Electro-activating of peroxymonosulfate via boron and sulfur co-doped macroporous carbon nanofibers cathode for high-efficient degradation of levofloxacin

Lewis acid sites-regulated microscopic interface on graphite felt surface for enhanced heterogeneous electro-Fenton process: Formation of confinement effect and generation of singlet oxygen

The short lifetime and limited diffusion capability of hydroxyl radicals (•OH) restrict the further development of heterogeneous electro-Fenton (Hetero-EF) technology. In contrast, singlet oxygen (1O2) demonstrates many advantages over •OH. In the present work, a porous confined graphite felt (PCGF) was prepared through in-situ etching of nickel oxide (NiOx) and used as the cathode for Hetero-EF, aiming at constructing a 1O2-dominated Hetero-EF system to enhance its degradation performance for various antibiotic pollutants in wastewater. The in-situ etching of NiOx introduced abundant Lewis acid sites within the porous architecture of PCGF, enabling the modulation of electrode's interfacial properties and selective adsorption of Lewis basic substances, thereby generating a characteristic "confinement effect". This enhanced interfacial interaction achieved 50.23 % adsorptive removal of oxytetracycline within 30 min without external power supply, facilitating the enrichment of pollutants at the cathode interface. Meanwhile, the "confinement effect" significantly enhanced the utilization efficiency of reactive oxygen species and the selectivity of 1O2. The PCGF electrode demonstrated excellent degradation performance across a wide range of pH and exhibited strong anti-interference capability. The results from radical quenching experiments and density functional theory calculations revealed that the generation of 1O2 proceeded through multiple routes involving hydrogen peroxide, •OH, and superoxide anions. The present study presents a novel strategy for advancing the development of 1O2-dominated Hetero-EF systems for treating antibiotic-containing wastewaters.

Spatially-confined removal of intracellular antibiotic resistance genes via electrochemical membranes: Influence of pore size on electrical stimulation and exogenous reactive oxygen species oxidation

Electrochemical membranes (EMs), as one of the most promising novel materials, offer the potential to eliminate antibiotic resistance genes (ARGs). However, there remain significant knowledge gaps regarding the removal pathways of ARGs within the spatially-confined pores of EMs, particularly for intracellular ARGs (iARGs). In this study, EMs with different pore sizes were utilized to treat synthetic water samples containing Escherichia coli genetically engineered with ARGs. It was thereby revealed that the removal efficiencies and pathways of iARGs are closely associated with the spatially-confined pores of EMs. Specifically, EMs with smaller pore sizes (e.g., 10 µm) are capable of removing more iARGs, mainly due to the synergistic effects of physical collision, direct electrical stimulation and exogenous reactive oxygen species (ROS) oxidation, with the latter two mechanisms being the predominant drivers. In contrast, EMs with larger pore sizes (e.g., 40 µm), show lower iARGs removal efficiencies. This is because the degradation of iARGs in these EMs relied more on exogenous ROS oxidation. In the case of large pores, cells can pass through the EMs without colliding with the pore walls, resulting in reduced exposure to physical collision and electrical stimulation. Additionally, the study found that 1O2 generated by EMs can penetrate into cells and opportunistically oxidize iARGs prior to their release into the extracellular environment. These findings provide valuable insights into the mechanisms and potential optimization strategies for EMs in curbing the horizontal transfer of ARGs.

Degradation of phenol by metal-free electro-fenton using a carbonyl-modified activated carbon cathode: Promoting simultaneous H2O2 generation and activation

The low yield of hydrogen peroxide, narrow pH application range, and secondary pollution due to iron sludge precipitation are the major drawbacks of the electro-Fenton (EF) process. Metal-free electro-Fenton technology based on carbonaceous materials is a promising green pollutant degradation technology. Activated carbon cathodes enriched with carbonyl functional groups were prepared using a two-step annealing method for the degradation of phenol pollutants. The •OH in the activation process of H2O2 were identified using the EPR test technique. The action mechanism of carbonyl groups on H2O2 activation was investigated in conjunction with density functional theory (DFT) calculations. The EPR tests demonstrated that the modified activated carbon could promote the in-situ activation of H2O2 to •OH. And the results of material analysis and DFT showed that C=O could facilitate the activation of hydrogen peroxide through the electron transfer mechanism as an electron-donating group. Electrochemical tests showed that both the oxygen reduction activity and 2e-ORR selectivity of the modified activated carbons were significantly improved. Compared with the original activated carbon cathode and EF, the degradation efficiency of phenol in the ACNH-1000/GF cathode was increased by 58.10% and 45.61%, respectively. Compared with EF, ACNH-1000/GF metal-free electro-Fenton effectively expands the pH application range, and is proven to be less affected by solution initial pH, while avoiding secondary pollution. The metal-free electro-Fenton system can save more than a quarter of the cost of EF system. This study has a deep understanding of the reaction mechanism of the carbonyl modified activated carbon, and provides valuable insights for the design of metal-free catalysts, so as to promote its application in the degradation of organic pollutants.

Unveiling electron transfer and radical transformation pathways in coupled electrocatalysis and persulfate oxidation reactions for complex pollutant removal

The degradation of multiple organic pollutants in wastewater via advanced oxidation processes might involve different radicals, of which the types and concentrations vary upon interacting with different pollutants. In this study, electrochemical activation of peroxymonosulfate (E/PMS) using advanced activated carbon cloth (ACC) as electrode was applied for simultaneous degradation of mixed pollutants, e.g., metronidazole (MNZ) and p-chloroaniline (PCA). 92.5 % of MNZ and 91.4 % of PCA can be degraded at the cathode and anode at a low current density and PMS concentration, respectively. The rate constants for the simultaneous removal of MNZ and PCA in the E/PMS/MNZ(PCA) system were 118 times and 6 times higher than those in the sole PMS system, and 2.5 times and 1.6 times higher than those in the E/Na2SO4/MNZ(PCA) system, respectively. Different electrochemical characteristics, EPR spectra and radical quenching tests verified that the degradation of MNZ and PCA in the optimal system proceeded primarily through non-radical-dominated oxidation, involving electron transfer and 1O2 effect. The system also exhibited low energy consumption (0.215 kWh/m-3·order-1), broad operational pH range, excellent removal efficiency for water matrix, and low by-products toxicity, indicating its strong potential for practical applications. The ACC, with its super stable, low cost, and electrochemical activity, make it as a promising materials applicable in the E/PMS system for degradation of multiple pollutants. The study further elucidated the mechanism of pollutant interaction with electrode materials in terms of radical and non-radical transformation, providing fundamental insight into the application of this system for treatment of complex wastewater.

Performance of a polymerization-based electrochemically assisted persulfate process on a real coking wastewater treatment

Industrial wastewater should be treated with caution due to its potential environmental risks. In this study, a polymerization-based cathode/Fe3+/peroxydisulfate (PDS) process was employed for the first time to treat a raw coking wastewater, which can achieve simultaneous organics abatement and recovery by converting organic contaminants into separable solid organic-polymers. The results confirm that several dominant organic contaminants in coking wastewater such as phenol, cresols, quinoline and indole can be induced to polymerize by self-coupling or cross-coupling. The total chemical oxygen demand (COD) abatement from coking wastewater is 46.8% and the separable organic-polymer formed from organic contaminants accounts for 62.8% of the abated COD. Dissolved organic carbon (DOC) abatement of 41.9% is achieved with about 89% less PDS consumption than conventional degradation-based process. Operating conditions such as PDS concentration, Fe3+ concentration and current density can affect the COD/DOC abatement and organic-polymer yield by regulating the generation of reactive radicals. ESI-MS result shows that some organic-polymers are substituted by inorganic ions such as Cl-, Br-, I-, NH4+, SCN- and CN-, suggesting that these inorganic ions may be involved in the polymerization. The specific consumption of this coking wastewater treatment is 27 kWh/kg COD and 95 kWh/kg DOC. The values are much lower than those of the degradation-based processes in treating the same coking wastewater, and also are lower than those of most processes previously reported for coking wastewater treatment.

Exploration of the mechanism of levofloxacin removal by N-doped-induced interfacial micro-electric field-activated persulfate

The defects formed by N doping always coexist with pyrrole nitrogen (Po) and pyridine nitrogen (Pd), and the synergistic mechanisms of H2O2 production and PMS activation between the different Po: Pd are unknown. This paper synthesized MOF-derived carbon materials with different nitrogen-type ratios as cathode materials in an electro-Fenton system using precursors with different nitrogen-containing functional groups. Several catalysts with different Po: Pd ratios (0:4, 1:3, 2:2, 3:1, 4:0) were prepared, and the best catalyst for LEV degradation was FC-CN (Po: Pd=3:1). X-ray Photoelectron Spectroscopy (XPS) and density-functional theory (DFT) calculations show that the introduction of nitrogen creates an interfacial micro-electric field (IMEF) in the carbon layer and the metal, accelerates the electron transfer from the carbon layer to the Co atoms, and promotes cycling between the Fe3+/Co2+ redox pairs, with the electron transfer reaching a maximum at Po: Pd = 3:1. FC-CN (Po: Pd=3:1) achieved more than 95 % LEV degradation in 90 min at pH = 3-9, with a lower energy consumption of 0.11 kWh m-3 order-1. and the energy consumption of the catalyst for LEV degradation is lower than that of those catalysts reported. In addition, the degradation pathway of LEV was proposed based on UPLC-MS and Fukui function. This study offers some valuable information for the application of MOF derivatives.

Efficient degradation and mineralization of polyethylene terephthalate microplastics by the synergy of sulfate and hydroxyl radicals in a heterogeneous electro-Fenton-activated persulfate oxidation system

The presence of polyethylene terephthalate (PET) microplastics (MPs) in waters has posed considerable threats to the environment and humans. In this work, a heterogeneous electro-Fenton-activated persulfate oxidation system with the FeS2-modified carbon felt as the cathode (abbreviated as EF-SR) was proposed for the efficient degradation of PET MPs. The results showed that i) the EF-SR system removed 91.3 ± 0.9 % of 100 mg/L PET after 12 h at the expense of trace loss (< 0.07 %) of [Fe] and that ii) dissolved organics and nanoplastics were first formed and accumulated and then quickly consumed in the EF-SR system. In addition to the destruction of the surface morphology, considerable changes in the surface structure of PET were noted after EF-SR treatment. On top of the emergence of the O-H bond, the ratio of C-O/C=O to C-C increased from 0.25 to 0.35, proving the rupture of the backbone of PET and the formation of oxygen-containing groups on the PET surface. With the verified involvement and contributions of SO4•- and •OH, three possible paths were proposed to describe the degradation of PET towards complete mineralization through chain cleavage and oxidation in the EF-SR system.

Functional biochar accelerates peroxymonosulfate activation for organic contaminant degradation via the specific B-C-N configuration

Functional biochar designed with heteroatom doping facilitates the activation of peroxymonosulfate (PMS), triggering both radical and non-radical systems and thus augmenting pollutant degradation efficiency. A sequence of functional biochar, derived from hyperaccumulator (Sedum alfredii) residues, was synthesized via sequential doping with boron and nitrogen. The SABC-B@N-2 exhibited outstanding catalytic effectiveness in activating PMS to degrade the model pollutant, acid orange 7 (Kobs = 0.0655 min-1), which was 6.75 times more active than the pristine biochar and achieved notable mineralization efficiency (71.98%) at reduced PMS concentration (0.1 mM). Relative contribution evaluations, using steady-state concentrations combined with electrochemical and in situ Raman analyses, reveal that co-doping with boron and nitrogen alters the reaction pathway, transitioning from PMS activation through multiple reactive oxygen species (ROSs) to a predominantly non-radical process facilitated by electron transfer. Moreover, the previously misunderstood concept that singlet oxygen (1O2) plays a central role in the degradation of AO7 has been clarified. Correlation analysis and density functional theory calculations indicate that the distinct BCN configuration, featuring the BC2O group and pyridinic-N, is fundamental to the active site. This research substantially advances the sustainability of phytoremediation by offering a viable methodology to synthesize highly catalytic functional biochar utilizing hyperaccumulator residues.

A critical review of persulfate-based electrochemical advanced oxidation processes for the degradation of emerging contaminants: From mechanisms and electrode materials to applications

The persulfate-based electrochemical advanced oxidation processes (PS-EAOPs) exhibit distinctive advantages in the degradation of emerging contaminants (ECs) and have garnered significant attention among researchers, leading to a consistent surge in related research publications over the past decade. Regrettably, there is still a lack of a critical review gaining deep into understanding of ECs degradation by PS-EAOPs. To address the knowledge gaps, in this review, the mechanism of electro-activated PS at the interface of the electrodes (anode, cathode and particle electrodes) is elaborated. The correlation between these electrode materials and the activation mechanism of PS is systematically discussed. The strategies for improving the performance of electrode material that determining the efficiency of PS-EAOPs are also summarized. Then, the applications of PS-EAOPs for the degradation of ECs are described. Finally, the challenges and outlook of PS-EAOPs are discussed. In summary, this review offers valuable guidance for the degradation of ECs by PS-EAOPs.

Simultaneous enhanced antibiotic pollutants removal and sustained permeability of the membrane involving CoFe2O4/MoS2 catalyst initiated with simple H2O2 backwashing

Membranes for wastewater treatment should ideally exhibit sustainable high permeate production, enhanced pollutant removal, and intrinsic physical rejection. In this study, CoFe2O4/MoS2 serves as a non-homogeneous phase catalyst; it is combined with polyether sulfone membranes via liquid-induced phase separation to simultaneously sustain membrane permeability and enhance antibiotic pollutant degradation. The prepared catalytic membranes have higher pure water flux (329.34 L m-2 h-1) than pristine polyethersulfone membranes (219.03 L m-2 h-1), as well as higher mean pore size, porosity, and hydrophilicity. Under a moderate transmembrane pressure (0.05 MPa), tetracycline (TC) in synthetic and real wastewater was degraded by the optimal catalytic membrane by 72.7 % and 91.2 %, respectively. Owing to the generation of the reactive oxygen species (ROS) during the Fenton-like reaction process, the catalytic membrane could exclude the natural organics during the H2O2 backwash step and selectively promote fouling degradation in the membrane channel. The irreversible fouling ratio of the catalyzed membrane was significantly reduced, and the flux recovery rate increased by up to 91.6 %. A potential catalytic mechanism and TC degradation pathways were proposed. This study offers valuable insights for designing catalytic membranes with enhanced filtration performance.

Defect Engineering of 2D Copper Tin Composite Nanosheets Realizing Promoted Electrosynthesis Performance of Hydrogen Peroxide

The transformation of the two-electron oxygen reduction reaction (2e-ORR) to produce hydrogen peroxide (H2 O2 ) is a promising green synthesis approach that can replace the high-energy consumption anthraquinone process. However, designing and fabricating low-cost, non-precious metal electrocatalysts for 2e-ORR remains a challenge. In this study, a method of combining complexation precipitation and thermal treatment to synthesize 2D copper-tin composite nanosheets to serve as the 2e-ORR electrocatalysts is utilized, achieving a high H2 O2 selectivity of 92.8% in 0.1 m KOH, and a bulk H2 O2 electrosynthesis yield of 1436 mmol·gcat -1 ·h-1 using a flow cell device. Remarkably, the H2 O2 selectivity of this catalyst decreases by only 0.5% after 10,000 cyclic voltammetry (CV) cycles. In addition, it demonstrates that the same catalyst can achieve 97% removal of the organic pollutant methyl blue in an aqueous system solution within 1 h using the on-site degradation technology. A reasonable control of defect concentration on the 2D copper-tin composite nanosheets that can effectively improve the electrocatalytic performance is found. Density functional theory calculations confirm that the surface of the 2D copper-tin composite nanosheets is conducive to the adsorption of the key intermediate OOH* , highlighting its excellent electrocatalytic performance for ORR with high H2 O2 selectivity.

Peroxymonosulfate-Based Electrochemical Advanced Oxidation: Complication by Oxygen Reduction Reaction

Peroxymonosulfate (PMS)-based electrochemical advanced oxidation processes (EAOPs) have received widespread attention in recent years, but the precise nature of PMS activation and its impact on the overall process performance remain poorly understood. This study presents the first demonstration of the critical role played by the oxygen reduction reaction in the effective utilization of PMS and the subsequent enhancement of overall pollutant remediation. We observed the concurrent generation of H2O2 via oxygen reduction during the cathodic PMS activation by a model nitrogen-doped carbon nanotube catalyst. A complex interplay between H2O2 generation and PMS activation, as well as a locally increased pH near the electrode due to the oxygen reduction reaction, resulted in a SO4•-/•OH-mixed oxidation environment that facilitated pollutant degradation. The findings of this study highlight a unique dependency between PMS-driven and H2O2-driven EAOPs and a new perspective on a previously unexplored route for further enhancing PMS-based treatment processes.

Validation of quenching effectiveness and pollutant degradation ability of singlet oxygen through model reaction system

Quenching method is widely used to assess the contribution of specified reactive species through the probe inhibition efficiency (IE) caused by adding excessive quencher. However, for reactive species with weak ability such as singlet oxygen (1O2), the quenching results are prone to ambiguity. In this study, an 1O2 system using furfuryl alcohol (FFA) as a probe was successfully constructed by methylene-blue-N vis-photosensitization, to discuss the quenching, interference elimination and pollutant degradation ability of 1O2. Inhibition of FFA transformation caused by both quenching and interrupting of 1O2 production was found. The quenching is affected by quencher dosage and ability, which depends on the second-order-rate constant (k). A high k means a strong ability, and less dosage is required to achieve the same IE. Comparison between the calculated ratio of reactive species consumed by quencher and experimental IE helps to judge the interruption of 1O2 production. None of the organic-solvents (methanol, ethanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, tetrahydrofuran, acetonitrile, acetone and chloroform) scavenged 1O2, which would be used as screening-agent for other reactive species (e.g., hydroxyl radicals) that would interrupt 1O2 contribution assessment. Besides, 1O2 was powerless to degrade most selected pollutants. These results encourage proper use of quenchers and better experimental design.

High-efficient degradation of chloroquine phosphate by oxygen doping MoS2 co-catalytic Fenton reaction

To degrade the antiviral and antimalarial drug chloroquine phosphate (CQP), an oxygen doping MoS2 nanoflower (O-MoS2-230) co-catalyst was prepared by a hydrothermal method to construct an O-MoS2-230 co-catalytic Fenton system (O-MoS2-230/Fenton) without pH adjustment (initial pH 5.4). Remarkable CQP degradation efficiency (99.5 %) could be achieved in 10 min under suitable conditions ([co-catalyst] = 0.2 g L-1, [Fe2+]0 = 70 μM, [H2O2]0 = 0.4 mM) with a reaction rate constant of 0.24 min-1, which was 4.8 times that of MoS2 co-catalytic Fenton system (MoS2/Fenton). Compared to MoS2/Fenton, the system had 1.5 times more Fe2+ (28.4 μM) and showed a 24.0 % increase in H2O2 activation efficiency, reaching 50.0 %. The electron paramagnetic resonance (EPR) determinations and active species trapping experimental data revealed that •OH and 1O2 were responsible for CQP degradation. The combination of experiments and density functional theory (DFT) calculation demonstrates that O doping in MoS2 modifies the surface charge distribution, leading to an increase in its conductivity, thus accelerating the Fe3+/Fe2+ cycle and promoting reactive oxygen species (ROS) generation. Furthermore, O-MoS2-230/Fenton system exhibited excellent stability. This work reveals the degradation mechanism of accelerated Fe3+/Fe2+ cycle and abundant ROS in the O-MoS2-230/Fenton system and provides a promising technology for antibiotic pollutant degradation.

Degradation of sulfamethoxazole by super-hydrophilic MoS2 sponge co-catalytic Fenton: Enhancing Fe2+/Fe3+ cycle and mass transfer

To promote the cycle of Fe2+/Fe3+ in co-catalytic Fenton and enhance mass transfer in an external circulation sequencing batch packed bed reactor (ECSPBR), super-hydrophilicity MoS2 sponge (TMS) modified by tungstosilicic acid (TA) was prepared for efficiently degrading sulfamethoxazole (SMX) antibiotics in aqueous solution. The influence of hydrophilicity of co-catalyst on co-catalytic Fenton and the advantages of ECSPBR were systematically studied through comparative research methods. The results showed that the super hydrophilicity increased the contact between Fe2+ and Fe3+ with TMS, then accelerated Fe2+/Fe3+ cycle. The max Fe2+/Fe3+ ratio of TMS co-catalytic Fenton (TMS/Fe2+/H2O2) was 1.7 times that of hydrophobic MoS2 sponge (CMS) co-catalytic Fenton. SMX degradation efficiency could reach over 90% under suitable conditions. The structure of TMS remained unchanged during the process, and the max dissolved concentration of Mo was lower than 0.06 mg/L. Additionally, the catalytic activity of TMS could be restored by a simple re-impregnation. The external circulation of the reactor was conducive to improving the mass transfer and the utilization rate of Fe2+ and H2O2 during the process. This study offered new insights to prepare a recyclable and hydrophilic co-catalyst and develop an efficient co-catalytic Fenton reactor for organic wastewater treatment.