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

Nitrogen-doped carbon-coated Cu0 activates molecular oxygen for norfloxacin degradation over a wide pH range

The Fenton-like activated molecular oxygen technology demonstrates significant potential in the treatment of refractory organic pollutants in wastewater, offering promising development prospects. We prepared a N-doped C-coated copper-based catalyst Cu0/NC3-600 through the pyrolysis of Mel-modified Cu-based metal-organic framework (MOF). The results indicate that the degradation of 20 mg/L norfloxacin (NOR) was achieved using 1.0 g/L Cu0/NC3-600 across a wide pH range, with a removal rate exceeding 95 % and total organic carbon (TOC) removals approaching 70 % after 60 min at pH 5-11. The nitrogen doping enhances the electronic structure of the carbon material, facilitating the adsorption of molecular oxygen. Additionally, the formed carbon layer effectively prevent copper leaching,contributing to increased stability to a certain extent. Subsequently, we propose the catalytic reaction mechanism for the Cu0/NC/air system. Under acidic conditions, Cu0/NC3-600 activates molecular oxygen to produce the •O2-, which serves as the primary active species for NOR degradation. While in alkaline conditions, the high-valent copper species Cu3+ is generated in conjunction with •O2-, both working simultaneously for NOR degradation. Furthermore, based on the LC-MS results, we deduced four possible degradation pathways. This work offers a novel perspective on expanding the pH range of copper-based catalysts with excellent ability to activate molecular oxygen for environmental water treatment.

Enhanced Degradation of Micropollutants in a Peracetic Acid/Mn(II) System with EDDS: An Investigation of the Role of Mn Species

Extensive research has been conducted on the utilization of a metal-based catalyst to activate peracetic acid (PAA) for the degradation of micropollutants (MPs) in water. Mn(II) is a commonly employed catalyst for homogeneous advanced oxidation processes (AOPs), but its catalytic performance with PAA is poor. This study showed that the environmentally friendly chelator ethylenediamine-N,N'-disuccinic acid (EDDS) could greatly facilitate the activation of Mn(II) in PAA for complete atrazine (ATZ) degradation. In this process, the EDDS enhanced the catalytic activity of manganese (Mn) and prevented disproportionation of transient Mn species, thus facilitating the decay of PAA and mineralization of ATZ. By employing electron spin resonance detection, quenching and probe tests, and 18O isotope-tracing experiments, the significance of high-valent Mn-oxo species (Mn(V)) in the Mn(II)-EDDS/PAA system was revealed. In particular, the involvement of the Mn(III) species was essential for the formation of Mn(V). Mn(III) species, along with singlet oxygen (1O2) and acetyl(per)oxyl radicals (CH3C(O)O•/CH3C(O)OO•), also contributed partially to ATZ degradation. Mass spectrometry and density functional theory methods were used to study the transformation pathway and mechanism of ATZ. The toxicity assessment of the oxidative products indicated that the toxicity of ATZ decreased after the degradation reaction. Moreover, the system exhibited excellent interference resistance toward various anions and humid acid (HA), and it could selectively degrade multiple MPs.

Amphichdiral enhancement on singlet oxygen generation and stable thallium immobilization using iron-driven copper oxide

Thallium (Tl) as a prominent priority contaminant in aquatic environment necessitates rigorous regulation. However, limited horizon devotes the impact of selective oxidation on the process of thallium purification. In this study, selective active radical of singlet oxygen (1O2) was continually generated for Tl(Ⅰ) oxidation accomplished with efficient Tl(Ⅲ) immobilization using iron-driven copper oxide (CuFe)/peroxymonosulfate (PMS). Fe-doping changed the active center of electronic structure for enhancing the catalytic and adsorptive reactivities, and installed magnetism for solid-liquid separation. Rapid reaction rate (0.253 min-1) coupled with vigorous elimination efficiency (98.32%) relied on electrostatic attraction, surface complexation, and H-bond interaction. EPR and XPS analyses demonstrated that the synergistic effects of ≡ Cu(Ⅰ)/≡Cu(Ⅱ) and ≡ Fe(Ⅲ)/≡Fe(Ⅱ) redounded to the sustained generation of 1O2 through the pathway of PMS → •O2- → 1O2, and 1O2 exploited an advantage to selectively oxidize Tl(Ⅰ) to Tl(Ⅲ). 3D isosurface cubic charts revealed that the immobilizing ability of Tl(Ⅲ) hydrate for CuFe was notably superior to that of Tl(Ⅲ) hydrate for CuO and Tl(Ⅰ) hydrate for CuO/CuFe, which further attested surface reactivity promoted stable immobilization form. This work develops the continuous generation of 1O2 and stable immobilization with the goal of efficiently cleansing Tl-containing wastewater.

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.

Oxidation of imidacloprid insecticide through PMS activation using CuFe2O4 nanoparticles: Role of process parameters and surface modifications

The contamination of water bodies by synthetic organic compounds coupled with climate change and the growing demand for water supply calls for new approaches to water management and treatment. To tackle the decontamination issue, the activation of peroxymonosulfate (PMS) using copper magnetic ferrite (CuMF) nanoparticles prepared under distinct synthesis conditions was assessed to oxidize imidacloprid (IMD) insecticide. After optimization of some operational variables, such as CuMF load (62.5-250 mg L-1), PMS concentration (250-1000 μM), and solution pH (3-10), IMD was completely oxidized in 2 h without interferences from leached metal ions. Such performance was also achieved when using tap water but was inhibited by a simulated municipal wastewater due to scavenging effects promoted by inorganic and organic species. Although there was evidence of the presence of sulfate radicals and singlet oxygen oxidizing species, only four intermediate compounds were detected by liquid chromatography coupled to mass spectrometry analysis, mainly due to hydroxyl addition reactions. Concerning the changes in surface properties of CuMF after use, no morphological or structural changes were observed except a small increase in the charge transfer resistance. Based on the changes of terminal surface groups, PMS activation occurred on Fe sites.

Trace Co(II) triggers peracetic acid activation in phosphate buffer: New insights into the oxidative species responsible for ciprofloxacin removal

Peracetic acid (PAA) emerges as a promising disinfectant and oxidant applied worldwide, and its application has been broadened for advanced oxidation processes (AOPs) in wastewater treatment. Current studies on transition metal-activated AOPs utilized relatively high concentrations of catalysts, leading to potential secondary pollution concerns. This study boosts the understanding of reaction mechanism in PAA activation system under a low-level concentration. Herein, trace levels of Co(II) (1 μM) and practical dosages of PAA (50-250 μM) were employed, achieving noticeable ciprofloxacin (CIP) degradation efficiencies (75.8-99.0%) within 20 min. Two orders of magnitude of the CIP's antibacterial activity significantly decreased after Co(II)/PAA AOP treatment, which suggested the effective ecological risk control capability of the reaction system. The degradation performed well in various water matrices and the primary reactive species is proposed to be CoHPO4-OO(O)CCH3 complexes with scavenging tests and electron paramagnetic resonance tests. The degradation pathway of fluoroquinolones including piperazine ring-opening (dealkylation and oxidation), defluorination, and decarboxylation, were systematically elucidated. This study boosts a comprehensive and novel understanding of PAA-based AOP for CIP degradation.

Investigating the evolution of reactive species in the CuO-mediated peroxymonosulfate activation process

The utilization of copper oxide (CuO) as a catalyst in the peroxymonosulfate (PMS) activation process holds great promise for effectively degrading aqueous organic pollutants, while the relevant mechanism remains inadequately understood. In this study, we delve into the evolution pathways of reactive species in the CuO/PMS system through a comprehensive series of experimental analyses. Our findings indicate that various reactive species are generated in the CuO/PMS system with the specific sequence, where the decomposition of surface Cu(II)-OOSO3- leads to the formation of surface Cu(III) species, which are responsible for the subsequent generation of HO•. The reactivity of these reactive species and the sequence of their generation explain the distinct oxidation behaviors of pollutants with different values of ionization potential (IP). In addition, singlet oxygen (1O2) may be produced during the PMS activation process, while its involvement in the oxidation of substrates is deemed negligible. This investigation presents a novel perspective, enhancing our comprehension of the mechanism underlying transition metal-mediated PMS activation processes. ENVIRONMENTAL IMPLICATION: The removal of refractory organic contaminations in water constitutes a fundamental concern within the realm of environmental pollution management. Peroxymonosulfate activation induced by transition metal oxides has garnered significant recognition as a promising technological approach for the degradation of aqueous organic contaminants, while the underlying mechanism remains enigmatic. In this study, we systematically investigate the evolution pathways of reactive species in the CuO/peroxymonosulfate system to reveal the mystery of the reaction mechanism between CuO and peroxymonosulfate. The outcomes of our study contribute to enhancing the practical applicability of transition metal-triggered PMS activation processes.

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.

Morphology-dependent activation of hydrogen peroxide with Cu2O for tetracycline hydrochloride degradation in bicarbonate aqueous solution

The design of efficient heterogeneous catalysts in bicarbonate-activated hydrogen peroxide systems (BAP) is a hot topic in wastewater treatment. In this work, Cu2O nanoparticles with different morphologies including cubic shape (c-Cu2O), octahedron shape (o-Cu2O) and spherical shape (s-Cu2O), were applied in BAP for the first time to degrade tetracycline hydrochloride (TC). Compared with Cu2+ ions and CuO, TC degradation was boosted in the presence of Cu2O in the BAP system, with the degradation rate following the order c-Cu2O > o-Cu2O > s-Cu2O. The morphology-dependent effects could be linearly correlated with the ratio of surface oxygen species (OS), but not with the surface area or Cu(I) ratio. The c-Cu2O catalyst with exposure of (100) facets contained 76.6% OS as the active site for H2O2 adsorption and activation, while the value was much lower for o-Cu2O and s-Cu2O with dominant (111) facets. The presence of HCO3- enhanced the interactions among Cu2O, H2O2 and TC, leading to facile oxidation of Cu(I) to Cu(II) by H2O2, and the formation of various reactive species such as hydroxyl radicals and Cu(III) contributed to TC degradation. This work provides a new method for enhancing H2O2 activation with heterogeneous catalysts by crystal facet engineering.

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

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

CoFe2O4 as a source of Co(II) ions for imidacloprid insecticide oxidation using peroxymonosulfate: Influence of process parameters and surface changes

Nanometric cobalt magnetic ferrite (CoFe2O4) synthesized by distinct methods was used for in situ chemical activation of peroxymonosulfate (PMS) under neutral conditions to oxidize imidacloprid (IMD) insecticide. The effect of CoFe2O4 load (0.125-1.0 g L-1) and PMS concentration (250-1000 μM) was investigated as well as the influence of phosphate buffer and Co(II) ions. PMS activation by Co(II) ions, including those leached from CoFe2O4 (>50 μg L-1), exhibited a strong influence on IMD oxidation and, apparently, without substantial contributions from the solid phase. Within the prepared solid materials (i.e., using sol-gel and co-precipitation methods), high oxidation rates (ca. 0.5 min-1) of IMD were attained in ultrapure water. Phosphate buffer had no significant influence on the IMD oxidation rate and level, however, its use and solution pH have shown to be important parameters, since higher PMS consumption was observed in the presence of buffered solutions at pH 7. IMD byproducts resulting from hydroxylation reactions and rupture of the imidazolidine ring were detected by mass spectrometry. At optimum conditions (0.125 g L-1 of CoFe2O4 and 500 μM of PMS), the CoFe2O4 nanoparticles exhibited an increase in the charge transfer resistance and an enhancement in the surface hydroxylation after PMS activation, which led to radical (HO● and SO4●-) and nonradical (1O2) species. The latter specie led to high levels of IMD oxidation, even in a complex water matrix, such as simulated municipal wastewater at the expense of one-order decrease in the IMD oxidation rate.

Enhancing dye degradation using a novel cobalt metal-organic framework as a peroxymonosulfate activator

Among transition metals, cobalt ions exhibit superior catalytic activity in the peroxymonosulfate (PMS) degradation of pollutants. However, practical application is hindered by their high rate of ion leaching and the propensity for particle reunion issues. In this study, a novel cobalt metal-organic framework catalyst, denoted as CUST-565 ([Co3(BTB)2(BIPY)2]·4.5H2O·DMA), was synthesized via a one-step solvothermal method. The obtained crystal was employed as a catalyst to activate PMS for degrading two pollutants, methyl orange (MO) and rhodamine B (RhB), in wastewater. The catalyst demonstrated efficacy in PMS, achieving 97% degradation of MO and 98% degradation of RhB within 30 min at an initial concentration of 20.0 mg L-1. Additionally, various factors affecting dye degradation, including PMS dosage, catalyst dosage, temperature, initial pH, and coexisting anions, were investigated. Radical quenching experiments confirmed the presence of sulfate radicals (SO4˙-), hydroxyl radicals (HO˙), superoxide radicals (O2˙-), and singlet oxygen (1O2) in the system. After four cycles, CUST-565 retained its ability to catalytically degrade approximately 80% of the pollutants. These observed stability and reusability properties, corroborated by a series of characterization analyses before and after use, suggest that CUST-565 exhibits reliable performance. This work contributes to the development of cobalt-PMS catalysts for efficiently degrading dyes in wastewater.

Overlooked Role of Coexistent Hydrogen Peroxide in Activated Peracetic Acid by Cu(II) for Enhanced Oxidation of Organic Contaminants

Cu(II)-catalyzed peracetic acid (PAA) processes have shown significant potential to remove contaminants in water treatment. Nevertheless, the role of coexistent H2O2 in the transformation from Cu(II) to Cu(I) remained contentious. Herein, with the Cu(II)/PAA process as an example, the respective roles of PAA and H2O2 on the Cu(II)/Cu(I) cycling were comprehensively investigated over the pH range of 7.0-10.5. Contrary to previous studies, it was surprisingly found that the coexistent deprotonated H2O2 (HO2-), instead of PAA, was crucial for accelerating the transformation from Cu(II) to Cu(I) (kHO2-/Cu(II) = (0.17-1) × 106 M-1 s-1, kPAA/Cu(II) < 2.33 ± 0.3 M-1 s-1). Subsequently, the formed Cu(I) preferentially reacted with PAA (kPAA/Cu(I) = (5.84 ± 0.17) × 102 M-1 s-1), rather than H2O2 (kH2O2/Cu(I) = (5.00 ± 0.2) × 101 M-1 s-1), generating reactive species to oxidize organic contaminants. With naproxen as the target pollutant, the proposed synergistic role of H2O2 and PAA was found to be highly dependent on the solution pH with weakly alkaline conditions being more conducive to naproxen degradation. Overall, this study systematically investigated the overlooked but crucial role of coexistent H2O2 in the Cu(II)/PAA process, which might provide valuable insights for better understanding the underlying mechanism in Cu-catalyzed PAA processes.

Reinvestigation on High-Valent Cobalt for the Degradation of Micropollutants in the Co(II)/Peroxymonosulfate System: Roles of Co(III)

Recently, reactive cobalt (Co) species, including Co(IV)-oxo and Co(II)-OOSO3- complexes, were proposed to be the primary intermediates formed during the process of activating peroxymonosulfate (PMS) by Co(II), mainly based on the observation that the methyl phenyl sulfoxide (MPSO) probe was transformed to methyl phenyl sulfone (MPSO2) in this process. However, in this work, we rationalized the results of the MPSO probe assay based on the chemistry of aqueous Co(III), an alternative reactive Co species. Moreover, 18O-labeled water experiments and Raman spectroscopy analysis clearly proved the Co(III) formation in the Co(II)/PMS system. In parallel, sulfate radicals (SO4•-) and hydroxyl radicals (HO•) were also involved in this system. Further, the relative contribution of Co(III) to the abatement of carbamazepine (CBZ), a representative micropollutant, in the Co(II)/PMS system was significantly increased by increasing the Co(II) dosage but was dramatically decreased by improving the PMS dosage and increasing the pH from 3 to 7. Additionally, the degradation pathway of CBZ by Co(III) and the Co(II)/PMS system was comparatively explored, confirming that Co(III) participated in the hydroxylation, carbonylation, deacetylation, and ring reduction of CBZ by the Co(II)/PMS system. Our work addresses the controversy regarding the reactive Co species involved in the Co(II)/PMS system with evidence of Co(III) as the chief one, which highlights the significance of re-evaluating the relative contribution of Co(III) in relevant environmental decontamination processes.

Efficient treatment of actual glyphosate wastewater via non-radical Fenton-like oxidation

Compared to radical oxidative pathway, recent research revealed that non-radical oxidative pathway has higher selectivity, higher adaptability and lower oxidant requirement. In this work, we have designed and synthesized Cu2O/Cu nanowires (CuNWs), by pyrolysis of copper chloride and urea, to selectively generate high-valent copper (CuIII) upon H2O2 activation for the efficient treatment of actual glyphosate wastewater. The detailed characterizations confirmed that CuNWs nanocomposite was comprised of Cu0 and Cu2O, which possessed a nanowire-shaped structure. The electron paramagnetic resonance (EPR) analysis, in situ Raman spectra, chronoamperometry and liner sweep voltammetry (LSV) verified CuIII, which mainly contributed to glyphosate degradation, was selectively generated from CuNWs/H2O2 system. In particular, CuI is mainly oxidized by H2O2 into CuIIIvia dual-electron transfer, rather than simultaneously releasing OH• via single electron transfer. More importantly, CuNWs/H2O2 system exhibited the excellent potential in the efficient treatment of actual glyphosate wastewater, with 96.6% degradation efficiency and chemical oxygen demand (COD) dropped by 30%. This novel knowledge gained in the work helps to apply CuNWs into heterogeneous Fenton-like reaction for environmental remediation and gives new insights into non-radical pathway in H2O2 activation.

Size-matched hierarchical porous carbon materials anchoring single-atom Fe-N4 sites for PMS activation: An in-depth study of key active species and catalytic mechanisms

Single-atom catalysts are considered to be one of the most promising catalysts for AOPs. However, how to design and synthesize cost-effective and highly loaded single-atom catalysts is the bottleneck limiting its development and application. In this study, we report a highly loaded single-atom iron catalyst (Fe-SAC-BC) using waste biomass as a carbon carrier to anchor Fe-N4 sites. The catalyst showed excellent catalytic performance and stability in wastewater treatment. Unlike conventional radical oxidation, the non-radical degradation process of Fe-N4 as the active site and high-valent iron-oxygen intermediates as the key active species identified by burst and probe experiments. DFT calculations and molecular dynamics simulations were applied to the catalytic mechanism of Fe-SAC-BC, in which Fe (III)-N4 is the most likely active site and Fe (IV)-OH is the most dominant active species. This study provides new strategies and understanding for the design of novel single-atom catalysts and the mechanistic probing of the non-radical pathways of AOPs.

Kinetic Modeling Assisted Analysis of Vitamin C-Mediated Copper Redox Transformations in Aqueous Solutions

The kinetics of oxidation of micromolar concentrations of ascorbic acid (AA) catalyzed by Cu(II) in solutions representative of biological and environmental aqueous systems has been investigated in both the presence and absence of oxygen. The results reveal that the reaction between AA and Cu(II) is a relatively complex set of redox processes whereby Cu(II) initially oxidizes AA yielding the intermediate ascorbate radical (A•-) and Cu(I). The rate constant for this reaction was determined to have a lower limit of 2.2 × 104 M-1 s-1. Oxygen was found to play a critical role in mediating the Cu(II)/Cu(I) redox cycle and the oxidation reactions of AA and its oxidized forms. Among these processes, the oxidation of the ascorbate radical by molecular oxygen was identified to play a key role in the consumption of ascorbic acid, despite being a slow reaction. The rate constant for this reaction (A • - + O 2 → DHA + O 2 • - ) was determined for the first time with a calculated value of 54 ± 8 M-1 s-1. The kinetic model developed satisfactorily describes the Cu/AA/O2 system over a range of conditions including different concentrations of NaCl (0.2 and 0.7 M) and pH (7.4 and 8.1). Appropriate adjustments to the rate constant for the reaction between Cu(I) and O2 were found to account for the influence of the chloride ions and pH on the kinetics of the process. Additionally, the presence of Cu(III) as the primary oxidant resulting from the interaction between Cu(I) and H2O2 in the Cu(II)/AA system was confirmed, along with the coexistence of HO•, possibly due to an equilibrium established between Cu(III) and HO•.

Mechanism insights into photo-assisted peroxymonosulfate activation on oxygen vacancy-enriched nolanites via an electron transfer regime

The utilization of photo-assisted persulfate activation for the removal of organic contaminants in water has garnered significant research interest in recent times. However, there remains a lack of clarity regarding specific contributions of light irradiation and catalyst structure in this process. Herein, a photo-assisted peroxymonosulfate (PMS) activation system is designed for the highly efficient degradation of organic contaminants on oxygen vacancy-enriched nolanites (Vo-FVO). Results suggest that the degradation of bisphenol A (BPA) in this system is a nonradical-dominated process via an electron transfer regime, in which VO improves the local electron density and thus facilitates the electron shuttling between BPA and PMS. During BPA degradation, PMS adsorbed at the surface of FVO-180 withdraws electrons near VO and forms FVO-PMS* complexes. Upon light irradiation, photoelectrons effectively restore the electron density around VO, thereby enabling a sustainable electron transfer for the highly efficient degradation of BPA. Overall, this work provides new insights into the mechanism of persulfate activation based on defects engineering in nolanite minerals.

Ozone- and Hydroxyl Radical-Induced Degradation of Micropollutants in a Novel UVA-LED-Activated Periodate Advanced Oxidation Process

In this study, novel light emitting diode (LED)-activated periodate (PI) advanced oxidation process (AOP) at an irradiation wavelength in the ultraviolet A range (UVA, UVA-LED/PI AOP) was developed and investigated using naproxen (NPX) as a model micropollutant. The UVA-LED/PI AOP remarkably enhanced the degradation of NPX and seven other selected micropollutants with the observed pseudo-first-order rate constants ranging from 0.069 ± 0.001 to 4.50 ± 0.145 min-1 at pH 7.0, demonstrating a broad-spectrum micropollutant degradation ability. Lines of evidence from experimental analysis and kinetic modeling confirmed that hydroxyl radical (•OH) and ozone (O3) were the dominant species generated in UVA-LED/PI AOP, and they contributed evenly to NPX degradation. Increasing the pH and irradiation wavelength negatively affected NPX degradation, and this could be well explained by the decreased quantum yield (ΦPI) of PI. The degradation kinetics of NPX by the UVA-LED/PI AOP in the presence of water matrices (i.e., chloride, bicarbonate, and humic acid) and in real waters were examined, and the underlying mechanisms were illustrated. A total of nine transformation products were identified from NPX oxidation by the UVA-LED/PI AOP, mainly via hydroxylation, dealkylation, and oxidation pathways. The UVA-LED/PI AOP proposed might be a promising technology for the treatment of micropollutants in aqueous solutions. The pivotal role of ΦPI during light photolysis of PI may guide the future design of light-assisted PI AOPs.

Enhancing Ferrate Oxidation of Micropollutants via Inducing Fe(V)/Fe(IV) Formation Needs Caution: Increased Conversion of Bromide to Bromate

This study explores the formation of bromate (BrO3-) in the copresence of Fe(VI) and bromide (Br-). It challenges previous beliefs about the role of Fe(VI) as a green oxidant and highlights the crucial role of intermediates Fe(V) and Fe(IV) in the conversion of Br- to BrO3-. The results show that the maximum concentration of BrO3- of 48.3 μg/L was obtained at 16 mg/L Br- and that the contribution of Fe(V)/Fe(IV) to the conversion was positively related to pH. The study suggests that a single-electron transfer from Br- to Fe(V)/Fe(IV) along with the generation of reactive bromine radicals is the first step of Br- conversion, followed by the formation of OBr- which was then oxidized to BrO3- by Fe(VI) and Fe(V)/Fe(IV). Some common background water constituents (e.g., DOM, HCO3-, and Cl-) significantly inhibited BrO3- formation by consuming Fe(V)/Fe(IV) and/or scavenging the reactive bromine species. While investigations proposing to promote Fe(V)/Fe(IV) formation in Fe(VI)-based oxidation to enhance its oxidation capacity have been rapidly accumulated recently, this work called attention to the considerable formation of BrO3- in this process.

Electrodeposited copper enhanced removal of 2,4-dichlorophenol in batch and flow reaction in Cu@CC-PS-MFC system

Combination of microbial fuel cell (MFC) and advanced oxidation process (AOP) is promising for pollutant removal. In this paper, Cu0-loaded carbon cloth cathode by electrodeposition (Cu@CC-PS-MFC) was applied to enhance 2,4-dichlorophenol (2,4-DCP) degradation based on persulfate (PS) activation in microbial fuel cell. Cu0 exhibited a typical structure of face-centered cubic metal polyhedron on carbon cloth. The removal of 2,4-DCP by Cu@CC-PS-MFC (75.6%) was enhanced by more than 50% compared to CC-PS-MFC (49.2%) after 1 h of reaction. 30 mg/L 2,4-DCP in Cu@CC-PS-MFC was completely removed and achieved a high mineralization (80.6%) after 9 h of reaction under optimized condition with low dissolved copper ion concentration (0.615 mg/L). Meanwhile, more than 90% removal of 2,4-DCP was stably achieved with flow operation condition (hydraulic residence time of 7.2 h). The change of copper valent state Cu0/Cu2O/CuO was the main mechanism of PS activation with main reactive species of O•H and O21. The bioanode of MFC enhanced the in-situ regeneration of ≡Cu+ and ≡Cu0 on the catalyst surface by transporting electrons, which was believed to contribute to good catalyst lifetime and excellent 2,4-DCP removal. Electrodeposited copper contributes to the enhanced degradation of 2,4-DCP with energy recovery at the same time which can further broaden the application MFC.

Hydroxylamine enhanced the degradation of diclofenac in Cu(II)/peracetic acid system: Formation and contributions of CH3C(O)O•, CH3C(O)OO•, Cu(III) and •OH

The slow reduction of Cu(II) into Cu(I) through peracetic acid (PAA) heavily limited the widespread application of Cu(II)/PAA system. Herein, hydroxylamine (HA) was proposed to boost the oxidative capacity of Cu(II)/PAA system by facilitating the redox cycle of Cu(I)/Cu(II). HA/Cu(II)/PAA system was quite rapid in the removal of diclofenac within a broad pH range of 4.5-9.5, with a 10-fold increase in the removal rate of diclofenac compared with the Cu(II)/PAA system at an optimal initial pH of 8.5. Results of UV-Vis spectra, electron paramagnetic resonance, and alcohol quenching experiments demonstrated that CH3C(O)O•, CH3C(O)OO•, Cu(III), and •OH were involved in HA/Cu(II)/PAA system, while CH3C(O)OO• was verified as the predominant reactive species of diclofenac elimination. Different from previously reported Cu-catalyzed PAA processes, CH3C(O)OO• mainly generated from the reaction of PAA with Cu(III) rather than CH3C(O)O• and •OH. Four possible elimination pathways for diclofenac were proposed, and the acute toxicity of treated diclofenac solution with HA/Cu(II)/PAA system significantly decreased. Moreover, HA/Cu(II)/PAA system possessed a strong anti-interference ability towards the commonly existent water matrix. This research proposed an effective strategy to boost the oxidative capacity of Cu(II)/PAA system and might promote its potential application, especially in copper-contained wastewater.

Facile synthesis of NaA zeolite supported Co2Fe1 for highly efficient degradation of Acid Orange 7 by activation of peroxymonosulfate

The development of heterogeneous Co-based catalysts with an effective combination mode of Co/Fe and supporter, a facile synthetic method, and a low treatment cost is an important environment challenge for azo dyes degradation by peroxymonosulfate (PMS) activation. In this study, NaA zeolite supported CoxFey with various molar ratio of Fe/Si and Co/Fe was synthesized by a facile hydrothermal process, and used to activate PMS for Acid Orange 7 (AO7) degradation. NaA zeolite supported Co2Fe1 with the Fe/Si molar ratio of 1:10 showed superior catalytic performance compared with other NaA zeolite supported CoxFey. In a system containing 0.6 g/L catalysts, 4 mM PMS, pH 5 and T = 30℃, 95.8% AO7 and 79.1% COD conversion could be achieved at 20 and 60 min, respectively, and the first order kinetic rate constant reached 0.14795 min-1. Moreover, NaA zeolite supported Co2Fe1/PMS system exhibited excellent catalytic effect in a wide pH range of 3-9. Temperature had an obvious effect on AO7 degradation, and the activation energy was 31.36 kJ/mol. HCO3- demonstrated an obvious depression on AO7 degradation, while Cl-, SO42- and H2PO4- had a relatively poor impact. Quenching experiments showed that both sulfate radicals ([Formula: see text]) and hydroxyl radicals (·OH) were generated in the PMS reaction system, and the [Formula: see text] was the dominant active radical. During 3 cycles experiments, an acceptable AO7 conversion ratio (91.8%) within 30 min arrived, suggesting the good stability of NaA zeolite supported Co2Fe1.

Heat induced superfast diclofenac removal in Cu(II)-activated peracetic acid system: Mediation from non-radical to radical pathway

A Cu(II)/heat coactivated peracetic acid (PAA) system for enhancing diclofenac (DCF) degradation was proposed in this work. The superiority of this synergetic activation strategy for PAA, working reactive species, catalytic mechanism and effects of reaction parameters on DCF elimination in this system were simultaneously investigated. Based on our results, the DCF loss rate in Cu(II)-heat/PAA process at pH 8.0 was about 49.3 and 4.2 times of that in Cu(II)/PAA and heat/PAA processes, respectively. Increasing the reaction temperature to 60 оC not only motivated the conversion of Cu(II) to Cu(I) but also facilitated the one-electron transfer between Cu(I) and PAA, boosting the generation of radicals. Organic radicals (mainly CH3C(O)O• and CH3C(O)OO•) were evidenced to be the core oxidizing substances dominating in the destruction of DCF while hydroxyl radical (•OH) made a minor contribution in this system by electron paramagnetic resonance (EPR) method together with scavenging experiments. This study broads the eyes into enhanced PAA activation initiated by homogenous Cu(II), providing a simple but efficient tool to degrade micropollutants.

Fast degradation of atrazine by nZVI-Cu0/PMS: Re-evaluation and quantification of reactive species, generation pathways, and application feasibility

Additive metal to zero-valent iron (ZVI) could enhance the reduction ability and the additive Cu0 was incorporated to ZVI to accelerate PMS activation with atrazine (ATZ) as target compound. The efficiencies of ATZ degradation and PMS decomposition climbed up firstly and then declined as Cu0 loading increased from 0.01 to 1.00 wt% with the maximums at 0.10 wt%. SO4•-, HO•, Fe(IV), O2•- and 1O2 were generated by nZVI-Cu0/PMS based on the results of electron paramagnetic resonance (EPR) and simultaneous degradation of nitrobenzene, ATZ, and methyl phenyl sulfoxide (PMSO). The rate constant of Fe(IV) and ATZ was estimated as 7 × 104 M-1∙s-1 via the variation of methyl phenyl sulfone (PMSO2)formation at different ATZ concentrations. However, Fe(IV) contributed negligibly to ATZ degradation due to the strong scavenging of Fe(IV) by PMS. SO4•- and HO• were the reactive species responsible for ATZ degradation and the yield ratio of SO4•- and HO• was about 8.70 at initial stage. Preliminary thermodynamic calculation on the possible activation ways revealed that the dominant production of SO4•- might originate from the atomic H reduction of PMS in the surface layer of nZVI-Cu0. Ten products of ATZ degradation were identified by HPLC/ESI/QTOF and the possible degradation pathways were analyzed combined with theoretical calculation on ATZ structure. The decrease of temperature or increase of solution pH led to the decline of ATZ degradation, as well as the individual addition of common ions (HCO3-, Cl-, SO42-, NH4+, NO3- and F-) and natural organic matters (NOM). In real water, ATZ was still efficiently degraded with the decontamination efficiency decreasing in the sequence of tap water > surface water > simulated wastewater > groundwater. For the treatment of ATZ-polluted continuous flow, nZVI-Cu0 in double-layer layout had a higher capacity than the single-layer mode. Meanwhile, the leaching TFe and TCu were limited. The results indicate nZVI-Cu0/PMS is applicable and the multiple-layer layout of nZVI-Cu0 is suggested for ATZ-polluted ground water and soil remediation.

Kinetics and mechanism of sulfate radical-and hydroxyl radical-induced disinfection of bacteria and fungal spores by transition metal ions-activated peroxymonosulfate

Peroxymonosulfate(PMS)-based advanced oxidation process have been recognized as efficient disinfection processes. This study comprehensively investigated the role of sulfate radical (SO4•-) and hydroxyl radical (•OH)-driven disinfection of bacteria and fungal spores by the PMS/metals ions (Me(II)) systems and modeled the CT value based on the relationship between survival and ∫[Radical]dt, with the aim to provide an accurate and quantitative kinetic data of inactivation processes. The results indicated that •OH played a more central role than SO4•- in the inactivation process, and bacteria were more vulnerable to radical attack than fungal spores due to the differences in antioxidant mechanisms and external structures. The k value of •OH -induced inactivation of E. coli was approximately 3-fold higher than that of A. niger, and the shoulder length of •OH -induced inactivation of E. coli was closely 52-fold shorter than that of A. niger after treated with the PMS/Co(II) system. The morphological and biochemical changes revealed that PMS/Me(II) treatment caused membrane damage, intracellular ROS accumulation and esterase activity loss in microorganisms. This study significantly improved the understanding of the contribution of radicals in the process of microbial inactivation by PMS/Me(II) and would provide important implications for the further development of technologies to cope with the highly resistant fungal spores in drinking water.

Trace Cu(II)-Mediated Selective Oxidation of Benzothiazole: The Predominance of Sequential Cu(II)-Cu(I)-Cu(III) Valence Transition and Dissolved Oxygen

Trace Cu(II), which inherently exists in soil and some water/wastewater, can trigger persulfate oxidation of some pollutants, but the oxidation capability and mechanism are not well understood, especially toward refractory pollutants. We report in this research that benzothiazole (BTH), a universal refractory pollutant typically originating from tire leachates and various industrial wastewater, can be facilely and selectively removed by peroxydisulfate (PDS) with an equimolar BTH/PDS stoichiometry in the presence of environmental-relevant contents of Cu(II) (below several micromoles). Comprehensive scavenging tests, electron spin resonance analysis, spectroscopy characterization, and electrochemical analysis, revealed that PDS first reduces the BTH-coordinated Cu(II) to Cu(I) and then oxidizes Cu(I) to high-valent Cu(III), which accounts for the BTH degradation. Moreover, once the reaction is initiated, the superoxide radical is probably produced in the presence of dissolved oxygen, which subsequently dominates the reduction of Cu(II) to Cu(I). This facile oxidation process is also effective in removing a series of BTH derivatives (BTHs) that are of environmental concern, thus can be used for their source control. The results highlight the sequential Cu(II)-Cu(I)-Cu(III) transition during PDS activation and the crucial role of contaminant coordination with Cu(II) in oxidative transformation.

Insight into Chinese medicine residue biochar combined with ultrasound for persulfate activation in atrazine degradation: Acanthopanax senticosus precursors, synergistic effects and toxicity assessment

The synergistic activation of persulfate by multiple factors could degrade pollutants more efficiently. However, the co-activation method based on metal ions has the risk of leakage. The non-metallic coupling method could achieve the same efficiency as the metal activation and meanwhile release environmental stress. In this study, the original biochar (BC) was prepared through using Chinese medicinal residue of Acanthopanax senticosus as the precursor. Compared with other biochar, the pore size structure was higher and toxicity risk was lower. The ultrasonic (US)/Acanthopanax senticosus biochar (ASBC)/persulfate oxidation system was established for Atrazine (ATZ). Results showed that 45KHz in middle and low frequency band cooperated with ASBC600 to degrade nearly 70 % of ATZ within 50 min, and US promoted the formation of SO₄^- and OH. Meanwhile, the synergy index of US and ASBC was calculated to be 1.18, which showed positive synergistic effect. Finally, the potential toxicity was examined by using Toxicity Characteristic Leaching Procedure (TCLP) and luminescent bacteria. This study provides a promising way for the activation of persulfate, which is expected to bring a new idea for the win-win situation of pollutant degradation and solid waste resource utilization.

Novel strategy for copper precipitation from cupric complexes wastewater: Catalytic oxidation or reduction self-decomplexation?

Cupric (Cu(II)) complexes in industrial wastewater are responsible for the failure of conventional alkaline precipitation, but the properties of cuprous (Cu(I)) complexes at alkaline circumstance have not been focused. This report proposed a novel strategy for the remediation of Cu(II)-complexed wastewater by coupling alkaline precipitation with green benign reductant, namely, hydroxylamine hydrochloride (HA). This remediation process (HA-OH) exhibits superior Cu removal efficiency that cannot be achieved with the same dosage of oxidants (3 mM). The possibility of Cu(I) activated O₂ catalysis and self-decomplexation precipitation were investigated, and the results identified that ¹O₂ was generated from Cu(II)/Cu(I) cycle, but it was insufficient to annihilate organic ligands. Cu(I) self-decomplexation was the dominate mechanism of Cu removal. For real industrial wastewater, HA-OH process can realize the efficient Cu₂O precipitation and Cu recovery. This novel strategy utilized intrinsic pollutant in wastewater without introducing other metals, complicated materials, and expensive equipment, broadening the insight for the remediation of Cu(II)-complexed wastewater.

Selective degradation of antibiotic in a novel Cu7S4/peroxydisulfate system via heterogeneous Cu(III) formation: Performance, mechanism and toxicity evaluation

Efficient degradation of antibiotic by peroxydisulfate (PDS)-based advanced oxidation processes in complex water environment is challenging due to the interference of impurities and the low activation efficiency of PDS caused by its symmetric structure. Herein, a novel Cu₇S₄/PDS system was developed, which can selectively remove tetracycline hydrochloride (TC) without interference of inorganic ions (e.g., Cl^- and HCO₃^-) and natural organic matter (e.g., humic acid). The results of quenching and probe experiments demonstrated that surface high-valent copper species (Cu(III)), rather than radicals and ¹O₂, are main active species for TC degradation. Cu(III) can be generated via Cu(I)/O₂ and Cu(II)/Cu(I)/PDS systems and the S species on the surface of Cu₇S₄ promotes the cycle of Cu(II)/Cu(I) and Cu(III)/Cu(II), resulting in continuous generation of Cu(III). In addition, the degradation pathways of TC were proposed based on product analysis and DFT theory calculations. The acute toxicity, developmental toxicity and mutagenicity of treated TC were significantly reduced according to the results of toxicity estimation software tool. This study shows a promising Cu₇S₄/PDS system for the degradation and detoxication of antibiotic in complex water environment, while also providing a comprehensive understanding of PDS activation by Cu₇S₄ to generate active Cu(III) species.

Copper Nanowire Networks: An Effective Electrochemical Peroxymonosulfate Activator toward Nitrogenous Pollutant Abatement

Herein, we developed an electrochemical filtration system for effective and selective abatement of nitrogenous organic pollutants via peroxymonosulfate (PMS) activation. Highly conductive and porous copper nanowire (CuNW) networks were constructed to serve simultaneously as catalyst, electrode, and filtration media. In one demonstration of the CuNW network's capability, a single pass through a CuNW filter (τ < 2 s) degraded 94.8% of sulfamethoxazole (SMX) at an applied potential of -0.4 V vs SHE. The exposed {111} crystal plane of CuNW triggered atomic hydrogen (H*) generation on sites, which contributed to effective PMS reduction. Meanwhile, with the involvement of SMX, a Cu-N bond was formed by the interactions between the -NH₂ group of SMX and the Cu sites of CuNW, accompanied by the redox cycling of Cu²⁺/Cu⁺, which was facilitated by the applied potential. The different charges of the active Cu sites made it easier to withdraw electrons and promote PMS oxidation. Theoretical calculations and experimental results were combined to suggest a mechanism for pollution abatement with CuNW networks. The results showed that system efficacy for the degradation of a wide array of nitrogenous pollutants was robust across a broad range of solution pH and complex aqueous matrices. The flow-through operation of the CuNW filter outperformed conventional batch electrochemistry due to convection-enhanced mass transport. This study provides a new strategy for environmental remediation by integrating state-of-the-art material science, advanced oxidation processes, and microfiltration technology.

Cu(II) assisted peroxymonosulfate for antibiotic resistant bacteria inactivation: A potential disinfection technology in swimming pool

Alternative disinfection technology to chlorination is required to control the risk of antibiotic resistance in swimming pools. In this study, copper ions (Cu(II)), which often exist in swimming pools as algicides, were used to activate peroxymonosulfate (PMS) for the inactivation of ampicillin-resistant E. coli. Cu(II) and PMS showed synergistic effects on E. coli inactivation in weak alkaline conditions, obtaining 3.4 log inactivation in 20 min with 10 μM Cu(II) and 100 μM PMS at pH 8.0. Quenching experiments indicated that radicals (i.e., OH and SO₄^-) were not the main disinfectors for E. coli inactivation. Based on the structure of Cu(II) and density functional theory calculations, the Cu(II)-PMS complex (Cu(H₂O)₅SO₅) was recommended as the active species for E. coli inactivation. Under the experimental conditions, the PMS concentration had a greater influence on E. coli inactivation than the Cu(II) concentration, possibly because increasing PMS concentration accelerates ligand exchange reaction and facilitates active species generation. By forming hypohalous acids, halogen ions could improve the disinfection efficiency of Cu(II)/PMS. The addition of HCO₃^- concentration (from 0 to 1.0 mM) and humic acid (0.5 and 1.5 mg/l) did not significantly inhibit the E. coli inactivation. The feasibility of adding PMS to waters containing Cu(II) for the inactivation of antibiotic-resistant bacteria was validated in actual swimming pool waters, where 4.7 log inactivation of E. coli was achieved in 60 min.

Phosphate enhanced Cu(II)/peracetic acid process for diclofenac removal: Performance and mechanism

Since limitedly existing researches suggested Cu(II) had deficiently catalytic ability to PAA, in this work, we tested the oxidation performance of Cu(II)/PAA system on diclofenac (DCF) degradation under neutral conditions. It was found that overwhelming DCF removal could be obtained in Cu(II)/PAA system at pH 7.4 using phosphate buffer solution (PBS) compared to poor loss of DCF without PBS, and the apparent rate constant of DCF removal in PBS/Cu(II)/PAA system was 0.0359 min^-1, 6.53 times of that in Cu(II)/PAA system. Organic radicals (i.e., CH₃C(O)O• and CH₃C(O)OO•) were evidenced as the dominant contributors to DCF destruction in PBS/Cu(II)/PAA system. PBS motivated the reduction of Cu(II) to Cu(I) through chelation effect, and then the activation of PAA by Cu(I) was facilitated. Besides, due to the steric hindrance of Cu(II)-PBS complex (CuHPO₄), PAA activation was mediated from non-radical-generating pathway to radical-generating pathway, leading to desirably effective DCF removal by radicals. The transformation of DCF mainly experienced hydroxylation, decarboxylation, formylation and dehydrogenation in PBS/Cu(II)/PAA system. This work proposes the potential of coupling of phosphate and Cu(II) in optimizing PAA activation for organic pollutants elimination.

Investigation on the reaction kinetic mechanism of polydopamine-loaded copper as dual-functional catalyst in heterogeneous electro-Fenton process

Heterogeneous electro-Fenton (HEF) process has been regarded as a promising method in environmental remediation. However, the reaction kinetic mechanism of the HEF catalyst for simultaneous production and activation of H₂O₂ remained confounded. Herein, the copper supported on polydopamine (Cu/C) was synthesized by a facile method and employed as a bifunctional HEFcatalyst, and the catalytic kinetic pathways were deeply investigated by using rotating ring-disk electrode (RRDE) voltammetry based on the Damjanovic model. Experimental results substantiated that a two-electron oxygen reduction reaction (2e^- ORR) and a sequential Fenton oxidation reaction were proceeded on 1.0-Cu/C, where metallic copper played a crucial role in the fabrication of 2e^- active sites as well as utmost H₂O₂ activation to produce highly reactive oxygen species (ROS), resulting in the high H₂O₂ productivity (52.2%) and the almost complete removal of contaminant ciprofloxacin (CIP) after 90 min. The work not only expanded the idea of reaction mechanism on Cu-based catalyst in HEF process but also provided a promising catalyst for pollutants degradation in wastewater treatment.

Ultrasmall nitrogen-doped Cu0·92Co2·08O4 nanocrystal-decorated cerium dioxide nanoparticles for fast and complete degradation of ranitidine via permonosulfate activation

A simple and efficient coagulation method was used for the rapid preparation of nitrogen-doped copper-cobalt oxide (N-Cu_0.92Co_2·08O₄) supported on cerium dioxide (CeO₂), that is, N-Cu_0.92Co_2·08O₄@CeO₂. A low concentration of N-Cu_0.92Co_2·08O₄@CeO₂ (0.15 g L^-1) was shown to rapidly activate permonosulfate (PMS) (0.15 g L^-1) to achieve 100% degradation of ranitidine within 10 min. A 100% degradation of ranitidine enabled by the catalyst was achieved over a wide range of pH (5.5-9.0), which could be completed within 8 min in the presence of anionic H₂PO₄^-. Moreover, the N-Cu_0.92Co_2·08O₄@CeO₂ catalyst enabled more than 90% degradation of various typical antibiotics within 30 min, including tetracycline, sulfaixoxazole, and chloramphenicol, with degradation rates of 100%, 93.51%, and 90.01%, respectively. Even after four catalytic cycles, N-Cu_0.92Co_2·08O₄@CeO₂ could be regenerated to achieve 100% degradation of ranitidine. Electrochemical analysis demonstrated that the combination of N-Cu_0.92Co_2·08O₄@CeO₂ and PMS immediately produced a strong current density, thereby rapidly producing reactive oxygen species (ROS) with high performance for the degradation of the target pollutant. Combined ion quenching and electron paramagnetic resonance analyses indicated that the main ROS was the non-free radical ¹O₂. Finally, a plausible ranitidine degradation pathway was deduced based on liquid chromatography-mass spectrometry (LC-MS) analysis, wherein the toxic substance N-nitrosodimethylamine was not produced during the degradation process. In short, this study provides a new perspective for preparing ternary metal catalysts for advanced oxidation processes with practical application significance.

Peroxymonosulfate activation by graphene oxide-supported 3D-MoS2/FeCo2O4 sponge for highly efficient organic pollutants degradation

To address conventional powder catalysts' recovery and aggregation issues that greatly restrain their practical application, a recoverable graphene oxide (GO)-supported 3D-MoS₂/FeCo₂O₄ sponge (SFCMG) was developed through a simple impregnation pyrolysis method. SFCMG can efficiently activate peroxymonosulfate (PMS) to produce reactive species for rapid degradation of rhodamine B (RhB), with 95.0% and 100% of RhB being removed within 2 min and 10 min, respectively. The presence of GO enhances the electron transfer performance of the sponge, and the three-dimensional melamine sponge serves as a substrate to provide a highly dispersed carrier for FeCo₂O₄ and MoS₂/GO hybrid sheets. SFCMG exhibits a synergistic catalytic effect of Fe and Co, and facilitates the redox cycles of Fe(III)/Fe(II) and Co(III)/Co(II) by MoS₂ co-catalysis, which enhances its catalytic activity. Electron paramagnetic resonance results demonstrate that SO₄^•-, ·O₂^- and ¹O₂ are all involved in SFCMG/PMS system, and ¹O₂ played a prominent role in RhB degradation. The system has good resistance to anions (Cl^-, SO₄^2-, and H₂PO₄^-) and humic acid and excellent performance for many typical contaminants degradation. Additionally, it works efficiently over a wide pH range (3-9) and possesses high stability and reusability with the metal leaching far below the safety standards. The present study extends the practical application of metal co-catalysis and offers a promising Fenton-like catalyst for the treatment of organic wastewater.

Overlooked impacts of natural organic matter conversion in a Fe(II)-induced peroxymonosulfate activation system for river water remediation

The peroxymonosulfate (PMS) process may be hindered severely due to natural organic matter (NOM) conversion in the treatment of emerging pollutants from river water, becoming a critical engineering and technical issue. In this study, a Fe(II)-induced river water (RW)/PMS catalytic system was constructed for investigating molecular transformation of NOM and related influence mechanism to sulfamethoxazole (SMX) degradation. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) analysis indicated that NOM molecules containing no more than one heteroatom in river may be attacked by hydroxyl radicals (OH) and then polymerized, converting into molecules with two or three heteroatoms during PMS oxidation. Based on the correlation analysis, CHONP-NOM, CHOSP-NOM and CHONSP-NOM showed a significant inhibition against SMX degradation, while CHONS-NOM exhibited a moderate inhibitory effect. Besides, more condensed aromatic structures, carbohydrates and tannins were generated via reactive species (OH and sulfate radicals (SO₄^-)) oxidation, radical addition and polymerization reactions. Notably, condensed aromatic structures, carbohydrates and tannins presented weak, modest and strong inhibition to SMX degradation, respectively. Based on the current results, the inhibition of target pollutants degradation would be mitigated via regulation of NOM molecules in a Fe(II)-induced PMS activation system, providing valuable information to reduce NOM impact. In addition, this study paves the way to achieve efficient removal of emerging pollutants from river water.

Effective degradation of tetracycline via recyclable free-standing three-dimensional copper-based graphene as a persulfate catalyst

Water pollution by antibiotics is a serious and growing problem. Given this challenge, a free-standing three-dimensional (3D) reduced graphene oxide foam supported copper oxide nanoparticles (3D-rGO-Cu_xO) was synthesized using GO as a precursor and applied as an efficient persulfate activator for tetracycline (TC) degradation. The influences of Cu_xO mass, solution pH, persulfate dosage, and common anions on the TC degradation were investigated in detail. Analytical techniques indicated that the 3D-rGO-Cu_xO showed a cross-linking three-dimensional network structure, and Cu_xO particles with irregular shapes were uniformly loaded on graphene pore walls. The XPS and Auger spectra of Cu confirmed that Cu₂O was the main component in solid copper compounds. The addition of Cu_xO was vitally important for the activation of the oxidation system, and the removal rate reached 98% with a Cu_xO load of 7:1. The pH showed little influence on the activation effect on TC degradation. For common anions, Cl^- and CO₃^2- had little influence on the system, while humic acid had a great inhibitory effect. The EPR test and quenching experiment revealed that the active substances in the oxidative degradation process mainly include SO₄^-·, ·OH, ¹O₂, and reactive Cu(III). Additionally, the 3D-rGO-Cu_xO material proved highly stable according to the replicated test results and was promising for the remediation of antibiotic-contaminated water.

Peroxymonosulfate activated by natural porphyrin derivatives for rapid degradation of organic pollutants via singlet oxygen and high-valent iron-oxo species

The activation of peroxymonosulfate (PMS) by sodium ferric chlorophyllin (SFC), a natural porphyrin derivative extracted from chlorophyll-rich substances, was systematically investigated for facile degradation of bisphenol A (BPA). SFC/PMS is capable of degrading 97.5% of BPA in the first 10 min with the initial BPA concentration of 20 mg/L and pH = 3, whereas conventional Fe²⁺/PMS could only remove 22.6% of BPA under identical conditions. It demonstrates a prominent flexibility to a broad pH range of 3-11 with complete pollutant degradation. A remarkable tolerance toward concomitant high concentration of inorganic anions (100 mM) was also observed, among which (bi)carbonates can even accelerate the degradation. The nonradical oxidation species, including high-valent iron-oxo porphyrin species and ¹O₂, are identified as dominant species. Particularly, the generation and participation of ¹O₂ in the reaction is evidenced by experimental and theoretical methods, which is vastly different from the previous study. The specific activation mechanism is unveiled by density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The results shed light on effective PMS activation by iron (III) porphyrin and the proposed natural porphyrin derivative would be a promising candidate for efficient abatement of recalcitrant pollutants toward complicated aqueous media in wastewater treatment.

Electron-transfer pathways insights into contaminants oxidized by Cu-OOSO3- intermediate: Effects of oxidation states of Cu and solution pH values

The copper-peroxy complex (Cu-OOSO₃^-) metastable intermediate has been confirmed to oxidize contaminants via a single-electron-transfer pathway or an oxygen-atom-transfer pathway. And the effects of Cu oxidation states and reaction pH conditions on the intermediate properties have not been explored in depth. Here, copper oxide (CuO_x) catalysts with different Cu oxidation states were synthesized by a simple precipitation method by controlling the reaction temperature from 0 to 45 °C. CuO_x displayed a strong catalytic dependence on the Cu oxidation state, and CuO_x-30 with Cu average valence on the catalyst surface of 1.61 was more reactive for catalytic degradation of bisphenol A with peroxymonosulfate (PMS). Notably, CuO_x-30, with the best electron-accepting ability, was easier to bonding with PMS to form the Cu-OOSO₃^- reactive complex, and the generated intermediate exhibited the strongest capacity to obtain electrons from contaminants. Moreover, the electron-transfer pathways were closely related to the average valence of Cu, and the contribution of the oxygen-atom-transfer pathway changed volcanic with increasing Cu valence. Meanwhile, the reaction predominantly involved the oxygen-atom-transfer pathway under acidic conditions (pH=3), while the contribution of the single-electron-transfer pathway raised with increasing pH values. Hence, this work was devoted to providing new insights into the CuO_x-inducing PMS activation and vital supplementary to the properties of the Cu-OOSO₃^- intermediate.

Targeted Decomplexation of Metal Complexes for Efficient Metal Recovery by Ozone/Percarbonate

Traditional methods cannot efficiently recover Cu from Cu(II)-EDTA wastewater and encounter the formation of secondary contaminants. In this study, an ozone/percarbonate (O₃/SPC) process was proposed to efficiently decomplex Cu(II)-EDTA and simultaneously recover Cu. The results demonstrate that the O₃/SPC process achieves 100% recovery of Cu with the corresponding k_obs value of 0.103 min^-1 compared with the typical ^•OH-based O₃/H₂O₂ process (81.2%, 0.042 min^-1). The carbonate radical anion (CO₃^•-) is generated from the O₃/SPC process and carries out the targeted attack of amino groups of Cu(II)-EDTA for decarboxylation and deamination processes, resulting in successive cleavage of Cu-O and Cu-N bonds. In comparison, the ^•OH-based O₃/H₂O₂ process is predominantly responsible for the breakage of Cu-O bonds via decarboxylation and formic acid removal. Moreover, the released Cu(II) can be transformed into stable copper precipitates by employing an endogenous precipitant (CO₃^2-), accompanied by toxic-free byproducts in the O₃/SPC process. More importantly, the O₃/SPC process exhibits excellent metal recovery in the treatment of real copper electroplating wastewater and other metal-EDTA complexes. This study provides a promising technology and opens a new avenue for the efficient decomplexation of metal-organic complexes with simultaneous recovery of valuable metal resources.

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.

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

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

Thiosulfate enhanced Cu(II)-catalyzed Fenton-like reaction at neutral condition: Critical role of sulfidation in copper cycle and Cu(III) production

Thiosulfate (S₂O₃^2-) has been proven to be an effective promoter of Fenton-like reactions by accelerating the metal ions cycle. However, up to now, little is known about the role of sulfur transformation and intermediate sulfur in the regulation of metal chemical cycle and reactive species production. Herein, free Cu(II) was selected as catalyst for the activation of H₂O₂. The introduction of S₂O₃^2- significantly enhanced the degradation of benzoic acid, and the degradation rate (k_obs) was 5.8 times that of Cu(II)/H₂O₂ system. The kinetic model revealed the transformation of sulfur species and demonstrated that sulfides (i.e., HS^-/S^2-, S₂O₃^2-) and S⁰ were the dominant electron donor for the reduction of Cu(II) into Cu(I). Consequently, the reduction and complexation roles of S₂O₃^2- significantly resolve the rate-limiting step and broaden the pH range of in Fenton-like reactions. Evidence for the critical role of high-valent copper (Cu(III)) and HO^• on BA degradation was obtained by scavengers experiments, electron paramagnetic resonance and fluorescent probes. Meanwhile, the Cu(II)/H₂O₂/S₂O₃^2- system also exhibited satisfactory anti-interference ability of the various matrix. Overall, this study offers mechanistic insight into sulfidation in Cu chemical cycle and Cu(III) generation, and highlights the potential of S₂O₃^2- for Fenton-like reactions to control pollutants.

Magnetic confinement-enabled membrane reactor for enhanced removal of wide-spectrum contaminants in water: Proof of concept, synergistic decontamination mechanisms, and sustained treatment performance

Membrane chemical reactors (MCRs) have demonstrated a great potential for simultaneous removal of wide-spectrum pollutants in advanced water treatment. However, current catalyst (re)loading and catalytic reactivity limitations obstruct their practical applications. Herein, as a proof-of-concept, we report a hollow fiber membrane chemical reactor (HF-MCR) with high and sustainable catalytic reactivity, enabled by novel magnetic confinement engineering of the catalysts. Namely, the zerovalent iron (ZVI) nanocatalysts were spatially dispersed and confined to nearly parallel magnetic induction lines, forming forest-like microwire arrays in the membrane lumen. Such arrays exhibited ultrahigh hydrodynamic stability. The HF-MCR integrated sequential membrane separation and Fenton-like catalysis, thus being capable of high and synergistic wide-spectrum decontamination. The membrane separation process completely removed large nanoplastics (NPs) via size exclusion, and thus the subsequent Fenton-like catalysis process enhanced removal efficiency of otherwise permeated bisphenol A (BPA) and phosphate (P) by in situ generated reactive oxygen species (primarily ¹O₂) and iron (oxyhydr)oxides, respectively. Furthermore, highly dispersed ZVI arrays and their continuous surface depassivation driven by magnetic gradient and hydrodynamic forces conferred abundant accessible catalytic sites (i.e., Fe⁰ and Fe^II) to stimulate Fenton-like catalysis. The consequent enhancement of BPA and P removal kinetics was 3-765 and 49-492 folds those in conventional (flow-through or batch) systems, respectively. Periodic ZVI reloading ensured sustained decontamination performance of the HF-MCR. This is the first demonstration of the magnetic confinement engineering that enables efficient and unlimited catalyst (re)loading and sustainable catalytic reactivity in the MCR for water treatment, which is beyond the reach of current approaches.

Thermal effect on sulfamethoxazole degradation in a trivalent copper involved peroxymonosulfate system

Persulfate (PS) activated by thermal or homogeneous metals can generate reactive oxygen species (ROS) and high-valence-state metals for contaminants degradation, showing great potential for applications. However, thermal effect in peroxymonosulfate (PMS) system with high-valence-state metal is still ambiguous. In this study, divalent copper (Cu(II)) catalysis was taken to explore thermal effect on PMS performance. Results showed that the Sulfamethoxazole (SMX) removal efficiency in the Cu(II)/PMS system at 60 min increased by only 5.9% with temperature increase from 30 °C to 60 °C. Moreover, SMX removal efficiency was excellent at neutral or basic pH, best with PMS concentration of 2.4 mM, and slightly affected by Cu(II) concentration. The singlet oxygen (¹O₂) was identified as main active species at low temperature while sulfate radicals (SO₄^-) was more effective at high temperature with Cu(II) co-activation. Also, trivalent copper (Cu(III)) was an important active species. The higher Cu(III) content, the better SMX removal efficiency, but the stronger intermediates toxicity. In combination with removal efficiency and intermediates toxicity at different temperatures, 30 °C was the optimal reaction temperature. Overall, this study provides new perspective on utilization of waste heat and high-valence-state metal for organic wastewater treatment in PMS systems.