Radical and Non-Free Radical Photocatalytic Pathways

Non-free radical photocatalysis with metal oxide catalysts is an important advanced oxidation process that enables the removal of various emerging environmental pollutants, such as tetracycline. Here, four hexagonal La2O3 photocatalysts with different densities of oxygen vacancy and crystalline features are synthesized and then further treated by ball milling. Ball milling of these La2O3 photocatalysts is found to increase the amount of oxygen vacancies on their surfaces and thereby the amount of 1O2 species produced by them. The photocatalytic degradation of TC by these La2O3 photocatalysts depends on the oxygen vacancies present on them. Furthermore, the ones with a strong (101) diffraction peak remove tetracycline from water systems largely with 1O2 and •OH species, whereas those with a weak (101) diffraction peak do so mainly via 1O2 and direct electron transfer (DET) process. Their overall catalytic properties are also studied by density functional theory calculations. Moreover, the organic products produced from tetracycline by La2O3 photocatalysts containing a strong (101) diffraction peak are found to be less toxic than those produced by La2O3 photocatalysts containing a weak (101) diffraction peak. This study also provides convincing evidence that the structures of La2O3 determine the species that is produced by it and that end up mediating photocatalytic reaction pathways (i.e., free radical versus non-free radical) to degrade an emerging environment pollutant.

Sonocatalytic Activity of Porous Carbonaceous Materials for the Selective Oxidation of 4-Hydroxy-3,5-dimethoxybenzyl Alcohol

Selective oxidation, which is crucial in diverse chemical industries, transforms harmful chemicals into valuable compounds. Heterogeneous sonocatalysis, an emerging sustainable approach, urges in-depth exploration. In this work, we investigated N-doped or non-doped carbonaceous materials as alternatives to scarce, economically sensitive metal-based catalysts. Having synthesized diverse carbons using a hard-template technique, we subjected them to sonication at frequencies of 22, 100, 500, and 800 kHz with a 50% amplitude. Sonochemical reaction catalytic tests considerably increased the catalytic activity of C-meso (non-doped mesoporous carbon material). The scavenger test showed a radical formation when this catalyst was used. N-doped carbons did not show adequate and consistent sonoactivity for the selective oxidation of 4-Hydroxy-3,5 dimethoxybenzyl alcohol in comparison with control conditions without sonication, which might be associated with an acid-base interaction between the catalysts and the substrate and sonoactivity prohibition by piridinic nitrogen in N-doped catalysts.

Photocathodic Activation of Peroxymonosulfate in a Photofuel Cell: A Synergetic Signal Amplification Strategy for a Self-Powered Photoelectrochemical Sensor

A self-powered photoelectrochemical (PEC) sensor has attracted widespread attention in the field of analysis, but it is still a challenge to enhance its response signals with rational strategies. In this work, a novel self-powered PEC sensing platform was developed for the quantitative detection of gatifloxacin (GAT) based on a photofuel cell consisting of two types of ZIF-derived ZnO/Co3O4 heterojunctions as photoactive materials. Peroxymonosulfate (PMS) was first used as an electron acceptor coupled with a photofuel cell to develop a synergetic signal amplification strategy. In a dual-photoelectrode system, the PMS activation on the ZnO@Co3O4 photocathode not only accelerated electron transfer from the Co3O4@ZnO photoanode to achieve strong signal intensity but also improved the sensing sensitivity by the oxidation reaction of generated highly active radicals to GAT. Compared with the absence of electron acceptors, the introduction of PMS produced a 2-fold enhancement in the signal output performance and a more than 72-fold improvement in the signal sensitivity. For the construction of the sensing interface, a molecularly imprinted polymer was assembled on the photocathode to specifically recognize GAT. The proposed sensor exhibited a detection range of 10-1 to 105 pM with a detection limit of 0.065 pM. The proposed sensing method has the advantages of sensitivity, simplicity, reliable stability, and anti-interference ability, which opens the door to the design of high-performance self-powered PEC sensors.

Precise coordination of high-loading Fe single atoms with sulfur boosts selective generation of nonradicals

Nonradicals are effective in selectively degrading electron-rich organic contaminants, which unfortunately suffer from unsatisfactory yield and uncontrollable composition due to the competitive generation of radicals. Herein, we precisely construct a local microenvironment of the carbon nitride-supported high-loading (~9 wt.%) Fe single-atom catalyst (Fe SAC) with sulfur via a facile supermolecular self-assembly strategy. Short-distance S coordination boosts the peroxymonosulfate (PMS) activation and selectively generates high-valent iron-oxo species (FeIV=O) along with singlet oxygen (1O2), significantly increasing the 1O2 yield, PMS utilization, and p-chlorophenol reactivity by 6.0, 3.0, and 8.4 times, respectively. The composition of nonradicals is controllable by simply changing the S content. In contrast, long-distance S coordination generates both radicals and nonradicals, and could not promote reactivity. Experimental and theoretical analyses suggest that the short-distance S upshifts the d-band center of the Fe atom, i.e., being close to the Fermi level, which changes the binding mode between the Fe atom and O site of PMS to selectively generate 1O2 and FeIV=O with a high yield. The short-distance S-coordinated Fe SAC exhibits excellent application potential in various water matrices. These findings can guide the rational design of robust SACs toward a selective and controllable generation of nonradicals with high yield and PMS utilization.

Insight into disparate nonradical mechanisms of peroxymonosulfate and peroxydisulfate activation by N-doped oxygen-rich biochar: Unraveling the role of active sites

In this study, we first comprehensively studied peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation mechanisms using N, O codoped sludge biochar (NOSB) to degrade organics from water. Among the catalysts, NOSB with a higher content of graphitic N, optimal edge nitrogen (pyridinic N and pyrrolic N), CO groups, sp2-hybridized C, and rich defects were demonstrated to be a superior catalyst. Therefore, by activating PDS and PMS, NOSB exhibited the highest rate of BPA degradation, which was 22-fold and 13-fold that of pristine sludge biochar, respectively. However, owing to different oxidation potentials and molecular structures, PMS and PDS show different degradation performances due to various catalytic mechanisms occurring, even with the same biochar. Due to the asymmetrical structure of PMS, electrons passed from PMS to NOSB and further generated singlet oxygen (1O2), which governs the degradation of bisphenol A with an auxiliary contribution of single electron transfer. Meanwhile, PDS is reduced at the Lewis basic sites of NOSB, forming inner-surface-bound {PDS-NOSB}, which was oxidizing around neighboring carbon and decomposed targets through transferring single and double electrons. NOSB is promising for practical applications because of its adaptation to a wide pH range, anions, high total organic carbon removal, tunable active sites, and re-usability for degrading organics via PMS/PDS activation. This study unveils knowledge about N, O codoped sludge biochar catalysts for activating PMS/PDS and advocates a great approach for organics' degradation in the environment.

Hierarchical Hollow Carbon Particles with Encapsulation of Carbon Nanotubes for High Performance Supercapacitors

A novel and sustainable carbon-based material, referred to as hollow porous carbon particles encapsulating multi-wall carbon nanotubes (MWCNTs) (CNTs@HPC), is synthesized for use in supercapacitors. The synthesis process involves utilizing LTA zeolite as a rigid template and dopamine hydrochloride (DA) as the carbon source, along with catalytic decomposition of methane (CDM) to simultaneously produce MWCNTs and COx -free H2 . The findings reveal a distinctive hierarchical porous structure, comprising macropores, mesopores, and micropores, resulting in a total specific surface area (SSA) of 913 m2  g-1 . The optimal CNTs@HPC demonstrates a specific capacitance of 306 F g-1 at a current density of 1 A g-1 . Moreover, this material demonstrates an electric double-layer capacitor (EDLC) that surpasses conventional capabilities by exhibiting additional pseudocapacitance characteristics. These properties are attributed to redox reactions facilitated by the increased charge density resulting from the attraction of ions to nickel oxides, which is made possible by the material's enhanced hydrophilicity. The heightened hydrophilicity can be attributed to the presence of residual silicon-aluminum elements in CNTs@HPC, a direct outcome of the unique synthesis approach involving nickel phyllosilicate in CDM. As a result of this synthesis strategy, the material possesses excellent conductivity, enabling rapid transportation of electrolyte ions and delivering outstanding capacitive performance.

Degradation of Ciprofloxacin in Water by Magnetic-Graphene-Oxide-Activated Peroxymonosulfate

Antibiotics are extensively applied in the pharmaceutical industry, while posing a tremendous hazard to the ecosystem and human health. In this study, the degradation performance of ciprofloxacin (CIP), one of the typical contaminants of antibiotics, in an oxidation system of peroxymonosulfate (PMS) activated by magnetic graphene oxide (MGO) was investigated. The effects of the MGO dosage, PMS concentration and pH on the degradation of CIP were evaluated, and under the optimal treatment conditions, the CIP degradation rate was up to 96.5% with a TOC removal rate of 63.4%. A kinetic model of pseudo-secondary adsorption indicated that it involves an adsorption process with progressively intensified chemical reactions. Furthermore, the MGO exhibited excellent recyclability and stability, maintaining strong catalytic activity after three regenerative cycles, with a CIP removal rate of 87.0%. EPR and LC-MS experiments suggested that •OH and SO4-• generated in the MGO/PMS system served as the main reactants contributing to the decomposition of the CIP, whereby the CIP molecule was effectively destroyed to produce other organic intermediates. Results of this study indicate that organic pollutants in the aqueous environment can be effectively removed in the MGO/PMS system, in which MGO has excellent catalytic activity and stabilization for being recycled to avoid secondary pollution, with definite research value and application prospects in the field of water treatment.

Mechanisms of interaction between metal-organic framework-based material and persulfate in degradation of organic contaminants (OCs): Activation, reactive oxygen generation, conversion, and oxidation

Metal-organic frameworks (MOFs)-based materials have been of great public interest in persulfate (PS)-based catalytic oxidation for wastewater purification, because of their excellent performance and selectiveness in organic contaminants (OCs) removal in complex water environments. The formation, fountainhead and reaction mechanism of reactive oxygen species (ROSs) in PS-based catalytic oxidation are crucial for understanding the principles of PS activation and the degradation mechanism of OCs. In the paper, we presented the quantitative structure-activity relationship (QSAR) of MOFs-based materials for PS activation, including the relationship of structure and removal efficiency, active sites and ROSs as well as OCs. In various MOFs-based materials, there are many factors will affect their performances. We discussed how various surface modification projects affected the characteristics of MOFs-based materials used in PS activation. Moreover, we revealed the process of ROSs generation by active sites and the oxidation of OCs by ROSs from the micro level. At the end of this review, we putted forward an outlook on the development trends and faced challenges of MOFs for PS-based catalytic oxidation. Generally, this review aims to clarify the formation mechanisms of ROSs via the active sites on the MOFs and the reaction mechanism between ROSs and OCs, which is helpful for reader to better understand the QSAR in various MOFs/PS systems.

Singlet oxygen in the removal of organic pollutants: An updated review on the degradation pathways based on mass spectrometry and DFT calculations

The degradation of pollutants by a non-radical pathway involving singlet oxygen (1O2) is highly relevant in advanced oxidation processes. Photosensitizers, modified photocatalysts, and activated persulfates can generate highly selective 1O2 in the medium. The selective reaction of 1O2 with organic pollutants results in the evolution of different intermediate products. While these products can be identified using mass spectrometry (MS) techniques, predicting a proper degradation mechanism in a 1O2-based process is still challenging. Earlier studies utilized MS techniques in the identification of intermediate products and the mechanism was proposed with the support of theoretical calculations. Although some reviews have been reported on the generation of 1O2 and its environmental applications, a proper review of the degradation mechanism by 1O2 is not yet available. Hence, we reviewed the possible degradation pathways of organic contaminants in 1O2-mediated oxidation with the support of density functional theory (DFT). The Fukui function (FF, f-, f+, and f0), HOMO-LUMO energies, and Gibbs free energies obtained using DFT were used to identify the active site in the molecule and the degradation mechanism, respectively. Electrophilic addition, outer sphere type single electron transfer (SET), and addition to the hetero atoms are the key mechanisms involved in the degradation of organic contaminants by 1O2. Since environmental matrices contain several contaminants, it is difficult to experiment with all contaminants to identify their intermediate products. Therefore, the DFT studies are useful for predicting the intermediate compounds during the oxidative removal of the contaminants, especially for complex composition wastewater.

Single atom manganese catalyst boosting selective oxidation of alcohols with activated peroxymonosulfate

Selective oxidations are important reactions in organic synthesis for fine chemical industry and conventional methods are expensive and produce a lot of toxic wastes. Herein, we demonstrate a facile and environmentally benign technique for liquid phase selective oxidation based on graphene-supported Mn single-atom-catalyst (SAMn-G) for efficient peroxymonosulfate (PMS) activation. The active Mn component in the developed SAMn-G catalyst reached single-atomic dispersion on graphene substrate via the coordination of individual Mn atoms with the doped N from the graphene framework. SAMn-G activated PMS via a nonradical-dominated pathway, which could convert aromatic alcohols into aldehydes or ketones at a mild temperature. The SAMn-G catalyst exhibited superior conversion and aldehyde selectivity in alcohol oxidation in comparison with their counterpart catalysts possessing either homogeneous Mn ions or oxide particles. The high activation efficiency of SAMn-G is due to the synergistic effect between Mn atoms and graphene substrate, as well as the dominated reaction pathway from nonradical oxidation, which is more selective than these free radicals to oxidize the alcohols. Concerted experimental evidence indicates that the non-radical oxidation process was highly possible to follow the electron transfer mechanism by PMS/organic adsorption on the surface of the catalyst. This study provides a fundamental understanding of PMS activation mediated by single atom catalyst for organic synthesis and the achieved insights can also help the catalyst design for other liquid phase selective oxidation processes.

Site Engineering of Covalent Organic Frameworks for Regulating Peroxymonosulfate Activation to Generate Singlet Oxygen with 100 % Selectivity

Singlet oxygen (1 O2 ) is an excellent reactive oxygen species (ROSs) for the selective conversion of organic matter, especially in advanced oxidation processes (AOPs). However, due to the huge dilemma in synthesizing single-site type catalysts, the control and regulation of 1 O2 generation in AOPs is still challenging and the underlying mechanism remains largely obscure. Here, taking advantage of the well-defined and flexibly tunable sites of covalent organic frameworks (COFs), we report the first achievement in precisely regulating ROSs generation in peroxymonosulfate (PMS)-based AOPs by site engineering of COFs. Remarkably, COFs with bipyridine units (BPY-COFs) facilitate PMS activation via a nonradical pathway with 100 % 1 O2 , whereas biphenyl-based COFs (BPD-COFs) with almost identical structures activate PMS to produce radicals (⋅OH and SO4 .- ). The BPY-COFs/PMS system delivers boosted performance for selective degradation of target pollutants from water, which is ca. 9.4 times that of its BPD-COFs counterpart, surpassing most reported PMS-based AOPs systems. Mechanism analysis indicated that highly electronegative pyridine-N atoms on BPY-COFs provide extra sites to adsorb the terminal H atoms of PMS, resulting in simultaneous adsorption of O and H atoms of PMS on one pyridine ring, which facilitates the cleavage of its S-O bond to generate 1 O2 .

Theoretical study of local S coordination environment on Fe single atoms for peroxymonosulfate-based advanced oxidation processes

Tuning the electronic structure of single atom catalysts (SACs) is an effective strategy to promote the catalytic activity in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). Herein, a series of Fe-based SACs with S_1/2/3/4-coordination numbers on graphene were designed to regulate the electronic structural of SACs at molecular level, and their effects on PMS activation were investigated via density function theory (DFT). The calculation results demonstrate that the electron structure of the active center can be adjusted by coordination environment, which further affects the activation of PMS. Among the studied Fe-S_X-C_4-X catalysts, with the increase of the S coordination number, the electron density of the Fe-S_X-C_4-X active center was optimized. The active center of the Fe-S₄-C₀ catalyst has a largest positive charge density, exhibiting the highest number of electron transfer. It also has a lower kinetic energy barrier (0.28 eV) for PMS dissociation. Organic pollutant such as bisphenol A (BPA) can achieve stable adsorption on Fe-S_X-C_4-X catalysts, which is conducive to subsequent oxidation by radicals. The dual index ∆f(r) indicates that the para-carbon atom of the hydroxyl group on the benzene ring of BPA is vulnerable to radical attack. This study highlights a theoretical support and a certain guide for designing efficient SACs to activate PMS.

Enhanced degradation of pharmaceuticals in wastewater by coupled radical and non-radical pathways: Further unravelling kinetics and mechanism

Advanced oxidation processes based on radicals and/or non-radical catalysis are emerging as promising technologies for eliminating pharmaceuticals (PhACs) from wastewater. However, the respective contributions of different removal pathways (radicals or non-radical) for PhAC degradation still lacks quantitative investigation. Zero-valent iron and carbon nanotubes are frequently used to generate both radicals and non-radical species via the activation of persulfate (Fe⁰/SWCNT/PDS). Herein, the removal kinetics of 1 μM PhACs are depicted, and the corresponding synergistic mechanism of the Fe⁰/SWCNT/PDS process is discussed. Coupled removal pathways showed the higher degradation of PhACs than the individual pathways. Radicals quenching studies combined with electron spin resonance characterisation suggested that the radical-based removal pathway tends to attack electron-deficient organics, whereas its counterpart is more likely to work on electron-rich organics. From the perspectives of the contribution rate, the redox cycles of conjugated Fe species play a more important role in the generation of radicals than free Fe species, and the faster electron transfer in the conductive bridge offered by SWCNT is responsible for the effective corrosion of Fe⁰ and the decomposition of PDS. Six real wastewater samples were used to prove the generality of the above removal contribution, regardless of the wastewater samples, and the results suggested that identical attack patterns were obtained in all real wastewater samples, although coexistence matrix slightly suppressed PhAC removal. This work provides a deeper insight into the high-performance working mechanism on synergistic interactions and contaminant removal in a combined catalysis system.

Effective Screening Descriptor for MXenes to Enhance Sulfur Reduction in Lithium-Sulfur Batteries

MXenes, two-dimensional transition (2D) metal carbides/nitrides, have shown promise as cathodic catalysts for accelerating the conversion of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries due to their diverse redox-active sites and rapid electron transfer. However, efficiently screening the optimal cathodic catalysts out of thousands of MXenes is challenging. To address this, we developed a model that accurately predicts the thermodynamic energy barrier of the rate-limiting step in Li-S batteries. Our model relates the local chemical reactivity of the MXene sites to the p-band center of the terminations and the electronegativity of subsurface transition metals. The accuracy of the model was verified through density functional theory calculations and contrast experiments in pure and Zn-doping MXenes qualitatively. By utilizing this model, we screened a large library of MXenes (27 types of five-atom-layer MXenes) and identified Ti₂CS₂, Mo₂CS₂, and W₂CS₂ as potential cathodic catalysts for Li-S batteries.

Selective activation of peroxymonosulfate govern by B-site metal in delafossite for efficient pollutants degradation: Pivotal role of d orbital electronic configuration

Radical and non-radical oxidation pathways have been universally validated in transition metals (TMs) oxides activated peroxymonosulfate (PMS) processes. However, achieving high efficiency and selectivity of PMS activation remains challenging due to the ambiguous tuning mechanism of TMs sites on PMS activation in thermodynamic scope. Herein, we demonstrated that the exclusive PMS oxidation pathways were regulated by d orbital electronic configuration of B-sites in delafossites (CuBO₂) for Orange I degradation (Co^III 3d⁶ for reactive oxygen species (ROSs) vs. Cr^III 3d³ for electron transfer pathway). The d orbital electronic configuration was identified to affect the orbital overlap extent between 3d of B-sites and O 2p of PMS, which induced B-sites offering different types of hybrid orbital to coordinate with O 2p of PMS, thereby forming the high-spin complex (CuCoO₂@PMS) or the low-spin complex (CuCrO₂@PMS), on which basis PMS was selectively dissociated to form ROSs or achieve electron transfer pathway. As indicated by thermodynamic analysis, a general rule was proposed that B-sites of less than half-filled 3d orbital tended to act as electron shuttle, i.e., Cr^III (3d³), Mn^III (3d⁴), interacting with PMS to execute an electron transfer pathway for degrading Orange I, while B-sites of between half-filled and full-filled 3d orbital preferred to be electron donator, i.e., Co^III (3d⁶), Fe^III (3d⁵), activating PMS to generate ROSs. These findings lay a foundation for the oriented design of TMs-based catalysts from the atomic level according to d orbital electronic configuration optimization, as so to facilitate the achievement of PMS-AOPs with highly selective and efficient remediation of contaminants in water purification practice.

Regulating the Charge Migration in CuInSe2 /N-Doped Carbon Nanorod Arrays via Interfacial Engineering for Boosting Photoelectrochemical Water Splitting

Regulating the charge migration and separation in photoactive materials is a great challenge for developing photoelectrochemical (PEC) applications. Herein, inspired by capacitors, well-defined CuInSe₂ /N-doped carbon (CISe/N-C) nanorod arrays are synthesized by Cu/In-metal organic frame-derived method. Like the charge process of capacitor, the N-doped carbon can capture the photogenerated electron of CISe, and the strong interfacial coupling between CISe and N-doped carbon can modulate the charge migration and separation. The optimized the CISe/N-C photoanode achieves a maximum photocurrent of 4.28 mA cm^-2 at 1.23 V versus reversible hydrogen electrode (RHE) in neutral electrolyte solution under AM 1.5 G simulated sunlight (100 mW cm^-2 ), which is 8.4 times higher than that of the CuInSe₂ photoanode (0.51 mA cm^-2 ). And a benefit of the strong electronic coupling between CISe and N-doped carbon, the charge transfer rate is increased to 1.3-13 times higher than that of CISe in the range of 0.6-1.1 V versus RHE. The interfacial coupling effects on modulating the carrier transfer dynamics are investigated by Kelvin probe force microscopy analysis and density functional theory calculation. This work provides new insights into bulk phase carrier modulation to improve the performance of photoanode for PEC water splitting.

Phosphorus doping significantly enhanced the catalytic performance of cobalt-single-atom catalyst for peroxymonosulfate activation and contaminants degradation

Increasing studies have been conducted to explore strategies for enhancing the catalytic performance of metal-doped C-N-based materials (e.g., cobalt (Co)-doped C₃N₅) via heteroatomic doping. However, such materials have been rarely doped by phosphorus (P) with the higher electronegativity and coordination capacity. In current study, a novel P and Co co-doped C₃N₅ (Co-xP-C₃N₅) was developed for peroxymonosulfate (PMS) activation and 2,4,4'-trichlorobiphenyl (PCB28) degradation. The PCB28 degradation rate increased by 8.16-19.16 times with Co-xP-C₃N₅ compared to conventional activators under similar reaction conditions (e.g., PMS concentration). The state-of-the-art techniques, including X-ray absorption spectroscopy and electron paramagnetic resonance etc., were applied to explore the mechanism of P doping for enhancing Co-xP-C₃N₅ activation. Results showed that P doping induced the formation of Co-P and Co-N-P species, which increased the contents of coordinated Co and improved Co-xP-C₃N₅ catalytic performance. The Co mainly coordinated with the first shell layer of Co₁-N₄, with successful P doping occurring in the second shell layer of Co₁-N₄. The P doping favored electron transfer from the C to N atom near Co sites and thus strengthened PMS activation owing to its higher electronegativity. These findings provide new strategy for enhancing the performance of single atom-based catalysts for oxidant activation and environmental remediation.

Nanoconfinement-enhanced Fenton-like polymerization via hollow hetero-shell carbon for reducing carbon emissions in organic wastewater purification

Lower reaction speed and excessive oxidant inputs impede the removal of contaminants from water via the advanced oxidation processes based on peroxymonosulfate. Herein, we report a new confined catalysis paradigm via the hollow hetero-shell structured CN@C (H-CN@C), which permits effective decontamination through polymerization with faster reaction rates and lower oxidant dosage. The confined space structures regulated the CN and CO and electron density of the inner shell, which increased the electron transfer rate and mass transfer rate. As a result, CN in H-CN@C-10 reacted with peroxymonosulfate in preference to CO to generate singlet oxygen, improving the second-order reaction kinetics by 503 times. The identification of oxidation products implied that bisphenol AF could effectively remove by polymerization, which could reduce carbon dioxide emissions. These favorable properties make the nanoconfined catalytic polymerization of contaminants a remarkably promising nanocatalytic water purification technology.

Constructing a Photocatalyst for Selective Oxidation of Benzyl Alcohol to Benzaldehyde by Photo-Fenton-like Catalysis

A photoactive metal-organic framework (MOF), [K(H₂O)][Cu(DPNDI)][Cu(DPNDI)(CH₃CN)(H₂O)] [Cu_1.5(DPNDI)_1.5H_1.5P₂W₁₈O₆₂]·2H₂O (Cu(Ι)W-DPNDI), was prepared by combining a functional photosensitizer N, N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI), copper(I) ions, and an oxidation catalyst [P₂W₁₈O₆₂]^6- into a single framework via a hydrothermal process. Cu(Ι)W-DPNDI exhibited a stable structure, strong light absorption capacity, a suitable band gap, and photoelectric properties, which provided favorable conditions for photocatalysis. In the confined space, the well-aligned Cu(I) ions and POM polyanions played a synergetic effect in the electron-transfer process and reactive oxygen species generation. By coupling photocatalysis and heterogeneous Fenton-like catalysis, Cu(Ι)W-DPNDI displayed high efficiency for the selective oxidation of aromatic alcohols, with up to >99% selectivity and 75% yield.

Enhancing Biochar-Based Nonradical Persulfate Activation Using Data-Driven Techniques

Converting biomass into biochar (BC) as a functional biocatalyst to accelerate persulfate activation for water remediation has attracted much attention. However, due to the complex structure of BC and the difficulty in identifying the intrinsic active sites, it is essential to understand the link between various properties of BC and the corresponding mechanisms promoting nonradicals. Machine learning (ML) recently demonstrated significant potential for material design and property enhancement to help tackle this problem. Herein, ML techniques were applied to guide the rational design of BC for the targeted acceleration of nonradical pathways. The results showed a high specific surface area, and O% values can significantly enhance nonradical contribution. Furthermore, the two features can be regulated by simultaneously tuning the temperatures and biomass precursors for efficient directed nonradical degradation. Finally, two nonradical-enhanced BCs with different active sites were prepared based on the ML results. This work serves as a proof of concept for applying ML in the synthesis of tailored BC for persulfate activation, thereby revealing the remarkable capability of ML for accelerating bio-based catalyst development.

Abnormal Biologic Distribution Related to Normal Saline Among 99mTc-Dimercaptosuccinic Acid Scans

The primary aim was to describe the incidence and causes of abnormal distribution of ^99mTc-dimercaptosuccinic acid (^99mTc-DMSA) among patients who underwent renal scans in Royal Hospital (Oman) in 2020. The secondary aim was to assess the effect of a specific batch of normal saline A (batch 132129) compared with another normal saline, B (batches 132589 and 133325), used in the preparation of ^99mTc-DMSA on the abnormal biodistribution of ^99mTc-DMSA. Methods: This was an ambidirectional cohort study that included all patients who underwent ^99mTc-DMSA renal scanning between January and December 2020. Both prospective and retrospective data collection was used. The collected data included possible causes of abnormal biodistribution, quality of ^99mTc-DMSA and normal saline, and time of ^99mTc-DMSA injection. Results: The total incidence of abnormal biodistribution was 26.5%, with the most common cause being a high creatinine level (29%). Normal saline batch A was significantly associated with abnormal biodistribution (49.7%), compared with batch B (6.6%) (P < 0.001). This association was more prominent among patients injected with the ^99mTc-DMSA preparation after 2 h (83.0%) compared with before 2 h (13.3%). Conclusion: A high incidence of abnormal biodistribution of ^99mTc-DMSA was detected and-for what is the first time, to our knowledge, in the literature-a specific preservative-free, normal saline that is up to standard has been identified as a significant cause of abnormal biodistribution. Nuclear medicine professionals and pharmaceutical companies should take note of this possible cause of abnormal ^99mTc-DMSA biodistribution.

Regeneration of methylene blue-saturated biochar by synergistic effect of H2O2 desorption and peroxymonosulfate degradation

Biochar, as an adsorbent, is widely used for the removal of organic pollutants in water body. Hence, after saturated adsorption, regeneration treatment is required to recover the adsorption performance of biochar. In this study, a biochar (P-GBC) prepared by phosphoric acid activation showed high adsorption capacity for methylene blue (MB) with the maximum adsorption capacity (Q_m) of 599.66 mg/g. Then, regeneration treatments using 4 mM peroxymonosulfate (PMS), 0.2 M hydrogen peroxide (H₂O₂) and their mixture were used to regenerate MB-saturated biochar with regeneration efficiencies of 58.24%, 66.01% and 94.88%, respectively. Combining with degradation and quenching experiments, it is found that synergistic effect of H₂O₂ desorption and PMS degradation is responsible for the enhancement of regeneration efficiency of P-GBC in H₂O₂-PMS system and enables a high mineralization rate of 82.68% for the MB adsorbed on P-GBC. Furthermore, EPR tests indicate that singlet oxygen (¹O₂) is assigned as the primary activate species for the degradation of MB and XPS analyses confirm that graphite nitrogen and carbonyl on P-GBC are the main active sites for the activation of PMS. Compared with conventional regenerants, H₂O₂-PMS system has the advantages of low dosage, high mineralization efficiency, and easy accessibility, and is also effective, sustainable and environmentally friendly for the regeneration of organic pollutants-saturated biochar.

Carbon-doped defect MoS2 co-catalytic Fe3+/peroxymonosulfate process for efficient sulfadiazine degradation: Accelerating Fe3+/Fe2+ cycle and 1O2 dominated oxidation

In order to accelerate Fe³⁺/Fe²⁺ cycle and boost singlet oxygen (¹O₂) generation in peroxymonosulfate (PMS) Fenton-like system, a co-catalyst of defect MoS₂ was prepared by C doping and C2-MoS₂/Fe³⁺/PMS system was structured. The removal efficiency of sulfadiazine (SDZ) antibiotics was nearly 100 % in 10 min in the system under the appropriate conditions ([co-catalysts] = 0.2 g/L, [PMS] = 0.1 mM, [Fe³⁺] = 0.4 mM, pH 3.5), and the reaction rate constant was 4.6 times that of Fe³⁺/PMS system. C doping MoS₂ could induce phase transition, yield more sulfur defects, and expedite electron transfer. Besides, exposed Mo⁴⁺ sites on C2-MoS₂ could significantly enhance the regeneration and stability of Fe²⁺ and further promote the activation of PMS. ·OH, SO₄·^-, and ¹O₂ were responsible for SDZ degradation in the system. Notably, ¹O₂ generation was efficiently promoted by sulfur defects and CO sites on C2-MoS₂, and ¹O₂ played the main role in SDZ degradation. Therefore, this co-catalytic system exhibited great anti-interference and stability, and organic contaminants could be efficiently and stably degraded in a 14-day long-term experiment. This work provides a new approach for improving the co-catalytic performance of MoS₂ for Fe³⁺ mediated Fenton-like technology, and offers a promising antibiotic pollutant removal strategy.

Efficient degradation of levofloxacin using a g-C3N4@glucose-derived carbon catalyst with adjustable N content via peroxymonosulfate activation

Metal-free carbon-based catalysts hold great promise for the degradation of organic pollutants by peroxymonosulfate (PMS) activation because they avoid the negative effects of metal catalysts such as harmful metal ions leaching. However, these carbon-based catalysts are limited by their high cost and complex synthesis, and the mechanisms for the activation of PMS are unclear. Herein, the N-rich carbon catalysts (GCN-x) derived from glucose and g-C₃N₄ were facilely synthesized by hydrothermal treatment and carbonization to explore the mechanism of PMS activation. The nitrogen content of catalysts could be adjusted by simply altering the ratio of glucose and g-C₃N₄. GCN-2.4 with a ratio of glucose and g-C₃N₄ of 2.4 displayed the highest efficiency for the degradation of pollutants represented by Levofloxacin. The electron paramagnetic resonance and quenching experiments demonstrated that the non-radical pathway was dominant in Levofloxacin degradation and singlet oxygen (¹O₂) was the main active specie. Further, we found ¹O₂ was generated from superoxide radical (• O₂^-) which has rarely been studied. Levofloxacin degradation rate was shown to be positively correlated with both the amount of graphitic N and pyridinic N. Graphitic N and pyridinic N were identified as the catalytic sites. The GCN-2.4/PMS system could also remove multifarious contaminants effectively. Overall, this research advances understanding of the role of N species in PMS activation and has potential practical application in wastewater treatment.

Enhanced activation of persulfate improves the selective oxidation of alcohols catalyzed by earth-abundant metal oxides embedded on porous N-doped carbon derived from chitosan

Metal clusters oxide were embedded in an N-doped carbon and used as catalysts for the activation of peroxydisulfate or peroxymonosulfate in the selective oxidation of benzyl alcohol. Quenching tests were done to investigate the reaction mechanism.

Insights into the mechanism of carbocatalysis for peracetic acid activation: Kinetic discernment and active site identification

Peracetic-acid-based advanced oxidation processes (PAA-AOPs) on metal-free catalysts have emerged as charming strategies for water contaminant removal. However, the involved reactive species and their corresponding active sites are ambiguous. Herein, using carbon nanotube (CNT) as a model carbocatalyst, we demonstrated that, under neutral conditions, the CNT-PAA* complex was the dominant reactive species to oxidize phenolic compounds via electron-transfer process (ETP), whereas the surface-bound hydroxyl radicals (^·OH_surface) played a minor role on the basis of quenching and electrochemical tests as well as Raman spectroscopy. More importantly, the experimental and density functional theory (DFT) calculation results collaboratively proved that the active site for ETP was the sp²-hybridized carbon on the CNT bulk, while that for radical generation was the edge-located hydroxyl group (C-OH), which lowered the energy barrier for cleaving the O-O bond in CNT-PAA* complex. We further discerned the oxidation kinetic constants (k_oxid) of different pollutants from the apparent kinetic constants in CNT/PAA system. The significant negative linear correlation between lnk_oxid and half-wave potential of phenolic compounds suggests that the pollutants with a lower one-electron oxidation potential (i.e., stronger electron-donating ability) are more easily oxidized. Overall, this study scrutinizes the hybrid radical and non-radical mechanism and the corresponding active sites of the CNT/PAA system, providing insights into the application of PAA-AOPs and the development of ETP in the remediation of emerging organic pollutants.

Changes in the catalytic activity of oxygen-doped graphitic carbon nitride for the repeated degradation of oxytetracycline

Metal-free carbonaceous catalysts have gained growing interest because of their excellence in organic pollutant degradation. However, most of them suffer from deactivation after use, and the origins have not been investigated or understood. In this study, the changes in the characteristics after multiple uses of a carbonaceous catalyst, i.e., oxygen-doped graphitic carbon nitride (O-gCN), were investigated to identify the key factors affecting its reactivity. The O-gCN was repeatedly used to remove an antibiotic (oxytetracycline, OTC) in the presence of peroxymonosulfate (PMS). OTC removal was significantly reduced as the O-gCN was repeatedly used. The reactivity of O-gCN used five times (O-gCN5) corresponded well with the decreased signals of DMPO-X, DMPO-O₂^•-, and TEMP-¹O₂ in electron paramagnetic resonance spectra. These signal changes were accompanied by a shift of the involved reactive species from ¹O₂ and OH^• for O-gCN to ¹O₂ and SO₄^•- for O-gCN5. The changes in activity and involved reactive species were attributed to the changes in the properties of O-gCN, considering the negligible OTC adsorption and slight PMS consumption. The results of X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in the degree of defects, graphene-like layers, and crystallinity in graphitic structures, but an increase in the fractions of N and O, for O-gCN5. However, the OTC degradation pathways and intermediates were not significantly different for O-gCN and O-gCN5. These results provide valuable information for developing strategies for the design, practical use, and regeneration of carbonaceous catalysts.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Electron delocalization triggers nonradical Fenton-like catalysis over spinel oxides

Nonradical Fenton-like catalysis offers opportunities to overcome the low efficiency and secondary pollution limitations of existing advanced oxidation decontamination technologies, but realizing this on transition metal spinel oxide catalysts remains challenging due to insufficient understanding of their catalytic mechanisms. Here, we explore the origins of catalytic selectivity of Fe-Mn spinel oxide and identify electron delocalization of the surface metal active site as the key driver of its nonradical catalysis. Through fine-tuning the crystal geometry to trigger Fe-Mn superexchange interaction at the spinel octahedra, ZnFeMnO₄ with high-degree electron delocalization of the Mn-O unit was created to enable near 100% nonradical activation of peroxymonosulfate (PMS) at unprecedented utilization efficiency. The resulting surface-bound PMS* complex can efficiently oxidize electron-rich pollutants with extraordinary degradation activity, selectivity, and good environmental robustness to favor water decontamination applications. Our work provides a molecule-level understanding of the catalytic selectivity and bimetallic interactions of Fe-Mn spinel oxides, which may guide the design of low-cost spinel oxides for more selective and efficient decontamination applications.