Visible light enhanced heterogeneous photo-degradation of Orange II by zinc ferrite (ZnFe2O4) catalyst with the assistance of persulfate

Activation of peroxymonosulfate by β-FeOOH@Cia-MoS2 for enhancing degradation of tetracycline: Significant roles of surface functional groups and Fe/Mo redox reactions

Vertically oriented interstitial atom carbon-anchored molybdenum disulfide (Cia-MoS2) nanospheres loaded with iron oxyhydroxide (β-FeOOH) were proposed for modulating the surface catalytic activity and stability of the unsaturated catalytic system. The β-FeOOH@Cia-MoS2 efficiently activated peroxymonosulfate (PMS) to degrade 95.4% of tetracycline (TC) within 30 min, owing to the more sulfur vacancies, higher surface hydroxyl density, redox ability and electronic transmission rate of β-FeOOH@Cia-MoS2. According to the characterization and analysis data, the multiple active sites (Fe, Mo and S sites) and oxygen-containing functional groups (CO, -OH) of β-FeOOH@Cia-MoS2 could promote the activation of PMS to form reactive oxygen species (ROS). The oxidation cycle of Fe(II)/Fe(III) and Mo(IV)/Mo(VI), the electron transfer mediator of rich sulfur vacancies, as well as oxygen-containing functional groups on the surface of β-FeOOH@Cia-MoS2 synergistically promoted the formation of ROS (1O2, FeIVO, SO4•- and •OH), among which 1O2 was the main active oxidant. In particular, the β-FeOOH@Cia-MoS2/PMS system could still degrade pollutants efficiently and stably after five recycling cycles. Furthermore, this system had a strong anti-interference ability in the actual water body. This study provided a promising strategy for the removal of difficult-to-degrade organic pollutants.

Highly efficient targeted adsorption and catalytic degradation of ciprofloxacin by a novel molecularly imprinted bimetallic MOFs catalyst for persulfate activation

Given the presence of emerging pollutants at low concentrations in water bodies, which are inevitably affected by background substances during the removal process. In this study, we synthesized molecularly imprinted catalysts (Cu/Ni-MOFs@MIP) based on bimetallic metal-organic frameworks for the targeted degradation of ciprofloxacin (CIP) in advanced oxidation processes (AOPs). The electrostatic interaction and functional group binding of CIP with specific recognition sites on Cu/Ni-MOFs@MIP produced excellent selective recognition (Qmax was 14.82 mg g-1), which enabled the active radicals to approach and remove the contaminants faster. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed the coexistence of ∙OH, SO42-, and 1O2, with ∙OH dominating the system. Based on experimental and theoretical calculations, the reaction sites of CIP were predicted and the possible degradation pathways and mechanisms of Cu/Ni-MOFs@MIP/PMS systems were proposed. This study opens up a new platform for the targeted removal of target pollutants in AOPs.

Enhanced activation of peroxymonosulfate for advanced oxidation processes using solid waste: A novel and easy implement high-value utilization process of slag

A simple, efficient and low energy-consuming process available to generate resultful radicals from PMS for organic pollutants removal had been employed in this study. Slag had been used as the activator for organic pollutants degradation under slag/PMS advanced oxidation process. In this work, effects of slag with or without pretreatment on pollutant removal were studied and radical species generated by slag were measured. Calcination pretreatment is one efficient method to enhance the degradation efficiency significantly. Due to Fe3O4 and Fe2O3 became the dominant phases after calcination, it was about 8.6-flods increasing after comparing the pollutant removal efficiency for different slag/PMS system with calcination pretreatment or not. Organic pollutant neither degraded in PMS system at 25 °C nor being absorbed by slag system for 60 min. On the contrary, up to 90% pollutant concentration reduction achieved in the slag/PMS process. During this process, both •OH and SO4•- had been detected once slag and PMS interaction in wastewater. Through the free radicals quenching tests,•OH should be the key free radical in this advanced oxidation process for the organic pollutant removal under this alkaline condition. In general, organic degradation rate was determined by the slag dosage, and the maximum degradation efficiency was mainly controlled by the PMS usage. This work is expected to broaden the high-value reutilization way for industrial solid waste.

Enhanced degradation of herbicides in groundwater using sulfur-containing reductants and spinel zinc ferrite activated persulfate

A challenge to successfully implementing an injection-based remedial treatment in aquifers is to ensure that the oxidative reaction is efficient and lasts long enough to contact the contaminated plume. Our objective was to determine the efficacy of zinc ferrite nanocomposites (ZnFe2O4) and sulfur-containing reductants (SCR) (i.e., dithionite; DTN and bisulfite; BS) to co-activate persulfate (S2O82-; PS) and treat herbicide-contaminated water. We also evaluated the ecotoxicity of the treated water. While both SCRs delivered excellent PS activation in a 1:0.4 ratio (PS:SCR), the reaction was relatively short-lived. By including ZnFe2O4 in the PS/BS or PS/DTN activations, herbicide degradation rates dramatically increased by factors of 2.5 to 11.3. This was due to the SO4- and OH reactive radical species that formed. Radical scavenging experiments and ZnFe2O4 XPS spectra results revealed that SO4- was the dominant reactive species that originated from S(IV)/PS activation in solution and from the Fe(II)/PS activation that occurred on the ZnFe2O4 surface. Based on liquid chromatography mass spectrometry (LC-MS), atrazine and alachlor degradation pathways are proposed that involve both dehydration and hydroxylation. In 1-D column experiments, five different treatment scenarios were run using 14C-labeled and unlabeled atrazine, and 3H2O to quantify changes in breakthrough curves. Our results confirmed that ZnFe2O4 successfully prolonged the PS oxidative treatment despite the SCR being completely dissociated. Toxicity testing showed treated 14C-atrazine was more biodegradable than the parent compound in soil microcosms. Post-treatment water (25 %, v/v) also had less impact on both Zea Mays L. and Vigna radiata L. seedling growth, but more impact on root anatomies, while ≤4 % of the treated water started to exert cytotoxicity (<80 % viability) on ELT3 cell lines. Overall, the findings confirm that ZnFe2O4/SCR/PS reaction is efficient and relatively longer lasting in treating herbicide-contaminated groundwater.

Efficient degradation of the refractory organic pollutant by underwater bubbling pulsed discharge plasma: performance, degradation pathway, and toxicity prediction

It is essential to develop an efficient technology for the elimination of refractory contaminants due to their high toxicity. In this study, a novel underwater bubbling pulsed discharge plasma (UBPDP) system was proposed for the degradation of Orange II (OII). The degradation performance experiments showed that by enhancing the peak voltage and pulse frequency, the degradation efficiency of OII increased gradually. The removal efficiencies under different air flow rates were close. Reducing OII concentration and solution conductivity could promote the elimination of OII. Compared with neutral and alkaline conditions, acidic condition was more beneficial to OII degradation. The active species including ·OH, ·O2-, 1O2, and hydrated electrons were all involved in OII degradation. The concentrations of O3 and H2O2 in OII solution were lower than those in deionized water. During discharge, the solution pH increased while conductivity decreased. The variation of UV-vis spectra with treatment time indicated the effective decomposition of OII. Possible degradation pathways were speculated based on LC-MS. The toxicity of intermediate products was predicted by the Toxicity Estimation Software Tool. Coexisting constituents including Cl-, SO42-, HCO3-, and humic acid had a negative effect on OII removal. Finally, the comparison with other technology depicted the advantage of the UBPDP system.

Review on magnetic spinel ferrite (MFe2O4) nanoparticles: From synthesis to application

Magnetic spinel ferrite materials offer various applications in biomedical, water treatment, and industrial electronic devices, which has sparked a lot of attention. This review focuses on the synthesis, characterization, and applications of spinel ferrites in a variety of fields, particularly spinel ferrites with doping. Spinel ferrites nanoparticles doped with the elements have remarkable electrical and magnetic properties, allowing them to be used in a wide range of applications such as magnetic fields, microwave absorbers, and biomedicine. Furthermore, the physical properties of spinel ferrites can be modified by substituting metallic atoms, resulting in improved performance. The most recent and noteworthy applications of magnetic ferrite nanoparticles are reviewed and discussed in this review. This review goes over the synthesis, doping and applications of different types of metal ferrite nanoparticles, as well as views on how to choose the appropriate magnetic ferrites based on the intended application.

Photocatalytic degradation of tetracycline hydrochloride by lanthanum doped TiO2@g-C3N4 activated persulfate under visible light irradiation

In this work, a visible light-driven La/TiO2@g-C3N4 photocatalyst was synthesized for the photodegradation of tetracycline hydrochloride (TCH) in the presence of peroxydisulfate (PDS) in an internal loop-lift reactor. The surface morphology and structure of La/TiO2@g-C3N4 have been characterized by XRD, SEM-EDS, FTIR, XPS, and UV/vis DRS. La/TiO2@g-C3N4 displays outstanding photocatalytic performance and reusability. After four reuse cycles of the vis/La/TiO2@g-C3N4/PDS system, the TCH degradation rate and efficiency still reached 0.083 min-1 and 97.68%, respectively. Reactive species in this system included free radicals SO4˙-, ˙OH, and ˙O2 -, as well as non-radicals e-, and h+, as established from the results of chemical quenching experiments. Moreover, a mechanism of action of the vis/La/TiO2@g-C3N4/PDS system for TCH degradation was proposed. The acute toxicity of the reaction solution towards Photobacterium phosphoreum T3 spp. in the vis/La/TiO2@g-C3N4/PDS process increased during the first 60 min and then decreased, illustrating that vis/La/TiO2@g-C3N4/PDS provided an effective and safe method for the removal of TCH.

Establishment of a novel system for photothermal removal of ampicillin under near-infrared irradiation: Persulfate activation, mechanism, pathways and bio-toxicology

One of the most effective ways to address the problems of low solar spectrum utilization in photocatalysis and the high cost of persulfate activation technology is to create a cost-effective synergistic photothermal persulfate system. In this work, a brand-new composite catalyst called ZnFe₂O₄/Fe₃O₄@MWCNTs (ZFC) was developed to activate PDS (K₂S₂O₈) from the aforementioned basis. ZFC's surface temperature could unbelievably reach 120.6 °C in 150 s together with the degrading synergistic system solution temperature could reach 48 °C under near-infrared light (NIR) in 30 min, thus accelerating the ZFC/PDS decolorization rate for reactive blue KN-R (150 mg/L) to 95% in 60 min. Furthermore, the ZFC's ferromagnetism bore it with good cycling performance, allowing it to maintain an 85% decolorization rate even after 5 cycles with OH·, SO₄^-·, ¹O₂, and O₂^-· dominating the degrading process. In the meantime, the DFT calculations of the kinetic constants for the entire process of S₂O₈^2- adsorption on Fe₃O₄ in dye degradation solution were in agreement with the outcomes of the experimental pseudo-first-order kinetic fitting. By analyzing the particular degradation route of ampicillin (50 mg/L) and the possible environmental impact of the intermediate using LC-MS and the toxicological analysis software (T.E.S.T.), respectively, it was shown that this system might function as an environmentally friendly method for removing antibiotics. This work may provide some productive research lines for the creation of a photothermal persulfate synergistic system and suggest fresh approaches to water treatment technology.

Insights into the degradation of diphenhydramine - An emerging SARS-CoV-2 medicine by UV/Sulfite

As Diphenhydramine (DPH) has been considered as a drug to treat SARS-CoV-2, the degradation of DPH from water was investigated and evaluated in this study by adopting an advanced oxidation/advanced reduction process - the UV/sulfite process. The UV/sulfite system was able to eliminate DPH within 6 mins under UV254nm and 1.0 mM sulfite. It was observed that the presence ofN O 3 - ,N O 2 - ,C l - ,H C O 3 - , andS O 4 2 - anions in water can affect the performance of UV/Sulfite degradation system. The mechanism of UV/sulfite/anions was evaluated which the presence ofN O 3 - in UV/sulfite process has revealed faster initial decay rate but lower final DPH removal. It was observed that the UV/Sulfite process was extremely sensitive to pH as the dissociation of ion species varied among pH. The reaction became sluggish in acidic solution due to the dissociation of less reactive species such as HSO3 -. In alkaline solution, SO3 2- was the dominant species, producing powerfulSO 3 ∙ - ande aq - when activated by UV at 254 nm. By conducting LC/MS analysis, the degradation pathway was proposed and can be summarized into four main pathways: hydroxylation, side chain cleavage, losing aromatic ring or ring opening. Scavenging tests were also carried out and validated the presence of various radicals contributing to the reaction, includinge aq - , H˙, OH˙, SO3 ˙-, O2 •- and SO4 ˙-.

Identification and characterization of Fe3O4/peroxodisulfate advanced oxidation products from sulfameter

Sulfonamides (SAs) are one of the most widely used antibiotics and their residuals in the environment could cause some negative environmental issues. Advanced oxidation such as Fenton-like reaction has been widely applied in the treatment of SAs polluted water. Degradation rates of 95%-99.7% were achieved in this work for the tested 8 SAs, including sulfisomidine, sulfameter (SME), phthalylsulfathiazole, sulfamethoxypyridazine, sulfamonomethoxine, sulfisoxazole, sulfachloropyridazine, and sulfadimethoxine, in the Fe₃O₄/peroxodisulfate (PDS) oxidation system after the optimization of PDS concentration and pH. Meanwhile, it was found that a lot of unknown oxidation products were formed, which brought up the uncertainty of health risks to the environment, and the identification of these unknown products was critical. Therefore, SME was selected as the model compound, from which the oxidation products were never elucidated, to identify these intermediates/products. With liquid chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS), 10 new products were identified, in which 2-amino-5-methoxypyrimidine (AMP) was confirmed by its standard. The investigation of the oxidation process of SME indicated that most of the products were not stable and the degradation pathways were very complicated as multiple reactions, such as oxidation of the amino group, SO₂ extrusion, and potential cross-reaction occurred simultaneously. Though most of the products were not verified due to the lack of standards, our results could be helpful in the evaluation of the treatment performance of SAs containing wastewater.

Facile synthesis of magnetic ZnFe2O4/AC composite to activate peroxydisulfate for dye degradation under visible light irradiation

Heterogeneous photocatalysis/persulfate oxidation process has been considered as a promising technology for dye contaminants removal. The magnetic ZnFe₂O₄/active carbon (AC) composites were hydrothermally synthesized and firstly used to activate peroxydisulfate (PDS) for rhodamine B (RhB) degradation under visible LED light irradiation. The optimized Vis-ZnFe₂O₄/AC(4/1)-PDS system can enhance the RhB degradation efficiency by 32.01% and 13.87% compared with Vis-ZnFe₂O₄-PDS and Vis-AC-PDS systems, respectively. The influence of operational parameters such as catalyst dosage (0.2 - 0.4 g L^-1), PDS concentration (1.0 - 2.0 g L^-1), temperature (25 - 45 °C), solution pH (2.7 - 10.9), and coexisting inorganic ions (Cl^-, NO₃^-, HCO₃^-, PO₄^3-, Cu²⁺, Fe³⁺, and Ca²⁺) on RhB degradation was studied, and 100% of RhB (20 mg L^-1) was degraded after 80 min at operational condition: 0.30 g L^-1 of ZnFe₂O₄/AC(4/1) and 1.5 g L^-1 of PDS, solution pH of 2.74, reaction temperature of 25 °C. The quenching experiments, EPR test, and XPS analysis were employed to reveal the proposed mechanism, which demonstrated that ¹O₂ played a more important role than other reactive species (SO₄^•-, •OH, O₂^•-, and h⁺) in RhB degradation. The generation of ¹O₂ via the two routes was as follows: (i) the in situ formed active oxygen (O^*) reacted with HSO₅^- to produce ¹O₂; (ii) O₂^•- was oxidized by h⁺ to form ¹O₂. After five consecutive cycles, the photodegradation efficiency of RhB by ZnFe₂O₄/AC(4/1) catalyst slightly decreased from 88.52 to 83.92%, indicating the excellent reusability of ZnFe₂O₄/AC(4/1) photocatalyst. As designed, Vis-ZnFe₂O₄/AC-PDS oxidation system can effectively remove RhB from the different real water matrices, and the degradation efficiency of RhB in tap water, river water, and secondary effluent was 78.24%, 79.55%, and 74.53% after 80 min of reaction, respectively.

Heterogeneous Activation of Peroxymonosulfate by a Spinel CoAl2O4 Catalyst for the Degradation of Organic Pollutants

Bimetallic catalysts have significantly contributed to the chemical community, especially in environmental science. In this work, a CoAl2O4 spinel bimetal oxide was synthesized by a facile co-precipitation method and used for the degradation of organic pollutants through peroxymonosulfate (PMS) activation. Compared with Co3O4, the as-prepared CoAl2O4 possesses a higher specific surface area and a larger pore volume, which contributes to its becoming increasingly conducive to the degradation of organic pollutants. Under optimal conditions (calcination temperature: 500 °C, catalyst: 0.1 g/L, and PMS: 0.1 g/L), the as-prepared CoAl2O4 catalyst could degrade over 99% of rhodamine B (RhB) at a degradation rate of 0.048 min−1, which is 2.18 times faster than Co3O4 (0.022 min−1). The presence of Cl− could enhance RhB degradation in the CoAl2O4/PMS system, while HCO3− and CO32− inhibit RhB degradation. Furthermore, the considerable reusability and universality of CoAl2O4 were testified. Through quenching tests, 1O2 and SO4•− were identified as the primary reactive species in RhB degradation. The toxicity evaluation verified that the degraded solution exhibited lower biological toxicity than the initial RhB solution. This study provides new prospects in the design of cost-effective and stable cobalt-based catalysts and promotes the application of PMS-based advanced oxidation processes for refractory wastewater treatment.

Efficient degradation of bisphenol A with MoS2/BiVO4 hetero-nanoflower as a heterogenous peroxymonosulfate activator under visible-light irradiation

Photocatalyst activated peroxymonosulfate (PMS) under visible-light irradiation to construct a photo-Fenton system has shown great application prospect for environmental remediation. In this study, MoS₂/BiVO₄ heterojunction nanoflowers were successfully synthesized by hydrothermal method and used to activate PMS under visible-light to achieve highly efficient degradation of bisphenol A (BPA). The constructed heterojunction showed excellent catalytic activity, which was attributed to the synergistic effect of effective separation of charge carriers and PMS activation. In the MoS₂/BiVO₄/PMS/vis system, 2-MoS₂/BiVO₄ (2-MB) exhibited the highest degradation rate constant for BPA (0.1747 min^-1), which was 91.9 times of pure MoS₂ and 38.0 times of pure BiVO₄, respectively. The electron paramagnetic resonance (EPR) and radical quenching experiments demonstrated that the oxidative degradation of BPA was mainly participated by SO₄^-, OH, ¹O₂ and h⁺ active species. Through the analysis of energy band structure and element valence state of photocatalyst and the identification of reaction intermediates, the degradation mechanism and degradation pathways were proposed. In addition, MoS₂/BiVO₄ heterojunction showed high catalytic ability for various organic pollutants (herbicides, pesticide intermediates, antibiotics and dyes), and common anions (Cl^-, SO₄^2- and NO₃^-) and humic acid (HA) had little effect on its degradation efficiency. This study has provided a new solution for the use of heterojunction photocatalysts for visible-light assisted PMS activation to achieve highly efficient degradation of organic pollutants.

Advanced Oxidation Processes Based on Sulfate Radicals for Wastewater Treatment: Research Trends

In this work, the recent trends in the application of the sulfate radical-based advanced oxidation processes (SR-AOPs) for the treatment of wastewater polluted with emerging contaminants (ECs) and pathogenic load were systematically studied due to the high oxidizing power ascribed to these technologies. Additionally, because of the economic benefits and the synergies presented in terms of efficiency in ECs degradation and pathogen inactivation, the combination of the referred to AOPs and conventional treatments, including biological processes, was covered. Finally, the barriers and limitations related to the implementation of SR-AOPs were described, highlighting the still scarce full-scale implementation and the high operating-costs associated, especially when solar energy cannot be used in the oxidation systems.

Facile synthesis of graphitic carbon nitride from acetic acid pretreatment to activate persulfate in presence of blue light for photocatalytic removal of metronidazole

Activation of persulfate (PS) in presence of blue LED light (λ_max ∼454 nm) using acetic acid modified graphitic carbon nitride (ACN) was investigated. Usage of acetic acid had improved the specific surface area (SSA, 21.89 m² g^-1) of ACN compared with pristine graphitic carbon nitride (GCN) and it also reduced interfacial charge transfer resistance in ACN. Subsequently, photocatalytic removal of metronidazole (MET) was investigated using ACN. It was observed that upward shift in the conduction band (CB) in ACN produced the reduction of PS to form sulfate radicals (SO₄^.-) (CB of ACN (-1.25 V vs normal hydrogen electrode (NHE); Bandgap = 2.77 eV) and GCN (-1.23 V vs NHE; Bandgap = 2.73 eV)), which enhanced the MET removal. Moreover, batch experiments were conducted to quantify the effects of PS dosage (0.08-0.40 g L^-1), ACN dosage (0.20-2 g L^-1), light intensity (15-45 W), and pH (2-13.50). ACN (1 g L^-1) and GCN (1 g L^-1) with 0.16 g L^-1 of PS have shown 100% and 76.1% MET (C_o-10 mg L^-1) removal within 300 min, respectively, and the removal followed zero-order kinetics (k ∼2.39 mg L^-1 h^-1). However, MET mineralization was approximately 30% with ACN. MET removal had decreased with increase in pH and almost complete inhibition was observed at pH ∼12. Overall, it was identified that SO₄^.- was the major reactive species whereas holes (h⁺) in the valence band (VB) of ACN (1.52 V vs NHE) played a minor role in MET removal.

Recent advancements of spinel ferrite based binary nanocomposite photocatalysts in wastewater treatment

A lot of studies on spinel ferrites (MFe₂O₄, M = divalent metal ion) and their binary nanocomposites as photocatalysts in the decontamination of wastewater have been performed, because MFe₂O₄ nanoparticles are relatively stable, biocompatible and low-cost efficient photocatalyst. The separation of MFe₂O₄ photocatalyst is easy owing to its excellent magnetic behavior. With this background, the recent developments on photocatalytic performances of MFe₂O₄ based binary nanocomposites were comprehensively reviewed. Especially, a focus on MFe₂O₄/metal oxides, MFe₂O₄/carbon based materials, MFe₂O₄/polymers, MFe₂O₄/metal nanoparticles and MFe₂O₄/other compounds for the photocatalytic degradation of dyes, emerging contaminants and inorganic pollutants has been thoroughly given. The advantages of MFe₂O₄ based nanocomposites as photocatalysts were also discussed. In addition, the possible pathway of active free radical generation by these photocatalysts under visible and ultraviolet irradiation has been explained. A comparison of photocatalytic activities of MFe₂O₄ based binary nanocomposites with recent reports has been carried out. This review concludes that MFe₂O₄ based binary nanocomposites have potential capacity in water purification technology. Nevertheless, their practical utilization in water treatment plants still needs to be further studied.

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.

RETRACTED: Visible-light-induced photocatalytic mitigation of ibuprofen using magnetic black TiO2-x/CaFe2O4 decorated on diatomaceous earth

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editors-in-Chief. Jun Wang and Youtao Song are listed as authors on the manuscript but have informed the journal that this occurred without their consent or knowledge of the submission and the email addresses provided were fake. Jun Wang and Youtao Song do not support the scientific conclusions of the article. Qiong Wu and Yan Chen furthermore note significant scientific errors with the article (including the wrong deconvolution method used for analysis of the XPS data, misuse of some characterization images and inability to reproduce some of the photodegradation data). One of the conditions of submission of a paper for publication is that all authors must be aware of and agree with its submission. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Fabrication of Bi1.81MnNbO6.72/sulfite system for efficient degradation of chlortetracycline

The design of eco-friendly Bi_1.81MnNbO_6.72/sulfite system for efficient degradation of chlortetracycline was achieved. The feasibility of synthesizing Bi_1.81MnNbO_6.72 by hydrothermal method was determined by X-ray diffraction. The magnetic test suggested that Bi_1.81MnNbO_6.72 possessed paramagnetic properties, indicating unpaired electrons were present. Scanning electron microscope and transmission electron microscopy images revealed that Bi_1.81MnNbO_6.72 octahedra exhibited exposed [1,1,1] crystal plane containing high density of Bi, Mn and Nb metal atoms. Large numbers of metal atoms will facilitate heterogeneous catalytic process. In a batch system with aeration, Bi_1.81MnNbO_6.72 could be used as sulfite activator for the disposal of chlortetracycline. The reaction kinetics of the degradation process conformed to the pseudo-second-order kinetic model. In Bi_1.81MnNbO_6.72/sulfite process, initial pH, Bi_1.81MnNbO_6.72 dosage, sulfite and chlortetracycline concentrations, as well as inorganic salt ions had great effect on chlortetracycline degradation. Under optimal conditions, the efficiency of Bi_1.81MnNbO_6.72/sulfite system for degradation of chlortetracycline could reach 76.2%. Moreover, Mn (II) plays a key role in the initiation of the catalytic reaction in Bi_1.81MnNbO_6.72/sulfite process. Generated SO₃^●‒ could act as main reactive species in Bi_1.81MnNbO_6.72/sulfite process, while HO^● was also involved. Three new degradation products were detected by UHPLC/MS/MS and the possible degradation pathways in this system were proposed. Based on this, we believe that Bi_1.81MnNbO_6.72/sulfite is a type of process for degradation of organic contaminants with research significance and application prospects.

Peroxymonosulfate Activation on a Hybrid Material of Conjugated PVC and TiO2 Nanotubes for Enhancing Degradation of Rhodamine B under Visible Light

Visible-light-driven photocatalysis is a robust technology for amending the negative effect of pollutants on the environment with a minimum energy use. Herein, we describe a simple approach to producing such a photocatalyst by coupling conjugated polyvinyl chloride (cPVC) with the TiO2 nanotube (TNT) thermolysis method. By activating peroxymonosulfate (PMS) to make a cPVC/TNT/PMS system using visible light as the source, we obtain a significant enhancement in the photocatalytic performance. We show that PMS use at a concentration of 3 mM can fully degrade rhodamine B (RhB) solution at a remarkably high concentration (200 mg L-1) just in 120 min under visible light. The cPVC/TNT/PMS system also shows excellent stability in recycling tests for at least five times. Further, by confining the active species in photocatalytic reactions, we report a thorough understanding of the extent of involvement from those radicals. Our work presents a robust approach to make a high-performance, visible-light-driven photocatalyst, which can be potentially used in practice.

Novel franklinite-like synthetic zinc-ferrite redox nanomaterial: synthesis, and evaluation for degradation of diclofenac in water

The current study investigates a novel redox technology based on synthetic franklinite-like zinc-ferrite nanomaterial with magnetic properties and redox nature for potential use in water treatment. Physicochemical characterization revealed the nanoscale size and AB2O4 spinel configuration of the zinc-ferrite nanomaterial. The redox activity of nanoparticles was tested for degradation of diclofenac (DCF) pharmaceutical in water, without any added external oxidants and under dark experimental conditions. Results revealed ~90% degradation in DCF (10 μM) within 2 min of reaction using 0.17 g/L Zn1.0Fe2.0O4. Degradation of DCF was due to chemical reduction by surface electrons on zinc-ferrite and oxidation by oxygen-based radicals. Three byproducts from reduction route and eight from oxidation pathways were identified in the reaction system. Reaction pathways were suggested based on the identified byproducts. Results demonstrated the magnetic zinc-ferrite is a standalone technology that has a great promise for rapid degradation of organic contaminants, such as DCF in water.

Catalytic degradation of ciprofloxacin by a visible-light-assisted peroxymonosulfate activation system: Performance and mechanism

Peroxymonosulfate (PMS) is extensively used as an oxidant to develop the sulfate radical-based advanced oxidation processes in the decontamination of organic pollutants and various PMS activation methods have been explored. Visible-light-assisted PMS activation to construct a Fenton-like process has shown a great potential for pollution control. In our work, BiVO₄ nanosheets were prepared using a hydrothermal process and used to activate PMS under visible light. A rapid degradation of ciprofloxacin (CIP) was achieved by dosing PMS (0.96 g/L), BiVO₄ (0.32 g/L) under visible light with a reaction rate constant of 77.72-fold higher than that in the BiVO₄/visible light process. The electron spin resonance and free radical quenching experiments indicate that reactive species of ^•O₂^-, h⁺, •OH and SO₄^•- all worked, where h⁺, •OH and SO₄^•- were found as the dominant contributors to the CIP degradation. The spectroscopic analyses further demonstrate that the photoinduced electrons were directly involved in the PMS activation process. The generated ^•O₂^- was partially utilized to activate PMS and more •OH was produced because of the chain reactions between SO₄^•- and H₂O/OH^-. In this process, PMS acted as an electron acceptor to transfer the photo-induced charges from the conduction band of BiVO₄ and PMS was successfully activated to yield the high-powered oxidative species. From the degradation intermediates of CIP detected by a liquid-chromatography-mass spectrometer, the possible degradation pathways were proposed. The substantially decreased toxicity of CIP after the reaction was also observed. This work might provide new insights into the visible-light-assisted PMS activation mechanisms and is useful to construct environmentally-friendly catalytic processes for the efficient degradation of organic pollutants.

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.

Ultrasound-assisted heterogeneous peroxymonosulfate activation with Co/SBA-15 for the efficient degradation of organic contaminant in water

A potential advanced oxidation process is provided by SBA-15 supported cobalt (Co/SBA-15) activated peroxymonosulfate (PMS, HSO₅^-) in the ultrasound (US) enhanced system, named Co/SBA-15/PMS/US process, for the elimination of refractory organic contaminants (ROCs) in water. This process exhibited favorable behavior with 95.5 % C.I. Acid Orange 7 (AO7) degradation using 5 mM PMS, 0.5 g/L Co/SBA-15 catalyst, 190 W US power at initial pH of 6.0 after 90 min reaction. Co/SBA-15 particles remained satisfied catalytic activity and stability with very low level of cobalt release in 10 successive cycles. The scavenge tests and electron paramagnetic resonance (EPR) result as well as the cobalt leaching concentration revealed that the reactive radicals (SO₄^- and OH) on catalyst surface were primarily responsible for AO7 oxidation, and a rational mechanism was elucidated accordingly. The presence of chloride ions and bicarbonate could improve AO7 removal. The probable pathway of AO7 degradation was proposed based on the intermediates identified. This Co/SBA-15/PMS/US process could be well applied for the destruction of other typical ROCs (bisphenol A, clofibric acid, and rhodamine B) and the treatment of lake and river water spiked with AO7, and this study may provide an efficient PMS technique for the remediation of ROCs in water.

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.

Efficient photocatalytic removal of orange II by a Mn3O4-FeS2/Fe2O3 heterogeneous catalyst

Elemental doping has been proven to be an effective strategy for increasing the catalytic activity and structural stability of Fenton catalysts. Therefore, this work reports that Mn-doped FeS₂/Fe₂O₃ (Mn₃O₄-FeS₂/Fe₂O₃) has excellent catalytic performance for the degradation of Orange II under simulated solar energy. Degradation experiment results showed that the sample with a manganese-iron molar ratio of 1:2 exhibited higher activity than others. The degradation rate of 20 mg/L OII reached 99.0% in 18 min under the conditions of 0.3 g/L Mn₃O₄-FeS₂/Fe₂O₃, 5 mM H₂O₂ and pH = 2.8. In addition to, the Mn₃O₄-FeS₂/Fe₂O₃ catalyst shows good reusability for Orange II and high activity for other dyes (MB, MG, Rh B and MO) under optimal conditions. Degradation mechanism study indicated that the heterogeneous Fenton reaction was promoted by retarding the recombination of photogenerated charge carriers and accelerating the cycle between Fe³⁺/Mn²⁺ and Fe²⁺/Mn³⁺, which improved photo-Fenton-like catalytic performance, resulting in the enhanced degradation of organic pollutant. Finally, a possible degradation pathway was proposed according to the results of liquid chromatography-mass spectrometry (LC-MS). In short, the catalyst has potential application value in wastewater treatment.

A facile heterogeneous system for persulfate activation by CuFe2O4 under LED light irradiation

In this study, the removal performance for rhodamine B (RB) by persulfate (PS) activated by the CuFe2O4 catalyst in a heterogeneous catalytic system under LED light irradiation was investigated. The effect of vital experimental factors, including initial solution pH, CuFe2O4 dosage, PS concentration, co-existing anion and initial RB concentration on the removal of RB was systematically studied. The removal of RB was in accordance with the pseudo first-order reaction kinetics. Over 96% of 20 mg L-1 RB was removed in 60 min using 0.5 g L-1 CuFe2O4 catalyst and 0.2 mM PS at neutral pH. In addition, free radical quenching experiments and electron spin resonance (EPR) experiments were performed, which demonstrated the dominant role of sulfate radical, photogenerated holes and superoxide radical in the CuFe2O4/PS/LED system. The morphology and physicochemical properties of the catalyst were characterized by XRD, SEM-EDS, TEM, N2 adsorption-desorption isotherm, UV-vis DRS, and XPS measurements. Moreover, 18.23% and 38.79% total organic carbon (TOC) removal efficiency was reached in 30 min and 60 min, respectively. The catalyst revealed good performance during the reusability experiments with limited iron and copper leaching. Eventually, the major intermediates in the reaction were detected by GC/MS, and the possible photocatalytic pathway for the degradation of RB in the CuFe2O4/PS/LED system was proposed. The results suggest that the CuFe2O4/PS/LED system has good application for further wastewater treatment.

Magnetically retrievable ferrite nanoparticles in the catalysis application

In the present review, we summarized the applications of magnetic spinel ferrite nanoparticles as catalysts in organic reactions and transformations. Catalytic applications are comprised of using mostly cobalt, nickel, copper, and zinc ferrites, along with their mixed-metal combinations based on nano ferrites. The spinel ferrites (SFs) are gained principally by wet-chemical, sol-gel or co-precipitation methods, more infrequently by the mechanical high-energy ball milling, spark plasma sintering, sonochemical technique, microwave heating or hydrothermal route. Catalytic processes with the application of ferrite nanoparticles are included decomposition (in particular photocatalytic), reactions of dehydrogenation, oxidation, alkylation, CC coupling, removing organic/inorganic contaminants from aqueous solutions. As significant and remarkable advantages, ferrite nanocatalysts not only are environmentally benign and compatible with green chemistry aspects but also can be simply recovered from reaction systems and recycled up to several times almost without significant loss of their catalytic activity.

Insight into the mechanisms for hexavalent chromium reduction and sulfisoxazole degradation catalyzed by graphitic carbon nitride: The Yin and Yang in the photo-assisted processes

As robust polymeric catalysts, graphitic carbon nitride (g-C₃N₄) has been known to have great application potential in environmental remediation. However, the mechanisms in the photo-assisted catalytic processes during the reduction or oxidation of pollutants are still difficult to discern and therefore not well studied. In this work, visible-assisted catalytic reduction of hexavalent chromium (Cr(VI)) or oxidation of sulfisoxazole (SIZ) by g-C₃N₄ with the addition of formic acid (FA) or potassium peroxydisulfate (PS) were systematically investigated. Effects of operation parameters such as g-C₃N₄ dosage, FA concentration, Cr(VI) concentration, solution pH, PS concentration were studied. The results showed g-C₃N₄ can be effective and robust catalyst for both the reduction (Yin) and oxidation (Yang) reactions in the environmental remediation. Mechanisms were studied by using electron spin resonance (ESR) spectroscopy. The results revealed the CO 2^- is the predominant radical for Cr(VI) reduction in the g-C₃N₄/FA/Vis system and the SO₄^- and OH are all the main radicals for the oxidation of SIZ in the g-C₃N₄/PS/Vis system. The photo-generated carriers by g-C₃N₄, act as radical initiator, were responsible for the production of the reactive radical species in aqueous solution. This work not only shed a new light on the application of semiconductor polymers for the removal of micropollutants and also will expand the applicability of the polymeric photocatalysts for environmental remediation.

Sulfate radical induced degradation of Methyl Violet azo dye with CuFe layered doubled hydroxide as heterogeneous photoactivator of persulfate

Persulfate (PS)-based advanced oxidation processes have aroused considerable attentions due to their higher efficiency and wider adaptability to the degradation of bio-recalcitrant organic contaminants. In this study, Cu-Fe layered doubled hydroxide (CuFe-LDH) was employed to degrade Methyl Violet (MV) through heterogeneous photo-activation of PS under visible-light irradiation. The reaction kinetics, degradation mechanism, catalyst stability were investigated in detail. Under the conditions of CuFe-LDH (3:1) dosage 0.2 g/L, PS concentration 0.2 g/L and without initial pH adjustment, 20 mg/L MV was almost completely degraded within 18 min. Electron Spin Resonance (ESR) test and radical quenching experiment indicated that sulfate radicals (SO₄^-) were the dominant reactive oxidants for the MV decolorization, while hydroxyl radicals (OH) were also involved. The CuFe-LDH/PS/Vis system was applicable at wide range of pH level (3-9). However, extreme pH level would lead to the reduction or transformation of SO₄^-. The catalyst CuFe-LDH exhibited excellent stability and maintained relatively high catalytic activity to PS even after four recycles. Mechanism study revealed that the redox cycle of Fe³⁺/Fe²⁺ and Cu²⁺/Cu³⁺ assisted by visible-light irradiation accounted for the enhanced generation of radicals in CuFe-LDH/PS/Vis system, resulting in the improved degradation of organic contaminants. Overall, the CuFe-LDH/PS/Vis process could be a promising approach for the removal of refractory organic pollutants in wastewater.

Oxidation of organic contaminant in a self-driven electro/natural maghemite/peroxydisulfate system: Efficiency and mechanism

Electro-assisted iron-mediated persulfate (PS) activation process has been successfully employed to oxidize organic contaminant. However, a majority of iron-based catalysts used for PS activation was synthesized through complicated or demanding procedures and may have potential risks on environment during the preparation process. Herein, natural maghemite (NM) which is abundant on the earth was employed to activate peroxydisulfate (PDS) in an electrolytic cell. The voltage was provided by microbial fuel cell (MFC) instead of external power as reported in the previous studies, so as to establish a self-driven electro/natural maghemite/PDS system (MFC/NM/PDS) for the oxidation of acid orange 7 (AO7). The results showed that above 90% removal efficiency of AO7 was achieved in a wide range of pH (3.0-9.0) after 100min reaction. Singlet oxygen was identified for the first time during PDS activation and surface bound sulfate radicals served as the dominant active species responsible for AO7 oxidation. The underlying mechanism of AO7 elimination in the MFC/NM/PDS system was elucidated through quenching tests, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) techniques. The variation of TOC and cytotoxicity to Escherichia coli was explored. The intermediate products formed were identified using LC-TOF-MS technique and a possible pathway of AO7 degradation was proposed.

Hydronium jarosite activation of peroxymonosulfate for the oxidation of organic contaminant in an electrochemical reactor driven by microbial fuel cell

Electro-assisted Fenton-like (EAFL) system based on sulfate radicals (SO₄^-) has been extensively explored for the degradation of recalcitrant organic contaminant. Nevertheless, external power supply should be provided uninterruptedly in the EAFL process and thus the high energy consumption is ineluctable. Recently, microbial fuel cell (MFC), a bio-electrochemical system where exoelectricigens are used to catalyze fuels into electricity energy has gained popularity mainly due to its renewability. Herein, a novel heterogeneous EAFL system, hydronium jarosite (HJ) activation of peroxymonosulfate (PMS) in an electrochemical reactor driven by an uncoated single-chamber MFC (MFC/HJ/PMS), was employed to decolorize acid orange 7 (AO7). The results suggest that the MFC/HJ/PMS system can remove AO7 efficiently in a wide pH range (3-9). The concentration of total iron leached could meet European Union discharge standards and hydronium jarosite could be used at least three circles. The results of electron paramagnetic resonance analysis and radical scavenging experiments indicate SO₄^- is the major active species responsible for the AO7 elimination. The work provides an efficient, energy-saving and cost-effective approach to treat organic wastewater and develops the conceivable utilization of hydronium jarosite, precipitates produced in hydrometallurgical process.

Electro-assisted heterogeneous activation of persulfate by Fe/SBA-15 for the degradation of Orange II

The removal of Orange II by activation of persulfate (S2O8(2-), PS) using synthesized Fe/SBA-15 in the electrochemical (EC) enhanced process was reported in this study. The reaction rate constants, degradation mechanism, catalyst stability, and evolution of mineralization and toxicity were detailed investigated. On the basis of radical scavenger results, both the sulfate radicals (SO4(-)) and hydroxyl radicals (OH) were responsible for the degradation of Orange II. A possible pathway is suggested to describe the degradation of Orange II according to the degradation intermediates identified. The results showed that the Fe/SBA-15 catalyst maintained strong reusability and stability with a low level of iron leaching. In addition, favorable mineralization efficiency in terms of COD removal efficiency (75.4%) and TOC removal efficiency (46.3%) was obtained when the reaction time was prolonged to 24h. The toxicity experiments implied that the toxicity of the treated solution ascended at the first 30min but then dropped to almost zero eventually. This study provides a proof-of-concept that can be applied widely for the PS remediation of contaminated water.