Heterogeneous Degradation of Organic Pollutants by Persulfate Activated by CuO-Fe3O4: Mechanism, Stability, and Effects of pH and Bicarbonate Ions

Synergistic activation of peroxydisulfate with magnetite and copper ion at neutral condition

Magnetite is known to exhibit high catalytic reactivity in Fenton-like reactions merely at low pH conditions. Here we report the association of Cu²⁺ ion can significantly enhance peroxydisulfate (PDS) activation with magnetite under environmental aquatic conditions (near neutral pH). Cu²⁺ is able to synergistically activate PDS with magnetite to generate radicals, e.g., SO₄^·-, at neutral or slightly alkaline pH, and such synergistic activation of PDS is promising to degrade various contaminants in groundwater. In-depth study reveals Cu²⁺ ion adsorbed on magnetite plays a crucial role in PDS activation. The adsorbed Cu²⁺ is labile to be reduced by the structural Fe(II) on magnetite to generate Cu⁺, which is relatively stable in the presence of magnetite at neutral or alkaline pH, but extremely unstable at acidic pH. The generated Cu⁺ on magnetite surface, rather than Cu²⁺, contributes to PDS activation in the reaction system, and the recycling of Cu⁺/Cu²⁺ sustains continuous activation of PDS. This study is among the first to report the synergistic activation of PDS by magnetite and Cu²⁺ ion at neutral pH, and unambiguously discern the role of Cu⁺ in PDS activation. The new mechanistic knowledge provides a more accurate understanding of PDS activation by natural minerals in environmental remediation.

The removal of azo dye from aqueous solution by oxidation with peroxydisulfate in the presence of granular activated carbon: Performance, mechanism and reusability

Granular activated carbon (GAC) was used as catalyst for the activation of peroxydisulfate (PDS) to decolorize and degrade Acid Orange 7 (AO7) in water. EPR spectra and radical quencher experiments were employed to identify the active species for AO7 oxidation in the PDS/GAC system. Linear sweep voltammetry (LSV) and chronoamperometry test were carried out to identify the contribution of nonradical mechanism for AO7 decay. The investigation of crucial operational parameters on the decolorization indicated 100 mg/L AO7 can be almost totally decolorized in a broad range of pH. Common inorganic anions adversely affect the AO7 decolorization process and the inhibition was in the order of: HCO₃^- > H₂PO₄^- > SO₄^2- > Cl^- > NO₃^-. UV-vis spectra showed the destruction of the aromatic moiety of AO7 molecule during the oxidation reaction of the PDS/GAC system. The transformation of nitrogen related to the azo bond in AO7 molecule in this system was observed by monitoring the released N-containing inorganic ions. Recycle experiments showed GAC cannot be reused directly but its catalytic ability can be restored by using electrochemical method.

Facile synthesis of Cu-CuFe2O4 nanozymes for sensitive assay of H2O2 and GSH

Artificial enzymes have drawn substantial research interest from the scientific community due to their advantages over natural enzymes. However, majority of artificial enzymes exhibit low affinity towards H2O2, which means that a high H2O2 concentration is needed for the oxidation of a substrate such as 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxTMB. With this concern, Cu-CuFe2O4 was facilely synthesized, wherein, Cu0 accelerates the redox capacity of Cu-CuFe2O4 as well as the electron transfer between CuFe2O4 and H2O2. These materials induce excellent activity as a peroxidase. Cu-CuFe2O4 shows high affinity towards H2O2 with lower Michaelis-Menten constant (Km) than the reported values for ferrites and Horseradish enzyme (HRP). Moreover, it took only 5 min to detect hydrogen peroxide (H2O2) and glutathione (GSH) through a colorimetric assay using Cu-CuFe2O4. Compared with CuFe2O4, the limit of detection (LOD) is about 90-fold lower for H2O2 using Cu-CuFe2O4. In addition, Cu-CuFe2O4 shows high stability as a nanozyme. Thus, the mechanism of the peroxidase-like nanozyme Cu-CuFe2O4 is proposed.

Peroxymonosulfate Activation by Fe-Co-O-Codoped Graphite Carbon Nitride for Degradation of Sulfamethoxazole

Graphite carbon nitride (g-C₃N₄) has a stable structure but poor catalytic capability for activating peroxymonosulfate (PMS). In this study, the codoping of g-C₃N₄ with bimetallic oxides (iron and cobalt) and oxygen was investigated to enhance its catalytic capability. The results showed that iron, cobalt, and oxygen codoped g-C₃N₄ (Fe-Co-O-g-C₃N₄) was successfully prepared, which was capable of completely degrading sulfamethoxazole (SMX) (0.04 mM) within 30 min, with a reaction rate of 0.085 min^-1, indicating the superior catalytic activity of Fe-Co-O-g-C₃N₄. The mineralization efficiency of SMX was 22.1%. Sulfate radicals and singlet oxygen were detected during the process of PMS activation. However, the role that singlet oxygen played in degrading SMX was not obvious. Surface-bound reactive species and sulfate radicals were responsible for SMX degradation, in which sulfate radicals contributed to 46.6% of SMX degradation. The superior catalytic activity was due to the synergistic effect of metal oxides and O-g-C₃N₄, in which O-g-C₃N₄ could act as a carrier and an activator as well as an electron mediator to promote the conversion of Fe(III) to Fe(II) and Co(III) to Co(II). Four main steps of SMX degradation were proposed, including direct oxidation of SMX, bond fission of N-C, bond fission of N-S, and bond fission of S-C. The effect of the pH, temperature, PMS concentration, chloridion, bicarbonate, and humic acids on SMX degradation was investigated. Cycling experiments demonstrated the good stability of Fe-Co-O-g-C₃N₄. This study first reported the preparation of bimetallic oxide and oxygen codoped g-C₃N₄, which was an effective PMS activator for degradation of toxic organic pollutants.

Regulating the redox centers of Fe through the enrichment of Mo moiety for persulfate activation: A new strategy to achieve maximum persulfate utilization efficiency

Persulfate Fe-based catalytic oxidation is considered as one of the most attractive strategy for the growing concerns of water pollution. However, the undesirable Fe^III/Fe^II redox cycle restrict them from attending the sustainable activity during practical applications. This study was intended to develop a new strategy to regulate the redox cycles of Fe^III/Fe^II by introducing the second redox center of MoS₄^2- in the interlayers of Fe-based layered double hydroxide (FeMgAl-MoS₄ LDH). Based on the first-order kinetic model, the fabricated FeMgAl-MoS₄ catalyst was 10-100 fold more reactive than the bench marked peroxymonosulfate (PMS) activators including FeMgAl LDHs and other widely reported nano-catalysts such as Co₃O₄, Fe₃O₄, α-MnO₂, CuO-Fe₃O₄ and Fe₃O₄. The enhanced catalytic activity of FeMgAl-MoS₄ LDH was related to the continuous regeneration of active sites (Fe^II/Mo^IV), excellent PMS utilization efficiency and generation of abundant free radicals. Moreover, the FeMgAl-MoS₄/PMS system shows an effective pH range from 3.0 to 7.0 and the degradation kinetics of parahydroxy benzoic acid (PHB) were not effected in the presence of huge amount of background electrolytes and natural organic matters. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR), chemical scavengers, XPS analysis and gas chromatography couple with mass spectrometer (GC-MS), a degradation pathway based on dominant free radicals (•SO₄^- and •OH), passing through the redox cycles of Fe^III/Fe^II and Mo^VI/Mo^IV was proposed for PMS activation. We believe that this strategy of regulating the redox center through MoS₄^2- not only provides a base to prepare new materials with stable catalytic activity but also broaden the scope of Fe-based material for real application of contaminated water.

Fe-Activated Peroxymonosulfate Enhances the Degradation of Dibutyl Phthalate on Ground Quartz Sand

Soil contamination by organic compounds has received worldwide concern for decades. Here, we found that dibutyl phthalate (DBP) could be degraded on moist quartz sand (QS, crystal, a typical soil constituent) during stirring, and the removal rate reached 57.2 ± 3.1% after 8 h of reaction. The introduction of peroxymonosulfate (PMS) and zerovalent iron (Fe⁰) substantially improved the decomposition of DBP to 94.2 ± 1.6% in 8 h, suggesting they have great contributions. DBP decomposition was caused by multiple reactive species, such as surface silicon-based radicals (like ≡SiO^•) and other reactive species like superoxide radical (O₂^•-), hydroxyl radical (^•OH), and sulfate radical (SO₄^•-). In the QS/ultrapure water system, DBP was mainly attacked by O₂^•- or ≡SiO^•, with the formation of hydrolysis products. In the iron@QS/PMS system, due to the activation of PMS by Fe⁰, SO₄^•- and ^•OH were produced while the latter led to DBP degradation, and thus hydroxyl substitution products of DBP were ubiquitous. DBP was hardly removed on amorphous supporters like silica gel, alumina, and red soil even with the presence of PMS and Fe⁰, indicating the indispensable role of surface radicals on crystals like QS. This work presents a new remediation technology for polluted soil, especially aquifer.

General synthesis of carbon and oxygen dual-doped graphitic carbon nitride via copolymerization for non-photochemical oxidation of organic pollutant

Earth-abundant, environmental-benign and durable catalysts are of paramount importance for remediation of organic pollutants, and graphitic carbon nitride (g-C₃N₄) is a promising nonmetallic material for this application. However, the catalytic oxidation on g-C₃N₄ suffers from low efficiency because of its chemical inertness if not irradiated with light. Herein, we develop a facile copolymerization strategy for the synthesis of carbon and oxygen dual-doped g-C₃N₄ using urea as g-C₃N₄ precursor and ascorbic acid (AA) as carbon and oxygen sources, which induces electronic structure reconfiguration. By replacing AA with other organic precursors, a series of C and O dual-doped g-C₃N₄ are successfully prepared, demonstrating the generality of the developed methodology. As a demonstration, the C and O dual-doped g-C₃N₄ using AA as the organic precursor (CN-AA_0.3) exhibits pronouncedly enhanced catalytic activity in peroxymonosulfate (PMS) activation for organic pollutant degradation without light irradiation compared with pristine g-C₃N₄ and single oxygen-doped g-C₃N₄. Experimental and theoretical results revealed the electron-poor C atoms and electron-rich O atoms as active sites for PMS activation in terms of simultaneous PMS oxidation and reduction. This work offers a universal approach to synthesize nonmetal dual-doped g-C₃N₄ with reconfigured electronic structure, stimulating the development of g-C₃N₄-based materials for diverse environmental applications.

Non-radical PMS activation by the nanohybrid material with periodic confinement of reduced graphene oxide (rGO) and Cu hydroxides

A new strategy was applied by periodic stacking of active sites of Cu and reduced graphene oxide (rGO) in the form of Cu-rGO LDH nanohybrid material. The experimental results revealed that newly prepared Cu-rGO LDH nanohybrid material was extremely reactive in PMS activation as evident from the degradation rate of 0.115 min^-1, much higher than Mn-rGO LDH (0.071 min^-1), Zn-rGO LDH (0.023 min^-1) or other benchmarked material used during the degradation of bisphenol A (BPA). This excellent activity of Cu-rGO LDH nanohybrid was attributed to the better PMS utilization efficiency as compared to the other catalysts. Additionally, the characterization techniques disclosed that the layer by layer arrangement of active sites in the Cu-rGO LDH catalyst promotes interfacial electron mobility owing to the synergistic association between Cu in LDH and interlayered rGO. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR) and chemical scavengers, singlet oxygen (¹O₂) was unveiled as dominant reactive species for pollutant removal, resulting from the recombination of superoxides (O₂^-) or reduction of active Cu centers. We believe that this novel Cu-rGO LDH/PMS system will open up a new avenue to design efficient metal-carbon nanohybrid catalysts for the degradation of emerging aquatic pollutants in a real application.

Biochar supported CuO composites used as an efficient peroxymonosulfate activator for highly saline organic wastewater treatment

Biochar supported copper oxide composite (BC-CuO) was synthesized and attempted to activate peroxymonosulfate (PMS) for treating highly saline (100-400 mM) wastewater. In the BC-CuO/PMS system, rapid removals of Methylene Blue (MB), Acid Orange 7, Rhodamine B, Atrazine and Ciprofloxacin from the highly saline system were observed within 30 min, attaining a high efficiency of 99.68%, 100%, 100%, 100% and 78.27%, respectively. Meanwhile, the BC-CuO/PMS can remove >88.61% of MB in other salt systems containing one or more salt components and 68.43% of COD from landfill leachate. Experimental results confirmed that sulfate radical (SO₄^▪-), hydroxyl radical (^▪OH) and singlet oxygen (¹O₂) all contributed to the pollutants degradation, but ¹O₂ was dominated in highly saline systems. On the basis of the characterization and analysis data, possible activation mechanisms of the oxygenated functional groups of biochar and hydroxylation of CuO surface accelerating the generation of ¹O₂ were proposed. BC-CuO activating PMS is a promising technique for the removal of organic pollutants from highly saline wastewater or complex background.

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

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

Novel CuCo2O4 Composite Spinel with a Meso-Macroporous Nanosheet Structure for Sulfate Radical Formation and Benzophenone-4 Degradation: Interface Reaction, Degradation Pathway, and DFT Calculation

A series of CuCo₂O₄ composite spinels with an interconnected meso-macroporous nanosheet morphology were synthesized using the hydrothermal method and subsequent calcination treatment to activate peroxymonosulfate (PMS) for benzophenone-4 (BP-4) degradation. As-prepared CuCo₂O₄ composite spinels, especially CuCo-H3 prepared by adding cetyltrimethylammonium bromide, showed superior reactivity for PMS activation. In a typical reaction, BP-4 (10.0 mg/L) was almost completely degraded in 15 min by the activation of PMS (200.0 mg/L) using CuCo-H3 (100.0 mg/L), with only 9.2 μg/L cobalt leaching detected. Even after being used six times, the performance was not influenced by the lower leaching of ions and surface-absorbed intermediates. The possible interface mechanism of PMS activation by CuCo-H3 was proposed, wherein a unique interconnected meso-macroporous nanosheet structure, strong interactions between copper and cobalt, and cycling of Co(II)/Co(III) and Cu(I)/Cu(II) effectively facilitated PMS activation to generate SO₄^•- and ^•OH, which contributed to BP-4 degradation. Furthermore, combined with intermediates detected by liquid chromatography quadrupole time-of-flight mass spectrometry and density functional theory calculation results, the degradation pathway of BP-4 involving hydroxylation and C-C bond cleavage was proposed.

Carbon doped Fe3O4 peroxidase-like nanozyme for mitigating the membrane fouling by NOM at neutral pH

Oxidation is a widely used method in drinking water treatment to mitigate the membrane fouling caused by the natural organic matters (NOM) from the surface water during ultra-filtration (UF) and nano-filtration (NF) processes, and H₂O₂ is one of the common oxidants for it. However, the oxidation capability of H₂O₂ at neutral pH is lower, compared to the acidic and alkaline conditions. In order to improve the efficiency of NOM oxidation at neutral pH, a carbon-doped Fe₃O₄ peroxidase-like nanozyme (CFPN) was synthesized in this study and used as a high-performance catalyst for H₂O₂ to generate hydroxyl radical. The oxygen-containing groups on the carbon structure of CFPN can form an acidic microenvironment, allowing H₂O₂ to produce hydroxyl radical by catalysis in neutral conditions. The results of hydrophilicity analysis, zeta potential, high-performance liquid size exclusion chromatography (HPSEC), Fourier transform infrared spectrum (FTIR) and flux indicated that the hydroxyl radical can oxidize the hydrophobic matters of humic acid (HA) into hydrophilic matters by Fenton reaction or electrophilic addition reaction, which can mitigate the fouling of NF membranes. The results of the same test for the bovine serum albumin (BSA) indicated that the hydroxyl radical can mitigate the fouling of UF membranes by degrading the tertiary and secondary structures of BSA and partly oxidizing the side chain groups. In addition, two types of surface water samples were used to verify the above mechanism, and the results indicated that the hydroxyl radical treatment at neutral pH is a new viable and effective strategy to significantly mitigate the NOM fouling of UF and NF membranes.

One-step preparation of ZVI-sludge derived biochar without external source of iron and its application on persulfate activation

Zero Valent Iron (ZVI) is an important and widely employed environmental remediation material in brownfield. However, the instability of fine size ZVI and the strong aggregation of nanoscale-ZVI limited its further application. To overcome these drawbacks, ZVI-Sludge Derived Biochar (SDBC) was prepared without external iron source through the one-step process of pyrolysis. The characterization results including SEM-EDX, XRD and XPS confirmed the successful loading of Fe⁰ on the surface of SDBC. The activation efficiency of persulfate (PS) in in-situ chemical oxidation system was studied. The environmental remediation properties of ZVI-SDBC/PS system were evaluated employing acid orange (AO7) and landfill leachate as target pollutants. ZVI-SDBC/PS system was highly efficient as that 99.0% of AO7 (0.06 mM) was removed by 0.925 mM of PS and 0.5 g L^-1 of ZVI-SDBC. In addition, total organic carbon (TOC) and ammonia in leachate were removed by 62.8% and 99.8%, respectively. The removal efficiency of AO7 was nearly independent on initial pH as that 89.1% and 99.1% of AO7 were removed at pH of 9.08 and 2.13 respectively. Hydroxyl radicals dominated in the reaction under neutral and alkaline conditions with contribution rates of 71.9% and 86.1% respectively. Noticeably, not only free radicals but also non-radical species such as singlet oxygen contributed to the degradation, which favored the pH-independent performance. The reuse performance of ZVI-SDBC was higher than these of previously reported ZVI-based catalysts as that the first-order rate constant of AO7 removal decreased not much from 0.0718 to 0.0502 min^-1 after the three-cycle reuse assays. In summary, ZVI-SDBC showed advantages such as the facile and chemical-saving preparation method, reliable disposal of municipal sewage sludge, remarkable efficiency and stability. These advantages proved ZVI-SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for environmental remediation in brownfield.

Bioavailability and translocation of metal oxide nanoparticles in the soil-rice plant system

To determine the bioavailability and translocation of metal oxide nanoparticles (MONPs) in the soil-rice plant system, we examined the accumulation and micro-distribution of ZnO nanoparticles (NPs), CuO NPs and CeO₂ NPs (50, 100 and 500 mg/kg) in the paddy soil and rice plants under flooded condition for 30 days using single-step chemical extraction and diffusive gradients in thin films (DGT) technique combined with micro X-ray fluorescence spectroscopy (μ-XRF). The results show that various MONPs changed the soil properties, especially the redox potential was enhanced to -165.33 to -75.33 mV compared to the control. The extraction efficiency of Zn, Cu and Ce in the paddy soil from high to low was EDTA, DTPA, CaCl₂ and DGT. Moreover, exposure to 500 mg/kg CuO NPs and CeO₂ NPs induced the primary accumulation of Cu and Ce elements in rice roots as high as 235.48 mg Cu/kg and 164.84 mg Ce/kg, respectively, while the Zn concentration in shoots was up to 313.18 mg/kg under highest ZnO NPs with a 1.5 of translocation factor. The effect of MONPs on the plant growth was mainly related to the chemical species and solubility of MONPs. Micro-XRF analysis shows that Zn was mostly located in the root cortex while Cu was primarily accumulated in the root exodermis and few Ce distributed in the root. Pearson correlation coefficients indicate that only DTPA-extracted metals in soil were significantly and well correlated to the Zn, Cu and Ce accumulation in rice seedlings exposed to MONPs. This work is of great significance for evaluating the environmental risks of MONPs in soil and ensuring the safety of agricultural products.

Evaluation and prospects of nanomaterial-enabled innovative processes and devices for water disinfection: A state-of-the-art review

This study provided an overview of established and emerging nanomaterial (NM)-enabled processes and devices for water disinfection for both centralized and decentralized systems. In addition to a discussion of major disinfection mechanisms, data on disinfection performance (shortest contact time for complete disinfection) and energy efficiency (electrical energy per order; E_EO) were collected enabling assessments firstly for disinfection processes and then for disinfection devices. The NM-enabled electro-based disinfection process gained the highest disinfection efficiency with the lowest energy consumption compared with physical-based, peroxy-based, and photo-based disinfection processes owing to the unique disinfection mechanism and the direct mean of translating energy input to microbes. Among the established disinfection devices (e.g., the stirred, the plug-flow, and the flow-through reactor), the flow-through reactor with mesh/membrane or 3-dimensional porous electrodes showed the highest disinfection performance and energy efficiency attributed to its highest mass transfer efficiency. Additionally, we also summarized recent knowledge about current and potential NMs separation and recovery methods as well as electrode strengthening and optimization strategies. Magnetic separation and robust immobilization (anchoring and coating) are feasible strategies to prompt the practical application of NM-enabled disinfection devices. Magnetic separation effectively solved the problem for the separation of evenly distributed particle-sized NMs from microbial solution and robust immobilization increased the stability of NM-modified electrodes and prevented these electrodes from degradation by hydraulic detachment and/or electrochemical dissolution. Furthermore, the study of computational fluid dynamics (CFD) was capable of simulating NM-enabled devices, which showed great potential for system optimization and reactor expansion. In this overview, we stressed the need to concern not only the treatment performance and energy efficiency of NM-enabled disinfection processes and devices but also the overall feasibility of system construction and operation for practical application.

A stable and easily prepared copper oxide catalyst for degradation of organic pollutants by peroxymonosulfate activation

A direct one-step calcination preparation of CuO catalyst (CuO-3) using polyethylene glycol (PEG) as nonionic polymeric structure directing agent was developed for activation of peroxymonosulfate (PMS). The morphological and physicochemical properties of the CuO-3 were characterized and the catalytic activity for degradation of organic pollutants was evaluated. The resultant CuO-3 with significantly enhanced surface area exhibited excellent catalytic performance of phenolic organic pollutants degradation. The reaction mechanism of the PMS/CuO system was systematically investigated with a series of radical quenching tests and the analysis of electron paramagnetic resonance (EPR) spectroscopy. Quite different from traditional hydroxyl radicals (OH) and sulfate radical (SO₄^-) based advanced oxidation processes, singlet oxygen (¹O₂) was identified as the dominate reactive species responsible for the degradation of organic pollutants. Moreover, the main formation pathway of ¹O₂ was also investigated. The results indicated that the superoxide radical (O₂^-) was involved in the generation of ¹O₂ as a crucial precursor. Also, the PMS/CuO-3 system exhibited satisfactory stability and reusability under neutral conditions as well as high removal of organic pollutants in the presence of inorganic anions. This work not only provides a novel and stable preparation method for CuO catalyst, but also gives a deeper insight into the mechanisms of PMS activation by CuO.

Degradation of benzene derivatives in the CuMgFe-LDO/persulfate system: The role of the interaction between the catalyst and target pollutants

A novel insight on the role of interactions between target pollutants and the catalyst in the copper-containing layered double oxide (LDO)-catalyzed persulfate (PS) system was elucidated in the present study. 4-Chlorophenol (4-CP), as a representative benzene derivative with a hydroxyl group, was completely removed within 5 min, which was much faster than the reaction of monochlorobenzene (MCB) without a hydroxyl group, with the degradation efficiency of 31.7% in 240 min. Through the use of radical quenching and surface inhibition experiments, it could be concluded that the interaction between 4-CP and CuMgFe-LDO, rather than free radicals, played a key role in the decomposition of 4-CP, while only the free radicals participated in the MCB degradation process. According to electron paramagnetic resonance and X-ray photoelectron spectroscopy data, the formation of a Cu(II)-complex between phenolic hydroxyl groups and surface Cu(II) was primarily responsible for the degradation of phenolic compounds, in which PS accepted one electron from the complex and generated sulfate radicals and chelated radical cations. The chelated radical cations transferred one electron to Cu(II) followed by Cu(I) generation and pollutant degradation successively.

Polyphenol-metal network derived nanocomposite to catalyze peroxymonosulfate decomposition for dye degradation

Persulfate based advanced oxidation process is a promising technology for refractory contaminants removal. Cobalt is considered as the most efficient metal in catalyzing peroxymonosulfate decomposition. Although different cobalt based nanomaterials have been developed, easy aggregation and metal ion leaching during catalytic reaction would result in its deficiency. To address the above issue, in this work, carbon supported Co/CoO core-shell nanocomposite was in-situ fabricated by using polyphenol-metal coordinate as precursor. Results indicated that cobalt nanoparticle with size of 10 nm was successfully prepared and well dispersed within the carbon matrix. By using as-prepared material as catalyst, 50 mg/L orange II was completely removed under the condition of 0.2 g/L peroxymonosulfate, 0.05 g/L catalyst, pH = 4.0-10.0. Both sulfate and hydroxyl radicals were formed during peroxymonosulfate decomposition, while sulfate radical dominated the pollutant removal. Mechanism study revealed that the cobalt was the key site for catalyzing peroxymonosulfate decomposition. This work might provide valuable information in designing and fabricating metal anchored carbon composite catalyst for efficiently and cost-effectively activate peroxymonosulfate.

CuCo2O4 supported on activated carbon as a novel heterogeneous catalyst with enhanced peroxymonosulfate activity for efficient removal of organic pollutants

CuCo₂O₄ was synthesized via a relatively simple method, and innovatively supported onto the activated carbon (AC) by calcination to obtain a novel heterogeneous catalyst (AC-CuCo₂O₄). Brilliant red 3BF (3BF) was selected as the probe compound to investigate the catalytic activity of AC-CuCo₂O₄ in the presence of peroxymonosulfate (PMS). The results showed that 98% removal rate could be achieved and the reaction rate constant (0.476 min^-1) was 5.2 times greater than that of CuCo₂O₄ alone (0.091min^-1), suggesting that the introduction of AC could greatly enhance the catalytic activity of pure CuCo₂O₄. Typically, the 3BF removal was as high as 96% after five cycles, showing the good stability of catalyst reuse. Additionally, the effects of the initial pH, catalyst dosage, PMS concentration and reaction temperature on the 3BF removal were investigated, demonstrating that AC-CuCo₂O₄ effectively remove 3BF over a wide pH range (5.0-10.0) and possessed temperature-tolerant performance. To further explore the 3BF removal mechanism, electron paramagnetic resonance technology combining with trapping agents was employed to confirm the involvement of reactive oxygen species including SO₄^•-, ^•OH, O₂^•- and ¹O₂, which distinctly differed from the reported CuCo₂O₄ for PMS activation. These findings provided an addition promising strategy in environmental remediation.

Synthesis of Spinel Ferrite MFe2O4 (M = Co, Cu, Mn, and Zn) for Persulfate Activation to Remove Aqueous Organics: Effects of M-Site Metal and Synthetic Method

Metal species and synthetic method determine the characteristics of spinel ferrite MFe₂O₄. Herein, a series of MFe₂O₄ (M = Co, Cu, Mn, Zn) were synthesized to investigate the effect of M-site metal on persulfate activation for the removal of organics from aqueous solution. Results showed that M-site metal of MFe₂O₄ significantly influenced the catalytic persulfate oxidation of organics. The efficiency of the removal of organics using different MFe₂O₄ + persulfate systems followed the order of CuFe₂O₄ > CoFe₂O₄ > MnFe₂O₄ > ZnFe₂O₄. Temperature-programmed oxidation and cyclic voltammetry analyses indicated that M-site metal affected the catalyst reducibility, reversibility of M²⁺/M³⁺ redox couple, and electron transfer, and the strengths of these capacities were consistent with the catalytic performance. Besides, it was found that surface hydroxyl group was not the main factor affecting the reactivity of MFe₂O₄ in persulfate solution. Moreover, synthetic methods (sol–gel, solvothermal, and coprecipitation) for MFe₂O₄ were further compared. Characterization showed that sol–gel induced good purity, porous structure, large surface area, and favorable element chemical states for ferrite. Consequently, the as-synthesized CuFe₂O₄ showed better catalytic performance in the removal of organics (96.8% for acid orange 7 and 62.7% for diclofenac) along with good reusability compared with those obtained by solvothermal and coprecipitation routes. This work provides a deeper understanding of spinel ferrite MFe₂O₄ synthesis and persulfate activation.

A Bimetallic Fe-Mn Oxide-Activated Oxone for In Situ Chemical Oxidation (ISCO) of Trichloroethylene in Groundwater: Efficiency, Sustained Activity, and Mechanism Investigation

Bimetallic Fe-Mn oxide (BFMO) has been regarded as a promising activator of peroxysulfate (PS), the sustained activity and durability of BFMO for long-term activation of PS in situ, however, is unclear for groundwater remediation. A BFMO (i.e., Mn_1.5FeO_6.35) was prepared and explored for PS-based in situ chemical oxidation (ISCO) of trichloroethylene (TCE) in sand columns with simulated/actual groundwater (SGW/AGW). The sustained activity of BFMO, oxidant utilization efficiency, and postreaction characterization were particularly investigated. Electron spin resonance (ESR) and radical scavenging tests implied that sulfate radicals (SO₄^•-) and hydroxyl radicals (HO^•) played major roles in degrading TCE, whereas singlet oxygen (¹O₂) contributed less to TCE degradation by BFMO-activated Oxone. Fast degradation and almost complete dechlorination of TCE in AGW were obtained, with reaction stoichiometry efficiencies (RSE) of ΔTCE/ΔOxone at 3-5%, much higher than those reported RSE values in H₂O₂-based ISCO (≤0.28%). HCO₃^- did not show detrimental effect on TCE degradation, and effects of natural organic matters (NOM) were negligible at high Oxone dosage. Postreaction characterizations displayed that the BFMO was remarkably stable with sustained activity for Oxone activation after 115 days of continuous-flow test, which therefore can be promising catalyst for Oxone-based ISCO for TCE-contaminated groundwater remediation.

One-Step Synthesis of Metal-Modified Nanomagnetic Materials and Their Application in the Removal of Chlortetracycline

Magnetic nanomaterials are promising heterogeneous catalysts for environmental applications. According to X-ray diffraction, Brunauer-Emmett-Teller method, scanning electron microscopy, high-resolution transmission electron microscopy, and vibrating-sample magnetometer, a kind of copper-modified nanomagnetic material (Cu-nFe₃O₄) was successfully prepared by a one-step synthesis method. Among them, compared with the two-step synthesis method of Cu/Fe₃O₄ and Cu/nFe₃O₄, Cu-nFe₃O₄ has the best effect on chlortetracycline (CTC) removal. The batch study results indicate that the maximum removal of chlortetracycline is 99.0% at a dosage = 2.0 g L^-1, copper loading = 0.8 mM, and C ₀ = 100 mg L^-1 at the optimum conditions within 90 min. The effects of humic acids (HA), NO₃ ^-, Cl^-, CO₃ ^2-, and PO₄ ^3- on the CTC removal by Cu-nFe₃O₄ are also investigated. Repeated experiments were performed on the prepared Cu-nFe₃O₄, indicating that Cu-nFe₃O₄ has good recyclability. The kinetics of the Cu-nFe₃O₄ removal of CTC was investigated, indicating that the reaction conformed to the double constant model and the reaction is mainly dominated by a chemical reaction with physical adsorption. Finally, the mechanism of the CTC removal by Cu-nFe₃O₄ in a heterogeneous environment was clarified. This study aims to provide an experimental basis for the environmental application of Cu-nFe₃O₄.

MnCeOX with high efficiency and stability for activating persulfate to degrade AO7 and ofloxacin

An efficient MnCeO_x composite was successfully synthesized for activation of persulfate to degrade acid orange 7 (AO7) and ofloxacin. Pollutants degradation efficiencies with different catalytic systems were investigated. Results showed the performance of MnCeO_x was better than MnO_x, CeO₂ and MnO_x + CeO₂. Thus, there was a clear synergistic effect (Se) between Mn and Ce in the composite, and the Se was 73.8% for AO7 and 39.6% for ofloxacin. In addition, AO7 removal fitted 1st order reaction while ofloxacin removal fitted 2nd order reaction in MnCeO_x/persulfate system. Moreover, MnCeO_x/persulfate system showed high efficiency in pH range of 5-9. Mechanism analysis showed that SO₄^- and OH on the surface of the catalyst were the main active species, and O₂^- also played an important role in pollutants degradation. Furthermore, MnCeO_x showed high activity in actual water. Finally, the possible degradation pathway of ofloxacin was proposed according to the high performance liquid chromatography-mass spectrometry result. Overall, this study provides an efficient and stable catalyst to activate persulfate to degrade refractory pollutants.

Use mechanochemical activation to enhance interfacial contaminant removal: A review of recent developments and mainstream techniques

Interfacial processes, including adsorption and catalysis, play crucial roles in environmental contaminant removal. Mechanochemical activation (MCA) emerges as a competitive method to improve the performance of adsorbents and catalysts. The development and application of MCA in the last decades are thereby systematically reviewed, particularly highlighting its contribution to interfacial process modulation. Two typical apparatuses for MCA are ball milling (BaM) and bead milling (BeM). Compared to BaM, BeM is able to yield a much higher MCA intensity, because it could pulverize bulk solid particles to nearly 100 nm. Since MCA intensity on the adsorbents and catalysts is directly responsible for the contaminant removal afterwards, quantitative and qualitative determination methods for valid MCA intensity are introduced. MCA benefits both the adsorption kinetics and capacity of powdered activated carbon by increasing the specific surface area. Carbon oxidation should be given an additional attention, but potentially favors the adsorption of heavy metals. MCA favors the catalyst performance by providing abundant surface functional group and increasing the free energy in the near-surface region. Finally, the future research needs are identified.

An efficient CuO-γFe2O3 composite activates persulfate for organic pollutants removal: Performance, advantages and mechanism

CuO-γFe₂O₃ was fabricated as a novel and effective persulfate (PS) catalyst to remove bio-refractory organic pollutants. Characterization results showed that CuO-γFe₂O₃ possessed a relatively large surface area among transition metal oxides which provided favorable adsorption and activation sites for PS to degrade pollutants. There was an obvious synergy between CuO and γFe₂O₃ in the composite, which played 84.7% role in Acid orange 7 (AO7) removal. Under the optimal conditions (CuO-γFe₂O₃ dosage = 0.6 g L^-1, PS dosage = 0.8 g L^-1, unadjusted solution pH), almost complete AO7 was rapidly eliminated in 5 min. Moreover, the wide workable pH range (2-13), good stability (0.82 mg L^-1 Cu leached, almost no Fe leached) and reusability (4 times) were the significant virtues of CuO-γFe₂O₃ for wastewater treatment. Besides, the reaction mechanism mainly based on the interaction among Cu(II/III) and Fe(II/III) species for sulfate radical (SO₄^-) generation was emphatically elucidated by the analyses of radicals, PS utilization, TOC removal and metal chemical states. Finally, CuO-γFe₂O₃+PS system displayed desirable removal of multiple organic pollutants with different molecular structures. In light of the prominent advantages of CuO-γFe₂O₃+PS, this work extended activated PS process in treating refractory organic wastewater.

Tuning of Persulfate Activation from a Free Radical to a Nonradical Pathway through the Incorporation of Non-Redox Magnesium Oxide

Nonradical-based advanced oxidation processes for pollutant removal have attracted much attention due to their inherent advantages. Herein we report that magnesium oxides (MgO) in CuOMgO/Fe₃O₄ not only enhanced the catalytic properties but also switched the free radical peroxymonosulfate (PMS)-activated process into the ¹O₂ based nonradical process. CuOMgO/Fe₃O₄ catalyst exhibited consistent performance in a wide pH range from 5.0 to 10.0, and the degradation kinetics were not inhibited by the common free radical scavengers, anions, or natural organic matter. Quantitative structure-activity relationships (QSARs) revealed the relationship between the degradation rate constant of 14 substituted phenols and their conventional descriptor variables (i.e., Hammett constants σ, σ^-, σ⁺), half-wave oxidation potential (E_1/2), and pK_a values. QSARs together with the kinetic isotopic effect (KIE) recognized the electron transfer as the dominant oxidation process. Characterizations and DFT calculation indicated that the incorporated MgO alters the copper sites to highly oxidized metal centers, offering a more suitable platform for PMS to generate metastable copper intermediates. These highly oxidized metals centers of copper played the key role in producing O₂^•- after accepting an electron from another PMS molecule, and finally ¹O₂ as sole reactive species was generated from the direct oxidation of O₂^•- through thermodynamically feasible reactions.

Synergistic Catalysis of Co(OH)2/CuO for the Degradation of Organic Pollutant Under Visible Light Irradiation

The exploration of advanced water treatment technologies e.g. heterogeneous photocatalysis is the most promising way to address organic pollution issues. Semiconductors based bimetallic photocatalysis with wide bandgap, have displayed splendid degradation performance in the UV light region, but their extension to the visible light/near infra-red region is still a matter of great concern. CuO, Co(OH)₂, CoO and Co(OH)₂/CuO nanocomposites were synthesized via simple co-precipitation method and further practiced for Rhodamine B (RhB) decomposition by introducing per-sulfate (PS) as a sacrificial agent. Results revealed that Co(OH)₂/CuO catalyst had shown robust catalytic activity for RhB photodegradation (degradation time 8 min, k = 0.864 min⁻¹) under light illumination, significantly less (12–60 times) than the other reported bimetallic catalysts. Catalyst also have verified excellent performance for a broader pH range (5–9) with excellent stability. Main reactive species responsible for the photocatalytic reaction were sulfate (SO₄^•−) and superoxide (O₂^•) radicals, duly verified by ESR and by using radical scavengers. With outstanding recycling abilities, this is probably the fewer successful attempt for RhB decolorization and can be highly favorable for effluent treatment by using the synergic effect of absorption and photodegradation.

Construction of Bi2O3/CuNiFe LDHs composite and its enhanced photocatalytic degradation of lomefloxacin with persulfate under simulated sunlight

Advanced oxidation methods based on photocatalysis and sulfate radicals have attached most interest towards contaminant degradation. However, there are a lack of coupling two methods in the field of pollutant degradation. In the present study, a new Bi₂O₃/CuNiFe LDHs composite was fabricated and it could efficiently activate persulfate (PS) for lomefloxacin (LOM) decomposition under simulated sunlight, in which 84.6% of LOM (10 mg·L^-1) was degraded over 40 min with 0.4 g·L^-1 of Bi₂O₃/CuNiFe LDHs composite and 0.74 mM of PS at natural pH. In addition, the Bi₂O₃/CuNiFe LDHs composite possessed good reusability and stability at least four runs. Moreover, active radical scavenging experiments indicated that hydroxyl radicals (HO·), sulfate radicals (SO₄·^-), superoxide radicals (O₂·^-) and hole (h⁺) were the main radicals under LOM degradation process. Subsequently, the possible degradation intermediates were determined and the decomposition pathways were put forward. At the same time, activated sludge inhibition experiments were performed to assess the variation of toxicity of LOM and its degradation intermediates during oxidation. Finally, possible reaction mechanism of Bi₂O₃/CuNiFe LDHs composite for PS activation under simulated sunlight was proposed.

Influence of the structure and composition of Fe-Mn binary oxides on rGO on As(III) removal from aquifers

Fe-Mn binary oxide (FMBO) possesses high efficiency for As(III) abatement based on the good adsorption affinity of iron oxide and the oxidizing capacity of Mn(IV), and the composition and structure of FMBO play important roles in this process. To compare the removal performance and determine the optimum formula for FMBO, magnetic graphene oxide (MRGO)-FMBO and MRGO-MnO₂ were synthesized with MRGO as a carrier to improve the dispersity of the adsorbents in aquifers and achieve magnetic recycling. Results indicated that MRGO-FMBO had higher As(III) removal than that of MRGO-MnO₂, although the ratios of Fe and Mn were similar, because the binary oxide of Fe and Mn facilitated electron transfer from Mn(IV) to As(III), while the separation of Mn and Fe on MRGO-MnO₂ restricted the process. The optimal stoichiometry x for MRGO-FMBO (Mn_xFe_3-xO₄) was 0.46, and an extraordinary adsorption capacity of 24.38 mg/g for As(III) was achieved. MRGO-FMBO showed stable dispersive properties in aquifers, and exhibited excellent practicability and reusability, with a saturation magnetization of 7.6 emu/g and high conservation of magnetic properties after 5 cycles of regeneration and reuse. In addition, the presence of coexisting ions would not restrict the practical application of MRGO-FMBO in groundwater remediation. The redox reactions of As(III) and Mn(IV) on MRGO-FMBO were also described. The deprotonated aqueous As(III) on the surface of MRGO-FMBO transferred electrons to Mn(IV), and the formed As(V) oxyanions were bound to ferric oxide as inner-sphere complexes by coordinating their "-OH" groups with Mn(IV) oxides at the surface of MRGO-FMBO. This work could provide new insights into high-performance removal of As(III) in aquifers.

Innovatively employing magnetic CuO nanosheet to activate peroxymonosulfate for the treatment of high-salinity organic wastewater

Magnetic CuO nanosheet (Mag-CuO), as a cheap, stable, efficient and easily separated peroxymonosulfate (PMS) activator, was prepared by a simple one-step precipitation method for the removal of organic compounds from salt-containing wastewater. The experiments showed that the removal efficiencies of various organic pollutants including Acid Orange 7, Methylene Blue, Rhodamine B and atrazine in a high-salinity system (0.2 mol/L Na₂SO₄) with the Mag-CuO/PMS process were 95.81%, 74.57%, 100% and 100%, respectively. Meanwhile, Mag-CuO still maintained excellent catalytic activity in other salt systems including one or more salt components (NaCl, NaNO₃, Na₂HPO₄, NaHCO₃). A radical-quenching study and electron paramagnetic resonance analysis confirmed that singlet oxygen (¹O₂) was the dominant reactive oxygen species for the oxidation of organic pollutants in high-salinity systems, which is less susceptible to hindrance by background constituents in wastewater than radicals (^•OH or SO₄^•-). The surface hydroxylation of the catalyst and catalytic redox cycle including Cu and Fe are responsible for the generation of ¹O₂. The developed Mag-CuO catalyst shows good application prospects for the removal of organic pollutants from saline wastewater.

Catalytic degradation of p-nitrophenol by magnetically recoverable Fe3O4 as a persulfate activator under microwave irradiation

In this study, Fe₃O₄ and microwave (MW) were combined to activate persulfate (PS) for the removal of organic matter, resulting in the enhanced degradation of p-nitrophenol (PNP) in solution. During the preparation of Fe₃O₄, the effect of sodium acetate was examined, and the results showed that the concentration of sodium acetate had little effect on the catalytic activity of the Fe₃O₄/PS/MW system but did have an effect on the Fe₃O₄ yield. In addition, with regards to the representative environmental factors, the degradation experiment showed that humic acid and the co-existing anions of chloride, sulfate, nitrate, and phosphate had little effects on p-nitrophenol removal; however, carbonate had a negative effect. In addition, the Fe₃O₄/PS/MW system performed well in the initial pH range of 3.0-9.0. According to the quenching experiment and electron paramagnetic resonance (EPR) detection, sulfate radicals and a minority of hydroxyl radicals play dominant roles in the degradation process. In addition, the role of Fe₃O₄ was confirmed to take part in the degradation process by X-ray photoelectron spectroscopy (XPS) analysis. Because of the good performance observed in the water matrices of tap water and the Songhua River, these results demonstrate the potential application of the Fe₃O₄/PS/MW system for wastewater treatment.

Electrochemically mediated calcium phosphate precipitation from phosphonates: Implications on phosphorus recovery from non-orthophosphate

Phosphonates are an important type of phosphorus-containing compounds and have possible eutrophication potential. Therefore, the removal of phosphonates from waste streams is as important as orthophosphate. Herein, we achieved simultaneously removal and recovery of phosphorus from nitrilotris (methylene phosphonic acid) (NTMP) using an electrochemical cell. It was found that the C-N and C-P bonds of NTMP were cleaved at the anode, leading to the formation of orthophosphate and formic acid. Meanwhile, the converted orthophosphate reacted with coexisting calcium ions and precipitated on the cathode as recoverable calcium phosphate solids, due to an electrochemically induced high pH region near the cathode. Electrochemical removal of NTMP (30 mg/L) was more efficient when dosed to effluent of a wastewater treatment plant (89% in 24 h) than dosed to synthetic solutions of 1.0 mM Ca and 50 mM Na₂SO₄ (43% in 168 h) while applying a current density of 28 A/m² and using a Pt anode and Ti cathode. The higher removal efficiency of NTMP in real waste water is due to the presence of chloride ions, which resulted in anodic formation of chlorine. This study establishes a one-step approach for simultaneously phosphorus removal and recovery of calcium phosphate from non-orthophosphates.

Comparison of radical and non-radical activated persulfate systems for the degradation of imidacloprid in water

The study focuses on degradation efficiency of non-radical activation and radical activation systems of persulfate (PS) to degrade imidacloprid (IMI) by using sodium persulfate (SPS) as PS source. Copper oxide (CuO)-SPS and CuO/biochar (BC)-SPS were selected as PS non-radical activation systems, and pyrite (PyR)-SPS was selected as PS radical activation system. The degradation by CuO-SPS, CuO/BC-SPS and PyR-SPS systems was investigated from acidic to basic conditions (pH 3.0-11.0). Highest degradation by CuO-SPS and CuO/BC-SPS systems was achieved over pH 11.0. In contrast, highest degradation by PyR-SPS system was achieved over pH 3.0, however, PyR-SPS system was also found effective up to pH 9.0. It was found that degradation was more efficient in PS radical activation system, indicating that IMI could be oxidized by radicals rather than by activated PS. Electron paramagnetic resonance (EPR) analysis was carried out to investigate the generation of sulfate (SO₄^-) and hydroxyl (OH) radicals, which indicated the presence of SO₄^- and OH in CuO-SPS, CuO/BC and PyR-SPS systems. However, free radical quenching analysis indicated that radicals were main reactive oxygen species for degradation. The lower degradation in PS non-radical activation systems was probably resulted from radicals existed as minor reactive oxygen species. The findings indicated that non-radical oxidation systems showed low reality for degradation and good degradation could be achieved by radical oxidation system. The degradation was also carried out in real waters to investigate the potential applicability of applied systems, which supported PyR-SPS system for effective degradation.

New Insights into the Generation of Singlet Oxygen in the Metal-Free Peroxymonosulfate Activation Process: Important Role of Electron-Deficient Carbon Atoms

A nonradical oxidation process via metal-free peroxymonosulfate (PMS) activation has recently attracted considerable attention for organic pollutant degradation; however, the origin of singlet oxygen (¹O₂) generation still remains controversial. In this study, nitrogen-doped carbon nanosheets (NCN-900) derived from graphitic carbon nitride were developed for activation of PMS and elucidation of ¹O₂ production. With a large specific surface area (1218.7 m² g^-1) and high nitrogen content (14.5 at %), NCN-900 exhibits superior catalytic activity in PMS activation, as evidenced by complete degradation of bisphenol A within 2 min using 0.1 g L^-1 NCN-900 and 2 mM PMS. Moreover, the reaction rate constant fitted by pseudo-first-order kinetics for NCN-900 reaches an impressive value of 3.1 min^-1. Electron paramagnetic resonance measurements and quenching tests verified ¹O₂ as the primary reactive oxygen species in the NCN-900/PMS system. Based on X-ray photoelectron spectroscopy analysis and theoretical calculations, an unexpected generation pathway of ¹O₂ involving PMS oxidation over the electron-deficient carbon atoms neighboring graphitic N in NCN-900 was unraveled. Besides, the NCN-900/PMS system is also applicable for remediation of actual industrial wastewater. This work highlights the important role of electron-deficient carbon atoms in ¹O₂ generation from PMS oxidation and furnishes theoretical support for further relevant studies.

Degradation of 2,4-dichlorophenol by CuO-activated peroxydisulfate: Importance of surface-bound radicals and reaction kinetics

Peroxydisulfate (PDS, S₂O₈^2-) is a promising oxidant for water treatment and contaminated groundwater remediation. It requires activation to generate sulfate radical (SO₄^-) and hydroxyl radical (OH) for indirect oxidation of organic pollutants. Recently, efforts were devoted to developing PDS activation systems for direct oxidation of organic pollutants without producing radicals. However, the mechanism was still ambiguous and the kinetics was either not quantified or empirical in nature. In this research, we examined the activation of PDS by CuO for the degradation of 2,4-dichlorophenol (2,4-DCP). Dual-compound control experiments, radical scavenging tests and electron paramagnetic resonance (EPR) studies showed that surface-bound OH generated from the adsorbed PDS was the main reactive species responsible for the degradation of 2,4-DCP. A kinetic model considering the important reaction steps, including the adsorption of PDS onto CuO, activation of adsorbed PDS to form surface-bound SO₄^- and then surface-bound OH, and degradation of 2,4-DCP by surface-bound OH, was developed to better elucidate the reaction kinetics. The results suggested that the overall reaction kinetics of 2,4-DCP degradation was regulated by the adsorption of PDS onto CuO and the electron transfer between surface Cu and adsorbed PDS to form surface-bound SO₄^-. The developed kinetic model could serve as a framework to characterize other persulfate oxidation systems relying on surface-bound radicals.

CuO-Co3O4@CeO2 as a heterogeneous catalyst for efficient degradation of 2,4-dichlorophenoxyacetic acid by peroxymonosulfate

CuO-Co₃O₄@CeO₂ nanoparticles used as a heterogeneous catalyst were prepared via a sol-gel method and characterized by various techniques. For comparison, a series of oxides was investigated for activating peroxymonosulfate (PMS) during the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The results indicated that CuO-Co₃O₄@CeO₂ exhibited the highest catalytic performance among the catalysts. Complete degradation of 2,4-D (20 mg/L) was realized within 45 min at 1 mM PMS, CuO-Co₃O₄@CeO₂ loading of 0.07 g/L, and pH of 6. Recycling experiments confirmed that CuO-Co₃O₄@CeO₂ was very stable, and the 2,4-D degradation efficiencies ranged from 100% to 97.5%, decreasing by only 2.5% after the fifth run. The outstanding catalysis of CuO-Co₃O₄@CeO₂ resulted from the synergy of cerium, cobalt, and copper. Electron paramagnetic resonance and radical scavenger experiments confirmed the production of SO₄^{• -} and ^•OH radicals in the CuO-Co₃O₄@CeO₂/PMS system, which were responsible for efficient decomposition of 2,4-D. Furthermore, the combination of CuO-Co₃O₄@CeO₂ andPMS was applied to treat natural water containing 2,4-D, and a high 2,4-D removal rate was also achieved. Based on these results, it was deduced that CuO-Co₃O₄@CeO₂ can be utilized as a catalyst to activate PMS and destroy organic contaminants in aqueous solution.

Continuous release of SO4˙− over g-C3N4/ZnO/Fe(iii) systems mediated by persulfates: the Fe(iii)/Fe(ii) cycling and degradation pathway

A process to obtain Fe(ii) by photogenerating electrons for the activation of persulfates and durable release of sulfate free radicals was proposed.

pH-Dependent Structure-Activity Relationship of Polyaniline-Intercalated FeOCl for Heterogeneous Fenton Reactions

In this study, we prepared polyaniline-intercalated iron oxychloride (FeOCl-PANI) by aqueous intercalation method to use it as a Fenton-like catalyst that was then assessed in terms of behavior of intercalation, structural evolution, Fenton-like activity, and catalytic mechanism. Gel-permeation chromatography demonstrated that the molecular weight (polymerization extent) of polyaniline fragment gradually increased with the increase of intercalation time. Interestingly, the polyaniline-intercalated materials with varying intercalation times exhibited distinctly different Fenton-like activity trends under acidic (pH 4) and neutral (pH 7) conditions. Specifically, Fenton-like degradation is favored with a shorter intercalation time under acidic conditions, while it is preferred with a longer intercalation time under neutral pH values. We propose that an additional pH-dependent charging of FeOCl-PANI with different polymerization extents of the intercalated polyaniline promotes a switch in the contaminant degradation pathway, leading to opposite trends in observable activity at different pH values. As a class of typical layered metal chalcogenohalides (MeAX, A = O, S, Se, X = Cl, Br, I), FeOCl-PANI is expected to provide new insights into the development of other similar materials. This work could be useful to further understand the H₂O₂ heterogeneous activation behavior, which is of significance to the application of iron-based heterogeneous Fenton oxidation.

A High-Efficiency CuO/CeO2 Catalyst for Diclofenac Degradation in Fenton-Like System

An efficient Fenton-like catalyst CuO/CeO₂ was synthesized using ultrasonic impregnation and used to remove diclofenac from water. The catalyst was characterized by N₂ adsorption-desorption, SEM-EDS, XRD, HRTEM, Raman, and XPS analyses. Results showed that CuO/CeO₂ possessed large surface area, high porosity, and fine elements dispersion. Cu was loaded in CeO₂, which increased the oxygen vacancies. The exposed crystal face of CeO₂ (200) was beneficial to the catalytic activity. The diclofenac removal experiment showed that there was a synergistic effect between CuO and CeO₂, which might be caused by more oxygen vacancies generation and electronic interactions between Cu and Ce species. The experimental conditions were optimized, including pH, catalyst and H₂O₂ dosages, and 86.62% diclofenac removal was achieved. Diclofenac oxidation by ·OH and adsorbed oxygen species was the main mechanism for its removal in this Fenton-like system.

One-step synthesis of zerovalent-iron-biochar composites to activate persulfate for phenol degradation

A novel zerovalen-iron-biochar composite (nZVI/SBC) was synthesized by using FeCl₃-laden sorghum straw biomass as the raw material via a facile one-step pyrolysis method without additional chemical reactions (e.g., by NaBH₄ reduction or thermochemical reduction). The nZVI/SBC was successfully employed as an activator in phenol degradation by activated persulfate. XRD, SEM, N₂ adsorption-desorption and atomic absorption spectrophotometry analysis showed that the nanosized Fe⁰ was the main component of the 4ZVI/SBC activator, which was a mesopore material with an optimal FeCl₃·6H₂O/biomass impregnation mass ratio of 2.7 g/g. The 4ZVI/SBC activator showed an efficient degradation of phenol (95.65% for 30 min at 25 °C) with a large specific surface area of 78.669 m²·g^-1. The recovery of 4ZVI/SBC activator after the degradation reaction of phenol can be realized with the small amount of dissolved iron in the water. The 4ZVI/SBC activator facilitated the activation of persulfate to degrade phenol into non-toxic CO₂ and H₂O. The trend of Cl^-, SO₄ ^2- and NO₃ ^- affected the removal efficiency of phenol by using the 4ZVI/SBC activator in the following order: NO₃ ^- > SO₄ ^2- > Cl^-. The one-step synthesis of the nanosized zerovalent-iron-biochar composite was feasible and may be applied as an effective strategy for controlling organic waste (e.g. phenol) by waste biomass.

Complexation Enhances Cu(II)-Activated Peroxydisulfate: A Novel Activation Mechanism and Cu(III) Contribution

While aqueous free Cu(II) ion is known to be ineffective to activate peroxydisulfate (PDS), here we report for the first time that Cu(II) complexes are potentially effective activators for PDS when the coordination involves suitable ligands. Using cefalexin (CFX) as a representative, studies show that the complex of Cu(II) with CFX can efficiently activate PDS to induce rapid degradation of CFX. Transformation products of CFX by PDS/Cu(II) differ substantially from those generated from the typical radical oxidation process, for example, PDS/Ag(I), but quite resemble the products from oxidation of CFX by Cu(III). Complexation with CFX increases the electron density of Cu(II), favoring electron transfer from Cu(II) to PDS to generate radicals and Cu(III). The produced Cu(III), rather than radicals, plays the primary role in the overall CFX degradation and regenerates Cu(II) in a catalytic cycle. This novel activation process can occur for a wide range of contaminants (cephalosporin, penicillin, and tetracycline antibiotics) and ligands when coordinated with Cu(II), and N-containing functional groups (e.g. amines) were found to form effective Cu(II) complexes for PDS activation. The new findings of this study further broaden the knowledge on PDS activation by aqueous Cu(II), and verify the contribution of Cu(III) to contaminant elimination.