Sulfate radicals induced from peroxymonosulfate by cobalt manganese oxides (Co(x)Mn(3-x)O4) for Fenton-Like reaction in water

Cobalt germanium hydroxides with asymmetric electron distribution and surface hydroxyl groups for superb catalytic degradation performances

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are attractive approaches for solving the global problem of water pollution, due to the generation of highly-active reactive oxygen species (ROS). Therefore, highly-efficient PMS activation is crucial for promoting the catalytic degradation of environmental pollutants. Here, bimetallic CoGeO2(OH)2 nanosheets with abundant surface hydroxyl groups (CGH) were synthesized via a simple hydrothermal route for PMS activation and degradation of various organic contaminants for the first time. The abundant surface hydroxyl groups (≡Co-OH/≡Ge-OH) could promptly initiate PMS to generate highly-active species: singlet oxygen (1O2), sulfate radicals (SO4·-) and hydroxyl radicals (HO•), while the asymmetric electron distribution among Co-O-Ge bonds derived from the higher electronegativity of Ge than Co further enhances the quick electron transfer to promote the redox cycle of Co2+/Co3+ and Ge2+/Ge4+, thereby achieving an outstanding catalytic capability. The optimal catalyst exhibits nearly 100 % catalytic degradation performance of dyes (Methylene blue, Rhodamine B, Methyl orange, Orange II, Methyl green) and antibiotics (Norfloxacin, Bisphenol A, Tetracycline) over a wide pH range of 3-11 and under different coexisting anion conditions (Cl-, HCO3-, NO3-, HA), suggesting the excellent adaptability for practical usage. This study could potentially lead to novel perspectives on the remediation of water areas such as groundwater and deep-water areas.

Size-Dependent Catalysis in Fenton-like Chemistry: From Nanoparticles to Single Atoms

State-of-the-art Fenton-like reactions are crucial in advanced oxidation processes (AOPs) for water purification. This review explores the latest advancements in heterogeneous metal-based catalysts within AOPs, covering nanoparticles (NPs), single-atom catalysts (SACs), and ultra-small atom clusters. A distinct connection between the physical properties of these catalysts, such as size, degree of unsaturation, electronic structure, and oxidation state, and their impacts on catalytic behavior and efficacy in Fenton-like reactions. In-depth comparative analysis of metal NPs and SACs is conducted focusing on how particle size variations and metal-support interactions affect oxidation species and pathways. The review highlights the cutting-edge characterization techniques and theoretical calculations, indispensable for deciphering the complex electronic and structural characteristics of active sites in downsized metal particles. Additionally, the review underscores innovative strategies for immobilizing these catalysts onto membrane surfaces, offering a solution to the inherent challenges of powdered catalysts. Recent advances in pilot-scale or engineering applications of Fenton-like-based devices are also summarized for the first time. The paper concludes by charting new research directions, emphasizing advanced catalyst design, precise identification of reactive oxygen species, and in-depth mechanistic studies. These efforts aim to enhance the application potential of nanotechnology-based AOPs in real-world wastewater treatment.

Preparation of MWCNT/CoMn2O4 nanocomposite for effectual degradation of picric acid via peroxymonosulfate activation

In recent years, using nanomaterials based on multi-wall carbon nanotubes (MWCNT) through the activation of peroxymonosulfate (PMS) has attracted more attention to the degradation of organic pollutants. This research presented a new route for the synthesis of MWCNT/CoMn2O4 nanocomposite for the degradation of picric acid using advanced oxidation processes (AOPs). Firstly, CoMn2O4 nanoparticles were prepared and then loaded on MWCNT using ultrasonic waves. The results of various analyzes confirmed the successful loading of nanoparticles on carbon nanotubes. As the degradation process proceeds through oxidation processes, the high electronic conductivity of MWCNT and the active sites of Mn and Co in the nanocomposite play an essential role in activating PMS to generate reactive oxygen species (ROS). An investigation of the reaction mechanism in different conditions showed that the highest speed of picric acid decomposition in the presence of nanocomposite (98%) was in 47 min. However, the scavenger test showed that HO· and SO4·- radicals are more important in the degradation process. Meanwhile, the results showed that removing picric acid using MWCNT/CoMn2O4 was more effective than CoMn2O4 alone and confirmed the interaction effect of MWCNT nanotubes with AB2O4 nanocatalyst.

Nitrogen-Doped Biochar for Enhanced Peroxymonosulfate Activation to Degrade Phenol through Both Free Radical and Direct Oxidation Based on Electron Transfer Pathways

Nowadays, super nitrogen-doped biochar (SNBC) material has become one of the most promising metal-free catalysts for activating peroxymonosulfate (PMS) to degrade organic pollutants. To understand the evolution of SNBC properties with fabrication conditions, a variety of SNBC materials were prepared and characterized by elemental analysis, N2 adsorption-desorption, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. We systematically investigated the activation potential of these SNBC materials for PMS to degrade phenol. SN1BC-800 with the best catalytic performance was obtained by changing the activation temperatures and the ratio of biochar to melamine. The effects of catalyst dosage, the PMS concentration, pH, and reaction temperature on phenol degradation were studied in detail. In the presence of 0.3 g/L SN1BC-800 and 1 g/L PMS, the removal rate of 20 mg/L phenol could reach 100% within 5 min. According to electron paramagnetic resonance spectra and free radical quenching experiments, a nonfree radical pathway of phenol degradation dominated by 1O2 and electron transfer was proposed. More interestingly, the excellent catalytic performance of the SN1BC-800/PMS system is universally applicable in the degradation of other typical organic pollutants. In addition, the degradation rate of phenol is still over 80% after five reuses, which shows that the SN1BC-800 catalyst has high stability and good application prospects in environmental remediation.

Advanced degradation of organic pollutants using sonophotocatalytic peroxymonosulfate activation with CoFe2O4/Cu- and Ce-doped SnO2 composites

The rampant upsurge of organic pollutants in aqueous media has become one of the major concerns nowadays. Finding non-specific catalysts that can target a wide range of organic pollutants is a key challenge. Eco-friendly oxidative radicals, such as promoted by peroxymonosulfate (PMS), are necessary for efficient water decontamination. We propose a multicomponent composite catalyst for activating PMS using a dual strategy of sonophotocatalysis. The composite integrates cobalt ferrite and Cu- or Ce-doped SnO2, with the at. % of doping metal and the mixture ratio carefully balanced. The top-performing architectures were able to decompose rhodamine B (20 ppm), a representative pollutant, in under 3 min and achieve over 70% mineralization in just 5 min. The synthesized nanocomposites demonstrated exceptional sonophotocatalytic performance, even when treating complex and diverse multipollutant solutions (80 ppm), achieving over 75% mineralization after 150 min. Considering their high stability and reusability, the proposed CoFe2O4/Cu- and Ce-doped SnO2 materials are among the state-of-the-art heterogeneous catalysts for mineralizing organic pollutants through PMS activation.

One-pot solvothermal synthesis of Cu-Fe-MOF for efficiently activating peroxymonosulfate to degrade organic pollutants in water:Effect of electron shuttle

Persulfate-based advanced oxidation processes (PS-AOPs) show a bright prospect in sewage purification. The development of efficient catalysts with simple preparation process and eco-friendliness is the key for their applying in practical water treatment. Herein, a bimetallic Cu-Fe metal organic framework (MOF) was simply synthesized by using one-pot solvothermal methods and employed for activating peroxymonosulfate (PMS) to degrade organic pollutants in water. The Cu-Fe-MOF/PMS exhibited excellent degradation efficiencies (over 95% in 30 min) for a variety of pollutants, including phenol, bisphenol A, 2,4-dichlorophenol, methyl blue, rhodamine B, tetracycline and sulfamethoxazole. The degradation efficiency was impacted by dosages of Cu-Fe-MOF, PMS concentrations, reaction temperature, solution pH and anionic species. Phenol could be efficiently decomposed in a wide pH range of 5-9, with the highest degradation and mineralization efficiency of nearly 100% and 70%, respectively. Free radicals and non-free radicals participated in degrading of phenol at the same time, with dominantly free radical process, because sulfate radicals (SO4·-) and hydroxyl radicals (·OH) were the primary active substances by contribution calculation. Cu-Fe-MOF was acted as electron shuttle between molecules of phenol and PMS, and the cooperation effect of Fe and Cu on the Cu-Fe-MOF promoted the electron transfer, achieving the high degradation efficiency of phenol. Thus, Cu-Fe-MOF is an ideal catalyst for activating PMS, which is conducive to promote the applying of catalyst-activated PMS processes for practical wastewater treatments.

Sea Urchin-like NiCo2O4 Catalyst Activated Peroxymonosulfate for Degradation of Phenol: Performance and Mechanism

How to efficiently activate peroxymonosulfate (PMS) in a complex water matrix to degrade organic pollutants still needs greater efforts, and cobalt-based bimetallic nanomaterials are desirable catalysts. In this paper, sea urchin-like NiCo2O4 nanomaterials were successfully prepared and comprehensively characterized for their structural, morphological and chemical properties via techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), among others. The sea urchin-like NiCo2O4 nanomaterials exhibited remarkable catalytic performance in activating PMS to degrade phenol. Within the NiCo2O4/PMS system, the removal rate of phenol (50 mg L-1, 250 mL) reached 100% after 45 min, with a reaction rate constant k of 0.091 min-1, which was 1.4-times higher than that of the monometallic compound Co3O4/PMS system. The outstanding catalytic activity of sea urchin-like NiCo2O4 primarily arises from the synergistic effect between Ni and Co ions. Additionally, a comprehensive analysis of key parameters influencing the catalytic activity of the sea urchin-like NiCo2O4/PMS system, including reaction temperature, initial pH of solution, initial concentration, catalyst and PMS dosages and coexisting anions (HCO3-, Cl-, NO3- and humic acid), was conducted. Cycling experiments show that the material has good chemical stability. Electron paramagnetic resonance (EPR) and quenching experiments verified that both radical activation (SO4•-, •OH, O2•-) and nonradical activation (1O2) are present in the NiCo2O4/PMS system. Finally, the possible degradation pathways in the NiCo2O4/PMS system were proposed based on gas chromatography-mass spectrometry (GC-MS). Favorably, sea urchin-like NiCo2O4-activated PMS is a promising technology for environmental treatment and the remediation of phenol-induced water pollution problems.

Efficient removal of tetracycline hydrochloride by high entropy oxides in visible photo-Fenton catalytic process

A novel type of oxide material, high entropy oxide (Mn0.2Fe0.2Co0.2Ni0.2Cu0.2)3O4 (MFO) composites with spinel structure were successfully synthesized by a simple solution combustion in this paper, and it was first applied to the degradation of antibiotic organic pollutants in water by photo-Fenton. SEM and BET characterization showed that the composite was porous and had a large specific surface area. XPS results showed that Fe, Mn, Cu, Co and Ni all participated in the redox reaction of the catalytic process. The redox pairs of Mn2+/Mn3+, Cu+/Cu2+, Co2+/Co3+, Ni2+/Ni3+ can accelerate the Fe2+/Fe3+ redox cycling in MFO to activate H2O2 and produce more reactive oxygen species. The catalytic performance of MFO composite was investigated using tetracycline hydrochloride (TC-HCl) as a model pollutant. The results displayed that the degradation rate of TC-HCl by MFO was 92.9% when the initial pH was 4, the dose of H2O2 was 50 mM, and the irradiation time was 60 min. The high entropy oxide MFO composites could build up an internal electric field, which restrains electron-hole recombination, improves the transfer of photogenerated charge carriers and maximize photocatalytic property. In addition, the free radical capture experiment determined that the main active species of the degradation reaction were e-, •O2- and •OH. The synergistic effect of the five components in the high entropy oxide strengthens lattice distortion and defects, increases oxygen vacancies, and thus has enhanced catalytic effect for TC-HCl degradation. This work shows that high entropy oxides have excellent catalytic performance for tetracycline organic pollutants, and it is speculated that high entropy oxides have good application prospects in the field of advanced oxidation technology for the degradation of organic pollutants.

Stability enhancing of perovskite LaCoO3 by compositing with oxygen doped MoS2 in Fenton-like reactions

Perovskite materials are reported to be effective in peroxymonosulfate (PMS) based Fenton-like reactions, the leaching rates of chalcogenide materials in perovskite materials are however serious, thus leading to bad performance in long-term stability. In this study, an O-doped MoS₂ is synthesized to composite with LaCoO₃, and the high catalytic activity of LaCoO₃ is well preserved with greatly decreased Co leaching. During the BPA degradation with PMS as oxidant, ∼100% degradation can be achieved in 20 min and this degradation efficiency can be maintained for ∼45 h in a simulated fixed bed reactor, which is almost 3 times longer than the pure LaCoO₃. With the compositing of O-doped MoS₂, the leached Co was greatly decreased and the dominated reactive oxidation species (ROS) transformed from SO₄^•- into O₂^•- with longer lifespan, thus resulting in the better stability. This study could promote the application of perovskite materials in the real industrial wastewater treatment.

Structure of a novel Co-based heterogeneous catalyst via Mn3(PO4)2 as a carrier to efficiently activate peroxymonosulfate for improving degradation of sulfonamides

Effective degradation of sulfonamides (SAs) in water is of global importance for decreasing its pathogenicity and bioaccumulation. In this study, Mn₃(PO₄)₂ was used as a carrier to fabricate a novel and high-efficient catalyst with Co₃O₄ anchored (Co₃O₄@Mn₃(PO₄)₂) for the activation of peroxymonosulfate (PMS) to degrade SAs. Surprisingly, the catalyst exhibited superior performance, and nearly 100% of SAs (10 mg L^-1) including sulfamethazine (SMZ), sulfadimethoxine (SDM), sulfamethoxazole (SMX), and sulfisoxazole (SIZ) was degraded by Co₃O₄@Mn₃(PO₄)₂-activated PMS within 10 min. A series of characterization of the Co₃O₄@Mn₃(PO₄)₂ composite were conducted and the main operational parameters of SMZ degradation were investigated. SO₄^•-, •OH, and ¹O₂ were determined to be the dominating reactive oxygen species (ROS) responsible for the degradation of SMZ. Co₃O₄@Mn₃(PO₄)₂ also exhibited excellent stability and the removal rate of SMZ still maintained over 99% even in the fifth cycle. The plausible pathways and mechanisms of SMZ degradation in the system of Co₃O₄@Mn₃(PO₄)₂/PMS were deduced on the basis of the analyses of LCMS/MS and XPS. This is the first report on high-efficient heterogeneous activating PMS by mooring Co₃O₄ on Mn₃(PO₄)₂ to degrade SAs, which provides us with a strategy to structure novel bimetallic catalysts for PMS activation.

Fulvic acid enhanced peroxymonosulfate activation over Co-Fe binary metals for efficient degradation of emerging bisphenols

Bisphenol F (BPF) and bisphenol S (BPS) are emerging bisphenols, which have become the main substitutes for bisphenol A (BPA) in industrial production and are also considered as new environmental pollution challenges. Thus, the necessity for an effective approach to remove BPF and BPS is essential. In this study, fulvic acid (FA) was used to modify Co-Fe binary metals (CFO) for peroxymonosulfate (PMS) activation. The characterization results demonstrated that CFO changed significantly in morphology after compounding with FA, with smaller particle size and 5.6 times larger specific surface area, greatly increasing the active sites of catalyst; Moreover, humic acid-like compounds increased the surface functional groups of CFO, especially phenolic hydroxyl, which could effectively prolong the PMS activation. The concentration of all reactive species, such as SO₄•^-, •OH, O₂•^-, and ¹O₂ increased in FA@CFO/PMS system. As a result, the degradation efficiency of CFO for both BPF and BPS was significantly improved after compounding FA, which also had a wide range of pH applications. The degradation pathways of both BPF and BPS were proposed based on liquid chromatography-mass spectrometry (LC-MS) analysis and the density functional theory (DFT) calculations. Our findings are expected to provide new strategies and methods for remediation of environmental pollution caused by emerging bisphenols.

Remediation of environmentally persistent organic pollutants (POPs) by persulfates oxidation system (PS): A review

Over the past few years, persistent organic pollutants (POPs) exhibiting high ecotoxicity have been widely detected in the environment. Persulfate-oxidation hybrid system is one of the most widely used novel advanced oxidation techniques and is based on the persulfate generation of SO₄^-∙ and ∙OH from persulfate to degrade POPs. The overarching aim of this work is to provide a critical review of the variety of methods of peroxide activation (e.g., light activated persulfate, heat-activated persulfate, ultrasound-activated persulfate, electrochemically-activated persulfate, base-activated persulfate, transition metal activated persulfate, as well as Carbon based material activated persulfate). Specifically, through this article we make an attempt to provide the important characteristics and uses of main activated PS methods, as well as the prevailing mechanisms of activated PS to degrade organic pollutants in water. Finally, the advantages and disadvantages of each activation method are analyzed. This work clearly illustrates the benefits of different persulfate activation technologies, and explores persulfate activation in terms of Sustainable Development Goals, technical feasibility, toxicity assessment, and economics to facilitate the large-scale application of persulfate technologies. It also discusses how to choose the most suitable activation method to degrade different types of POPs, filling the research gap in this area and providing better guidance for future research and engineering applications of persulfates.

Biochar loaded with cobalt ferrate activated persulfate to degrade naphthalene

Considering the simple preparation of biochar and the excellent activation performance of cobalt ferrate material, a biochar supported cobalt ferrate composite was synthesized by a solvothermal method. The material was used to activate persulfate (PS) to degrade naphthalene (NAP) in water. The structure and morphology characterization showed that the composite (CoFe₂O₄-BC) was successfully prepared. Under the conditions of 0.25 g L^-1 CoFe₂O₄-BC and 1 mM PS, 90.6% NAP (the initial concentration was 0.1 mM) was degraded after 30 minutes. The degradation kinetics of NAP followed the pseudo-first-order kinetic model with a rate constant of 0.0645 min^-1. With the increase of the dosage of activator and PS, the removal rate of NAP could be increased to 99.5%. The coexistence of anions and humic acids inhibited the removal of NAP. The acid environment promoted the removal of NAP while the alkaline environment inhibited it. After four cycles of CoFe₂O₄-BC material, the removal rate of NAP decreased from 90.6% to 79.4%. The removal of TOC was about 45% after each cycle. After the first cycle, the concentration of leached cobalt ion and leached iron ion was about 310 μg L^-1 and 30 μg L^-1 respectively. The free radical quenching experiments showed that SO₄ ^-˙ and OH˙ were the main causes of NAP removal, and the possible degradation path of NAP was elucidated by DFT calculation.

Co-Mn spinel oxides trigger peracetic acid activation for ultrafast degradation of sulfonamide antibiotics: Unveiling critical role of Mn species in boosting Co activity

Activation of peracetic acid (PAA) to generate powerful oxidizing species has become a promising advanced oxidation processes (AOPs) in wastewater treatment, yet the development of low-cost and high-performance activators is still a primary challenge. Herein, a range of Co-Mn spinel oxides (Co_3-xMn_xO₄) with varying levels of Co and Mn were successfully elaborated, in which Co_1.1Mn_1.9O₄ exhibited remarkable performance in PAA activation, outperforming most reported heterogeneous catalysts. Extensive quenching experiments and electron spin resonance (ESR) analysis indicated that acetylperoxyl radical (CH₃C(O)OO^●) was the predominated oxidizing species responsible for sulfamethoxazole (SMX) degradation. Density functional theory (DFT) calculations revealed that doping with Mn not only promoted the electron transfer and accelerated reduction of Co(III) to Co(II), but also lowered the energy barrier for PAA activation. Moreover, the prominent chemisorption and activation of PAA with Co_1.1Mn_1.9O₄ was also benefitted from the significant role of Mn in optimizing the distribution of bonding and antibonding states on Co 3d orbitals. Unexpectedly, high levels of Cl^-greatly facilitated SMX degradation due to the mass production of HOCl from the chain reactions of various radicals with Cl^-. This work provides new insights into bimetallic activation of PAA, and the knowledge obtained will further advance the application of PAA-based AOPs.

Mechanistic insights into efficient peroxymonosulfate activation by NiCo layered double hydroxides

The efficient removal of organic refractory pollutants such as dyes and antibiotics in wastewater is crucial for protecting the environment and human health. In this work, a NiCo-layered double hydroxide (NiCo-LDH) with a uniform microspherical, hierarchical structure and a high surface area was successfully synthesized as an effective peroxymonosulfate (PMS) activator for the degradation of various organic dyes and antibiotics. The influence of various parameters on the catalytic activity of the NiCo-LDH was determined. Radical scavenger studies unveiled the major reactive oxygen species (ROSs) generated in the NiCo-LDH/PSM system to be ¹O₂, SO₄^•-, and O₂^•-. Ex-situ X-ray photoelectron spectroscopy (XPS) analysis uncovered the role of Co sites and oxygen vacancy as active sites and revealed the reversible redox properties of NiCo-LDH based on Co²⁺/Co³⁺ cycles. The activation mechanism and Rhodamine B (RhB) degradation pathways were experimentally studied and proposed. The NiCo-LDH is highly versatile, reusable and stable as shown by post-catalysis characterizations. This work shows the excellent catalysis performances and provides insights into the activation mechanism of PMS by NiCo-LDH for organic pollutant remediation.

Mechanism analysis of efficient degradation of carbamazepine by chalcopyrite-activated persulfate

In this study, natural chalcopyrite (NCP) was used to activate peroxymonosulfate (PMS) to degrade carbamazepine (CBZ) oxidatively. Before and after the NCP reaction, the physical and chemical properties were characterized by SEM-EDS, XRD, XPS, XRF, and VSM. The effects of the amount of NCP and PMS, the initial pH value, and the reaction temperature on the catalytic performance of NCP were systematically studied. The research results show that the degradation efficiency of the NCP/PMS system for CBZ can reach 82.34% under the optimal reaction conditions, and the degradation process follows a pseudo-second-order kinetic model. The results of the radical quenching experiment and EPR analysis show that the active species in the system are OH·, SO₄^-·, and ¹O², of which SO₄^-· is the main active species. In addition, this study shows that the NCP/PMS system can degrade CBZ with high efficiency of 90.73% only with the assistance of 0.15 g/L Fe⁰. This study determined the optimal reaction conditions for natural chalcopyrite to activate PMS to degrade CBZ and clarified the activation mechanism, which broadened the application of natural ores in the field of water treatment.

Fabrication of a magnetic Mn(ii) cross-linked chitosan-amine/glutaraldehyde nanocomposite for the rapid degradation of dyes and aerobic selective oxidation of ethylbenzene†

Owing to the great demand for using sustainable, renewable, and widely available materials in catalytic systems for the conversion of waste/toxic material to high value-added and harmless products, biopolymers derived from natural sources have demonstrated great promise as an alternative to state-of-the-art materials that suffer from high costs and limitations. These have encouraged us to design and fabricate a new super magnetization of Mn–Fe₃O₄–SiO₂/amine-glutaraldehyde/chitosan bio-composite (MIOSC-N-et-NH₂@CS-Mn) for advanced/aerobic oxidation process. The morphological and chemical characterization of the as-prepared magnetic bio-composite was assessed using ICP-OES, DR UV-vis, BET, FT-IR, XRD, FE-SEM, HR-TEM, EDS, and XPS techniques. The PMS + MIOSC-N-et-NH₂@CS-Mn system was capable of degrading methylene orange (98.9% of removal efficiency) and selectively oxidizing ethylbenzene to acetophenone (conversion 93.70%, selectivity 95.10% and TOF 214.1 (10³ h⁻¹) within 8.0 min and 5.0 h, respectively. Moreover, MO was efficiently mineralized (TOC removal of ∼56.61) by MIOSC-N-et-NH₂@CS-Mn with 60.4%, 5.20, 0.03 and 86.02% of the synergistic index, reaction stoichiometric efficiency, specific oxidant efficiency, and oxidant utilization ratio in wide pH ranges, respectively. An understanding of its vital parameters and relationship of catalytic activity with structural, environmental factors, leaching/heterogenicity test, long-term stability, inhibitory effect of anions in water matrix, economic study and response surface method (RSM) were evaluated in detail. Overall, the prepared catalyst could be employed as an environmentally friendly and low-cost candidate for the enhanced activation of PMS/O₂ as an oxidant. Additionally, MIOSC-N-et-NH₂@CS-Mn exhibited great stability, high recovery efficiency, and low metal leaching, which eliminated the harsh condition reaction and supplied practical application performance for water purification and selective aerobic oxidation of organic compounds.

Optimization of the catalytic degradation of dyes and aerobic oxidation of ethylbenzene by Mn@Cross-linked Magnetic Chitosan-Amin-Glutaraldehyde.

Low-Temperature Reduction Synthesis of γ-Fe2O3-x@biochar Catalysts and Their Combining with Peroxymonosulfate for Quinclorac Degradation

Biochar loading mixed-phase iron oxide shows great advantages as a promising catalyst owing to its eco-friendliness and low cost. Here, γ-Fe₂O_3-x@biochar (E/Fe-N-BC) composite was successfully prepared by the sol-gel method combined with low-temperature (280 °C) reduction. The Scanning Electron Microscope (SEM) result indicated that γ-Fe₂O_3-x particles with the size of approximately 200 nm were well-dispersed on the surface of biochar. The CO derived from biomass pyrolysis is the main reducing component for the generation of Fe (II). The high content of Fe (II) contributed to the excellent catalytic performance of E/Fe-N-BC for quinclorac (QNC) degradation in the presence of peroxymonosulfate (PMS). The removal efficiency of 10 mg/L of QNC was 100% within 30 min using 0.3 g/L γ-Fe₂O_3-x@biochar catalyst and 0.8 mM PMS. The radical quenching experiments and electron paramagnetic resonance analysis confirmed that •OH and SO₄•^- were the main radicals during the degradation of QNC. The facile and easily mass-production of γ-Fe₂O_3-x@biochar with high catalytic activity make it a promising catalyst to activate PMS for the removal of organic pollutants.

Ascorbic acid enhanced MnFe2O4/peroxymonosulfate oxidation of organic pollutant: Key role of singlet oxygen generation and Fe/Mn cycling

The activated peroxymonosulfate (PMS) process has been widely applied for degrading organic pollutants. However, its application is limited by low metal cycling, and the contribution of oxygen species remains unclear. Here, the crystal structure, surface morphology, and elemental valence of the synthesized manganese ferrite (MnFe₂O₄) catalyst were investigated by SEM, HRTEM, XRD, and XPS. A novel MnFe₂O₄/PMS/ascorbic acid (AA) system was constructed to enhance the Fe/Mn cycling on the surfaces of the MnFe₂O₄ catalyst. The addition of AA can significantly increase the decomposition of organic pollutants, and the apparent rate constant of the MnFe₂O₄/PMS/AA system is 8.2 times higher than that of MnFe₂O₄/PMS. AA facilitates the reduction of Fe/Mn(III) and the dissolution of Fe/Mn(II), creating a Fe/Mn cycle between the heterogeneous and homogeneous interfaces of the catalyst. Furthermore, AA greatly increases the activity of adsorbed oxygen on the catalyst surfaces, generating a large amount of singlet oxygen (¹O₂), which contributes significantly to the destruction of organic pollutants. The efficient, fast, and environmentally friendly PMS activation method in this study can provide reliable technical support for treating refractory organic pollutants in water.

Sulfite activation by cobaltosic oxide nanohydrangeas for tetracycline degradation: Performance, degradation pathways and mechanism

Sulfite has been used as a classic reductant for the dehalogenation and reduction of organic compounds for a long time, it is recently deemed as a promising alternative (for persulfate) to generate sulfate radical for wastewater treatment due to its low price and eco-toxicity. In contrast with the enormous work developed in the field of tetracycline (TC) degradation via PMS activization, sulfite activization could play a important role in TC degradation but there is only very few available reports in this area. Herein, the novel and efficient CoNHs nanocatalyst is designed and developed, via immobilization of hydrangea-shaped Co₃O₄ nanoparticles onto graphitic carbon nanosheet (GCN), for the degradation of tetracycline via sulfite activation. The detailed characterizations have confirmed that CoNHs possesses a nanohydrangea-shaped structure with high microporosity. The comparison with other supports (such as CeO₂ and MoS₂), CoNHs provides the highest degradation efficiency in TC degradation, due to the synergistic effect between Co₃O₄ and GCN. Free radical quenching experiments and EPR analysis confirm that SO₄•^- and O₂•^- are major reactive oxygen species in the CoNHs/sulfite system. This work could provide a simple, economical and durable cobalt-based catalyst for organic wastewater treatment via sulfite activation.

Heterogeneous Metal-Activated Persulfate and Electrochemically Activated Persulfate: A Review

The problem of organic pollution in wastewater is an important challenge due to its negative impact on the aquatic environment and human health. This review provides an outline of the research status for a sulfate-based advanced oxidation process in the removal of organic pollutants from water. The progress for metal catalyst activation and electrochemical activation is summarized including the use of catalyst-activated peroxymonosulfate (PMS) and peroxydisulfate (PDS) to generate hydroxyl radicals and sulfate radicals to degrade pollutants in water. This review covers mainly single metal (e.g., cobalt, copper, iron and manganese) and mixed metal catalyst activation as well as electrochemical activation in recent years. The leaching of metal ions in transition metal catalysts, the application of mixed metals, and the combination with the electrochemical process are summarized. The research and development process of the electrochemical activation process for the degradation of the main pollutants is also described in detail.

Improvement of sulfur and water resistance with Fe-modified S-MnCoCe/Ti/Si catalyst for low-temperature selective catalytic reduction of NO with NH3

The low-temperature SCR of NO_x by NH₃ is restricted in application since the catalysts is easily poisoned by sulfur and water. The Fe modified Mn-Co-Ce/TiO₂/SiO₂ catalysts synthesized via impregnation method and sulfating were evaluated for low-temperature NH₃-SCR in the presence of SO₂ and H₂O. The calcination temperature and loading amounts of Mn, Fe, Co and Ce were optimized. Adding of Fe into S-MnCoCe/Ti/Si played an important role in resistance to sulfur and water poisoning. The optimal calcination temperature was 380 °C and the optical mass loading of the catalyst was 10% of Mn, 10% of Fe, 1% of Co and 4% of Ce. The optimal S-MnFeCoCe/Ti/Si catalyst maintained high NO_x conversion of 93% at reaction temperature of 160 °C in the presence of 50 ppm SO₂ and 10 vol% H₂O. The catalytic activity did not continue to fall after two times of repeated used in the temperature range of 100-200 °C, indicating its excellent sulfur and water durability and stability in the presence of SO₂ and H₂O. The interaction between MnO_x and FeO_x enhanced sulfur and water durability rather than other bi-metal interactions. Furthermore, the mechanism of Fe improving resistance to SO₂ and H₂O was discussed.

Assembly of UiO-66 onto Co-doped Fe3O4 nanoparticles to activate peroxymonosulfate for efficient degradation of fenitrothion and simultaneous in-situ adsorption of released phosphate

Although sulfate radical-based advanced oxidation processes (SR-AOPs) have shown great potential for the efficient degradation of various organic contaminants, there is few research on the removal of organophosphorus pesticides (OPPs) through SR-AOPs. In this work, Co-doped Fe₃O₄ magnetic particles encapsulated by zirconium-based metal-organic frameworks (Co-Fe₃O₄@UiO-66) were prepared and employed to activate peroxymonosulfate (PMS) for the elimination of fenitrothion (FNT) and the simultaneous in-situ adsorption of produced phosphate. The catalyst exhibited efficient catalytic performance, achieving above 90.0% removal of FNT (10 mg/L) in the presence of PMS (1 mM) within 60 min. Moreover, the produced phosphate during the degradation process was also completely adsorbed onto the catalyst. Both sulfate and hydroxyl radicals were responsible for the degradation of FNT. The degradation products of FNT in the system were identified and the possible pathways were proposed. This study represents a promising and adoptable strategy to develop other versatile composite nanomaterials in a green manner hence broadening its environmental application range, as it can not only remove OPPs by catalytic oxidation but also immobilize degraded phosphorus by adsorption.

Controlling oxygen vacancies of CoMn2O4 by loading on planar and tubular clay minerals and its application for boosted PMS activation

A representative transition metal oxide (TMO), CoMn₂O₄ (CMO), is recognized as an effective peroxymonosulfate (PMS) activator with disadvantages like limited reactive sites and metal leakage. Herein, novel catalysts were synthesized by anchoring CMO on kaolinite (Kln) and halloysite (Hal) matrixes, two natural clay minerals with lamellar and tubular structures, for PMS activation in pharmaceutical degradation. Hal and Kln helped to control the crystallinity of CMO spontaneously with induce oxygen vacancies (OVs), which significantly enhanced the working efficiency. The reaction rate constants of Hal/CMO and Kln/CMO towards OFX degradation were nearly triple and twice that of bare CMO, respectively, with a 60% decrease in metal usage. The formation of OVs provided additional active sites for the reaction and accelerated the electron transfer. CMO/Hal and CMO/Kln exhibited better stability and durability than CMO, while CMO/Kln showed higher structural stability with lower metal leaching after 3 rounds of reaction. The higher crystallinity of CMO/Kln resulted in less OVs, but higher structural stability. The universal applicability of CMO/Hal and CMO/Kln were verified by using three other pharmaceuticals as probes. This work shed light on the modification of TMO catalysts by introducing clay mineral substrates for the efficient and ecofriendly remediation of pharmaceuticals in wastewater.

New perspective of ceria nanodots for precise tumor therapy via oxidative stress pathway

Ceria-based nanomaterials have aroused major attentions among the biomedical application research field in recent years. Most of the researches have mainly focused on promoting the functional healing therapies of normal cells/organs with cerium oxide compounds, while the applications of ceria-based materials employed on cancer curing processes have been merely mentioned. To explore the possible capabilities of cerium oxide nanomaterials exterminating tumor cells, innovatively, we synthesized the eco-friendly pure cerium oxide nanodots (CNDs), proving the prominent ability of CNDs used in tumor chemotherapy (CDT) via Fenton reaction with the highly presence of H₂O₂ (acidic pH) in tumor tissues. CNDs reacted with the self-produced H₂O₂ of tumor cells, which generated piled up toxic hydroxyl radical (·OH). The accumulated virulent ·OH restrained the growth of cancer cells intensively. This peroxidase-like activity, provided a distinguished paradigm for effective cancer curing treatment. We also verified the biosafety of CNDs applied on normal cells. Notably, not only did CNDs be harmless to normal cells, but also it protected them from the damages of reactive oxygen species (ROS). In normal cells/tissues, under the microenvironment of neutral pH and low level of H₂O₂, the CNDs could effectively function as an annihilator inhibiting ROS. They reduced the damages caused by ROS, exhibiting catalase-like activity. The research we studied, which estimated CNDs thoroughly, has provided a new perspective to the future researches of the cerium oxide biomaterial applications.

Electrospinning of ZIF-67 Derived Co-C-N Composite Efficiently Activating Peroxymonosulfate to Degrade Dimethyl Phthalate

In this work, an efficient cage-core peroxymonosulfate (PMS) catalyst was synthesized by applying an electrospinning–calcination process to the cobalt–zeolitic imidazole framework (ZIF-67) crystals for the catalytic degradation of dimethyl phthalate (DMP). The morphology and surface properties of the synthesized materials (ZIF-67, Z600 and ZP400/600/800) were well characterized. ZP600 showed great performance for the catalytic degradation of DMP in the initial pH range of 7.5–10.5. The removal rate of DMP could reach 90.4% in 60 min under optimum dosages of reagents (catalyst = 0.1 g/L, PMS = 0.5 mM, DMP = 6 ppm), and the mineralization degree of contaminant could reach 65%. By quenching experiments, it was determined that sulfate radical (SO4−·) and hydroxyl radical (·OH) dominated the degradation process. Moreover, due to the good magnetism, ZP600 could be easily separated from liquid and showed great reusability in five-cycle reaction experiments. Surprisingly, with the cover of cage-like polyacrylonitrile (PAN) fibers, the cobalt leaching amount of ZP600 decreased by about 87%. This study would expand the application of the electrospinning process in the development of functional materials for water purification.

In Situ Growth of Nitrogen-Doped Carbon Nanotubes Based on Hierarchical Ni@C Microspheres for High Efficiency Bisphenol A Removal through Peroxymonosulfate Activation

N-doped carbon nanotubes (NCNTs) are promising metal-free heterogeneous catalysts toward peroxymonosulfate (PMS) activation in advanced oxidation processes for wastewater remediation. However, conventional CNTs always suffer from serious agglomeration and low N content, which renders their design synthesis as an important topic in the related field. With hierarchical Ni@C microspheres as a nutritious platform, we have successfully induced in situ growth of NCNTs on their surface by feeding melamine under high-temperature inert atmospheres. These as-grown NCNTs with a small diameter (ca. 20 nm) are firmly rooted in Ni@C microspheres and present loose accumulation on their surface, and their relative content can be tailored easily by manipulating the mass ratio of melamine to Ni@C microspheres. The investigation on bisphenol A (BPA) removal reveals that the loading amount of NCNTs affects the catalytic performance greatly, and the optimum ratio of melamine to Ni@C microspheres is 5.0 because the corresponding MNC-5.0 possesses sufficient surface N sites and moderate electron transfer, resulting in powerful PMS activation and sufficient utilization of reactive oxidative species (ROS). MNC-5.0 also addresses its advantages as compared with other NCNTs from post treatment and spontaneous growth strategies. The primary ROS responsible for BPA degradation are identified as hydroxyl radical, sulfate radical, superoxide radical, and singlet oxygen through quenching experiments and electron paramagnetic resonance, and the corresponding catalytic mechanism is also put forward based on these results.

Mechanism of peroxymonosulfate activation and the utilization efficiency using hollow (Co, Mn)3O4 nanoreactor as an efficient catalyst for degradation of organic pollutants

Development of efficient catalysts for peroxymonosulfate (PMS) activation and further understanding its mechanism on organic pollutants degradation is of significant importance for advanced oxidation processes (AOPs). Herein, hollow (Co, Mn)₃O₄ catalysts were synthesized by calcination of Co, Mn containing metal-organic frameworks (MOFs) and further used to evaluate the effectiveness of organic pollutants (Bisphenol A (BPA), atrazine (ATZ), and diethyl phthalate (DEP)) degradation by PMS activation. The PMS utilization efficiency in (Co, Mn)₃O₄/PMS system (36.4%) was estimated to be 28.0% and 43.8% higher than that of Co₃O₄/PMS and Mn₅O₈/PMS system, respectively. Notably, the metal leaching in (Co, Mn)₃O₄/PMS system was significantly suppressed. The utilization efficiency also reveals an inverse proportionality relationship with BPA mineralization but decreases with increasing initial pH value. A synergy between oxides of Co and Mn was perceived to enhance PMS utilization efficiency and BPA degradation. The results indicate enhanced catalytic performance with (Co, Mn)₃O₄ compared to Co₃O₄ derived from Co-MOF and other reported catalysts, with 99% of BPA degradation within 4 min. The oxidation mechanism was then proposed based on the electron paramagnetic resonance (EPR) and XPS results. Our findings might have contributed to designing heterogeneous catalysts for efficient PMS utilization in AOPs.

Urchin-like Co3O4 anchored on reduced graphene oxide with enhanced performance for peroxymonosulfate activation in ibuprofen degradation

Urchin-like Co₃O₄ anchored on reduced graphene oxide was easily prepared with hydrothermal reaction by using a cheap and green agent. First, the surface morphology and physicochemical properties of Co₃O₄-rGO were characterized. Compared with Co₃O₄, Co₃O₄-rGO possessed excellent activity in peroxymonosulfate (PMS) activation for ibuprofen (IBU) degradation. Then, the influences of Co₃O₄-rGO dosage, IBU concentration, PMS concentration and pH on IBU and TOC removal were investigated, respectively. Furthermore, both ·OH and SO₄^•- were identified to be the main active species, and SO₄^•- made the predominant contribution. In addition, residual PMS and SO₄^•- quantification demonstrated that Co₃O₄-rGO could activate PMS more effectively, and produce more SO₄^•-. The mechanistic study revealed that the valence state conversion of Co²⁺/Co³⁺ was the critical PMS activation mechanism. Moreover, the enhanced activity of Co₃O₄-rGO is accounted for the combination of multiple unique characteristics, including excellent electronic transmission (Co²⁺ to Co³⁺, Co²⁺ to PMS), more active sites, and chemical bonds between Co₃O₄ and rGO. 13 degradation products were determined and possible degradation routes were proposed based on the results of LC-MS/MS. Finally, the Co₃O₄-rGO/PMS system also exhibited satisfactory removal of IBU in real water matrices.

Identification and manipulation of active centers on perovskites to enhance catalysis of peroxymonosulfate for degradation of emerging pollutants in water

Perovskites (the general formula of ABO₃) with versatile substrates can serve as desirable catalysts to initiate advanced oxidation processes (AOPs) for environmental remediation. However, the knowledge regarding the active centers remains piecemeal and unclear, such as how the redox metal centers of B site, inert metals of A site, oxygen vacancies, and direct oxidation of catalysts govern the chemical degradation of aqueous pollutants. This study aimed to identify principal alternations in physicochemical and electrical properties of ABO₃-based perovskites modified with partial/overall substitution at A/B sites and synthesized at different conditions. In order to probe varied catalytic activity of these catalysts, ofloxacin (OFX) was used as a model micro-pollutant. Results showed that the OFX degradation by activation of peroxymonosulfate (PMS) with LaFeO₃ perovskite was favored by the Sr substitution at A site, Cu substitution at B site, and increasing calcination temperature. Evolution of ¹O₂, ^•OH and SO₄^•- have proven for efficient OFX oxidation, as evidenced by results from in-situ electron paramagnetic resonance (EPR) analyses and quenching tests. Specifically, the introduction of Sr at A site can facilitate PMS self-decomposition to produce more ¹O₂ due to the increased abundance of surface oxygen vacancies. In contrast, the Cu substitution at B site improved the surface oxygen vacancies, as well as the electrical conductivity, which can further accelerate ^•OH and SO₄^•- generation for the OFX degradation. This study provides deeper insights into the underlying mechanisms governing the catalytic activity of perovskites. These findings build a basis for better decontamination of hazardous environmental organic pollutants.

Interfacial engineering coupling with tailored oxygen vacancies in Co2Mn2O4 spinel hollow nanofiber for catalytic phenol removal

Herein, one-dimensional Co₂Mn₂O₄ (CMO) hollow nanofibers with a general spinel structure were constructed by electrospinning and tunning thermal-driven procedures. The resultant catalyst was endowed with appreciable active interfacial engineering effect, which revealed improved peroxymonosulfate (PMS) activation efficiency in catalytic phenol degradation with nearly 12.9 folds increment in reaction rate constant compared to the hydrothermally synthesized counterpart. Besides, tailored oxygen-vacancy sites including chemical environment and contents in the bimetallic spinel were rationally validated compared to the monometal spinel counterparts. The improved catalytic phenol degradation by reactive-oxidative-species (ROS) from PMS was well correlated with the more active Co(II) and Mn(II) species, reactive active oxygen-vacancy and the interfacial engineering effect in the CMO catalyst. These correlations were comprehensively demonstrated by various characterization techniques, catalytic results, and Density-Functional-Theoretical (DFT) calculations of the adsorption and activation of PMS. Besides, the results revealed that the specific content of cobalt species in the structural unit of the Co₂Mn₂O₄ spinel resulting from the optimized thermal treatment could further improve the catalytic activity by the intermetallic synergy along with the beneficial electron transfer cycles. This work provides a practical understanding of the improvement of interfacial systems in catalysis efficiency and environmental remediation.

Efficient removal of organic pollutants by a Co/N/S-doped yolk-shell carbon catalyst via peroxymonosulfate activation

Carbon-based catalysts with heteroatom doping and hollow structures are desired for advanced oxidation processes (AOPs). Herein, dual-shelled Co, N, and S codoped hollow carbon nanocages were developed by wrapping zeolitic imidazolate framework-67 (ZIF-67) with trithiocyanuric acid (TCA) and performing subsequent carbonization. The optimal composite catalyst (Co-NC-CoS) exhibited excellent catalytic performance toward different organic pollutants. Almost complete removal of 4-NP (60 mg/L^-1) was achieved within 20 min by 10 mg of catalyst and 0.2 g/L^-1 peroxymonosulfate (PMS). Moreover, the catalyst showed good stability and reusability. The effects of catalyst and PMS dose, pollutant concentration, pH and common anions were investigated, and reactive oxygen species (ROS) were studied by scavenger experiments and electron paramagnetic resonance (EPR) tests. The results show that multidoped atoms S, Co and N all contributed to the degradation system. Several lines of evidence suggested that S could change the catalytic process from Co³⁺/Co²⁺ to Co³⁺/Co²⁺/Co⁰ reduction due to its low redox potential. Degradation was achieved through both radical and nonradical pathways, where sulfate radicals (SO₄^·̶), hydroxyl radicals (^·OH) and singlet oxygen (¹O₂) were primary reactive species. Overall, this work may suggest that the novel multi heteroatom-doped catalysts with complex structures can be developed for environmental remediation.

One-step pyrolysis for preparation of sulfur-doped biochar loaded with iron nanoparticles as an effective peroxymonosulfate activator for RhB degradation

In this study, sulfur-doped biochar loaded with iron nanoparticles (Fe/S-BC) was easily prepared by a one-pot pyrolysis method using anhydrous FeCl3, Na2S2O3·5H2O, and cherry stone powder as raw materials and...