Activated Peroxymonosulfate System Research Articles

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.

Peroxymonosulfate promoted dioxygen activation with Mn(II)-nitrilotriacetic acid complexes for sulfadiazine degradation

In the field of peroxymonosulfate (PMS) activation technology, there is a pressing need to reduce PMS consumption and enhance its utilization rate. The present study demonstrates that the introduction of dissolved oxygen (DO) into the Mn(II)-nitrilotriacetic acid (NTA)-activated PMS system significantly enhances the degradation efficiency of sulfadiazine and increases the PMS utilization rate from approximately 15.0 to 41.3 %. Mechanistic analysis reveals that the Mn(II)-NTA/PMS system generates sulfate radicals as well as intermediate valent manganese species in the absence of DO; while in the presence of DO, Mn(II) is oxidized to Mn(III) by dioxygen to form superoxide anions and Mn(III), which can be further oxidized by PMS to higher valence states such as Mn(V) and Mn(VII). Consequently, the production of free radicals decreases while intermediate valent manganese species become more abundant. Additionally, O2•− can also reduce both Mn(VII) and Mn(IV) back to their lower oxidation state (Mn(II)). The cooperative interactions between these active species enhance the efficiency of catalytic cycles of manganese species. Moreover, the influence of multiple factors, the degradation products, and their associated toxicity assessment were investigated. Overall, this research provides valuable insights into the design of highly efficient PMS and DO activation systems.

Efficient degradation of tetracycline by cobalt ferrite modified alkaline solution nanofibrous Ti3C2Tx MXene activated peroxymonosulfate system: Mechanism analysis and pathway

Magnetic CoFe2O4 nanoparticles have received considerable attention as an activator for peroxymonosulfate (PMS) in the degradation of tetracycline. However, it is still challenging to construct CoFe2O4 composites with good dispersion and highly exposed reactive sites. Herein, the KOH fiber-functionalized MXene matrix decorated by cobalt ferrite nanoparticles (denoted as CoFe2O4@Alk-MXene) was developed by electrostatic self-assembly method. The layered fibrotic structure effectively disperses and fixes cobalt ferrite nanoparticles, increasing the exposure of reactive sites. The as-prepared CoFe2O4@Alk-MXene material exhibited rapid removal of 100% tetracycline hydrochloride (TC-HCl) within 10 minutes by activating PMS, leveraging the excellent conductivity of alkalized MXene and the efficient activation of transition metal atoms. The experimental and theoretical analysis revealed that the electron transfer process of Ti2+/Ti4+, Co2+/Co3+ and Fe3+/Fe2+, as well as the free radical and non-free radical attack behaviors produced by the adsorption of PMS by the composite, are the primary mechanisms for achieving rapid removal of pollutants. A comprehensive degradation mechanism and potential pathways were proposed based on these findings. Overall, CoFe2O4@Alk-MXene/PMS emerges as a promising catalytic system for TC removal.

Protocatechuic acid enhanced Fe(III) activated peroxymonosulfate system for Sulfamethoxazole degradation in groundwater

The advanced oxidation process based on Fe(Ⅱ) activated is easy to produce Fe(Ⅲ) accumulation, and the slow process of Fe(III)/Fe(II) conversion greatly hinders pollutant degradation performance of Fe(III)/peroxymonosulfate (PMS) system. Herein, protocatechuic acid (PCA)-regulated Fe(III)-activated PMS system was proposed for remediation of SMX-contaminated groundwater. The results presented the highest degradation efficiency (97.2 %) at room temperature and neutral pH with appropriate PCA-Fe(III) ratio (1:3) and PS concentration (1 mM), which was 89.5 % higher than that of the system without PCA, and over 60 % higher than that of other acid-regulated systems. The excellent degradation performance was principally owing to the reduction and chelation of PCA, which expedited the circulation of Fe(III)/Fe(II) via generating PCA-Fe chelate and benzoquinone, thus promoting the PMS activation. Moreover, SO4•−, O•H, O2•−, and 1O2 worked together to contribute to SMX decomposition, and 1O2 played a dominant role. In addition, the system had strong tolerance to co-existing ions (e.g., CO32−, Cl−, and NO3−) and humic acid in groundwater, Cl-, NO3− and HA had no significant effect on SMX degradation, and although CO32− reduced the degradation efficiency of SMX, more than 80 % of SMX was removed after reaction. And the system possessed universal applicability to real water bodies and different pollutants. Overall, the PCA/Fe(III)/PMS system presented preeminent application potential for the remediation of organics-polluted groundwater.

Effect of the Fe0/PMS advanced oxidation system on the removal of aromatic organic compounds

The aromatic organic compounds present in groundwater environments have low contents, high toxicity, long half-lives and stable chemical properties, which increase the difficulty of degradation under natural conditions. In this study, an zero-valent iron activated peroxymonosulfate system (Fe0/PMS) was constructed to remove common aromatic organic compounds in groundwater. The results showed that at an initial pH of 7.0, Fe0=0.3 g/L, PMS= 0.5 mM, and initial concentration of organic matter (C0) =0.1 mM, the removal efficiency of the seven aromatic organic compounds by the Fe0/PMS system reached more than 70 %, which shows good removal ability. Alcohol quenching tests and liquid chromatography time-of-flight mass spectrometry tests showed that the main active oxygen species in the system were SO4•─ and OH•, which could efficiently degrade aromatic organic compounds through electrophilic substitution, hydroxylation, carbonylation and decarboxylation reactions and reduce the biological toxicity of organic compounds in wastewater to a certain extent. In the long-term dynamic reaction process, the removal rate of aromatic organic compounds in actual groundwater by the Fe0/PMS system can be maintained above 75 %, and the complex structure can be effectively destroyed. This research can provide a theoretical basis for the efficient treatment of aromatic organic compounds in groundwater.

Ranitidine degradation in layered double hydroxide activated peroxymonosulfate system: impact of transition metal composition and reaction mechanisms.

Ranitidine, a competitive inhibitor of histamine H2 receptors, has been identified as an emerging micropollutant in water and wastewater, raising concerns about its potential impact on the environment and human health. This study aims to address this issue by developing an effective removal strategy using two types of layered double hydroxide (LDH) catalysts (i.e., CoFeLDH and CoCuLDH). Characterization results show that CoFeLDH catalyst has superior catalytic properties due to its stronger chemical bond compared to CoCuLDH. The degradation experiment shows that 100% degradation of ranitidine could be achieved within 20min using 25mg/L of CoFeLDH and 20mg/L of peroxymonosulfate (PMS). On the other hand, CoCuLDH was less effective, achieving only 70% degradation after 60min at a similar dosage. The degradation rate constant of CoFeLDH was 10 times higher than the rate constant of CoCuLDH at different pH range. Positive zeta potential of CoFeLDH made it superior over CoCuLDH regarding catalytic oxidation of PMS. The catalytic degradation mechanism shows that sulfate radicals played a more dominant role than hydroxyl radicals in the case of LDH catalysts. Also, CoFeLDH demonstrated a stronger radical pathway than CoCuLDH. XPS analysis of CoFeLDH revealed the cation percentages at different phases and proved the claim of being reusable even after 8 cycles. Overall, the findings suggest that CoFeLDH/PMS system proves to be a suitable choice for attaining high degradation efficiency and good stability in the remediation of ranitidine in wastewater.

Porous-carbon/manganese composite catalyst transformed from waste biomass as peroxymonosulfate activator for carbamazepine degradation

Activation of peroxymonosulfate (PMS) with solid catalysts for organic pharmaceutical degradation still faces challenge due to the demand of inexpensive catalysts. In this study, manganese-oxidizing microalgae (MOM) and its associated biogenic manganese oxides (BMO) were employed to prepare biomass-transformed porous-carbon/manganese (B-PC/Mn) catalyst through high-temperature calcination (850 °C). Remarkably, 100 % of carbamazepine (CBZ) was degraded within 30 min in the B-PC/Mn/PMS system. The degradation kinetic constant was 0.1718 min−1, which was 44.0 times higher than that of the biomass-transformed porous carbon mixed with MnOx activated PMS system. 1O2 was generated in the B-PC/Mn/PMS system, which is responsible for CBZ degradation. The MOM-BMO-associated structure greatly increased the specific surface areas and the contents of the C = O and pyrrolic-N groups, which facilitated PMS activation. The structure also induced the generation of Mn5C2, which exhibited a strong adsorption towards PMS. This study provides a novel strategy for preparing catalysts by using waste biomass.

Waste self-heating bag derived CoFe2O4 composite enhances peroxymonosulfate activation: Performance, mechanism, and adaptability under high-salinity conditions

In order to achieve the environmental goal of waste treatment by waste, waste self-heating bags, a common household waste rich in iron oxide, activated carbon, and vermiculite, were reutilized as the raw material for the one-pot fabrication of a CoFe2O4 composite (CoFe2O4-CV). The performance, mechanism, and application potential of CoFe2O4-CV for high-salinity wastewater remediation were investigated. The results indicated that the presence of activated carbon and vermiculite promoted the dispersion of CoFe2O4 nanoparticles, which enhanced the catalytic performance of peroxymonosulfate (PMS) activation for Rhodamine B (RhB) degradation. At a concentration of 0.1 g/L CoFe2O4-CV and 0.5 mmol/L PMS, > 99% of RhB was eliminated within 15 min. CoFe2O4-CV also exhibited splendid recyclability due to its strong magnetism and stability. Quenching experiments and spectroscopic studies showed that dissolved free sulfate radicals (SO4•-), surface-bound SO4•- (≡SO4•-), singlet oxygen (1O2), and high-valence metal-oxo species (≡Co(IV)=O/≡Fe(IV)=O) jointly contributed to RhB degradation. Non-radical pathways involving ≡SO4•-, 1O2, and ≡Co(IV)=O/≡Fe(IV)=O also played a crucial role. Moreover, ion competition experiments indicated that the CoFe2O4-CV activated PMS system showed anti-interference ability towards humic acid and high-concentration anions. Thus, the CoFe2O4-CV/PMS system achieved the effective removal of RhB and other dye contaminants under high-salinity conditions. This work demonstrates the practical possibility of waste reutilization treating high-salinity wastewater based on an advanced oxidation process.

Novel calcium oxide activated peroxymonosulfate system for methylene blue removal: Identification of key influencing factors, transformation pathway and toxicity assessment

The activation of peroxymonosulfate (PMS) has gained significant interest in the removal of organic pollutants. However, traditional methods usually suffer from drawbacks such as secondary contamination and high energy requirements. In this study, we propose a green and cost-effective approach utilizing calcium oxide (CaO) to activate PMS, aiming to construct a simple and reliable PMS based advanced oxidation processes (AOPs). The proposed CaO/PMS system achieved fast degradation of methylene blue (MB), where the degradation rate of CaO/PMS system (0.24 min−1) was nearly 2.67 times that of PMS alone (0.09 min−1). Under the optimized condition, CaO/PMS system exhibited remarkable durability against pH changes, co-exists ions or organic matters. Furthermore, singlet oxygen (1O2) was identified as the dominant reactive oxygen species by electron paramagnetic resonance (EPR) and quenching tests. Accordingly, the degradation pathways of MB are proposed by combing the results of LC/MS analysis and density functional theory (DFT) calculations, and the predicted ecotoxicity of the generated byproducts evaluated by EOCSAR could provide systematic insights into the fates and environmental risks of MB. Overall, the study provides an eco-friendly and effective strategy for treating dyeing wastewater, which should shed light on the application of PMS based AOPs.

Synergistic effect of iron and nitrogen on porous carbon to improve electron transfer efficiency resulting in the enhancement of tetracycline hydrochloride removal

Developing transition metal/nitrogen carbon catalysts for efficient pollutant removal presented an attractive option for water environment remediation. In this work, the iron (Fe), nitrogen (N) co-doped porous carbon nanoparticles (FeN/C) were prepared for heterogeneous activation of peroxymonosulfate and efficient oxidation of tetracycline hydrochloride (TC). Fe nanoparticles were encapsulated in the carbon to reduce the loss of Fe during the catalysis processes. As a catalyst, the sample of 20FeN/C exhibited an excellent catalytic activity of tetracycline hydrochloride with a removal rate of 91.2 % and a rate constant of 0.6653 min−1 in peroxymonosulfate (PMS) system. And the prepared catalysts presented the strong adaptability, which was worked efficient in a wide range pH and some anions solution. The high efficiency could attribute to the interaction of Fe and N, which effectively improved the electron transfer efficiency in this 20FeN/C activated PMS system. Combining with the results of electron paramagnetic resonance (EPR), in-situ Raman spectra, and X-ray photoelectron spectroscopy (XPS), electrons transfer was confirmed as a dominating non-radical process of TC degradation. It was confirmed that the doping of iron and nitrogen could collectively promote the electron transfer between material and PMS, and the activated PMS* reacted with TC via electron-rich nitrogen active sites of the material surface, then the TC degradation was enhanced. The received finding is of great significance to supplement the mechanism of electron transfer and provides a new idea on the synthesis of iron/nitrogen co-doped carbon catalysts to achieve high efficiency of TC removal.

Highly efficient activation of peroxymonosulfate by cobalt ferrite anchored in P-doped activated carbon for degradation of 2,4-D: Adsorption and electron transfer mechanism

The dispersing effect of carbon materials on nanoparticles can enhance the full exposure of their active sites. Herein, phosphorus (P)-doped activated carbon-supported trace cobalt ferrite composites (P-CoFe@BCX) were achieved by two-step pyrolysis for efficient peroxymonosulfate (PMS) activation and water pollution remediation. The removal efficiency of 2,4-dichlorophenoxyacetic acid (2,4-D) was optimized by adjusting the coupling ratio of carbon substrate and cobalt ferrite. P-CoFe@BC5/PMS oxidation system (0.10 g L-1, 0.50 mM) eliminated 98.3% of 2,4-D (20.0 mg L-1) within 60 min at unadjusted pH. The constructed adsorption enrichment and oxidative degradation pathways are highly efficient in utilizing reactive oxygen species (ROS), and the dual tracks of free and non-free radicals achieve the rapid degradation of 2,4-D. P-doped activated carbon acts as an electron shuttle to accelerate electron transfer between active sites and enhances the adsorption efficiency of 2,4-D and PMS onto the composites. In addition, the P-CoFe@BC5/PMS oxidation system still exhibited strong 2,4-D removal performance at a wide pH range of 2.0–10.0. The inhibitory effect of environmental components was related to their concentration, such as chloride, bicarbonate, sulfate and humic acid. Density functional theory calculations show that ROS tends to attack the CO bond on the 2,4-D branch chain, and the degradation products show lower biological toxicity. Hence, the constructed cobalt ferrite anchored P-doped activated carbon activated PMS system has great potential in treating organic wastewater.

The efficient degradation of paracetamol using covalent triazine framework-derived Fe-N-C activated peroxymonosulfate via a non-radical pathway: Analysis of high-valent iron oxide, singlet oxygen and electron transfer

The abundant and environmentally friendly metal iron (Fe) is an excellent candidate to activate peroxymonosulfate (PMS) for the oxidative decomposition of organic pollutants. However, Fe-based activators have disadvantages of high efficiency only in a narrow pH range and easily generated Fe-sludge. Therefore, developing wide pH range efficient and stable Fe-based PS activators is needed. In this study, iron–nitrogen-carbon (Fe-N-C) activators were prepared using covalent organic frameworks containing homogeneous micropores and high porosity as a precursor. The Fe-Nx-rich activator showed an outstanding activity and a high stability in the heterogeneously activated PMS system. It found that the 10 mg/L paracetamol (PCT) could be degraded completely within 5 min when adding 30 mg/L activator and 3 mM PMS. Furthermore, the system shows good performance in an extensive buffer pH range (2.6–10.67). The quenching experiments and intermediate product tests supported that the high-valent iron-oxo species is the major reactive oxygen species (ROS) in this system, and the designed experiments confirmed that Fe-N as the active site that in charge of activating PMS. This work provides insights for improving the activation efficiency and expanding the pH working range of iron-based catalysts in the field of advanced persulfate oxidation.

Electro-activation of peroxymonosulfate by β-PbO2 partial filling/covering TiO2 nanotube arrays anode for alkaloid berberine degradation: Performance, mechanism and practicability

An interlocking “T-shape” structure was built by uniform filling β-PbO2 crystalline inside the trace Ti3+ self-doping TiO2 nanotube arrays (TNAs) channels and depositing the cauliflower-like β-PbO2 clusters on its upper surface through a facile current pulse deposition method. We elaborated the interfacial engineering strategy for generating compact oxide layers at TNAs bottoms and growing β-PbO2 crystalline from the selectively conductive TNAs bottoms. Different characterization techniques and electrochemical analyses were conducted to characterize the morphology, structure, and electrochemical property of the β-PbO2 partial filling/covering TNAs (β-PbO2/TNAs/Ti) materials. We also systematically investigated and elucidated the performance and mechanism of β-PbO2/TNAs/Ti anode activated peroxymonosulfate (PMS) system via berberine removal/mineralization, reactive oxygen species (ROS) identification/contribution, intermediates analysis, energy consumption and practical applicability estimation. Results illustrated that filling β-PbO2 inside TNAs can efficiently improve the directional electron-transfer efficiency, oxygen evolution over-potential, tolerance to the varied water matrices and service lifetime of β-PbO2/TNAs/Ti anode activated PMS system. The ROS including •OH, SO4∙- and 1O2 that generated from PMS electro-activation are responsible for efficient berberine degradation through two pathways. This study will provide a general approach to construct the versatile tube-filled TNAs-based materials for wide applications in water/wastewater treatment.

Adjusting radical/non-radical species ratio in MnO2/CoFe2O4 activated peroxymonosulfate system through changing inner-outer positioning for enhanced endocrine disrupting chemicals degradation: A comparative study

Herein, binary composite catalysts based on MnO2 and CoFe2O4 were prepared to degrade bisphenol A (BPA) and dimethyl phthalate (DMP) by coupling with peroxymonosulfate (PMS), in which CoFe2O4 was located either at the outer (MnO2@CoFe2O4) or at the inner (CoFe2O4@MnO2) positioning. The catalysts possessed higher degradation efficiency than both pristine CoFe2O4 and MnO2, in which MnO2@CoFe2O4 provided the highest PMS activation capability. The positioning of each component influenced significantly the variety and intensity of the generated reactive oxidative species, in which MnO2@CoFe2O4 generated more hydroxyl radical (OH) whereas CoFe2O4@MnO2 generated more non-radical singlet oxygen (1O2). Therefore, MnO2@CoFe2O4 could degrade both BPA and DMP with high degradation rate, while CoFe2O4@MnO2 only exhibited promising degradation efficiency towards BPA since DMP was inert to 1O2. Comparatively, CoFe2O4@MnO2 had better catalytic stability and water matrix adaptability than MnO2@CoFe2O4 when degrading BPA, since OH was vulnerable water with complicated compositions. This study provides a new insight for the design and selection of composite catalyst towards the degradation of organic pollutants with discrepant structures and properties.

The overlooked role of Co(OH)2 in Co3O4 activated PMS system: Suppression of Co2+ leaching and enhanced degradation performance of antibiotics with rGO

Cobalt oxide (Co3O4) activated peroxymonosulfate (PMS) system was extensively studied due to its excellent catalytic performance. However, the relatively high cobalt (Co2+) leaching (up to 2 mg/L) would pose high ecotoxicological risks. Herein, we identified the existence of Co(OH)2 on the surface of Co3O4 were the major source of Co2+ leaching in the Co3O4 activated PMS system. Furthermore, the Co2+ leaching was effectively suppressed by converting Co(OH)2 to Co3O4 via pyrolysis treatment. In addition, reduced graphene oxide (rGO) was engaged to enhance the degradation performance of antibiotics in the Co3O4 activated PMS system. The oxygen functionalities of rGO would catalyze PMS to generate sulfate radicals (SO4−) and trigger the non-radical pathway of singlet oxygen (1O2). We have achieved outstanding catalytic performance for carbamazepine (CAZ) degradation with low Co2+ leaching, as CAZ (5 mg/L) could be completely degraded in 30 min. Combining experimental investigation and theoretical calculation, we also revealed the degradation pathways and mechanisms that CAZ would be oxidized and detoxified by 1O2 and SO4−. We have provided a simple approach to inhibit the Co2+ leaching and enhance the catalytic performance of Co3O4 activated PMS system for the effective control of antibiotics.

Accelerated Removal of Acid Orange 7 by Natural Iron Ore Activated Peroxymonosulfate System with Hydroxylamine for Promoting Fe(III)/Fe(II) Cycle

In this study, peroxymonosulfate (PMS) was activated by cheap and readily available natural iron ore to remove Acid Orange 7 (AO7) in water with the assistance of hydroxylamine (HA). Results show that the presence of HA could accelerate the Fe(II)/Fe(III) cycle on the ore surface, promoting the activation of PMS to generate reactive oxidative species. The effects of ore dosage, PMS dosage, HA dosage and initial pH on the degradation of AO7 were investigated in the HA/Ore/PMS system. Under the optimal conditions, the removal of AO7 could reach 93.1% during 30 min, which was 41.4% higher than the ore/PMS system. The AO7 removal increased with the increase of HA, PMS and ore dosage, but was unaffected by the initial solution pH. Based on radical scavenging experiments and EPR tests, the dominant reactive species in the HA/Ore/PMS system were revealed to be the sulfate radical (SO4•−), singlet oxygen (1O2), superoxide radical (O2•−) and hydroxyl radical (•OH), which were responsible for the AO7 degradation. Furthermore, the possible reaction mechanism of PMS activation was proposed. This study provides an efficient technique for the removal of azo dye organic contaminant in water, which has great practical significance.

Magnetic spent coffee biochar (Fe-BC) activated peroxymonosulfate system for humic acid removal from water and membrane fouling mitigation

Applying membrane technology to water purification has been done for several decades now and is widespread. However, membrane fouling is a serious problem and continues to limit the success of membrane processes. In this study, magnetic biochar (Fe-BC) was prepared using easily available spent coffee grounds to activate peroxymonosulfate (PMS) as a UF membrane pretreatment strategy. Results showed that the average removal rates of humic acid (HA, 10 mg/L) were 55.23 % and 73.55 %, at the Fe-BC dosage of 300 mg/L and PMS dosage of 300 mg/L and 900 mg/L, respectively. The Fe-BC/PMS pretreatment significantly reduced the total (44 %) and reversible (61 %) UF membrane fouling after five filtration cycles at a relatively high flux of 200 L/m2·h, and the Fe-BC and PMS dosage of 100 mg/L. Modeling fit results indicated that pretreatment shifted complete blocking to standard blocking. Therefore, stopping HA-induced membrane fouling could be possible if the load is reduced and complete blocking alleviated.

N-doped carbon supported cobalt electrospun nanofibers activated peroxymonosulfate system for benzothiazole degradation: Multifunctional role of nitrogen species

Nitrogen doping is an effective way to enhance the activation performance in peroxymonosulfate (PMS) heterogeneous catalysis. However, the unique role of different nitrogen species was still controversial. Herein, N-doped carbon supported cobalt catalyst was synthesized by electrostatic spinning method and employed to activated PMS. Firstly, various nitrogen species in catalyst including graphitic N, pyridinic N, pyrrolic N and Co-Nx was identified. Subsequently, the specific role of various nitrogen species was revealed by a series of experiments (adsorption experiments, degradation experiments, quenching tests, characterization analysis.), that is: (1) graphitic N changes the electrical of surrounding C atoms for PMS adsorption; (2) pyrrolic N with special pentacyclic structure leaded to obvious defects in carbon structure, thus enhancing the PMS activation ability of carbon materials; (3) pyridinic N bind with metal Co to form Co-Nx, which acted as an efficient active site for PMS activation. In addition, the effects of pH, temperature, and coexisting ions were also studied. This study revealed the activation behavior of different N species on N-doped carbon supported transition metal base catalysts, which provides theoretical basis for further synthesis of N-containing catalysts with high activation efficiency and release the activation potential of N species.

Multiwall carbon nanotube decorated hemin/Mn-MOF towards BPA degradation through PMS activation

Heterogeneous catalysis of organic contaminants in water has been a research concern. In this study, Fe-Mn bimetallic MOF was prepared with low concentration of hemin (0.18 mmol) as Fe source. Meanwhile, multiwall carbon nano tube (CNT) was further decorated on it. Finally, CNT-hemin/Mn-MOF with high peroxymonosulfate (PMS) catalytic effect was successfully synthesized. CNT-hemin/Mn-MOFs could catalytic PMS to degrade BPA within 30 min. This excellent catalytic effect was attributed to the reinforced redox reaction between Mn and the Fe of hemin, which would transfer more electrons. Furthermore, CNT and the N elements of hemin could promote electron transfer in this process. In addition, the degradation mechanism of BPA by CNT-hemin/Mn-MOF activated PMS system was also proposed. Results manifested that the non-free radical degradation pathway initiated by 1O2 and the free radical degradation pathway dominated by·OH were the main reasons for BPA degradation. Besides, a small amount of·SO4−,·O2- and direct electron transfer participated degradation. Two BPA degradation pathways have also been deduced. This work may broaden the horizons for the development of MOFs synthesis for the degradation of environmental pollutants.

Breaking rate-limiting steps in a red mud-sewage sludge carbon catalyst activated peroxymonosulfate system: Effect of pyrolysis temperature

The active sites on biochar surface could be increased via pyrolysis of sewage sludge (SS) with mixing red mud (RM), improving its catalytic activity effectively. Pyrolysis temperature plays an important role in the regulation of active sites on the catalyst surface. Herein, the RM-SS carbon-based catalysts (RSDBC) were prepared under different pyrolysis temperatures to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. It was found that the rate-limiting step (first oxidation stage) of the RSDBC-500/PMS system could be broken by increasing the pyrolysis temperature from 500 °C to 700 °C, leading to a 1.9-fold increase in SMX degradation efficiency within 120 min. Furthermore, the specific surface area (SSA) and the content of CO, defects, Fe(II), pyridinic N, and graphite N sites of RSDBC increased during the elevation of temperature (500-700 °C), thereby facilitating PMS activation and active species production. The breakage of the rate-limiting step provided the theoretical basis for the optimal preparation of sludge biochar-based catalysts, which is beneficial to promote the application of RSDBC/PMS system in wastewater treatment.