Peroxymonosulfate Research Articles

Mechanisms and degradation pathways of tetracycline by Co7Fe3 nanoparticles anchored porous carbon activated peroxymonosulfate

In recent years, catalysts based on transition metals have been extensively employed for the activation of peroxymonosulfate (PMS) in the removal of tetracycline (TC) from aquatic environments. However, the efficiency of single transition metals and heterogeneous transition metals as catalysts has been somewhat limited. In this study, different bimetallic Co-Fe catalysts embedded in a porous carbon (Co7Fe3-500/600/700/800) were synthesized using a straightforward single-step calcination process at varying temperatures, addressing the issues of poor activation performance of single transition metals and low dispersion of active components in heterogeneous transition metals. The Co7Fe3-500/600/700/800 enhanced the electronic configuration, establishing electron-rich and highly active zones that promoted electron transfer between the Co and Fe transition metals. The results showed that Co7Fe3-600, exhibited excellent PMS activation performance, removing 95.1 % of TC from the solution within 10 min. Additionally, Co7Fe3-600 showed strong adaptability and resistance to interference under various environmental conditions. DFT calculations, HPLC-MS analysis and T.E.S.T analysis were used to predict potential degradation intermediates during TC degradation and assess their biological toxicity. This research introduces an innovative strategy for formulating sophisticated bimetallic alloy catalysts and contributes fresh perspectives on the mechanisms involved in the PMS activation process by bimetallic catalysts.

Synergistic Catalysis of Cobalt Single Atoms and Clusters Loaded on Carbon Film: Enhancing Peroxymonosulfate Activation for Degradation of Norfloxacin

AbstractMany existing research focuses on the differences or performance comparisons between single‐atom or small‐sized nanocluster catalysts, but there is a lack of comprehensive research on the coupling relationship between the structure and activity and the mechanism of synergy. This study investigates the combined catalytic potential of cobalt single atoms (SAs) and nanoclusters (NCs) for enhanced peroxymonosulfate (PMS) activation to degrade norfloxacin (NFX). A novel CoSAs‐NCs/CN/TiO2 catalyst is synthesized, featuring cobalt SAs and NCs uniformly dispersed on the carbon film wrapping TiO2, and the degradation efficiency of the NFX solution is almost completely degraded, with a mineralization rate of 76.35%. Density functional theory (DFT) calculations indicate that the synergistic interaction between cobalt SAs and NCs promotes more efficient PMS adsorption and activation and significantly reduces the activation energy barrier, which enhances electron transfer and increases reactive oxygen species (ROS) generation. This research highlights the robust and versatile nature of this novel catalyst system in addressing various contaminants. This study elucidates the activation mechanism of catalysts, providing new ideas for advanced oxidation processes (AOPs) in environmental remediation, linking the structure and performance of catalysts, and emphasizes the practicality and importance of the CoSAs‐NCs/CN/TiO2 catalyst in effectively and long‐term remediation of water pollutants.

Elucidating the role of double-confined effect in hollow MOFs/GO catalytic membrane for deep arsenic pollution treatment

The significance of addressing arsenic contamination is huge, given its widespread environmental impact and detrimental effects on human health. Herein, we developed a double-confined catalytic membrane capable of activating peroxymonosulfate (PMS) by integrating hollow Prussian blue analogues (H-PBA) with a unique void-confinement effect into graphene oxide (GO) laminates. This delicately designed H-PBA/GO membrane displayed 98.8 % p-arsanilic acid (p-ASA) removal with a 9.03 s retention time, surpassing most reported studies. Our experiments underscored that the dual-confined architecture not only drove mass transfer but also bolstered reactant concentration, thereby multiplying catalytic activities. Remarkably, this double-confinement conduced to a sustained dominance of surface-radicals (SO4−) and singlet oxygen (1O2), bolstering p-ASA degradation across a broad pH spectrum and numerous aqueous realms, inclusive of high salinity waters pertinent to desalination pre-treatment processes. Crucially, the H-PBA/GO membrane demonstrated over 90 % degradation of p-ASA and immobilized total As, unfaltering over 80 h of continuous operation. This signified an evolution in membrane technology, promising enhanced and steadfast performance. This innovation bore profound implications for devising double-confined efficacious and robust catalysts, poised to revolutionize advanced wastewater treatment, notably augmenting desalination systems by fortifying pre-treatment and safeguarding reverse osmosis membranes from organic and arsenic fouling.

Flotation separation of ilmenite and titanaugite modified by Fe2+-assisted peroxymonosulfate oxidation: Performance and activation mechanism

Efficient separation of ilmenite and titanaugite has always been recognized challenge in modern mineral processing. The use of a heterogeneous Fenton-like oxidation process composed of peroxymonosulfate (PMS) and Fe2+ is promising to address this issue. Flotation findings indicated that effective recovery of ilmenite could be achieved under weak acidic conditions, and a TiO2 recovery of 81.56 % and a grade of 32.16 % concentrate was collected. A series of characterization analyses confirmed that the PMS-Fe2+-mediated Fenton-like reaction in the ilmenite system generated more •OH and SO4•- radicals, which oxidized Fe2+ to Fe3+ on its surface, thus improving the active sites on ilmenite surface. Moreover, PMS-Fe2+ promoted the positive shift of surface charge on ilmenite, facilitating NaOL adsorption and making the surface more hydrophobic. NaOL primarily interacted with Fe active sites on the ilmenite surface and Mg2+ and Ca2+ active sites on the titanaugite surface in the formation as chemisorption. Thus, PMS-Fe2+ activated ilmenite mainly via augmenting the quantity and reactivity of Fe active sites on the surface. In summary, these findings provide the innovative pathways to implement the advanced oxidation processes in mineral flotation.

Preparation of printing and dyeing sludge biochar/macromolecule polymer microsphere as a non-sacrificial persulfate activator with excellent reusability and reduced heavy metals leaching

Biochar-based environmental functional materials offer a promising approach for the resourceful utilization of printing and dyeing sludge (PADS). However, pollutant desorption and heavy metal leaching pose potential environmental risks. In this study, we developed a novel PADS biochar (PADSBC) macromolecule polymer microsphere with outstanding reusability and stability. This microsphere effectively activated peroxymonosulfate (PMS) for the degradation of sulfadiazine (SDZ) while significantly reducing heavy metal leaching compared with PADSBC. The SDZ removal efficiency was not influenced by the type of macromolecule polymers (calcium alginate (CA), cellulose nanofibers (CNF), and polyvinyl alcohol (PVA)) incorporated into PADSBC. In the CA-PADSBC800 microsphere/PMS system, 97 % of SDZ was removed within 40 min, primarily through 1O2-induced oxidative degradation (62 %) and adsorption by CA-PADSBC800 (29 %). Additionally, CA-PADSBC800 prevented SDZ desorption for over five consecutive cycles, while PADSBC800 exhibited 25 % desorption. The presence of HCO3- and humic acids slightly delayed SDZ removal, while Cl- slightly accelerated it. Doping CA, CNF, and CA + CNF into PADSBC800 reduced the leaching of Cu and Cr by over 90 %, and Ni by over 80 %, under both experimental conditions and simulated surface water and landfill leachate situations. The excellent performance of the PADSBC-macromolecule polymer microspheres was attributed to the presence of carboxyl, hydroxyl, and C = O functional groups.

CO2(OH)2CO3 and Fe doped Co2(OH)2CO3 prepared as efficient and stable catalysts for activation of PMS: Two systems comparison and key role of high-valent metal-oxo species in mechanism revealing

High-valent metal-oxo species [M(IV) = O] exhibited high selectivity and chemical efficiency in advanced oxidation processes for removing organic pollutants, making their manipulation essential in catalytic systems. However, the low and unsustainable efficiency of generating M(IV) = O posed significant challenges. In this research, Co2(OH)2CO3 were successfully prepared via a one-pot hydrothermal method to efficiently activate peroxymonosulfate (PMS) with high-valent cobalt-oxo species [Co (IV) = O] as the primary active oxidation species. Building upon this foundation, COC was modified through variations in metal types and elemental ratios, in which magnetically enriched FexCo2-x(OH)2CO3 was synthesized by gradient Fe doping with higher catalytic efficiency and stability. The insertion of Fe resulted in the lengthening of the Co-O bond and improved the valence distribution of cobalt on the COC surface. Besides, it enabled part of the electrons to be transferred from the Fe active center to the Co active center, breaking the limitation of the traditional two-electron transfer and realizing the stable generation of more high-valent metals. Both reaction systems achieved efficient degradation of sulfadimethoxine (SDM) within 30 min and were able to completely degrade SDM within 30 min even after three cycles. FexCo2-x(OH)2CO3 maintained excellent catalytic performance even after 30 days of exposure to air. In both systems, high-valence metals played a dominant role, while the contributions of hydroxyl radicals and sulfate radicals were negligible. Overall, the two groups of developed catalysts both showed remarkable stability and pollutant removal performance in anions, humic acid, Different antibiotics and real water systems, which provided a new perspective on antibiotic removal.

N-coordinated iron sites dispersed in porous carbon frameworks to activate peroxymonosulfate for efficient sulfisoxazole degradation and real hospital wastewater decontamination

Herein, an N-coordinated Fe site dispersed in porous carbon frameworks (Fe-NC) fabricated from zeolitic imidazolate frameworks encapsulated with iron acetylacetonate (Fe(acac)3 @ZIFs) was employed to activate peroxymonosulfate (PMS) for the attenuation of sulfisoxazole (SIZ) and treating real hospital wastewater. The constructed Fe-NC/PMS system exhibited good catalytic stability for SIZ degradation, maintaining excellent degradation performance over multiple cycles with virtually no leaching. The quenching experiments, electron paramagnetic resonance (EPR) capture analyses, and semi-quantitative measurements showed that singlet oxygen (1O2) and high-valent metal-oxo species were mainly responsible for SIZ degradation by Fe-NC/PMS. Significantly, ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS/MS) was used to trace 134 pharmaceutical contaminants in real hospital wastewater. Effective degradation was achieved for 87 % of the pharmaceutical contaminants by the Fe-NC/PMS process. Seventy-four pharmaceutical contaminants were eliminated. Taken together, this work successfully established the Fe-NC/PMS technology using the developed iron-based materials and explored its application to real hospital wastewater treatment, providing an eco-friendly and effective strategy for treating wastewater.

Tubular nanofiber membranes combined with Z-scheme CuS@Co3S4 heterojunction catalyst for high-efficient removal of polyvinyl alcohol from waste water with high COD

Polyvinyl alcohol (PVA), a typical water-soluble polymer with huge global production, is becoming one of the most ubiquitous pollutants and indeed the villain of the piece contributing high chemical oxygen demand (COD) in wastewater. Membrane technology is an effective method for wastewater purification, in particular, with the combination of peroxymonosulfate (PMS)-assisted advanced oxidation or photocatalytic process, is capable of maintaining high water flux and anti-fouling. Herein, a ZIF-67 derived Z-scheme CuS@Co3S4 heterojunction catalyst immobilized by poly (m-phenylene isophthalamide) (PMIA) tubular nanofiber membrane (CuS@Co3S4/PMIA-TNM) is designed using a polyester braided tube as interior reinforcement. The resultant membrane features with outstanding superhydrophilicity and commendable porosity (82.1%), leading to a significantly enhanced permeability (water flux > 82.3L·m-2·h-1). Meanwhile, the membrane shows promising PVA removal efficiency (> 99.9%) with a high COD removal efficiency (~ 83.4%) and enhanced antifouling capacity (flux recovery ratio > 99.7%) with the assistance of PMS driven by an ultra low-power LED lamp. The universal applicability and environmental adaptability are also verified in various reaction conditions. In terms of ecotoxicological impacts of the PVA wastewater before and after treatment on aquatic organisms, Zebrafish embryonic development dynamically demonstrated that the treated PVA waste water by the developed hybrid membrane is healthy for fish to grow. Our study definitely opens up a new avenue to develop high-performance catalytic membranes for PVA-based wastewater treatment.

Mechanistic insights and performance evaluation of ZnFe-Modified bovine manure biochar in activating peroxymonosulfate for efficient thiamethoxam degradation: A combined DFT calculation and degradation pathway analysis

The study explored the degradation of thiamethoxam (THM) in water using modified bovine manure biochar as a catalyst for the first time, due to its potential harm to living organisms and frequent detection in natural water bodies. Experimental findings revealed that the rate constants for peroxymonosulfate (PMS)-catalyzed THM degradation by bovine manure biochar modified with ZnCl2 and K2FeO4 (ZnFeBC) increased by 76.78 times compared to unmodified biochar (BC), achieving a 100% degradation rate within 60 min. ZnFeBC exhibited excellent PMS activation performance across various pH levels. XPS characterization and Density Functional Theory (DFT) calculations have revealed that Fe element cycling occurs on the ZnFeBC surface, resulting in increased charge transfer rates at the reaction interface. The main active sites responsible for PMS activation were found to be Fe0 and Fe3O4. The degradation mechanism of THM by the ZnFeBC/PMS system involved SO4•-, •OH, 1O2 and electron transfer. This catalyst demonstrated strong pH adaptability and outstanding catalytic degradation capabilities for various pollutants, making it highly suitable for widespread wastewater treatment applications, while also providing a new way for resource reutilization of bovine manure.

The removal of antibiotic resistance bacteria and genes and inhibition of RP4 plasmid-mediated conjugative transfer by citric acid chelated Fe(II) catalyzing peroxymonosulfate systems: Performance and mechanisms

The excessive and inappropriate usage of antibiotics accelerated the appearance and proliferation of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs), posing a considerable threat to human health and ecological systems. The objectives of this study were to construct Fe(II) chelated by citric acid (CA) catalyzing peroxymonosulfate (PMS) systems with different dosages for the elimination of ARB (E. coli DH5α) and ARGs (tetA, tetR, and blaTEM-1), and to reveal the mechanisms on ARGs conjugation transfer. The processes still maintained high ARB/ARGs removal rates in various water matrices (tap water, river water, sewage, and farm wastewater). The results demonstrated Fe(II)-CA/PMS system in high dosages ([Fe(Ⅱ)] = 0.10 mM; [CA] = 0.08 mM; [PMS] = 0.40 mM) significantly enhanced the removal of ARB (8-log) and ARGs (5.11-log tetA, 1.01-log tetR, and 0.62-log blaTEM-1) by promoting the production of reactive oxygen species (ROSs), thereby inhibiting conjugative transfer completely. Interestingly, Fe(II)-CA/PMS treatment at low dosages ([Fe(Ⅱ)] = 0.0025 mM; [CA] = 0.002 mM; [PMS] = 0.02 mM) still inhibited the transfer of ARGs (2.26 × 10−4, 0.65-fold), mainly through downregulation of genes related with ROS synthesis, DNA damage repair (SOS response), ATP synthesis, and transfer-related genes, as well as upregulation of globally regulatory genes. These results presented a hopeful strategy for holding back the dissemination of antibiotic resistance in environments.

Degradation of organic dyes by Peroxymonosulfate activated with Zn/Co-ZIF

In this study, we successfully synthesized a bimetallic metal-organic framework material Zn/Co-ZIF to start Peroxymonosulfate (PMS) for organic dye degradation in the water body. Material characterization was evaluated by advanced methods, such as XRD, FT-IR, SEM, EDX, and BET. The influence of different factors on methylene blue (MB) decomposition rate was investigated. The results show that Zn/Co-ZIF has a porous structure, a high specific surface area and decomposes 98.22% MB (20 mg/L) in 4 minutes under reaction conditions of 40 mg/L catalyst, 0.814mM PMS, pH = 7. The decomposition efficiency of dyes increases in the order CR (79.85%) <RhB (90.81 %) < DB71 (96.07%) < MO (97.63%) < MB (98.22%). The main ROS for the degradation MB in this study were SO4—-, O2—- and 1O2. This shows that Zn/Co-ZIF materials are potential heterogeneous catalysts to activate PMS to decompose organic pollutants in water.

N vacancies and OH/C=O co-modified g-C3N4 photoactivated peroxymonosulfate for the degradation of tetracycline: Synergistic promotion effect between excitons and carriers

Activation of peroxymonosulfate (PMS) to generate reactive oxygen species (ROS) for pollutant degradation via metal-free photocatalysts is an important green wastewater treatment and remediation method, but the pathway for generating ROS via exciton effects in catalysts is often overlooked. In this study, OH/C=O co-modified N-defective rod-shaped carbon nitride (Nv-CN-O) was designed and synthesized by soft template and alkali hydrothermal method. In the Nv-CN-O/PMS/Light system, there was a synergistic degradation of tetracycline (TC) by carriers and excitons, with a degradation rate 2.15 times higher than that of CN/PMS/Light. N vacancies and OH/C=O enhanced the adsorption to PMS, accelerated the charge transfer process, and activated PMS to generate ·O2− dominated reactive species. The functional group OH/C=O promoted the production of triplet excitons that through the energy transfer pathway to promote the production of 1O2. Abundant ROS were involved in the TC degradation process, and three possible TC degradation pathways were proposed. Nv-CN-O has strong anti-interference ability in actual water bodies, shows a promoting effect on the degradation of TC, which has practical application potential.

Peroxymonosulfate Activation by Fe@N Co-Doped Biochar for the Degradation of Sulfamethoxazole: The Key Role of Pyrrolic N

In this study, Fe, N co-doped biochar (Fe@N co-doped BC) was synthesized by the carbonization–pyrolysis method and used as a carbocatalyst to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) removal. In the Fe@N co-doped BC/PMS system, the degradation efficiency of SMX (10.0 mg·L−1) was 90.2% within 40 min under optimal conditions. Radical quenching experiments and electron spin resonance (ESR) analysis suggested that sulfate radicals (SO4•−), hydroxyl radicals (•OH), and singlet oxygen (1O2) participated in the degradation process. After the reaction, the proportion of pyrrolic N decreased from 57.9% to 27.1%. Pyrrolic N served as an active site to break the inert carbon network structure and promote the generation of reactive oxygen species (ROS). In addition, pyrrolic N showed a stronger interaction with PMS and significantly reduced the activation energy required for the reaction (∆G = 23.54 kcal/mol). The utilization potentiality of Fe@N co-doped BC was systematically evaluated in terms of its reusability and selectivity to organics. Finally, the intermediates of SMX were also detected.

Insight into the nonradical selective oxidation mechanism for versatile organic pollutants removal by perovskite activated peroxymonosulfate system

The heterogeneous catalysis of peroxymonosulfate (PMS) through nonradical pathway has shown many advantages in environmental remediation. It is necessary to unveil the factors affecting oxidation routes and selectivity toward different organic pollutants. Herein, a series of ABO3-type BiFexCo1-xO3 perovskite catalysts were fabricated via simple hydrothermal process to realize the changeover of catalytic activity and mechanism in PMS activation and pollutants oxidation. The as-prepared BiFe0.5Co0.5O3 (BFCO-3) achieved a 98 % removal efficiency of SMZ with a high kinetic constant (kobs = 0.334 min−1) in 10 min. The superior catalytic performance was ascribed to the introduction of bimetals at B-site, which enhanced electron donating capacity to PMS, confirming by d-band center calculations. Several parameters such as inorganic anions and humic acids affected the SMZ degradation slightly, owing that singlet oxygen was verified to be the primary reactive species in the BFCO-3/PMS system. Moreover, twelve organic pollutants including amoxicillin crystalline (AMX), cephalexin hydrate (CFX), ciprofloxacin (CIP), levofloxacin (LFX), Sulfadiazine (SDZ), sulfamethoxazole (SMZ), 4-acetamidophenol (ACP), benzoic acid (BA), bisphenol A (BPA), carbamazepine (CBZ), metronidazole (MNZ) and naproxen (NPX) were utilized to investigate the selective oxidation mechanism. A linear correlation between lnkobs and their half-wave potential (φ1/2) values (except for BA and MNZ) suggesting the dominant role of nonradical catalysis where phenolic compounds with lower anodic potential tend to lose electrons are more easily degraded. Furthermore, the reactive sites of representative SMZ for electrophilic species attack were precisely identified based on the Fukui index. And the degradation intermediates of SMZ were further determined by LC-MS/MS technology for proposing their degradation pathway and predicting ecotoxicity. This study not only provides an efficient advanced oxidation system for organic pollutants removal but also advances our understanding of the selective oxidation mechanism in nonradical-dominated catalytic process.

MoS2@Hydrochar nanocomposites with cost-effective fluid turbulent eddies induced piezoelectric catalytic peroxymonosulfate utilization efficiency for water polluted dye degradation

Piezoelectric materials can induce strain due to the fluid turbulent force produced during fluid shaking, which may be used to activate peroxymonosulfate (PMS). In this study, the effective interfacial interaction of few-odd-numbered layered MoS2 nanosheets and hydrochar (HC) nanocomposites as the piezoelectric material was used in a hydrodynamics energy-driven piezoelectric catalytic PMS activation process (piezo-PMS activation process) for Eriochrome Black T dye degradation. The results showed that Black T dye was efficiently degraded with an efficiency of 99.23 % within 15 min and a pseudo-first-order rate constant of 3.10 min−1 in the MoS2@HC-(6.5:3.5)/PMS/Shaking system. To clearly see the influence of hydraulic gradient (G) value, the hydrodynamics energy-driven piezo-PMS activation process for Black T dye degradation was performed at different shaking frequencies. The results indicated an optimal G value of (14.106 s−1) for Black T dye degradation. Notably, the MoS2@HC-(6.5:3.5)/ PMS/Shaking system produced the lowest EE/O value (34.05 kWhm−3 order−1), resulting in energy savings over 127 times of HC and 9 times of MoS2. Furthermore, piezoelectrochemical measurements of MoS2@HC-(6.5:3.5) indicated that these superior performances primarily resulted from the synergistic effects of MoS2 and HC. This led to a stronger piezoelectric response with effective piezo-generated charge separation, which in turn improved the efficiency of producing reactive species. Combining the scavenger test, FT-IR, and zeta potential analysis, we determined that •OH and SO4•− played a major role, while O2•− and 1O2 played a secondary role in Black T dye degradation. The steady-state concentrations of [•OH]ss, and [SO4•−]ss were 14.52 × 10−14 M and 20.00 × 10−14 M, respectively in the fluid turbulent force driven piezo-PMS activation process. Furthermore, a plausible degradation pathway of Black T dye was proposed based on the assessment of carbon number reduction, the mean oxidation number of organic carbon (MOC) and the predicted TOC/color index.

CoFe2O4-catalytic ceramic membrane for efficient carbamazepine removal via peroxymonosulfate activation

Poor water removal of low-molecular-weight anthropogenic contaminants is always a key problem in low-pressure membrane filtration process. In this work, we successfully designed and fabricated a novel cobalt-based bimetallic catalytic ceramic membrane (CoFe2O4@CM-2) with peroxymonosulfate (PMS) activation and membrane filtration dual functionality, employing a facile impregnation-filtration-calcination method. The resulting CoFe2O4@CM-2/PMS filtration system was specifically tailored for the removal of carbamazepine (CBZ). Our results demonstrate that the CoFe2O4@CM-2/PMS system achieved efficient removal of CBZ from contaminated waters. Under optimal conditions (PMS dosage of 0.5 mM and an operating flux of 40 L·m−2·h−1), the CoFe2O4@CM-2/PMS system exhibited remarkable CBZ removal efficiency, reaching up to 96.5 %. This efficiency was 32.2 and 19.3 times higher than that achieved by ceramic membrane filtration alone and PMS treatment alone, respectively. Additionally, the CoFe2O4@CM-2/PMS system facilitated 37.0 % mineralization of CBZ and up to 87 % utilization of PMS in the permeate. Furthermore, the CoFe2O4@CM-2/PMS system demonstrated robust performance, removing over 91 % of CBZ across a pH range of 3–9 and maintaining stability stability in the presence of humic acid (HA) interference. Its exceptional anti-fouling ability effectively mitigates membrane flux loss compared to single membrane filtration process. Quenching test, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) analyses revealed that 1O2, SO4-∙ and ·OH were the primary active substances in the system, while the redox cycle of Co2+/Co3+ played a crucial role in PMS activation. Moreover, the presence of iron (Fe) in the CoFe₂O₄@CM-2 expedited the Co2+/Co3+ cycle and enhanced PMS activation. This study introduces an innovative approach for fabricating ceramic membranes with catalytic degradation capabilities for organic pollutants and suggests promising avenues for integrating separation and advanced oxidation processes (AOPs) in future applications.

Synergistic activation of peroxymonosulfate for tetracycline hydrochloride degradation with SrTiO3/Ti3C2Tx photocatalyst

Peroxymonosulfate (PMS) is a promising technology for increasing the oxidation capacity and promoting the production of active species in the photocatalytic system. SrTiO3, a material with a perovskite crystal structure in a cubic form, can activate PMS on its surface and generate non-radical 1O2. Herein, SrTiO3/Ti3C2Tx (ST) composites were successfully synthesized using a hydrothermal method based on SrTiO3 materials. The photocatalytic activation of PMS resulted in the degradation of tetracycline hydrochloride (TC-HCl), with the ST-10 (10 wt% SrTiO3/Ti3C2Tx) composite showing the highest efficiency in TC removal and rapid degradation kinetics, achieving complete TC removal within 10 min. The synergistic interaction between the two components in ST-10 significantly enhanced the activation of peroxymonosulfate (PMS), leading to an increased production of free radicals. The larger specific surface area and presence of –OH groups in the composite material facilitated the adsorption and chemical bonding of PMS molecules, thereby improving their overall performance. Quench experiments and electron paramagnetic resonance analysis identified •SO4−, •OH, •O2– and 1O2 as the primary active species responsible for the degradation of TC. Additionally, the degradation pathway of TC was elucidated through mass spectrometry analysis. This study provides valuable insights for the development of effective photocatalysts as promising PMS catalysts in environmental applications.

Atomically dispersed Fe-N4 sites in activation of peroxymonosulfate for wastewater purification: Mechanism of non-radical pathways and their quantification

Single-atom catalysts are promising alternatives to homogeneous and heterogeneous catalysts in the advanced oxidation processes for contaminant degradation; however, quantifying the exact contribution of nonradical reactive oxygen species has remained challenging. Herein, Fe single atoms anchored on nitrogen-doped carbonaceous substrates (Fe SAs-N-C) were synthesized for peroxymonosulfate (PMS) activation toward pollutant degradation. Fe SAs-N-C achieved high activity within 30 min, which is 17.20 and 5.08 times higher than those of N-C catalysts without or with Fe nanoparticles, respectively. A synergistic mechanism of singlet oxygen (1O2) and electron transfer for dominating pollutant degradation was revealed. The former contributed 78.50 % while the latter contributed 21.50 % in pollutant elimination. Density functional theory calculations uncovered that the O atom in −SO4 moiety of PMS was adsorbed on the Fe atoms, leading to the OH bond elongation and generating 1O2. While the absorbed O atom in OO bond near to −SO4 moiety of PMS tended to enlarge the OO bond and accelerate the electron transfer. The adsorbed PMS was prone to being decomposed into 1O2 due to a lower energy barrier (0.43 eV) of 1O2 rate-determining step than that of electron transfer (0.95 eV). Fe-N4 sites are both electron transfer channels and 1O2 formation sites. This work provides insights into the quantitative contributions of non-radical active species to pollutant degradation.

Hydroxylamine hydrochloride-driven activation of NiFe2O4 for the degradation of phenol via peroxymonosulfate

In this study, hydroxylamine hydrochloride (HA) was employed to enhance the activation of NiFe2O4 towards peroxymonosulfate (PMS) for the effective degradation of phenol. NiFe2O4 particles were synthesized via a simple hydrothermal method, followed by characterization of their surface morphology, and microstructure. Upon the addition of HA to the system of NiFe2O4/PMS, the degradation activity is significantly enhanced. The degradation efficiency of phenol reached 98.5% after 60 min using 0.6 g/L NiFe2O4, 3 mmol/L PMS, 2 mmol/L HA at pH 7, which increased by 4.76 times compared to the system without HA. The study further explored the activation mechanism of the NiFe2O4/HA/PMS system, revealing that HA significantly enhanced the conversion of Fe3+/Fe2+ and the leaching of metal ions, thereby accelerating the reaction rate. In addition, the NiFe2O4/HA/PMS system proved effective across a broad range of pH values. This study provides new insights and perspectives into enhancing peroxymonosulfate activation coupled with metal oxides catalysts through the use of reducing agents.

Selective oxidation of organic pollutants by unactivated and carbonate-activated peroxymonosulfate (PMS): Mechanism, kinetics, and transformation pathway

Although the activation mechanisms of peroxymonosulfate (PMS) by various homogeneous and heterogeneous catalysts have been reported, the chemistry of PMS in catalyst-free systems and its interaction with background oxygenated anions remains poorly understood. In this study, the unactivated PMS and carbonate-activated PMS (CO32–/PMS) systems for removal of various organic pollutant (including oxytetracycline (OTC), metronidazole (MNZ), methylene blue (MB), and acid orange G (OG)) were investigated. The results showed that 74.5 %, 90.21 %, 1.22 %, and 2.25 % of OTC, MB, OG, and MNZ were removed, respectively within 180 min in the unactivated PMS system due to the formation of ·OH and 1O2. 95.88 %, 100 %, 100 %, and 6.09 % of OTC, MB, OG, and MNZ were removed, respectively in the CO32–/PMS system, which is primary due to the generation of 1O2. The removal efficiencies of these four pollutants were significantly improved under alkaline conditions. In addition, the TOC removal rates were 21.88 % for MB and 26.53 % for OTC within 180 min in the CO32–/PMS system. The presence of Cl− and SO42− can greatly enhance the OTC removal efficiency both in the unactivated and CO32–/PMS systems. Through the high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, OTC degradation products in the unactivated PMS and CO32–/PMS systems were identified, revealing six different reaction mechanisms, including hydroxylation (+16 Da), decarbonylation (−28 Da), demethylation (−14 Da), secondary alcohol oxidation (−2 Da), deamination (−15 Da), and dehydration (−18 Da). This study provides insight into the reaction mechanism of catalyst-free PMS systems and may promote the application of unactivated PMS and CO32–/PMS systems for the remediation of organic contaminated water.