Sulfate Radical-based Advanced Oxidation Processes Research Articles

Carbon defects-enriched NBC-C3N5@CoMn with ultrafast modulation of redox couples for efficient degradation of contaminant

The inefficiency of catalysts in sulfate radical-based advanced oxidation processes (SR-AOPs) is primarily attributed to the sluggish circulation of redox couples. Herein, a carbon defects-enriched NBC-C3N5@CoMn (NCC) was synthesized through a self-assembly approach. The carbon defects within the NCC induce the electron trap effect, thereby facilitating the efficient cycling of redox couples in photo-Fenton-like processes during contaminant degradation. This effect enables the self-regeneration of the NCC catalyst. The reductive redox couples (Co (II) and Mn (II)) are continuously regenerated following the degradation process. Within the NCC, CoMn layered double hydroxides (LDHs) act as primary active sites, promoting the generation of hydroxyl radicals (•OH), sulfate radicals (SO4•-) and singlet oxygen (1O2) through continuous electron gain and loss. Additionally, the internal electric field established within the NCC further accelerates electron transfer. Density Functional Theory (DFT) calculations confirm that the carbon defects-enriched NCC exhibits lower adsorption energies and higher electron transfer efficiencies than carbon defect-deficient NCC. This study introduces a novel photocatalyst with self-regenerating capabilities, presenting an innovative approach to regulate redox couples in SR-AOPs for sustainable degradation.

“Frozen” π-π stacking on perylene diimide molecules induces oxygen vacancies synergistic activation of persulfate towards degradation of tetracycline

Oxygen vacancy-rich self-assembled perylene diimide (OV-SA-PDI) supramolecules were prepared via freeze-drying, which froze the molecular backbone by retaining π-π stacking to induce additional OVs. The OVs content on OV-SA-PDI (1.956 × 1013 spins·mm−3) was 1.9 times that of SA-PDI (1.029 × 1013 spins·mm−3) with vacuum drying. The photocatalytic performance of OV-SA-PDI was demonstrated to be excellent in activating persulfate (PS) to degrade tetracycline (TC), achieving a remarkable degradation efficiency of 94.6% in 60 min under visible light (Vis). Mechanistic studies revealed a synergistic interaction among OV-SA-PDI, PS, and Vis to produce an abundance of active species. Vis activated a small portion of PS to produce ∙OH and SO4∙−, whereas the photogenerated electrons generated by OV-SA-PDI directly cleaved the O-O bond to produce abundant SO4∙−. Furthermore, the OVs acted as an electron trap to promote carrier separation and produced 10.0 μM 1O2 within 12 min. The active species were determined to decompose TC into low-toxicity products with lower molecular weights (m/z = 352, 340, and 227). This study presented a novel approach to the introduction of OVs into organic semiconductors and offered a mechanistic analysis of the synergistic relationship between defective organic semiconductors and sulfate radical-based advanced oxidation processes for wastewater treatment.

FeCo@hydrochar nanocomposites as efficient peroxymonosulfate activator for organic pollutant degradation.

Sulfate radical-based advanced oxidation processes (SR-AOPs) are renowned for their exceptional capacity to degrade refractory organic pollutants due to their wide applicability, cost-effectiveness, and swift mineralization and oxidation rates. The primary sources of radicals in AOPs are persulfate (PS) and peroxymonosulfate (PMS) ions, sparking significant interest in their mechanistic and catalytic aspects. To develop a novel nanocatalyst for SR-AOPs, particularly for PMS activation, we synthesized carbon-coated FeCo nanoparticles (NPs) using solvothermal methods based on the polyol approach. Various synthesis conditions were investigated, and the NPs were thoroughly characterized regarding their structure, morphology, magnetic properties, and catalytic efficiency. The FeCo phase was primarily obtained at [OH-] / [Metal] = 26 and [Fe] / [Co] = 2 ratios. Moreover, as the [Fe]/[Co] ratio increased, the degree of xylose carbonization to form a carbon coating (hydrochar) on the NPs also increased. The NPs exhibited a spherical morphology with agglomerates of varying sizes. Vibrating-sample magnetometer analysis (VSM) indicated that a higher proportion of iron resulted in NPs with higher saturation magnetization (up to 167.8 emu g-1), attributed to a larger proportion of FeCo bcc phase in the nanocomposite. The best catalytic conditions for degrading 100ppm Rhodamine B (RhB) included 0.05g L-1 of NPs, 2mM PMS, pH 7.0, and a 20-min reaction at 25°C. Notably, singlet oxygen was the predominant specie formed in the experiments in the SR-AOP, followed by sulfate and hydroxyl radicals. The catalyst could be reused for up to five cycles, retaining over 98% RhB degradation, albeit with increased metal leaching. Even in the first use, dissolved Fe and Co concentrations were 0.8 ± 0.3 and 4.0 ± 0.5mg L-1, respectively. The FeCo catalyst proved to be effective in dye degradation and offers the potential for further refinement to minimize Co2+ leaching.

Efficient removal of tetrabromobisphenol A in the Mn1Fe0.5Al0.5-LDO@BC/peroxymonosulfate water purification system

Tetrabromobisphenol A (TBBPA) brominated flame retardants in water posed threat to the ecological system due to its persistence and biomagnification. In this work, an efficient water purification system based on sulfate radical-based advanced oxidation processes (SR-AOPs) with Mn1Fe0.5Al0.5-LDO@BC as the core was constructed by adjusting the key preparation parameters, optimizing catalyst performance and exploring operating conditions. Under the optimal conditions of Mn1Fe0.5Al0.5-LDO@BC/PMS system (calcination temperature of 600 oC, 0.1 g/L Mn1Fe0.5Al0.5-LDO@BC, 0.15 mM PMS, pH value of 7–), 15 mg/L TBBPA was almost completely degraded within 30 min. Mn1Fe0.5Al0.5-LDO@BC/PMS water purification system exhibited resistance to inorganic anions and humic acid. In addition, Mn1Fe0.5Al0.5-LDO@BC reflected better cycle stability and ecological environmental protection. Electron paramagnetic resonance (EPR) and quenching experiments verified the existence of a large number of dominant active species in the water purification system, especially the contribution of O2•– and 1O2 to the degradation of TBBPA. Finally, the catalytic mechanism and possible degradation pathway of TBBPA were elucidated, and the toxicity of the intermediates was predicted. This work provided novel insights into the efficient purification of TBBPA brominated flame retardants in wastewater.

Dual activation of peroxymonosulfate with FeS2@Co3O4-C catalyst and visible light for the efficient degradation of tetracycline

Antibiotics have garnered global attention as a pressing concern due to their wide spread discharge to the environment and resulting significant threats to both human health and the environment. The Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) technique has already been verified as an effective process for pollutant degradation. Herein, FeS2@Co3O4-C composites, utilizing ZIF-67-derived Co3O4-C as the substrate material, were fabricated using a single-step solvothermal technique for the degradation of tetracycline (TC) by activated peroxymonosulfate (PMS) in combination with visible light irradiation. In the FeS2@Co3O4-C/PMS/Vis system, the FeS2@Co3O4-C showed better activation performance than the single chemical activation system or photocatalytic system, with 97.2 % TC removed in 20 min. The FeS2@Co3O4-C composite material was thoroughly investigated employing X-ray diffraction (XRD) for analyzing its crystal structure, transmission electron microscopy (TEM) for detailed structural insights, scanning electron microscopy (SEM) for morphological examination, and X-ray photoelectron spectroscopy (XPS) for the elemental valence states. The quenching experiments, along with EPR test, revealed that the primary active oxygen species consisted of 1O2, O2·-, and h+. The results presented here suggest the impressive stability and recyclability of FeS2@Co3O4-C making it a potential candidate as an efficient catalyst for initiating the activation of PMS in degrading persistent organic pollutants present in water.

Insight into the sulfite activation by Fe-rich sludge-derived biochar for efficient organic contaminant degradation: The role of iron species

Sulfate radical-based advanced oxidation processes driven by sulfite [S(IV)] activation offer a sustainable and cost-effective approach for environmental remediation. The utilization of abundant iron oxide species in Fe-rich sludge for S(IV) activation presents a cost-effective and eco-friendly solution, making it an attractive option for Fe-rich sludge disposal and water treatment. Herein, an efficient S(IV) activation system was developed by using Fe-rich sludge-derived biochar (FBC) for the first time. The performance of S(IV) activation by different pyrolyzed FBCs was evaluated in terms of tetracycline (TC) degradation. The highest degradation efficiency of TC was achieved 95.0 % in the S(IV)/FBC700 under the optimum conditions. The reactive radical species responsible for TC degradation in the system were confirmed to be SO4•−. The present work opens up new possibilities for the development of novel advanced oxidation processes utilizing the waste Fe-rich sludge.

Study on high-efficiency sulfide removement using sulfate radical-based AOPs and its oxidation mechanism of refractory gold ore

Pyrite enclosure poses a significant challenge in refractory gold ore processing, inhibiting gold leaching. This study explores Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) as an effective alternative for pretreating such ores. The oxidation pretreatments were performed under heat and ultrasound activation methods, including heat and ultrasound, and the influences of pretreatment time, pH, ultrasound power, pretreatment temperature, and precursor (PDS) concentration were investigated. Both ultrasonic and heat activation effectively mitigate the negative impact of pyrite enclosure on gold leaching. Specifically, the gold leaching rate improved from 21.9 % to 46.1 % and 74.9 % with heat and ultrasound activation, respectively The and generated by PDS dominate the pyrite oxidation according to EPR and quenching tests. Meanwhile, the SR-AOPs treatment also promotes the interactions between pyrite enclosure and leaching agent, reducing the negative influences of pyrite. Kinetic studies indicated that the oxidation processes are different under heat and ultrasound activation. Heat activation is governed by an interfacial chemical reaction, with an activation energy of 25.57 kJ/mol. In contrast, ultrasound-induced cavitation and microjets remove the oxidation layer, disrupt the pyrite crystal structure, and expose encapsulated gold. These effects accelerate pyrite oxidation, shifting the kinetic control step from interfacial chemical reaction to internal diffusion, with a reduced activation energy of 35.06 kJ/mol.

Highly efficient activation of sulfite by oxygen vacancies-enriched ZnCe0.4Fe1.6O4 for methylparaben degradation

The exploitation of a novel catalyst was of great significance for sulfate radical-based advanced oxidation processes (AOPs) using sulfite as the precursor of sulfate radical. Herein, oxygen vacancies-enriched ZnCe0.4Fe1.6O4 was prepared and applied to activate sulfite for the degradation of methylparaben (MeP). ZnCe0.4Fe1.6O4 showed superior catalytic activity than that of ZnFe2O4, allowing an 85.2 % removal efficiency of MeP within 60 min. The initial pH showed a significant effect on the catalytic performance, and about 92.1 % of MeP could be removed at pH of 9.56 in ZnCe0.4Fe1.6O4/sulfite system. The quenching experiments and EPR tests verified SO4− and OH were the main reactive oxygen species (ROS) in ZnCe0.4Fe1.6O4/sulfite system. The catalytic mechanism was elucidated further by X-ray photoelectron spectroscopy (XPS) analysis of ZnCe0.4Fe1.6O4 before and after the reaction. The recycles of Zn2+/Zn3+, Fe2+/Fe3+ and Ce3+/Ce4+ were the key factor for the activation of sulfite, and oxygen vacancies on catalyst surface promoted the activation of sulfite. The degradation intermediates of MeP were determined by a liquid chromatography-mass spectrometer (LC-MS) and the degradation pathway was proposed. The reusability of ZnCe0.4Fe1.6O4 was evidenced by the recycling experiments. In addition, ZnCe0.4Fe1.6O4/sulfite system exhibited excellent applicability in treating other organic contaminants.

Wastewater Treatment: The Emergence of Cobalt Ferrite and Its Composites in Sulfate Radical-Based Advanced Oxidation Processes

Wastewater Treatment: The Emergence of Cobalt Ferrite and Its Composites in Sulfate Radical-Based Advanced Oxidation Processes

New insights into antifouling property and interfacial mechanism in photo-Fenton membrane distillation

Membrane distillation (MD), boasting high interception efficiency and low operational pressures, emerges as an innovative membrane technology. However, the occurrence of membrane fouling due to interaction between natural organic matter (NOM) and inorganic ions during the MD process curtails water purification efficiency, thereby constraining its potential applications. To address this quandary, this study integrates sulfate radical-based advanced oxidation processes (SR-AOPs) into MD technology to bolster membrane fouling control. A straightforward hydrothermal method coupled with vacuum filtration was employed to synthesize a Co3O4/Nitrogen-modified carbon quantum dots (NCDs)/PVDF (CN-PVDF) membrane for the first time, which was utilized in the MD treatment of simulated humic acid (HA) wastewater. Under visible light irradiation (1.9 kW/m2), CN-PVDF membrane activation of peroxymonosulfate (PMS) effectively altered the chemical attributes of the MD feed solution and reduced organic matter concentration. Moreover, it dismantled the carboxyl sites on HA that interact with Ca2+, consequently attenuating the formation of organic–inorganic complex pollutants. The XDLVO analysis showcased that photo-Fenton oxidation led to a diminishment in pollutant hydrophobicity, correlating with a 17.59 kT reduction in pollutant-membrane adsorption and a 7.47 kT amplification in adhesion barriers. This strategy transformed the initial two-stage fouling mode into a singular one, which significantly decreased the flux decline and the fouling layer thickness. Furthermore, the CN-PVDF membrane demonstrated self-cleaning capabilities via photo-Fenton. This study advances an innovative approach to bolster the fouling resistance of MD membranes and provides substantial theoretical support for the integration of SR-AOPs and MD technologies.

Efficiency and mechanism of phosphoric acid modified biochar loaded nanoscale zero-valent iron activated peroxymonosulfate for the degradation of bisphenol A

The degradation efficiency of bisphenol A (BPA) using sulfate radical-based advanced oxidation processes still requires further improvement. Herein, we prepared phosphoric acid-modified biochar-supported nZVI (PBC/nZVI) through liquid-phase reduction. Under optimized conditions, including a PBC/nZVI dosage of 1.2 g/L, pH 9.0, and PMS concentration of 2.0 mmol/L, the BPA degradation rate reached up to 92.66 % within 60 min with the mineralization rate of 45.5 %. The presence of Cl−, HCO3− and CO32− promoted the degradation of BPA, while NO3− had minimal effect. Conversely, H2PO4− and humic acid exhibited varying degrees of inhibition. The degradation of BPA involved four reactive oxygen species (•OH, SO4•−, O2•−, and 1O2), with 1O2 playing a prominent role. The pathways of •OH-induced oxidation and SO4•−-induced hydroxylation were identified as the mechanisms through which BPA was degraded. These findings highlighted the potential of PBC/nZVI as a rapid and efficient material for BPA degradation.

Highly efficient peroxymonosulfate activation by CoFe2O4@attapulgite–biochar composites: Degradation properties and mechanism insights

Sulfate radical-based advanced oxidation processes (SR-AOPs) have been considered as a promising approach for degrading organic pollutants. Herein, CoFe2O4 anchored on attapulgite-biochar composites (CoFe2O4@ATP–BC) were synthesized by a sol-gel co-pyrolysis method and showed excellent catalytic performance, reusability and stability in activating peroxymonosulfate (PMS) for the degradation of Rhodamine B (RhB). The effects of PMS concentration, catalyst dosage, temperature, initial pH, NOM and inorganic ions on the removal of RhB were investigated. The radical quenching experiments and electron paramagnetic resonance (EPR) measurement confirmed that 1O2, O2∙− and surface-bound ∙OH and SO4∙− were major reactive oxygen species (ROS) in the RhB degradation by CoFe2O4@ATP–BC/PMS system, indicating that radical and non-radical degradation pathways were both involved. The possible catalytic mechanism of PMS by CoFe2O4@ATP–BC was proposed including the interface reaction and bulk reaction. The main degradation intermediates were identified by liquid chromatograph-mass spectrometry (LC-MS), and three possible degradation pathways of RhB were deduced accordingly. In general, the CoFe2O4@ATP–BC/PMS system provided fundamentals of theoretical and applied research to further develop supported bimetallic oxides for advanced oxidation treatment of organic wastewater.

Activation of peroxydisulfate via BiCoFe-layered double hydroxide for effective degradation of aniline.

The sulfate radical-based advanced oxidation processes (SR-AOPs) is a promising method for the degradation of pollutants, with the development of highly efficient catalysts for persulfate activation has been widely concerned. The novel BiCoFe-LDH (BCF-x) was synthesized successfully by coprecipitation method, which can activate peroxydisulfate (PDS) efficiently to degrade aniline. Comparative analysis with pure CoFe-LDH revealed a remarkable increase in reaction rate constant by approximately 14.66 times; the degradation rate of aniline (10mg/L) was 100% in 60min with the condition of 0.5g/L BCF-1.5 and 0.5g/L PDS, due to BCF-1.5 which was characterized as a complex of CoFe-LDH and Bi2O2CO3, promoting electron transport to improve the efficiency of activated PDS. In the reaction system, SO4•-, ·OH, and 1O2 were responsible for the aniline degradation and ·OH was the primary one. Furthermore, this work proposes a reaction electron transfer catalytic mechanism, which provided a new insight and good application prospect for efficient activation of PDS for pollutant degradation.

Powdered activated carbon (PAC)-assisted peroxymonosulfate activation for efficient urea elimination in ultrapure water production from reclaimed water

Urea is a problematic pollutant in reclaimed water for ultrapure water (UPW) production. The sulfate radical-based advanced oxidation process (SR-AOP) has been recognized as an effective method for urea degradation. However, conventional metal-based catalysts for peroxymonosulfate (PMS) activation are unsuitable for UPW production due to issues related to metal ion leaching. In this study, the use of powdered activated carbon (PAC) was investigated for the removal of urea from reclaimed water. The PAC exhibited a high degree of defects (ID/IG = 1.709) and various surface oxygen functional groups (C–OH, C=O, and C–O), which greatly enhanced its catalytic capability. The PAC significantly facilitated PMS activation in the PMS + PAC system, leading to the complete urea decomposition. The PMS + PAC system demonstrated excellent urea removal efficiency within a wide pH range, except for pH < 3. Among the various anions present, the CO32− and PO43− inhibited urea degradation, while the coexistence of Cl− promoted urea removal. Furthermore, the feasibility test was evaluated using actual reclaimed water. The quenching test revealed that SO4−·, ·OH, and O2−· played crucial roles in the degradation of urea in the PAC-assisted SR-AOP. The oxygen functional groups (C–OH and O–C=O) and defect sites of PAC clearly contributed to PMS activation.

Bimetallic iron-nickel phosphide as efficient peroxymonosulfate activator for tetracycline hydrochloride degradation: Performance and mechanism

Sulfate radical-based advanced oxidation processes with (SR-AOPs) are widely employed to degrade organic pollutants due to their high efficiency, cost-effectiveness and safety. In this study, a highly active and stable FeNiP was successfully prepared by reduction and heat treatment. FeNiP exhibited high performance of peroxymonosulfate (PMS) activation for tetracycline hydrochloride (TC) removal. Over a wide pH range, an impressive TC degaradation efficiency 97.86% was achieved within 60 min employing 0.1 g/L FeNiP and 0.2 g/L PMS at room temperature. Both free radicals of SO4·-, ·OH, ·O2− and non-free radicals of 1O2 participated the TC degradation in the FeNiP/PMS system. The PMS activation ability was greatly enhanced by the cycling between Ni and Fe bimetal, and the active site regeneration was achieved due to the existence of the negatively charged Pn−. Moreover, the FeNiP/PMS system exhibited substantial TC degradation levels in both simulated real-world disturbance scenarios and practical water tests. Cycling experiments further affirmed the robust stability of FeNiP catalyst, demonstrating sustained degradation efficiency of approximately 80% even after four cycles. These findings illuminate its promising potential across natural water bodies, presenting an innovative catalyst construction approach for PMS activation in the degradation of antibiotic pollutants.

Enhanced antibiotic degradation via photo-assisted peroxymonosulfate over graphitic carbon nitride nanosheets/CuBi2O4: Highly efficiency of oxygen activation and interfacial charge transfer

Improving the activation capacity of peroxymonosulfate (PMS) to increase radical and non-radical production is critical for antibiotic degradation. However, how to boost reactive oxygen species (ROS) and speed interfacial charge transfer remains an essential challenge. We report a coupling system of 10 %CNNS/CuBi2O4 photocatalyst and sulfate radical-based advanced oxidation processes (SO4−-AOPs) to enhance the activation of PMS and improve antibiotic degradation. Owing to highly efficient oxygen activation and interfacial charge transfer, the degradation efficiency of the photo-assisted PMS system was as high as 51.6 times and 2.8 times that of photocatalyst and SO4−-AOPs alone, respectively. Importantly, the highly efficient oxygen activation resulted in the production of O2−, which in turn could utilize the excess electrons generated through efficient interfacial charge transfer to convert into non-radical 1O2. The total organic carbon (TOC) elimination effectiveness of the photo-assisted PMS system reached 82 % via the synergy of radicals and non-radicals (O2−, OH, 1O2, SO4−, h+). This system also had excellent potential for reducing the generation and toxicity of disinfection by-products (DBPs), as evidenced through significant reductions in concentrations of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloronitromethane (TCNM) by 76 %, 64 %, and 35 %, respectively, providing an effective and eco-friendly strategy for antibiotic treatment.

Photocatalytic Degradation of Rhodamine B via Fe-g-C3N4 Activated Sulfate Radical-Based Advanced Oxidation Processes and the Synergistic Mechanism

Photocatalytic Degradation of Rhodamine B via Fe-g-C3N4 Activated Sulfate Radical-Based Advanced Oxidation Processes and the Synergistic Mechanism

Green rGO/FeNPs nanocomposites activated peroxydisulfate for the removal of mixed 17β-estradiol and estriol

Reduced graphene oxide/iron nanoparticles (rGO/FeNPs) synthesized by the chemical method have been used in Fenton oxidation of organic contaminants, yet little is known about biosynthesized rGO/FeNPs using green tea extract (GT) as how to activate persulfate in sulfate radical-based advanced oxidation processes. In this study, rGO/FeNPs were used to activate peroxydisulfate (PDS) for 17β-estradiol (βE2) and estriol (E3) removal. The rGO/FeNPs-PDS system removed 83.6% of βE2 and 62.5% of E3 within 240 min, which was confirmed by a combination of adsorption and degradation via both radical and non-radical pathways. Four main reactive species in βE2 and E3 degradation were observed, i.e., hydroxyl radical (·OH), sulfate radical (SO4·−), singlet oxygen (1O2) and electron transfer, with the respective contributions of ·OH (32.9 and 34.7%), SO4·− (16.1 and 19.7%), 1O2 (12.2 and 14.1%) and electron transfer (8.0 and 7.2%). Analysis of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), Electron Paramagnetic Resonance (EPR) and electrochemical measurements all indicated that beside the well-known role of Fe, CO from rGO through the generation of ·OH, SO4·−, 1O2 and electron transfer, as well as GT through electron transfer also participated in the activation of PDS. Finally, the degradation pathways of βE2/E3 were proposed. Overall, this study provides a new insight into the biosynthesis of rGO/FeNPs to activate PDS for the oxidation of mixed emerging contaminants.

Pilot-scale sulfate radical-based advanced oxidation for wastewater reuse: simultaneous disinfection, removal of contaminants of emerging concern, and antibiotic resistance genes

Wastewater reuse addresses water scarcity, but contaminants of emerging concern (CECs), pathogens and antibiotic resistance genes (ARGs) pose health and environmental risks. The European Union (EU) has enacted Regulation (EU) 2020/741, establishing wastewater reuse standards for agriculture. This study evaluates for the first time the effectiveness of four sulfate radical-based advanced oxidation processes (SR-AOPs), based on the combination of peroxymonosulfate (PMS) with O3 and H2O2, applied at pilot plant, for the simultaneous elimination of microorganisms, CECs, and ARGs, in actual urban wastewater treatment plant (UWWTP) effluents. The system PMS/H2O2/UV-A improved the disinfection effectiveness, compared to PMS/UV-A, especially using a molar ratio 1:3 (0.5 mM PMS:1.5 mM H2O2), achieving complete elimination of total aerobic microorganisms in 90 min. However, this double oxidation system, does not improve CECs removal compared to PMS/UV-A in neither of the two molar ratios studied (1:1 or 1:3), and none of these treatments significantly reduced the prevalence of ARGs. However, the PMS/O3 system demonstrated the ability to remove total aerobic microorganisms in 20 min and Escherichia coli in 5 min, 94 % of CECs, and 6 out of the 8 ARGs, demonstrating to be the most effective treatment. However, the system showed phytotoxicity, inhibiting seed growth by 10–30 %, probably associated with the by-products formed in the reaction between organic matter and ozone. This result highlights that SR-AOPs are promising processes with the capability to achieve the simultaneous removal of different contaminant groups, reducing the risks associated with wastewater reuse. Their application at larger scales is increasingly closer.

Single‐Atom Catalysts Originated from Metal–Organic Frameworks for Sulfate Radical‐Based Advanced Oxidation Processes: Critical Insights into Mechanisms

AbstractThe widely discussed single‐atom catalysts (SACs) are regarded as a kind of attractive material for sulfate radical‐based advanced oxidation processes (SR‐AOPs) owing to their maximum atomic utilization efficiency and outstanding stability. Currently, metal–organic frameworks (MOFs) have appeared as prospective precursors for building SACs due to extensive chelating sites, functional adjustability, and structural tunability. However, there are few critical and systematic reviews about the application of MOF‐derived SACs in SR‐AOPs, especially in‐depth analysis of the mechanisms. Therefore, this review seeks to offer a thorough summary of the development of MOF‐derived SACs in SR‐AOPs. First, the unique advantages of MOFs as derivative precursors for SACs are discussed thoroughly. Afterward, the current synthesis strategies are elaborated categorically to unveil the formation process of single atoms and their coordination environments. Notably, the roles of different reaction sites including the generation of reactive species and mediating electron transfer are further analyzed to explain mechanisms comprehensively. Thereafter, the characterization techniques and theoretical calculations for mechanisms studies are also highlighted. Eventually, critical insights into present challenges and future developments are proposed, which are expected to enhance the catalytic efficiency of MOF‐derived SACs in SR‐AOPs.