Enhanced peroxymonosulfate activation for phenol degradation over MnO2 at pH 3.5-9.0 via Cu(II) substitution

Enhanced removal of antibiotic-resistant bacteria and resistance genes by three-dimensional electrochemical process using MgFe2O4-loaded biochar as both particle electrode and catalyst for peroxymonosulfate activation

In this study, MgFe2O4-loaded biochar (MFBC) was used as a three-dimensional particle electrode to active peroxymonosulfate (EC/MFBC/PMS) for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The results demonstrated that, under the conditions of 1.0 mM PMS concentration, 0.4 g/L material dosage, 5 V voltage intensity, and MFBC preparation temperature of 600 °C, the EC/MFBC600/PMS system achieved complete inactivation of E. coli DH5α within 5 min and the intracellular sul1 was reduced by 81.5 % after 30 min of the treatment. Compared to EC and PMS alone treatments, the conjugation transfer frequency of sul1 rapidly declined by 92.9 % within 2 min. The cell membrane, proteins, lipids, as well as intracellular and extracellular ARGs in E. coli DH5α were severely damaged by free radicals in solution and intracellular reactive oxygen species (ROS). Furthermore, up-regulation was observed in genes associated with oxidative stress, SOS response and cell membrane permeability in E. coli DH5α, however, no significant changes were observed in functional genes related to gene conjugation and transfer mechanisms. This study would contribute to the underlying of PMS activation by three-dimensional particle electrode, and provide novel insights into the mechanism of ARB inactivation and ARGs degradation under PMS advanced oxidation treatment.

From waste to catalyst: Growth mechanisms of ZSM-5 zeolite from coal fly ash & rice husk ash and its performance as catalyst for tetracycline degradation in fenton-like oxidation

Coal fly ash (CFA), an industrial solid waste, can be utilized to synthesize Zeolite Socony Mobil-5 (ZSM-5) by incorporating an external silica source. In this study, a series of ZSM-5 zeolites were synthesized using rice husk ash (RHA) as the primary silica source and CFA as the primary aluminum source under controlled hydrothermal reaction conditions, and the growth mechanism of ZSM-5 was investigated. The process of ZSM-5 growth was featured by the transformation of hyperpoly silico-aluminate in CFA and RHA into monomers. These monomers formed crystal nuclei connected in a five-membered ring structure under the influence of Tetrapropyl ammonium hydroxide (TPAOH). The surplus monomeric silica-aluminate grew on the nucleus surface due to the addition of the silica source within RHA (RHA-SiO2), ultimately resulting in the development of ZSM-5 zeolite. Characterization results demonstrated that RHA-SiO2 exhibited favorable physical and chemical properties during the ZSM-5 synthesis, with a crystallinity of 99.03%, a specific surface area of 321.19 m2/g, a weight loss of only 3.06% at 800 °C and a total acidity of 0.65 mmol/g. To evaluate the catalytic performance of ZSM-5, Fe/Cu-modified ZSM-5 was developed and used as the catalyst for the degradation of tetracycline (TC) in Fenton-like oxidation. The results indicated that Fe/Cu-ZSM-5 exhibited excellent activity and stability as the catalyst for TC degradation and mineralization. The maximum TC degradation rate reached 99.02% in 10 min and the TOC removal could be up to 69.32% in 2 h. Characterization results indicated that the Fe/Cu ions redox cycle accelerated the generation of active species (1O2 and ˙OH) in Fenton-like systems. The ZSM-5 zeolite synthesized from solid waste demonstrated superb stability and catalytic activity, leading to the effective removal of TC. Since real wastewater generally contains various pollutants, future research efforts should focused on multi-pollutant treatment.

Intramolecular generation of endogenous Cu(III) for selectively self-catalytic degradation of Cu(II)-EDTA from wastewater by UV/peroxymonosulfate

HO•/SO4•--based advanced oxidation processes for the decomplexation of heavy metal-organic complexes usually encounter poor efficiency in real scenarios. Herein, we reported an interesting self-catalyzed degradation of Cu(II)-EDTA with high selectivity in UV/peroxymonosulfate (PMS). Chemical probing experiments and competitive kinetic analysis quantitatively revealed the crucial role of in situ formed Cu(III). The Cu(III) species not only oxidized Cu(II)-EDTA rapidly at ∼3 × 107 M-1 s-1, but also exhibited 2-3 orders of magnitude higher steady-state concentration than HO•/SO4•-, leading to highly efficient and selective degradation of Cu(II)-EDTA even in complex matrices. The ternary Cu(II)-OOSO3- complexes derived from Cu(II)-EDTA decomposition could generate Cu(III) in situ via the Cu(II)-Cu(I)-Cu(III)-Cu(II) cycle involving intramolecular electron transfer. This method was also applicable to various Cu(II) complexes in real electroplating wastewater, demonstrating higher energy efficiency than commonly studied UV-based AOPs. This study provids a proof of concept for efficient decomplexation through activating complexed heavy metals into endogenous reactive species.

Effective degradation of phenol by activating PMS with bimetallic Mo and Ni Co-doped g C3N4 composite catalyst: A Fenton-like degradation process promoted by non-free radical 1O2

The application of bimetal supported graphite phase carbon nitride in activated peroxymonosulfate (PMS) process has become a research hotspot in recent years. In this study, 8-g C3N4/Mo/Ni composite catalyst material was successfully prepared by doping Mo and Ni in graphite phase carbon nitride. The bimetallic active sites were formed in the catalyst, and PMS was activated by the metal valence Mo6+/Mo4+ and Ni2+/Ni(0) through redox double cycle to effectively degrade phenol. When pH was neutral, the degradation rate of 20 mg/L phenol solution with 8-g C3N4/Mo/Ni (0.35 g/L) and PMS (0.6 mM) could reach 95% within 20 min. The degradation rate of 8-g C3N4/Mo/Ni/PMS catalytic system could reach more than 90% within 20min under the condition of pH range of 3-11 and different anions. Meanwhile, the degradation effects of RhB, MB and OFX on different pollutants within 30min were 99%, 100% and 82%, respectively. Electron spin resonance and quenching experiments showed that in 8-g C3N4/Mo/Ni/PMS system, the degradation mechanism was mainly non-free radicals, and the main active species in the degradation process was 1O2. This study provides a new idea for the study of bimetal supported graphite phase carbon nitride activation of PMS and the theoretical study of degradation mechanism.

Epsilon-MnO2 simply prepared by redox precipitation as an efficient catalyst for ciprofloxacin degradation by activating peroxymonosulfate

Four kinds of manganese oxides were successfully prepared by hydrothermal and redox precipitation methods, and the obtained oxides were used for CIP removal from water by activating PMS. The microstructure and surface properties of four oxides were systematically characterized. The results showed that ε-MnO2 prepared by the redox precipitation method had large surface area, low crystallinity, high surface Mn(III)/Mn(Ⅳ) ratio and the highest activation efficiency for PMS, that is, when the concentration of PMS was 0.6 g/L, 0.2 g/L ε-MnO2 could degrade 93% of CIP within 30 min. Multiple active oxygen species, such as sulfate radical, hydroxyl radical and singlet oxygen, were found in CIP degradation, among which sulfate radical was the most important one. The degradation reaction mainly occurred on the surface of the catalyst, and the surface hydroxyl group played an important role in the degradation. The catalyst could be regenerated in situ through the redox reaction between Mn4+ and Mn3+. The ε-MnO2 had the advantages of simple preparation, good stability and excellent performance, which provided the potential for developing new green antibiotic removal technology.

Synergistic enhancement of redox pairs and functional groups for the removal of phenolic organic pollutants by activated PMS using silica-composited biochar: Mechanism and environmental toxicity assessment

In present work, a novel catalyst of cobalt supported on silica-composited biochar (Co@ACFA-BC) derived from fly ash and agricultural waste was synthesized. A series of characterizations confirmed that Co3O4 and Al/Si-O compounds were successfully embedded on the surface of biochar, which triggered superior catalytic activity for PMS activation towards phenol degradation. Particularly, the Co@ACFA-BC/PMS system could completely degrade phenol in the wide pH range, and was almost unaffected by environmental factors including humic acid (HA), H2PO4-, HCO3-, Cl-, and NO3-. Further quenching experiment and EPR analysis proved that both radical (SO4·-, ·OH, O2·-) and non-radical (1O2) pathways were involved in the catalytic reaction system, and the excellent PMS activation was attributed to the electron pair cycling of Co2+/Co3+ and the active sites provided by Si-O-O and Si/Al-O bonds on the catalyst surface. Meanwhile, the carbon shell effectively inhibited the leaching of metal ions, enabling the Co@ACFA-BC catalyst to maintain excellent catalytic activity after four cycles. Finally, biological acute toxicity assay demonstrated that the toxicity of phenol could be significantly reduced after being treated by Co@ACFA-BC/PMS. Overall, this work provides a promising strategy for solid waste valorization and a feasible methodology for green and efficient treatment of refractory organic pollutants in water environment.

Enhanced arsenite removal in aqueous with Fe-Ce-Cu ternary oxide nanoparticle

Arsenite is both more harmful and challenging to get out of water than arsenate. For enhanced As (III) removal, a ternary oxide nanoparticle (FCCTO) mainly composed of iron(Fe), with a small proportion of cerium(Ce) and copper(Cu) was created using a coprecipitation-calcination process. FCCTO was found to be effective in removing As (III) from water, with factors such as adsorbent dose, pH, temperature, and coexisting anions influencing its efficiency. The surface area of FCCTO reached 180.2 m2/g and the doping significantly increased its pore volume and diameter. The adsorption process on FCCTO was endothermic and spontaneous. Ce and Cu in FCCTO were able to efficiently oxidize 81.3% As (III) to As(V). Abundant sites were provided by surface hydroxyl groups for arsenic adsorption. The maximal As(III) adsorption capacity of this adsorbent under the synergistic impact of oxidation and adsorption was 101.5 mg/g. After five cycles, the FCCTO's As(III) adsorption rate dropped to 60% as a result of tetravalent Ce consumption. Surface complexation, redox, and adsorption all had a significant impact on the adsorption process. Overall, FCCTO was an excellent adsorbent with benefits of being facile fabrication, environmentally, recyclable, and having a high As(III) adsorption capacity.

Impact of aqueous environments on hydrogen peroxide activation by manganese oxides: Kinetics and the critical role of bicarbonate

MnO₂ activating H₂O₂ is a promising way in the field of advanced oxidation processes (AOPs) and in situ chemical oxidation (ISCO) to remove contaminants. However, few studies have focused on the influence of various environmental conditions on the performance of MnO₂-H₂O₂ process, which restricts the application in real world. In this study, the effect of essential environmental factors (ionic strength, pH, specific anions and cations, dissolved organic matter (DOM), SiO₂) on the decomposition of H₂O₂ by MnO₂ (ε-MnO₂ and β-MnO₂) were investigated. The results suggested that H₂O₂ degradation was negatively correlated with ionic strength and strongly inhibited under low pH conditions and with phosphate existence. DOM had a slight inhibitory effect while Br^-, Ca²⁺, Mn²⁺ and SiO₂ placed negligible impact on this process. Interestingly, HCO₃^- inhibited the reaction at low concentrations but promoted H₂O₂ decomposition at high concentrations, possibly due to the formation of peroxymonocarbonate. This study may provide a more comprehensive reference for potential application of H₂O₂ activation by MnO₂ in different water systems.

Electro-enhanced activation of peroxymonosulfate by a novel perovskite-Ti4O7 composite anode with ultra-high efficiency and low energy consumption: The generation and dominant role of singlet oxygen

Traditional free radicals-dominated electrochemical advanced oxidation processes (EAOPs) and sulfate radical-based advanced oxidation processes (SR-AOPs) are limited by pH dependence and weak reusability, respectively. To overcome these shortcomings, electro-enhanced activation of peroxymonosulfate (PMS) on a novel perovskite-Ti₄O₇ composite anode (E-PTi-PMS system) was proposed. It achieved an ultra-efficient removal rate (k = 0.467 min^-1) of carbamazepine (CBZ), approximately 36 and 8 times of the E-PTi and PTi-PMS systems. Singlet oxygen (¹O₂) played a dominant role in the E-PTi-PMS system and transformed from SO₄^•-, O₂^•-, ^•OH and oxygen vacancy (V_o^••). The electric field expedited the decomposition and utilization of PMS, promoting the generation of radicals and expanding the formation pathway of ¹O₂. The E-PTi-PMS system presented superiorities over wide pH (3-10) and less dosage of PMS (1 mM), expanding the pH adaptability and reducing the cost of EAOPs. Simultaneously, the excellent reusability (30 cycles) solved the bottleneck of recycling catalysts in SR-AOPs via an ultra-low energy (0.025 kWh/m³-log). This work provides a promising alternative towards high-efficiency and low-cost treatment of polluted waters.

Catalytic Degradation of Ciprofloxacin in Aqueous Solution by Peroxymonosulfate Activated with a Magnetic CuFe2O4@Biochar Composite

A magnetic copper ferrite and biochar composite (CuFe2O4@BC) catalyst was prepared by an improved sol-gel calcination method and initially used for the removal of antibiotics ciprofloxacin (CIP) by activated peroxymonosulfate (PMS). Using CuFe2O4@BC as the activator, 97.8% CIP removal efficiency could be achieved in 30 min. After a continuous degradation cycle, CuFe2O4@BC catalyst still exhibited great stability and repeatability and could also be quickly recovered by an external magnetic field. Meanwhile, the CuFe2O4@BC/PMS system presented good stability for metal ion leaching, which was far less than the leaching of metal ions in the CuFe2O4/PMS system. Moreover, the effects of various influencing factors, such as initial solution pH, activator loading, PMS dosage, reaction temperature, humic acid (HA), and the inorganic anions were explored. The quenching experiments and the electron paramagnetic resonance (EPR) analysis manifested that hydroxyl radical (•OH), sulfate radical (SO4•−), superoxide radical (O2•−), and singlet oxygen (1O2) were generated in the CuFe2O4@BC/PMS system, while 1O2 and O2•− are mainly involved in the degradation process. The synergistic effect between CuFe2O4 and BC enhanced the structural stability and electrical conductivity of the material, which promoted the bonding between the catalyst and PMS, resulting in the enhanced catalytic activity of CuFe2O4@BC. This indicates that CuFe2O4@BC activating PMS is a promising remediation technique for CIP-contaminated water.

Single-Atom MnN5 Catalytic Sites Enable Efficient Peroxymonosulfate Activation by Forming Highly Reactive Mn(IV)-Oxo Species

Four-nitrogen-coordinated transitional metal (MN₄) configurations in single-atom catalysts (SACs) are broadly recognized as the most efficient active sites in peroxymonosulfate (PMS)-based advanced oxidation processes. However, SACs with a coordination number higher than four are rarely explored, which represents a fundamental missed opportunity for coordination chemistry to boost PMS activation and degradation of recalcitrant organic pollutants. We experimentally and theoretically demonstrate here that five-nitrogen-coordinated Mn (MnN₅) sites more effectively activate PMS than MnN₄ sites, by facilitating the cleavage of the O-O bond into high-valent Mn(IV)-oxo species with nearly 100% selectivity. The high activity of MnN₅ was discerned to be due to the formation of higher-spin-state N₅Mn(IV)═O species, which enable efficient two-electron transfer from organics to Mn sites through a lower-energy-barrier pathway. Overall, this work demonstrates the importance of high coordination numbers in SACs for efficient PMS activation and informs the design of next-generation environmental catalysts.

Modified birnessite MnO2 as efficient Fenton-like catalysts through electron transfer process between the simultaneously surface-activated peroxymonosulfate and pollutants

The development of efficient and eco-friendly Mn-based hybrids for the degradation of biorefractory organic pollutants via peroxymonosulfate (PMS) activation is highly desired. In this study, a novel graphite nanosheet (GNs)-based Fe-Mn bimetallic oxide (Fe doped birnessite MnO₂, FeMn/GNs) was synthesized under mild conditions. Compared with monometallic Fe or Mn oxide on GNs, FeMn/GNs exhibited a higher surface area, decreased Mn oxidation states, stronger interaction with GNs, and more active sites for PMS adsorption. Among different Fe/Mn ratios, Fe₂Mn₁/GNs showed the optimum performance for bisphenol A (BPA) degradation with the first-order rate constant of 0.22 min^-1, which was about 8.5 and 12.9 times higher than that of Mn/GNs and Fe/GNs, respectively. Different from the pollutant-catalyst-PMS electron transfer mechanism for Mn/GNs, the direct two-electron transfer in FeMn/GNs+PMS system, was mainly processed between the simultaneously activated BPA and PMS. This was probably based on the double adsorption sites of Fe and Mn species on the same catalyst: PMS was adsorbed by Fe species through hydroxyl groups, while BPA was mainly coordinated with Mn species due to the layered structure and hydrophobicity of the Mn oxide. This study is expected to provide the rational design of efficient Mn-based hybrids for PMS activation.

Peroxymonosulfate activated by composite ceramic membrane for the removal of pharmaceuticals and personal care products (PPCPs) mixture: Insights of catalytic and noncatalytic oxidation

A composite manganese-based catalytic ceramic membrane (Mn-CCM) was developed by a solid-state sintering method, and its effectiveness toward activation of peroxymonosulfate (PMS) for the degradation of 11 pharmaceutical and personal care products (PPCPs) mixture was tested. The optimized Mn-CCMs/PMS system showed remarkable degradation efficiencies for PPCPs mixture with total removal >90% in ultrapure water, river water and natural organic matter (NOM) solution. The Mn-CCMs/PMS system showed the contribution of different phenomena in PPCPs removal in the order of catalytic oxidation (54.7%, Mn-CCMs/PMS) > noncatalytic oxidation (42.3%, PMS oxidation) > adsorption (3.0%, by Mn-CCMs). The singlet oxygen (¹O₂) was the dominant reactive oxygen specie for the degradation of PPCPs in all water matrices proved by the quenching experiments and electro-paramagnetic resonance (EPR) spectroscopy. The extraordinary stability of Mn-CCMs for the activation of PMS has been noted in terms of repeatability experiments for PPCPs degradation with fewer leaching of Mn (1.9 to 3.6 µg/L). Mineralization was achieved in the range of 28-65% for different water matrices. The toxicity of the PPCPs mixture was reduced by 85.9%. The Mn-CCMs/PMS system showed a reduction (25-100%) in precursors of different carbon- and nitrogen-based disinfection by-products. This study found the Mn-CCMs/PMS system as a feasible purification unit for removing trace concentrations of PPCPs (ng/L) in real drinking water matrices.

Magnetic Co/CoOx@NCNT catalysts for activation of potassium peroxymonosulfate to deteriorate phenol from wastewater

Phenols are of much toxicological and they must be effectively removed from the wastewater from industries as well as sewage treatment. Such removal demands a special and strong composite. So, this piece of research aims to activate Potassium peroxymonosulfate (PPMS) with the large surface area of magnetite nitrogen-fixed porous carbon nanotube composites (Co/CoOx@NCNT). Increases in the graphitization degree and structural control brought about by the incorporation of reduced Graphite oxide (rGO) significantly increased the catalyst activity of Co/CoOx@NCNT. It was found that PPMS activation for phenol removal by Co/CoOx@NCNT was nearly as effective as by homogeneous Co²⁺, with nearly 100% removal efficiency in 10 min. Both high reusability and high recycling of Co/CoOx@NCNT were accomplished simultaneously by proving the technology of viability in practical applications. The PPMS activation mechanism in the Co/CoOx@NCNT/PPMS system was driven by the electron transmission from contaminants to PPMS through the sp^2- hybrid carbon nanotubes and nitrogen system. The selectivity of the Co/CoOx@NCNT/PPMS system to remove diverse organic compounds was determined by batch experiments. Due to the insignificant impact of radicals reactive on pollutant breakdown, the ability to inhibit species (such as Cl^- and natural organic materials) from a minor role was significantly decreased. These results not only shed light on the process of PPMS heterogeneous activation but also provided a framework for the balanced project of highly effective nanocarbon-based catalysts for PPMS activation.

Electric field-enhanced coupled with metal-free peroxymonosulfate activactor: The selective oxidation of nonradical species-dominated system

Nowadays metal-free persulfate-based advanced oxidation processes (AOPs) have been intensively investigated, however, the catalysts are often too complex to fully consider their application potential. Conventional AOPs usually suffer from severe interference in real water matrix, thus, selective oxidation is practically and scientifically challenging as it could avoid unnecessary inputs of energy and possible secondary pollutants. In this study, a remarkably synergistic effect was achieved when conventional amorphous boron/peroxymonosulfate (Boron/PMS, 0.67 × 10^-2 min^-1) system was combined with electrolysis (E-Boron/PMS, 1.54 × 10^-2 min^-1) to degrade sulfamethoxazole (SMX). Evidenced by selectively quenching tests with kinetic evaluation, electron paramagnetic resonance (EPR), solvent-exchange experiment and electrochemical analysis, the dominated reactive oxygen species in E-Boron/PMS system tended to be ¹O₂, instead of the ^•OH and SO₄^•-. Mechanistic study unveiled that ¹O₂ was generated via accelerated PMS self-decomposition, triggered by interface alkalization and hydroxyl radicals transfer at the cathode interface. ¹O₂ is considered to be selective to the electron-rich organic compounds, thus E-Boron/PMS system was superior to conventional radical-dominated system (Boron/PMS) for SMX removal in the co-presence of common inorganic anions, showing the great merits of selective oxidation in nonradical system. These findings provided new insights into effective and selective oxidation of SMX via E-Boron/PMS system, which shed new light on the development of nonradical system.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Electrochemically activated peroxymonosulfate with mixed metal oxide electrodes for sulfadiazine degradation: Mechanism, DFT study and toxicity evaluation

Electrochemically activated peroxymonosulfate with mixed metal oxide electrodes (EA-PMS-MMO/MMO) is an emerging advanced oxidation process. It performed well on the degradation of sulfadiazine (SDZ), whose removal rate reached 81.13% within 30 min. Both the MMO anode and cathode played an irreplaceable role in PMS activation. HO^•, SO₄^•-, O₂^•- and ¹O₂ were confirmed to be the major reactive species in the system, among which ¹O₂ was the most abundant. The generation mechanism of the reactive species and the overall mechanism of the system were proposed. Four degradation pathways of SDZ were speculated based on density functional theory. The acute and chronic toxicity of SDZ and its degradation intermediates was evaluated by the quantitative structure-activity relationship method, and the overall toxicity was significantly reduced after the degradation by EA-PMS-MMO/MMO. The results show that EA-PMS-MMO/MMO affords a reliable technology for the degradation of organic contaminants and has promising potential for application.

The enhanced removal of arsenite from water by double-shell CuOx@MnOy hollow spheres (DCMHS): behavior and mechanisms

To facilitate removing As(III) from water through an "oxidation-adsorption" process, the double-shell CuO_x@MnO_y hollow spheres (DCMHS) have been fabricated via a two-step co-precipitation route combined with the soft-template method. The surface characterization results showed that Mn oxides were formed without segregation and uniformly distributed on the surface of CuO_x hollow spheres. DCMHS could achieve outstanding performance to remove As(III) with an As maximum adsorption capacity of 32.15 mg/g. Meanwhile, the kinetics results illustrated that the oxidative activity of DCMHS was strengthened due to its specific structure, and part of As(III) was converted to As(V) during the adsorption process. Also, air aeration could further enhance As(III) oxidation and thus improving As removal. The As(III) removal performance could be maintained under neutral and weak alkaline conditions. Phosphate, silicate, and carbonate anions could depress the removal performance, while chloride ions and sulfate anions barely influenced As removal. Moreover, DCMHS could be regenerated using NaOH and KMnO₄ solutions without breaking the hollow sphere structure. Based on the spectroscopic analysis results, As(III) molecules were converted to As(V) via two pathways, including the oxidation by Mn oxides or superoxide radicals. The Cu-Mn synergistic effect could not only enhance the oxidative activity of Mn oxides but also produce superoxide radicals via the activation of surface-adsorbed oxygen molecules. Afterwards, the newly formed As(V) could be attached to the hydroxyl groups through surface complexation. Therefore, this work has provided insights into the morphology design of Mn-oxide-containing adsorbents and supplemented the interface reaction mechanisms for enhancing As(III) removal.

Enhancement on the degradation of naproxen in Cu0 activated peroxymonosulfate system by complexing reagents

In recent years, there has been growing interest in the mechanism (radical or nonradical) of persulfate activation processes. In this study, the enhancement of naproxen (NPX) degradation in a Cu⁰/peroxymonosulfate (PMS) system by complexing reagents was investigated. Surprisingly, neocuproine (NCP) alters the nature of reactive species in the Cu⁰/PMS system. A high-valent copper species, Cu(III)-NCP, was found to dominate NPX degradation rather than radicals under acid conditions for the first time. Moreover, systematically designed experiments revealed that the Cu(III)-NCP complex was a strong selective oxidant that reacted with organics through a single electron transfer pathway. Meanwhile, the degradation efficiency of NPX was highly dependent on the solution pH and dosage of Cu⁰ and NCP, but was irrelevant to the concentration of NPX. Additionally, the enhancement of NCP on other copper based PMS activation systems (i.e., Cu²⁺/HA/PMS and Cu⁰/HA/PMS systems) was investigated. Considering that the released copper can be removed by a simple precipitation method to meet the effluent standards, the new complex-enhanced Cu⁰/PMS system provided a new method to enhance the degradation efficiencies of pollutants by a copper-catalyzed Fenton-like system.

Rapid purification of As(III) in water using iron-manganese composite oxide coupled with sulfite: Importance of the SO5•- radicals

Manganese (Mn)-containing composite metal adsorbents are very effective at removing arsenite (As(III)) from contaminated water, however, the low removal speed and oxidation efficiency have limited their further application. In this study, a nonhomogeneous catalytic oxidation-adsorption system was constructed by coupling iron-manganese composite oxide (FeMnO_x) with sulfite (S(IV)) to enhance the recovery of oxidative capacity and accelerate the removal of As(III). Experimental results showed that the FeMnO_x/S(IV) system decreased the As(III) concentration from 1079 to <10 µg/L within 10 min and almost completely oxidized As(III) to As(V). In contrast, FeMnO_x alone removed only 82.4% of As(III) within 30 min, and 60.0% of the adsorbed As(III) was not oxidized. Meanwhile, the adsorption capacity of FeMnO_x/S(IV) system for As(III) was considerably higher than that of the only-FeMnO_x system (76.5 > 46.3 mg/g). The efficient and fast As(III) removal was attributed to the SO₅^•- radical generated by S(IV) acting as the driving force for the redox cycle between As(III) and Mn(II/III/IV). Several environmental factors (e.g., solution pH and inorganic anions) and the reusability and practicality of FeMnO_x were systematically investigated, and the results further confirmed the superiority of the FeMnO_x/S(IV) system in As(III) removal. In particular, the proposed FeMnO_x nanocellulose aerogel effectively purified arsenic-contaminated groundwater using a fixed-bed column. Thus, FeMnO_x-S(IV) coupling is very promising for the purification of arsenic-contaminated water bodies.

Manganese oxides activated peroxymonosulfate for ciprofloxacin removal: Effect of oxygen vacancies and chemical states

Ciprofloxacin (CIP) as an anti-inflammatory drug is frequently detected in various water resources. Recently, Sulfate Radical-based advanced oxidation processes with manganese oxides have been recognized as a highly effective method for CIP degradation. Herein, ε-MnO₂ was obtained through a convenient drying process. After different atmospheric treatments, MnO and Mn₂O₃ were fabricated for subsequent degradation experiments. The results show that MnO exhibits better catalytic activity than Mn₂O₃, with high removal efficiency of almost 84.3% for CIP. Quenching test and electron paramagnetic resonance spectra confirm that ¹O₂ is the dominant species during reaction, while ·OH and SO₄^·- play a supporting role. A related discussion about the role of valence states of Mn and oxygen vacancies is presented, which can provide a theoretical basis for further development of Mn/peroxymonosulfate system.

Electro-enhanced sulfamethoxazole degradation efficiency via carbon embedding iron growing on nickel foam cathode activating peroxymonosulfate: Mechanism and degradation pathway

The combination of peroxymonosulfate (PMS) activation by hetero-catalysis and electrolysis (EC) attracted incremental concerns as an efficient antibiotics degradation method. In this work, carbon embedding iron (C@Fe) catalysts growing on nickel foam (NF) composite cathode (C@Fe/NF) was prepared via in-situsolvothermal growth and carbonization method and used to activate PMS toward sulfamethoxazole (SMX) degradation. The EC-[C@Fe/NF(II)]-PMS system exhibited an excellent PMS activation, with 100% SMX removal efficiency achieving within 30 min. Reactive oxygen species (ROS) generation and their roles in SMX degradation were confirmed by quenching experiments and electron paramagnetic resonance. It was found that singlet oxygen (¹O₂) and surface-bound radicals were responsible for SMX degradation, and ¹O₂ contributed the most. Furthermore, the possible SMX degradation pathways were proposed on the base of the detected degradation intermediates and density functional theory (DFT) calculation. Toxicity changes were also assessed by the Ecological Structure Activity Relationships (ESAR). This work provides a practicable strategy for synergistically enhancing PMS activation efficiency and promoting antibiotics removal.

Electro-activation of peroxymonosulfate by a graphene oxide/iron oxide nanoparticle-doped Ti4O7 ceramic membrane: mechanism of singlet oxygen generation in the removal of 1,4-dioxane

Electro-activation of peroxymonosulfate (PMS) has been widely investigated for the degradation of organic pollutants. Herein, we employ graphene oxide (GO)/Fe₃O₄ nanoparticles (NPs) doped into a Ti₄O₇ reactive electrochemical membrane through strong chemical bonding as the cathode to activate PMS for the degradation of 1,4-dioxane (1,4-D). The strong chemical interaction between GO, Fe₃O₄-NPs, and Ti₄O₇ via Fe-O---GO---O-Ti bonds enhances the electron-transfer efficiency and provides catalytically active sites that boost the electro-activation of PMS. As a result, the 1,4-D oxidation rate of the GO/Fe₃O₄-NPs@Ti₄O₇ REM cathode is ~3 times higher (7.21 × 10^-3 min^-1) than those of other Ti₄O₇ ceramic membranes, and ¹O₂ plays a key role (59.9%) in the degradation of 1,4-D. The ¹O₂ generation mechanism in the electro-activation process of PMS was systematically investigated, and we claimed that ¹O₂ is mainly generated from the precursors H₂O₂ and O₂^•-/HO₂^• rather than by O₂ or ^•OH, as has been reported in previous studies. A flow-through mode test in the PMS electro-activation system is firstly reported, and the 1,4-D decay efficiency is 7.1 times higher than that obtained by a flow-by mode, showing that an improved PMS mass transfer efficiency enhances the conversion to reactive oxygen species.

Self-enhanced and efficient removal of As(III) from water using Fe-Cu-Mn composite oxide under visible-light irradiation: Synergistic oxidation and mechanisms

Here, we prepared a novel nanostructured Fe-Cu-Mn composite oxide (FCMO_x) adsorbent using an ultrasonic coprecipitation method. The maximum adsorption capacity of As(III) and As(V) reached 158.5 and 115.2 mg/g under neutral conditions, respectively. The effects of several environmental factors (coexisting ions, solution pH, etc.) on the removal of inorganic arsenic using FCMO_x were studied through batch experiments. The results showed that except for PO₄^3- and high initial pH, it was not significantly affected by ionic strength and other existing anions, implying a higher selectivity and adaptability. Combined with EPR, FTIR, and XPS analysis, we concluded that the Cu component and the reactive oxygen species (ROS) it generates played a decisive role in maintaining the stability of the redox cycle between Mn(IV)/Mn(III)/Mn(II) and enhancing the oxidation efficiency of As(III). Meanwhile, the adsorption mechanism of As(V) was mainly through the replacement of the FCMO_x surface -OH to form stable inner-sphere arsenic complexes, while the removal mechanism of As(III) may involve the process of synergistic oxidation and chemisorption coupling. Additionally, the effective removal of As from the simulated As-contaminated water and its satisfactory reuse performance make FCMO_x adsorbents favorable candidates for the removal of As-contaminated water in the future.

Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting Ni_xCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of Ni_xCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into Ni_xCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), rather than sulfate radicals (SO₄^•-) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni₁₅Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO₄^•-and •OH, and demonstrated that O₂^•- and ¹O₂ concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O₂^•- mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni₁₅Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni₁₅Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.

Phenol removal kinetics from synthetic wastewater by activation of persulfate using a catalyst generated from shipping ports sludge

Disposal sludges from shipping docks contain elements that have the potential to catalyze the desired treatment process. The current work was designed to decompose phenol from wastewater by activation peroxymonosulfate (PMS) using a catalyst made from sea sediments (at 400 °C for 3 h). The catalyst had a crystalline form and contained metal oxides. The parameters of pH (3-9), catalyst dose (0-80 mg/L), phenol concentration (50-250 mg/L), and PMS dose (0-250 mg/L) were tested to specify the favorable phenol removal. The phenol removal of 99% in the waste sludge catalyst/PMS system was achieved at pH 5, catalyst quantity of 30 mg/L, phenol content of 50 mg/L, PMS dose of 150 mg/L, and reaction time of 150 min. From the results, it was implied that the pH factor was more important in removing phenol with the studied system than other factors. By-products and phenol decomposition pathways were also provided. The results showed that the sea sediment catalyst/PMS system is a vital alternative for removing phenol from wastewater medium.

Oxygen vacancy induced peroxymonosulfate activation by Mg-doped Fe2O3 composites for advanced oxidation of organic pollutants

Oxygen vacancy engineering has emerged as an effective approach to improve the performance of catalysts for peroxymonosulfate (PMS) activation. Herein, we report a facile precipitation method followed by calcination to synthesize cost-effective and environmentally friendly magnesium-doped hematite (Mg/Fe₂O₃) composites. Multiple characterization results reveal that the incorporation of Mg can significantly increase the oxygen vacancies and specific surface area of 5%Mg/Fe₂O₃, leading to a significantly enhanced performance in degrading Rhodamine B (RhB) through PMS activation. In a typical reaction, almost complete RhB (10 mg/L) removal can be achieved by the activation of PMS (0.2 g/L) using 5%Mg/Fe₂O₃ (0.5 g/L). Moreover, the as-synthesized catalyst exhibits a broad pH working range (3.96-10.69), high stability, and recyclability. The effects of several parameters (e.g., catalyst amount, PMS dosage, solution pH and temperature, and coexisting inorganic anions) on the removal of RhB in the 5%Mg/Fe₂O₃/PMS system are investigated. A plausible PMS activation mechanism is proposed, and ¹O₂ and O₂^- are identified as the predominant reactive species in RhB degradation instead of SO₄^- and OH. This study provides new insights into the development of highly efficient iron-based catalysts and highlights their potential applications in environmental purification.

Efficient degradation of ciprofloxacin by magnetic γ-Fe2O3-MnO2 with oxygen vacancy in visible-light/peroxymonosulfate system

In this work, the magnetic γ-Fe₂O₃-MnO₂ bifunctional catalyst with oxygen vacancy was synthesized for peroxymonosulfate (PMS) activation under visible light. The activity of γ-Fe₂O₃-MnO₂ was investigated by ciprofloxacin (cipro) degradation. Results showed that 98.3% of cipro (50 μM) was removed within 30 min in visible-light/PMS system mediated by γ-Fe₂O₃-MnO₂ (2:1) with fine-tuned oxygen vacancy. The cipro degradation data fitted well with pseudo-first-order kinetic model with the highest kinetic constant of 0.114 min^-1. Besides, the γ-Fe₂O₃-MnO₂ exhibited stability, recyclability and practicability. High selectivity for cipro degradation was observed with coexisting anions in visible-light/γ-Fe₂O₃-MnO₂/PMS system. Furthermore, the enhanced mechanism of PMS activation under visible light with γ-Fe₂O₃-MnO₂ was proposed. The appropriate oxygen vacancy enhanced the separation of photo-induced carriers and Z scheme heterostructure maintained the highest redox potential. Accordingly, the synergistic effect of photocatalysis and PMS activation enhanced cipro degradation. Free radical and non-radical species including , h⁺, ¹O₂, •OH and co-existed in the coupled system. Impressively, this study provides a handy approach for oxygen vacancy regulation in metallic oxides composite and an easily recycled catalyst with high-activity in coupled oxidation system towards antibiotic degradation.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Synthesis of oxygen vacancy-enriched N/P co-doped CoFe2O4 for high-efficient degradation of organic pollutant: Mechanistic insight into radical and nonradical evolution

Oxygen vacancy-enriched N/P co-doped cobalt ferrite (NPCFO) was synthesized using ionic liquid as N and P sources, and then the catalytic performance and mechanism of NPCFO upon peroxymonosulfate (PMS) activation for the degradation of organic pollutants were investigated. The as-synthesized NPCFO-700 exhibited excellent catalytic performance in activating PMS, and the degradation rate constant of 4-chlorophenol (4-CP) increased with the increase of OV concentration in NPCFO-x. EPR analysis confirmed the existence of ·OH, SO₄^·-, and ¹O₂ in the NPCFO-700/PMS system, in which OV could induce the generation of ¹O₂ by PMS adsorption and successive capture, and also served as electronic transfer medium to accelerate the redox cycle of M²⁺/M³⁺ (M denotes Co or Fe) for the generation of radical to synergistically degrade organic pollutants. In addition, the contribution of free radical and nonradical to 4-CP degradation was observed to be strongly dependent on solution pH, and SO₄^·- was the major ROS in 4-CP degradation under acid and alkaline condition, while ¹O₂ was involved in the degradation of 4-CP under neutral condition due its selective oxidation capacity, as evidenced by the fact that such organic pollutants with ionization potential (IP) below 9.0 eV were more easily attacked by ¹O₂. The present study provided a novel insight into the development of transition metal-based heterogeneous catalyst containing massive OV for high-efficient PMS activation and degradation of organic pollutants.

Insights into catalytic activation of peroxymonosulfate for carbamazepine degradation by MnO2 nanoparticles in-situ anchored titanate nanotubes: Mechanism, ecotoxicity and DFT study

Developing efficient pharmaceuticals and personal care products (PPCPs) degradation technologies is of scientifical and practical importance to restrain their discharge into natural water environment. This study fabricated and applied a composite material of amorphous MnO₂ nanoparticles in-situ anchored titanate nanotubes (AMnTi) to activate peroxymonosulfate (PMS) for efficient degradation and mineralization of carbamazepine (CBZ). The degradation pathway and toxicity evolution of CBZ during elimination were deeply evaluated through produced intermediates identification and theoretical calculations. AMnTi with a composition of (0.3MnO₂)•(Na_1.22H_0.78Ti₃O₇) offered high activation efficiency of PMS, which exhibited 21- and 3-times degradation rate of CBZ compared with the pristine TNTs and MnO₂, respectively. The high catalytic activity can be attributed to its unique structure, leading to a lattice shrinkage and small pores to confine the PMS molecule onto the interface. Therefore, efficient charge transfer and catalytic activation through MnOTi linkage occurred, and a MnTi cycle mediating catalytic PMS activation was found. Both hydroxyl and sulfate radicals played key roles in CBZ degradation. Theoretical calculations, i.e., density functional theory (DFT) and computational toxicity calculations, combined with intermediates identification revealed that CBZ degradation pathway was hydroxyl addition and NC cleavage. CBZ degradation in this system was also a toxicity-attenuation process.

Homogeneous activation of peroxymonosulfate using a low-dosage cross-bridged cyclam manganese(II) complex for organic pollutant degradation via a nonradical pathway

The high dosage of catalyst requirement and weak anti-interference ability limit current heterogeneous manganese (Mn) catalyst/peroxymonosulfate (PMS) systems to remediate the organic polluted wastewater in complicated environment. Inspired by the concept of atom economy, herein, a homogenous manganese complex bearing a cross-bridged cyclam ligand Mn(cbc)Cl₂ (MnL, L = cbc = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)) is capable of activating PMS for reactive brilliant red K-2BP (RBR K-2BP) degradation. The dosage of MnL for PMS activation was low, in a range of 0.38∼3.8 mg/L. The quenching experiments demonstrated that the degradation was a nonradical-controlled process. Using methyl phenyl sulfoxide (PMSO) as a probe, the dominated degradation process of substrate was via an oxygen transfer pathway. Moreover, a high-valent Mn-oxo [(O)Mn^VLCl₂]⁺ was directly detected using electrospray ionization mass spectrometry (ESI/MS). This system showed excellent anti-interference ability to both anions and humic acid, a typical natural organic matter. The atom economy, represented by an index ((mg pollutant)/h/(g catalyst)), showed that MnL 22737 in PMS activation was much higher than those of Mn-based heterogeneous catalytic systems 67∼960 and was only behind that of iron-tetraamidomacrocyclic ligand Fe-TAML 59139. This work provides insights into designing an atom-economic Mn-based PMS activator for efficient treatments for organic pollutants in a complicated environment.

Copper substituted zinc ferrite with abundant oxygen vacancies for enhanced ciprofloxacin degradation via peroxymonosulfate activation

In this paper, copper substituted zinc ferrite (ZCFO) catalyst with rich oxygen vacancies (OVs) was synthesized via a simple one pot sol-gel combustion method, and firstly used for peroxymonosulfate (PMS) activation to degrade a typical antibiotic ciprofloxacin (CIP). Only ∼15 min was required to achieve 96.6% of CIP degradation using ZCFO as the catalyst, and the pseudo-first-order reaction constant was about 95 times higher than that of conventional zinc ferrite (1.90 min^-1 vs 0.02 min^-1). ZCFO catalyst showed great stability and reusability based on the successive degradation cycles and could be easily recovered through magnetic separation. Besides, the effects of catalyst loading, PMS concentration, reaction temperature, initial solution pH, coexisting anions and humic acid (HA) on CIP degradation were systematically investigated. Radical quenching tests and electron paramagnetic resonance (EPR) revealed that sulfate radical (SO₄^-.), hydroxyl radical (OH∙), superoxide radical (O₂^∙-) and singlet oxygen (¹O₂) were involved in the ZCFO/PMS system, among which O₂^∙- and ¹O₂ were the dominant reactive oxygen species (ROS). The excellent catalytic activity of ZCFO was ascribed to the dual active sites of Fe and Cu and large amount of OVs after Cu substitution, which was beneficial to generate ROS for CIP removal.

Trace Cupric Species Triggered Decomposition of Peroxymonosulfate and Degradation of Organic Pollutants: Cu(III) Being the Primary and Selective Intermediate Oxidant

Activation of persulfates to degrade refractory organic pollutants is currently a hot topic of advanced oxidation. Developing simple and effective activation approaches is crucial for the practical application of persulfates. We report in this research that trace cupric species (Cu(II) in several μM) can efficiently trigger peroxymonosulfate (PMS) oxidation of various organic pollutants under slightly alkaline conditions. The intermediate oxidant dominating this process was investigated with electron paramagnetic resonance (EPR), chemical probing, and in situ Raman spectroscopy. Unlike conventional PMS activation, which generates sulfate radical, hydroxyl radical, or singlet oxygen as major oxidants, Cu(III) was confirmed to be the primary and selective intermediate oxidant during the Cu(II)/PMS oxidation. Hydroxyl radical is the secondary intermediate oxidant formed from the reaction of Cu(III) with OH^-. Hybrid oxidation by the two oxidants imparts Cu(II)/PMS with high efficiency in the degradation of a series of pollutants. The results of this work suggest that, with no need of introducing complex catalysts, trace Cu(II) inherent in or artificially introduced to some water or wastewater can effectively trigger PMS oxidation of organic pollutants.

Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks

Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.

Novel α-Fe2O3/MXene nanocomposite as heterogeneous activator of peroxymonosulfate for the degradation of salicylic acid

The development of non-cobalt-based heterogeneous catalysts with efficient catalytic activity, good stability and nontoxicity is very important for the application of peroxymonosulfate-based advanced oxidation processes (AOPs) in water treatment. In this work, with two dimensional MXene as the catalyst substrate, a novel α-Fe₂O₃/MXene (FM) nanocomposite was fabricated through a facile solvothermal method. Systematic characterization demonstrated that the MXene substrate could facilitate the size reduction and good dispersion of α-Fe₂O₃ nanoparticles. The FM nanocomposite achieved high efficiency and stability towards activating peroxymonosulfate (PMS) to produce free radicals for the degradation of salicylic acid (SA) in aqueous solution. The operating parameters, including catalyst dosage, PMS dosage, SA concentration and initial pH value, were evaluated and analysed. The co-existence of sulfate radicals (SO₄^-) and hydroxyl radicals (OH) was confirmed using electron paramagnetic resonance spectroscopy and radical scavenger tests, while SO₄^-was identified as the main reactive species in the FM/PMS catalytic system. The possible mechanisms for the electron transfer and radical generation during the process of PMS activation by the FM nanocomposite are further investigated using XPS and in situ Raman analysis. The results provide an avenue for rationally constructing and developing alternative catalysts for the treatment of organics in wastewater.

Facile template synthesis of dumbbell-like Mn2O3 with oxygen vacancies for efficient degradation of organic pollutants by activating peroxymonosulfate

A novel dumbbell-like Mn₂O₃ microstructure prepared under mild conditions was used as a catalyst to PMS activation for RhB degradation. In the Mn₂O₃/PMS system, the reactive oxygen species were revealed in the degradation process by PMS activation.

Mn-based catalysts for sulfate radical-based advanced oxidation processes: A review

Sulfate radical-based advanced oxidation processes (AOPs) have drawn increasing attention during the past two decades, and Mn-based materials have been proven to be effective catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS) to degrade many contaminants. This article presents a comprehensive review of various Mn-based materials to activate PMS and PDS. The activation mechanisms of different Mn-based catalysts (i.e., Mn oxides MnO_x, MnO_x hybrids, and MnO_x‑carbonaceous material composites) were first summarized and discussed in detail. Besides the commonly reported free radicals (SO₄^-• and ^•OH), non-radical mechanisms such as singlet oxygen and direct electron transfer have also been discovered for selected materials. The effects of pH, inorganic ions, natural organic matter (NOM), dissolved oxygen content, temperature, and the crystallinity of the materials on the catalytic reactivity were also discussed. Then, important instrumentations and technologies employed to characterize Mn-based materials and to understand the reaction mechanisms were concisely summarized. Three common overlooks in the experimental designs for examining the PMS/PDS-MnO_x systems were also discussed. Finally, future research directions were suggested to further improve the technology and to provide a guidance to develop cost-effective Mn-based materials to activate PMS/PDS.