A nonradical reaction-dominated phenol degradation with peroxydisulfate catalyzed by nitrogen-doped graphene

Metal-free carbon-based anode for electrochemical degradation of tetracycline and metronidazole in wastewater

Degradation of antibiotics through electrocatalytic oxidation has recently been comprehended as a promising strategy in wastewater treatment. Herein, nitrogen and sulphur doped graphene oxide (N,S-rGO) nanosheets were synthesized and employed as metal-free anodic material for electrochemical degradation of antibiotics, viz. metronidazole (MNZ) and tetracycline (TC). The synthesized anodic material was characterized using various spectral techniques and further the electrochemical behaviour of N,S-rGO was thoroughly examined. Thereafter, the N,S-rGO material was then employed as the anode material towards the electrocatalytic degradation of antibiotics. Parameters such as initial concentration of the antibiotics and current densities were varied and their effect towards the degradation of MNZ and TC were probed. Notably, the N,S-rGO based anode has shown impressive removal efficiency of 99% and 98.5%, after 120 min of reaction time for MNZ and TC, respectively, under optimized conditions. The obtained results including the kinetic parameters, removal efficiency and electrical efficiency ensure that the prepared anodic material has huge prospective towards real-time application for removal of antibiotics from water.

Super-amphiphilic graphene promotes peroxymonosulfate-based emulsion catalysis for efficient oil purification

Oil fractions containing highly toxic and hazardous organic contaminants can not only cause severe environmental disasters, but also an undesired waste of resources. Given the exceptional performance of persulfates in the removal of persistent and refractory organic pollutants from aqueous media, herein, a peroxymonosulfate-based Pickering emulsion catalytic (PPEC) system was constructed for the hazardous oil purification, using super-amphiphilic graphene as a solid emulsifier and a heterogeneous catalyst simultaneously. Combined detailed instrumental analysis with theoretical calculations, we find that the incorporation of pyridinic N and its oxide significantly facilitated the formation of super-amphiphilic graphene and successfully induced the formation of Pickering emulsion. In addition to stabilizing the PPEC system, super-amphiphilic graphene can also achieve efficient removal of Sudan III (simulated lipophilic organic pollutant) by activating peroxymonosulfate (PMS) to generate •O₂^- and ¹O₂. Results showed that 80 mg/L Sudan III (20 mL) could be fully degraded within 30 min using 10 mL 5 mmol PMS. More significantly, our proposed PPEC system also exhibited excellent property in the purification of practical waste engine oil. This study provides new insights into the purification and recovery of waste oil.

Degradation of phenolic pollutants by persulfate-based advanced oxidation processes: metal and carbon-based catalysis

Wastewater recycling is a solution to address the global water shortage. Phenols are major pollutants in wastewater, and they are toxic even at very low concentrations. Advanced oxidation process (AOP) is an emerging technique for the effective degradation and mineralization of phenols into water. Herein, we aim at giving an insight into the current state of the art in persulfate-based AOP for the oxidation of phenols using metal/metal-oxide and carbon-based materials. Special attention has been paid to the design strategies of high-performance catalysts, and their advantages and drawbacks are discussed. Finally, the key challenges that govern the implementation of persulfate-based AOP catalysts in water purification, in terms of cost and environmental friendliness, are summarized and possible solutions are proposed. This work is expected to help the selection of the optimal strategy for treating phenol emissions in real scenarios.

Carbon nanotube-based materials for persulfate activation to degrade organic contaminants: Properties, mechanisms and modification insights

Removal of harmful organic matters from environment has great environmental significance. Carbon nanotube (CNT) materials and their composites have been demonstrated to possess excellent catalytic activity towards persulfate (PS) activation for the degradation of organic contaminants. Herein, detailed information concerning the function, modification methods and relevant mechanisms of CNT in persulfate-based advanced oxidation processes (PS-AOPs) for organic pollutant elimination has been reviewed. The activation mechanism of PS by CNT might include radical and nonradical pathways and their synergistic effects. The common strategies to improve the stability and catalytic capability of CNT-based materials have also been put forward. Furthermore, their practical application potential compared with other catalysts has been described. Finally, the challenges faced by CNT in practical application are clearly highlighted. This review should be of value in promoting the research of PS activation by CNT-based materials for degradation of organic pollutants and the corresponding practical applications.

Carbon materials in persulfate-based advanced oxidation processes: The roles and construction of active sites

Many researchers have paid more attention to the progress of carbon materials owing to their advantages, such as high activity, low cost, large surface area, high conductivity and high stability. Carbon materials have been widely used in persulfate-based advanced oxidation processes (PS-AOPs), especially for graphene (G), carbon nanotubes (CNTs) and biochar (BC). Various strategies are applied to promote their activity, however, up to now, the relationship between the structures of carbon materials and their activities in PS-AOPs has not been specifically reviewed. The methods to switch reaction pathway (radical and nonradical pathways) in carbon-persulfate-based AOPs have not been systematically explored. Hereon, this review illustrated the active sites of G, CNTs, BC and other carbon materials, and generalized the modification methods to promote the activity of carbon materials and to switch reaction pathway in PS-AOPs. The roles of carbon materials in PS-AOPs were discussed around reactive oxygen species (ROS) and the structures. ROS are frequently complex in AOPs, but main ROS generation is related to the active sites on carbon materials. The structures of carbon materials (e.g., metal-carbon bonds, the electron-deficient C atoms, unbalanced electron distribution and graphitized structures) play a decisive role in the nonradical pathway. Finally, future breakthroughs of carbon materials were proposed for practical engineering and multi-field application.

Synergistic oxytetracycline adsorption and peroxydisulfate-driven oxidation on nitrogen and sulfur co-doped porous carbon spheres

Metal-free carbonaceous catalysts are receiving increasing attention in wastewater treatment. Here, nitrogen and sulfur co-doped carbon sphere catalysts (N,S-CSs₉₀₀-OH) were synthesized using glucose and L-cysteine via a hydrothermal method and high temperature alkali activation. The N,S-CSs₉₀₀-10%-OH exhibited excellent catalytic performance for the degradation of oxytetracycline (OTC). The degradation rate was 95.9% in 60 min, and the reaction equilibrium rate constant was 0.0735 min^-1 (k_0-15 min). The synergistic effect of adsorption-promoting degradation was demonstrated in the removal process of OTC. The excellent adsorption capacity of N,S-CSs₉₀₀-10%-OH ensured the efficient oxidation of OTC. N,S-CSs₉₀₀-10%-OH reduced the activation energy of the OTC degradation reaction (Ea=18.23 kJ/mol). Moreover, the pyrrolic N, thiophene S and carbon skeleton played an important role in the degradation of OTC based on density function theory, and the catalytic mechanism was expounded through radical and nonradical pathways. The active species involved in the reaction were O₂^•-, ¹O₂, SO₄^•- and •OH, of which O₂^•- was the primary reactive species. This study provides a new insight into the reaction mechanism for efficient treatment of organic pollutants using metal-free doped porous carbon materials.

Bimetal organic framework/graphene oxide derived magnetic porous composite catalyst for peroxymonosulfate activation in fast organic pollutant degradation

A magnetic nitrogen-doped porous carbon material (Co/CoO_x@NC) with large surface area was synthesized for peroxymonosulfate (PMS) activation. The addition of reduced graphene oxide (rGO) remarkably improved the catalytic performance of Co/CoO_x@NC due to its enhancement on graphitization degree and structural regulation. Co/CoOx@NC exhibited excellent PMS activation for phenol removal with almost 100% removal efficiency in 10 min, close to that of homogeneous Co²⁺. Simultaneously, good reusability and recyclability of Co/CoO_x@NC was achieved, demonstrating its feasibility for practical application. The PMS activation process in Co/CoO_x@NC/PMS system was dominant by efficient mediation of electron transfer from pollutants to PMS through the sp²-hybridized carbon and nitrogen network. Batch tests of various organic compounds removal revealed the specific selectivity related to the electron-donating ability in Co/CoO_x@NC/PMS system. As the negligible role of reactive radicals on pollutants degradation, the inhibition of interfering species (e.g., Cl^-, natural organic matters) was largely weakened. Present study not only provided a strategy for rationally designing highly efficient nanocarbon-based catalysts on PMS activation, but also presented new insight into the mechanism of PMS heterogeneous activation.

Soybean residue based biochar prepared by ball milling assisted alkali activation to activate peroxydisulfate for the degradation of tetracycline

The advanced oxidation process (AOPs) has caused great concern in recent years. Among them, biochar has been widely studied as a catalyst for advanced oxidation process because of its low price and low environmental risk. In this study, a novel ball milling assisted KOH activation biochar (MKBC) was prepared and applied in peroxydisulfate (PDS) activation to degrade tetracycline hydrochloride (TC-H). In comparison with the oxidation (3.48%) by PDS alone and adsorption (36.19%) by MKBC alone, the removal rate of TC-H was increased to 84.15% in the MKBC/PDS system, indicating that MKBC can successfully activate PDS. Besides, the catalytic activity of the MKBC to activate PDS for the degradation of TC-H is 58.33% higher than that of pristine biochar (PBC). In addition, MKBC has outstanding stability that after three repeated experiments, the removal rate of TC-H by the MKBC/PDS system still remains 77.35%. Meanwhile, the mechanism was investigated that the singlet oxygen (1O2) seized the principal position in the degradation of TC-H in the PDS/MKBC system. This study explored a novel, solvent-free and economic method to propose this extraordinary biochar, which provided a new strategy for the future research of biochar.

Facile synthesis of iron oxide supported on porous nitrogen doped carbon for catalytic oxidation

Iron oxide (Fe_xO_y) supported on porous nitrogen doped carbon is synthesized by a facile pyrolysis method. SiO₂ and NaNO₃ are used as the template and activation agent respectively for porous structure generation and large specific surface area (SSA) creation. The obtained materials show superior catalytic oxidation ability and can activate peroxymonosulfate (PMS) in a wide pH range (3-9) to degrade organic pollutants. The degradation process is a two-stage reaction, including a rapid initial decay and a following slow reaction stage. According to the free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy analysis, and electrochemical tests, the superoxide radical (O₂^-) and singlet oxygen (¹O₂) are proved to play crucial roles in organics degradation. The high SSA (773 m² g^-1), abundant of structural defects, and synergistic effect between Fe_xO_y and the nitrogen doped carbon are the key factors for the enhanced activity. The catalysts in this study can be synthesized easily and contain no toxic metals, thus should have great potential in the wastewater remediation.

Effective defect generation and dual reaction pathways for phenol degradation on boron-doped carbon nanotubes

A new type of metal-free catalyst was successfully prepared by doping boron (B) in the carbon nanotube. The catalyst had 99.4% removal of phenol in 60 min at pH 7 by activating peroxymonosulfate (PMS). In order to explore the origin of the high catalytic activity, the samples were characterized by Raman and electron paramagnetic resonance (EPR), and the reactive oxygen species (ROS) in the process of catalytic degradation were investigated. The Raman results showed that the defect sites increased after doping, which indicated that the B doping increases the active sites on the surface of the carbon nanotubes. Identification experiments of ROS found that not only hydroxyl radicals (·OH) and sulfate radical ( S O 4 - ∙ ) , but also singlet oxygen (1O2) exist in the system. The presence of multiple free radicals indicated the existence of free radical reaction pathway, and the presence of 1O2 confirmed the existence of non-radical reaction pathway. These results indicated that there were dual reaction pathways for the activation of persulfate by B-doped carbon nanotubes, which was the intrinsic nature for the high catalytic activity of the system.

Hexachloroethane dechlorination in sulfide-containing aqueous solutions catalyzed by nitrogen-doped carbon materials

This study demonstrated that nitrogen-doped carbon materials (NCMs) could effectively catalyze the chlorine elimination process in hexachloroethane (HCA) declorination in sulfide-containing environments for the first time. The k_obs values of HCA dechlorination by sulfide in the presence of 10 mg/L NCMs were higher than that of no mediator at pH 7.3 by one or two orders of magnitude. The catalytic capabilities of NCMs on HCA dechlorination were evident in common ranges of natural pH (5.3-8.9) and it could be accelerated by the increase of pH but be suppressed by the presence of dissolved humic acid. Moreover, NCMs exhibited much better catalytic capability on HCA dechlorination compared to the carbon materials, mainly owing to the combined contributions of pyridine N, including enhanced nucleophilic attack to HCA molecule by generating newborn C-S-S and activation of HCA molecule by elongating C-Cl bonds. The functions of pyridine N in micron-sized NCMs with mesopores were better than in nano-sized NCMs on HCA dechlorination. These findings displayed the potential of NCMs, when released into sulfide-containing environments, may significantly increase the dechlorination of chlorinated aliphatic hydrocarbons.

Oily sludge derived carbons as peroxymonosulfate activators for removing aqueous organic pollutants: Performances and the key role of carbonyl groups in electron-transfer mechanism

In this work, low-cost carbon-based materials were developed via a facile one-pot pyrolysis of oily sludge (OS) and used as catalysts to activate peroxymonosulfate (PMS) for removing aqueous recalcitrant pollutants. By adjusting the pyrolysis temperature, the optimized OS-derived carbocatalyst manifested good performance for PMS activation to abate diverse organic pollutants in water treatment. Particularly, an average removal rate of 0.87 mol phenol per mol PMS per hour at a catalyst dosage of 0.2 g L^-1 is attained by the OS-derived carbocatalyst, higher than many other documented catalysts. A series of experimental evidences consolidated that organic pollutants were oxidized mainly via electron-transfer mechanism albeit the detection of singlet oxygen (¹O₂) from PMS activation driven by the OS-derived carbocatalyst. Specifically, the proportion of carbonyl groups (C˭O) in the carbocatalyst adopted with selective modification treatments to tailor the surface chemistry was found to be linearly correlated with the catalytic activity and theoretical calculations demonstrated that the reactions between C˭O and PMS to form surface reactive complexes were more energetically favorable compared to ¹O₂ generation. Herein, this study not only offers a new strategy for reusing OS as value-added persulfate activators but also deepens the fundamental understanding on the nonradical regime.

Identifying the Persistent Free Radicals (PFRs) Formed as Crucial Metastable Intermediates during Peroxymonosulfate (PMS) Activation by N-Doped Carbonaceous Materials

A nonradical mechanism involved in peroxymonosulfate (PMS) activation in carbonaceous materials (CMs) is still controversial. In this study, we prepared N-doped CMs, including hollow carbon spheres (NHCSs) and carbon nanotubes (N-CNTs), to probe the crucial intermediates during PMS activation. The results suggested that the higher efficiency and lower activation energy (13.72 kJ mol^-1) toward phenol (PN) degradation in an NHCS/PMS system than PMS alone (∼24.07 kJ mol^-1) depended on a typical nonradical reaction. Persistent free radicals (PFRs) with a g factor of 2.0033-2.0045, formed as crucial metastable intermediates on NHCS or N-CNT in the presence of PMS, contribute largely to the organic degradation (∼73.4%). Solid evidence suggested that the formation of PFRs relied on the attack of surface-bonded ^•OH and SO₄^•- or peroxides in PMS, among which surface-bonded SO₄^•- was most thermodynamically favorable based on theoretical calculations. Electron holes within PFRs on NHCSs shifted the Fermi level to the positive energy with the valance band increasing from 1.18 to 1.98 eV, promoting the reactivity toward nucleophilic substances. The degradation intermediates of aromatic compounds (e.g., PN) and electron rearrangement triggered the evolution of PFRs from oxygen-centered to carbon-centered radicals. Moreover, due to the specific electron configuration, graphitic N on NHCS was critical for stabilizing the PFRs. This study provides insightful understanding of the fate of organic contaminants and the structure-activity relationship of reactivity of CMs toward PMS activation.

Nonradicals induced degradation of organic pollutants by peroxydisulfate (PDS) and peroxymonosulfate (PMS): Recent advances and perspective

Nonradical persulfate oxidation processes have emerged as a new wastewater treatment method due to production of mild nonradical oxidants, selective oxidation of organic pollutants, and higher tolerance to water matrixes compared with radical persulfate oxidation processes. Since the case of the nonradical activation of peroxydisulfate (PDS) was reported on CuO surface in 2014, nonradical persulfate oxidation processes have been extensively investigated, and much achievement has been made on realization of nonradical persulfate activation processes and understanding of intrinsic reaction mechanism. Therefore, in the review, nonradical pathways and reaction mechanisms for oxidation of various organic pollutants by PDS and peroxymonosulfate (PMS) are overviewed. Five nonradical persulfate oxidation pathways for degradation of organic pollutants are summarized, which include surface activated persulfate, catalysts-free or catalysts mediated electron transfer, ¹O₂, high-valent metals, and newly derived inorganic oxidants (e.g., HOCl and HCO₄^-). Among them, the direct oxidation processes by persulfate, nonradical based persulfate activation by inorganic/organic molecules and in electrochemical methods is first overviewed. Moreover, nonradical based persulfate activation mechanisms by metal oxides and carbon materials are further updated. Furthermore, investigation methods of interaction between persulfate and catalyst surface, and nature of reactive species are also discussed in detail. Finally, the future research needs are proposed based on limited understanding on reaction mechanism of nonradical based persulfate activation. The review can offer a comprehensive assessment on nonradical oxidation of organic pollutants by persulfate to fill the knowledge gap and provide better guidance for future research and engineering application of persulfate.

Synergetic adsorption and Fenton-like degradation of tetracycline hydrochloride by magnetic spent bleaching earth carbon: Insights into performance and reaction mechanism

In this study, the synergetic adsorption and Fenton-like degradation of tetracycline hydrochloride (TCH) by magnetic spent bleaching earth carbon (Mag-SBE@C) with H₂O₂ were developed and performed, with 91.5% of TCH degradation efficiency and 42.1% of TOC removal efficiency. The effects of the reaction parameters (temperature, initial pH, catalyst dosage, molar ratio of TCH to H₂O₂) on TCH degradation in Mag-SBE@C/H₂O₂ system were studied. Under the optimal conditions (temperature 41.1 °C, initial pH 4.89 and molar ratio of H₂O₂ to TCH 114.435) forecasted by response surface methodology (RSM), high TCH degradation efficiency (99%) was achieved. Also, four cycling tests were performed to confirm the excellent stability and regeneration ability of Mag-SBE@C in presence of H₂O₂. In addition, the characteristics of Mag-SBE@C after reaction are analyzed in details via scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Brunner-Emmet-Teller (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrum (FTIR) and X-ray diffraction (XRD), and it was found that Fe₃O₄ nanoparticles on Mag-SBE@C surface acted as co-catalyst and participated in degradation and improved reaction efficiency, while its properties were not greatly changed. The quenching experiments showed that hydroxyl radicals on Mag-SBE@C surface (OH_adsorption) were dominant in Mag-SBE@C/H₂O₂ system. Meanwhile, three possible TCH degradation pathways were given based on the possible intermediates determined by liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-Q-TOF-MS/MS). Mag-SBE@C is an excellent heterogeneous Fenton-like catalyst, exhibiting greatly potential to antibiotics elimination.

Enhanced adsorption and catalytic peroxymonosulfate activation by metal-free N-doped carbon hollow spheres for water depollution

Rational design of metal-free carbon-based heterogeneous catatlyst for wastewater remediation via peroxymonosulfate (PMS) activation is highly desirable. Here, hollow structured porous carbon with abundant N, a high graphitization degree, and a large specific surface area and pore volume (1301 m²/g and 1.12 cm³/g) was synthesized by the pyrolysis of core-shell structured composites consisting of polystyrene (PS) cores and Zeolitic imidazolate frameworks-8 (ZIF-8) shells. The hollow structured carbon (CPS@ZIF-8) was characterized thoroughly and applied for phenol degradation by the activation of PMS. The effects of operation conditions such as the catalyst and PMS dose, phenol concentration, initial pH, and temperature on phenol removal were investigated comprehensively. Moreover, the main reactive species involved in phenol oxidation were investigated, and a plausible mechanism for the degradation of phenol is proposed. The results show that CPS@ZIF-8 exhibited an excellent phenol adsorption and degradation performance, which can be mainly ascribed to its large surface area, abundance of nitrogen and hollow porous structure. Moreover, both the nonradical pathway (involving ¹O₂) and the radical pathway (involving SO₄^- and O₂^-) were found to be involved in the decomposition of phenol.

Electrochemical/Peroxymonosulfate/NrGO-MnFe2O4 for Advanced Treatment of Landfill Leachate Nanofiltration Concentrate

A simple one-pot method was used to successfully embed manganese ferrite (MnFe2O4) nanoparticles on the nitrogen-doped reduced graphene oxide matrix (NrGO), which was used to activate peroxymonosulfate to treat the landfill leachate nanofiltration concentration (LLNC) with electrochemical enhancement. NrGO-MnFe2O4 and rGO-MnFe2O4 were characterized by various means. This indicates that nitrogen-doped could induce more graphene oxide (GO) spall and reduction to produce more active centers, and was favorable for uniformly loading MnFe2O4 particles. The comparison between electrochemical/peroxymonosulfate/NrGO-MnFe2O4 (EC/PMS/NrGO-MnFe2O4) system and different catalytic systems shows that electrochemical reaction, NrGO and MnFe2O4 can produce synergies, and the chemical oxygen demand (COD) removal rate of LLNC can reach 72.89% under the optimal conditions. The three-dimensional (3D-EEM) fluorescence spectrum shows that the system has a strong treatment effect on the macromolecules with intense fluorescence emission in LLNC, such as humic acid, and degrades into substances with weak or no fluorescence characteristics. Gas chromatography-mass spectrometry (GC-MS) indicates that the complex structure of refractory organic compounds can be simplified, while the simple small molecular organic compounds can be directly mineralized. The mechanism of catalytic degradation of the system was preliminarily discussed by the free radical quenching experiment. Therefore, the EC/PMS/NrGO-MnFe2O4 system has significant application potential in the treatment of refractory wastewater.

The Intrinsic Nature of Persulfate Activation and N-Doping in Carbocatalysis

Persulfates activation by carbon nanotubes (CNT) has been evidenced as nonradical systems for oxidation of organic pollutants. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) possess discrepant atomic structures and redox potentials, while the nature of their distinct behaviors in carbocatalytic activation has not been investigated. Herein, we illustrated that the roles of nitrogen species in CNT-based persulfate systems are intrinsically different. In PMS activation mediated by nitrogen-doped CNT (N-CNT), surface chemical modification (N-doping) can profoundly promote the adsorption quantity of PMS, consequently elevate potential of derived nonradical N-CNT-PMS* complexes, and boost organic oxidation efficiency via an electron-transfer regime. In contrast, PDS adsorption was not enhanced upon incorporating N into CNT due to the limited equilibrium adsorption quantity of PDS, leading to a relatively lower oxidative potential of PDS/N-CNT system and a mediocre degradation rate. However, with equivalent persulfate adsorption on N-CNT at a low quantity, PDS/N-CNT exhibited a stronger oxidizing capacity than PMS/N-CNT because of the intrinsic higher redox potential of PDS than PMS. The oxidation rates of the two systems were in great linearity with the potentials of carbon-persulfate* complexes, suggesting N-CNT activation of PMS and PDS shared the similar electron-transfer oxidation mechanism. Therefore, this study provides new insights into the intrinsic roles of heteroatom doping in nanocarbons for persulfates activation and unveils the principles for a rational design of reaction-oriented carbocatalysts for persulfate-based advanced oxidation processes.

Modification of graphite felt doped with nitrogen and boron for enhanced removal of dimethyl phthalate in peroxi-coagulation system and mechanisms

To enhance the generation of hydrogen peroxide (H₂O₂), a modified graphite felt cathode doped with nitrogen and boron was developed and used in peroxi-coagulation system to degrade dimethyl phthalate (DMP). After a simple modification method, the yield of H₂O₂ on cathode increased from 9.39 to 152.8 mg/L, with current efficiency increased from 1.61 to 70.3%. Complete degradation of DMP and 80% removal of TOC were achieved within 2 h at the optimal condition with pH of 5, cathodic potential of - 0.69 V (vs. SCE), oxygen aeration, and electrode gap of 1 cm. Possible mechanism with synergistic effect of electro-Fenton and electrocoagulation process in the peroxi-coagulation system was revealed via quenching experiments. The prospect of this system in the effluent of landfill leachate and domestic sewage was studied, achieving 50% and 61% of DMP removal in 2 h. This efficient system with simple modified cathode had promising prospects in practical applications.

Pig manure-derived nitrogen-doped mesoporous carbon for adsorption and catalytic oxidation of tetracycline

Ordered nitrogen-doped mesoporous carbon (NMC) was successfully synthesized with pig manure as the precursor. The resulting NMC materials exhibited excellent capacity of adsorption and potassium persulfate (PS) activation when used as catalysts for the oxidative degradation of tetracycline antibiotics (tetracycline hydrochloride (TH) as the target). For an initial TH concentration of 35 mg/L, the maximum adsorption capacity of NMC material prepared at 700 °C (NMC700) was 122.0 mg/g, and the degradation efficiency in the PS reaction system was 94.8% within 120 min. Investigation of the mechanism indicated that the NMC700 material with specific surface area (SSA) of 275.5 m²/g and 0.7% graphitic N content, provided a large amount of active sites for adsorption and catalytic oxidation of TH. Based on the results of selective degradation and electron paramagnetic resonance (EPR) experiments, a non-radical pathway for the degradation of pollutants was proposed. Chronoamperometry evaluation also supported the conclusion that the NMC material enhanced electron transfer to activate persulfate, accelerating the removal of TH.

High-performance porous graphene from synergetic nitrogen doping and physical activation for advanced nonradical oxidation

Porous nitrogen-doped reduced graphene oxide (NRGO) is successfully synthesized from graphene oxide via the combination of CO₂ activation and nitrogen doping with ammonia. The performances of the carbon materials are evaluated by catalytic activation of perroxymonosulfate (PMS) for phenol degradation. The effect of the treatment sequence of CO₂ activation and nitrogen doping on the catalytic activity of the derived product is investigated. The material obtained by CO₂ activation-nitrogen doping (P-NRGO) shows better activity than the one obtained from nitrogen doping-CO₂ activation (N-PRGO). The activation mechanisms are also investigated by radical scavenging test, and the P-NRGO/PMS system is unveiled to rely on the nonradical oxidation pathway. The turnover frequencies (TOFs) of these RGOs are also calculated, and the P-NRGO has the largest TOF of 58.39. Based on the analysis of synthesis method and catalytic activity, it is proposed that new catalytic sites are generated on P-NRGO. Density functional theory (DFT) calculations also illustrated that the most reactive sites are the structure vacancies with two nitrogen atoms, which is consistent with the results. The conclusion in this study provides new insights into the synergistic effect of N-doping and structural defects of carbon materials and the induced nonradical pathway in advanced oxidation.