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

Enhanced activation of peroxymonosulfate with cobalt-doped manganese-iron oxides for contaminant degradation: Regulation of oxygen vacancy defects

Peroxymonosulfate (PMS) based on heterogeneous catalytic reaction was a promising advanced oxidation process (AOP) to remove refractory contaminants. However, the contaminant degradation efficiency was challenged by the limited number of catalytic active site and low capacity for durable electron transfer. In this study, cobalt-doped manganese-iron oxides (CoxMn1-xFe2O4) rich in oxygen vacancy (Ov) were synthesized using a microwaved hydrothermal method and applied to activate PMS for bisphenol A (BPA) degradation, which achieved the complete removal of BPA within 30 min. In all samples, Co0.5Mn0.5Fe2O4 exhibited good catalytic activity for PMS, which was approximately 21.10 times higher than that of MnFe2O4. The results of density functional theory calculations and in-situ characterization demonstrated that the enhanced performance was ascribed to the generation of Ov and the enrichment of active site, which significantly accelerated the cycling of redox pairs and improved the PMS adsorption, which was more favorable to the formation of active specie in the electron transport process. The oxidation process involved both free radical and non-radical mechanisms, with main reactive species of O2-, and 1O2 being responsible for BPA degradation. In addition, the effects of different aqueous matrices, the results of reusability experiments, and ecotoxicity assessment experiments demonstrated the viability of the Co0.5Mn0.5Fe2O4/PMS system for real sewage purification. This research revealed a structural regulation method to enhance the catalytic activity of the material and offered new perspectives on the engineering of rich Ov.

Optimizing in-situ upgrading of heavy crude oil via catalytic aquathermolysis using a novel graphene oxide-copper zinc ferrite nanocomposite as a catalyst

Unconventional resources, such as heavy oil, are increasingly being explored and exploited due to the declining availability of conventional petroleum resources. Heavy crude oil poses challenges in production, transportation, and refining, due to its high viscosity, low API gravity, and elevated sulfur and metal content. Improving the quality of heavy oil can be achieved through the application of steam injection, which lowers the oil's viscosity and enhances its flow. However, steam injection alone falls short of meeting the growing demand for higher-quality petroleum products. Catalytic upgrading is therefore being investigated as a viable solution to improve heavy oil quality. This study experimentally investigates the application of two novel catalysts, namely copper-substituted zinc ferrite (ZCFO) synthesized via the sol-gel combustion method and a graphene oxide-based nanocomposite (GO-ZCFO) with different ratios, for catalyzing aquathermolysis reactions in the steam injection process, with the aim of enhancing the in-situ upgrading of heavy oil. These catalysts underwent characterization using X-ray powder diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Transmission Electron Microscopy (TEM). Their catalytic performance was assessed utilizing a high-pressure/high-temperature reactor (300 ml), with a comprehensive analysis of the changes in the physical and chemical properties of the heavy oil before and after upgrading. This analysis included measurements of sulfur content, SARA fractions, viscosity, API gravity, and Gas Chromatography (GC) of saturated hydrocarbons and evolved gases. All upgrading experiments, including both catalytic and non-catalytic aquathermolysis processes, were conducted under a reaction time of 6 h, a reaction temperature of 320 °C, and high pressure (86-112 bar). The results indicated that the introduction of the proposed catalysts as additives into the upgrading system resulted in a significant reduction in sulfur content. This, in turn, led to a decrease in resin and asphaltene content, an increase in the content of saturated hydrocarbon, particularly low-molecular-weight alkanes, and ultimately, a reduction in viscosity along with higher API gravity of the crude oil. GO-ZCFO with a weight ratio (50:50) exhibited the best catalytic performance. The heavy crude oil, upgraded with this 50:50 ratio, exhibited significant enhancements, including a 29.26% reduction in sulfur content, a 21.27% decrease in resin content, a 37.60% decrease in asphaltene content, a 46.92% increase in saturated hydrocarbon content, a 66.48% reduction in viscosity, and a 25.49% increase in API gravity. In comparison, the oil upgraded through non-catalytic aquathermolysis showed only marginal improvements, with slight reductions in sulfur content by 5.41%, resin content by 3.60%, asphaltene content by 11.36%, viscosity by 17.89%, and inconsiderable increases in saturated hydrocarbon content by 9.9% and API gravity by 3.02%. The GO-ZCFO, with its high catalytic activity, stands as a promising catalyst that contributes to improving the in-situ upgrading and thermal conversion of heavy crude oil.

The remediation performance and mechanism for tetracycline from groundwater using controlled release materials containing mesoporous MnOx with different morphology

Aiming at the effective remediation of antibiotic contaminants in groundwater, in-situ chemical oxidation (ISCO), using controlled release materials (CRMs) as an oxidant deliverer, has emerged as a promising technique due to their long-term effective pollutant removal performance. This study used different microstructures of mesoporous manganese oxide (MnOx) and sodium persulfate as active components to fabricate CRMs. Following that, a comparative study of tetracycline (TC) degradation and the formation of reactive oxygen species (ROS) by mesoporous MnOx powder and CRMs were conducted. The ROS formed during peroxodisulfate (PDS) activation by powder catalysts and CRMs differed, but MnOx powder catalysts and CRMs both had good reaction stoichiometric efficiency (RSE) for PDS, thus completely mineralizing TC. In PDS activation by mesoporous MnOx powder, oxygen vacancies (OVs) caused by defects in the catalysts contributed to the generation of singlet oxygen (1O2). The 1O2 and free radicals (·SO4- and ·OH) both worked as major ROS participating in TC degradation. Concerning the release of CRMs in static groundwater, the immobilization of catalysts inside CRMs made it difficult to release 1O2 in the solution, thus slowing the degradation of TC by CRMs containing MnOx(1) in static groundwater. In the TC remediation in dynamic groundwater, the water flowing slowly passed through the CRM layer, and TC molecules were trapped. Therefore, 1O2 degraded the trapped TC in the CRM layer in dynamic groundwater. Compared to TC, the toxicity of most intermediates during the TC degradation by CRMs has decreased in static and dynamic groundwater.

Addition of silver nanoparticles to the zinc ferrite/polyaniline composition for boosting its visible photocatalytic degradation

Enhancing the photocatalytic activity of ZnFe2O4 with a good energy band gap to degrade industrial waste under sunlight illumination can help to develop green environments. Here, to improve the photocatalytic efficiency of ZnFe2O4 ferrites, they were merged with polyaniline (PAni) and silver (Ag) nanoparticles to synthesize Ag@ZnFe2O4-PAni plasmonic nanostructures. The as-synthesized nanostructures were characterized using a series of advanced characterization techniques to confirm successful formation and investigate photocatalytic improvement origins. It was found that incorporating Ag NPs along with the PAni to ZnFe2O4 increases its absorption power and red-shifts its energy band gap, which increases the electron-hole production rate by exposure to light in ZnFe2O4. Contribution of the surface plasmon resonance effect of Ag NPs and conjugated double bonds of PAni to charge transfer mechanisms in Ag@ZnFe2O4-PAni material increased charge separation during photocatalytic process, boosting the photodegradation performance of ZnFe2O4.

Introducing and Boosting Oxygen Vacancies within CoMn2O4 by Loading on Planar Clay Minerals for Efficient Peroxymonosulfate Activation

CoMn2O4 (CMO) has been recognized as an effective peroxymonosulfate (PMS) activator; however, it still shows disadvantages such as limited reactive sites and metal leakage. Herein, an effective and environmentally friendly composite catalyst, CMO/Kln, was synthesized by anchoring CMO on kaolinite (Kln), a natural clay mineral with a special lamellar structure, to activate peroxymonosulfate (PMS) for the degradation of residue pharmaceuticals in water. The abundant hydroxyl groups located on the surface of Kln helped induce rich oxygen vacancies (OVs) into composite CMO/Kln, which not only acted as additional active sites but also accelerated working efficiency. In addition, compared with bare CMO, CMO/Kln showed lower crystallinity, and the adoption of the Kln substrate contributed to its structural stability with lower metal leaching after three rounds of reaction. The universal applicability of CMO/Kln was also verified by using three other pharmaceuticals as probes. This work shed light on the adoption of natural clay minerals in modifying CMO catalysts with promoted catalytic activity for the efficient and eco-friendly remediation of pharmaceuticals in wastewater.

Peroxymonosulfate activation by cobalt-doped ferromanganese magnetic oxides through singlet oxygen and radical pathways for efficient sulfadiazine degradation

In this paper, cobalt-doped MnFe2O4 (CMFO-0.4) with oxygen vacancies was successfully synthesised by the sol-gel method and applied as a high-performance catalyst for the activation of peroxomonosulfate (PMS). The catalyst showed an excellent catalytic effect for the degradation of sulfadiazine (SDZ) by activated PMS, and the degradation rate can reach 100% in 10 minutes. The effects of different conditions on the degradation of SDZ were investigated, and it was determined that the optimal concentrations of catalyst and PMS were 0.2 g L-1 and 1 mM, respectively, and had good degradation effects in the pH 5-11 range. Free radical quenching experiments, XPS, and electron paramagnetic resonance (EPR) analyses revealed the presence of hydroxyl radicals (˙OH), sulphate radicals (SO4˙-), singlet oxygen (1O2), and superoxide radicals (˙O2 -) in the CMFO-0.4/PMS system, with 1O2 being the main reactive oxygen species (ROS). In addition, CMFO-0.4 has good reusability and adaptability to the presence of other substances.

Comparative study of reactive oxygen species and tetracycline degradation pathways in catalytic peroxodisulfate activation by asymmetric mesoporous TiO2 and the corresponding controlled-release materials

The removal of trace amounts of antibiotics from water environments while simultaneously avoiding potential environmental hazards during the treatment is still a challenge. In this work, green, harmless, and novel asymmetric mesoporous TiO2 (A-mTiO2) was combined with peroxodisulfate (PDS) as active components in a controlled-release material (CRM) system for the degradation of tetracycline (TC) in the dark. The formation of reactive oxygen species (ROS) and the degradation pathways of TC during catalytic PDS activation by A-mTiO2 powder catalysts and the CRMs were thoroughly studied. Due to its asymmetric mesoporous structure, there were abundant Ti3+/Ti4+ couples and oxygen vacancies in A-mTiO2, resulting in excellent activity in the activation of PDS for TC degradation, with a mineralization rate of 78.6%. In CRMs, ROS could first form during PDS activation by A-mTiO2 and subsequently dissolve from the CRMs to degrade TC in groundwater. Due to the excellent performance and good stability of A-mTiO2, the resulting constructed CRMs could effectively degrade TC in simulated groundwater over a long period (more than 20 days). From electron paramagnetic resonance analysis and TC degradation experiments, it was interesting to find that the ROS formed during PDS activation by A-mTiO2 powder catalysts and CRMs were different, but the degradation pathways for TC were indeed similar in the two systems. In PDS activation by A-mTiO2, besides the free hydroxyl radical (·OH), singlet oxygen (1O2) worked as a major ROS participating in TC degradation. For CRMs, the immobilization of A-mTiO2 inside CRMs made it difficult to capture superoxide radicals (·O2-), and continuously generate 1O2. In addition, the formation of sulfate radicals (·SO4-), and ·OH during the release process of CRMs was consistent with PDS activation by the A-mTiO2 powder catalyst. The eco-friendly CRMs had a promising potential for practical application in the remediation of organic pollutants from groundwater.

Vitamin C-regulated CoAl- layered double hydroxide with oxygen vacancies to efficiently activate peroxydisulfate for sulfamethoxazole removal triggered via reactive oxygen and high-valent cobalt species

In this study, a vitamin C-regulated CoAl-layered double hydroxide with abundant oxygen vacancies was synthesized via a simple hydrothermal process. The resulting CoAl-layered double hydroxide was employed to activate peroxydisulfate for removal of sulfamethoxazole. The effect of the experimental parameters such as pH, catalyst dose and peroxydisulfate concentration on sulfamethoxazole removal was investigated. The current system exhibited excellent catalytic performance for sulfamethoxazole removal in a broad pH range (i.e., pH 3.0-11.0). Under the optimized condition, 94.2% of sulfamethoxazole was degraded within 15 min, accompanied by a 67.6% reduction in chemical oxygen demand. The effective sulfamethoxazole degradation could be attributed to four pathways. Firstly, the ≡ Co2+ in catalyst reacted with peroxydisulfate to generate reactive species, including SO4•-, •OH, O2•- and 1O2, which could degrade sulfamethoxazole. Secondly, the oxygen vacancies could modulate intrinsic electrons, resulted in the surface activation of catalyst and accelerated charge transfer, which was favorable for the degradation of sulfamethoxazole. Thirdly, the presence of vitamin C not only promoted the formation of oxygen vacancies but also expanded the interlayer spacing of layered double hydroxide. A large interlayer spacing facilitated the diffusion of peroxydisulfate and pollutants in the interlayer and improved the utilization efficiency of the active site. Lastly, the high-valent cobalt species exhibited excellent oxidation ability and enhanced the catalyst performance through continuously being employed as an electron acceptor. This study provided a valuable insight for the design and application of Co-based catalysts in peroxydisulfate-based advanced oxidation processes.

Activation of peroxymonosulfate by Cu-Ni-Fe layered double oxides for degradation of butyl 4-hydroxybenzoate: Synergistic effect of oxygen vacancy and Cu(I)

In this study, Cu hybridization coupling oxygen defect engineering was adopted to synthesis of CuNiFe layered double oxides (CuNiFe-LDOs) in peroxymonosulfate (PMS) activation for degradation of methyl 4-hydroxybenzoate. The morphology and crystal structure of CuNiFe-LDOs was characterized in detail, which exhibited regular layered-structure at a Cu:Ni doping ratio of 1:1 and annealing temperature of 400 °C, and presented the crystal of CuxO@Fe3O4-NiO. Besides, the X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results demonstrated that abundant oxygen vacancies (OVs) and low oxidation state Cu species were composed in CuNiFe-LDOs400. The Cu1·5Ni1·5Fe1-LDOs400/PMS system showed excellent catalytic performance toward the degradation of butyl 4-hydroxybenzoate (BuP), and resistant to the effect of pH value and background inorganic anions. Based on quenching experiments and EPR measurements, singlet oxygen (1O2) was identified as the dominant active species during the heterogeneous catalytic process, which was generated by the synergistic interaction between OVs-Cu(I) site and PMS. In this process, the electron-drawing property of OVs promoted the adsorption of PMS molecule on Cu(I) site, followed by the accumulation of electron and cleavage of O-O bond to generate intermediate oxygen radical species, which donated one electron to eventually generate singlet oxygen.

Epsilon-MnO2 simply prepared by redox precipitation as an efficient catalyst for ciprofloxacin degradation by activating peroxymonosulfate

Four kinds of manganese oxides were successfully prepared by hydrothermal and redox precipitation methods, and the obtained oxides were used for CIP removal from water by activating PMS. The microstructure and surface properties of four oxides were systematically characterized. The results showed that ε-MnO2 prepared by the redox precipitation method had large surface area, low crystallinity, high surface Mn(III)/Mn(Ⅳ) ratio and the highest activation efficiency for PMS, that is, when the concentration of PMS was 0.6 g/L, 0.2 g/L ε-MnO2 could degrade 93% of CIP within 30 min. Multiple active oxygen species, such as sulfate radical, hydroxyl radical and singlet oxygen, were found in CIP degradation, among which sulfate radical was the most important one. The degradation reaction mainly occurred on the surface of the catalyst, and the surface hydroxyl group played an important role in the degradation. The catalyst could be regenerated in situ through the redox reaction between Mn4+ and Mn3+. The ε-MnO2 had the advantages of simple preparation, good stability and excellent performance, which provided the potential for developing new green antibiotic removal technology.

Mn-MOF derived manganese sulfide as peroxymonosulfate activator for levofloxacin degradation: An electron-transfer dominated and radical/nonradical coupling process

Recently, transition metal sulfides have attracted much attention due to their better catalytic capacities as peroxymonosulfate (PMS) activator than their metal oxide counterparts. However, the systematic studies on PMS activation using transition metal sulfides are still lacking. In this work, manganese sulfide (MnS) materials were synthesized via a MOFs-derived method and utilized for PMS activation to degrade levofloxacin (LVF) in water for the first time. As expected, MnS exhibited remarkable LVF degradation efficiency by PMS activation, which was distinctly higher than Mn₂O₃. The results of quenching experiments, electro spin resonance identification and electrochemical tests indicated that electron-transfer progress was the dominant mechanism in α-MnS/PMS system. Meanwhile, the presence of ¹O₂ and radicals further became the removal of LVF by α-MnS/PMS system into a radical/nonradical coupling process. The superior electrical conductivity of α-MnS than α-Mn₂O₃ was revealed by DFT calculations, which resulted in the higher catalytic capacity of α-MnS. The result of XPS also indicated the S species in MnS accelerated the recycle of Mn(IV)/Mn(II) and then promoted the generation of radicals. Furthermore, the influence of various environmental conditions on LVF removal and the reusability of α-MnS were also investigated, which demonstrated the high application potential of α-MnS/PMS system. Finally, six possible pathways of LVF oxidation in the system were proposed based on the identified byproducts and their ecotoxicity was evaluated with ECOSAR method. This work promotes the fundamental understanding of PMS activation by α-MnS and provides useful information for practical application of manganese sulfide in water treatment.

Structural regulatory mechanism of phosphotungstate acid decorated graphene oxide quantum dots-chitosan aerogel and its application in ciprofloxacin degradation

Chitosan modified AGQD (amine modified graphene oxide quantum dots) and then combined with H₃PW₁₂O₄₀ to obtain CS_x@AGQD-HPW₁₂ via facile process and applied for CIP removal through pre-adsorption and photocatalytic processes. The application of chitosan could regulate the morphology and photoelectric properties effectively. CS_0.5@AGQD-HPW₁₂ was found to have the optimal CIP removal performance among all the products, the corresponding adsorption removal efficiency and pre-adsorption photocatalysis process were 72.1 % and 98.8 %, respectively. Results of toxicity assessment confirmed photocatalytic degradation process could mitigate the ecotoxicity of CIP effectively. The optimal TOC (total organic carbon) removal efficiency was about 52.1 %. Possible pathways for CIP degradation and reaction mechanism were proposed based on the results of intermediates analysis and trapping experiments. This demonstrated a novel approach to chitosan application and an eco-friendly way to remove CIP by adsorption-photocatalysis process.

Catalytic Degradation of Ciprofloxacin in Aqueous Solution by Peroxymonosulfate Activated with a Magnetic CuFe2O4@Biochar Composite

A magnetic copper ferrite and biochar composite (CuFe2O4@BC) catalyst was prepared by an improved sol-gel calcination method and initially used for the removal of antibiotics ciprofloxacin (CIP) by activated peroxymonosulfate (PMS). Using CuFe2O4@BC as the activator, 97.8% CIP removal efficiency could be achieved in 30 min. After a continuous degradation cycle, CuFe2O4@BC catalyst still exhibited great stability and repeatability and could also be quickly recovered by an external magnetic field. Meanwhile, the CuFe2O4@BC/PMS system presented good stability for metal ion leaching, which was far less than the leaching of metal ions in the CuFe2O4/PMS system. Moreover, the effects of various influencing factors, such as initial solution pH, activator loading, PMS dosage, reaction temperature, humic acid (HA), and the inorganic anions were explored. The quenching experiments and the electron paramagnetic resonance (EPR) analysis manifested that hydroxyl radical (•OH), sulfate radical (SO4•−), superoxide radical (O2•−), and singlet oxygen (1O2) were generated in the CuFe2O4@BC/PMS system, while 1O2 and O2•− are mainly involved in the degradation process. The synergistic effect between CuFe2O4 and BC enhanced the structural stability and electrical conductivity of the material, which promoted the bonding between the catalyst and PMS, resulting in the enhanced catalytic activity of CuFe2O4@BC. This indicates that CuFe2O4@BC activating PMS is a promising remediation technique for CIP-contaminated water.

Carbonyl heterocycle modified mesoporous carbon nitride in photocatalytic peroxydisulfate activation for enhanced ciprofloxacin removal: Performance and mechanism

Polymer carbon nitride is considered to be a promising photocatalyst with broad application prospects in water treatment. However, the defects of pristine polymer carbon nitride (PCN), such as small specific surface area, fast photogenerated electron-hole recombination, and low mass transfer efficiency, limit its photocatalytic activity. In this work, by introducing 2-thiouracil into the precursor, a carbonyl heterocycle-containing mesoporous carbon nitride photocatalyst (TCN) was successfully obtained with significantly enhanced peroxydisulfate (PDS) photocatalytic activity. In this study, the modulation mechanism of carbonyl heterocycle introduction on surface electronic structure and the band structure were fully discussed by means of a combination of experiments and theoretical calculations. The carbonyl and vicinal carbon-modified heterocycles dominated the electrons, while the adjacent heptazine ring dominated the holes. The photogenerated electron-hole pair recombination efficiency and the electron transition energy barrier were greatly reduced. According to the findings of density functional theory (DFT) calculations, the introduction of carbonyl and vicinal C modulated the electronic structure of catalyst, enhanced the adsorption of PDS at the carbonyl ortho N site, which promoted the electronic interaction between TCN and PDS molecules. Experiments showed that the free radical pathway and non-radical pathway coexisted in TCN/PDS/Vis system. The reactive oxygen species were mainly derived from PDS molecules. DFT calculations provided a more comprehensive theoretical basis for the experimental results. This study provided a fresh perspective on the rational design of carbon nitride-based catalysts and the reaction mechanism of persulfate advanced oxidation systems.

Peroxymonosulfate activated by composite ceramic membrane for the removal of pharmaceuticals and personal care products (PPCPs) mixture: Insights of catalytic and noncatalytic oxidation

A composite manganese-based catalytic ceramic membrane (Mn-CCM) was developed by a solid-state sintering method, and its effectiveness toward activation of peroxymonosulfate (PMS) for the degradation of 11 pharmaceutical and personal care products (PPCPs) mixture was tested. The optimized Mn-CCMs/PMS system showed remarkable degradation efficiencies for PPCPs mixture with total removal >90% in ultrapure water, river water and natural organic matter (NOM) solution. The Mn-CCMs/PMS system showed the contribution of different phenomena in PPCPs removal in the order of catalytic oxidation (54.7%, Mn-CCMs/PMS) > noncatalytic oxidation (42.3%, PMS oxidation) > adsorption (3.0%, by Mn-CCMs). The singlet oxygen (¹O₂) was the dominant reactive oxygen specie for the degradation of PPCPs in all water matrices proved by the quenching experiments and electro-paramagnetic resonance (EPR) spectroscopy. The extraordinary stability of Mn-CCMs for the activation of PMS has been noted in terms of repeatability experiments for PPCPs degradation with fewer leaching of Mn (1.9 to 3.6 µg/L). Mineralization was achieved in the range of 28-65% for different water matrices. The toxicity of the PPCPs mixture was reduced by 85.9%. The Mn-CCMs/PMS system showed a reduction (25-100%) in precursors of different carbon- and nitrogen-based disinfection by-products. This study found the Mn-CCMs/PMS system as a feasible purification unit for removing trace concentrations of PPCPs (ng/L) in real drinking water matrices.

Insight into advanced oxidation processes for the degradation of fluoroquinolone antibiotics: Removal, mechanism, and influencing factors

The enrichment and transport of antibiotics in the environments pose many potential hazards to aquatic animals and humans, which has become one of the public health challenges worldwide. As a widely used class of antibiotics, fluoroquinolones (FQs) generally accumulated in the environments as traditional sewage treatment plants cannot completely remove them. Advanced oxidation processes (AOPs) have been shown to be a promising method for the abatement of antibiotic contamination. In this review, influencing factors and relevant mechanisms of FQs removal by various AOPs were summarized. Compared with other AOPs, photocatalytic ozone may be considered as a cost-effective method for degrading FQs. Finally, the benefits and application restrictions of AOPs were discussed, along with proposed research directions to provide new insights into the control of FQs pollutant via AOPs in practical applications.

Magnetic Behavior of Virgin and Lithiated NiFe2O4 Nanoparticles

A series of virgin and lithia-doped Ni ferrites was synthesized using egg-white-mediated combustion. Characterization of the investigated ferrites was performed using several techniques, specifically, X-ray Powder Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and High-resolution transmission electron microscopy (HRTEM). XRD-based structural parameters were determined. A closer look at these characteristics reveals that lithia doping enhanced the nickel ferrite lattice constant (a), unit cell volume (V), stress (ε), microstrain (σ), and dislocation density (δ). It also enhanced the separation between magnetic ions (LA and LB), ionic radii (rA, rB), and bond lengths (A-O and B-O) between tetrahedral (A) and octahedral (B) locations. Furthermore, it enhanced the X-ray density (Dx) and crystallite size (d) of random spinel nickel ferrite displaying opposing patterns of behavior. FTIR-based functional groups of random spinel nickel ferrite were determined. HRTEM-based morphological properties of the synthesized ferrite were investigated. These characteristics of NiFe2O4 particles, such as their size, shape, and crystallinity, demonstrate that these manufactured particles are present at the nanoscale and that lithia doping caused shape modification of the particles. Additionally, the prepared ferrite’s surface area and total pore volume marginally increased after being treated with lithia, depending on the visibility of the grain boundaries. Last, but not least, as the dopant content was increased through a variety of methods, the magnetization of virgin nickel ferrite fell with a corresponding increase in coercivity. Uniaxial anisotropy, rather than cubic anisotropy, and antisite and cation excess defects developed in virgin and lithia-doped nickel ferrites because the squareness ratio (Mr/Ms) was less than 0.5. Small squareness values strongly recommend using the assessed ferrites in high-frequency applications.

Catalytic ozonation of phenol by ZnFe2O4/ZnNCN: performance and mechanism

A novel magnetic catalyst was synthesized and applied in heterogeneous catalytic ozonation process. The ZnFe₂O₄/ZnNCN material was synthesized by hydrothermal and high-temperature calcination method and characterized by XPS, XRD, FTIR, VSM, and SEM techniques. In the system of O₃/ZnFe₂O₄/ZnNCN, the removal rates of phenol and chemical oxygen demand (COD) reached 93% and 43% at 60 min. Further analysis shows that ZnFe₂O₄/ZnNCN has a significant catalytic effect on O₃, which is demonstrated by the first-order kinetic constant being 1.93 times than O₃ alone. The catalyst exhibits excellent cycling stability during repeated catalytic ozonation process and can be fully recycled under an applied magnetic field. The role of hydrogen peroxide (H₂O₂) and surface hydroxyl groups was investigated, and a mechanism for catalytic ozonation was proposed. This work not only builds an efficient catalytic ozonation system, but also provides a potential modification strategy for spinel oxides.

Spinel ferrites materials for sulfate radical-based advanced oxidation process: A review

In the past decade, the sulfate radical-based advanced oxidation processes (SR-AOPs) have been increasingly investigated because of their excellent performance and ubiquity in the degradation of emerging contaminants. Generally, sulfate radicals can be generated by activating peroxodisulfate (PDS) or peroxymonosulfate (PMS). To date, spinel ferrites (SF) materials have been greatly favored by researchers in activating PMS/PDS for their capability and unique superiorities. This article reviewed the recent advances in various pure SF, modified SF, and SF composites for PDS/PMS activation. In addition, synthesis methods, mechanisms, and potential applications of SF-based SR-AOPs were also examined and discussed in detail. Finally, we present future research directions and challenges for the application of SF materials in SR-AOPs.

Ascorbic acid enhanced MnFe2O4/peroxymonosulfate oxidation of organic pollutant: Key role of singlet oxygen generation and Fe/Mn cycling

The activated peroxymonosulfate (PMS) process has been widely applied for degrading organic pollutants. However, its application is limited by low metal cycling, and the contribution of oxygen species remains unclear. Here, the crystal structure, surface morphology, and elemental valence of the synthesized manganese ferrite (MnFe₂O₄) catalyst were investigated by SEM, HRTEM, XRD, and XPS. A novel MnFe₂O₄/PMS/ascorbic acid (AA) system was constructed to enhance the Fe/Mn cycling on the surfaces of the MnFe₂O₄ catalyst. The addition of AA can significantly increase the decomposition of organic pollutants, and the apparent rate constant of the MnFe₂O₄/PMS/AA system is 8.2 times higher than that of MnFe₂O₄/PMS. AA facilitates the reduction of Fe/Mn(III) and the dissolution of Fe/Mn(II), creating a Fe/Mn cycle between the heterogeneous and homogeneous interfaces of the catalyst. Furthermore, AA greatly increases the activity of adsorbed oxygen on the catalyst surfaces, generating a large amount of singlet oxygen (¹O₂), which contributes significantly to the destruction of organic pollutants. The efficient, fast, and environmentally friendly PMS activation method in this study can provide reliable technical support for treating refractory organic pollutants in water.

Degradation of ciprofloxacin by persulfate activated with pyrite: mechanism, acidification and tailwater reuse

Residues of ciprofloxacin (CIP) in the environment pose a threat to human health and ecosystems. This study investigated the degradation of CIP by persulfate (PS) activated with pyrite (FeS2). Results showed that when [CIP] = 30 μM, [FeS2] = 2.0 g L-1, and [PS] = 1 mM, the CIP removal rate could reach 94.4% after 60 min, and CIP mineralization rate reached 34.9%. The main free radicals that degrade CIP were SO4˙- and HO˙, with contributions of 34.4% and 35.7%, respectively. Additionally, compared to the control (ultrapure water), CIP in both tap water and river water was not degraded. However, acidification could eliminate the inhibition of CIP degradation in tap water and river water. Furthermore, acidic tailwater from CIP degradation could be utilized to adjust the pH of untreated CIP, which could greatly promote the degradation of CIP and further reduce disposal costs. The reaction solution was not significantly biotoxic and three degradation pathways of CIP were investigated. Based on the above results and the characterization of FeS2, the mechanism of CIP degradation in the FeS2/PS system was that FeS2 activated PS to generate Fe(iii) and SO4˙-. The sulfide in FeS2 reduced Fe(iii) to Fe(ii), thus achieving an Fe(iii)/Fe(ii) cycle for CIP degradation.

A Review of Sulfate Radical-Based and Singlet Oxygen-Based Advanced Oxidation Technologies: Recent Advances and Prospects

In recent years, advanced oxidation process (AOPs) based on sulfate radical (SO4●−) and singlet oxygen (1O2) has attracted a lot of attention because of its characteristics of rapid reaction, efficient treatment, safety and stability, and easy operation. SO4●− and 1O2 mainly comes from the activation reaction of peroxymonosulfate (PMS) or persulfate (PS), which represent the oxidation reactions involving radicals and non-radicals, respectively. The degradation effects of target pollutants will be different due to the type of oxidant, reaction system, activation methods, operating conditions, and other factors. In this paper, according to the characteristics of PMS and PS, the activation methods and mechanisms in these oxidation processes, respectively dominated by SO4●− and 1O2, are systematically introduced. The research progress of PMS and PS activation for the degradation of organic pollutants in recent years is reviewed, and the existing problems and future research directions are pointed out. It is expected to provide ideas for further research and practical application of advanced oxidation processes dominated by SO4●− and 1O2.

Controlling oxygen vacancies of CoMn2O4 by loading on planar and tubular clay minerals and its application for boosted PMS activation

A representative transition metal oxide (TMO), CoMn₂O₄ (CMO), is recognized as an effective peroxymonosulfate (PMS) activator with disadvantages like limited reactive sites and metal leakage. Herein, novel catalysts were synthesized by anchoring CMO on kaolinite (Kln) and halloysite (Hal) matrixes, two natural clay minerals with lamellar and tubular structures, for PMS activation in pharmaceutical degradation. Hal and Kln helped to control the crystallinity of CMO spontaneously with induce oxygen vacancies (OVs), which significantly enhanced the working efficiency. The reaction rate constants of Hal/CMO and Kln/CMO towards OFX degradation were nearly triple and twice that of bare CMO, respectively, with a 60% decrease in metal usage. The formation of OVs provided additional active sites for the reaction and accelerated the electron transfer. CMO/Hal and CMO/Kln exhibited better stability and durability than CMO, while CMO/Kln showed higher structural stability with lower metal leaching after 3 rounds of reaction. The higher crystallinity of CMO/Kln resulted in less OVs, but higher structural stability. The universal applicability of CMO/Hal and CMO/Kln were verified by using three other pharmaceuticals as probes. This work shed light on the modification of TMO catalysts by introducing clay mineral substrates for the efficient and ecofriendly remediation of pharmaceuticals in wastewater.

Sulfate-accelerated photochemical oxidation of arsenopyrite in acidic systems under oxic conditions: Formation and function of schwertmannite

The weathering of arsenopyrite is closely related to the generation of acid mine drainage (AMD) and arsenic (As) pollution. Solar radiation can accelerate arsenopyrite oxidation, but little is known about the further effect of SO₄^2- on the photochemical process. Here, the photooxidation of arsenopyrite was investigated in the presence of SO₄^2- in simulated AMD environments, and the effects of SO₄^2- concentration, pH and dissolved oxygen on arsenopyrite oxidation were studied as well. SO₄^2- could accelerate the photooxidation of arsenopyrite and As(III) through complexation between nascent schwertmannite and As(III). Fe(II) released from arsenopyrite was oxidized to form schwertmannite in the presence of SO₄^2-, and the photooxidation of arsenopyrite occurred through the ligand-to-metal charge-transfer process in schwertmannite-As(III) complex along with the formation of reactive oxygen species in the presence of O₂. The photooxidation rate of arsenopyrite first rose and then fell with increasing SO₄^2- concentration. In the pH range of 2.0-4.0, the photooxidation rate of arsenopyrite progressively increased in the presence of SO₄^2-. This study reveals how SO₄^2- promotes the photooxidation of arsenopyrite and As release in the AMD environment, and improves the understanding of the transformation and migration of As in mining areas.

Sustainably recycling spent lithium-ion batteries to prepare magnetically separable cobalt ferrite for catalytic degradation of bisphenol A via peroxymonosulfate activation

A selective separation-recovery process based on tuning organic acid was proposed to the resource recycling of spent lithium-ion batteries (LIBs) for the first time. The low-cost preparation of CoFe₂O₄, reuse of waste acid and recovery of Li can be realized in this process, simultaneously. Li and Co in spent LIBs can be leached efficiently using citric acid as a leaching agent, and separated effectively from leaching solution by tuning oxalic acid content. The results from the characterizations of the prepared CoFe₂O₄ (CoFe₂O₄-LIBs) show that it possesses higher ratio of Co(II)/Co(III) and Fe(II)/Fe(III), larger surface specific area and more number of acid sites in comparison with pure CoFe₂O₄. Besides, CoFe₂O₄-LIBs was used to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA). Interestingly, its degradation performance is superior to that of pure CoFe₂O₄ and the related Co-based catalysts. The excellent degradation performance can be maintained in presence of inorganic ions (e.g., Cl^-, HCO₃^-, H₂PO₄^- and NO₃^-) with high concentration or humic acid. Moreover, surface-bound SO₄^∙- is considered as the main reactive species for the degradation of BPA. More importantly, CoFe₂O₄-LIBs can be readily recycled by using an external magnet and own superior ability of regeneration.

Adsorption of polycyclic aromatic hydrocarbons over CuZnFeAl–LDH modified by sodium dodecyl sulfate

Polycyclic aromatic hydrocarbons (PAHs) have received extensive attention due to being highly toxic, mutagenic, and carcinogenic organic pollutants. As a result, a series of adsorbents have been designed and developed to solve the problem. In this paper, CuZnFeAl–S has been explored as a highly efficient adsorbent for PAHs. First, CuZnFeAl–LDH was prepared using a coprecipitation method and then calcined at 500 °C to obtain CuZnFeAlO. Finally, CuZnFeAl–S was prepared by modifying CuZnFeAlO with sodium dodecyl sulfate (SDS). The physical and chemical properties of the adsorbents were characterized by XRD, N₂ adsorption–desorption, SEM, ICP, FT-IR, TG-DSC, and IGC; subsequently their adsorption performance was investigated. The results show that the surface properties of CuZnFeAl–S changed from hydrophilic to hydrophobic after SDS modification, which enhanced the adsorption of PAHs obviously. The removal of naphthalene and phenanthrene on CuZnFeAl–S reached 97.3% and 90.3%, respectively. And the adsorption process of naphthalene and phenanthrene conforms to Langmuir adsorption and Freundlich adsorption, respectively. Besides, the adsorption thermodynamics indicate that the adsorption of PAHs was a spontaneous exothermic reaction. The highly efficient PAH adsorption performance of CuZnFeAl–S is the synergistic result of various molecule interactions, such as hydrogen bonding, π–π interactions, and electrostatic attraction.

CuZnFeAl–S improves the adsorption of polycyclic aromatic hydrocarbons, which has a profound impact on environmental treatment.

Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting Ni_xCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of Ni_xCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into Ni_xCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), rather than sulfate radicals (SO₄^•-) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni₁₅Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO₄^•-and •OH, and demonstrated that O₂^•- and ¹O₂ concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O₂^•- mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni₁₅Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni₁₅Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.

Enhanced degradation of tetracycline in water over Cu-doped hematite nanoplates by peroxymonosulfate activation under visible light irradiation

Herein, Cu-doped hematite nanoplates (named as CuHNPs) with abundant oxygen-vacancies were prepared through a facile one-pot solvothermal method and used for efficient peroxymonosulfate (PMS) activation to degrade tetracycline (TC) in water. The catalytic activity of optimal CuHNPs-7.5 catalyst to activate PMS for the degradation of TC in water under visible light irradiation is 7.74 and 2.93 times higher than that of pure one without and with visible light irradiation. CuHNPs-7.5 exhibited excellent degradation for TC in the broad pH range from 2.14 to 10.75, and the removal of TC was barely inhibited by co-anions. The combination of free radicals and non-radical pathway, including sulfate radicals (SO₄^·-), hydroxide radicals (·OH), superoxide radical (·O₂^-) and single oxygen (¹O₂), contributed to TC oxidation. The introduction of Cu²⁺ not only accelerated the transformation of Fe(III)/Fe(II) redox cycle but also induced rich oxygen defects in the structure of hematite, boosting more generation of reactive oxygen species (ROSs) for TC degradation. Density functional theory (DFT) calculation and electrochemical impedance spectroscopy (EIS) tests confirmed the accelerated electrons transfer of CuHNPs-7.5 in PMS activation. This study provides a strategy to construct effective catalysts of PMS activation combining radicals and non-radical pathways for environmental remediation.

Efficient degradation of ciprofloxacin by magnetic γ-Fe2O3-MnO2 with oxygen vacancy in visible-light/peroxymonosulfate system

In this work, the magnetic γ-Fe₂O₃-MnO₂ bifunctional catalyst with oxygen vacancy was synthesized for peroxymonosulfate (PMS) activation under visible light. The activity of γ-Fe₂O₃-MnO₂ was investigated by ciprofloxacin (cipro) degradation. Results showed that 98.3% of cipro (50 μM) was removed within 30 min in visible-light/PMS system mediated by γ-Fe₂O₃-MnO₂ (2:1) with fine-tuned oxygen vacancy. The cipro degradation data fitted well with pseudo-first-order kinetic model with the highest kinetic constant of 0.114 min^-1. Besides, the γ-Fe₂O₃-MnO₂ exhibited stability, recyclability and practicability. High selectivity for cipro degradation was observed with coexisting anions in visible-light/γ-Fe₂O₃-MnO₂/PMS system. Furthermore, the enhanced mechanism of PMS activation under visible light with γ-Fe₂O₃-MnO₂ was proposed. The appropriate oxygen vacancy enhanced the separation of photo-induced carriers and Z scheme heterostructure maintained the highest redox potential. Accordingly, the synergistic effect of photocatalysis and PMS activation enhanced cipro degradation. Free radical and non-radical species including , h⁺, ¹O₂, •OH and co-existed in the coupled system. Impressively, this study provides a handy approach for oxygen vacancy regulation in metallic oxides composite and an easily recycled catalyst with high-activity in coupled oxidation system towards antibiotic degradation.

Hierarchical multi-active component yolk-shell nanoreactors as highly active peroxymonosulfate activator for ciprofloxacin degradation

The reasonable design of the structure and composition of catalysts was essential to improve the catalytic performance of advanced oxidation processes (AOPs). Herein, we reported a simple strategy to synthesize hierarchical Co₃O₄-C@CoSiO_x yolk-shell nanoreactors with multiple active components by using metal-organic frameworks (MOFs). The novel nanoreactors are further used to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. The effects of reaction parameters (pH value, co-existing ions, reaction temperature, etc.) on CIP degradation were systematically investigated. Especially, ∼98.2% of CIP was degraded within 17 min under the optimal conditions, together with the low cobalt leaching and excellent reusability. The appreciable catalytic performance improvement might be due to the synergistic effect of the structure and component design: (1) the hierarchical yolk-shell structure endowed the catalyst with high surface area (∼232.47 m²/g) and fully exposed active sites; (2) abundant highly active ≡Co-OH⁺ were formed on the surface of CoSiO_x; (3) the presence of oxygen vacancies and nitrogen-doped carbon promoted the decomposition of PMS through a non-radical process. The results revealed both the radical (SO₄^∙-, ∙OH and O₂^∙-) and non-radical (¹O₂ and direct charge transfer) should be responsible for the CIP degradation. Moreover, the possible degradation pathways of CIP were proposed through the identification of intermediates using LC-MS/MS techniques and density functional theory (DFT) calculation. Our work highlights that multi-component catalysts derived from MOFs with novel structure have broad application prospects in AOPs.

Different activation methods in sulfate radical-based oxidation for organic pollutants degradation: Catalytic mechanism and toxicity assessment of degradation intermediates

With the continuous development of industrialization, a growing number of refractory organic pollutants are released into the environment. These contaminants could cause serious risks to the human health and wildlife, therefore their degradation and mineralization is very critical and urgent. Recently sulfate radical-based advanced oxidation technology has been widely applied to organic pollutants treatment due to its high efficiency and eco-friendly nature. This review comprehensively summarizes different methods for persulfate (PS) and peroxymonosulfate (PMS) activation including ultraviolet light, ultrasonic, electrochemical, heat, radiation and alkali. The reactive oxygen species identification and mechanisms of PS/PMS activation by different approaches are discussed. In addition, this paper summarized the toxicity of degradation intermediates through bioassays and Ecological Structure Activity Relationships (ECOSAR) program prediction and the formation of toxic bromated disinfection byproducts (Br-DBPs) and carcinogenic bromate (BrO₃^-) in the presence of Br^-. The detoxification and mineralization of target pollutants induced by different reactive oxygen species are also analyzed. Finally, perspectives of potential future research and applications on sulfate radical-based advanced oxidation technology in the treatment of organic pollutants are proposed.

Surface dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) for heterogeneous peroxymonosulfate activation to degrade diclofenac: Performance, mechanism and toxicity assessment

Advanced oxidation processes (AOPs) based on heterogeneous catalytic activated peroxymonosulfate (PMS) have been becoming alternatives to conventional wastewater treatment technologies to directly degrade chemical contaminants. To build dual/multi redox cycles of different metal ions may be an effective means for better PMS activation. Herein, this study designed Mn₃O₄/CuBi₂O₄ with dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) to activate PMS for efficiently decomposing and mineralizing diclofenac sodium (DCF). Under optimal reaction conditions, DCF (50 mg/L) was degraded totally within 10 min, and TOC removal rate reached up to 74.3%. The possible mechanism of PMS activation by Mn₃O₄/CuBi₂O₄ was proposed, wherein dual redox cycles of Mn(III)/Mn(IV) and Cu(I)/Cu(II) on Mn₃O₄/CuBi₂O₄ effectively facilitated PMS activation to generate ·O₂^-, ¹O₂, SO₄·^- and ·OH, which was responsible for DCF degradation. Moreover, combined with degraded products detected by high resolution liquid chromatography coupled to mass spectrometry and corresponding toxic assessment results, the possible degradation pathways of DCF were proposed and the relative toxicity of degraded products was evaluated. This work may be useful for developing stronger heterogeneous activators of PMS to construct more efficient AOPs for purifying wastewater.

Tuning of Structural, Dielectric, and Electronic Properties of Cu Doped Co–Zn Ferrite Nanoparticles for Multilayer Inductor Chip Applications

Herein, we report the synthesis of nanoparticles and doping of Cu-doped Co–Zn ferrites using the auto-combustion sol–gel synthesis technique. X-ray diffraction studies confirmed the single-phase structure of the samples with space group Fd3m and crystallite size in the range of 20.57–32.69 nm. Transmission electron microscopy micrographs and selected area electron diffraction patterns confirmed the polycrystalline nature of the ferrite nanoparticles. Energy-dispersive X-ray spectroscopy revealed the elemental composition in the absence of any impurity phases. Fourier-transform infrared studies showed the presence of two prominent peaks at approximately 420 cm−1 and 580 cm−1, showing metal–oxygen stretching and the formation of ferrite composite. X-ray photoelectron spectroscopy was employed to determine the oxidation states of Fe, Co, Zn, and Cu and O vacancies based on which cationic distributions at tetrahedral and octahedral sites are proposed. Dielectric spectroscopy showed that the samples exhibit Maxwell–Wagner interfacial polarization, which decreases as the frequency of the applied field increases. The dielectric loss of the samples was less than 1, confirming that the samples can be used for the fabrication of multilayer inductor chips. The ac conductivity of the samples increased with increasing doping and with frequency, and this has been explained by the hopping model. The hysteresis loops revealed that coercivity decreases slightly with doping, while the highest saturation magnetization of 55.61 emu/g was obtained when x = 0.1. The magnetic anisotropic constant was found to be less than 0.5, which suggests that the samples exhibit uniaxial anisotropy rather than cubic anisotropy. The squareness ratio indicates that the samples are useful in high-frequency applications.

Enhanced peroxymonosulfate activation over heterogeneous catalyst Cu0.76Co2.24O4/SBA-15 for efficient degradation of sulfapyridine antibiotic

The largest source of resistant bacteria or viruses is the overuse and misuse of antibiotics in humans and animals. These resistant bacteria or viruses may evolve into superbacteria or superviruses, which causes global plague. Therefore, it is significant to find a highly efficiency and low-cost method to eliminate antibiotics in water environment from inappropriate discharge. Here, a highly active and highly stable heterogeneous catalyst, Cu0.76Co2.24O4/SBA-15 (CCS) was prepared for peroxymonosulfate (PMS) activation in aim of decomposing persistent sulfapyridine (SPD). The reaction mechanism was thoroughly investigated via in situ quenching test and in situ electron paramagnetic resonance. Four reactive species, SO4·-, O2·-, 1O2 and ·OH were generated in Cu0.76Co2.24O4/SBA-15/PMS (CCSP) system. The SO4·- and O2·- were dominant active species responsible for SPD degradation. Co(Ⅱ)↔Co(Ⅲ)↔Co(Ⅱ) redox reaction cycle was constructed due to the different redox potential of Co(Ⅱ)/Co(Ⅲ), HSO5-/SO4∙-, and HSO5-/SO5∙-. Interestingly, Cu(Ⅰ) could urge the redox reaction cycle for PMS activation to be more thermodynamically feasible. Therefore, CCS possessed a highly catalytic activity and excellent stability. Meanwhile, the anions interference test indicated Cl-, NO3-, HCO3-, and H2PO4- had almost no inhibitory effect on SPD degradation over this catalytic system. We sincerely expected that this catalyst system would be applied extensively into antibiotics degradation in real water bodies.

Evolution of Singlet Oxygen by Activating Peroxydisulfate and Peroxymonosulfate: A Review

Advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) or peroxymonosulfate (PMS) activation have attracted much research attention in the last decade for the degradation of recalcitrant organic contaminants. Sulfate (SO₄^•−) and hydroxyl (^•OH) radicals are most frequently generated from catalytic PDS/PMS decomposition by thermal, base, irradiation, transition metals and carbon materials. In addition, increasingly more recent studies have reported the involvement of singlet oxygen (¹O₂) during PDS/PMS-based AOPs. Typically, ¹O₂ can be produced either along with SO₄^•− and ^•OH or discovered as the dominant reactive oxygen species (ROSs) for pollutants degradation. This paper reviews recent advances in ¹O₂ generation during PDS/PMS activation. First, it introduces the basic chemistry of ¹O₂, its oxidation properties and detection methodologies. Furthermore, it elaborates different activation strategies/techniques, including homogeneous and heterogeneous systems, and discusses the possible reaction mechanisms to give an overview of the principle of ¹O₂ production by activating PDS/PMS. Moreover, although ¹O₂ has shown promising features such as high degradation selectivity and anti-interference capability, its production pathways and mechanisms remain controversial in the present literatures. Therefore, this study identifies the research gaps and proposes future perspectives in the aspects of novel catalysts and related mechanisms.

Nanostructured Mg substituted Mn-Zn ferrites: A magnetic recyclable catalyst for outstanding photocatalytic and antimicrobial potentials

With recently increasing the environmental problems and expected energy crisis, it is necessary to synthesis a low-cost, efficient, and UV-light responsive photocatalyst for contaminants' degradation. The nanostructured spinel ferrite Mn_0.5Zn_0.5-xMg_xFe₂O₄ NPs (x = 0.0, 0.125, 0.25, 0.375 and 0.50) were synthesized via the sol-gel method. The crystallite size was lied in nano regime ranging from 21.8 to 36.5 nm. The surface chemical composition of the Mn_0.5Zn_0.5-xMg_xFe₂O₄ NPs was investigated via XPS analysis. Mossbauer spectra showed that the peaks were shifted to higher values of the maximum magnetic field as the Mg content increased, indicating that the crystallinity is enhanced while the crystal size is decreased. Also, various parameters such as the photocatalyst dose, dyes concentration, pH, point of zero charge, and the metals leaching were studied. The point of zero charge (PZC) has found at pH = 2.38. The Mn_0.5Zn_0.125Mg_0.375Fe₂O₄ NPs showed an excellent UV-assisted photocatalytic activity against Chloramine T (90 % removal efficiency) and Rhodamine B (95 % removal efficiency) after 80 min as compared to pure Mn_0.5Zn_0.5Fe₂O₄ ferrite NPs. Besides, it a recyclable catalyst at least four times with a negligible reduction of photocatalytic activity with slight elements leaching. Furthermore, the Mn_0.5Zn_0.25Mg_0.25Fe₂O₄ NPs showed a high antimicrobial activity towards pathogenic bacteria and yeats.

Recent Advances in Magnetic Nanoparticles and Nanocomposites for the Remediation of Water Resources

Water resources are of extreme importance for both human society and the environment. However, human activity has increasingly resulted in the contamination of these resources with a wide range of materials that can prevent their use. Nanomaterials provide a possible means to reduce this contamination, but their removal from water after use may be difficult. The addition of a magnetic character to nanomaterials makes their retrieval after use much easier. The following review comprises a short survey of the most recent reports in this field. It comprises five sections, an introduction into the theme, reports on single magnetic nanoparticles, magnetic nanocomposites containing two of more nanomaterials, magnetic nanocomposites containing material of a biologic origin and finally, observations about the reported research with a view to future developments. This review should provide a snapshot of developments in what is a vibrant and fast-moving area of research.