Catalyst For Peroxymonosulfate Activation Research Articles

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

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

Enhanced removal of antibiotic-resistant bacteria and resistance genes by three-dimensional electrochemical process using MgFe2O4-loaded biochar as both particle electrode and catalyst for peroxymonosulfate activation

In this study, MgFe2O4-loaded biochar (MFBC) was used as a three-dimensional particle electrode to active peroxymonosulfate (EC/MFBC/PMS) for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The results demonstrated that, under the conditions of 1.0 mM PMS concentration, 0.4 g/L material dosage, 5 V voltage intensity, and MFBC preparation temperature of 600 °C, the EC/MFBC600/PMS system achieved complete inactivation of E. coli DH5α within 5 min and the intracellular sul1 was reduced by 81.5 % after 30 min of the treatment. Compared to EC and PMS alone treatments, the conjugation transfer frequency of sul1 rapidly declined by 92.9 % within 2 min. The cell membrane, proteins, lipids, as well as intracellular and extracellular ARGs in E. coli DH5α were severely damaged by free radicals in solution and intracellular reactive oxygen species (ROS). Furthermore, up-regulation was observed in genes associated with oxidative stress, SOS response and cell membrane permeability in E. coli DH5α, however, no significant changes were observed in functional genes related to gene conjugation and transfer mechanisms. This study would contribute to the underlying of PMS activation by three-dimensional particle electrode, and provide novel insights into the mechanism of ARB inactivation and ARGs degradation under PMS advanced oxidation treatment.

Activation of peroxymonosulfate by CoS2 loaded air-laid cloth for rapid degradation of organic pollutants in a shallow continuous flow reactor

Activation of peroxymonosulfate by heterogeneous catalyst is an efficient process for organic pollutants removal. However, it is difficult for solid-liquid separation of the heterogeneous catalysts in slurry-like batch reaction. In this work, CoS2 particles were deposited onto an air-laid cloth (denoted as CoS2-ALC) and were used as a catalyst for activation of peroxymonosulfate (PMS). Unlike traditional slurry-like batch reaction forms, a shallow continuous flow reactor was designed for the installation of a CoS2-ALC, thereby improving the activation efficiency of persulfate and rapid solid-liquid separation. The degradation kinetics constant for carbamazepine (CBZ) by the CoS2-ALC/PMS process was 0.0748 min−1, which is 374, 150, 150 times higher than that the CoS2-ALC adsorption process, PMS/ALC oxidation process and PMS alone process, respectively. The significantly enhanced degradation efficiency was due to the S in CoS2 promoting the cycling of Co2+/Co3+, thereby enhancing the generation of free radical. Parameters such as CoS2 deposition amount, PMS concentration, water flow rate, water flow height, water flow direction, solution pH, humic acid and anions that affecting the degradation efficiencies were studied. In addition, the degradation by-products of CBZ as well as their toxicity were detected, and a possible degradation pathway were proposed. Finally, expanded outdoor experiments and cycling experiment demonstrated that the CoS2-ALC/PMS process is potentially useful in practical settings of wastewater treatment.

A novel strategy for efficient utilization of carbon residue from biomass gasification loaded NiCo2O4 to construct composite catalysts for activation of peroxymonosulfate to effectively remove antibiotics

Carbon residue (CR) derived from biomass gasification is a type of solid waste discharged from the biomass gasifier. CR is a carbon-rich material with a large specific surface area. Herein, NiCo2O4 nanoparticles were generated in situ on CR via a facile solvothermal method and the NiCo2O4-CR (NCCR) composite catalysts were prepared via solvothermal synthesis followed calcination method. The catalytic activity of NCCR was investigated by activating peroxymonosulfate (PMS) for the ciprofloxacin (CIP) degradation. The NCCR/PMS system exhibited the degradation efficiency, TOC removal efficiency, and removal reaction rate constant (k) of 93.86 %, 44.09 %, and 0.049 min−1 for CIP in 60 min, respectively, which were 1.17, 1.21 and 1.20 times of those in the NiCo2O4/PMS system, suggesting that CR had a positive impact on the improvement of the catalytic properties of NiCo2O4. Significantly, NCCR showed remarkable performance in terms of pH adaptation range, resistance to environmental disturbances, reusability, and other contamination applications. SO4•–, O2•– and 1O2，as the dominant reactive oxygen species, disrupt the molecular structure of CIP. PMS activation with NCCR mainly form free radicals and non-free radicals catalyzed by the redox couples of Co (III)/Co (II) and Ni (III)/Ni (II). Specially, Co (IV) = O also form and participate in the CIP degradation via a non-free radical pathway. Three possible degradation pathways of CIP were suggested by the degradation intermediates. The CIP degradation in the NCCR/PMS system was a process of reducing toxicity, protecting water ecosystem. The study provides a method to improve the catalytic properties of transition metal for activating PMS to purify antibiotic contamination wastewater, and opens a novel insight to deal with the solid waste from biomass gasification.

Undaria pinnatifida (wakame)-derived Fe, N co-doped graphene-like hierarchical porous carbon as highly efficient catalyst for activation of peroxymonosulfate (PMS) toward degradation of tetracycline (TC)

The use of biomass as a catalyst offers a cost-effective and efficient approach for various processes, including the activation of peroxymonosulfate (PMS) to degrade contaminants. In this study, we successfully obtained Fe and N co-doped graphene-like hierarchical porous structure carbon (Fe-N/BC) by using undaria pinnatifida (wakame) as the precursor. The Fe-N/BC catalyst was utilized to activate PMS and degrade tetracycline (TC). Characterization results demonstrated an even distribution of Fe and N on the surface of the porous structure carbon. Compared to BC@PMS and N/BC@PMS, the Fe-N/BC@PMS system exhibited excellent degradation performance, achieving an 83.9 % degradation of TC in just 5 min with an ultralow catalyst dosage (Ca = 0.05 g/L) and a high TC concentration (TC = 0.03 g/L). Furthermore, experiments on radicals quenching and electron paramagnetic resonance (EPR) analysis indicated that singlet oxygen (1O2), a non-radical species, was demonstrated as the primary reactive oxygen species (ROS). The degradation mechanical analysis suggested that zero-valent iron (Fe0), pyridinic N, graphitic N, and Fe-Nx in the Fe-N/BC were the reason for the high catalytic activity. Moreover, the degradation pathways of TC were suggested through the use of LC-MS. Additionally, the ECOSAR system was employed to assess the toxicity of the intermediate products. This study reveals the active site and its mechanism in Fe-N composite biocarbon catalysts, providing a new method for synthesizing algal biocarbon catalysts.

Co-catalytic of aluminosilicate stabilized cobalt for peroxymonosulfate activation to degrade levofloxacin

Stabilization of Co was essential to address its pollution. In this work, geopolymerization was used to stabilize the Co2+ in the presence of alumina-silicate under hydrothermal process, in which the Co2+ is hypothesized to be a substitute of cation to balance the charge. Then the Co2+ could be incorporated into the geopolymer stably being named as AlxSiyCoz-T. Interestingly, the Co2+ stabilized AlxSiyCoz-T was recycled and reused for peroxymonosulfate (PMS) activation. The stability and catalytic activity of the AlxSiyCoz-T in PMS activation was evaluated. Results showed that the alumina and silicate geopolymerization played positive role in Co2+ stabilization, what were determined by the molar ratio of alumina to silicate, hydrothermal process. Besides, the AlxSiyCoz-T performed favorable activity in PMS activation for LEV degradation with an efficiency of 98.84 % and rate constant of 0.1154 min−1. In this case, the Co2+ was the main catalyst in PMS activation, while the alumina-silicate geopolymerization not only contributed to Co2+ stabilization, but also resulted in the formation of oxygen vacancy. Then the co-catalytic of alumina-silicate in PMS activation was understood by the synergy factor. The Co2+ leaching efficiency of AlSi2Co4-200 is only 0.011 %, confirming the heterogeneous catalytic in PMS activation. The AlxSiyCoz-200 performed favorable stability that could be used for five cycles at least. 1O2, SO4−• and •OH contributed to LEV degradation. Thus, the alumina and silicate geopolymerization could play important role in stabilization and co-catalytic for activating PMS, performing the dual effect on waste treatment and resource recycle.

NiCo2N nanosheets catalyzed peroxymonosulfate activation to generate 1O2 and SO4•- for efficient pollutant degradation: The role of nitrogen atoms

Advanced heterogeneous catalysts are essential for enhancing peroxymonosulfate (PMS) activation. Herein, a novel and highly highly-efficient PMS activation catalyst, NiCo2N nanosheets (NiCo2N NS), is reported. Owing to the strong electron transfer ability of Ni-N and Co-N, the NiCo2N NS/PMS system exhibit outstanding degradation performance and high cycling stability (100 % degradation after four cycles). The Co 3d orbital electrons in NiCo2N are closer to the to the Fermi level than that in NiCo2O4 NS, resulting in its higher chemical reactivity with PMS. When PMS is adsorbed onto Ni-N and Co-N sites through a “bridge” mode, the O-O bond is broken instantaneously to generate SO4•- and HO*. The formed HO* is then deprotonated to O*, followed by a reaction with another O* to generate 1O2. This study reports the first use of transition-metal nitride as a heterogeneous catalyst in PMS activation and provides insights into the key role of N atoms.

Co3O4@ZIF-67 core–shell heterogeneous catalyst for degradation of dye contaminants

Advanced oxidation processes based on sulfate radicals (SR-AOPs) are gaining more and more attention for their efficient treatment of refractory organic contaminants, and the rational design of catalyst is the key for the effectiveness of the method. In this paper, a Co3O4@ZIF-67 core–shell heterogeneous catalyst for activation of peroxymonosulfate (PMS) to degrade methylene blue (MB), a refractory dye, was prepared successfully. Under conditions of 20 mg/L catalyst, PMS 100 mg/L and and 25 °C temperature, nearly 100 % degradation of MB (10 mg/L) occured within 5 min, indicating that the core–shell catalyst possessed excellent catalytic performance. Furthermore, this core–shell structure provided stability for the nanoparticles (NPs) as less leaching of Co ions was observed. To identify the reactive species involved, quenching tests and electron paramagnetic resonance (EPR) were carried out. The results found that radical species including •OH, SO4∙- and non-radical (1O2) contributed to the degradation of MB and 1O2 was the leading one. Some important parameters, such as PMS and Co3O4@ZIF-67 doses, were explored and evaluated. Moreover, cycling study was conducted and Co3O4@ZIF-67 showed good recyclability. This work puts forward an idea of developing high-performance catalysts with structure more stable.

Carbon Nanotube-Supported FeCo2O4 as a Catalyst for an Enhanced PMS Activation of Phenol Removal

Peroxymonosulfate (PMS) activation has gained increasing attention for its water remediation. In this work, carbon nanotube-supported FeCo2O4 nanoparticles (FeCo2O4/CNT) were prepared and showed tremendous potential as a catalyst for PMS activation. The synergistic effect between FeCo2O4 and CNT in FeCo2O4/CNT promotes its better catalytic performance than individual CNT or FeCo2O4. The synthesized FeCo2O4/CNT could reach 100% phenol removal with a k value of 0.30 min−1 within 15 min ([PMS] = 0.3 g L−1, [FeCo2O4/CNT] = 0.3 g L−1). FeCo2O4/CNT can adapt well to a wide pH range (4–9) and a complex water component (with inorganic ions or organic matter). Moreover, the catalytic mechanism investigation suggested that both radical and non-radical pathways are accountable for the efficient removal of phenol.

Cobalt nanoparticles supported on porous carbon nanofiber as efficient catalyst for heterogeneous activation of peroxymonosulfate towards the degradation of organic pollutants

In this work, cobalt-porous carbon nanofiber (Co-PCNF) was developed as a robust catalyst for the activation of peroxymonosulfate (PMS) to eliminate organic pollutants in water. Carbamazepine (CBZ) was severed as the probe to examine the ability of Co-PCNF for activating PMS. The microporous honeycomb-like structure endowed Co-PCNF with excellent catalytic activity to activate PMS as evidenced by the rapid removal rate of CBZ (0.1269 min–1) in the existence of 0.1 g/L Co-PCNF and 0.25 g/L PMS. The degradation rate of CBZ can be maintained at 89 % after five runs and the leaching concentration of Co2+ can be neglected, suggesting the extraordinary stability of Co-PCNF reuse. Meanwhile, this system was used to degrade other organic contaminates and achieved satisfactory results, confirming the good universality of Co-PCNF/PMS system. Furthermore, the effects of catalyst and PMS dosage, pH, and co-existing ions on CBZ removal were discussed. Finally, radical identification results prove that SO4·–,·OH, 1O2, and O2·– are generated during the process of PMS activation, and a possible activation mechanism is proposed based on the aforementioned findings. This study can not only provide a method for organic pollutants elimination, but also offer a reference for designing robust heterogeneous PMS catalysts.

Phosphorus doping significantly enhanced the catalytic performance of cobalt-single-atom catalyst for peroxymonosulfate activation and contaminants degradation

Increasing studies have been conducted to explore strategies for enhancing the catalytic performance of metal-doped C-N-based materials (e.g., cobalt (Co)-doped C3N5) via heteroatomic doping. However, such materials have been rarely doped by phosphorus (P) with the higher electronegativity and coordination capacity. In current study, a novel P and Co co-doped C3N5 (Co-xP-C3N5) was developed for peroxymonosulfate (PMS) activation and 2,4,4′-trichlorobiphenyl (PCB28) degradation. The PCB28 degradation rate increased by 8.16–19.16 times with Co-xP-C3N5 compared to conventional activators under similar reaction conditions (e.g., PMS concentration). The state-of-the-art techniques, including X-ray absorption spectroscopy and electron paramagnetic resonance etc., were applied to explore the mechanism of P doping for enhancing Co-xP-C3N5 activation. Results showed that P doping induced the formation of Co-P and Co-N-P species, which increased the contents of coordinated Co and improved Co-xP-C3N5 catalytic performance. The Co mainly coordinated with the first shell layer of Co1-N4, with successful P doping occurring in the second shell layer of Co1-N4. The P doping favored electron transfer from the C to N atom near Co sites and thus strengthened PMS activation owing to its higher electronegativity. These findings provide new strategy for enhancing the performance of single atom-based catalysts for oxidant activation and environmental remediation.

Synthesis of MMT−CuFe2O4 Composite as a Peroxymonosulfate Activator for the Degradation of Reactive Black 5

AbstractCopper ferrite nanoparticles loaded on montmorillonite (MMT−CuFe2O4) were prepared by co‐precipitation method and applied as catalyst for activation of peroxymonosulfate (PMS) in degradation of reactive black 5 (RB5). The maximum removal efficiency of RB5 completely depends on the operating parameters and the highest removal percentage was obtained at MMT−CuFe2O4 dosage of 250 mg/L, PMS concentration of 4 mM, initial RB5 concentration of 50 mg/L and time of 15 min. The presence of anions such as Cl−, NO3−, HCO3−, and SO42− showed a significant limitation in the degradation of RB5 in the MMT−CuFe2O4/PMS system. Trapping experiments showed that ⋅OH and SO4⋅− radicals were involved in the catalytic degradation of RB5, however ⋅OH is the major specie in the catalysis system. Consecutive cycles were considered for testing the reusability of MMT−CuFe2O4; its results showed the stability of five consecutive cycles. The toxicity test was evaluated using Daphnia magna and the results illustrated a substantial drop in the toxicity of the solution treated. The significant reduction of TOC during RB5 degradation and the production of SO42−, NH4+ and NO3− confirm the proper progress of pollutant mineralization. The high catalytic performance of the catalyst in a short time compared to other removal systems emphasizes that MMT−CuFe2O4 can be suggested as a promising catalyst for the degradation of RB5 from aqueous solutions.

Autocatalytic formed bamboo-like N-doped carbon nanotubes encapsulated with Co nanoparticles as highly efficient catalyst for activation of peroxymonosulfate toward degradation of tetracycline

Co-based catalysts activated peroxymonosulfate (PMS) for organic pollutants degradation has been extensively studied. Co dissolution of Co-based catalysts would result in secondary environmental contamination. Co autocatalysis the formation of bamboo-like N-doped carbon nanotubes to confine Co nanoparticles (Co NPs). Herein, the N-doped carbon nanotubes encapsulated Co (Co@NCTs) were successfully synthesized through a one-step high-temperature calcination method at different temperatures. Co@NCTs-800 exhibited excellent catalytic performance, the degradation efficiency of tetracycline (TC) could reach 94.5% with only 0.05 g/L catalyst in activating PMS. In addition, the encapsulation of carbon nanotubes inhibits the dissolution of Co, the Co2+ dissolution was 0.0594 mg/L in 40 min in the system of Co@NCTs-800/PMS. Free radical quenching tests, electron paramagnetic resonance, and electrochemical measurements revealed that the non-radical route was dominated by tetracycline degradation, with singlet oxygen (1O2) and electron transfer as the principal active species. The N-doped carbon nanotubes can effectively encapsulate Co, which not only reduces the leaching of Co but also play a synergistic role with Co in degrading organic pollutants. In addition to this, the degradation mechanism and pathways of TC were further investigated. The Co@NCTs-800/PMS system was also able to successfully decompose a variety of organic contaminants, demonstrating that it has real application potential in wastewater.

Indium-doped β-MnO2 catalyst for activation of peroxymonosulfate to generate singlet oxygen with complete selectivity

Singlet oxygen (1O2) has been regarded as an excellent active species for the effective degradation of pollutants. However, generating 1O2 with high selectivity still remains a significant challenge. Herein, 1O2 generation of 100% selectivity for peroxymonosulfate (PMS) activation was achieved by a strategy of indium-doped β-MnO2 catalyst, affording a dimethyl phthalate degradation rate of 93% within 180 min. Indium active sites served as the active center of the PMS adsorption, and the redox cycling of indium among different valances promoted PMS activation by breaking S–O bond. Density functional theory calculation results demonstrated that HSO5-could be easily adsorbed at indium site to generate 1O2 via effective electron transfer. The indium active sites and oxygen vacancies jointly regulated the PMS decomposition by a non-radical pathway with simultaneous 1O2 generation. This work developed a novel indium-doped β-MnO2 catalyst for complete selective generation of 1O2 for highly efficient degradation of pollutants.

A novel Fe/Mo co-catalyzed graphene-based nanocomposite to activate peroxymonosulfate for highly efficient degradation of organic pollutants

A novel 3D α-FeOOH@MoS2/rGO nanocomposite was successfully fabricated by a simple in situ hydrothermal method. It is a highly efficient heterogeneous catalyst in activation of peroxymonosulfate (PMS) for rapid degradation of rhodamine B (RhB), with 99.9% of RhB removed within 20 min. The introduction of rGO contributes to uniform dispersion and sufficient contact of α-FeOOH and MoS2 nanosheets. Highly active Mo(IV) enhances the reduction of Fe(III), improves Fe(III)/Fe(II) conversion and promotes the generation of O21, which ensures an improved catalytic activity. MoS2/rGO hybrid can effectively solve the problem of material reunion and make α-FeOOH exhibit excellent catalytic performance. The α-FeOOH@MoS2-rGO/PMS system is a co-catalytic system based on the active components of α-FeOOH and MoS2. The main reactive oxygen species in the α-FeOOH@MoS2-rGO/PMS system are O21, SO4.− and ⋅O2−, which contribute to a high reactivity over a wide range of pH (5–9). Besides, this system is highly resistant to anions (Cl−, SO42−) and natural organic matter (humic acid), and can be widely used for degradation of common organic pollutants. The α-FeOOH@MoS2/rGO is a promising Fenton-like catalyst for refractory organic wastewater treatment.

Confinement of ZIF-derived copper-cobalt-zinc oxides in carbon framework for degradation of organic pollutants

Developing efficient heterogeneous catalysts for peroxymonosulfate (PMS) activation is extraordinarily desirable in water purification. In this work, a well-defined core-shell copper-cobalt-zinc oxides consisting of Cu0.92Co2.08O4 and ZnCo2O4 wrapped by carbon (CuCoZnO/C) was fabricated by a simple one-step calcination using metal-organic frameworks (MOFs) as templates. The as-obtained catalysts were fully characterized and utilized to activate PMS for phenol degradation, and almost 100% degradation efficiency could be achieved within 10 min. The distinct hollow structure allowed the high instantaneous concentration of organic pollutant in a microenvironment, thus providing a driving force to improve the reaction rate. Owing to the mesoporous and adsorptive carbon as well as active Cu0.92Co2.08O4 shell, most SO4•− radical was confined to catalyst surface immediately once produced rather than release into the bulk solution, making the enriched reactant molecules contact active sites more easily. Further investigation found that both surface-bound SO4•− and 1O2 were dominantly participated in the catalytic process, achieving an ultrafast pollutant degradation. This work offered a new design for multiple complex oxides from MOFs and extended the development of Co-based heterogenous catalyst in PMS activation for the environmental remediation.

Ultrasonic treatment enhances the formation of oxygen vacancies and trivalent manganese on α-MnO2 surfaces: Mechanism and application

Catalytic activity is the main obstacle limiting the application of peroxymonosulfate (PMS) activation on transition metal oxide catalysts in organic pollutant removal. Herein, ultrasonic treatment was applied to α-MnO2 to fabricate a new u-α-MnO2 catalyst for PMS activation. Dimethyl phthalate (DMP, 10 mg/L) was almost completely degraded within 90 min, and the pseudofirst-order rate constant for DMP degradation in the u-α-MnO2/PMS system was ∼7 times that in the initial α-MnO2/PMS system. The ultrasonic treatment altered the crystalline and pore structures of α-MnO2 and produced defects on the u-α-MnO2 catalyst. According to the XPS, TG, and EPR results, higher contents of trivalent Mn and oxygen vacancies (OVs) were produced on the catalyst surfaces. The OVs induced the decomposition of PMS to produce 1O2, which was identified as the main reactive oxygen species (ROS) responsible for DMP degradation. The u-α-MnO2 catalyst presented great reusability, especially by ultrasonic regeneration of OVs toward the used catalyst. This study provides new insights into regulating OVs generation and strengthening catalyst activity in the PMS activation process for its application in water purification.

Built-in electric field mediated peroxymonosulfate activation over biochar supported-Co3O4 catalyst for tetracycline hydrochloride degradation

The strong electronic interaction between heterogeneous composite catalysts facilitates the charge separation and transfer, which is favorable for the enhancement of catalytic performance. Herein, the rape straw derived biochar (BC) supported ultrafine Co3O4 composites were synthesized for tetracycline hydrochloride (TC) degradation via activating peroxymonosulfate (PMS), and the built-in electric field (BIEF) driven catalytic degradation mechanism was proposed. The results indicated that 20 wt% Co3O4/BC catalyst could achieve 90% degradation efficiency of TC within 20 min, and demonstrated that BC not only served as a support to significantly inhibit the agglomeration of Co3O4 nanoparticles and improve the stability of catalyst, but also behaved as an activator of PMS to participate in the catalytic degradation reaction. Both radical pathway (SO4·-, ·OH and O2·-) and non-radical process (1O2 and direct electron transfer) were involved in the Co3O4/BC/PMS system, and the role of the latter is more prominent, in which Co2+/Co3+ redox cycle and C = O groups on the BC were the possible active sites. Furthermore, the density functional theory (DFT) calculations revealed that a BIEF pointing from BC to Co3O4 at the interface was formed, which could act as the internal driving force for electron transfer to accelerate the redox cycle of Co2+/Co3+ and induce the direct electron transfer, and thus resulting in the better degradation of TC. This work not only offered a mechanistic insight into synergistic effects of composite catalyst in PMS activation, but also provided a win–win strategy of realizing the resource utilization of agricultural waste and environmental remediation simultaneously.

Mechanistic insights into carbo-catalyzed persulfate treatment for simultaneous degradation of cationic and anionic dye in multicomponent mixture using plastic waste–derived carbon

Upcycling waste into value-added products for utilization in wastewater abatements has been explored in a number of treatment technologies. One such waste, single-use plastic, which poses significant adverse environmental and economic impact, has been chosen and converted into graphitic carbon to reduce the waste burden sustainably and economically. The sorptive and catalytic performance of synthesized plastic waste-derived carbon (PWC) was evaluated using brilliant green (BG) and eosin yellow (EY) as target pollutants. The adsorption capacity of PWC was very low for BG (7.41 mg/g) and EY (4.93 mg/g). The coupling of PWC with peroxymonosulfate (PMS) promoted dye degradation. Complete degradation of the dye, with ~61% reduction in TOC and ~95% reduction in toxicity, was achieved by oxidative treatment (initial concentration: 10 mg/L). The functionalities of PWC facilitated better electron transfer to PMS for its effective activation, which led to the production of SO4•- and OH•. The quenching study confirmed that the degradation of dyes was primarily due to SO4•-. Additionally, the pathways of dye degradation were proposed based on the intermediates identified. Thus, this study established the high potential of PWC as a metal-free catalyst in PMS activation for the abatement of organic pollutants.

Transition metal single-atom embedded on N-doped carbon as a catalyst for peroxymonosulfate activation: A DFT study

Single-atom catalysts perform excellently in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs), for which the generation of reactive oxygen species (ROS) is essential to the degradation of emerging organic pollutants in water. However, the detailed PMS activation mechanisms remain elusive. Density functional theory (DFT) calculation as a powerful approach can overcome the limitations of the experimental studies, providing a molecular-level perspective of catalytic process. This study conducted DFT calculations to clarify the electronic structures and PMS adsorption and activation mechanisms of a series of transition metal single-atom catalysts. According to the DFT study, significant electronic interaction and negative formation energy make nitrogen-doped carbon (N@C) supports suitable for stabilizing metal atoms (Me) to form MeN@C catalysts. As the active site, single metal atom adsorbs the oxygen atoms of PMS by electrostatic and magnetic interactions, and transfer electrons from MeN@C to activate PMS. Different adsorption configurations and the subsequent PMS activation lead to the generation of various ROS, including the SO4•- radical, •OH radical, singlet oxygen (1O2), high-valent metal-oxo species, and surface-activated PMS*. Electron transfer mediated by surface-activated PMS* may dominate in all MeN@C/PMS systems. The generation of free radicals can be difficult for some systems. High-valent metal-oxo species are readily formed by FeN@C/PMS and MnN@C/PMS, whereas 1O2 tends to be produced by CoN@C/PMS, NiN@C/PMS, and CuN@C/PMS. The findings will provide a theoretical basis for the design and synthesis of effective MeN@C catalysts for the AOPs to remove emerging organic pollutants from water and wastewater.