Peroxymonosulfate Oxidizes Amino Acids in Water without Activation

In situ activation of peroxymonosulfate with bioelectricity for sulfamethoxazole sustainable removal

Conventional electrochemical activation of peroxymonosulfate (PMS) is not very cost-effective and practical by the excessive input of energy. The electricity generated by photosynthetic microalgae fuel cells (MFCs) is utilized to activate PMS, which would achieve the combination of green bioelectricity and advanced oxidation processes for sustainable pollutants degradation. In this study, a novel dual-chamber of MFCs was constructed by using microalgae as anode electron donor and PMS as cathode electron acceptor, which was operating under both close-circuit and open-circuit conditions. Under close-circuit condition, 1-12 mM PMS in cathode was successfully in situ activated, where 32.00%-99.83% of SMX was removed within 24 h, which was about 1.21-1.78 times of that in the open-circuit of MFCs. Meanwhile, a significant increase in bioelectricity generation in MFCs was observed after the accumulation of microalgae biomass (4.65-5.37 mg/L), which was attributed to the efficient electron separation and transfer. Furthermore, the electrochemical analysis demonstrated that SMX or its products were functioned as electronic shuttles, facilitating the electrochemical reaction and altering the electrical capacitance. The quenching experiments and voltage output results reflected that complex active radical (SO4⋅-, ⋅OH, and 1O2) were involved in SMX removal. Seven degradation products of SMX were detected and S-N bond cleavage was the main degradation pathway. Predicted toxicity values calculated by ECOSAR program showed that all the products were less toxic or nontoxic. Finally, the density functional theory (DFT) calculations revealed that the O and N atoms on SMX were more susceptible to electrophilic reactions, which were more vulnerable to be attacked by reactive species. This study provided new insights into the activation of PMS by bioelectricity for SMX degradation, proposing the mechanisms for PMS activation and degradation sites of SMX.

Were Persulfate-Based Advanced Oxidation Processes Really Understood? Basic Concepts, Cognitive Biases, and Experimental Details

Persulfate (PS)-based advanced oxidation processes (AOPs) for pollutant removal have attracted extensive interest, but some controversies about the identification of reactive species were usually observed. This critical review aims to comprehensively introduce basic concepts and rectify cognitive biases and appeals to pay more attention to experimental details in PS-AOPs, so as to accurately explore reaction mechanisms. The review scientifically summarizes the character, generation, and identification of different reactive species. It then highlights the complexities about the analysis of electron paramagnetic resonance, the uncertainties about the use of probes and scavengers, and the necessities about the determination of scavenger concentration. The importance of the choice of buffer solution, operating mode, terminator, and filter membrane is also emphasized. Finally, we discuss current challenges and future perspectives to alleviate the misinterpretations toward reactive species and reaction mechanisms in PS-AOPs.

Reactivity of unactivated peroxymonosulfate and peroxyacetic acid with thioether micropollutants: Mechanisms and rate prediction

Thioether compounds, prevalent in pharmaceuticals, are of growing environmental concern due to their prevalence and potential toxicity. Peroxy chemicals, including peroxymonosulfate (PMS) and peroxyacetic acid (PAA), hold promise for selectively attacking specific thioether moieties. Still, it has been unclear how chemical structures affect the interactions between thioethers and peroxy chemicals. This study addresses this knowledge gap by quantitatively assessing the relationship between the structure of thioethers and intrinsic reaction rates. First, the results highlighted the adverse impact of electron-withdrawing groups on reactivity. Theoretical calculations were employed to locate reactive sites and investigate structural characteristics, indicating a close relationship between thioether charge and reaction rate. Additionally, we established a SMILES-based model for rapidly predicting PMS reactivity with thioether compounds. With this model, we identified 147 thioether chemicals within the high production volume (HPV) and Food and Drug Administration (FDA) approved drug lists that PMS could effectively eliminate with the toxicity (-lg LC50) decreasing. These findings underscore the environmental significance of thioether compounds and the potential for their selective removal by peroxides.

Singlet oxygen-mediated fluconazole degradation during the activation of chlorine dioxide with sulfite

Singlet oxygen (1O2)-mediated advanced oxidations have received considerable attention due to their strong capacity to resist the water matrix and high selectivity for organic pollutants. In this study, the activation of chlorine dioxide with sulfite (sulfite/ClO2 process) to effectively produce 1O2 was proposed to degrade fluconazole (FLC) and simultaneously control the formation of disinfection byproducts (DBPs). The results revealed that FLC could be rapidly degraded by 78.6 % within 10 s by the sulfite/ClO2 process. Radical quenching tests and electron paramagnetic resonance (EPR) measurements confirm that 1O2 produced by the cleavage of epoxides formed by the combination of triazole electron-rich groups in FLC with peroxymonosulfate (PMS) was the main active species in the sulfite/ClO2 process. The degradation of FLC was favored under alkaline conditions because of the fast electron transfer rate at higher pH values. The presence of chloride (Cl-), bicarbonate (HCO3-), and humic acid (HA) hindered the degradation of FLC mainly because they compete with PMS for the electron-rich groups produced by the reaction. The degradation intermediates of FLC were identified by UPLC‒MS/MS, and their transformation pathways were deduced by the condensed Fukui function (CFF) theory. Using sulfite/ClO2 as a pretreatment process to treat real potable water, aldehydes, ketones, carboxylic acids and other intermediates may be produced via the carboxylation and carbonylation reactions mediated by 1O2, therefore promoting the formation of DBPs during the following chlorination. This study provided a new perspective that while 1O2 is effectively produced in the sulfite/ClO2 process for contaminant degradation, the formation of DBPs during subsequent chlorination should be cautioned.

A Co-based nitrogen-doped lignin carbon catalyst with high stability and wide operating window for rapid degradation of antibiotics

Co-based catalysts play a crucial role in the activation of peroxymonosulfate (PMS) for degradation contaminants. However, the practical application of such catalysts is hindered by challenges like the self-aggregation of Co nanoparticles and leaching of Co2+. In this study, the Co-based catalyst Co-N/C@CL was synthesized from carboxymethylated lignin obtained by grafting abundant carboxymethyl groups into alkali lignin, in which the presence of these carboxymethyl groups enhanced its water solubility and allowed the formation of stable macromolecular complexes with Co2+. This catalyst exhibited a high specific surface area (521.8 m2·g-1) and a uniform distribution of Co nanoparticles. Consequently, the Co-N/C@CL/PMS system could completely remove 20 ppm tetracycline (TC) in 2 min at a rate of 2.404 min-1. Experimental results and DFT calculations revealed that the synergistic effect of lignin carbon and Co NPs accelerated the cleavage and electron transfer of OO bonds, thus promoting the formation of 1O2, OH and SO4-, with 1O2 emerging as the predominant contributor. Moreover, Co-N/C@CL displayed excellent cycling stability and low Co2+ leaching. This work not only provides a feasible strategy for the preparation of highly active and stable Co-based carbon materials but also offers a promising catalyst for the efficient degradation of TC.

Degradation of methotrexate by unactivated and solar-activated peroxymonosulfate in water: Moiety-specific reaction kinetics and transformation product-associated risks

Anticancer drugs have raised worldwide concern owing to their ubiquitous occurrence and ecological risks, necessitating the development of efficient removal strategies in water and wastewater treatment. Although peroxymonosulfate (PMS) is known to be a promising chemical in water decontamination, limited information is available regarding the removal efficiency of anticancer drugs by PMS and solar/PMS systems. This study first reports the moiety-specific reaction kinetics and mechanisms of methotrexate (MTX), an anticancer drug with widespread attention, by PMS (unactivated) and solar-activated PMS in water. It was found that MTX abatement by the direct PMS oxidation followed second-order kinetics, and the pH-dependent rate constants increased from 0.4 M-1 s-1 (pH 5.0) to 1.3 M-1 s-1 (pH 8.0), with a slight decrease to 1.1 M-1 s-1 at pH 9.0. The presence of chloride and bromide exerted no obvious influence on the removal of MTX by PMS. Furthermore, the chemical reactivity of MTX and its seven substructures with different reactive species was evaluated, and the degradation contributions of the reactive species involved were quantitatively analyzed in the solar/PMS system. The product analysis suggested similar reaction pathways of MTX by PMS and solar/PMS systems. The persistence, bioaccumulation, and toxicity of the transformation products were investigated, indicating treatment-driven risks. Notably, MTX can be removed efficiently from both municipal and hospital wastewater effluents by the solar/PMS system, suggesting its great potential in wastewater treatment applications. Overall, this study systematically evaluated the elimination of MTX by the unactivated PMS and solar/PMS treatment processes in water. The obtained findings may have implications for the mechanistic understanding and development of PMS-based processes for the degradation of such micropollutants in wastewater.

Quantitative probing of reactive oxygen species and their selective degradation on contaminants in peroxymonosulfate-based process enhanced by picolinic acid

The processes of Fe(III) activated peroxymonosulfate (PMS) in degrading contaminants have been extensively studied. Herein, a biodegradable chelating agent, picolinic acid (PICA), was introduced to the PMS/Fe(III) process to improve the reaction efficiency. The emphases of this study were placed on the quantification of steady-state concentrations of reactive oxygen species (ROS). Experiments presented that five types of ROS, including Fe(IV), SO4•-, HO•, 1O2 and O2•- coexisted in this system. Four typical probe compounds were used to quantify the steady-state concentration of ROS under different variables. The steady-state concentration of Fe(IV) ([Fe(IV)]ss) was 3-5 orders of magnitude higher than that of other ROS, followed by 1O2 and SO4•-, whereas HO• had the lowest concentration. The reaction between PMS and PICA was first explored in our study and results showed that 1O2 and O2•- would form in this reaction. Owing to the hybrid oxidation by multiple ROS, this system showed high oxidation capacity, and could effectively degrade a variety of pollutants. The contributions of ROS to the alleviation of pollutants varied depending on their concentrations and specific reactivity of substrates. Generally, organic contaminants with phenol structures were prone to react with Fe(IV). Overall, this study compared the steady-state concentrations of different ROS and revealed the intrinsic ROS formation mechanisms.

Reactions of neonicotinoids with peroxydisulfate: The generation of neonicotinoid anion radicals and activation pathway to form sulfate radicals

To activate persulfate to generate reactive species such as sulfate radical (SO₄^•-) for micropollutants abatement, external energy or chemicals are often needed. In this study, a novel SO₄^•- formation pathway was reported during the oxidation of neonicotinoids by peroxydisulfate (S₂O₈^2-, PDS) without any other chemical additions. Thiamethoxam (TMX) was used as a representative neonicotinoid and SO₄^•- was the dominant specie contributing to its degradation during PDS oxidation at neutral pH. TMX anion radical (TMX^•-) was found to activate PDS to generate SO₄^•- with the second-order reaction rate constant determined to be (1.44 ± 0.47)× 10⁶ M^-1s^-1 at pH 7.0 by using laser flash photolysis. TMX^•- was generated from the TMX reactions with superoxide radical (O₂^•-), which was formed from the hydrolysis of PDS. This indirect PDS activation pathway via anion radicals was also applicable to other neonicotinoids. The formation rates of SO₄^•- were found to negatively linearly correlated with E_gap (LUMO-HOMO). The DFT calculations indicated the energy barrier of anion radicals to activate PDS was greatly reduced compared to the parent neonicotinoids. The pathway of anion radicals' activation of PDS to form SO₄^•- improved the understanding of PDS oxidation chemistry and provided some guidance to enhance oxidation efficiency in field applications.

Application of KHSO5 for remediation of soils polluted by organochlorides: A comprehensive study on the treatment's efficacy, environmental implications, and phytotoxicity

Soil pollution caused by complex organochloride mixtures has been increasing in many parts of the world in recent years; as a result, countless numbers of people are exposed to dangerous pollutions; hence, the treatment of organochlorides-polluted soils is gaining considerable attention. In this study, the potential of unactivated peroxymonosulfate (KHSO₅) in remediating soil co-contaminated with trichlorophenol, para-dichlorobenzene, and para-chloro-meta-cresol was investigated. In addition, the treatment's collateral effect on critical soil properties was explored. The result revealed that treating 10 g of soil with 20 mL of 5 mM KHSO₅ for 60 min could oxidize 70.49% of the total pollutants. The pH of the soil was decreased following the treatment. The significant decrease, (p < 0.05), in the soil organic matter following the remediation has affected cation exchange capacity, and available nitrogen. It was also observed that the treatment reduced the β-glucosidase, urease, invertase, and cellulase activities significantly, (p < 0.05). The treatment, on the other hand, brought negligible effects on available phosphorus, available potassium, and particle size distribution. The phytotoxicity tests, which included seed germination and root elongation and soil respiration tests revealed that the treatment did not leach toxins into the treated soil. The treatment method was found to be relatively ecofriendly and cost effective.

Efficient degradation of clothianidin and thiamethoxam in contaminated soil by peroxymonosulfate process

The widespread use of neonicotinoids has led to their frequent detection in the environment and potential environmental risk in recent years. Clothianidin (CLO) and thiamethoxam (TMX), as the second generation of neonicotinoid insecticides, are usually used as seed agents with a high risk of residue in the soil. Efficient degradation of CLO and TMX in soil using peroxymonosulfate (PMS) process was investigated in the present study. The degradation efficiencies of CLO and TMX reached 91.4% and 98.6% in 60 min with the addition of 20 mM PMS at pH 5.5 and 25℃. High degradation efficiencies of CLO were achieved with a high PMS dosage and temperature or a low CLO concentration and initial pH. The degradation of CLO was reduced in the presence of high concentration of inorganic anions (Cl^-, HCO₃^-). Soil organic matter might be one critical factor in the degradation of CLO and TMX. Radical scavenger experiments confirmed SO₄^•- and ¹O₂ were the dominant reactive species on the CLO and TMX degradation. Based on the detected degradation intermediates, the degradation pathways of CLO and TMX include dichlorination, hydroxylation, cleavage of C-N or C-C bond and further oxidation in the PMS-based soil. Overall, the PMS process is one effective and economical method for the remediation of the neonicotinoid contaminated soil.

Degradation of 1,2,3-trichloropropane by unactivated persulfate and the implications for groundwater remediation

Persulfate (PS) is widely used as an in situ chemical oxidation (ISCO) technology for groundwater and soil remediation. While conventional theory generally assumes that PS needs to be "activated" to produce reactive radicals for pollutant degradation, herein, PS without explicit activation system was discovered for the degradation of 1,2,3-TCP with the generation of reactive oxidation species (ROS). Comparison of five common ISCO oxidants (PS, peroxymonosulfate, hydrogen peroxide, potassium permanganate, and sodium percarbonate) indicated that only unactivated PS was able to degrade 1,2,3-TCP in both pure water and 12 natural water samples. 50 μM 1,2,3-TCP degradation can be continued as long as there is enough PS (50 mM). The degradation rate of 1,2,3-TCP increased 450 % when the PS concentration increased from 10 mM to 50 mM and 500 % when the temperature increased from 25 °C to 45 °C. Electron paramagnetic resonance (EPR) analyzes, hydroxyl radicals (·OH) probe reaction and radical quenching experiments confirmed the involvement of both sulfate radicals (SO₄·-) and ·OH that were responsible for 1,2,3-TCP degradation and ·OH played a more important role. HCO₃^-, Cl^- and NOM are three groundwater matrix species that are most likely to inhibit PS oxidation of 1,2,3-TCP. Compared to activated PS, unactivated PS is more promising and more practical for groundwater remediation, since it has several advantages: (1) longer lifetime and better long-term availability; (2) ability of enduring contaminant degradation; (3) applicable for low-permeability zones remediation and potential to alleviate contaminant rebound or tailing problems; (4) environmental friendly; and (5) lower cost. Overall, results of this study show that unactivated PS is a promising in situ remediation technology that may be a good candidate for the most challenging low permeable zone remediation.

Fe-Fe Double-Atom Catalysts for Murine Coronavirus Disinfection: Nonradical Activation of Peroxides and Mechanisms of Virus Inactivation

Peroxides find broad applications for disinfecting environmental pathogens particularly in the COVID-19 pandemic; however, the extensive use of chemical disinfectants can threaten human health and ecosystems. To achieve robust and sustainable disinfection with minimal adverse impacts, we developed Fe single-atom and Fe-Fe double-atom catalysts for activating peroxymonosulfate (PMS). The Fe-Fe double-atom catalyst supported on sulfur-doped graphitic carbon nitride outperformed other catalysts for oxidation, and it activated PMS likely through a nonradical route of catalyst-mediated electron transfer. This Fe-Fe double-atom catalyst enhanced PMS disinfection kinetics for inactivating murine coronaviruses (i.e., murine hepatitis virus strain A59 (MHV-A59)) by 2.17-4.60 times when compared to PMS treatment alone in diverse environmental media including simulated saliva and freshwater. The molecular-level mechanism of MHV-A59 inactivation was also elucidated. Fe-Fe double-atom catalysis promoted the damage of not only viral proteins and genomes but also internalization, a key step of virus lifecycle in host cells, for enhancing the potency of PMS disinfection. For the first time, our study advances double-atom catalysis for environmental pathogen control and provides fundamental insights of murine coronavirus disinfection. Our work paves a new avenue of leveraging advanced materials for improving disinfection, sanitation, and hygiene practices and protecting public health.

Exploring Br-'s roles on non-brominated NDMA formation during ozonation: Reactive oxygen species contribution and brominated intermediate path validation

Bromide ions (Br^-) affected non-brominated nitroso-dimethylamine (NDMA) formation during ozonation, but the mechanism is still unclear. 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene) di-semicarbazide (TMDS) was chosen to further probe this problem. The results indicated that low levels of Br^- (≤20 μM) enhanced NDMA from 3.27 to 7.56 μg/L, while its amount slightly dropped to 6.22 μg/L raising Br^- to 100 μM. It was experimentally verified that intermediates 1,1-dimethylsemicarbazide (DMSC) and 1,1-dimethylhydrazine (UDMH) played important roles on promoting NDMA generation, whose contribution rates were 40.2% and 32.2%, respectively. The brominated substances with higher NDMA molar yields were detected. ∙OH reduced NDMA formation without Br^-, while it played promotion role with Br^-; the corresponding contribution rates were - 26.9% and 29.2%, respectively. No matter with or without Br^-, both ∙O₂^- and ^lO₂ brought a boost to NDMA formation, their contribution ratios were 34.9% and 58.1% without Br^-, while raised significantly to 64.6% and 81.5% when Br^- existed. Br^- not only facilitated NDMA formation, but also benefited the degradation of TMDS. Based on the calculation results and intermediates detected, the influence mechanisms of Br^- were proposed. The results would provide theoretical basis and technical guarantee for treating NDMA precursors and bromide co-existing water in the future.

N-nitrosodimethylamine formation during oxidation of N,N-dimethylhydrazine compounds by peroxymonosulfate: Kinetics, reactive species, mechanism and influencing factors

This study found that peroxymonosulfate (PMS) oxidation without activation has the potential to generate a suspected human carcinogen, N-nitrosodimethylamine (NDMA), in water containing N,N-dimethylhydrazine compounds. Considerable amounts of NDMA formed from three compounds by PMS oxidation were observed. 1,1,1',1'-Tetramethyl-4,4'-(methylene-di-p-phenylene) disemicarbazide (TMDS), which is an industrial antiyellowing agent and light stabilizer, was used as a representative to elucidate the kinetics, transformation products, mechanism and NDMA formation pathways of PMS oxidation. TMDS degradation and NDMA formation involved direct PMS oxidation and singlet oxygen (¹O₂) oxidation. The oxidation by PMS/¹O₂ was pH-dependent, which was related to the pH-dependent characteristics of the reactive oxygen species and intermediates. The degradation mechanism of TMDS mainly included the side chain cleavage, dealkylation, and O-addition. NDMA was generated from TMDS mainly via O-addition and 1,1-dimethylhydrazine (UDMH) generation. The cleavage of amide nitrogen in O-addition products and primary amine nitrogen in UDMH are likely the key steps in NDMA generation. The results emphasized that the formation of harmful by-products should be taken into account when assessing the feasibility of PMS oxidation.

Mn2O3 as an Electron Shuttle between Peroxymonosulfate and Organic Pollutants: The Dominant Role of Surface Reactive Mn(IV) Species

The environmentally benign Mn oxides play a crucial role in the transformation of organic contaminants, either through catalytically decomposing oxidants, e.g., peroxymonosulfate (PMS), or through directly oxidizing the target pollutants. Because of their dual roles and the complex surface chemical reactions, the mechanism involved in Mn oxide-catalyzed PMS activation processes remains obscure. Here, we clearly elucidate the mechanism involved in the Mn₂O₃ catalyzed PMS activation process by means of separating the PMS activation and the pollutant oxidation process. Mn₂O₃ acts as a shuttle that mediates the electron transfer from organic substrates to PMS, accompanied by the redox cycle of surface Mn(IV)/Mn(III). Multiple experimental results indicate that PMS is bound to the surface of Mn₂O₃ to form an inner-sphere complex, which then decomposes to form long-lived surface reactive Mn(IV) species, without the generation of sulfate radicals (SO₄^•-) and hydroxyl radicals (HO^•). The surface reactive Mn(IV) species are proposed to be responsible for the degradation of organic contaminants (e.g., phenol) and the formation of singlet oxygen (¹O₂), followed by the regeneration of the surface Mn(III) sites on Mn₂O₃. This study advances the fundamental understanding of the underlying mechanism involved in transition metal oxide-catalyzed PMS activation processes.

Surface oxygen vacancies formation on Zn2SnO4 for bisphenol-A degradation under visible light: The tuning effect by peroxymonosulfate

Visible light catalysis has been widely coupled with persulfate activation for refractory pollutants removal, while the exact role of persulfate played in such composite system is still questionable. In this work, the relation between peroxymonosulfate (PMS) induced structure change and visible light responsive activity of inverse spinel: i.e., Zn₂SnO₄, was deciphered. Under the visible light illumination (λ> 420nm) PMS addition would endow the composite system with pollutant removal performance. Batch test revealed that 60% of bisphenol-A (5 mg L^-1) was mineralized within 3 h reaction time, by dosing 0.81 mM PMS and 0.1 g L^-1 catalyst. The above oxidative system was also effective for other refractory pollutants elimination. Further analysis indicated that PMS could reduce the band gap of spinel from 2.75 to 2.52 eV and thereby enabling its visible light activity. Photogenerated h⁺ induced •OH and e^- mediated •O₂^- contributed to the pollutant removal while h⁺ played a leading role. Density functional theory revealed that PMS would capture oxygen atom of spinel and induce surface oxygen vacancy defect structure formation. Also, three-oxygen atom coordinated Zn was identified as the possible catalyze site. This work is valuable for deep understanding the exact role of persulfate in photocatalytic system.

Cu(II) assisted peroxymonosulfate oxidation of sulfonamide antibiotics: The involvement of Cu(III)

Cu(II) is generally considered to be a poor activator for PMS decomposition, thus the potential impact of trace Cu(II) on PMS induced oxidation of typical pollutants is always overlooked. In this study, we reported that trace Cu(II) could significantly promote PMS induced degradation of four selected sulfonamide antibiotics (SAs), namely, sulfamehoxazole (SMX), sulfathiazole (STZ), sulfamerazine (SMZ), and sulfamonomethoxine (SMM). Different from conventional PMS-induced oxidation process, high-valent Cu(III) was ascertained as the primary reactive intermediate for SAs degradation, which was confirmed by raman tests and electron paramagnetic resonance (EPR). High concentrations of Cu(II) or PMS were beneficial to degradation of the selected contaminants. In PMS/Cu(II) oxidation system, all the selected SAs could undergo several different degradation pathways including continuous oxidation of aniline group, hydroxylation and S-N bond cleavage. In particular, for six-membered SAs, such as SMZ and SMM, a SO₂ extrusion pathway was also detected. The potential mechanism for Cu(III) formation was also proposed, which was believed to be highly related to the nature of the SAs. Hydroxylamine-SAs (N⁴-OH-SAs), generated from direct PMS oxidation of SAs, was deduced as the "promoter" for the whole oxidation process. And the generation of Cu(III) was likely to proceed through the interaction between PMS and Cu(I), which possibly derived from the reduction of Cu(II) by N⁴-OH-SAs. The results obtained in this study validated the contribution of Cu(III) to the elimination of pollutants and expanded our understanding of the oxidation process of PMS in the presence of trace amounts of Cu(II).

Mechanism of unactivated peroxymonosulfate-induced degradation of methyl parathion: Kinetics and transformation pathway

Although various activated peroxymonosulfate (PMS) processes have been applied widely for the destruction of recalcitrant organics due to its high generation potential of various electrophiles reactive oxygen species (e.g., sulfate and hydroxyl radicals and singlet oxygen), non-radical-based PMS reactions with pollutants are poorly understood. Especially, relatively little information exists on the reactivity of PMS towards organic ester compounds such an organophosphorus pesticides (OPPs). Herein, we systematically studied the unactivated PMS-induced transformation of methyl parathion, a stubborn and toxic OPP. Specifically, direct reaction rather than electrophile radical-based oxidation was responsible for the rapid degradation of methyl parathion. The contribution of the produced singlet oxygen (¹O₂) from the self-decomposition of PMS to methyl parathion degradation can be neglected. The degradation rate constant (k_obs) was strongly dependent on PMS loading and solution pH. The implication of the PMS reaction with methyl parathion for environment treatment was further evaluated by investigating the effects of common water matrices such as sediment humic acids, Cl^-, and natural water. The identified metabolic products revealed that exposure to PMS resulted in hydrolysis and oxidation to methyl parathion. Further study demonstrated that PMS was also capable of effectively oxidizing other typical OPPs without explicit activation. This study provides novel insights into the reaction of methyl parathion with PMS, which indicate feasibility for the decontamination of OPP-contaminated environments.

Peracids - New oxidants in advanced oxidation processes: The use of peracetic acid, peroxymonosulfate, and persulfate salts in the removal of organic micropollutants of emerging concern - A review

In recent years, there has been increasing interest in using of advanced oxidation processes in water and wastewater decontamination. As a new oxidants peracids, mainly peracetic acid (PAA) and peracid salts, i.e. peroxymonosulfate (PMS) and persulfate (PS) are used. The degradation process of organic compounds takes place with the participation of radicals, including hydroxyl (^•OH) and sulfate (SO₄^•-) radicals derived from the peracids activation processes. Peracids can be activated in homogeneous systems (UV radiation, d-electron metal ions, e.g. Fe²⁺, Co²⁺, Mn²⁺, base, ozonolysis, thermolysis, radiolysis), or using heterogeneous activation (metals with zero oxidation state, metal oxides, quinones, activated carbon, semiconductors). As a result of oxidation, products of a lower mass than the parent compounds, less toxic, and more susceptible to biodegradation are formed. An important task is to investigate the effect of the peracid activation method and matrix composition on the efficiency of contamination removal. The article presents the latest information about the application of peracids in the removal of organic micropollutants of emerging concern (mainly focuses on endocrine disrupted compounds). The most important information on peracetic acid, peroxymonosulfate and persulfate salts, and methods of their activation are presented. Current uses of these oxidants in organic micropollutants removal are also described. Information was collected on the factors influencing the oxidation process and the effectiveness of pollutant removal. This paper compares PAA, PMS and PS-based processes for the first time in terms of kinetics and efficiency.

Accelerated oxidation of the emerging brominated flame retardant tetrabromobisphenol S by unactivated peroxymonosulfate: The role of bromine catalysis and formation of disinfection byproducts

Tetrabromobisphenol S (TBBPS) is an emerging brominated flame retardant (BFR) that can cause endocrinological abnormalities in aquatic species and is neurotoxic and cytotoxic to humans. Herein, we investigated the oxidation of TBBPS by unactivated peroxymonosulfate (PMS) in aqueous solution. Results show that PMS was capable of oxidizing TBBPS without activation, and the transformation of TBBPS was pH-dependent. Interestingly, the unactivated PMS oxidation of TBBPS exhibited an autocatalytic behavior. Radical quenching experiments and electron paramagnetic resonance (EPR) analyzes ruled out the involvement of hydroxyl radical (HO•) and sulfate radical (SO₄^•‑) as reactive species. While the generation of singlet oxygen (¹O₂₎ was confirmed in PMS solution, it was also not responsible for TBBPS oxidation. The bromine substituents are believed to be responsible for the autocatalysis observed during PMS oxidation. We propose that the initial oxidation of TBBPS by PMS resulted in the release of bromide ions (Br^-) via debromination, which could be rapidly oxidized to hypobromous acid (HOBr). 3,5-Dimethyl-1H-pyrazole (DMPZ) trapping coupled with liquid chromatography-mass spectrometry (LC-MS) analysis evidenced the formation of HOBr in PMS/TBBPS system. Therefore, the presence of Br^-, albeit at trace level, could significantly accelerate the oxidation of TBBPS in PMS solution via HOBr formation. The intermediate products of TBBPS were identified by solid phase extraction (SPE) coupled with high resolution-mass spectrometry (HR-MS). The oxidation of TBBPS by unactivated PMS was likely initiated through a single electron transfer mechanism, and the transformation pathways included β-scission, debromination, and cross-coupling reactions. Further oxidation and ring-opening of the intermediates yielded three brominated disinfection byproducts (Br-DBPs), including bromoform (CHBr₃), mono-, and di-bromoacetic acids (MBAA and DBAA), as quantified by gas chromatography (GC). The presence of natural organic matter (NOM) inhibited the oxidation of TBBPS and reduced the yields of Br-DBPs. Our results indicate that unactivated PMS was efficient in the abatement of TBBPS in aqueous solution due to the accelerated oxidation by bromine catalysis; however, the formation of brominated intermediate products and Br-DBPs should be scrutinized due to their potential carcinogenicity and mutagenicity.

Fe-based single-atom catalysis for oxidizing contaminants of emerging concern by activating peroxides

We prepared a single-atom Fe catalyst supported on an oxygen-doped, nitrogen-rich carbon support (SAFe-OCN) for degrading a broad spectrum of contaminants of emerging concern (CECs) by activating peroxides such as peroxymonosulfate (PMS). In the SAFe-OCN/PMS system, most selected CECs were amenable to degradation and high-valent Fe species were present for oxidation. Moreover, SAFe-OCN showed excellent performance for contaminant degradation in complex water matrices and high stability in oxidation. Specifically, SAFe-OCN, with a catalytic center of Fe coordinated with both nitrogen and oxygen (FeN_xO_4-x), showed 5.13-times increased phenol degradation kinetics upon activating PMS compared to the catalyst where Fe was only coordinated with nitrogen (FeN₄). Molecular simulations suggested that FeN_xO_4-x, compared to FeN₄, was an excellent multiple-electron donor and it could potential-readily form high-valent Fe species upon oxidation. In summary, the single-atom Fe catalyst enables efficient, robust, and sustainable water and wastewater treatment, and molecular simulations highlight that the electronic nature of Fe could play a key role in determining the activity of the single-atom catalyst.

Visible-light-driven peroxymonosulfate activation in photo-electrocatalytic system using hollow-structured Pt@CeO2@MoS2 photoanode for the degradation of pharmaceuticals and personal care products

In this study, we constructed an innovative photo-electrocatalysis-assisted peroxymonosulfate (PEC/PMS) system to degrade pharmaceuticals and personal care products (PPCPs). A hollow-structured photoanode (i.e., Pt@CeO₂@MoS₂) was specifically synthesized as a photoanode to activate PMS in the PEC system. As proof of concept, the Pt@CeO₂@MoS₂ photoanode exhibited superior degradation performance toward carbamazepine (CBZ) with PMS assistance. Specifically, the kinetic constant of PEC/PMS (k = 0.13202 min^-1) could be enhanced about 87.4 times compared to that of the PEC system (0.00151 min^-1) alone. The PMS activation mechanism revealed that the synergistic effect between the hollow material and the change of surface valence states (Ce³⁺ to Ce⁴⁺) and (Mo⁴⁺ to Mo⁶⁺) contribute to enhancing the degradation efficiency of the visible-light-driven PEC/PMS process. The scavenger testing and EPR showed that ¹O₂, O₂^•-, SO₄^•- and •OH play dominant roles in the SR-AOPs. Furthermore, the applicability of Pt@CeO₂@MoS₂ used in SR-AOPs was systematically investigated regarding of the reaction parameters and identification of intermediates and dominant radicals as well as the mineralization rate and stability. The outcomes of this study can provide a new platform for environmental remediation.

Direct oxidation of peroxymonosulfate under natural solar radiation: Accelerating the simultaneous removal of organic contaminants and pathogens from water

This study investigates the effectiveness of non-activated peroxymonosulfate (PMS) as oxidative agent for water purification in the presence and absence of natural solar radiation. The inactivation of three pathogens (Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa) and degradation of three Contaminants of Emerging Concern (CECs) (Trimethoprim-TMP, Sulfamethoxazole-SMX and Diclofenac-DCF) was simultaneously assessed in isotonic water (IW) by testing a wide range of PMS concentrations (from 0.0001 to 0.01 mM). A significant oxidative effect of PMS in darkness was obtained for both bacteria and CEC abatement, but when irradiated with solar light, results demonstrated a great enhancement on all bacterial kinetic rates, reaching >5 Log reduction in 30 min (1.5 kJL^-1 of Q_UV) with 0.005 mM of oxidant as the best concentration. For CECs, higher degradation performance was obtained with 0.01 mM, 80% removal of DCF, SMX and TMP was achieved in 16 min (1.5 kJL^-1), 27 min (9.4 kJL^-1) and 150 min (16.8 kJL^-1), respectively. Besides, the influence of inorganic species on the global PMS/solar system performance was assessed by testing its effectiveness in distilled water (DW), natural well water (WeW) and diluted well water (d-WeW) at 0.01 mM. Results revealed that (i) high chloride concentration (IW) has an important positive effect, (ii) the presence of a complex inorganic chemical water composition reduced the system efficiency (WeW), and (iii) no differences were obtained from the presence of low or high contents of carbonates/bicarbonates (WeW versus d-WeW), obtaining the following global PMS/solar efficiency performance order: IW > DW > WeW = d-WeW.

Microcystis aeruginosa removal by peroxides of hydrogen peroxide, peroxymonosulfate and peroxydisulfate without additional activators

Harmful algal bloom (HAB) is one of the most globally severe challenges in ecological system and water safety. Hydrogen peroxide has been commonly used in the management/treatment. Solid oxidants (e.g., peroxymonosulfate (PMS) and peroxydisulfate (PDS)) may outperform liquid H₂O₂ due to ease in transportation, handling, and applications. However, the information on applications of PMS and PDS in algae treatment is limited. In this study, the two solid peroxides and H₂O₂ were investigated for the removal of the blue-green algae of Microcystis aeruginosa. H₂O₂ and PMS effectively removed algae in 2 d at pH 5.0, 7.0 and 9.0, while PDS was only effective at pH 5.0. The change in pH and the release of dissolved organic carbon were insignificant at 0.2 mM H₂O₂ and PMS. The PMS could degrade microcystin-LR and phycobiliproteins. The studies of phycobiliproteins degradation and scanning electron microscopy indicated that PMS might cause the cell inactivation mainly by damaging the chemical components in algae cell wall and membrane while H₂O₂ might mainly enter the cell to form oxidation pressure to kill algae. The scavenger experiments showed that radicals were not crucial in H₂O₂ and PDS applications. Similarly, the algae removal by PMS was obtained mainly by non-radical pathways; about 77% was direct PMS oxidation and no more than 3% was singlet oxygen-mediated process, while radical pathways of sulfate radical and hydroxyl radical accounted for 18% and 2%, respectively. For the realistic algae-contaminated natural water, the PMS effectively lasted for 60 d, while the H₂O₂ lasted for 12 d. This research work demonstrates that the PMS is promising in control of HAB. The findings can provide some useful design and application parameters of PMS technology for better management/treatment of algae-contaminated water.

Selective oxidation and direct decolorization of cationic dyes by persulfate without activation

The aim of this work was to investigate the selective oxidation and direct decolorization of selected organic dyes (Methylene Blue (MB), Rhodamine B (RhB) and Orange II (OrgII)) by persulfate (PDS) without activation. Results show that the decolorization rate of MB was up to 58.0% within 10 minutes, while those of RhB and OrgII were only about 29.6% and 3.0% after 80 minutes, respectively. In comparison with the negligible impacts of pH from 2.0 to 9.0 on MB and OrgII decolorization, RhB decolorization rate obviously varied with the pH changes, and acid pH condition was beneficial for RhB decolorization. Quenching tests implied that the decolorization of dyes by PDS without activation was a nonradical oxidation process rather than sulfate radical oxidation. A plausible mechanism is that the decolorization process is attributed to the charged states of the dyes at different pH conditions, and thus direct electron transfer from dyes to PDS may occur, which is responsible for the bleaching of dyes. This study points out the potential bleaching capability of PDS without activation on cationic dyes, which may have important implications for selective oxidation treatment of dye wastewater.

Remediation of trichloroethylene contaminated soil by unactivated peroxymonosulfate: Implication on selected soil characteristics

The advanced oxidation process (AOP) based on activated Peroxymonosulfate (PMS) has been attracting many people in the field of soil and water remediation in many ways while ignoring the shortcomings. The high cost of activators, and energy input, as well as the expense to separate the catalyst and transition metal reducing agent from the treated soil, were some disadvantages of using activated PMS. Based on the above rationales of problems related to the use of activated PMS, this study aimed to study the performance of using unactivated peroxymonosulfate for the advanced oxidation process to remediate soil contaminated by trichloroethylene (TCE), and to evaluate the synergistic effect on selected soil properties after treatment. The results showed that within 45 min, a single injection of 5 mM PMS at its initial pH value can degrade 86.90% of the total TCE in the soil. However, when PMS was continuously injected, the removal rate was increased to 95.25%. The direct reaction of TCE and PMS was the main cause of degradation. PMS can degrade TCE in a wide pH range (pH 3-11), but the maximum degradation was at pH = 2.9 (the initial pH of PMS). After the treatment, the soil organic matter (SOM) was degraded significantly. In contrast, FTIR, SEM, and hydrometer tests conducted on the soil showed that the treatment had no significant effect on the functional groups and particle size distribution of the treated soil. The study on the effect of the treatment on the concentration of bioavailable heavy metals in the treated soil showed that only manganese and copper metals were significantly increased after the treatment. According to the results obtained in this study, it is more beneficial and feasible to use unactivated peroxymonosulfate in the advanced oxidation process when remediating soil contaminated by chlorinated organic matter.

Nonradicals induced degradation of organic pollutants by peroxydisulfate (PDS) and peroxymonosulfate (PMS): Recent advances and perspective

Nonradical persulfate oxidation processes have emerged as a new wastewater treatment method due to production of mild nonradical oxidants, selective oxidation of organic pollutants, and higher tolerance to water matrixes compared with radical persulfate oxidation processes. Since the case of the nonradical activation of peroxydisulfate (PDS) was reported on CuO surface in 2014, nonradical persulfate oxidation processes have been extensively investigated, and much achievement has been made on realization of nonradical persulfate activation processes and understanding of intrinsic reaction mechanism. Therefore, in the review, nonradical pathways and reaction mechanisms for oxidation of various organic pollutants by PDS and peroxymonosulfate (PMS) are overviewed. Five nonradical persulfate oxidation pathways for degradation of organic pollutants are summarized, which include surface activated persulfate, catalysts-free or catalysts mediated electron transfer, ¹O₂, high-valent metals, and newly derived inorganic oxidants (e.g., HOCl and HCO₄^-). Among them, the direct oxidation processes by persulfate, nonradical based persulfate activation by inorganic/organic molecules and in electrochemical methods is first overviewed. Moreover, nonradical based persulfate activation mechanisms by metal oxides and carbon materials are further updated. Furthermore, investigation methods of interaction between persulfate and catalyst surface, and nature of reactive species are also discussed in detail. Finally, the future research needs are proposed based on limited understanding on reaction mechanism of nonradical based persulfate activation. The review can offer a comprehensive assessment on nonradical oxidation of organic pollutants by persulfate to fill the knowledge gap and provide better guidance for future research and engineering application of persulfate.

A comparison study of levofloxacin degradation by peroxymonosulfate and permanganate: Kinetics, products and effect of quinone group

Permanganate (Mn(VII)) as a selective oxidant has been widely used in water treatment process. Recently, peroxymonosulfate (PMS) was recognized as an emerging selective oxidant, which showed appreciable reactivity toward organic compounds containing electron-rich functional groups. In this study, the oxidation of a model fluoroquinolone antibiotic levofloxacin (LEV) by Mn(VII) and PMS was comparatively investigated. Degradation of LEV by PMS followed second-order kinetics and showed strong pH dependency with apparent second-order rate constants (k_app) of 0.15-26.52 M^-1 s^-1 at pH 5.0-10.0. Oxidation of LEV by Mn(VII) showed autocatalysis at pH 5.0-7.0, while no autocatalysis was observed at pH 8.0-10.0 (k_app = 2.23-4.16 M^-1 s^-1). Such unusual oxidation kinetics was attributed to the in-situ formed MnO₂ from Mn(VII) consumption. The performance of PMS and Mn(VII) for the degradation of LEV was also examined in real waters. PMS primarily react with the aliphatic N4 amine on the piperazine ring of LEV, and Mn(VII) reacted with both the aliphatic N4 amine and aromatic N1 amine. Both PMS and Mn(VII) could efficiently eliminate the antibiotic activity of LEV. Benzoquinone showed activating effect on both PMS and Mn(VII) oxidation, but their activation mechanisms were totally different.

Direct oxidation of antibiotic trimethoprim by unactivated peroxymonosulfate via a nonradical transformation mechanism

Application of activated peroxymonosulfate (PMS) to generate sulfate radical or hydroxyl radical is a promising strategy for wastewater treatment, while our knowledge on the background reaction, namely, the direct interaction between PMS and target contaminants is quite limited. In this contribution, the degradation kinetics, stoichiometry, products and mechanism of the reaction between unactivated PMS and trimethoprim (TMP), one of the most commonly detected micro-pollutants in the aquatic system were investigated systematically. The results indicated that TMP was susceptible to degradation by direct PMS oxidation via a non-radical process. By recording the decay of two reactants simultaneously, the stoichiometric ratio between PMS and TMP was estimated to be approximately 1. Higher PMS levels exhibited a promotion effect on PMS decay. And the degradation was pH-dependent, basic conditions were favorable for TMP degradation, which could be well modeled based on the species-specific reactions. The two amine groups on the pyrimidine ring were identified as the reactive sites. After direct attacks by PMS, they would be oxidized to form hydroxylamine-products, namely, N⁸-OH-TMP and N⁹-OH-TMP. These two hydroxylamine-products were quite stable and resistant to further oxidation by PMS, preventing the formation of more toxic nitroso- and nitro-products. The new findings in the present work would provide beneficial information on the strategy choice for the elimination of specific pollutants, like TMP, as PMS also exhibits relatively high reactivity towards them.

Rapid transformation of H1-antihistamines cetirizine (CET) and diphenhydramine (DPH) by direct peroxymonosulfate (PMS) oxidation

With growing interest in advanced oxidation processes (AOPs), the number of research studies on peroxymonosulfate (PMS) mediated pollutant degradation has increased significantly due to its high radical generation potential upon activation. However, rare studies have focused on the non-radical based PMS reactions. In this study, degradation of model H₁-antihistamines cetirizine (CET) and diphenhydramine (DPH) by unactivated PMS was investigated. Addition of scavengers to the reaction mixture ruled out the involvement of hydroxyl radical (OH), sulfate radical (SO₄^-), singlet oxygen (¹O₂) and superoxide anion radical (O₂^-), indicating direct PMS oxidation as the predominant reaction path. Such a mechanism was further supported by the N-oxide products identified by mass spectrometry and nuclear magnetic resonance (NMR) analyses. Solution pH had a pronounced influence on the degradation kinetics regardless the presence or absence of transition metal Fe(II). The highest species dependent second order rate constants were k_HSO5-/DPH0 of 175 ± 15.9 M^-1 s^-1 and k_HSO5-/CET- of 36.6 ± 0.16 M^-1 s^-1. The addition of 100 μM Fe(II) promoted OH mediated degradation of H₁-antihistamines and their N-oxide products. This study demonstrated selective transformation with the potential for extensive degradation employing both the direct and catalytic PMS oxidative processes.

Selective oxidation of H1-antihistamines by unactivated peroxymonosulfate (PMS): Influence of inorganic anions and organic compounds

The rapid and selective peroxymonosulfate (PMS) induced transformation of H₁-antihistamines cetirizine (CET) and diphenhydramine (DPH) can be influenced by the presence of common organic and inorganic water constituents. Presence of HCO₃^- and/or CO₃^2-, which often exhibit powerful inhibition on the advanced oxidation processes (AOPs), can enhance the PMS mediated transformation of CET/DPH. The observed promotion is demonstrated by the changed solution pH through detailed kinetic studies. The impact of halide ions is remarkable, with I^- inhibiting the process through consumption of PMS, while Cl^- increases slightly the transformation kinetics through the formation and subsequent reactions of HOCl. The CET/DPH degradation in the Br^-/PMS system is influenced by the generation of reactive species such as HOBr which leads to different reaction pathways as compared to PMS alone. The results demonstrated the performance of PMS can be tailored through varying the experimental parameters. In addition, the presence of model organic constituents found in water, e.g., humic acid, phenol, pyridine or sorbate, has a minimal effect on the PMS mediated oxidation processes, highlighting the strong application potential of PMS in water treatment.

Development of 3-dimensional Co3O4 catalysts with various morphologies for activation of Oxone to degrade 5-sulfosalicylic acid in water

Since 5-sulfosalicylic acid (SFA) has been increasingly released to the environment, SO₄^--based oxidation processes using Oxone have been considered as useful methods to eliminate SFA. As Co₃O₄ has been a promising material for OX activation, the four 3D Co₃O₄ catalysts with distinct morphologies, including Co₃O₄-C (with cubes), Co₃O₄-P (with plates), Co₃O₄-N (with needles) and Co₃O₄-F (with floral structures), are fabricated for activating OX to degrade SFA. In particular, Co₃O₄-F not only exhibits the highest surface area but also possesses the abundant Co²⁺ and more reactive surface, making Co₃O₄-F the most advantageous 3D Co₃O₄ catalyst for OX activation to degrade SFA. The mechanism of SFA by this 3D Co₃O₄/OX is also investigated and the corresponding SFA degradation pathway has been elucidated. The catalytic activities of Co₃O₄ catalysts can be correlated to physical and chemical properties which were associated with particular morphologies to provide insights into design of 3D Co₃O₄-based catalysts for OX-based technology to degrade emerging contaminants, such as SFA.