Efficient degradation of carbamazepine by easily recyclable microscaled CuFeO2 mediated heterogeneous activation of peroxymonosulfate

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

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

Cellulose acetate-based electrospun nanofiber aerogel with excellent resilience and hydrophobicity for efficient removal of drug residues and oil contaminations from wastewater

Cellulose acetate (CA)-based electrospun nanofiber aerogel (ENA) has drawn extensive attention for wastewater remediation due to its unique separation, inherent porosity and biodegradability. However, the low mechanical strength, poor durability, and limited adsorption ability hinder its further applications. We herein propose using silane-modified ENA, namely T-CA@Si@ZIF-67 (T-ENA), with enhanced resilience, hydrophobicity, durability and hetero-catalysis to remediate a complex wastewater containing oil and drug residues. The robust T-ENA was fabricated by pre-doping tetraethyl orthosilicate (TEOS) and ligand in its spinning precursors, followed by in-situ anchoring of porous ZIF-67 on the electrospun nanofibers (ENFs) via seeding method before freeze-drying and thermal curing (T). Results show that the T-ENA displays enhanced mechanical stability/resilience and hydrophobicity without compromise of its high porosity (>98 %) and low density (10 mg/cm3) due to the silane cross-linking. As a result, the hydrophobic T-ENA shows over 99 % separation efficiency towards different oil-water solutions. Meanwhile, thanks to the enhanced adsorption-catalytic ability and the activation of peroxymonosulfate (PMS) from the porous ZIF-67, fast degradation of carbamazepine (CBZ) residue in the wastewater can be achieved within 20 min. This work might provide a novel strategy for developing CA aerogels to remove organic pollutants.

Peroxymonosulfate activation by Fe-Mn Co-doped biochar for carbamazepine degradation

Antibiotics in aquatic environments present a serious threat to the ecological environment and human health. Activation of carbon-catalyzed persulfate is a prospective approach for oxidizing antibiotics. There is a pressing need for inexpensive carbon catalysts of high quality. In this study, biochar (BC) modified by Fe, Mn and Fe@Mn was employed to activate peroxymonosulfate (PMS) to degrade carbamazepine (CBZ) in water. The surface of Fe@Mn BC had a dense, stalactite-like morphology comprising a square chassis that was elliptical. The catalyst Fe@Mn-BC possessed the optimal degradation effect (99%) on CBZ at 100 min. Electron paramagnetic resonance spectroscopy and the quenching spectrum suggested that ˙O2- and 1O2 contributed to CBZ degradation.

Enhanced persulfate activation by ethylene glycol-mediated bimetallic sulfide for imidacloprid degradation

CuFeS2 is regarded as a promising catalyst for heterogeneous activation to remove organic contaminants in wastewater. However, effects of solvents in regulating material synthesis and catalytic activity are still not clear. Herein, we reported the role of water, ethanol, ethylene glycol (EG), glycerol, and polyethylene glycol 200 on the synthesis of CuFeS2 micro-flowers and their performance in activating persulfate (PS) to remove imidacloprid (IMI) pesticide. The results showed that the solvent had an effect on the morphology, crystallinity, yields, specific surface areas and unpaired electrons of CuFeS2 micro-flowers. The degradation experiments revealed the efficient catalytic activity of EG-mediated CuFeS2 for heterogeneous PS activation. SO4•- and •OH were identified in EG-CuFeS2/PS system and •OH (90.4%) was the dominant reactive species. Meanwhile, stable 20% of η[PMSO2] (the molar ratio of PMSO2 generation to PMSO consumption) was achieved and demonstrated that Fe(IV) was also involved in the degradation process. Moreover, S2- promoted the cycling of Fe3+/Fe2+ and Cu2+/Cu+, enhancing the synergistic activation and reusability of the catalyst. Density functional theory (DFT) calculations verified that PS was adsorbed by Fe atom and electron transfer occurred on the catalyst surface. Three possible degradation pathways of IMI were proposed by analysis of the degradation intermediates and their toxicities were evaluated by ECOSAR. This study not only provides a theoretical foundation for catalyst design, but also promotes the industrial application of bimetallic sulfide Fenton-like catalysts for water management.

Harnessing the power of natural minerals: A comprehensive review of their application as heterogeneous catalysts in advanced oxidation processes for organic pollutant degradation

The release of untreated wastewater into water bodies has become a significant environmental concern, resulting in the accumulation of refractory organic pollutants that pose risks to human health and ecosystems. Wastewater treatment methods, including biological, physical, and chemical techniques, have limitations in achieving complete removal of the refractory pollutants. Chemical methods, particularly advanced oxidation processes (AOPs), have gained special attention for their strong oxidation capacity and minimal secondary pollution. Among the various catalysts used in AOPs, natural minerals offer distinct advantages, such as low cost, abundant resources, and environmental friendliness. Currently, the utilization of natural minerals as catalysts in AOPs lacks thorough investigation and review. This work addresses the need for a comprehensive review of natural minerals as catalysts in AOPs. The structural characteristics and catalytic performance of different natural minerals are discussed, emphasizing their specific roles in AOPs. Furthermore, the review analyzes the influence of process factors, including catalyst dosage, oxidant addition, pH value, and temperature, on the catalytic performance of natural minerals. Strategies for enhancing the catalytic efficiency of AOPs mediated by natural minerals are explored, mainly including physical fields, reductant addition, and cocatalyst utilization. The review also examines the practical application prospects and main challenges associated with the use of natural minerals as heterogeneous catalysts in AOPs. This work contributes to the development of sustainable and efficient approaches for organic pollutant degradation in wastewater.

Iron (II) phthalocyanine loaded tourmaline efficiently activates PMS to degrade pharmaceutical contaminants under solar light

Iron (II) phthalocyanine (FePc) is loaded on the surface of the tourmaline (TM) by the reflow method to obtain FePc/TM. This research effectively prevents the π-π stacking of FePc, increased the effective utilization rate of PMS activation under solar light, and further improved the catalytic performance of the catalytic system. The catalytic oxidation efficiency of FePc/TM on carbamazepine (CBZ) and sulfadiazine (SD) can reach 99% under solar light for 15 and 5 min, the total organic carbon (TOC) removal rate can reach 58% and 69% under solar light for 120 min. After 6 cycles, the CBZ removal rate remained above 95%. In addition, the FePc/TM catalytic system has an excellent removal rate for other pharmaceuticals. The results of spin-trapped electron paramagnetic resonance and classical quenching experiments show that FePc/TM can effectively activate PMS to generate active species under solar light, including superoxide radical (•O2-), singlet oxygen (1O2), hydroxyl radicals(•OH), and sulphate radicals (SO4•-). The intermediates of CBZ were identified by Ultra-high performance liquid chromatography and high resolution mass spectrometry, and the degradation pathway was proposed. As the reaction progresses, all CBZ and intermediates are reduced and converted into small acids, or mineralized to H2O, CO2. This work provides an alternative method for the design of efficient activation of PMS activation catalysts under solar light to eliminate residual pharmaceuticals in actual water bodies.

Insights into the mechanism of persulfate activation with carbonated waste metal adsorbed resin for the degradation of 2,4-dichlorophenol

Superabsorbent resin (SAR) saturated with heavy metals poses a threat to surrounding ecosystem. To promote the reutilization of waste, resins adsorbed by Fe²⁺ and Cu²⁺ were carbonized and used as catalysts (Fe@C/Cu@C) to activate persulfate (PS) for 2,4-dichlorophenol (2,4-DCP) degradation. The heterogeneous catalytic reaction was mainly responsible for 2,4-DCP removal. The synergistic effect of Fe@C and Cu@C was propitious to 2,4-DCP degradation. Fe@C/Cu@C with a ratio of 2:1 showed the highest performance of 2,4-DCP removal. 40 mg/L 2,4-DCP was completely removed within 90 min under reaction conditions of 5 mM PS, pH = 7.0 and T = 25 °C. The cooperation of Fe@C and Cu@C facilitated the redox cycling of Fe and Cu species to supply accessible PS activation sites, enhancing ROS generation for 2,4-DCP degradation. Carbon skeleton enhanced 2,4-DCP removal via radical/nonradical oxidation pathways and via its adsorption to 2,4-DCP. SO₄˙-, HO˙ and O₂^•- were the dominate radical species involved in 2,4-DCP destruction. Meanwhile, the possible pathways of 2,4-DCP degradation were proposed based on GC-MS. Finally, recycling tests proved catalysts exhibited recyclable stability. Aiming to resource utilization, Fe@C/Cu@C with satisfactory catalysis and stability, is promising catalyst for contaminated water treatment.

Synergetic Photocatalytic Peroxymonosulfate Oxidation of Benzotriazole by Copper Ferrite Spinel: Factors and Mechanism Analysis

The development of oxidation processes with the efficient generation of powerful radicals is the most interesting and thought-provoking dimension of peroxymonosulfate (PMS) activation. This study reports the successful preparation of a magnetic spinel of CuFe₂O₄ using a facile, non-toxic, and cost-efficient co-precipitation method. The prepared material exhibited a synergetic effect with photocatalytic PMS oxidation, which was effective in degrading the recalcitrant benzotriazole (BTA). Moreover, central composite design (CCD) analysis confirmed that the highest BTA degradation rate reached 81.4% after 70 min of irradiation time under the optimum operating conditions of CuFe₂O₄ = 0.4 g L^-1, PMS = 2 mM, and BTA = 20 mg L^-1. Furthermore, the active species capture experiments conducted in this study revealed the influence of various species, including ^•OH, SO₄^•-, O₂^•-, and h⁺ in the CuFe₂O₄/UV/PMS system. The results showed that SO₄^•- played a predominant role in BTA photodegradation. The combination of photocatalysis and PMS activation enhanced the consumption of metal ions in the redox cycle reactions, thus minimizing metal ion leaching. Additionally, this maintained the reusability of the catalyst with reasonable mineralization efficiency, which reached more than 40% total organic carbon removal after four batch experiments. The presence of common inorganic anions was found to have a retardant effect on BTA oxidation, with the order of retardation following: HCO₃^- > Cl^- > NO₃^- > SO₄^2-. Overall, this work demonstrated a simple and environmentally benign strategy to exploit the synergy between the photocatalytic activity of CuFe₂O₄ and PMS activation for the treatment of wastewater contaminated with widely used industrial chemicals such as BTA.

Enhanced degradation of tetracycline by Cu(II) complexation in the FeS/sulfite system

This study applied a mineral material of FeS to activate sulfite for efficient degradation of TTC in the presence of Cu(II) based on the identified complexation mechanism through UV-Vis spectra, FTIR spectroscopy and DFT calculation. pH plays an important role in TTC degradation and the initial pH of 6 and 7 were the divide in the contributions of FeS/sulfite oxidation and complex-precipitation. TTC-Cu(II) exhibits a superior promoting effect on the TTC degradation in FeS/sulfite system due to the improvement of TTC electron transfer reactivity and Fe(II) dissolution from FeS. Moreover, the formation of Cu(I) improved the recycling of Fe(II) from Fe(III). Dissolved oxygen-dependent free radicals' generation was confirmed, and TTC degradation was mainly attributed to SO₄^·- and ·OH. The characterization of FeS surface through XPS, XRD, SEM-EDS, Fe(II) deactivation tests, together with the comparison of pseudo-first-order rate constants for TTC degradation by FeS and ferrous ion supported the important role of surface and dissolved Fe(II) in sulfite activation. Furthermore, reasonable degradation pathways of TTC have been proposed according to the detected products by LC-MS. This work highlights the important role of pH, DO and Cu(II) complexation in sulfite activation and TTC degradation, furnishing theoretical support for further relevant studies.

The synergistic interactions of reaction parameters in heterogeneous peroxymonosulfate oxidation: Reaction kinetic and catalytic mechanism

The reaction parameters including catalyst dosage, oxidant amount, initial contaminant concentration and pH etc. play the crucial roles in the heterogeneous persulfate oxidation processes, while the synergistic interactions among these reaction parameters are still obscure. We herein took an efficient heterogeneous persulfate oxidation system "bimetallic Mn_xCo_3-xO₄ solid solution (MnCo) activated peroxymonosulfate (PMS)" for carbamazepine (CBZ) removal from water. MnCo/PMS system exhibited outstanding performance that CBZ was completely removed within 10 min. The CBZ degradation performance was ascribed to the radical oxidation of SO₄^·- and O₂·^-, the nonradical oxidation of ¹O₂, the redox cycles between Mn and Co species and synergistic interactions among MnCo, PMS and CBZ. By monotonously or synchronously adjusting the MnCo dosage, PMS amount and initial CBZ concentration, the inherent connections of different reaction parameters were established. Strong and different synergistic interactions between MnCo and PMS, and among MnCo, PMS and CBZ, were existed due to the formation of three different reaction modes when reaction parameters met certain conditions. The features of the modes were "two-stage, the following auto-deceleration", "one-stage, constant velocity" and "two-stage, the following auto-acceleration". This discovery may provide new insights into the synergistic interactions of reaction parameters in advanced oxidation processes for wastewater treatment.

Relying on the non-radical degradation of oxytetracycline by peroxymonosulfate activated with a magnetic Cu/Fe composite: performance and mechanism

CuFe-1 nanoparticles were successfully synthesized, and they could effectively activate peroxymonosulfate to assist the degradation of oxytetracycline.

Au@CoS-BiVO4 {010} Constructed for Visible-Light-Assisted Peroxymonosulfate Activation

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO4 {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO4 {010} and {110} facets. The visible-light response of m-BiVO4 was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO4 {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co2+ + HSO5−→ Co3+ + •SO4− + OH−). On the other hand, holes accumulated on m-BiVO4 {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO4 loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater.

Environmentally Benign Formation of Nickel Hexacyanoferrate-Derived Mesoframes for Heterogeneous Catalysis

The tetramethylammonium hydroxide (TMAH)-controlled alkaline etching of nickel hexacyanoferrate (NiHCF) mesocrystals is explored. The alkaline etching enables the formation of hollow framework structures with an increased surface area, the exposure of active Ni and Fe sites and the retention of morphology. The ambient reaction conditions enable the establishment of a sustainable production. Our work reveals novel perspectives on the eco-friendly synthesis of hollow and colloidal superstructures for the efficient degradation of the organic contaminants rhodamine-B and bisphenol-A. In the case of peroxomonosulfate (PMS)-mediated bisphenol-A degradation, the rate constant of the etched mesoframes was 10,000 times higher indicating their significant catalytic activity.

Fenton-like chain reactions by coupling nanoscale tungsten powders and peroxydisulfate: Performance and mechanistic insights

In this study, Fenton-like chain reaction is constructed by coupling nanoscale tungsten powders (nW⁰) and peroxydisulfate (PDS). The nanoscale tungsten powders/peroxydisulfate (nW⁰/PDS) system exhibits a high oxidation efficiency toward diverse pollutants and expands the effective pH range up to 9.8. Results reveal ^•OH and sulfate radical (SO₄^•-) were confirmed to be responsible for 4,4'-ethylidenebisphenol (EBP) degradation, especially ^•OH. The corrosion process of nW⁰ results in the in-situ production of H₂O₂ and the transient-state tungsten species (W (x, x < VI)), initiating the reaction of H₂O₂ and tungsten species to generate ^•OH. PDS can accelerate nW⁰ corrosion to enhance the Fenton-like reaction, and can be activated by tungsten species (nW⁰ and W (x, x < VI)) to produce ^•OH and SO₄^•-. Integrated the analysis results of LC-QTOF-MS/MS, EBP degradation pathways were proposed. This study reveals the high oxidation efficiency over a wide pH range in the nW⁰/PDS system and provides new insight into the tungsten species induced Fenton-like reaction.

Degradation of Bisphenol A by ozonation in rotating packed bed: Effects of operational parameters and co-existing chemicals

Bisphenol A (BPA), a typical endocrine disrupting chemical, widely exists in water and threatens human health. The degradation of BPA by ozone in water is limited by the gas-mass transfer due to the low solubility of ozone. In this study, a rotating packed bed (RPB) was employed to create a high gravity environment to intensify the ozone mass transfer and BPA degradation. The effects of operational parameters (rotation speed of RPB, pH of the solution, ozone concentration, BPA concentration, gas volumetric flow rate and liquid volumetric flow rate) on BPA degradation efficiency and overall volumetric mass transfer coefficient of ozone were investigated. The results show that RPB effectively promoted the ozone mass transfer and BPA degradation and can be used for the ozonation of micropollutants that have fast reaction rates with ozone. Quenching experiments suggest that both ozone and HO∙ participated in BPA degradation from acidic to alkaline environments. In addition, the effects of co-existing chemicals on BPA degradation efficiency were studied. The addition of H₂O₂ or Cl^- had no obvious impact on BPA degradation; the addition of HCO₃^- is beneficial for BPA degradation while the addition of fulvic acid suppressed the degradation. These results indicate that the pH value, which affects the reaction rate between ozone and BPA, is a major factor to be considered during the ozonation of BPA in RPB.

A novel route for catalytic activation of peroxymonosulfate by oxygen vacancies improved bismuth-doped titania for the removal of recalcitrant organic contaminant

In this work, bismuth-doped titania (Bi_xTiO₂) with improved oxygen vacancies was synthesized by sol-gel protocol as a novel peroxymonosulfate (PMS, HSO₅^-) activator. HSO₅^- and adsorbed oxygen molecules could efficiently be transformed into their respective radicals through defect ionization to attain charge balance after their trapping on oxygen vacancies of the catalyst. XRD study of Bi_xTiO₂ with 5 wt% Bi (5BiT) revealed anatase, crystalline nature, and successful doping of Bi into TiO₂ crystal lattice. The particle size obtained from BET data and SEM observations was in good agreement. PL spectra showed the formation rates of ^•OH by 3BiT, 7BiT, 5BiTC, and 5BiT as 0.720, 1.200, 1.489, and 2.153 μmol/h, respectively. 5BiT catalyst with high surface area (216.87 m² g^-1) and high porosity (29.81%) was observed the excellent HSO₅^- activator. The catalytic performance of 0BiT, 3BiT, 5BiT, and 7BiT when coupled with 2 mM HSO₅^- for recalcitrant flumequine (FLU) removal under dark was 10, 27, 55, and 37%, respectively. Only 5.4% decrease in catalytic efficiency was observed at the end of seventh cyclic run. Radical scavenging studies indicate that SO₄^•- is the dominant species that caused 62.0% degradation. Moreover, strong interaction between Bi and TiO₂ through Bi-O-Ti bonds prevents Bi leaching (0.081 mg L^-1) as shown by AAS. The kinetics, degradation pathways, ecotoxicity, and catalytic mechanism for recalcitrant FLU were also elucidated. Cost-efficient, environment-friendly, and high mineralization recommends this design strategy; Bi_xTiO₂/HSO₅^- system is a promising advanced oxidation process for the aquatic environment remediation.

Uncertainty and misinterpretation over identification, quantification and transformation of reactive species generated in catalytic oxidation processes: A review

The identification of reactive radical species using quenching and electron paramagnetic resonance (EPR) tests has attracted extensive attention, but some mistakes or misinterpretations are often present in recent literature. This review aims to clarify the corresponding issues through surveying literature, including the uncertainty about the identity of radicals in the bulk solution or adsorbed on the catalyst surface in quenching tests, selection of proper scavengers, data explanation for incomplete inhibition, the inconsistent results between quenching and EPR tests (e.g., SO₄^•- is predominant in quenching test while the signal of ^•OH predominates in EPR test), and the incorrect identification of EPR signals (e.g., SO₄^•- is identified by indiscernible or incorrect signals). In addition, this review outlines the transformation of radicals for better tracing the origin of radicals. It is anticipated that this review can help in avoiding mistakes while investigating catalytic oxidative mechanism with quenching and EPR tests.

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

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

A novel electrocatalytic filtration system with carbon nanotube supported nanoscale zerovalent copper toward ultrafast oxidation of organic pollutants

In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0-7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu²⁺/Cu⁺ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and ¹O₂via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu²⁺-O-O-SO₃^-), and then ¹O₂ will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.

Performance indicators for a holistic evaluation of catalyst-based degradation-A case study of selected pharmaceuticals and personal care products (PPCPs)

Considerable efforts have been made to develop effective and sustainable catalysts, e.g., carbon-/biochar-based catalyst, for the decontamination of organic pollutants in water/wastewater. Most of the published studies evaluated the catalytic performance mainly upon degradation efficiency of parent compounds; however, comprehensive and field-relevant performance assessment is still in need. This review critically analysed the performance indicators for carbon-/biochar-based catalytic degradation from the perspectives of: (1) degradation of parent compounds, i.e., concentrations, kinetics, reactive oxidative species (ROS) analysis, and residual oxidant concentration; (2) formation of intermediates and by-products, i.e., intermediates analysis, evolution of inorganic ions, and total organic carbon (TOC); and (3) impact assessment of treated samples, i.e., toxicity evolution, disinfection effect, and biodegradability test. Five most frequently detected pharmaceuticals and personal care products (PPCPs) (sulfamethoxazole, carbamazepine, ibuprofen, diclofenac, and acetaminophen) were selected as a case study to articulate the performance indicators for a holistic evaluation of carbon-/biochar-based catalytic degradation. This review also encourages the development of alternative performance indicators to facilitate the rational design of catalysts in future studies.

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

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

Copper- and Nitrogen-Codoped Graphene with Versatile Catalytic Performances for Fenton-Like Reactions and Oxygen Reduction Reaction

Copper- and nitrogen-codoped reduced graphene oxide material (Cu/N-rGO) was prepared with a hydrothermal method. Its versatile catalytic performances were demonstrated toward the oxidative degradation of rhodamine B (RhB) and oxygen reduction reaction (ORR). The Cu and N codoping of graphene enhanced not only its activation ability toward H2O2, but also its electrocatalytic ability for ORR. It was observed that the use of 3%Cu/N-rGO together with 40 mmol·L−1 H2O2 and 4 mmol·L−1 Na2CO3 could remove more than 94% of the added RhB (30 mg·L−1) in 20 min through a catalytic Fenton-like degradation. Quenching experiments and electron paramagnetic resonance (EPR) measurements indicated that the main reactive species generated in the catalytic oxidation process were surface-bound •OH. The modified graphene also showed good electrocatalytic activity for ORR reaction in alkaline media through a four-electron mechanism. On the electrode of Cu/N-rGO, the ORR reaction exhibited an onset potential of −0.1 V and a half-wave potential of −0.248 V, which were correspondingly close to those on a Pt/C electrode. In comparison with a Pt/C electrode, the 3%Cu/N-rGO electrode showed much greater tolerance to methanol. Such outstanding catalytic properties are attributed to the abundant active sites and the synergism between Cu and N in Cu/N-rGO.

Homogeneous catalytic activation of peroxymonosulfate and heterogeneous reductive regeneration of Co2+ by MoS2: The pivotal role of pH

The application of MoS₂ to enhance Co(II)/peroxymonosulfate (Co(II)/PMS) system for organic pollutants degradation was developed, and the mechanism for pH dependent catalytic activity in the MoS₂ co-catalyzed Co(II)/PMS processes was systematically investigated. It was found that MoS₂ presented enhancement effect for Co(II)/PMS system in the tested pH range from 4.0 to 7.0, especially at pH 5.5 and 6.0. The pseudo first order reaction rates for Rhodamine B (RhB) degradation in MoS₂-Co²⁺/PMS system at pH 5.5 and 6.0 were 3.2 and 1.8 times that in Co²⁺/PMS system (Co²⁺ 2 μmol L^-1, PMS 0.2 mmol L^-1, MoS₂ 0.5 g L^-1). The redox recycle of Co³⁺/Co²⁺ was promoted by Mo(IV) and S(-II) on MoS₂ surface and regenerated Co²⁺ induced homogeneous activation of PMS for the robust production of free radical with the major of hydroxyl radicals. Increasing MoS₂ dosage, Co²⁺ and PMS concentration can linearly raise RhB degradation rate in MoS₂-Co(II)/PMS system. Moreover, MoS₂ exhibited excellent catalytic and chemical stability in recyclability and reuse for catalytic decontamination in MoS₂-Co(II)/PMS system. This work gains new insight into the enhancement effect of MoS₂ in the meal ions/PMS system, and provides a high performance wastewater treatment process of Co(II)/PMS at low concentrated Co²⁺.

Improved bioelectricity production using potassium monopersulfate as cathode electron acceptor by novel bio-electrochemical activation in microbial fuel cell

Potassium monopersulfate (PMS) without a catalyst as cathode electron acceptor was first established to improve the electricity generation performance of a microbial fuel cell (MFC) in this study. The work investigated the performance with pure PMS (PPMS) and compound PMS (CPMS). The concentration and initial pH of PMS had an effect on the electricity generation, which increased with higher PMS concentration and lower catholyte pH. In the PPMS-MFC system, the maximum voltage (0.972 V), power density (16.37 W/m³), optimal exchange current density (2.000 A/m³) and minimum polarization impedance (Rp: 97.33 Ω) were reached at 10 mM PMS and pH 3.0. However, the maximum power density (8.60 W/m³) was exhibited at 70 mM PMS and pH 3.0 in the CPMS system. Additionally, high COD removals of 99.41% and 98.71% in anode chambers were obtained in the two systems, respectively. Sulfate radicals (SO₄^-) and hydroxyl radicals (OH) played significant roles in the PPMS-MFC, while HClO was also a contributor in addition to SO₄^- and OH in the CPMS-MFC. Furthermore, SO₄^- and OH was generated in situ in the cathode to promote the reduction reaction. The inorganic anion had different effects on electricity generation. Finally, while energy was recovered, rhodamine B (RhB) was added to the cathode chamber and then removed successfully in PPMS-MFC system. This work confirmed that only PMS could be activated by bio-electrochemical method, which is an energy-saving, environmentally friendly and effective activation approach, and thus, it could be used as an efficient acceptor in a MFC.

Photo-assisted catalytic degradation of acetaminophen using peroxymonosulfate decomposed by magnetic carbon heterojunction catalyst

Catalytic oxidative degradation of acetaminophen (ACT) was evaluated using magnetic mesoporous carbon (MNPs@C) coupled with UV light and peroxymonosulfate (PMS). The performance of hybrid system (i.e., MNPs@C/UV/PMS) was assessed as a function of some operational factors (e.g., reaction time and different concentrations of catalyst, PMS and ACT) in a batch system. MNPs@C represented a high magnetic response and was easily recovered from aqueous solution via an external magnet. A significant synergistic effect was observed among the applied techniques in MNPs@C/UV/PMS system for ACT degradation. After 40 min reaction, the removal efficiencies of 97.4 and 63.5% were obtained for ACT and TOC, respectively. Both adsorption and oxidation mechanisms were responsible simultaneously for ACT removal in MNPs@C/UV/PMS system. Under optimum conditions, the removal rates of ACT and TOC were reduced slightly to 91.7 and 49.4% after five consecutive catalyst uses, which indicates the excellent reusing potential of MNPs@C. In addition, a high stability was detected for as-prepared catalyst during recycling tests, since the quantity of leached Fe was <0.2 mg/L. Methanol and tert-butyl alcohol showed a strong quenching effect on the performance of MNPs@C/UV/PMS system, demonstrating the dominant role of SO₄^•- and HO radicals in ACT degradation process. MNPs@C in comparison with ferrous ions, as a homogeneous catalyst, showed a better performance in the activation of PMS and ACT degradation. Integration of MNPs@C, UV and PMS exhibited an excellent performance into ACT removal over 40 min reaction, which can be utilized as an effective and promising technique for the efficient decontamination of polluted waters.

Efficient degradation of AO7 by ceria-delafossite nanocomposite with non-inert support as a synergistic catalyst in electro-fenton process

CuFeO₂/CeO₂ as a novel catalyst was synthesized and its catalytic performance was evaluated for electro-Fenton degradation of acid orange 7 (AO7). It was demonstrated from the characterization results that the rhombohedral structure of CuFeO₂ and face-centered cubic fluorite structure of CeO₂ remained stable after nanocomposite construction. The impact of such operating parameters as pH, current intensity and, catalyst amount was investigated and the optimum conditions (100 mgL^-1 AO7, pH 3, 150 mgL^-1 CuFeO₂/CeO₂, I: 150 mA) determination led to 99.3% AO7 removal and 79.1% COD removal in 60 min. The introduction of CeO₂ as non-inert support had a significant impact on H₂O₂ electro-generation as an important step in AO7 removal. CuFeO₂/CeO₂ presented negligible metal leaching (iron 4.13%, copper 2.4%, and cerium 0.33%) which could be due to the strong interaction between active species and support. The nanocomposite performed efficiently in salty systems and two samples of real wastewaters due to Brønsted acidity character of ceria, which makes it a potential choice in industrial applications. The good performance of nanocomposite could be the result of the synergistic effect between Fe, Cu, and Ce. Regarding scavenging measurements results, the electro-Fenton process followed the Haber-Weiss mechanism. The by-products detection was performed using GC-MS analysis to propose an acceptable pathway for EF degradation of AO7. The BMG kinetics model (1/b = 0.969 (min) and 1/m = 0.269 (min^-1)) was matched with the experimental data and described the kinetics of reaction very well. The catalytic activity of CuFeO₂/CeO₂ almost remained after six cycles. Based on the obtained results, CuFeO₂/CeO₂ using the benefit of the synergistic effect of Ce³⁺ with Fe²⁺ and Cu⁺can be introduced as a promising novel catalyst for the electro-Fenton reaction in wastewater treatment.

Degradation of triphenyl phosphate (TPhP) by CoFe2O4-activated peroxymonosulfate oxidation process: Kinetics, pathways, and mechanisms

The aryl organophosphate flame retardant triphenyl phosphate (TPhP) has been frequently detected in environment and biota, and the potential risks of TPhP to aquatic organisms have also been demonstrated. The degradation of TPhP by CoFe₂O₄ activated peroxymonosulfate (PMS) was studied in this work. At initial pH of 7.0, 10 μM TPhP could be removed by 99.5% with 0.25 g/L CoFe₂O₄ and 0.5 mM PMS after 6 min oxidation, indicating the excellent performance of CoFe₂O₄ activated PMS process on the treatment of TPhP. The influence of PMS and CoFe₂O₄ dosage, initial pH, humic acid (HA), and anions (Cl^-, NO₃^-, and HCO₃^-) on TPhP degradation were investigated systematically. Results showed that the degradation of TPhP was enhanced with increasing PMS concentrations from 0.1 to 1 mM, while it reduced as CoFe₂O₄ dosage increased. TPhP degradation efficiencies depended on solution pH with neutral pH showing the optimum degradation conditions. Recycling experiment indicated that the CoFe₂O₄ nanoparticles (NPs) possessed high potential for reusability. The radical identification experiments were performed and SO₄•^- was confirmed as the dominant radicals in TPhP degradation, and activation mechanism of PMS by CoFe₂O₄ NPs was hence explained. Humic acids (HA) (2-20 mg/L) as the representative organic natural matter existing in environment inhibited TPhP removal. Anions including Cl^-, NO₃^-, and HCO₃^- all reduced TPhP degradation. In addition, TPhP degradation products were identified by liquid chromatography-mass spectrometry, and the degradation pathways of TPhP were proposed accordingly.

Efficient degradation of drug ibuprofen through catalytic activation of peroxymonosulfate by Fe3C embedded on carbon

Ibuprofen (IBU), a nonsteroidal anti-inflammatory drug, is becoming an important member of pharmaceuticals and personal care products (PPCPs) as emerging pollutants. To degrade IBU, magnetic Fe₃C nanoparticles embedded on N-doped carbon (Fe₃C/NC) were prepared as a catalyst by a sol-gel combustion method. As characterized, the Fe₃C/NC nanoparticles were composed of a NC nano-sheet and capsulated Fe₃C particles on the sheet. The Fe₃C/NC nanoparticles were confirmed an efficient catalyst for peroxymonosulfate (PMS) activation to generate sulfate radicals (SO₄^•-), single oxygen (¹O₂) and hydroxyl radicals (•OH) toward the degradation of IBU. The added IBU (10 mg/L) was almost completely removed in 30 min by using 0.1 g/L Fe₃C/NC and 2 g/L PMS. The catalyst was confirmed to have good ability and excellent reusability through leaching measurements and cycle experiments. A catalytic mechanism was proposed for the catalytic activation of PMS on Fe₃C/NC, which involves both Fe₃C reactive sites and N-doped carbon matrix as reactive sites in Fe₃C/NC. Moreover, the degradation pathway of IBU in the Fe₃C/NC-PMS system was proposed according to the detections of degradation intermediates.

Oxidative removal of carbamazepine by peroxymonosulfate (PMS) combined to ionizing radiation: Degradation, mineralization and biological toxicity

Carbamazepine is one of pharmaceutical and personal care products (PPCPs) and has been widely used to treat depression and seizures, and it cannot be effectively removed during the conventional wastewater treatment processes. In this study, three processes were used for the carbamazepine degradation, including single radiation, radiation in the presence of peroxymonosulfate (PMS) and radiation followed by PMS oxidation. The results show that radiation in the presence of PMS could enhance the degradation and mineralization of carbamazepine, decreasing the absorbed dose required for completely degrading carbamazepine from 800 Gy to 300 Gy, no matter what the molar ratio of PMS to carbamazepine was. The radiation followed by PMS oxidation significantly increased the mineralization, and the maximum mineralization achieved 46.5% at the dose of 600 Gy. Eight intermediates were tentatively identified. Compared to single radiation process, the radiation in the presence of PMS enhanced the transformation of intermediates and the release of ammonium ion. In real wastewater, the radiation in the presence of PMS could effectively remove carbamazepine and considerably decreased the biological toxicity of the wastewater containing carbamazepine.

Cu@Co-MOFs as a novel catalyst of peroxymonosulfate for the efficient removal of methylene blue

In this study, for the first time, we describe the single step synthesis of a Cu particle-doped cobalt-based metal-organic framework (Cu@Co-MOF) using a hydrothermal method. The as-prepared materials were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy-energy disperse spectroscopy, thermogravimetry, and X-ray photoelectron spectroscopy, which confirmed the incorporation of zero-valent copper on the surface of the Co-MOFs. The heterogeneous catalytic activity of Cu@Co-MOFs was tested to activate peroxymonosulfate (PMS) for the removal of methylene blue (MB). The ratio of n(Cu)/n(Co) in the Cu@Co-MOFs showed a strong impact on the catalytic activity of the Cu@Co-MOFs, whereas a n(Cu)/n(Co) of 1 : 1 exhibited the best catalytic performance and obtained 100% MB removal within 30 min. The effects of initial pH, reaction temperature, PMS concentration, and catalyst dosages were investigated in this study. The stability and reusability of the Cu@Co-MOFs were also investigated. The results showed a low decline in the MB removal with the increase in cycle numbers, whereas 100% MB was removed by prolonging the reaction time. Heterogeneous reactions taking place in the pores and surface of the Cu@Co-MOFs played an important role in the generation of the sulfate radicals (SO4˙-) and hydroxyl radicals (·OH) that were the primary reactive species responsible for MB degradation.

Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C₃N₄) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C₃N₄ exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C₃N₄. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C₃N₄ surface via C-O bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C₃N₄. Superoxide radical (·O₂^-) dominates the degradation of DCF, while holes (h⁺) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f⁰) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and C-N bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C₃N₄-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation

Metal-free photocatalysts have attracted growing concern in recent years. In this work, a new class of carbon quantum dots (CQDs) modified porous graphitic carbon nitride (g-C₃N₄) is synthesized via a facile polymerization method. With the optimal CQDs loading, the CQDs modified g-C₃N₄ exhibits ∼15 times higher degradation kinetic towards diclofenac (DCF) than that of pure g-C₃N₄. The enhanced photocatalytic activity can be ascribed to the improved separation of charge carriers as well as the tuned band structure. Moreover, a photosensitation-like mechanism is proposed to elucidate the photo-generated electrons transfer and reactive radicals formation. CQDs are anchored to g-C₃N₄ surface via CO bond, which provide channels for the preferential transfer of photo-excited electrons on DCF molecule to the conduction band of g-C₃N₄. Superoxide radical (·O₂^-) dominates the degradation of DCF, while holes (h⁺) show a negligible contribution. Density functional theory (DFT) calculation successfully predicts that the sites on DCF molecule with high Fukui index (f⁰) are preferable to be attacked by radicals. DCF degradation pathway mainly includes ring hydroxylation, ring closure and CN bond cleavage processes. Acute toxicity estimation indicates the formation of less toxic intermediates/products compared to DCF after photocatalysis. Moreover, the hybrid photocatalysts exhibit good reusability in five consecutive cycles. This work not only proposes a deep insight into photosensitation-like mechanism in the photocatalysis system by using C₃N₄-based materials, but also develops new photocatalysts for potential application on removal of emerging organic pollutants from waters and wastewaters.

Highly efficient catalysis of chalcopyrite with surface bonded ferrous species for activation of peroxymonosulfate toward degradation of bisphenol A: A mechanism study

Chalcopyrite nanoparticles (CuFeS₂ NPs) with abundant surface bonded ferrous were successfully prepared, characterized and used as a catalyst for peroxymonosulfate (PMS) activation and BPA degradation. The effect of reaction parameters such as initial pH, catalyst load, PMS concentration, initial BPA concentration and reaction temperature on BPA degradation in CuFeS₂-PMS system was systematically investigated. As a bimetallic sulfide, CuFeS₂ exhibits ultra-high activity for PMS activation compared with Cu₂S, FeS₂, CuFeO₂ and Co₃O₄. It was found that by co-use of 0.1 g L^-1 CuFeS₂ and 0.3 mmol L^-1 PMS, 20 mg L^-1 of BPA was almost completely degraded (99.7%) and reached a mineralization rate of 75% within 20 min. The highly catalytic activity of CuFeS₂ is closely related to two aspects: one is that S^2- in the catalysts promotes the cycling of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ cycles on the surface, and the other is the synergistic effect of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ cycles in the PMS activation. These interesting findings shed some new insight on the development of metal sulfides for the oxidative treatment of organic contaminants.

Activation CuFe2O4 by Hydroxylamine for Oxidation of Antibiotic Sulfamethoxazole

A new potential oxidation process is provided by CuFe₂O₄/hydroxylamine (HA) system for degradation of antibiotics in water. The CuFe₂O₄/HA system can generate reactive oxygen species (ROS) for the degradation of sulfamethoxazole (SMX). The addition of radical scavengers, including benzoquinone (BQ) and catalase (CAT), inhibited the oxidation of SMX in CuFe₂O₄/HA system. Electron transfer in the CuFe₂O₄/HA system played a key function for the generation of ROS and the degradation of SMX. The main ROS, was the superoxide radical (O₂^•-) mainly generated from adsorbed oxygen (O_2(A)), which came from the oxidation of the lattice oxygen (O^2-_(L)) in CuFe₂O₄. The CuFe₂O₄/HA system was effectively applicable for a broad pH range (approximately 5-10). In addition, the activation mechanism for CuFe₂O₄/HA system was studied with the target contaminant SMX. Finally, the degradation pathways of SMX were proposed under the optimal conditions in CuFe₂O₄/HA system.

Wastewater cleanup using Phlebia acerina fungi: An insight into mycoremediation

The scarcity of available drinking water has led the researchers to develop novel and cost-effective ways of bioremediation process for wastewater treatment. Bioremediation is a cost-effective and environmentally sound method for the removal of toxic compounds. Such approach is not only a chemical-less effort but also an energy savior. In the present work Phlebia acerina, a white rot wood rotting fungi have been used to degrade the toxic wastewater pollutants. Congo Red (CR) and Eriochrome Black T (EBT) have been selected as model pollutants to test the wastewater cleaning ability of the fungus. The Lignin modifying enzyme (LME) and Cellulolytic enzyme assays (CMC) potential of Phlebia acerina helped in understanding the dye degradation mechanism. Under the optimum conditions, the fungi was able to degrade as high as 92.4% CR while the EBT was degraded to a maximum of 50%. Phlebia acerina was found to show first-order kinetics of dyes degradation. Further, the seed germination and antimicrobial assay of treated and untreated water were carried out in order to establish the formation of non-toxic end product after degradation.

Photocatalytic activation of peroxymonosulfate by TiO2 anchored on cupper ferrite (TiO2@CuFe2O4) into 2,4-D degradation: Process feasibility, mechanism and pathway

A thorough study of photo-oxidation efficiency of TiO₂@CuFe₂O₄ dissociating peroxymonosulfate (PMS) is reported in detail. The origin of high catalytic activity was discussed as evidence by numerous controlled trials and several operational parameters. Based on quenching tests, possible mechanism and pathway of degradation were proposed. 2,4-dichlorophenoxyacetic acid (2,4-D) degradation in TiO₂@CuFe₂O₄/UV/PMS system could abide pseudo-first-order kinetics. Moreover, reaction rate constant (K_obs) showed a linear increasing trend as PMS and catalyst concentrations increased. Over 97.2% of 2,4-D (20 mg/L) was degraded within 60 min at 0.3 mM PMS and 0.1 g/L TiO₂@CuFe₂O₄. However, the water matrix species inhibited 2,4-D degradation to different amounts and the inhibiting effect was as follows: HCO₃- > NO₃-  > Cl- > SO₄^2-. As-prepared catalyst showed a high ability of PMS activation, compared to other studied oxidants. Particularly, sulfate radicals were accounted for 2,4-D degradation in the catalytic oxidation reaction. TiO₂@CuFe₂O₄ catalyst displayed the excellent recyclability and durability. Identification of intermediates and end-products brought about the conclusion that enhanced degradation involving dechlorination, dehydrogenation, hydroxylation, and ring cleavage, through SO₄^-, OH, O₂^- and holes attack during TiO₂@CuFe₂O₄/PMS photocatalysis of 2,4-D. As conclusion, integration of TiO₂, CuFe₂O₄ and UV light to efficient activation of PMS can be proposed as a successful and promising method to wastewater treatment effectively, because of the cogeneration of different reactive oxidizing species, simple and easy recovery of catalyst and good catalytic activity.

Heterogeneous activation of peroxymonosulfate by LaCo1-xCuxO3 perovskites for degradation of organic pollutants

Recently cobalt-based heterogeneous catalysts have been widely investigated for peroxymonosulfate (PMS) activation in sulfate radical-based advanced oxidation processes. However, the improvement of the catalytic performance for PMS activation remains to be a challenge. As the limiting step, the rapid transformation of Co^II/Co^III redox pairs is crucial for PMS activation. Perovskites attract increasing attention due to their controllable oxidation state of B-site metal and formation of oxygen vacancies, which accelerates the cycle of redox pairs. LaCo_1-xM_xO₃ (M = Cu, Fe and Mn) perovskites as heterogeneous catalysts of PMS were synthesized for the degradation of phenol. The results showed that LaCo_0.4Cu_0.6O₃ exhibited the highest catalytic activity. The pseudo first-order kinetic constant of phenol degradation on LaCo_0.4Cu_0.6O₃ is 0.302 min^-1, being about 5 times as high as Co²⁺ with same molar concentration of cobalt in LaCo_0.4Cu_0.6O₃. XPS analysis confirmed that substitution of copper could promote the cycle of Co^II/Co^III, thus enhance the catalytic efficiency for PMS activation. The facilitated cycle of Co^II/Co^III played a crucial role in the generation of sulfate radicals, hydroxyl radicals and singlet oxygen. And sulfate radical was the primary radical responsible for pollutants degradation. The results provide insights into constructing novel perovskite catalysts for the removal of organic pollutants in water.

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-Like Reaction and Organic Pollutant Degradation

The development of efficient heterogeneous Fenton catalysts is mainly by "trial-and-error" concept and the factor determining H₂O₂ activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O-O bond in H₂O₂ is the key parameter determining the Fenton catalyst's activity. CuFeO₂ nanocubes and nanoplates with different surface facets of {110} and {012} are used to compare the effect of exposed facets on Fenton activity. The results indicate that ofloxacin (OFX) degradation rate by CuFeO₂ {012} is four times faster than that of CuFeO₂ {110} (0.0408 vs 0.0101 min^-1). In CuFeO₂ {012}-H₂O₂ system, OFX is completely removed at a pH range 3.2-10.1. The experimental results and theoretical simulations show that ^•OH is preferentially formed from the reduction of absorbed H₂O₂ by electron from CuFeO₂ {012} due to suitable elongation of O-O (1.472 Å) bond length in H₂O₂. By contrast, the O-O bond length is elongated from 1.468 to 3.290 Å by CuFeO₂ {110} facet, H₂O₂ tends to be dissociated into -OH group and passivates {110} facet. Besides, the new formed ≡Fe²⁺* on CuFeO₂ {012} facet can accelerate the redox cycle of Cu and Fe species, leading to excellent long-term stability of CuFeO₂ nanoplates.

Synthesis of Cu2O-CuFe2O4 microparticles from Fenton sludge and its application in the Fenton process: the key role of Cu2O in the catalytic degradation of phenol

This paper presents the key role of Cu2O in Fenton catalysis using Cu2O-CuFe2O4 magnetic microparticles, which were prepared using Fenton sludge as an iron source. The catalytic activity of the as-prepared Cu2O-CuFe2O4 and CuFe2O4 microparticles was evaluated in a heterogeneous Fenton system for the degradation of recalcitrant phenol. The Cu2O-CuFe2O4 microparticles demonstrated relatively superior catalytic performance as compared to CuFe2O4 microparticles when used as a Fenton catalyst. The relatively higher catalytic activity of Cu2O-CuFe2O4 for phenol degradation during the Fenton process could be attributed to the availability of both monovalent [Cu(i)] and divalent [Cu(ii)] as well as Fe(ii)/Fe(iii) redox pairs, which could react quickly with H2O2 to generate hydroxyl radicals (HO˙). An electron bridge was formed between Cu(i) and Fe(iii), which accelerates the formation of Fe(ii) species in order to boost the reaction rate. Highly reactive and excessively available Cu(i) species for as prepared Cu2O-CuFe2O4 microparticles could be considered to be rather crucial for the generation of highly reactive HO˙ radical species. In addition, the as-prepared Cu2O-CuFe2O4 magnetic microparticles exhibited sound stability and reusability.