Activation of persulfate with 3D urchin-like CoO-CuO microparticles for DBP degradation: A catalytic mechanism study

Decomplexation of Cu(II)-EDTA by synergistic activation of persulfate with alkali and CuO: Kinetics and activation mechanism

Heavy metals usually coexist with a variety of chelating agents to form heavy metal complexes in industrial wastewater. The decomplexation of heavy metal complexes is the crucial step before the removal of heavy metals via alkaline precipitation process. An efficient synergistic activation of persulfate (PS) with alkali and CuO was used for the simultaneous decomplexation of Cu-ethylenediamine tetraacetic acid (Cu(II)-EDTA) (3.14 mM) and the Cu(II) precipitation. The experimental results demonstrated that nearly complete removal of Cu(II) could be achieved by synergistic activation of PS with alkali and CuO at pH 11 after 2 h of decomplexation reaction. However, sole PS could not effectively decomplex Cu(II)-EDTA (13.5%), while the alkaline activation of PS could accomplish 57.0% removal of Cu(II). Radical scavenger tests indicated that reactive oxygen species (ROS) including SO₄^•-, •OH and O₂^•- were responsible for the decomplexation of Cu(II)-EDTA in the synergistic activation of PS with alkali and CuO. As a heterogeneous activator, CuO possessed excellent reusability and long-lasting catalytic activity and the rate constant value (k) of Cu(II) removal showed an increase (from 0.0326 min^-1 in the first cycle to 0.0491 min^-1 in the 24^th cycle) with 24 cycles experiments. Furthermore, the biotoxicity evaluation of treated solution revealed that the biotoxicity of Cu(II)-EDTA contaminated wastewater could be effectively mitigated by the synergistic activation of PS with alkali and CuO because of the efficient precipitation of Cu(II) and oxidative degradation of EDTA organic ligands, which was favorable for the subsequent biochemical treatment.

A review on efficient removal of phthalic acid esters via biochars and transition metals-activated persulfate systems

As emerging contaminants, PAEs (Phthalic Acid Esters or Phthalate Esters) have been extensively utilized in industrial production to soften the rigid plastics (plasticizers), and their related products are widely distributed in our daily life. The PAEs can readily transfer from the products to the surrounding environment due to not being chemically bound to the products. In this study, we analyzed the PAEs' properties, usage, and consumption in the world, as well as toxicity to human beings. As endocrine-disrupting chemicals (EDCs), PAEs can disturb the normal hormones reactions, resulting in developmental and reproductive problems. Thus, we have to concern the removal strategies of PAEs. We summarized two novel approaches, including biochars and persulfate (PS) oxidation for effectively removing PAEs in the literature. Their characteristics, removal mechanisms, and the main impact factors on the removal of PAEs were highlighted. Moreover, transition metal-activated PS showed good performance on PAEs degradation. Furthermore, the synergy of biochars and transition metals-PS can overcome the disadvantages of a single approach, and show better performance on the removal of PAEs. Finally, we put forward vital strategies to update two approaches (including the combined) for enhancing the removal of PAEs. It is expected that the researchers or scientists can get a hint on effectively remediating PAEs-contaminated sites via the biochars' sorption/transition metals-PS or the combined two from this review paper.

Ag2O and NiO Decorated CuFe2O4 with Enhanced Photocatalytic Performance to Improve the Degradation Efficiency of Methylene Blue

Dye wastewater is a serious threat to human health and life. It is an important task for researchers to treat it efficiently. Among many treatment methods, the photo-Fenton method can rapidly degrade organic pollutants. In this study, a ternary photocatalyst, Ag2O-NiO/CuFe2O4, was prepared and applied for a photo-Fenton reaction to degrade methylene blue (MB). MB had the best degradation effect when 10 mg of the catalyst were used in an 80 mL reaction system for measurement. The degradation rate of MB was up to 96.67% in 60 min with a high degradation rate constant k=5.67×10-2min-1. The total organic carbon (TOC) degradation rate was 78.64% with a TOC degradation rate constant of k=2.57×10-2min-1. Therefore, this study fully proves that Ag2O-NiO/CuFe2O4 can catalyze the photo-Fenton reaction and effectively degrade MB.

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

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

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

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

Strong adsorption of tetracycline hydrochloride on magnetic carbon-coated cobalt oxide nanoparticles

The overuse of antibiotics, including tetracycline hydrochloride (TC), seriously threatens human health and ecosystems. In this work, magnetic carbon-coated cobalt oxide nanoparticles (CoO@C) were prepared by one-step annealing method and used as an adsorbent for efficient removal of TC from aqueous solution. The characteristic of the materials was studied by SEM, TEM, and XRD, revealing CoO nanoparticles (≤10 nm) were coated by carbon layer. Several influencial parameters, such as annealing temperature and pH on adsorption of TC, were explored, and found that the maximum adsorption capacity of CoO@C on TC reached as high as 769.43 mg g^-1. Furthermore, CoO@C displayed excellent stability and reusability. After four repeated use of the adsorbent, the adsorption capacity still remained at 90% of the initial capacity. The pseudo-second order model and Temkin model proved that it was an exothermic chemical adsorption process. Furthermore, after analysis of FT-IR, Zeta-potential, XPS, the positive charge on the surface of CoO@C forms a strong electrostatic interaction with TC, and in addition, a surface bond is formed between the adsorbent and the TC molecule. This work provides a novel and efficient adsorbent for the purification of TC-containing wastewater.

Photodegradation Pathways of Typical Phthalic Acid Esters Under UV, UV/TiO2, and UV-Vis/Bi2WO6 Systems

Photolysis and photocatalysis of typical phthalic acid esters (dimethyl phthalate, DMP; diethyl phthalate, DEP; dibutyl phthalate, DBP) were carried out in UV, UV/TiO2, and UV-Vis/Bi2WO6 systems. All of the selected phthalic acid esters and their decomposition byproducts were subjected to qualitative and quantitative analysis through HPLC and GC-MS. The results of 300 min of photolysis and photodegradation reaction were that each system demonstrated different abilities to remove DMP, DEP, and DBP. The UV/TiO2 system showed the strongest degradation ability on selected PAEs, with removal efficiencies of up to 93.03, 92.64, and 92.50% for DMP, DEP, and DBP in 90 min, respectively. UV-Vis/Bi2WO6 had almost no ability to remove DMP and DEP. However, all of the systems had strong ability to degrade DBP. On the other hand, the different systems resulted in various byproducts and PAE degradation pathways. The UV system mainly attacked the carbon branch and produced o-hydroxybenzoates. No ring-opening byproducts were detected in the UV system. In the photocatalytic process, the hydroxyl radicals produced not only attacked the carbon branch but also the benzene ring. Therefore, hydroxylated compounds and ring-opening byproducts were detected by GC-MS in both the UV/TiO2 and UV-Vis/Bi2WO6 photocatalytic systems. However, there were fewer products due to direct hole oxidation in the UV-Vis/Bi2WO6 system compared with the UV/TiO2 system, which mainly reacted with the pollutants via hydroxyl radicals.