Peroxymonosulfate System Research Articles

Significant enhancement on ammonia removal by thermal/peroxymonosulfate system with bromide ion: Performance, influencing factors and mechanism

Although thermal-activated peroxymonosulfate (PMS) system possesses good performance on the removal of organic pollutants, thermal/PMS system exhibited poor capacity to remove ammonia nitrogen (NH4+-N). This study demonstrated the huge enhancement on the removal of NH4+-N by thermal/PMS system with the commonly coexistent bromide ion (Br-). The elimination of NH4+-N by thermal/PMS/Br- system fitted the pseudo-zero-order kinetics model well, while the corresponding kobs in the presence of 200 μM Br- was 5.76 times greater than that by thermal/PMS system. Bromine (HBrO) was confirmed as the dominant oxidant responsible for removing NH4+-N and TN, while the radicals of HO⋅, SO4⋅- and Br⋅ were also generated but made minor contribution to removing NH4+-N. HBrO was mostly produced by PMS reacting directly with Br-, while these radicals were produced from the cleavage of the O-O bond in PMS and the reaction between PMS and HBrO under high temperature. Thermal/PMS/Br- system exhibited superior performance on TN removal (up to 90 %) than that by thermal/PMS system (less than 5 %) and Cl--enhanced system (about 80 %). The main removal product of NH4+-N was identified as the environmentally friendly gas of N2, although nitrate was also detected. Neutral pH condition was the optical pH for NH4+-N removal. Increasing reaction temperature, PMS dosage and Br- concentration were beneficial to accelerating the removal of NH4+-N. Cations of Cu2+ and Fe3+, anions of SO42-, CO32- and NO3-, humic acid and the actual water matrix of landfill leachate negligibly influenced the removal of NH4+-N, while Cl- exhibited strong enhancement on NH4+-N removal. In summary, this study provided an effective method to improve the oxidizing capacity of thermal/PMS system, especially for NH4+-N removal in wastewater containing Br-.

Accelerated peroxymonosulfate activation over defective perovskite with anchored cobalt nanoparticles for organic contaminant removal

In this study, a novel perovskite oxide (Co@D-PBSC) for activation peroxymonosulfate (PMS) to degrade organic pollutants in wastewater was developed. Cobalt nanoparticles (Co NPs) and oxygen vacancies (OVs) were introduced to the perovskite oxide lattice via a non-stoichiometric ratio and separate-out strategy. The OVs and Co NPs provided abundant active sites for the activation of PMS and the generation of reactive oxygen species. The Co metal-OVs bridge promote the adsorption of PMS, meanwhile, Co nanoparticles accelerate the Co2+/Co3+ redox cycle, resulting in the production of the main reactive substance, sulfate radicals (SO4•−). The results of catalytic experiments showed that 85 % of ofloxacin (OFX) degradation efficiency was obtained within 1 min at 0.1 g/L Co@D-PBSC, 0.3 g/L PMS, 20 mg/L OFX (150 mL), and solution pH 7.0, which indicated that Co@D-PBSC/PMS system exhibits excellent performance. This work demonstrated an efficient perovskite catalyst for PMS activation in wastewater treatment and provided a useful catalyst design strategy for the advanced oxidation processes (AOPs).

Efficient degradation of levofloxacin using peroxymonosulfate activated by a novel magnetic catalyst derived from waste walnut shell biomass

Developing an economical and efficient catalyst derived from biochar and metal-organic frameworks (MOFs) for the activation of peroxymonosulfate (PMS) to degrade pollutants holds promise for practical applications. Herein, a simple in-situ synthesis method was designed to generate zeolitic imidazole framework with Co-based (ZIF-67) on the surface of waste walnut shell biomass, and novel derived magnetic catalysts (BC@CobC, Biochar@Co base Carbon) were obtained by high-temperature carbonization. This structure could avoid the drawbacks of structural collapse and particle agglomeration of MOF derivatives, while the presence of biochar could accelerate electron transfer and improve the activation performance. For the degradation of levofloxacin, the removal rate in the 0.5-BC@CobC/PMS system reached 89.88 % in 15 min with a mineralization of 60.43 % when the dosage of catalyst was 0.01 g L−1. Capture experiments and EPR tests showed that SO4−•, •OH, •O2− and 1O2 were jointly participated in the levofloxacin degradation process. Meanwhile, the BC@CobC/PMS system was minimally affected by the pH, co-existing inorganic anions, and natural active substances. It is worth noting that the BC@CobC/PMS system also had excellent removal effect on other typical organic pollutants, and the removal rate could reach 100 %. Cycling experiments showed that BC@CobC maintained high catalytic activity after multiple recycling. The degradation pathway of levofloxacin was also analyzed. Compared to the existing reports, the catalyst is economically superior, with much improved pollutant removal, and boasts a lower catalyst usage. This work will provide a viable idea in terms of reusing biomass waste and activating PMS for wastewater treatment.

A novel cobalt-iron bimetallic hydrochar for the degradation of triclosan in the aqueous solution: performance, reusability, and synergistic degradation mechanism

Low activation performance is a critical issue limiting the practical application of low-cost biochar in the advanced oxidation. Given the high potential of transition metals in the persulfate activation process and abundant oxygen-containing groups of hydrochar, hydrochar derived from cobalt (Co)-modified iron (Fe)-enriched sludge was synthesized and its performance and activation mechanism for the degradation of triclosan were investigated. Co modification significantly altered the morphology of hydrochar, and the increased Co–Fe mass ratios transformed hydrochar from granular to rose-shaped lamellar and then to helical sheet structures. Specific surface area, defect degree, and oxygen-containing groups of hydrochar increased with increasing cobalt-iron mass ratios. The highest removal of triclosan was up to 98% in the hydrochar/peroxymonosulfate (PMS) system under a wide range of pHs (3–10) and still remained higher than 90% after four cycles. Both Radical (mainly hydroxyl radical) and nonradical pathways (singlet oxygen and electron transfer) were evidenced to play roles in the triclosan removal. Fe3+ promoted the regeneration of Co2+ and realized the efficient circulation of Co3+/Co2+. A ternary system consisting of electron donor (triclosan)-electron mediator (hydrochar)-electron acceptor (PMS) provided channels for electron transfer. No measurable Co and Fe were released during the reaction, and the toxicity of degradation intermediates was lower than that of triclosan. Beside triclosan, rhodamine B, bisphenol A, sulfamethoxazole, and phenol were also almost degraded completely in this oxidation system. This study provides a promising way for the enhancement of catalytic activity of carbonaceous material.

One-step rapid removal of Cu(II) complexes via dual-active-site MOF catalysis with Peroxymonosulfate: Cooperative oxidation and adsorption

The removal of heavy metal complexes (HMCs) from wastewater is challenging due to their structural stability. Traditional methods require advanced oxidation processes (AOPs) for decomplexation, followed by chemical precipitation or adsorption. This study proposes a one-step approach using Co-imidazolate zeolitic framework-67 (ZIF-67) for simultaneous oxidation-decomplexation and in-situ adsorption of HMCs. The ZIF-67/peroxymonosulfate (PMS) system achieves 97.8 % removal of Cu(II)-citric acid complex (Cu-CA) in 60 mins, even under alkaline conditions, and demonstrates strong selectivity against ions like Ca, Mg, Na, and humic acid (HA). It effectively treats various contaminated water sources, achieving over 90 % removal efficiency for Cu(II) complexes such as oxalic acid (OA) and ethylenediaminetetraacetic acid (EDTA). The mechanism involves sulfate radicals (SO4•−) and singlet oxygen (1O2) for decomplexation, followed by amine groups in MOFs capturing Cu(II) ions through coordination interactions. This work offers a straightforward one-step method for HMCs contamination mitigation.

A metal-free Z-scheme PPy/MCN heterojunction for antibiotic removal via synergism of photocatalysis and peroxymonosulfate activation

Developing an active and synergistic system based on photocatalysis and peroxymonosulfate (PMS) activation is considered an effective strategy for efficient removal of antibiotics. However, photocatalytic heterojunctions generally comprise metallic catalysts that can cause metal leaching and secondary pollution, and a clear understanding of the synergy between photocatalysis and PMS activation is still missing. Herein, a metal-free Z-scheme polypyrrole (PPy)/melamine-derived graphitic carbon nitride (MCN) heterojunction photocatalyst was synthesized via calcination and in-situ loading for catalyzing the degradation of ciprofloxacin (CIP) and other emerging pollutants in a visible light-emitting diode (LED)/PMS synergistic system, which showed a significantly higher activity than the single LED and PMS systems. The optimal 0.5 %PPy/MCN (0.5 % is the mass ratio of PPy in the mixture of PPy/MCN) performed well under a wide pH range (3–11), while exhibiting superior anti-interference for common water constituents and outstanding reusability and stability. The 0.5 %PPy/MCN/LED/PMS synergistic system showed the highest kinetic constant (0.0643 1/min), which increased 3.00, 6.77 and 2.91-fold over the 0.5 %PPy/MCN/PMS, 0.5 %PPy/MCN/LED, and MCN/LED/PMS system, respectively. Mechanistic investigation and theoretical calculations revealed that PPy, with its high conductivity and strong light absorption ability, facilitated the generation and separation of e−/h+ in the 0.5 %PPy/MCN/LED/PMS system and activated PMS for generating reactive species such as 1O2, which degraded cCIP together with h+. Furthermore, electron transfer pathway (ETP) was elucidated using electrochemical characterizations. CIP was degraded via ring opening, cleavage hydroxylation, ammonia oxidation and elimination reactions, which substantially reduced the toxicity of CIP. Overall, this study may help the rational design of metal-free catalysts and provide a deep insight for the LED/PMS synergistic mechanisms.

Carboxymethyl chitosan modification of cobalt-zinc bimetallic MOF for tetracycline hydrochloride removal: Exploration of the enhancement mechanism of the process

This study synthesized a carboxymethyl chitosan-modified bimetallic Co/Zn-ZIF (CZ@CMC) with strong hydrophilicity and adsorption performance via the one-pot method. Tetracycline hydrochloride (TCH) was used as the model contaminant to evaluate the adsorption and peroxymonosulfate (PMS) activation properties of CZ@CMC. Mechanism showed that the adsorption behavior occurred through pore filling, electrostatic attraction, surface complexation, hydrogen bonding, and π-π stacking. In addition, a CZ@CMC/PMS system was constructed, which had excellent catalytic performance. The hydrophilicity and selective adsorption properties of CMC conferred a greatly accelerated CZ@CMC in catalyzing the PMS process with kobs of 0.095 min−1, in which OH, 1O2, SO4–, O2–, and Co(III) were the main ROS which quenching tests, EPR, and chemical probe experiments verified. In addition, the degradation pathways of TCH were obtained utilizing DFT and HPLC-MS and analyzed to show that the system possessed a good detoxification capacity. This work is expected to provide a green, efficient, and stable strategy to enhance the adsorption properties of catalytic materials and subsequently their co-catalytic properties.

Co@C Nanocatalyst: Enhanced Activation of Peroxymonosulfate for Paracetamol Degradation

A core–shell Co@C composite catalyst was prepared, characterized and used to activate peroxymonosulfate (PMS) for the degradation of paracetamol in water. Hybridized structures containing Co and graphitized carbon act as independent active sites for PMS activation initiating both radical and nonradical oxidation. A 91.57% paracetamol removal was reached in the Co@C/PMS system at 60 min. Radical quenching and electron paramagnetic resonance (EPR) tests show that nonradical 1O2 played predominant roles in the advanced oxidation process, while the other three radicals [Formula: see text], •OH and [Formula: see text]. also played a certain role in paracetamol degradation. After four cycles, the degradation could still reach 70%, which proves that the Co@C composite catalyst exhibits good stability.

Insight into the Discriminative Efficiencies and Mechanisms of Peroxy Activation via Fe/Cu Bimetallic Catalysts for Wastewater Purification.

Fe/Cu bimetallic catalysts have a synergistic effect that can effectively enhance catalytic activity, so Fe/Cu bimetallic catalysts have been extensively studied. However, the efficacy and mechanisms of Fe/Cu bimetallic catalysts' peroxidation activation have rarely been explored. In this study, Fe/Cu bimetallic materials were fabricated to catalyze different oxidizing agents, including peroxymonosulfate (PMS), peroxydisulfate (PDS), peroxyacetic acid (PAA), and hydrogen peroxide (H2O2), for the degradation of sulfamethoxazole (SMX). The Fe/Cu/oxidant systems exhibited an excellent degradation efficiency of sulfamethoxazole (SMX). In the Fe/Cu/PMS, Fe/Cu/PDS, and Fe/Cu/PAA systems, the main reactive oxygen species (ROS) responsible for SMX degradation were hydroxyl radical (•OH) and singlet oxygen (1O2), while the main ROS was only •OH in the H2O2 system. The differences in the surface structure of the materials before and after oxidation were examined, revealing the presence of a large amount of flocculent material on the surface of the oxidized PMS material. Anion experiments and actual body experiments also revealed that the PMS system had a strong anti-interference ability. Finally, a comprehensive comparison concluded that the PMS system was the optimal system among the four oxidation systems. Overall, this work revealed that the PMS oxidant has a better catalytic degradation of SMX compared to other oxidizers for Fe/Cu, that PMS generates more ROS, and that the PMS system has a stronger resistance to interference.

Peroxymonosulfate activation by iron-cobalt bimetallic phosphide modified nickel foam for efficient dye degradation

Novel catalysts with multiple active sites and rapid separation are required to effectively activate peroxymonosulfate (PMS) for the removal of organic pollutants from water. Therefore, an integrated catalyst for PMS activation was developed by directly forming Co–Fe Prussian blue analogs on a three-dimensional porous nickel foam (NF), which were subsequently phosphorylated to obtain cobalt-iron bimetallic phosphide (FeCoP@NF). The FeCoP@NF/PMS system efficiently degraded dye wastewater within 20 min. The system exhibited excellent catalytic degradation over a broad pH range and at high dye concentrations due to the presence of unique asymmetrically charged Coa+ and Pb− dual active sites formed by cobalt phosphides within FeCoP@NF. These active sites significantly enhanced the catalytic activity of PMS. The activation mechanism of PMS involves phosphorylation that accelerates electron transfer from FeCoP@NF to PMS, to generate SO4·–, ·OH, O2·–, and 1O2 active species. Three-dimensional FeCoP@NF could be readily recycled and showed good stability for PMS activation. In this study, a highly efficient, stable, and readily recyclable integrated catalyst was developed. This catalyst system effectively resolves the separation and recovery issues associated with conventional powder catalysts and has a wide range of potential applications in wastewater treatment.

Enhanced Orange II Removal Using Fe/Mn/Mg2-LDH Activated Peroxymonosulfate: Synergistic Radical Oxidation and Adsorption

In this study, Fe/Mn/Mg2-LDH was utilized for the first time as a catalyst for peroxymonosulfate (PMS) activation to facilitate the removal of Orange II. This composite was characterized using various techniques, such as XRD, FTIR, SEM-EDS, BET, and XPS. The results revealed a well-defined lamellar structure of Fe/Mn/Mg2-LDH with a metal molar ratio of Fe/Mn/Mg at 1:1:2. Moreover, the structural stability of Fe/Mn/Mg2-LDH was confirmed through the XRD, FTIR, and SEM. Fe/Mn/Mg2-LDH exhibited a good adsorption capacity towards Orange II and highly efficient PMS activation. The optimal removal efficiency of Orange II (98%) was achieved under the conditions of pH 7.0, [PMS] = 1.0 mmol L−1, [Fe/Mn/Mg₂-LDH] = 1.6 g L−1, and [Orange II] = 50 μM. Additionally, this system demonstrated good adaptability across a wide pH range. The presence of Cl− and humic acids (HA) did not significantly inhibit Orange II removal, whereas inhibitory effects were observed in the presence of CO32− and PO43−. The removal mechanism of Orange II was attributed to a synergy of adsorption and oxidation processes, wherein the generated surface radicals (SO4•−ads and HO•ads) on the surface of the Fe/Mn/Mg2-LDH played a predominant role. Furthermore, the Fe/Mn/Mg2-LDH exhibited good reusability, maintaining a removal rate of 90% over five cycles of recycling. The Fe/Mn/Mg2-LDH/PMS system shows promising potential for the treatment of wastewater contaminated with refractory organic pollutants.

Synergistic activation of peroxymonosulfate by 3D CoNiO2/Co core-shell structure biochar catalyst for sulfamethoxazole degradation

In this study, a 3D CoNiO2/Co core–shell structure biochar catalyst derived from walnut shell was synthesized by hydrothermal and ion etching methods. The prepared BC@CoNi-600 catalyst exhibited exceptional peroxymonosulfate (PMS) activation. The system achieved 100 % degradation of sulfamethoxazole (SMX). The reactive oxygen species in the BC@CoNi-600/PMS system included SO4−, OH, and O2−. Density functional theory calculations explored the synergistic effects between nickel–cobalt bimetallic and carbon matrix during PMS activation. The unique 3D core–shell structure of BC@CoNi-600 features an outer nickel–cobalt bimetallic layer with exceptional PMS adsorption capacity, while protecting the zero-valence Co of the inner layer from oxidation. Based on the experimental-data, machine learning modeling mechanism, and information theory, a nonlinear modeling method was proposed. This study utilizes a machine learning approach to investigate the degradation of SMX in complex aquatic environments. This study synthesized a novel biochar-based catalyst for activated PMS and provided unique insights into its environmental applications.

Composite catalyst regenerated from spent Cu-Bi-spinel adsorbent and its Fenton-like photocatalysis mechanism for efficient removal of sulfamethoxazole

Reutilization of spent adsorbent by converting the adsorbed organic pollutants into carbon matrix has attracted more attention in recent years, which delivers a greener way for the preparation of catalysis and environment remediation. In this work, CuBi2O4 after adsorption of pollutant sulfamethazine was further transformed to a photocatalyst CBO-WC500 with high catalytic efficiency for degradation of typical pharmaceuticals. The XAFS analysis proved that Cu-C chemical bond was constructed during the preparation process. The obtained CBO-WC500 was applied to remove sulfamethoxazole (SMX) through photocatalytic Fenton-like reaction, and removal efficiency reached 88.9 % after 60 minutes with the initial 5 mg•L−1 SMX and 0.2 g•L−1 catalyst in peroxymonosulfate (PMS) system. The results showed that the introduction of carbon stem from waste improved separation of photo-generated carriers and electron transfer capability, thus more photo-induced electrons could participate in reaction with PMS. Moreover, Cu(I) and Cu(II) in CBO-WC500 with Cu-Bi-spinel structure played a vital role in PMS activation. Led by electron transportation, reactive species (1O2, •OH, SO4•-) originated from PMS contributed to degradation of SMX, and degradation pathway of target pollutant was proposed based on analysis of intermediates. Removal efficiency of CBO-WC500 for SMX kept stable after several cycles’ utilization, and it also showed decent eliminating performance of mixed pollutants in different water matrix. This study has provided a potential way for resource reuse of adsorbed pollutant and realizing reutilization of spent adsorbent as photocatalyst with higher efficiency.

Hydrogen peroxide enhanced Cu(II)/peroxymonosulfate system for naproxen degradation in natural water matrix and simultaneously reduced the formation potential of halogenated by-products

The susceptibility to the natural water matrix and the risk-generating halogenated by-products in the Cu(II)/peroxymonosulfate system heavily restricted its practical application. This study first demonstrated hydrogen peroxide (H2O2) could remarkably improve the anti-interference capacity of the Cu(II)/peroxymonosulfate system in the natural water matrix through promoting the copper species cycle [Cu(II)/Cu(I)]. A complete naproxen (NPX) removal was achieved at pH 10.0 for 180 s with the H2O2/Cu(II)/peroxymonosulfate system, and the degradation rate of NPX was 28 times greater than its counterpart without H2O2·H2O2 functioned as an electron donor to reduce Cu(II) to Cu(I), while the formed Cu(I) preferentially interacting with peroxymonosulfate to generate reactive species. Several reactive species, including Cu(III), •OH and SO4•−, participated in NPX degradation, while Cu(III) primarily contributed to NPX abatement. The NPX abatement in the H2O2/Cu(II)/peroxymonosulfate system was strongly pH-dependent, with weakly alkaline circumstances being more beneficial to its removal. Additionally, Cl−, H2PO42− and humic acid in the natural water matrix had the slight impact on NPX elimination with the H2O2/Cu(II)/peroxymonosulfate system, whereas H2PO42− and humic acid strongly suppressed NPX elimination in the Cu(II)/peroxymonosulfate system. Furthermore, the generation of halogenated by-products could be suppressed in treating halide-containing wastewater with the H2O2/Cu(II)/peroxymonosulfate system. To sum up, this research offered a new strategy to strengthen the anti-interference capacity of the Cu(II)/peroxymonosulfate system and simultaneously inhibiting halogenated by-product production. The finding should be important for studying the synergistic effect of dual oxidants in treating Cu(II)-containing wastewater.

The insights into facet-dependent catalytic performance of Cu2O in peroxymonosulfate activation for effective degradation of antibiotics

It was of great significance to improve the performance of catalysts in peroxymonosulfate (PMS) activation for water pollution control. Herein, Cu2O-based catalysts with different exposed facets were synthesized by a feasible method, and later employed for activating PMS to conduct the degradation tests of tetracycline (TC). With the increase of exposed (100) facet, the specific surface area of Cu2O was improved and the interface charge transfer resistance was reduced. More interestingly, benefiting from the exposure of (100) facet, the electron-donating ability of Cu2O was boosted, and the adsorption energy of PMS over Cu2O was also reduced, thereby creating favorable conditions for PMS activation. As guessed, Cu2O-1 with (100) facet can quickly activate PMS to achieve the effective degradation of TC, and the highest removal efficiency of TC over Cu2O-1 can be up to 97.56 % within 15 min. Furthermore, Cu2O-1 with good anti-interference showed satisfactory reusability, and the degradation intermediates of TC were the low toxic or nontoxic. In the Cu2O-1/PMS system, various reactive oxygen species were detected, including SO4•–, OH•, O2•– and 1O2, and wherein the contribution of 1O2 to TC degradation was the greatest. In short, current work shared some valuable insights into persulfate-based advanced oxidation processes.

Facilely tuning the coating layers of Fe nanoparticles from iron carbide to iron nitride for different performance in Fenton-like reactions

In this study, a series of Fe-based materials are facilely synthesized using MIL-88A and melamine as precursors. Changing the mass ratio of melamine and MIL-88A could tune the coating layers of generated zero-valent iron (Fe0) particles from Fe3C to Fe3N facilely. Compared to Fe/Fe3N@NC sample, Fe/Fe3C@NC exhibits better catalytic activity and stability to degrade carbamazepine (CBZ) with peroxymonosulfate (PMS) as oxidant. Free radical quenching tests, open-circuit potential (OCP) test and electron paramagnetic resonance spectra (EPR) prove that hydroxyl radicals (OH) and superoxide radical (O2−) are dominant reactive oxygen species (ROSs) with Fe/Fe3C@NC sample. For Fe/Fe3N@NC sample, the main ROSs are changed into sulfate radicals (SO4−) and high valent iron-oxo (Fe (IV)=O) species. In addition, the better conductivity of Fe3C is beneficial for the electron transfer from Fe0 to the Fe3C, thus could keep the activity of the surface sites and obtain better stability. DFT calculation reveals the better adsorption and activation ability of Fe3C than Fe3N. Moreover, PMS can also be adsorbed on the Fe sites of Fe3N with shorter FeO bonds and longer SO bonds than on Fe3C, the Fe (IV)=O is thus present in the Fe/Fe3N@NC/PMS system. This study provides a novel strategy for the development of highly active Fe-based materials for Fenton-like reactions and thus could promote their real application.

Tungsten sulfide highly boosted Fe(III)/peroxymonosulfate system for rapid degradation of cyclohexanecarboxylic acid: Performance, mechanisms, and applications

In this study, the Fe(III)/WS2/peroxymonosulfate (PMS) system was found to remove up to 97% of cyclohexanecarboxylic acid (CHA) within 10 min. CHA is a model compound for naphthenic acids (NAs), which are prevalent in petroleum industrial wastewater. The addition of WS2 effectively activated the Fe(III)/PMS system, significantly enhancing its ability to produce reactive oxidative species (ROS) for the oxidation of CHA. Further experimental results and characterization analyses demonstrated that the metallic element W(IV) in WS2 could provide electrons for the direct reduction of Fe(III) to Fe(II), thus rapidly activating PMS and initiating a chain redox process to produce ROS (SO4•−, •OH, and 1O2). Repeated tests and practical exploratory experiments indicated that WS2 exhibited excellent catalytic performance, reusability and anti-interference capacity, achieving efficient degradation of commercial NAs mixtures. Therefore, applying WS2 to catalyze the Fe(III)/PMS system can overcome speed limitations and facilitate simple, economical engineering applications.

Improving the non-free radical activated peroxymonosulfate capability of sludge biochar through sacrificial template method: Efficacy and mechanism evaluation

Improving the non-free radical activation ability of persulfate has great significance for the degradation of persistent contaminant in complex water environments. Here, special nitrogen-doped sludge-based catalysts for peroxymonosulfate (PMS) activation were developed through sacrificial template method by employing polymer surfactant (PS) as template agent. The PS usage and acid etching significantly improved the catalyst’s non-radical activation performance for PMS, the contribution of singlet oxygen (1O2) and electron transfer pathway (ETP) to bisphenol A (BPA) removal could be well matched to 72.31 % and 27.69 % in NCF-1/PMS system, respectively. Such non-radical activation characteristic ensures that NCF-1/PMS systems exhibit super oxidation ability of BPA (Kobs = 0.3714 min−1) and strong anti-interference ability to environmental matrixes via simultaneously enhancing both 1O2 and ETP. The critical roles of graphitic N and as-formed Si-O-C sites in activating PMS were revealed through electrochemical analysis, in-situ characterization technology and theoretical calculations. Density functional theory calculations confirmed that the PS addition and desilication process reduced the adsorption energy of the NCF-1 for PMS, and achieved lower energy barrier to cleave the O–H bond of NCF-1/PMS complex, significantly achieving the surge in the major active species of 1O2. This study provides novel regulatory strategies to modulate the non-radical path for persistent pollutant treatment.

Highly efficient activation of peroxymonosulfate by MOF derived CoS2@C for degradation of ciprofloxacin

The cobalt disulfide/carbon composite CoS2@C was successfully synthesized using cobalt metal–organic frameworks (MOFs) with different ligands as templates by pyrolysis method. The as-prepared CoS2@C were applied as catalysts of peroxymonosulfate (PMS) for the degradation of antibiotics. The CoS2@C-3, which was prepared using Co-MOF-74 as self-template, exhibited extraordinarily high activity to PMS, more than 90 % of ciprofloxacin (CIP) was degraded in 10 min with a rate constant of 0.249 min−1. Furthermore, the CoS2@C-3/PMS system demonstrated exceptional resistance to humic acid (HA), significant environmental stability, and a wide range of pH adaptation. The SO4•−, ·OH, and 1O2 induced from heterogeneous and homogeneous activation of PMS were identified as reactive oxygen specieses (ROSs) responsible for oxidation of CIP. In addition, electron transfer and Co(IV) = O also participated in the CIP degradation process. According to the results, a plausible catalytic mechanism for PMS by CoS2@C was elucidated, in which S is crucial to the regeneration of ≡Co(II) in situ. Four potential degradation pathways were proposed after the CIP intermediate products were analysed by HPLC-MS. The findings of this study might offer us some insight into how metal sulfides made from MOFs can be effectively used to eliminate contaminants by activating PMS.

Iron anchored carbon–nitrogen catalyst for enhanced activation performance of peroxymonosulfate: Synergy of 1O2 and high-valent iron

Herein, Iron anchored in carbon–nitrogen nanosheets (Fe-CNx) catalysts were synthesized successfully through one-step in situ pyrolysis for activating peroxymonosulfate (PMS) to degrade sulfachloropyridazine (SCP). Fe-CN800/PMS could realized the complete removal SCP in 20 min (kobs = 0.644 min−1). Its reaction rates were 214.7 times higher than that in PMS system. Additionally, Fe-CN800 could effectively activate PMS in a wide range of pH (3–10.6). The relationship between the content of Fe-CNx functional groups and the catalytic performance indicated that C = O and Fe-N4 were the main active sites. The structural–functional association between active sites and reactive oxygen species (ROS) was revealed by regression analysis and Density Functional Theory calculations, indicating that C = O stimulated 1O2 production, while HV-Fe was derived from C = O and Fe-N4. Moreover, the PMS activation was enhanced via electron transfer between Fe(II) and Fe(III). Based on LC-MS and Fukui index, the action of ROS during SCP decomposition was analyzed, and proposed three probable pathways for SCP degradation. The transformation pattern of the structure and toxicity of the intermediates was revealed via T.E.S.T. analysis, and plant growth experiments showed that the effect of the treated SCP solution on Brassica napus significantly decreased. Finally, Fe-CN800 exhibited excellent stability, with SCP removal remaining above 95 % in five cycles and Fe leaching concentrations lower than ones which have been reported catalysts. This work provided new insights for the precise design of more efficient PMS catalysts. It will provide a fundamental basis for the practical application in wastewater treatment based on PMS-AOPs.