Mechanism Of Peroxymonosulfate Activation Research Articles

3D layer-by-layer amorphous MoSx assembled from [Mo3S13]2- clusters for efficient removal of tetracycline: Synergy of adsorption and photo-assisted PMS activation

Peroxymonosulfate (PMS) activation and photocatalysis are effective technologies to remove organic pollutants, but the adsorption effect of the catalyst is usually unheeded in degradation process. Herein, a bifunctional catalyst of amorphous MoSx (a-MoSx) with 3D layer-by-layer superstructure was synthesized by assembling basic active units [Mo3S13]2- of MoS2. The large interlayer spacing and high exposure of active sites render a-MoSx to have excellent synergy of adsorption and photo-assisted PMS activation for tetracycline (TC) degradation. Experiments and DFT calculation show that TC can be efficiently enriched on a-MoSx by pore filling, π-π interaction, hydrogen bonding and high adsorption energy. Subsequently, PMS can be quickly activated through electron transfer with a-MoSx, resulting in high TC degradation efficiency of 96.6% within 20 min. In addition, the synergistic mechanism of adsorption and photo-assisted PMS activation was explored, and the degradation pathway of TC was expounded. This work is inspirational for constructing bifunctional catalysts with superior synergistic adsorption and catalytic capabilities to remove refractory organic pollutants in water.

Magnetic CuFe2O4 nanoparticles immobilized on mesoporous alumina as highly efficient peroxymonosulfate activator for enhanced degradation of tetracycline hydrochloride

Nanoscaled magnetic copper ferrite (CuFe2O4) is widely used as a peroxymonosulfate (PMS) activator but suffers from agglomeration owing to its inherent magnetic properties and high surface energy. In this work, spinel structured CuFe2O4 anchored on mesoporous alumina (denoted as CFO@AO) were synthesized, characterized, and applied as a PMS activator for the removal of tetracycline hydrochloride (TC·HCl). Approximately 97.5 % of TC·HCl was decomposed within 10 min in 30 %–CFO@AO (0.2 g/L)/PMS (0.3 g/L) system, and the corresponding kinetic rate constant of 30 %–CFO@AO/PMS (0.417 min−1) was around 1.57 times higher than that of CuFe2O4/PMS (0.266 min−1), which indicating that the existence of synergistic catalysis between CuFe2O4 and Al2O3 enhanced the degradation of TC·HCl. Moreover, nano-sized CuFe2O4 were successfully anchored on the surface of Al2O3 because of FeOAl bond, which could account for the enhanced catalytic activity, superior pH flexibility, and high chemical stability and reusability of 30 %–CFO@AO. Quenching experimentals, electron paramagnetic resonance, and methyl phenyl sulfoxide (PMSO) chemical probe assays confirmed that both radical oxidation (OH) and non-radical oxidation (1O2 and Fe(IV)O) were proposed in the developed CFO@AO/PMS system, and OH played a key role in the process. Meanwhile, the PMS activation mechanism by CFO@AO composite was also analyzed based on the results of adsorption energy, which was calculated via DFT. Based on UPLC–MS technique, a possible degradation pathway for TC·HCl destruction in 30 %–CFO@AO/PMS system was proposed. The toxicity assessment showed that the catalytic degradation of TC·HCl in 30 %–CFO@AO/PMS system reduced the toxicity of most of degradation intermediates. Present work proved that CuFe2O4@Al2O3 composite is an efficient, environment-friendly, and recyclable heterogeneous catalyst for practical wastewater treatment via PMS activation.

Heat enhanced bisphenol AF degradation in CoFe2O4@BC activated peroxymonosulfate process: Mechanism and the role of inorganic anions

Carbon-based materials and heat activated peroxymonosulfate (PMS) have emerged as promising technologies for the remediation of contaminated water. This study investigated the feasibility of Bisphenol AF (BPAF) degradation by coupling CoFe2O4@BC catalyst with heat activated PMS technology. Heat significantly enhanced the catalytic performance of CoFe2O4@BC for PMS activation, resulting in 87.0 % removal of BPAF. Meanwhile, the effects of PMS concentration, CoFe2O4@BC catalyst dosage, initial pH, and the inorganic anions on BPAF degradation were investigated. The presence of HCO3− and HPO42− were found to enhance BPAF degradation by promoting PMS decomposition, while humic acid (HA) significantly inhibited BPAF removal. Electron paramagnetic resonance (EPR) and quenching experiments suggested that sulfate radicals (SO4•−) were the dominant reactive oxygen species (ROS) in the system, with hydroxyl radicals (•OH) and singlet oxygen (1O2) also contributing to BPAF degradation. Based on the Density Functional Theory (DFT) and intermediates analysis, two degradation pathways of BPAF were proposed, including hydroxylation and β-scission reactions. This work reveals the underlying mechanism of PMS activation under the coupling of heat with the CoFe2O4@BC system and presents a potential method for contaminants decomposition.

One-step synthesis of CoxS/Ni3S2@NF on 3D nickel foam with different sulfur sources as a novel heterogeneous catalyst efficient activation of peroxymonosulfate in lomefloxacin degradation

In this study, we have successfully synthesized Co9S8/CoS/Ni3S2 and Co3S4/Ni3S2 materials in situ on three-dimensional (3D) nickel foam (NF) substrates using a one-step hydrothermal process with different sulfur sources. Under the experimental conditions of catalyst dosage of 0.50 cm × 0.50 cm and peroxymonosulfate (PMS) dosage of 0.30 g/L, the Co3S4/Ni3S2@NF catalyst exhibited superior catalytic performance in activating PMS and degrading 91.0 % of lomefloxacin (LOM) as compared to 76 % of Co9S8/CoS/Ni3S2@NF. Both Co9S8/CoS/Ni3S2@NF and Co3S4/Ni3S2@NF showed excellent stability and performed effectively over a wide pH range. The Co9S8/CoS/Ni3S2@NF and Co3S4/Ni3S2@NF demonstrated significant differences in morphology, crystal plane properties, surface functional groups, chemical composition, elemental valence states, and coordination environment as revealed by XRD, TEM, SEM, FTIR, and XPS analyses, contributing to their distinct mechanisms and performance in LOM degradation. Additionally, the NF acted as a support carrier, exposing multiple active sites to enhance electron transport and providing a nickel source for the catalytic reaction. The degradation of LOM in the CoxS/Ni3S2@NF&PMS system was thoroughly investigated, revealing the involvement of SO4−, OH, 1O2, and electron transfer in the process. Additionally, the mechanism of PMS activation and the pathway of LOM decomposition in the reaction system were elucidated by theoretical analysis. Furthermore, the ecotoxicity of the by-products generated during LOM degradation was assessed using the ECOSAR software. In summary, the CoxS/Ni3S2@NF catalysts proved to be efficient, stable, easily prepared, environmentally friendly, and recyclable heterogeneous nanocomposites. It is a promising candidate for heterogeneous PMS process.

Facet-dependent peroxymonosulfate activity and mechanism of CuO for degradation of organic pollutants

CuO is currently used as an effective activator for peroxymonosulfate (PMS), which exhibits complex radical, nonradical, or both activation pathways. However, there exists a knowledge gap concerning the relationship between CuO exposed facets and the PMS activation pathway, which should require further investigation. This study employed a simple and facile hydrothermal method to controllably prepare CuO samples with exposed {010} and {001} facets (referred to as CuO-010 and CuO-001, respectively). The main aim was to further study the facet-dependent PMS activation mechanism. The experimental results showed that the CuO-001 exhibited significantly higher activation efficiency than the CuO-010 due to the different surface atomic arrangement. Furthermore, scavenging experiments and EPR analyses revealed that CuO-010 exhibited both radical (SO4•− and •OH) and non-radical (1O2) pathways, synergistically degraded tetracycline (TC) and 4-nitrophenol (4-NP). Conversely, the CuO-001 displayed non-radical (1O2) and Cu(Ⅲ) intermediates, collaborating to oxidize the degradation of TC and 4-NP. More importantly, the generated 1O2 species and Cu(Ⅲ) intermediates exhibited a preference for reacting with amino or phenolic compounds containing electron-rich functional groups. Moreover, the CuO-001 also showed excellent resistance to anion interference, stability, and compatibility of a wide pH range. The outcomes of this study provide new insights into the comprehensiveness facet-dependent activation of PMS and the design of efficient metal oxide catalysts using the facet strategy for effective degradation of amino/phenolic pollutants in wastewater.

Electronic interaction between biochar and montmorillonite toward enhanced peroxymonosulfate activation

Biochar works as the catalyst for activating peroxymonosulfate (PMS) to produce highly oxidizing radicals to remove organic contaminants from wastewater, but its activity requires further improvement. Recent research demonstrates that the PMS activation performance of biochar is closely related to the oxygen-containing functional groups (OFGs). Therefore, biochar/montmorillonite (BC/Mt) composites are designed for activating PMS toward degrading tetracycline. The negative charge of Mt. induced the electron transfer form Mt. to BC, which increases the nucleophilicity of CO groups that promote the activation of PMS to •OH and SO4•− radicals. Meanwhile, the pyrolysis path of rice straw is tuned by Mt., and the amount of COO groups is increased from 8.99% to 9.79% that promotes the generation of 1O2. Moreover, electron paramagnetic resonance and quenching experiments reveal that the activation mechanism of PMS by the BC/Mt. is comprised of both the radical and the non-radical pathway. Consequently, the tetracycline degradation kinetics using the optimized BC/Mt. (0.117 min−1) is higher than either bare BC (0.0866 min−1) or bare Mt. (0.0258 min−1), highlighting the significance of the rational design of electrocatalysts toward the enhanced catalytic chemistry. This work provides a facile route to improve the catalytic performance of biochar by hybridizing with clay minerals and is of great significance to promote the practical application of PMS-based advanced oxidation processes.

Unravelling the activation mechanism of oxidants using copper ferrite nanopowder and its application in the treatment of real waters contaminated by phenolic compounds

Copper ferrites (CuFe2O4) nanopowder was prepared via hydrothermal method followed by annealing at 500 °C, and XRD, SEM, XPS and UPS were employed for its characterization. CuFe2O4 was tested for the catalytic degradation of bisphenol A (BPA) in the dark and under UVA light, both in the presence of peroxymonosulfate (PMS) or peroxydisulfate (PDS) as radical precursor under natural pH of 6.2. While the individual photo-induced processes i.e., photocatalysis (using CuFe2O4 alone) and photolysis of either PMS or PDS, exhibited limited efficiencies in BPA degradation, a significant increase of performance was observed by combining CuFe2O4 and UVA light with either PMS or PDS with a synergy effect of 3.8 and 34.1, respectively. Under the optimal conditions, employing 0.5 g/L of nanopowder, the degradation constant of 25 µM BPA was 0.211 min−1 with 2 mM of PMS and 0.018 min−1 with 2 mM of PDS, and resulted in the complete degradation of BPA within less than 20 min. The activation mechanism of PMS and PDS using CuFe2O4 was elucidated, revealing sulfate radicals as the primary reactive species in PMS-containing systems, whereas a predominantly non-radical pathway was observed in the presence of PDS. Indeed, advanced spectroscopic techniques indicated that surface copper played an important role in the non-radical pathway. Furthermore, the CuFe2O4/PMS/UVA system exhibited high performance in the degradation of different phenolic compounds including BPA, phenol and p-nitrophenol in real water matrices. These achievements were observed across different real water matrices with a particular emphasis on sewage treatment plant water.

Application of 3D hierarchical porous NiCo-spinel nanosheet array for enhancement of synergistic activation of peroxymonosulfate: Degradation, Intermediates, mechanism and degradation pathway of tetracycline

The rational design of the morphology and structure of bimetallic-based heterogeneous Fenton-like catalyst derived from metal-organic-frameworks (MOFs) for peroxymonosulfate (PMS) activation via a non-radical pathway is attractive but challenging. Herein, a spinel-type 3D hierarchical porous NiCo2O4 nanosheet array for the activation of PMS is rationally designed by surfactant-assisted interfacial engineering. The experimental results showed that the NiCo2O4/PMS system demonstrated remarkable oxidative degradation of tetracycline (TC) through 1O2 attack and electron transfer process. In literature, it was thought that the PMS activation process in above system is dominated by radical pathway. In this work, we employ surfactant modified-nanostructure engineering to design hierarchical mesoporous nanosheet array structures and combined them with intrinsic bimetallic synergy to enhance catalytic activity, and interestingly the strategy transformed the PMS activation pathway into a nonradical (1O2 and electron transfer)-dominated process. This is benefit from the favorable morphological and electronic structure of the designed catalysts to facilitate mass transfer and electron transfer processes. The system also possessed a broad spectrum for degrading other typical contaminants, and was effective in tolerating actual water matrix and pH changes, as well as resisting interference from anions and organic matter. Furthermore, the robust stability of the structure and catalytic activity make it promising for practical water treatment. It can be expected that this proposal will provide insights for the delicate structural design and the understanding of its PMS activation mechanism of bimetallic-based Fenton-like catalysts, as well as for the efficient degradation of emerging organic pollutants.

Novel MIL-68(Fe)/MoS2 composites promote peroxymonosulfate activation for efficiently removing Rhodamine B

The development of efficient catalysts to activate peroxymonosulfate (PMS) for pollutant degradation has captured tremendous attentions. Herein, a series of high-performance MIL-68(Fe)/MoS2 (68M) composite catalysts with Fe-Mo bimetallic active sites were synthesized. Several characterization results confirmed the successful preparation of these composite materials. The PMS activation by MIL-68(Fe)/MoS2 was systematically evaluated by degrading Rhodamine B (RhB). It was shown that the RhB removal rate could reach up to 99% within 15 min with catalyst and PMS dosage of 0.2 g/L and 0.4 mM, respectively. It could be attributed to the synergistic effects of Fe-site, Mo-site and S-vacancy. The RhB removal rate could achieve 91%− 99% under a broad PH range (2−10) in 68M-10/PMS system. The RhB removal efficiency still maintained higher-level (92.2%) after being used for five cycles, suggesting the outstanding reusability of 68M-10. The PMS activation mechanism was explored by XPS, EPR and the RhB degradation pathway was also proposed based on HR-MS results. Above results highlighted the bright application prospect of the synthesized catalysts in solving the increasing dye crisis.

Sliver-doped α-MnO2 to enhance peroxymonosulfate activation for efficient degradation of sulfamethoxazole: Cooperation between radical and non-radical mechanisms

The application of metal doping has emerged as a prominent approach for modifying transition-metal-based heterogeneous catalysts in activating peroxymonosulfate (PMS). Herein, silver-doped α-MnO2 (Ag-α-MnO2) was synthesized via a one-step hydrothermal approach and utilized for activating PMS to degrade sulfamethoxazole (SMX). The catalyst was systematically characterized and examined to determine that the efficientdispersionof Ag increased thespecific surface area and pore volume of α-MnO2. The degradation experiments demonstrated that SMX could be efficiently degraded by a combination of PMS and Ag-α-MnO2 within 60 min. The apparent kinetic rate constant was 0.039 min−1, which was approximately ten times higher than that of α-MnO2. The impacts of external water conditions on catalytic performance and the stability of Ag-α-MnO2 were subsequently investigated. Density functional theory calculations revealed that Ag as a crucial active center reduced the PMS adsorption energy, promoted electron transfer, and orchestrated electron distribution. EPR spectra, quenching experiments, electrochemical tests, and XPS analysis were performed to validate the radical and non-radical mechanisms, including SO4−, OH, O2− and 1O2. The two redox cycles of Ag+/Ag0 and Mn4+/Mn3+ on the surface of Ag-α-MnO2 contributed to the activation of PMS. Additionally, probable degradation pathways for SMX were presented. This study provides an initially valuable insight into the cooperative mechanism of PMS activation for SMX degradation employing Mn-based catalysts doped with precious metal silver.

Design of active dual atom Ni-Co-2H-MoS2 catalyst: Synergistic effect of Ni-adsorption and co-catalysis for activating peroxymonosulfate

Peroxymonosulfate (PMS)-based advanced oxidation processes synergistically activated by dual atom catalysts (DACs) have become a cutting-edge technology for environmental remediation. Herein, a Ni-Co-2H-MoS2 (NCMS) DAC was successfully prepared by introducing bimetals (Ni and Co) into the framework of the 2H-MoS2 co-catalyst through a host–guest strategy. The NCMS/PMS catalysis system exhibits significant decontamination performance for tetracycline, and its removal efficiency of 99.6% is 3.7 times and 4.0 times higher than that of the Ni-2H-MoS2/PMS and Co-2H-MoS2/PMS single atom catalysts, respectively. Besides, density functional theory (DFT) was employed to disclosure the role of the active sites of NCMS DAC, investigate the influence of heteronuclear diatomic doping on electron aggregation and delocalization, and analyze the mechanism of PMS activation and TC degradation. Experimental results and theoretical simulations demonstrate that Ni and Co atoms of NCMS exert a reasonable regulation effect on the coordination environment and electronic structure, thereby promoting PMS activation with a unique synergy mode. The introduction of Ni lowers the adsorption energy barrier of PMS on the DAC, facilitating subsequent PMS activation. Meanwhile, the interaction between Co and Mo accelerates valence restoration and evolution of Co2+/Co3+ and Mo4+/ Mo5+/ Mo6+, further improving catalytic activity. This work provides a novel strategy for the on-demand design of Fenton-like reactions by regulating microenvironment of the catalyst.

The activation mechanism of peroxymonosulfate and peroxydisulfate by modified hydrochar: Based on the multiple active sites formed by N and Fe

Modified hydrochar (NHC@Fe), with multiple functional groups and transition metal oxide-containing surface, was successfully synthesized by one-step hydrothermal method. The differences in its catalytic activity for peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation were studied in detail. Experimental and DFT studies showed that abundant active sites, namely, transition metals and functional groups on NHC@Fe provided multiple effective pathways for the activation of persulfate (PS). The NHC@Fe/PMS and NHC@Fe/PDS systems could degrade about 80% of tetracycline hydrochloride (TC) in 120 min and were found to be better than those modified by iron or nitrogen alone. This emphasized the advantage of N–Fe co-modification in persulfate activation. Although the Fe2+/Fe3+ cycle accelerated the activation, the activation of PMS mainly relied on Fe3+, whereas that of PDS mainly relied on Fe2+. Moreover, Fe–N, pyrrolic N, pyridine N, C–O, and O–CO groups also played a key role in the activation process, but the dominant action sites were not the same. Multiple free radicals, such as SO4•—, •OH, O2•—, and 1O2 were generated in PMS and PDS activation systems. 1O2 induced non-free radical pathway was mainly involved in the degradation of TC in both activation systems, but the generation pathway of 1O2 was more direct and rapid in the PDS system. This study provides detailed DFT models of the active sites activated by PMS and PDS and discusses the activation pathways of PMS and PDS along with the similarities and differences in ROS reaction mechanisms.

The utilization of microwaves in revitalizing peroxymonosulfate for tetracycline decomposition: optimization via response surface methodology

Abstract Antibiotic contamination in water has received significant attention in recent years for the reason that the residuals of antibiotics can promote the progression of antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs). It is difficult to treat antibiotics using conventional biological treatment methods. In order to investigate an efficient new method of treating antibiotics in water, in this study, microwave (MW) was employed in revitalizing peroxymonosulfate (PMS) to treat typical antibiotic tetracycline (TC). The Box–Behnken design (BBD) was applied to organize the experimental schemes. The response surface methodology (RSM) optimization was run to derive the best experimental conditions and validated using actual data. Moreover, the main mechanisms of PMS activation via MW were resolved. The results demonstrated that the relationship between TC removal rate and influencing factors was consistent with a quadratic model, where the P-value was less than 0.05, and the model was considered significant. The optimal condition resulting from the model optimization were power = 800 W, [PMS] = 0.4 mM, and pH = 6.0. Under such conditions, the actual removal of TC was 99.3%, very close to the predicted value of 99%. The quenching experiment confirmed that SO4•− and •OH were jointly responsible for TC removal.

Shape stability control of a 3D-printed clay/biochar-based monolith to support Fe catalyst for continuous levofloxacin degradation with low metal leaching

Disposing of wet solid waste sludge has become a prominent issue because it has high environmental risks. Herein, a clay/biochar-based monolith (CBM) is prepared using a three-dimensional (3D) printing design method. The CBM is loaded with iron (Fe) and used as a catalyst (Fe/CBM) to activate peroxymonosulfate (PMS) for degrading levofloxacin (LVF) in an aqueous solution. The monolith preparation process is inexpensive, and the monolith has designable flow paths that facilitate improved mass transport and material recycling. ZnCl2, as a chemical activator, is added to the 3D-printed slurry to improve the catalytic performance of Fe/CBM. Oscillatory stress sweep and frequency sweep tests prove that incorporating ZnCl2-containing sludge in the slurry effectively increases the elastic modulus and critical stress, improving structural stability and constructability. The slurry containing 10% sludge (S10%-Zn with 1 M ZnCl2), exhibits 30% higher static yield stress than the slurry containing only clay and water (S0%). Fe/CBM is prepared by loading Fe active sites onto the surface of CBM via an impregnation method, and it leaches very low amounts of Fe (<0.2 mg/L) and other heavy metals (e.g., Cd, and Pd, etc). Fe/CBM-S10%-Zn/PMS with 10% mass fraction of sludge exhibits much higher (∼80% at 20 min) degradation efficiency than Fe/CBM-S0%/PMS (∼15% at 20 min) and Fe/CBM-S10%/PMS (∼43% at 20 min). Combining with XPS results, when ZnCl2 is added to the slurry, the content of Fe2+ in the catalytic material increases, improving the catalytic performance. The PMS activation mechanism of Fe/CBM-S10%-Zn for LVF degradation is also discussed, which is ascribed to the radical and nonradical pathways. This provides new insights on how to recycle solid waste and make high-performance clay/biochar-based monolith catalysts for the continuous wastewater treatment.

In situ interfacial engineering modulated adsorption and electron transfer boosting peroxymonosulfate activation for micro-contaminates degradation over CoOx nanosheet

Cobalt-based oxides have attracted extensive attention in heterogeneous catalytic peroxymonosulfate (PMS) activation towards emerging pollutants degradation, while the improvement of their catalytic performance is still a severe challenge. Herein, a CoOx ultrathin nanosheet composed of in situ interfacial Co3O4 and CoO (CoOx-Ar-350) was synthesized and employed in PMS activation for micro-contaminates removal. The catalyst shows 100 % bisphenol A (BPA) conversion within 2 min ([BPA] = 20 mg/L, [Catalyst] = 20 mg/L, [PMS] = 200 mg/L) with a remarkable reaction rate of 2.69 min−1, which is 3.84 and 2.66 times of pure Co3O4 and CoO, respectively. Characterization and theoretical calculation results indicates that the interfacial synergy between Co3O4 and CoO could modulate the adsorption behavior and enhance the electron acceptance of PMS, which boosts the breaking of O-O bonds and the generation of reactive oxygen species (ROS) and thereby the pollutant removal efficiency. The ROS quenching and capture experiments demonstrate that the enhanced OH and 1O2 play significant contribution during the degradation process. This work provides a novel in situ interfacial engineering for the development of highly efficient catalyst and reveals the activity enhancement mechanism for PMS activation.

Key role of La in La@nZVI/rGO for the efficient and steady PMS activation towards ofloxacin degradation via a non-radical process

The nano zero-valent iron (nZVI)/peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are promising for removal of antibiotic contaminants in groundwater. However, the inherent defects of rapid passivation and inactivation limit the efficient and steady application of nZVI. Herein, the lanthanum@nZVI/rGO (La@nZVI/rGO) was synthesized in which nZVI was coated with La and distributed evenly on reduced graphene oxide (rGO) matrix. The introduction of La coating protected the nZVI from direct contact with PMS molecules thus the La@nZVI/rGO appeared efficient and steady activization of PMS to degrade ofloxacin (OFX) without rapid inactivation. The removal rate was promoted to 96.5 % compared with the uncoated nZVI/rGO (only 85.2 %). The degradation reaction represented steady and continuous activation of PMS with pseudo-first-order kinetics (0.0451 min−1). While the two-stage kinetics of nZVI/rGO/PMS with initial 0.2581 min−1 and instant 0.0024 min−1 resulted from the rapid inactivation of nZVI. The reaction of La@nZVI/rGO/PMS exhibited minimal leaching of Fe ions (less than 1.8 µg/L) while it reached 6.4 mg/L in nZVI/rGO/PMS. XRD and XPS analyses further demonstrated the excellent durability of La@nZVI/rGO and the obvious passivation of nZVI/rGO. ESR and quenching tests confirmed that La coating regulated the PMS activation and ROS generation mechanism. The degradation was dominated by 1O2-induced non-free radical process in La@nZVI/rGO/PMS system and different from radical oxidation in nZVI/rGO/PMS. Moreover, the dissolved oxygen and XPS analysis revealed the important role of La coating and oxygen vacancy in the catalytic degradation. This work could provide a novel understanding of the nZVI with protective coating in AOPs environmental remediation.

Efficient peroxymonosulfate activation by Aurivillius phase Bin+1Fen-3Ti3O3n+3(n = 4, 5, 6) for wastewater purification

Aurivillius phase layered perovskites, Bin+1Fen-3Ti3O3n+3(n = 4, 5, 6), have been deemed as promising photocatalysts for degrading organic pollutants in wastewater. However, the inferior photocatalytic performance has greatly limited its application. Here, Bin+1Fen-3Ti3O3n+3 (n = 4, 5, 6) nano-shelves were fabricated and applied as heterogeneous photocatalysts in peroxymonosulfate (PMS) activation for tetracycline hydrochloride degradation. Compared with Bin+1Fen-3Ti3O3n+3(n = 4, 5, 6), the Bin+1Fen-3Ti3O3n+3(n = 4, 5, 6)/PMS system demonstrated an excellent enhancement for tetracycline hydrochloride removal under visible light illumination. Among the synthesized photocatalysts, Bi7Ti3Fe3O21/PMS showed the highest catalytic activity, with the calculated kinetic constant reaching as high as 0.0394 min−1, which was about 78.8 higher than that of Bi7Ti3Fe3O21. The improved tetracycline hydrochloride degradation performance of Bi7Ti3Fe3O21/PMS is attributed to the presence of abundant oxygen vacancies in Bi7Ti3Fe3O21, which can not only boost the separation of electron-hole pairs but also facilitate PMS activation and radical generation. Besides, the scavenging experiments and electron spin resonance analysis showed that sulfate radicals, superoxide radicals, hydroxyl radicals, and holes could effectively degrade tetracycline hydrochloride. Overall, these findings are beneficial for understanding the mechanism of PMS activation by Aurivillius phase layered perovskites-based catalysts and are helpful for the practical application of sulfate-based technology for wastewater purification.

Enhanced activation of peroxymonosulfate by Fe/N co-doped ordered mesoporous carbon with dual active sites for efficient removal of m-cresol

The novel Fe-N co-doped ordered mesoporous carbon with high catalytic activity in m-cresol removal was prepared by urea-assisted impregnation and simple pyrolysis method. During the preparation of the Fe-NC catalyst, the complexation of N elements in urea could anchor Fe, and the formation of C3N4 during urea pyrolysis could also prevent migration and aggregation of Fe species, which jointly improve the dispersion and stability of Fe. The FeN4 sites and highly dispersed Fe nanoparticles synergistically trigger the dual-site peroxymonosulfate (PMS) activation for highly efficient m-cresol degradation, while the ordered mesoporous structure of the catalyst could improve the mass transfer rate of the catalytic process, which together promote catalytic degradation of m-cresol by PMS activation. Reactive oxygen species (ROS) analytic experiments demonstrate that the system degrades m-cresol by free radical pathway mainly based on SO4-· and ·OH, and partially based on ·OH as the active components, and a possible PMS activation mechanism by 5Fe-50 for m-cresol degradation was proposed. This study can provide theoretical guidance for the preparation of efficient and stable catalysts for the degradation of organic pollutants by activated PMS.

Co3O4 electronic-structure tuning via Se doping for peroxymonosulfate activation: Synergy of reactive-oxygen species generation and adsorption–desorption strength

Increasing peroxymonosulfate (PMS) activation efficiency by Co3O4 to produce more reactive sites remains a challenge. Here, we report Se doping to simultaneously tune oxygen vacancy densities, Co2+ active site levels, and the Co3O4 3d-band center for activating PMS to degrade levofloxacin (LEV). The Se-doped Co3O4 (Se@Co3O4) was fabricated by pyrolyzing a mixture of Se powder and Co3O4 precursors. It had many more Co2+ active sites and oxygen vacancies relative to Co3O4. This favored generation of reactive oxygen species that degraded LEV in bulk solution. Density functional theory calculations revealed a downshift of the Co 3d-band in Se@Co3O4 with an enhanced electron-donating ability and an optimized adsorption–desorption strength, which increased reactive oxygen production and subsequent leave from hetero-surface to extinct LEV in bulk solution. Se@Co3O4 exhibited over 95% degradation of 10 mg/L LEV with 0.2 g/L PMS activated within 25 min at 25 °C, while Co3O4 exhibited 20% degradation under the same conditions. The first-order rate constant for LEV degradation by Se@Co3O4 was approximately 42 times that of Co3O4, and it exhibited good PMS activation over the pH range 5.0–9.0. LEV degradation conditions and effects of water matrices were optimized and explored, respectively. The Se@Co3O4/PMS system could still degrade over 85% of LEV after five cycles, as well as pefloxacin, p-nitrophenol, tetracycline and rhodamine B. This suggests its excellent universality. The potential mechanism of PMS activation by the Se@Co3O4 and probable LEV degradation routes were discussed based on the outcomes of active reactive species tests and LEV degradation intermediates confirmed by liquid chromatography-mass spectrometry. This work revealed that Se doping promoted electronic modulation in Se@Co3O4 for PMS activation, and indicated potential high-performance Fenton-like catalysts.

Heterogeneous Fe-Co dual-atom catalyst outdistances the homogeneous counterpart for peroxymonosulfate-assisted water decontamination: New surface collision oxidation path and diatomic synergy.

Heterogeneous catalysts lag far behind their homogeneous counterparts in activating peroxymonosulfate (PMS) for water decontamination due to the low site intrinsic activity and sluggish mass transfer. The single-atom catalyst can bridge the gap between heterogeneous and homogeneous catalysts, but the difficulty to break scaling relations originating from the site monotony restricts further efficiency upgradation. Herein through modulating the crystallinity of NH2-UIO-66, a porous carbon support with ultrahigh surface area (1721.71 m2 g-1) is obtained to anchor the dual-atom FeCoN6 site, which exhibits superior turnover frequency over single-atom FeN4 and CoN4 sites (13.07 versus 9.97, 9.07 min-1). The as-synthesized composite thus outperforms the homogeneous catalytic system (Fe3++Co2+) for sulfamethoxazole (SMZ) degradation, and the catalyst-dose-normalized kinetic rate constant (99.26L min-1 g-1) exceeds reported values by 1∼2 orders of magnitude. Moreover, only 20mg of the catalyst can run a fluidized-bed reactor to realize continuous zero discharge of SMZ in multiple actual waters for up to 8.33h. Unlike all reported reaction routes, the catalysis on the diatomic site follows a new surface collision oxidation path, i.e. the dispersed catalyst adsorbs PMS to generate surface-activated PMS with high potential, which collides with surrounding SMZ and directly seizes electron from it to induce pollutant oxidation. Theoretical calculation indicates that the enhanced activity of FeCoN6 site stems from the diatomic synergy, leading to stronger PMS adsorption, larger near-Fermi-level density of states and optimal global Gibbs free energy evolution. Overall, this work provides an effective strategy of constructing heterogeneous dual-atom catalyst/PMS process to achieve faster pollution control than homogeneous system, and sheds light on the interatomic synergetic mechanism for PMS activation.