Nonradical Oxidation Process Research Articles

Electron transfer mechanism mediated MOF-derived nanoflowers catalyst for promoting peroxymonosulfate activation and ciprofloxacin degradation

Three MOF-derived nanoparticles were synthesized by manganese doping and calcination of ZIF-67 precursor. The surface physicochemical properties of these materials were compared using SEM, TEM, XRD, FTIR and BET analyses. Among them, cobalt-manganese oxide nanoflowers (CoMn2O4-NFs) exhibited excellent catalytic performance in the degradation of ciprofloxacin (CIP) by activated peroxymonosulfate (PMS), achieving 100 % removal within 30 minutes with a rate constant (kobs) of 0.2960 min−1. The catalytic mechanism was elucidated by quenching experiments, EPR, electrochemical analysis and X-ray photoelectron spectroscopy (XPS). The results show that the non-radical oxidation process was initiated mainly by direct electron transfer and 1O2 (∼80 %), with a small contribution from the radical SO4·- (∼20 %). The nano-confined structure on the surface of CoMn2O4-NFs makes it easy to combine with PMS to form CoMn2O4-NFs/PMS* complexes, which directly capture electrons from CIP to complete the degradation process. The double redox cycle of cobalt-manganese ions and oxygen vacancies on CoMn2O4-NFs could accelerate the electron transfer process. CoMn2O4-NFs maintained high removal efficiency (>99 %) over a wide pH range (3−11), with minimal interference from most environmental anions, demonstrating strong stability and interference resistance. This study provides insights into using metal-based materials for oxidative degradation of organic pollutants via non-radical pathways.

Singlet Oxygen Formation Mechanism for the H2O2-Based Fenton-like Reaction Catalyzed by the Carbon Nitride Homojunction.

The singlet oxygen (1O2) oxidation process activated by metal-free catalysts has recently attracted considerable attention for organic pollutant degradation; however, the 1O2 formation remains controversial. Simultaneously, the catalytic activity of the metal-free catalyst limits the practical application. In this study, carbon nitride (HCCN) containing an intramolecular homojunction, a kind of metal-free catalyst, exhibits excellent activity compared to g-C3N4 (CN) and crystalline carbon nitride (HCN) for tetracycline hydrochloride degradation through the H2O2-based Fenton-like reaction. The rate constant for HCCN increased about 16.1 and 8.9 times than that of CN and HCN, respectively. The activity of HCCN was enhanced, and the dominant reactive oxygen species (ROS) changed from hydroxyl radicals (•OH) to 1O2 with an increase in pH from 4.5 to 11.5. A novel formation pathway of 1O2 was revealed. This result is different from the normal reference, in which •OH is always the primary ROS in the H2O2-based Fenton-like reaction. This study may provide a possible strategy for the investigation on the nonradical oxidation process in the Fenton-like reaction.

Investigating oxidant-catalyst interactions in the persulfate system: Implications for efficient removal of phenolics and antibiotics

Persulfate (PS) activation by carbon catalyst holds both scientific and practical significance to curb the toxicity effects of organic pollutants in the natural water environment. Here, we investigated a relatively unfamiliar characteristics (i.e., oxidant-catalyst interaction) that influence the removal efficiency in PS activated system, utilizing N-doped mesoporous carbon hollow spheres (N-MCHS; size ∼385 nm) as a catalyst. The selection of this catalyst was motivated by its desired physicochemical characteristics such as high dispersibility, uniformly distributed pores and high specific surface area (1109 m2 g−1) for catalytic application. The removal performance was studied by degrading bisphenol A at very low PS (0.25 mM) and catalyst (10.0 mg L−1) concentrations. Through this study, we established a correlation between the surface charge of N-MCHS and PS interaction on the catalytic performance. Further, electron spin resonance (ESR) and radical scavenger studies were carryout out to prove the nonradical oxidation process. Electrochemical studies provided a strong evidence for PS complexation and electron transfer during oxidative removal of bisphenol A. Additional studies with different phenolics and antibiotics demonstrated that N-doping significantly accelerates the degradation rate and enhances the removal efficiency. The results of present study unveil the potential use of PS+N-MCHS in the degradation of different organic contaminants at low catalyst dosages.

Origins of Selective Oxidation in Carbon-Based Nonradical Oxidation Processes toward Organic Pollutants: Quantitative Structure-Activity Relationships (QSARs).

Metal-free carbon material-mediated nonradical oxidation processes (C-NOPs) have emerged as a research hotspot due to their excellent performance in selectively eliminating organic pollutants in aqueous environments. However, the selective oxidation mechanisms of C-NOPs remain obscure due to the diversity of organic pollutants and nonradical active species. Herein, quantitative structure-activity relationship (QSAR) models were employed to unveil the origins of C-NOP selectivity toward organic pollutants in different oxidant systems. QSAR analysis based on adsorption and oxidation descriptors revealed that C-NOP selectivity depends on the oxidation potentials of organic pollutants rather than on adsorption interactions. However, the dominance of electronic effects in selective oxidation decreases with increasing structural complexity of organic pollutants. Moreover, the oxidation threshold solely depends on the inherent electronic nature of organic pollutants and not on the reactivity of nonradical active species. Notably, the accuracy of substituent descriptors (Hammett constants) and theoretical descriptors (e.g., highest occupied molecular orbital energy, ionization potential, and single-electron oxidation potential) is significantly influenced by the complexity and molecular state of organic pollutants. Overall, the study findings reveal the origins of organic pollutant-oriented selective oxidation and provide insight into the application of descriptors in QSAR analysis.

The non-radical, non-ROS, and non-Cu(III) oxidation of inert pollutants significantly enhanced by CuO-MgO composites

Peroxydisulfate (PDS) is an appealing oxidant to eliminate water pollutants due to the relatively low cost and high stability compared with other peroxides. It needs to be activated for application, with non-radical producing processes being specifically preferred to obtain high selectivity and to reduce useless consumption of active species by ubiquitous chloride ions. Unfortunately, most of the current non-radical oxidation processes of PDS are ineffective toward inert pollutants. Here we report a novel non-radical PDS oxidation process initiated by CuO-MgO composites toward effective removing refractory iodinated contrast media compounds (ICMs). The optimized CuO-MgO composite was 18-times more efficient than CuO in activating PDS to remove iopamidol, a typical refractory ICM, and exhibited much lower Cu2+ leaching. Interestingly, the enhanced oxidation is not related to radicals, reactive oxygen species (ROS), or high valent Cu(III). We revealed with a series of surface characterization and density functional theory calculation that the CuO-MgO composite has Cu2+-Mg2+ heterojunctions of high electron density, thus is more active than CuO alone for PDS activation. PDS interacted with the composite surface in inner-sphere mode; consequently, the surface-bound PDS abstracted electrons directly from inert pollutants. Due to the lower oxidation power than traditional radicals, PDS/CuO-MgO oxidation of the ICM probe was insensitive to chloride and produced less hydroxyl- and nitro- degradation products. This research highlights that Cu2+-Mg2+ heterojunctions can play an important role in enhancing the non-radical and non-ROS oxidation capability of PDS toward inert pollutants.

2D ZIF-L arrays supported on zinc foam to activate peroxymonosulfate for degrading sulfamethoxazole through both radical and non-radical pathways

The development of easy recovery and high efficiency heterogeneous catalysts for activating peroxymonosulfate (PMS) is of great significance in the treatment of environmental pollutants. In this study, we successfully immobilized 2D ZIF-L arrays on a zinc foam (ZF) through a room temperature deposition method, creating a self-supporting ZIF-L/ZF catalyst. The ZIF-L/ZF exhibited high catalytic efficiency and durable recyclability for activating PMS to degrade sulfamethoxazole (SMX). Within 10 min, a 97 % degradation efficiency of SMX was achieved, which could be attributed to the unique integrated architecture and Co2+/Co3+ redox cycle of the catalyst. Furthermore, the effects of various environmental factors on catalytic activity were evaluated. By identifying the reactive species, both radical and non-radical oxidation process occurred during PMS activation. Additionally, the ZIF-L/ZF could be easy reused over 10 cycles, demonstrating a practical application value. We also proposed a possible degradation pathway for SMX based on Fukui index calculations and HPLC-MS. Our findings provide valuable insights into the construction of self-supporting catalyst for pollutant removal.

Single atom manganese catalyst boosting selective oxidation of alcohols with activated peroxymonosulfate

Selective oxidations are important reactions in organic synthesis for fine chemical industry and conventional methods are expensive and produce a lot of toxic wastes. Herein, we demonstrate a facile and environmentally benign technique for liquid phase selective oxidation based on graphene-supported Mn single-atom-catalyst (SAMn-G) for efficient peroxymonosulfate (PMS) activation. The active Mn component in the developed SAMn-G catalyst reached single-atomic dispersion on graphene substrate via the coordination of individual Mn atoms with the doped N from the graphene framework. SAMn-G activated PMS via a nonradical-dominated pathway, which could convert aromatic alcohols into aldehydes or ketones at a mild temperature. The SAMn-G catalyst exhibited superior conversion and aldehyde selectivity in alcohol oxidation in comparison with their counterpart catalysts possessing either homogeneous Mn ions or oxide particles. The high activation efficiency of SAMn-G is due to the synergistic effect between Mn atoms and graphene substrate, as well as the dominated reaction pathway from nonradical oxidation, which is more selective than these free radicals to oxidize the alcohols. Concerted experimental evidence indicates that the non-radical oxidation process was highly possible to follow the electron transfer mechanism by PMS/organic adsorption on the surface of the catalyst. This study provides a fundamental understanding of PMS activation mediated by single atom catalyst for organic synthesis and the achieved insights can also help the catalyst design for other liquid phase selective oxidation processes.

Effective remediation of leachate concentrate by peroxymonosulfate in a catalytic ceramic membrane filtration process: Performance and mechanism

Membrane concentrated landfill leachate has been characterized by complex component and degradation resistant. In this work, a new catalytic ceramic membrane (CuCM) was developed by in-situ integrating copper oxide in the membrane and used in combination with peroxymonosulfate (PMS) for leachate concentrate treatment. The performance and key factors of the CuCM/PMS system were systematically studied. Results showed that the CuCM/PMS system experienced promising efficiency in the pH range of 3 ∼ 11. The highest COD, TOC, UV254 and Color removal efficiency achieved by the CuCM-3/PMS system under the conditions of pH = 7.0 and CPMS = 10 mM, which reached up to 63.4%, 50.5%, 75.1% and 90.2%, respectively. The possible mechanism of leachate remediation was proposed and non-free radicals (Cu(Ⅲ), 1O2) played an important role in the CuCM/PMS system for leachate remediation. The fluorescence spectrum and GC–MS analysis showed that the refractory organics with a high molecular weight in the leachate concentrate were mostly oxidized into small molecules, which also alleviated the membrane fouling. In addition, the slight decrease in COD (7.4%) and TOC (9.7%) after 6 cycles revealed the good catalytic stability and reusability of CuCM-3/PMS. This work provides a feasible strategy for leachate concentrate remediation via a nonradical oxidation process.

MgFe2O4/MgO modified biochar with oxygen vacancy and surface hydroxyl groups for enhanced peroxymonosulfate activation to remove sulfamethoxazole through singlet oxygen-dominated nonradical oxidation process

Nonradical oxidation plays a crucial role in the contaminant degradation due to their high selectivity and anti-interference ability. In this study, we report that peroxymonosulfate (PMS) activated by MgFe2O4/MgO modified biochar (MMFBC) achieves almost complete nonradical oxidation process dominated by 1O2 for degradation of sulfamethoxazole (SMX). The experimental results show that MMFBC exhibits excellent performance for SMX degradation, and is not susceptible to interference from coexisting ions and different water matrices. Oxygen vacancy (OV) and surface − OH groups on MMFBC surface are detected and considered to be crucial for nonradical processes. Characterizations and theoretical calculations reveal that the co-adsorbed PMS and dissolved oxygen (O2) near OV form a localized high-density electron transfer process. With the premise of hydrogen bonding between PMS and surface − OH groups, PMS acts as an electron donor to OV, which in turn transfers electron to O2 through the iron cycle involving Fe(II)/Fe(III). Finally, the electron acceptor O2 undergoes conversion into O2−, which subsequently transforms into 1O2 to achieve nonradical oxidation processes. This work provides an in-depth investigation into the OV and surface − OH groups mediated nonradical oxidation mechanism, and proposes a novel insight into electron-transfer processes among PMS, O2 and catalyst.

Adsorption and catalytic degradation of phenol in water by a Mn, N co-doped biochar via a non-radical oxidation process

A modified biochar material (Mn/C-KOH) was synthesized from chitosan using KOH and MnCl2 as the activators via a one-pot pyrolysis process. The characterization suggested that the two activators promoted its textural properties, led to a surface area of 1223 m2/g and modified the surface chemical groups. Mn/C-KOH with a Mn-doping dosage of 0.27 wt% was an adsorbent and outstanding catalyst for removing phenol via peroxydisulfate (PDS) activation. A 55% adsorption rate of phenol was achieved within 10 min at a concentration of 30 mg/L. A 95% degradation rate and a 75% mineralization rate of phenol (30 mg/L) were obtained through the activation of PDS (200 mg/L). And, the catalytic degradation system could tolerate a wide pH range from 3 to 9. The intrinsic pyridinic N and CC/CC groups of the chitosan-derived biochar played dominant roles in the adsorption. The simultaneous activation of KOH and MnCl2 enhanced the proportion of CO groups of Mn/C-KOH, and CO groups served as the catalytic active sites for PDS activation. The electron transfer and 1O2-mediated non-radical processes that were induced by the formation of a dioxirane intermediate between Mn/C-KOH and PDS were responsible for the phenol degradation. This work offers a modification for the biomass-derived catalysts and is beneficial to the understanding of non-radical mechanism in AOPs.

A nonradical oxidation process initiated by Ti-peroxo complex showed high specificity toward the degradation of tetracycline antibiotics

Nonradical oxidation has received wide attention in advanced oxidation processes for environmental remediation. Understanding the relationship between material characteristics and their ability to initiate nonradical oxidation processes is the key to better material design and performance. Herein, a novel titanium-based metal-organic framework MIL-125-Ti/H2O2 system was established to show a highly selective degradation efficacy toward tetracycline antibiotics. MIL-125-Ti with the abundance of TiO6 octahedra units was found to effectively activate H2O2 under dark conditions by forming an oxidative Ti-peroxo complex. The presence of the Ti-peroxo complex, confirmed by UV-visible spectrophotometer, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy characterizations, showed superior degradation (>95% removal rate) of oxytetracycline hydrochloride (OTC), doxycycline hydrochloride, chlortetracycline hydrochloride, and tetracycline. Density functional theory calculations were performed to assist the elucidation on the mechanism of H2O2 activation and antibiotics degradation. The MIL-125-Ti/H2O2 system was highly resistant to halogens and background organics, and could well maintain its original catalytic activity in actual water matrices. It retained the ability to degrade 75% of OTC within ten test cycles. This study provides new insight into the nonradical oxidation process initiated by the unique Ti-peroxo complex of Ti-based MOF.

Topological defects strengthened nonradical oxidation performance of biochar catalyzed peroxydisulfate system

Nonradical oxidation based on peroxydisulfate (PDS) activation has attracted increasing attention for selective degradation of organic pollutants. Herein, topological defects were introduced into biochar (BC) via removing N atoms in N-doped BC (NBC) in an attempt to improve the nonradical catalytic performance. Compared to the pristine BC and NBC, the introduction of topological defects could achieve up to 36.6- and 8.7-times catalytic activity enhancement, respectively. More importantly, it was found that the catalytic activity was dominated by topological defects, which was verified by the significant positive correlation between the pseudo-first-order rate constants and the content of topological defects. Theoretical calculations suggested that topological defects enhanced the electron-donating ability of BC by reducing the energy gap, which made the electrons transfer to PDS molecules more easily. As a result, holes were generated after the carbon defects lost electrons, and induced a nonradical oxidation process. Benefiting from the merits of nonradical oxidation, the developed BC/PDS system showed superior performance in removing electron-rich contaminants in the presence of inorganic anions and in the actual environments. This study not only provides a potential avenue for designing efficient biochar-based catalysts, but also advances the mechanism understanding of nonradical oxidation process induced by carbon defects.Graphical

Remediation of sulfonamides-contaminated groundwater through in-situ activation of peroxymonosulfate by supported hierarchical CuO/MgO nanosheets

Groundwater contamination by sulfonamides (SAs) has aroused great concern due to their potential risks to ecosystem and public health. In this work, degradation of SAs with different substituents was studied via a single oxygen dominated peroxymonosulfate (PMS) activation process. Recoverable hierarchical CuO/MgO nanosheets (NSs) with highly exposure of active sites and open diffusion channels was employed as a PMS activator. The degradation behavior of sulfamethoxazole (SMX), sulfamethazine (SMZ), sulfadiazine (SDZ), sulfamerazine (SMR) and sulfathiazole (STZ) was studied via batch reactions, revealing an efficient heterogeneous oxidation process. In a fixed-bed column of the supported hierarchical CuO/MgO NSs, simultaneous degradation of the five SAs in complicated water matrix was observed with high removal efficiency, long-term stability and strong anti-interference capability toward background constituents of groundwaters. Kinetic experiments and mechanistic study elucidated PMS was activated by CuO and MgO synergically that incorporating with defective-rich MgO induced highly oxidative Cu3+. The activation of PMS over MgO was mediated by surface oxygen vacancies, while thermal feasible redox cycle of Cu3+/Cu2+ responsible for the activation of PMS over defective CuO. This study may help to understand the simultaneous degradation of different SAs in a nonradical oxidation process and provide a feasible technology for in-situ remediation of SAs-contaminated groundwater.

Non-radical transformation of oxytetracycline by Vo-MnO@C/Pt0.8Au0.2-anode-activated peroxymonosulfate: Influencing factors, mechanism, and toxicity assessment

Non-radical oxidation processes based on electrochemically activating peroxymonosulfate (PMS) have attracted considerable attention owing to their mild oxidative properties and selective degradation of organic pollutants. In this study, a Vo-MnO@C/Pt0.8Au0.2 modified anode is prepared to activate PMS and generate non-radical oxidation that produces singlet oxygen (1O2) for oxytetracycline (OTC) degradation. Here, the PMS is not only an oxidant but also the only supporting electrolyte, which can effectively reduce the influx of additional ions. Efficient OTC degradation is achieved in a wide pH range (pH = 3–9) and is not inhibited in natural water samples, even in the case of the seawater sample (100 % removal in 60 min). About 96.8 % of OTC at a concentration of 10 mg/L could be degraded with 10 mA cm−2, pH = 9.0, and 1.0 mM PMS in 60 min. Furthermore, the Vo-MnO@C/Pt0.8Au0.2/EPMS system can efficiently degrade various antibiotics. In particular, the 1O2 plays a critical role in OTC degradation. Electro-catalysis and oxygen vacancies (Vo) contribute to the activation of PMS along a non-radical pathway, which is further confirmed through quenching experiments and electron paramagnetic resonance (EPR) tests. In addition, the Toxicity Estimation Software Tool (T.E.S.T) and flow cytometry tests indicate that the Vo-MnO@C/Pt0.8Au0.2/EPMS system reduces the toxicity of OTC-contaminated water. Owing to its reusability with a degradation efficiency of about 90 % after four cycles, the Vo-MnO@C/Pt0.8Au0.2/EPMS system has good prospects for practical application. In summary, our work highlights the potential of a non-radical oxidation process for decontaminating pharmaceutical and personal care products (PPCPs) in complex water matrices.

Singlet oxygen-dominated non-radical oxidation in biochar/peroxymonosulfate system for efficient degradation of tetracycline hydrochloride: Surface site and catalytic mechanism

BackgroundBiochar has attracted much attention in peroxymonosulfate (PMS) activation for the elimination of organic pollutants in water. However, the factor to determine the catalytic efficiency of biochar and the evolution of reactive oxygen species (ROS) remain equivocal and elusive. Method & resultIn this study, Camellia oleifera shell-derived biochar (COSB) was prepared by one-step pyrolysis. The pyrolysis temperature could tune the catalytic performance of COSB. Owing to more C=O groups and defects, the COSB-1000 prepared at 1000 °C showed the optimal activity in PMS activation. In the presence of 0.4 g∙L−1 of COSB-1000 and 1.0 g∙L−1 PMS, 91.57% of tetracycline hydrochloride (TC, 20 mg·L−1) was degraded within 105 min. In addition, the COSB-1000/PMS system demonstrated good anti-interference ability and a wide pH applicability from 3.0 to 11.0. Quenching experiment and electron spin resonance (EPR) spectroscopy suggested that the non-radical oxidation process dominated by the generated 1O2, which was converted from O2•−, play the vital role in TC degradation by the COSB-1000/PMS system. Furthermore, four possible degradation pathways of TC in the COSB-1000/PMS system are proposed by the mass spectroscopy, and the growth-inhibition of Escherichia coli showed that the degradation intermediates were low toxicity. Significant findingsThe results here shed light on the generation of 1O2 by biochar and deepen the insight for the environmentally-friendly catalysts derived from biomass in activating PMS for wastewater treatment.

Oxidative degradation of sulfamethazine in aqueous solution by the activation of Na2S2O8 over vinasse‐derived N,S‐codoped mesoporous carbon

AbstractN,S‐codoped mesoporous carbon (S/NMC) as an effective catalyst toward the catalytic persulfate oxidation of sulfamethazine (SMZ) was fabricated conveniently using vinasse as the C/N source, Na2S as the S precursor and nano‐SiO2 as the template, respectively. The effect of S precursor dosage on the textural properties and surface chemistry of S/NMCs were characterized by N2 adsorption/desorption, Raman spectra, X‐ray diffractometer (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS). It was found that more S precursor dosage presented an enhanced SMZ degradation performance due to the significant role of more S precursor dosage: (i) larger specific surface area and (ii) more active surface groups including pyridine N, graphite N, quinone‐like O and thiophene‐like S. In addition, quenching experiments showed that free radical and nonradical oxidation processes are the main processes of SMZ degradation. The findings provided a new idea for the resource utilization of vinasse and the development of catalytic persulfate oxidation of organic pollution.

Metal-free amorphous carbon nitride with N-vacancies for efficient photocatalytic decontamination: a case of peroxydisulfate-based nonradical oxidation mechanism

The elaborate design of the peroxydisulfate-based nonradical oxidation process. Nitrogen vacancies enhanced the surface affinity between the catalyst and PDS, and thus, the formation of the key complex (i.e., ACN–PDS*).

Activation of peroxymonosulfate by sulfonated cobalt (II) phthalocyanine for the degradation of organic pollutants: The role of high-valent cobalt-oxo species

Sulfate radicals (SO4•−) are typically regarded to be the dominant active species in the cobalt-activated peroxymonosulfate (PMS) processes. In this study, a water-soluble sulfonated cobalt (II) phthalocyanine (CoPcS) was applied as a molecular catalyst to activate PMS and break down organic contaminants. The CoPcS/PMS system was shown to be dominated by high-valent cobalt-oxo species (Co(IV)) rather than the conventional SO4•− and hydroxyl radical (•OH) based on methyl phenyl sulfoxide (PMSO) chemical probe, radical quenching experiments, and electron paramagnetic resonance (EPR). The nonradical oxidation process was found to be predominant in acid conditions (pH 3–5), whereas the radical oxidation pathway co-occurred in neutral or alkaline medium conditions (pH 7–8). Organic contaminants with low ionization potential (IP) can be effectively and selectively removed by the CoPcS/PMS system. More notably, the removal of organic pollutants in the CoPcS/PMS system was not significantly impacted by the ubiquitous inorganic anions (such as SO42−, HCO3−, H2PO4− and HPO42−) or dissolved organic matter (e.g., humic acid). The promoting effect for the removal of levofloxacin was observed under the high concentration of HPO42- conditions. The CoPcS/PMS system demonstrated resistance to the environmental matrix and maintained its oxidation capacity at the practical aqueous substrates (tap water and secondary effluent).

Novel construction of the catalyst from red mud by the pyrolysis reduction of glucose for the peroxymonosulfate-induced degradation of m-cresol.

Red mud of low cost is regarded as a promising alternative to heterogeneous catalysts for activating peroxymonosulfate (PMS) to degrade m-cresol. Improper valence states of metal oxides and coated active substances in red mud greatly hampered its wide application. To solve this problem, the modified red mud (WRMG/700) was prepared by the pyrolysis reduction of glucose in N2 atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS) analysis confirmed the production of Fe3O4, MnO and NiO in red mud and their gathering on the surface of particles. WRMG/700 exhibited the excellent performance toward PMS activation for the m-cresol degradation with 99.02% degradation efficiency and a pH-independent catalytic activity between initial pH 3-8. The removal efficiency of COD increased with the reaction time under the optimized degradation conditions. The free radical scavenging experiments and electron paramagnetic resonance (EPR) test confirmed 1O2 played a dominant role during m-cresol degradation in the WRMG/700/PMS system, implying m-cresol degradation was a non-radical oxidation process. Accordingly, the possible reaction mechanism was proposed. WRMG/700 retained its activation performance even after five recycles. This study showed a low cost and simple operation process for m-cresol elimination.

Adsorption and catalysis of peroxymonosulfate on carbocatalysts for phenol degradation: The role of pyrrolic-nitrogen

Persulfate-based nonradical oxidation processes are appealing for removing refractory aromatic organic contaminants in wastewater purification. Here, ultrathin nitrogen-doped carbonaceous catalysts with different pyrrolic-N contents were developed by a facile modifiable g-C3N4-templated strategy. We observed that N-C-6 has the highest pyrrolic-N content, and the presence of N-C-6 with Peroxymonosulfate (PMS) achieved almost 98 % degradation for phenol degradation within 30 min. Moreover, the decisive role of pyrrolic-N in activating PMS was illustrated through experiments, instrument characterization and theoretical calculations: the more pyrrolic-N-doping could exhibit the higher redox potential of the metastable complex with PMS, and the stronger interaction between both materials, the greater PMS adsorption, as a result, the oxidation rate of phenol is faster by charge abstraction reactions. The results provide a new strategy for the intrinsic roles of heteroatom doped carbon materials to activate persulfates.