Peroxymonosulfate Activation Performance Research Articles

High yielded Co–C derived from polyester-Cobalt carbothermal reduction for efficient activation of peroxymonosulfate to degrade levofloxacin

A kind of high yield and recyclable Cobalt–Carbon composite (Zn1Co5/PnC) was prepared by carbothermal reduction process, in which the cobalt acetate and zinc acetate were considered as Zn and Co precursors, and the polyester waste was evolved as the carbon precursor. The morphology, structure and composition of the composite were characterized using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Results showed that evaporation of zinc contributed to the formation of porous carbon structure, and the Co nanoparticles were wrapped and protected by the porous carbon matrix. The Zn1Co5/PnC activated peroxymonosulfate (PMS) system (Zn1Co5/PnC/PMS) was constructed to degrade the levofloxacin (LEV). The activity and mechanism of LEV degradation was understood. The LEV degradation efficiency was high to 96.60% within 90 min in the presence of Zn1Co5/P4C. Moreover, the Zn1Co5/P4C still maintained favorable PMS activation performance after five-cycle runs. The results show that the Zn1Co5/P4C played positive role in activating the PMS, it may be due to the facts that the polyester derived carbon could supported the Co while the evaporated Zn could increase the surface area of Zn1Co5/P4C, leading to the increased activity. The possible degradation pathways were proposed by identifying the intermediate products through liquid chromatography-mass spectrometry analysis. This study put forward a promising method to use polyester waste to synthesize high yield cobalt-carbon composite for degrading the antibiotic in wastewater.

Peroxymonosulfate-Activation-Induced Phase Transition of Mn3O4 Nanospheres on Nickel Foam with Enhanced Catalytic Performance.

The transformations of physicochemical properties on manganese oxides during peroxymonosulfate (PMS) activation are vital factors to be concerned. In this work, Mn3O4 nanospheres homogeneously loaded on nickel foam are prepared, and the catalytic performance for PMS activation is evaluated by degrading a target pollutant, Acid Orange 7, in aqueous solution. The factors including catalyst loading, nickel foam substrate, and degradation conditions have been investigated. Additionally, the transformations of crystal structure, surface chemistry, and morphology on the catalyst have been explored. The results show that sufficient catalyst loading and the support of nickel foam play significant roles in the catalytic reactivity. A phase transition from spinel Mn3O4 to layered birnessite, accompanied by a morphological change from nanospheres to laminae, is clarified during the PMS activation. The electrochemical analysis reveals that more favorable electronic transfer and ionic diffusion occur after the phase transition so as to enhance catalytic performance. The generated SO4•- and •OH radicals through redox reactions of Mn are demonstrated to account for the pollutant degradation. This work will provide new understandings of PMS activation by manganese oxides with high catalytic activity and reusability.

Enhanced activation performance of peroxymonosulfate by NiCo2O4/SnO2 composite for metronidazole degradation under visible light

In this study, a NiCo2O4/SnO2 complex was successfully synthesized by a convenient hydrothermal method and used for the catalytic degradation of metronidazole (MNZ) by activating peroxymonosulfate (PMS). The physicochemical properties of NiCo2O4/SnO2 were identified by a series of characterization methods. The remarkable PMS activation performance of NiCo2O4/SnO2 originated from the formation of a heterojunction between NiCo2O4 and SnO2, which led to the improvement of the light response ability and the electron conduction efficiency of the composite. The composite catalyst displayed almost 100 % MNZ degradation efficiency within 30 min under visible light. The degradation efficiency of MNZ can be maintained in a wide pH range (3−11). Furthermore, the effect of catalyst dosage, PMS concentration and MNZ concentration on the catalytic process were investigated by changing the experimental parameters. The various anions and different water substrates had only a minor influence on the degradation process of MNZ. In addition, quenching experiments and electron paramagnetic resonance techniques were employed to detect active groups in the reaction process. The results showed that superoxide radicals (O2•-), hydroxyl radicals (OH•), singlet oxygen (1O2), and sulfate radicals (SO4•-) were the main causes of MNZ degradation. Meanwhile, the liquid phase mass spectrometry (LCMS) and Toxicity Estimation Software Tool (T.E.S.T) were utilized to identify the intermediate products and their biological toxicity in the degradation process, and demonstrating a significant decline of biotoxicity compared with MNZ. Generally, this work will provide a new feasible scheme for the effective treatment of organic contaminants in water.

Peroxymonosulfate Activation by CuO-Fe2O3-Modified Ni Foam: A 1O2 Dominated Process for Efficient and Stable Degradation of Tetracycline

The post-separation of powder catalysts restricts the practical application of peroxymonosulfate (PMS)-based advanced oxidation technology. Hence, we fabricated CuO-Fe2O3-modified Ni foam (CFO-NF) using a facile hydrothermal method for an efficient PMS activation. The CFO-NF/PMS system could achieve a 97.9% tetracycline hydrochloride (TC) removal efficiency in 60 min with four pieces of CFO-NF and 0.4 mmol L−1 of PMS. The removal efficiency was maintained at ˃85% even after five cycles, indicating the excellent stability of CFO-NF composites. The conversion among Fe(III)/Fe(II), Cu(II)/Cu(I), and Ni(III)/Ni(II) accelerated the PMS decomposition, verifying the synergy between CuO-Fe2O3 and Ni foam. The trapping experiments and EPR detection confirmed that abundant active species (•OH, SO4•−, O2•−, and 1O2) were produced in the CFO-NF/PMS system, accounting for the existence of radical pathways and a non-radical pathway, in which 1O2 (non-radical pathway) was dominated. This study developed a novel CuO-Fe2O3-modified Ni foam with a superior PMS activation performance, a high stability, and a recoverability for eliminating refractory organic pollutants.

Ternary transition metal organic frameworks (MOFs) CuZn-MIL101 (Fe) for peroxymonosulfate activation to degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA): A non-radical pathway dominated by singlet oxygen

In this study, ternary CuZn-MIL101(Fe) MOFs were prepared by introducing Cu and Zn ions into MIL-101(Fe) to obtain catalysts with excellent peroxymonosulfate (PMS) activation properties. The comprehensive characterization analysis revealed that although the adsorption performance of CuZn-MIL101(Fe) decreased, the PMS activation performance was significantly improved and complete degradation of MCPA was reached in 20 min. Calculation of the specific rate constants (kSA) yielded that the intrinsic activity of CuZn-MIL101(Fe) for PMS was 34 and 37 times higher than that of CuZn0.25-MIL101(Fe) and Cu0.25Zn-MIL101(Fe), respectively. The quenching experiments combined with electron paramagnetic resonance (EPR) spectroscopy verified the composition of the active substances in the system, whose contributions were in the order of O21 > ·OH > SO4⋅− > O2⋅. Using PMSO as a probe, an important role of high-valent iron was found in the system. The HOMO-LUMO gap of MCPA was calculated to be 0.205 eV by density functional theory (DFT), and the difference in adsorption energy of MCPA when adsorbing different radicals was investigated. The intermediate products were obtained by GC-MS and analyzed for toxicity, and the mechanism of singlet oxygen-dominated degradation of MCPA was proposed, which laid the foundation for the subsequent in-depth study of phenoxyacetic acid-based herbicides.

Efficient Activation of Peroxymonosulfate by V-Doped Graphitic Carbon Nitride for Organic Contamination Remediation.

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have been developed as an ideal pathway for completely eradication of recalcitrant organic pollutants from water environment. Herein, the V-doped graphitic carbon nitride (g-C3N4) is rationally fabricated by one-step thermal polymerization method to activate PMS for contamination decontamination. The results demonstrate the V atoms are successfully integrated into the framework of g-C3N4, which can effectively improve light absorption intensity and enhance charge separation. The V-doped g-C3N4 displays superior catalytic performance for PMS activation. Moreover, the doping content has a great influence on the activation performances. The radical quenching experiments confirm •O2-, SO4•-, and h+ are the significant species in the catalytic reaction. This work would provide a feasible strategy to exploit efficient g-C3N4-based material for PMS activation.

Insights into the mechanism of multiple Cu-doped CoFe2O4 nanocatalyst activated peroxymonosulfate for efficient degradation of Rhodamine B

The multiple metal catalyst as a promising nanomaterial has shown excellent activity in the peroxymonosulfate (PMS) activation for pollutant degradation. However, the role of special sites and in-depth understanding of the PMS activation mechanism are not fully studied. In this study, a Cu-doped CoFe2O4 nanocatalyst (0.5CCF) was synthesized by a sol-gel and calcination method, and used for PMS activation to remove Rhodamine B (RhB). The results showed that the Cu doping obviously enhanced the catalytic performance of CoFe2O4, with 99.70% of RhB removed by 0.5CCF while 74.91% in the CoFe2O4 within 15 min. Based on the X-ray photoelectron spectroscopy and electrochemical analysis, this could be ascribed to the more low valence of Co and Fe species generated on the 0.5CCF and faster electron transfers occurred in the 0.5CCF due to the Cu doping. In addition, Cu doping could provide more reaction sites for the 0.5CCF to activate PMS for RhB removal. The metal species and the surface hydroxyl were the reaction sites of PMS activation, and the surface hydroxyl played an important role in surface-bound reactive species generation. During the PMS activation, the Cu not only activated PMS to produce reactive oxygen species (ROS), but also regenerated Co2+ and Fe2+ to accelerate the PMS activation. The non-radical of 1O2 was the main ROS with a 99.35% of contribution rate, and the SO5•– self-reaction was its major source. This study provides a new insight to enhance the PMS activation performance of multiple metal catalysts by Cu doping in wastewater treatment.

MOFs-derived Mn/C composites activating peroxymonosulfate for efficient degradation of sulfamethazine: Kinetics, pathways, and mechanism

Both manganese oxides (MnOx) and carbon materials hold promise for persulfate activation to remediate polluted waterbodies. However, the aggregation of MnOx during the calcination synthesis and lower activity to persulfate of carbon materials seriously limit their industrial application. In this work, two Mn/C composites (MnOx-NA and MnOx-A) were synthesized from manganese-metal organic frameworks (MOFs) under nitrogen atmosphere and air atmosphere calcination respectively. The prepared MnOx-NA exhibited more excellent peroxymonosulfate (PMS) activation performance than MnOx-A, and almost 100% sulfamethazine (SMT) could be removed by the MnOx-NA/PMS system within 30 min. Moreover, the MnOx-NA/PMS system exhibited impressive stability even after 10 cycles and displayed high anti-interference ability to Cl−, ClO4−, CO32−, SO42−, NO3− and humic acid (HA). In addition, the oxidation system could efficiently remove SMT in different aqueous matrices. Three possible pathways of SMT degradation were proposed according to the LC-MS analysis. Electron paramagnetic resonance (EPR), quenching experiments, and cyclic voltammetry experiments revealed that SMT degradation predominantly occurred through a catalyst-mediated electron transfer pathway. Material characterization and electrochemical impedance spectroscopy (EIS) analysis showed that the derived carbon species strengthened the MnOx-NA's electron-transfer capability and promoted the uniform distribution of MnOx particles on the carbon materials surface, which significantly improved MnOx-NA's PMS activation performance. This study introduces a facile method for the design of Mn/C composites PMS activator and provides theoretical guidance for water pollution remediation.

Peroxymonosulfate activation in ultrasound-driven molybdenum disulfide piezocatalysis: The effect of sulfur vacancy

Although peroxymonosulfate (PMS) can be efficiently activated by ultrasound-driven piezocatalyst, there are still uncertainties on the mechanisms. Herein, molybdenum disulfide piezocatalysts with different sulfur vacancy (VS) types were prepared by hydrothermal (MoS2–H) and solvothermal methods (MoS2–S). The configuration of Vs in MoS2 was characterized by X-ray photoemission spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and O2 diffuse reflectance infrared Fourier transform spectroscopy (O2-DRIFTS). Surface in-plane VS and edge VS dominated on MoS2–H and MoS2–S. MoS2–S exhibits higher PMS activation performance with 85.0% degradation rate of 4-chlorophenol within 2 h. Although in-plane VS feature a stronger PMS adsorption energy compared with edge VS (−1.64 vs. −0.94 eV), PMS activation is not favorable at the in-plane VS sites of MoS2 (MoS2–H). In piezo-polarized MoS2, the separated charge carriers accumulate at the edges, where edge VS (MoS2–S), as the active site, strengthens the coupling between electrons and PMS. As a result, the O–O bond length in PMS is increased from 1.467 to 1.470 Å, enabling the facile activation of PMS with the generation of more abundant ·OH and ·SO4− radicals. This work clearly explains the PMS activation mechanism from both experimental and theoretical aspects and provides directions to tailor the structure and atom vacancies of piezocatalysts.

Cobalt-doped boosted the peroxymonosulfate activation performance of LaFeO3 perovskite for atrazine degradation

In this work, cobalt (Co) doped perovskite with a molecular formula of LaFe0.9Co0.1O3 (LFCO) was synthesized, and was successfully employed for peroxymonosulfate (PMS) activation to eliminate atrazine (ATZ) from water. In contrast with alone perovskite without doped Co (LFO), the PMS activation performance was significantly improved. The influences of experimental parameters including LFCO dosage, PMS content, and reaction pH on the elimination of ATZ were discussed. Based on the consequences of quenching experiments and electron paramagnetic resonance test, OH and SO4− were confirmed to be the primary active species in the LFCO/PMS system. LFCO surface chemistry analysis combined with density functional theory (DFT) calculations were utilized to systematically reveal the underlying activation pathway of LFCO and suggested that there is a synergetic function between Co and Fe in PMS activation via accelerating redox cycle of surface metal ions. Additionally, the application potential of the LFCO/PMS system was discussed by demonstrating its resistance to common water matrix. The possible transformation pathway of ATZ in the LFCO/PMS system was proposed according to the findings of UPLC-QTOF-MS/MS. This research sheds light on the role of bimetallic oxides in PMS activation for degrading organic contaminants.

Strongly coupled Fe/N co-doped graphitic carbon nanosheets/carbon nanotubes for rapid degradation of organic pollutants via peroxymonosulfate activation: Performance, mechanism and degradation pathways

Exploration of magnetic carbon-based catalysts with high catalytic activity and recyclability is essential for peroxymonosulfate (PMS) activation. A feasible method for the synthesis of Fe/N co-doped graphitic carbon nanosheets/carbon nanotubes (Fe/N-GCNS@CNTs) using a one-step pyrolysis procedure was proposed in this paper. The Fe/N-GCNS@CNTs possessed an interconnected carbon framework composed of GCNS and CNTs. The carbon framework could not only improve the mass transfer efficiency and mineralization capability of Fe/N-GCNS@CNTs, but it could also protect the Fe nanoparticles against metal leaching. The as-obtained Fe/N-GCNS@CNTs-800 demonstrated excellent performance for PMS activation to degrade organic pollutants. 100% of 50 mg/L rhodamine B (RhB) was rapidly degraded in 5 min when PMS (0.5 mM) and 50 mg/L Fe/N-GCNS@CNTs-800 were added. Meanwhile, the Fe/N-GCNS@CNTs-800/PMS system possessed a broad efficient pH range (3.0–9.0), good anti-interference capacity (anions and HA), and low iron leaching concentration (138 µg/L). Fe/N-GCNS@CNTs-800 could be magnetically separated from the suspension very easily because of its good saturation magnetization (11.25 emu/g). In addition, quenching experiments, electron spin resonance (ESR) measurements, and electrochemical assessments demonstrated that radical (.OH and SO4⋅−) and non-radical (1O2 and electron transfer) processes cooperated to contribute to the rapid RhB degradation. XPS analysis revealed that the primary catalytic active sites of Fe/N-GCNS@CNTs-800 were pyridinic N, C=O groups, and Fe/Fe3C species. LC-MS analyses were used to propose possible RhB degradation pathways. This study provided an intrinsic mechanism of PMS activation by magnetic carbon-based catalysts for the removal of organic pollutants in water treatment.

Unravelling the synergy of Eu dopant and surface oxygen vacancies confined in bimetallic oxide for peroxymonosulfate activation

The rational regulation of electron transfer between Co-based catalysts and peroxymonosulfate (PMS) plays a key role in the photo-Fenton catalytic oxidation process. In this study, a novel Eu-doped ZnCo2O4 composite was successfully prepared via a simple hydrothermal calcination method, and firstly used for PMS activation to degrade 1,1-diamino-2,2-dinitroethene (FOX-7). Among all samples, Eu0.4-ZnCo2O4 exhibited remarkable PMS activation performance, which was about 5.67 times higher than that of undoped ZnCo2O4. The enhanced catalytic performance could be attributed to the generation of abundant oxygen vacancies (OVs), which greatly promoted the separation of carriers and accelerated the cycling of the Co3+/Co2+ redox pairs. The corresponding Co3+/Co2+ and oxygen defects/lattice oxygen (ODef/OLat) ratios regulated catalytic-activity relationship were successfully established by regression analysis. Radical quenching tests and electron paramagnetic resonance (EPR) revealed that non-radical pathway dominated the degradation process, and singlet oxygen (1O2) was the main active species. Importantly, theoretical calculations demonstrated that the synergy of doping and OVs could effectively improve adsorption energy and enhance electron transfer for promoting the activation of PMS. This study offers a deep insight into the catalytic reaction mechanism and provides a new strategy for developing heterogeneous photocatalysts in activating PMS for environmental remediation.

FexN produced in pharmaceutical sludge biochar by endogenous Fe and exogenous N doping to enhance peroxymonosulfate activation for levofloxacin degradation

For preparing high performance biochar to be applicated in persulfate-based oxidation treatment of wastewater, the feasibility of deriving Fe-N biochar from pharmaceutical sludge by endogenous Fe and exogenous N doping was investigated. With exogenous urea doping, FexN contained biochar (PZBC800U) was successfully derived from endogenous Fe(OH)3 contained pharmaceutical sludge. PZBC800U effectively activated peroxymonosulfate (PMS) to remove 80 mg·L−1 levofloxacin (LEV) within 90 min. The main mechanism of PMS activation by PZBC800U for LEV degradation was revealed as non-radical pathways dominated by 1O2 generation and direct electron transfer. The formation of FexN combined with the increase of pyridinic-N in the biochar changed the electronic structure, improved the electron transfer ability, and thus achieved the excellent PMS activation capacity of the biochar. The vital function of endogenous Fe(OH)3 was verified by comparing PZBC800U to Fe leached and extra Fe added controls. A total of 18 intermediates in the degradation of LEV were identified, and degradation pathways were proposed. Combined with the average local ionization energy calculation, the priority of piperazine breakage during LEV degradation was experimentally proved and mechanistically elucidated. This study provides a new insight into FexN biochar preparation from pharmaceutical sludge and the mechanisms of its excellent PMS activation performance for LEV degradation.

Isomorphic substitution of goethite by cobalt: Effects on the pathway and performance of peroxymonosulfate activation

Isomorphic substitution of Goethite (α-FeOOH) by metal elements with similar radii can greatly alter its physicochemical properties. Herein, a cobalt-substituted α-FeOOH (FeCox) was synthesized by simple coprecipitation on the atomic scale. The effect on the activation of peroxymonosulfate (PMS) was explored using tetracycline (TC) as a model pollutant. Compared with the α-FeOOH, the performance of FeCo10 on PMS activation was greatly enhanced, and 95.4 % of TC was removed within 10 min. Cobalt substitution significantly decreased the metal ion leaching of the catalyst, and the iron and cobalt leaching of FeCo10 was only 4.023 and 33.614 μg/L. Co substitution altered the activation pathway of α-FeOOH for PMS. Electron paramagnetic resonance (EPR) and quenching experiments indicated that singlet oxygen (1O2) was the dominant reactive oxygen species (ROS) in the reaction system. The activation of PMS was achieved by the process that PMS was first complexed with hydroxyls (–OH) on the surface of FeCo10, after which Fe and Co species in FeCo10 broke the peroxide bond. The reaction system could operate efficiently under different concentrations (2–250 mM) of Cl-, HCO3-, SO42- and NO3-. The excellent catalytic performance of FeCo10 was due to the structural defects caused by the introduction of Co, which significantly increased the –OH sites and electron transmission capacity of the catalyst. This work has proved that isomorphic substitution was an effective strategy for improving the PMS activation performance of α-FeOOH.

Highly efficient activation of peroxymonosulfate by Co, S co-doped bamboo biochar for sulfamethoxazole degradation: Insights into the role of S

Recently, highly efficient activation of peroxymonosulfate (PMS) by S-doped cobalt-based catalysts are receiving increased attention. The effect of S is worth exploring since it has a great influence on PMS activation performance. In this work, dimethyl sulfoxide was adopted as an S source and loaded on bamboo biochar (BB) with Co to form CoS/BBC, which served as an efficient catalyst for PMS activation to degrade sulfamethoxazole (SMX). The experiment results showed that CoS/BBC exhibits an excellent catalytic activity and the SMX (20 mg/L) can be completely degraded under the attack of species of ·OH, SO4-·, 1O2 and electron transfer. The SMX degradation conformed to pseudo first-order kinetics with rate constant reaching 0.442 min−1 in 10 min under the optimal conditions (a catalyst dose of 0.02 g/L, a PMS dose of 0.3 g/L and an initial pH = 7.0). The electrochemical experiments and density functional theory (DFT) calculation revealed that the introduction of S can accelerate electron transfer and promote the decomposition of PMS while facilitating Co(III)/Co(II) redox cycling. Furthermore, liquid chromatograph-mass spectrometer (LC-MS) and ecological structure activity relationships (ECOSAR) proved that the degradation process of SMX in CoS/BBC/PMS system has low ecotoxicity and is harmless to the environment. This work provides a new strategy for enhancing electron transfer by S-doped metal materials and the synthesis of efficient catalysts for SMX removal.

Oxygen vacancies-enriched Cu/Co bimetallic oxides catalysts for high-efficiency peroxymonosulfate activation to degrade TC: Insight into the increase of Cu+ triggered by Co doping

Bimetallic CuCo-doped graphene-like carbon nanosheets (CuCo@GCNs) were synthesized via a facile and efficient process using agarose as carbon templates to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. In this study, CuCo@GCNs/PMS system exhibited excellent TC removal efficiency (0.182 min−1), which was unaffected by various water matrices and applicable to a wide pH range (3.44–8.44). Radicals (SO4•−, •OH, and O2•−) and non-radical (1O2) pathways collectively contributed to catalytic TC oxidation based on quenching experiments and electron paramagnetic resonance (EPR) analysis. Density functional theory (DFT) calculations revealed that the mechanism of PMS molecules activated on the surface of CuCo@GCNs, in which CoO provided more catalytic sites while Cu2O further enhanced electron transfer. Moreover, the synergistic effect of CuCo bimetal could accelerate redox cycles of Cu+/Cu2+ and Co2+/Co3+, inducing the generation of abundant oxygen vacancies (OVs), thus enhancing PMS activation performance. Three potential TC degradation pathways were proposed according to fifteen possible intermediates detected by liquid chromatography-mass spectrometry (LC-MS). In brief, this work provides an efficient CuCo@GCNs heterogeneous catalyst and a new insight into PMS activation, which extends the application of bimetallic materials for environmental remediation.

Exploration the mechanisms underlying peroxymonosulfate activation by nano-cubic spinel M2MnO4 nanoparticles for degrading trichloroethylene

In this study, the morphology and surface characteristics of different MxMn3-xO4 (M = Co, Zn, Cu, Fe; x = 1, 2) nanoparticles and their catalytic performance for peroxymonosulfate (PMS) activation to degrade trichloroethylene (TCE) were compared. The characterization results showed that a highly crystalline manganese structure was synthesized, and cubic spinel (M2MnO4) and tetragonal spinel (MMn2O4) were confirmed. The experimental results indicated that, compared with the tetragonal spinel catalysts, the cubic spinel catalysts exhibited higher PMS-specific catalytic activity and TCE removal efficiency due to the reduction in electron transfer resistance and the increase of the surface area. In addition, all the synthesized nanoparticles exhibited remarkable reusability, a low metal dissolution rate, and a wide applicable pH range (4 to 11) for efficient PMS activation. The free radical-scavenging experiments and electron paramagnetic resonance (EPR) analysis further verified the role of ∙HO and SO4∙− in the removal of TCE and the large amount of stronger free radicals (SO4∙−) generated by the cubic spinels. This study revealed that stable cubic spinel nanoparticles can be synthesized at room temperature by adjusting the ratio of manganese and transition metals; these nanoparticles showed excellent catalytic performance for PMS activation. These research results are important for the synthesis of heterogeneous catalytic oxidation catalysts.

Enhanced peroxymonosulfate activation in the morphotropic phase boundary of molybdenum doped LaCoO3-δ perovskite

Perovskite oxides, with an ABO3 general formula, have attracted much attention as effective peroxymonosulfate (PMS) activators because of their composition adjustability and chemical stability. A doping strategy has been applied to enhance the PMS activation capability with the modulation of the crystal structure of the parent LaCoO3-δ perovskite by substituting Co atoms located at the B-site, with high valence state transition metals. Herein, a series of LaCo1-xMoxO3-δ perovskites were prepared with different Mo content, showing a phase transformation from rhombohedral to cubic-like structures. LaCo0.95Mo0.05O3-δ compound is located at the so-called morphotropic phase boundary (MPB) boosting PMS activation performance as well as enhanced stability. The presence of local inhomogeneities, observed as oxygen vacancies, has been detected in the MPB region enhancing the catalytic effect of pollutant degradation. Mo doping induced Co reduction that contributed to the enhanced PMS activation. Sulfate radical was identified to be the dominating reactive specie for LaCo1-xMoxO3-δ catalyzed PMS activation. This work contributes first, to clarifying the role of Mo doping to boost PMS activation, and second to highlighting the crucial role of the reduced oxidation state as well as the oxygen vacancies in the MPB for PMS activation. Impressive results were obtained when LaCo0.95Mo0.05O3-δ compound was deposited in a Lab-grade photoreactor with LED technology, reaching a complete removal of paracetamol in the first minute. This study provided new insight into the rational design of PMS activator and developed a new strategy for heterogeneous active PMS at a photoreactor with immobilized catalysts.

Three-dimensional nitrogen-doped graphene oxide beads for catalytic degradation of aqueous pollutants

Metal-free graphene-based catalysts have demonstrated excellent performance in advanced oxidation processes (AOPs). However, the recovery and reusability of these nanocatalysts are still a major issue. In this study, three dimensional (3D) nitrogen-doped reduced graphene oxide beads (NrGOb) were synthesized via a self-assembly method and then applied in heterogeneous activation of peroxymonosulfate (PMS) for the oxidation of hydroxybenzoic acid (HBA). The materials (NrGOb) were annealed at various temperatures ranging from 500 to 1000 °C, and the resulting NrGOb derived from 800 °C (NrGOb-800) exhibited the best performance for PMS activation. To avoid the challenging recovery, the degradation experiments were also performed in a packed-bed catalytic reactor. Various reaction parameters were investigated to optimize the efficiency of the system. Electron paramagnetic resonance (EPR) and quenching tests were carried out to differentiate the contribution of reactive radicals (SO4•-and•OH) in the degradation process and then aided in illustrating the degradation mechanism. Finally, the stability and reusability of the catalytic beads were investigated. The efficiency slightly declined with increased cycles; however, catalyst regeneration would be able to partially restore the active sites. The results suggest the feasibility of exploiting graphene-based macrostructures on the AOPs platform for the degradation of organic pollutants in commercial wastewater treatment plants.

Peroxymonosulfate activation by concave porous S/N co-doped carbon: Singlet oxygen-dominated non-radical efficient oxidation of organics

Developing high-efficient, low-cost and environmentally friendly catalysts is essential for activating peroxymonosulfate (PMS) but remains a challenge. Recently, novel catalysts of transition metal-nitrogen co-doped carbon materials, especially Fe-N-C, have attracted much attention due to their superior performance for PMS activation. Herein, FeSO4 and ZnSO4 were added during the synthesis of ZIF-8, obtained concave N, S co-doped iron-based carbon materials (Fe-S@NC) with mesoporous structure through high-temperature pyrolysis. This porous carbon material with a depressed surface not only promoted the exposure of active sites, but also accelerated mass transfer. The synergistic effect of Fe atoms and heteroatoms significantly enhanced the activation ability of the material to PMS. Benefiting from these advantages, only 2 mg/L Fe-S1@NC and 0.5 mM PMS was required to achieve the rapid degradation of acetaminophen (ACT) (99.7%, 0.7290 min-1). Besides, the activation system has a wide pH adaptability and low leaching iron concentration. Then the reaction mechanism of Fe-S1@NC/PMS system was investigated by quenching experiments and electron paramagnetic resonance technique (EPR), it was proposed that singlet oxygen (1O2) was the primary reactive species responsible for the degradation of ACT. This study provides new insight for the design of carbon catalysts in advanced oxidation field.