Magnetic EDTA functionalized CoFe2O4 nanoparticles (EDTA-CoFe2O4) as a novel catalyst for peroxymonosulfate activation and degradation of Orange G

High-performance, stable CoNi LDH@Ni foam composite membrane with innovative peroxymonosulfate activation for 2,4-dichlorophenol destruction

In this study, the cobalt-nickel layered double hydroxides (CoNi LDH) were synthesized with a variety of Co/Ni mass ratio, as CoxNiy LDHs. In comparison, Co1Ni3 LDH presented the best peroxymonosulfate (PMS) activation efficiency for 2,4-dichlorophenol removal. Meanwhile, CoNi LDH@Nickel foam (CoNi LDH@NF) composite membrane was constructed for enhancing the stability of catalytic performance. Herein, CoNi LDH@NF-PMS system exerted high degradation efficiency of 99.22% within 90 min for 2,4-DCP when [PMS]0 = 0.4 g/L, Co1Ni3 LDH@NF = 2 cm × 2 cm (0.2 g/L), reaction temperature = 298 K. For the surface morphology and structure of the catalyst, it was demonstrated that the CoNi LDH@NF composite membrane possessed abundant cavity structure, good specific surface area and sufficient active sites. Importantly, ·OH, SO4·- and 1O2 played the primary role in the CoNi LDH@NF-PMS system for 2,4-DCP decomposition, which revealed the PMS activation mechanism in CoNi LDH@NF-PMS system. Hence, this study eliminated the stability and adaptability of CoNi LDH@NF composite membrane, proposing a new theoretical basis of PMS heterogeneous catalysts selection.

Hydrothermal preparation of NiO/La-NaTaO3 composite photocatalyst for degradation of ammonium dibutyl dithiophosphate wastewater

The discharge of a large amount of flotation reagents wastewater can cause significant environmental pollution. In this study, NiO/La-NaTaO3 nano-photocatalyst was prepared and applied to degrade synthetic flotation reagent ammonium dibutyl dithiophosphate wastewater. Various characterization results confirmed the successful synthesis of NiO/La-NaTaO3, and UV-vis DRS analysis revealed a band gap of 3.96 eV for 4 wt% NiO/2.5% La-NaTaO3. Under UV light, the degradation rate of 20 mg 4 wt% NiO/2.5% La-NaTaO3 photocatalyst reached its optimum within 4.5 h at pH=3, exhibiting a 1.45 times improvement compared to pure NaTaO3. Radical trapping experiments and EPR results showed that ·OH and·O2- showed major contribution to the degradation. Furthermore, photocatalytic mechanisms and toxicity evolution were investigated, demonstrating the potential application of photocatalytic methods for treating flotation reagent wastewater.

Tetracycline hydrochloride degradation by activation of peroxymonosulfate with lanthanum copper Ruddlesden-Popper perovskite oxide: Performance and mechanism

ABO₃-type perovskite oxides have been regarded as a kind of potential catalyst for peroxymonosulfate (PMS) activation. But some limitations such as specific pH conditions and coexisting ion interference restrict its practical application. Herein, a lanthanum copper Ruddlesden-Popper perovskite oxide (La₂CuO₄) was successfully synthesized through the sol-gel process and applied in the activation of PMS. And for the first time the La₂CuO₄/PMS system was used for tetracycline hydrochloride (TC-HCl) degradation. Results showed that La₂CuO₄ was a potential PMS activation catalyst in the removal of antibiotics. At optimized condition (0.2 g/L catalysts, 1 mM PMS, pH₀ 6.9), 96.05% of TC-HCl was removed in 30 min. In experiments of debugging control conditions, over a wide pH range of 3-11, more than 90% of TC-HCl can be removed. In the natural water treatment process, TC-HCl removal rates of about 84.2% and 70.3% were obtained in tap water and River water, respectively. According to the reusability and stability tests and the results of FTIR and XPS analysis, La₂CuO₄ had high structural and chemical stability. Electron paramagnetic resonance (EPR) suggested that the active species including ·OH, SO₄^-· and ¹O₂ were detected in degradation reaction. Finally, reasonable reaction mechanisms and possible degradation pathways of TC-HCl were proposed. These results indicate that La₂CuO₄ can act as a potential catalyst for PMS activation to degrade TC-HCl in water.

Biochar loaded with cobalt ferrate activated persulfate to degrade naphthalene

Considering the simple preparation of biochar and the excellent activation performance of cobalt ferrate material, a biochar supported cobalt ferrate composite was synthesized by a solvothermal method. The material was used to activate persulfate (PS) to degrade naphthalene (NAP) in water. The structure and morphology characterization showed that the composite (CoFe₂O₄-BC) was successfully prepared. Under the conditions of 0.25 g L^-1 CoFe₂O₄-BC and 1 mM PS, 90.6% NAP (the initial concentration was 0.1 mM) was degraded after 30 minutes. The degradation kinetics of NAP followed the pseudo-first-order kinetic model with a rate constant of 0.0645 min^-1. With the increase of the dosage of activator and PS, the removal rate of NAP could be increased to 99.5%. The coexistence of anions and humic acids inhibited the removal of NAP. The acid environment promoted the removal of NAP while the alkaline environment inhibited it. After four cycles of CoFe₂O₄-BC material, the removal rate of NAP decreased from 90.6% to 79.4%. The removal of TOC was about 45% after each cycle. After the first cycle, the concentration of leached cobalt ion and leached iron ion was about 310 μg L^-1 and 30 μg L^-1 respectively. The free radical quenching experiments showed that SO₄ ^-˙ and OH˙ were the main causes of NAP removal, and the possible degradation path of NAP was elucidated by DFT calculation.

Preparation of VCo-MOF@MXene composite catalyst and study on its removal of ciprofloxacin by catalytically activating peroxymonosulfate: Construction of ternary system and superoxide radical pathway

The synergistic effect between transition metal active centers and the generation of multiple removal pathways has a significant impact on the catalytic activation efficiency of peroxymonosulfate. In this work, a kind of composite catalyst was prepared by growing VCo-metal-organic frameworks (VCo-MOF) in-situ on the surface of Ti3C2Tx by a solvothermal method. The morphology and structure are characterized by Transmission Electron Microscope (TEM), Energy Dispersion Spectrum (EDS), Atomic Force Microscope (AFM), etc. Response surface methodology was used to optimize the experimental conditions. Only 5 mg catalyst can be used to effectively activate PMS and remove 96.14 % ciprofloxacin (CIP, 20 mg/L) within 30 min. The removal effect of catalyst on CIP in different actual water environment was explored. In addition, the fluorescence spectrum test also verified the effective removal of ciprofloxacin. V-Co-Ti ternary system provides a wealth of active sites for CIP removal. Cyclic voltammetry (CV) and lear sweep voltammetry (LSV) tests showed the existence of the electron transfer pathway. The results of density functional theory (DFT) calculation show that VCo-MOF@Ti3C2Tx has excellent adsorption and activation ability for PMS. At the same time, the hydrophilicity of the catalyst makes PMS more inclined to react with water molecules, which promotes the formation of a unique superoxide radical path.

Synthesis and surface modification of magnetic Fe3O4@SiO2 core-shell nanoparticles and its application in uptake of scandium (III) ions from aqueous media

The main objective of this work is to produce an eco-friendly and economically nano-adsorbent which can separate scandium metal ions Sc from a model aqueous phase prior to applying these adsorbents in industrial filed. The magnetic core-shell structure Fe3O4@SiO2 nanoparticles were synthesized by modified Stöber method and functionalized with (3-aminopropyl) triethoxysilane APTES as a coupling agent and ethylenediaminetetraacetic acid (EDTA) as a ligand. Magnetic nano support adsorbents exhibit many attractive opportunities due to their easy removal and possibility of reusing. The ligand grafting was chemically robust and does not appreciably influence the morphology or the structure of the substrate. To evaluate the potential, the prepared hybrid nanoparticles were used as nano-adsorbent for Sc ions from model aqueous solutions due to the fact that rare earth elements (REEs) have a strong affinity for oxygen and nitrogen donors. The iron oxide nanoparticles were prepared by co-precipitation method at pH 10 and pH 11 to get the best morphology and nanoscale dimensions of iron oxide magnetic nanoparticles. The particle size, morphology, specific surface area, and surface modification were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and X-ray powder diffraction (XRD). The results showed that the Fe3O4 nanoparticles with average particle size of 15 ± 3 nm were successfully synthesized at pH 11, and 25 °C. Moreover, the prepared Fe3O4 nanoparticles were coated with amorphous SiO2 and functionalized with amino and carboxyl groups. The adsorption study conditions of Sc are as follows: the initial concentrations of the Sc model solution varied 10-50 mg/L, 20 mL volume, 20-80 mg of the Fe3O4@SiO2-COO adsorbent, pH range of 1-5, and 5 h contact time at 25 °C temperature. The adsorption equilibrium was represented with Langmuir, Freundlich, and Temkin isotherm models. Langmuir model was found to have the correlation coefficient value in good agreement with experimental results. However, the adsorption process followed pseudo-second-order kinetics.

Efficient activation of peroxymonosulfate by Co-doped mesoporous CeO2 nanorods as a heterogeneous catalyst for phenol oxidation

Sulfate radical-based advanced oxidation processes have received considerable attentions in the remediation of organic pollutants due to their high oxidation ability. In this study, a novel Co3O4/CeO2 catalyst was fabricated and employed as a peroxymonosulfate (PMS) activator to generate SO4•- for phenol degradation. The Co3O4/CeO2 catalyst exhibited a good catalytic performance at a wide pH range of 3.4 to 10.8, and 100% phenol (20 mg/L) was removed within 50-min reaction under optimal conditions with 0.2 g/L catalyst and 2.0 g/L PMS at room temperature. The transformation products and total organic carbon during the degradation process were also determined. The quenching experiments and electron paramagnetic resonance spectra revealed that sulfate radical (SO4•-) rather than other species such as singlet oxygen (1O2) and hydroxyl radical (•OH) was primarily responsible for phenol degradation in the Co3O4/CeO2/PMS system, and a rational mechanism was proposed. Moreover, the recycling experiments as well as low cobalt leaching concentration manifested satisfactory reusability and stability. The effects of various inorganic anions and natural organic matter in real water matrix on phenol oxidation were further evaluated. We believe that the Co3O4/CeO2 composites have promising applications of PMS activation for the degradation of organic pollutants in wastewater treatment.

Enhanced catalytic peroxymonosulfate activation over carbon shells encapsulating cobalt ferrite via radical and nonradical routes

Well-defined carbon shells encapsulating CoFe2O4 deliver superior performance in catalytic PMS activation for organics degradation with a reaction rate constant of 0.269 min-1, 4.7 times the hollow CoFe2O4 and 2.7 times the solid carbon sphere encapsulated one. This is attributed to the comprehensive effects of the Co2+ and C[double bond, length as m-dash]O active sites for free radical and nonradical mechanisms. The nanostructured materials outperformed most of the carbon- or cobalt-iron-based catalysts.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

Spiderweb-Like Fe-Co Prussian Blue Analogue Nanofibers as Efficient Catalyst for Bisphenol-A Degradation by Activating Peroxymonosulfate

Prussian blue and its analogues (PBA) based nanomaterials have been widely applied to removing pollutants in the recent years. However, easy aggregation and poor recycling largely limit their practical applications. In this work, spiderweb-like Fe-Co Prussian blue analogue/polyacrylonitrile (FCPBA/PAN) nanofibers were prepared by electrospinning and applied to degrading bisphenol-A (BPA) by activating peroxymonosulfate (PMS). Detailed characterization demonstrated that a high loading of FCPBA (86% of FCPBA in FCPBA/PAN) was successfully fixed on the PAN nanofibers. 67% of BPA was removed within 240 min when 500 mg·L⁻¹ PMS and 233 mg·L⁻¹ FCPBA/PAN were introduced in 20 mg·L⁻¹ BPA solution at initial pH of 2.8. Electron paramagnetic resonance (EPR) and radical inhibition experiments were performed to identify the possible degradation mechanism. For comparison, a low loading of FCPBA nanofibers (0.6FCPBA/PAN nanofibers, 43% of FCPBA in FCPBA/PAN) were also prepared and tested the catalytic performance. The results showed that the activity of FCPBA/PAN was much higher than 0.6FCPBA/PAN. Furthermore, a FCPBA/PAN packed column was made as a reactor to demonstrate the reusability and stability of FCPBA/PAN nanofibers, which also exhibited the bright future for the industrial application. This work makes it possible to fabricate efficient PBA nanocatalysts with excellent recyclability and promotes the application of PBA in industrial areas.

Application of nickel foam-supported Co3O4-Bi2O3 as a heterogeneous catalyst for BPA removal by peroxymonosulfate activation

Nickel foam (NF)-functionalized Co₃O₄-Bi₂O₃ nanoparticles (CBO@NF) synthesized using a facile one-step microwave-assistant method were employed as catalysts to activate peroxymonosulfate (PMS) with bisphenol A (BPA) as the target pollutant. The crystallinity, morphology, and chemical valence state of the synthesized CBO@NF were analyzed using XRD, SEM, and XPS, respectively. Moreover, effects of the preparation parameters, including the calcination temperature and calcination time as well as the loading dosage, were evaluated in detail. A degradation efficiency of 95.6% was achieved within 30 min with the optimal degradation system. The CBO@NF/PMS system shows great catalytic activity in a pH range from 3.0 to 11.0. The stability and reusability of the CBO@NF supported catalyst was evaluated through a recycling experiment. In addition, the possible degradation mechanism was also explored using a quenching experiment and electron paramagnetic resonance (EPR) detection. The result shows that both the surface-bound SO₄^- and OH play significant roles during the degradation process, where the electron transfer of Co²⁺/Co³⁺, Bi³⁺/Bi⁵⁺, and Ni²⁺/Ni³⁺ realizes the sustained regeneration of the active radicals. This work provides new insight for the practical applications of sulfate radical-based advanced oxidation processes (SR-AOPs) in wastewater treatment.

Heterogeneous activation of peroxymonosulfate by hierarchical CuBi2O4 to generate reactive oxygen species for refractory organic compounds degradation: morphology and surface chemistry derived reaction and its mechanism

Activation of peroxymonosulfate (PMS) by a novel hierarchical CuBi₂O₄ generated reactive oxygen radical for degradation refractory organic compounds in aqueous solution, which would be controlled by the morphology and surface chemistry of solid catalyst. It's found that the activation ability of CuBi₂O₄ toward PMS was highly dependent on the morphology and surface hydroxyl group, as using rhodamine B (RhB) as the model compound. The spherical CuBi₂O₄, which possessed higher density of surface hydroxyl group, exhibited better catalytic activity in RhB degradation than scattered cluster CuBi₂O₄, and as-prepared CuBi₂O₄ could efficiently activated PMS to degrade RhB within a wide pH range as an absolute heterogeneous process. The emerging organic chemicals, including bisphenol A, 1H-benzotriazole, and carbamazepine, could also be effectively removed in this novel CuBi₂O₄/PMS. Furthermore, activation mechanism of PMS by as-prepared CuBi₂O₄ was proposed, the existence of surface hydroxyl group bonded with Cu(II), and inward electron transfer cycling reaction between Cu(II)/Cu(I) facilitated the effective activation of PMS to generate SO₄^·- and ·OH. In addition, the intermediates of RhB formed in this process were identified by silylation derivatation-GC-MS and LC-high-resolution MS/MS, and degradation pathway was proposed.

Synthesis of Co3O4-Bi2O3 using microwave-assisted method as the peroxymonosulfate activator for elimination of bisphenol A

In this work, Co₃O₄-Bi₂O₃ was successfully synthesized using a microwave-assisted method [Co₃O₄-Bi₂O₃(MW)] and employed as a peroxymonosulfate (PMS) activator for bisphenol A removal. A reference catalyst was prepared using the same preparation conditions but different heating mode and labeled as Co₃O₄-Bi₂O₃(CH). The series of Co₃O₄-Bi₂O₃ was characterized using XRD, SEM, and N₂ adsorption to detect their crystallinity, morphology, and surface area, among others. Results indicated that both microwave and calcination significantly affected the characteristic and catalytic activity of the catalyst. Moreover, the microwave-irradiated catalyst calcined at 300 °C showed higher catalytic activity and mineralization percentage for BPA degradation than the conventionally heated catalyst calcined at the same temperature. Microwave temperature and microwave time of the proposed microwave-assisted method were also investigated. Compared with other catalysts, the present catalyst showed considerably superior preparation time and degradation efficiency. This study broadens a new horizon for advanced oxidation process using a PMS activator.

Activation of peroxymonosulfate by surfactants as the metal-free catalysts for organic contaminant removal

The present work described that tertiary ammonium surfactants containing bromide ion as novel metal-free catalysts were innovatively coupled with peroxymonosulfate (PMS) to build a simple catalytic oxidation system, possessing outstanding catalytic ability with organic dye Reactive Red M-3BE (RR M-3BE) as the target pollutant. Furthermore, cetyltrimethylammonium bromide (CTAB), a representative of cationic surfactant, was selected to further investigate the catalytic oxidation performance. It is found that at the critical micelle concentration (CMC) of CTAB, the oxidation efficiency of the CTAB/PMS system was optimal due to the strong electrostatic attraction between the CTA⁺ micelle and reactive anions (Br^- and HSO₅^-), concentrating HSO₅^- and Br^- at the micellar surface, which accelerated the catalytic oxidation reaction between Br^- and HSO₅^-, generating a mass of highly active reactive species. A hybrid method that combined radical scavenger (methanol) with electron paramagnetic resonance (EPR) technology was adopted for the investigation of reactive species, and the results indicated that hydroxyl radical (•OH) was generated and had a major role in the process. The findings from this work provide a practicable pathway for highly efficient PMS activation in wastewater treatment, and also initiate a promising research area of surfactants in the field of environmental catalysis.