Catalysts For Advanced Oxidation Processes Research Articles

Nanographite: A highly active and durable metal-free ozonation catalyst with application in natural waters

The development of metal-free heterogeneous catalysts for advanced oxidation processes has emerged as a key focus for both academia and industry. We report on research that seeks to establish a correlation between the crystallographic, physicochemical, textural, and morphological properties of a series of graphite-based solids and their activities as metal-free ozonation catalysts in aqueous media. Our findings show that nanographite (NG) outperforms traditional graphite-based solids, activated carbon and Co3O4. The enhanced activity of NG is due to defective nanosized graphitic structures with high surface areas. NG exhibits an exceptional activity, durability, and recyclability that surpasses other known catalysts. Our study employs electron spin resonance and selective quenching experiments that reveal the generation of 1O2 during catalytic ozonation. Significantly, NG shows excellent catalytic efficiency even when using natural surface river water or seawater. This study illustrates the importance of the natural properties of graphite-based materials as active and durable ozonation catalysts in water.

Interface engineering-induced perovskite/spinel LaCoO3/Co3O4 heterostructured nanocomposites for efficient peroxymonosulfate activation to degrade levofloxacin

Conventional perovskite oxides (ABO3) tend to suffer from their inactive surfaces and limited active sites that reduce their catalytic activity and stability, while interface engineering is a facile modulating technique to boost the catalyst's inherent activity by constructing heterogeneous interfaces. In this study, perovskite/spinel LaCoO3/Co3O4 nanocomposites with heterogeneous interfaces were synthesized via sol-gel and in-situ gradient etching methods to activate peroxymonosulfate (PMS) for degrading levofloxacin (LEV). LaCoO3 on the surface was etched into spinel Co3O4, and LaCoO3/Co3O4 nanocomposites with two crystal structures of perovskite and spinel were successfully formed. The surface-modified LaCoO3/Co3O4 exhibited superior catalytic performance with a reaction rate constant more than 2 times that of the original LaCoO3, as well as excellent pH adaptability (3–11) and reusability (more than 6 recyclings) for LEV degradation. Besides, multiple characterization techniques were carried out to find that LaCoO3/Co3O4 possessed a larger specific surface area and richer oxygen vacancies after surface modification, which provided more active sites and accelerated mass transfer rate. The mechanism of reactive oxygen species involved in the reaction system was proposed that LaCoO3/Co3O4 not only reacted with PMS directly to produce SO4•− and •OH but also its surface hydroxyl group helped to form the [≡Co(Ⅲ)OOSO3]+ reactive complex with PMS to produce O2•− and 1O2. In addition, electrochemical experiments demonstrated that the surface electronic structure of LaCoO3/Co3O4 was effectively regulated, exhibiting a faster electron transfer rate and facilitating the redox process. By detecting and identifying degradation intermediates, three degradation pathways for LEV were proposed. Our work provided profound insights into the design of efficient and long-lasting catalysts for advanced oxidation processes.

Ultrasmall nitrogen-doped Cu0·92Co2·08O4 nanocrystal-decorated cerium dioxide nanoparticles for fast and complete degradation of ranitidine via permonosulfate activation

A simple and efficient coagulation method was used for the rapid preparation of nitrogen-doped copper-cobalt oxide (N–Cu0.92Co2·08O4) supported on cerium dioxide (CeO2), that is, N–Cu0.92Co2·08O4@CeO2. A low concentration of N–Cu0.92Co2·08O4@CeO2 (0.15 g L−1) was shown to rapidly activate permonosulfate (PMS) (0.15 g L−1) to achieve 100% degradation of ranitidine within 10 min. A 100% degradation of ranitidine enabled by the catalyst was achieved over a wide range of pH (5.5–9.0), which could be completed within 8 min in the presence of anionic H2PO4−. Moreover, the N–Cu0.92Co2·08O4@CeO2 catalyst enabled more than 90% degradation of various typical antibiotics within 30 min, including tetracycline, sulfaixoxazole, and chloramphenicol, with degradation rates of 100%, 93.51%, and 90.01%, respectively. Even after four catalytic cycles, N–Cu0.92Co2·08O4@CeO2 could be regenerated to achieve 100% degradation of ranitidine. Electrochemical analysis demonstrated that the combination of N–Cu0.92Co2·08O4@CeO2 and PMS immediately produced a strong current density, thereby rapidly producing reactive oxygen species (ROS) with high performance for the degradation of the target pollutant. Combined ion quenching and electron paramagnetic resonance analyses indicated that the main ROS was the non-free radical 1O2. Finally, a plausible ranitidine degradation pathway was deduced based on liquid chromatography–mass spectrometry (LC–MS) analysis, wherein the toxic substance N-nitrosodimethylamine was not produced during the degradation process. In short, this study provides a new perspective for preparing ternary metal catalysts for advanced oxidation processes with practical application significance.

Insight into iron oxychloride composite bone char for peroxymonosulfate activation: Mechanism of singlet oxygen evolution for selective degradation of organic pollutants

The activity of iron-based catalysts in advanced oxidation processes (AOPs) is limited by the redox cycle of Fe(III) and Fe(II). In this work, iron oxychloride (FeOCl) with a unique layered structure was loaded on the bone char (BC) to enhance the activation of peroxymonosulfate (PMS). Characterization of the FeOCl-BC catalyst reveals that the loading of FeOCl changed the composition and structure of BC and BC reduced the bond gap of FeOCl. Acetaminophen (APAP) as a target pollutant could be almost completely degraded at neutral pH, and the removal rate reached 0.6597 min−1. APAP could also be selectively oxidized by FeOCl-BC/PMS system in the presence of some inorganic anions (SO42−, NO3−, and Cl−) and humic acid. Quenching experiments, electron paramagnetic resonance (EPR), chemical probes, and linear sweep voltammetry (LSV) confirm that the primary oxidation mechanism of the FeOCl-BC/PMS system was dominated by 1O2. The 1O2 was generated from the conversion of O2•− and the self-dissociation of PMS, involving the formation of metastable iron intermediates and the redox cycle of Fe(III) and Fe(II). The unique structure of FeOCl, the transport of lattice oxygen and the enrichment of electrons by carbon defects play an essential role in generating reactive species. In this work, the limitation of the redox cycle of Fe(III) and Fe(II) was broken by loading FeOCl on the surface of BC, and a new catalytic mechanism was proposed. This work provides a new perspective for the construction of efficient iron-based catalysts and the practical application of PMS-based AOPs.

Peroxymonosulfate-assisted photocatalysis by a novel Ti3C2-based heterojunction catalyst (g-C3N4/Ti3C2/MnFe2O4) for enhanced degradation of naphthalene

Given the urgency of polycyclic aromatic hydrocarbons (PAHs) remediation and a lack of recoverable efficient catalysts for advanced oxidation processes (AOPs), a novel g-C3N4/Ti3C2/MnFe2O4 (CTM) catalyst based on the co-catalyst function of Ti3C2 (MXene) was fabricated via in situ calcination and liquid surface self-assembly, employed in a peroxymonosulfate (PMS) -assisted photocatalytic system to degrade naphthalene (NAP). Almost 100% of the NAP was removed within 45 min with pseudo-first-order kinetic constants about 2.74 and 1.97 times of those in the absence of Ti3C2 or visible light, respectively, confirming the positive role of the moderate Ti3C2 and the synergism between PMS activation and photocatalysis. The effect of initial solution pH, various inorganic anions, and actual water conditions on the reaction and stability tests revealed the potential of CTM catalysts in practical applications. There existed both free radical and non-radical pathways for NAP degradation, in which singlet oxygen (1O2) was identified as the main reactive oxygen species. This study provided a promising perspective for the rational design of efficient and stable Ti3C2-based heterojunction catalysts and their application in PMS-assisted photocatalytic systems for the effective degradation of persistent organic pollutants.

Facet tailoring and Cu doping promoted photo-assisted peroxymonosulfate activation by oxygen-deficient α-MnO2 for efficient mineralization of bisphenol a

Revealing the synergistic mechanism between facets and metal doping during catalytic processes is an efficient approach to improve the catalytic performance. Herein, the synergetic effects between Cu doping and crystal facets over α-MnO2 on the peroxymonosulfate (PMS) activation towards bisphenol A (BPA) degradation under full-spectrum light irradiation were studied in details for the first time. The Cu-doped α-MnO2 with (100), (110), and (310) facets were synthesized by hydrothermal method. The Cu-doped (110)/PMS/Light system presented the highest BPA removal efficiency with high 1O2 generation and selectivity, being superior over the Cu-doped (100), Cu-doped (310) and pristine (110) counterparts. The corresponding mechanism showed that Cu doping for α-MnO2 enhanced the absorption of light, the formation of oxygen vacancies and electronic conductivity as well as PMS activation, especially for the (110) facet, as compared to the (100) and (310) facets. In addition, density functional theory (DFT) calculations and characterizations indicated that the synergetic effect between facet and oxygen vacancies played an important role in 1O2 generation. Moreover, oxygen vacancies accelerated the complexation of PMS with surface Mn(IV) and improved the generation of 1O2, different to that due to Mn(III). Toxicity assessment showed that BPA was partially decomposed into highly toxic intermediates during the degradation process. However, Cu doping and light synergistically improved the mineralization rate of pollutants, removing 95% of the total organic carbon (TOC) and reducing the toxicity of the intermediates. The ultrahigh TOC removal was attributed to the joint effect of 1O2, O2− and electron transfer. This work therefore provides an efficient and highly selective PMS catalyst for 1O2 generation, and reveals the synergistic mechanism between metal doping and crystal facets of the catalyst in advanced oxidation processes.

Role of superoxide radical and singlet oxygen in peroxymonosulfate activation by iron-doped bone char for efficient acetaminophen degradation

Bone char is a hydroxyapatite-rich product obtained by calcining animal bones. However, the role of inorganic hydroxyapatite is often overlooked in bone char-catalyzed persulfate systems. In this work, iron was doped into swine bone-derived biochar (Fe-BC) by simple impregnation, and the Fe-BC catalysts were used for the first time to activate peroxymonosulfate (PMS). The obtained Fe-BC/PMS system could rapidly degrade the target pollutants (0.0529 s−1, 90 s) employing singlet oxygen (1O2) as the dominant reactive oxygen species (ROS). The characterization results demonstrated that iron was mainly intercalated into the catalyst by substituting calcium sites in swine bone biochar, and the Fe-BC composition was significantly affected by annealing temperature. A comprehensive study including quenching experiments, electron paramagnetic resonance (EPR), chemical probes, and linear sweep voltammetry (LSV) revealed that 1O2 was the dominant ROS. According to the characterization results, 1O2 was generated from the conversion of superoxide radical (O2•−) and the self-dissociation of PMS. Iron was the main active site of Fe-BC catalysts, and the carbon defects and oxygen-containing groups also played roles in catalyzing PMS. The Fe-BC/PMS system exhibited outstanding oxidative capability over a wide pH range (3.0–9.0) and was resistant to interference from some high concentrations of anions (Cl−, NO3–, and SO42−). This work provides a new perspective on using animal bone-derived biochar catalysts in advanced oxidation processes.

A Review on Wastewater Treatment Containing Organic Pollutants Using Advance Oxidation Processes

Advanced oxidation processes (AOPs) are the technologies that generally use the hydroxyl radicals, the ultimate oxidant for the remediation of organic contaminants in wastewater. These are highly effective novel methods speeding up the oxidation process. AOPs can combine with Fenton (H2O2/Fe2+), photo-Fenton (H2O2/UV/Fe2+), and electro-Fenton, heterogeneous photooxidation using titanium dioxide (TiO2/hv), singlet molecular oxygen process, singlet oxygen-photo-Fenton process, sonolysis, peroxidation combined with ultraviolet light (H2O2/UV), UV alone, UV/O3, UV/S2O8-2, UV/Chlorine, peroxone (O3/H2O2), peroxone combined with ultraviolet light (O3/H2O2/UV), O3/UV system, O3/TiO2/ H2O2 and O3/TiO2/Electron beam irradiation. Ozone (O3), catalyst or ultraviolet (UV) irradiation to offer a powerful treatment processes of wastewater. Future research should be focused on enhancing the properties of heterogeneous catalysts in AOPs. This review report of different AOPs utilized for the removal of various phenolic compounds and textile dyes in wastewater.

Hollow Co/CoO/Carbon nanofibers promoted PMS decomposition for the degradation of Rhodamine B

Carbon nanofibers with hollow structures have an excellent application prospect in various fields because of their high specific surface area and abundant active sites. PAN-based hollow carbon nanofiber doped with Co/CoO (H–Co/CoO–CNF) was successfully prepared and used as a catalyst to activate peroxymonosulfate (PMS) and degrade Rhodamine B (RhB). The catalyst showed a surprising degradation rate (98.89%) of RhB within 15 min and had good degradation performance in a wide pH range (pH 1.5–11.2). Compared with solid fibers, H–Co/CoO–CNF shows better cyclic characteristics. The catalyst is also magnetic and recoverable easily due to the addition of Co/CoO. Two pathways of both radical (SO4•−) and non-radical (1O2) exist during the RhB degradation process are confirmed through electron paramagnetic resonance (EPR) analysis and radical quenching experiments. This work provides a new idea for hollow fibers loaded with metals and their oxides and can guide the development of catalysts for advanced oxidation processes in the future.

Decomposition of carbon-based catalysts in advanced oxidation processes: A neglected but noteworthy problem

Carbon-based catalysts have been widely investigated in the field of advanced oxidation processes (AOPs), however their structural stability during the AOPs has been neglected. In this study, the decomposition of different carbonaceous materials, including g-C3N4, biochar, biochar/g-C3N4 composite, graphene oxide and COF in sulfate radical-based and hydroxyl radical-based AOPs was investigated, mainly focusing on g-C3N4 and modified g-C3N4 in peroxymonosulfate (PMS)-based AOPs. The g-C3N4 prepared with different precursors and modified g-C3N4 were selected to investigate their structural stability in PMS-based AOPs in detail. The results showed that both g-C3N4 and modified g-C3N4 were partially decomposed in the PMS-based AOPs leading to the carbon dissolution in solution. The concentration of dissolved carbon varied with the precursor of g-C3N4 and experimental conditions such as PMS concentration and inorganic ions. Modified g-C3N4 presented higher concentration of dissolved carbon than pristine g-C3N4. Based on the results of experiments and characterization, the decomposition of g-C3N4 and modified g-C3N4 were mainly due to their interaction with PMS. Modified g-C3N4 had higher adsorption capacity for PMS than pristine g-C3N4 leading to the enhanced interaction with PMS. The dissolved carbon from modified g-C3N4 would not affect the removal efficiency, but the mineralization efficiency of targeted organic pollutants. In addition, the dissolved components of g-C3N4 and modified g-C3N4 showed acute toxicity. In addition to g-C3N4-based catalysts, other materials such as covalent organic compound and graphene oxide could be also decomposed partially. The decomposition of g-C3N4 was also found in the peroxydisulfate and hydrogen peroxide-based AOPs. This study provided insight into the structural stability of g-C3N4-based catalysts in the PMS-based AOPs, which deserved much attention in the future studies from the point view of the design and environmental application of g-C3N4-based catalysts.

MOF-derived single-atom catalysts: The next frontier in advanced oxidation for water treatment

Over the last decade, single-atom catalysts (SACs) have emerged as a new frontier in the field of advanced oxidation processes (AOPs), since they allow combining the advantages of homogeneous and heterogeneous catalysts, eventually maximizing the atomic efficiency. Metal-organic frameworks (MOFs), periodic porous structures formed through self-assembly of transition metal cations and organic ligands, are regarded as an ideal precursor for the synthesis of SACs. In this review, the synthetic strategies and characterization methods for MOF-derived SACs are described, with special focus on experimental techniques and theoretical simulations employed to verify the existence of single atoms and metal-binding sites. In addition, applications of these catalysts in water treatment by AOPs and electrochemical AOPs based on the activation of persulfate and H2O2 are discussed, paying attention to reaction mechanisms investigated via DFT calculations. Finally, perspectives and research challenges for future development of MOF-derived SACs as catalysts in AOPs are commented.

CoNi alloy anchored onto N-doped porous carbon for the removal of sulfamethoxazole: Catalyst, mechanism, toxicity analysis, and application

Developing highly efficient, stable, recyclable, and application value heterogeneous catalysts in advanced oxidation processes has essential application value in the degradation of refractory pollutants. In this paper, the CoNi alloy anchored onto N-doped porous carbon (CoNi-600@NC) catalyst was prepared using bimetallic doped metal-organic frameworks as precursors. The magnetic CoNi-600@NC can activate peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX). Therefore, SMX can be removed 100% within 25 min. CoNi-600@NC/PMS has a broad pH (3–9) application range, good applicability, and repeatability. Radical quenching, quantitative and electrochemical experiments proved that the degradation of SMX was dominated by free radical (Superoxide anions) and non-free radical pathways (surface-bound radicals). Mechanistic analysis showed that the interaction between Co-Nx/pyridine N-sites and graphitized carbon with PMS induced the formation of surface-bound active species. Moreover, CoNi nanoparticles promoted the redox cycle of metals. The synergistic catalytic mechanisms between the CoNi alloy and the abundant functional groups gave CoNi-600@NC excellent catalytic properties and applicability. Using density functional theory predicted the reaction sites of SMX and proposed four degradation pathways. The toxicity of intermediates was comprehensively evaluated. In addition, a CoNi-600@NC continuous flow reactor was constructed with a daily treatment capacity of 45 L and 100% SMX removal. This study expands the application of persulfate advanced oxidation technology by synthesizing recyclable magnetic catalysts and provides new synergistic degradation mechanisms for removing refractory organics.

Peroxydisulfate activation by 2D MOF-derived Ni/Fe3O4 nanoparticles decorated in 3D graphene oxide network

Metal organic framework (MOF)-derived materials normally have three-dimensional (3D) structure, while little attention has been paid to two-dimensional (2D) MOF-derived materials with high catalytic activity. Nevertheless, the underlying agglomeration and metal leaching issues of 2D MOF-derived catalysts hinder their real applications. In this work, we report a bimetallic nanocomposite (Ni-Fe-C-600-acid/GO) derived from 2D Ni-Fe-MOF and graphene oxide (GO) network. Employing Ni(0) and Fe3O4 as active site, the Ni-Fe-C-600-acid/GO shows high efficiency in peroxydisulfate (PDS) activation for the removal of p-chloroaniline (PCA), and the catalyst/PCA dosage ratio (0.8) is substantially lower than those of the previous studies (3.9–156.9). The prepared catalysts demonstrate high catalytic activity over a wide pH range of 3–9 and maintain high efficiency after five cycles with good tolerance to inorganic anions. The singlet oxygen is identified as the predominant active species and relatively weak contributions from sulfate free radicals and hydroxyl radicals are confirmed. This catalysis system presents new insights in 2D MOF-derived catalysts in advanced oxidation processes.

Metal–Organic Frameworks as Powerful Heterogeneous Catalysts in Advanced Oxidation Processes for Wastewater Treatment

Nowadays, the contamination of wastewater by organic persistent pollutants is a reality. These pollutants are difficult to remove from wastewater with conventional techniques; hence, it is necessary to go on the hunt for new, innovative and environmentally sustainable ones. In this context, advanced oxidation processes have attracted great attention and have developed rapidly in recent years as promising technologies. The cornerstone of advanced oxidation processes is the selection of heterogeneous catalysts. In this sense, the possibility of using metal–organic frameworks as catalysts has been opened up given their countless physical–chemical characteristics, which can overcome several disadvantages of traditional catalysts. Thus, this review provides a brief review of recent progress in the research and practical application of metal–organic frameworks to advanced oxidation processes, with a special emphasis on the potential of Fe-based metal–organic frameworks to reduce the pollutants present in wastewater or to render them harmless. To do that, the work starts with a brief overview of the different types and pathways of synthesis. Moreover, the mechanisms of the generation of radicals, as well as their action on the organic pollutants and stability, are analysed. Finally, the challenges of this technology to open up new avenues of wastewater treatment in the future are sketched out.

Effect of the chloride ion on advanced oxidation processes catalyzed by Fe-based metallic glass for wastewater treatment

Fe-based metallic glasses (Fe–MGs) are potential candidate catalysts for advanced oxidation processes (AOPs) for recalcitrant organic pollutant degradation. However, industrial wastewater and natural contaminated sites usually contain abundant inorganic ions, like the chloride ion (Cl−), which significantly affect AOPs, but their influence on MG-activated AOPs still remains unclear. Through the study of three commonly used oxidants, hydrogen peroxide (H2O2), peroxydisulfate (PDS), and peroxymonosulfate (PMS), the effect of Cl− on the FeSiB-catalyzed process of degradation of the typical azo dye Orange II was investigated. Evidence indicates that the addition of Cl− resulted in the monotonous inhibition of the degradation process when the H2O2/FeSiB and PDS/FeSiB systems were employed, but promoted effect was detected with the PMS/FeSiB system, which is different from the previously observed dual effect of Cl−. It is closely relative with FeSiB induced unique variety of degradation pathways, including radicals, non-radicals (1O2), and direct reduction degradation. Moreover, the presence of Cl− significantly affected the systems’ absorbable organic halogen content and the amount of Fe leached into the solution. The results of this work will provide essential references for Fe-based MG used as AOP catalysts in field applications and the development of advanced MGs with excellent adaptability to complex environments.

Rapid degradation of organic pollutants by Fe3O4@PDA/Ag catalyst in advanced oxidation process

Over the past decades, the development of novel catalysts on the degradation of organic pollutants has attracted increasing attention. In this work, we synthesized silver decorated magnetic nanoparticles (Fe3O4@PDA/Ag NPs) to activate H2O2 for organic pollutants removal via advanced oxidation processes (AOPs). The catalyst was prepared through in-situ reduction of AgNO3 by the polydopamine (PDA) layer on Fe3O4 NPs. Chemiluminescence results obtained from luminol/H2O2 system revealed that the catalyst exhibited excellent catalytic effect on the decomposition of H2O2 into reactive oxygen species (ROS) and superoxide radical (O2―) was mainly responsible for the oxidative degradation. Importantly, the fast evolution frequency of oxygen gas bubbles produced in the reaction of Ag NPs and H2O2 could generate vigorous fluid convection and autonomous motion of catalyst when H2O2 concentration reached 1%. Additionally, the catalyst can suspend in solution for several minutes. Therefore, by coupling the vigorous motion with slow sedimentation velocity, the catalyst can realize rapid degradation of organic pollutants without external mixing force. The Fe3O4@PDA/Ag NPs catalysts not only showed a high removal efficiency of malachite green, but also can be applied for the degradation of other dyes, making it to be a promise candidate for environmental remediation. With the merits of excellent catalytic effect, fast degradation speed, and simplicity of operation, the prepared catalysts exhibits great potential in the practical field.

Efficient degradation of Health-threatening organic pollutants in water by atomically dispersed Cobalt-Activated peroxymonosulfate

Degrading health-threatening organic pollutants (HTOPs) in water systems through advanced oxidation processes (AOPs) is an effective way to treat environmental wastewater; however, such processes require advanced catalysts. This study combined complexation effects and structural confinement strategies to rapidly prepare Co2+-isolated metal–organic framework polymers and utilized a thermal treatment process to achieve the efficient anchoring of atom-dispersed Co in a boron–carbon-nitrogen matrix (denoted as SACoN/BCN), which can improve the utilization of Co catalytic sites. SACoN/BCN effectively activated peroxymonosulfate (PMS), with the ratio and mineralization rate of sulfamethazine (SMT) removed by degradation within 40 min reached 95.2 % and 70.0 %, respectively. Radical inhibition experiments and electron paramagnetic resonance (EPR) tests showed that 1O2 generated from SACoN/BCN-activated PMS was the key reactive oxygen species that promoted HTOP degradation. Density functional theory calculations revealed that, following the introduction of electron-deficient B heteroatoms, electrons in PMS will be injected into SACoN/BCN, thereby realizing strong adsorption and further activation of PMS. The cytotoxicity of SACoN/BCN is almost negligible because of the chemical bonding (or entrapment) of Co atoms in the inorganic boron–carbon-nitrogen matrix, thereby preventing Co from forming mobile CoII ions in the aqueous system. This research provides information for advanced catalysts for the removal of HTOPs and experimental and theoretical inspiration for the preparation of single-atom catalysts for advanced oxidation processes and the mechanism of PMS activation.

Microwave (MW)-assisted design of cobalt anchored 2D graphene-like carbon nanosheets (Co@GCNs) as peroxymonosulfate activator for tetracycline degradation and insight into the catalytic mechanism

Developing a rapid and cost-effective strategy to design catalysts for advanced oxidation processes (AOPs) has significant implications for environmental remediation. In this study, cobalt anchored 2D graphene-like carbon nanosheets (Co@GCNs) catalysts were fabricated by simple coordination of metal precursors into agarose through microwave (MW)-assisted method to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. Among them, the Co@GCN-1 exhibited excellent dispersibility and catalytic performance. The Co@GCN-1/PMS system could completely degrade TC (20 mg L–1) within 20 min, whose reaction rate constant (0.273 min−1) was about 6.5 times that of the Co3O4/PMS system (0.0362 min−1) and 14.1 times of the GCN/PMS system (0.0194 min−1), respectively. Additionally, the degradation performance was applicable in a wide pH range (3.84–9.03) and still reached an efficiency of>90% after five cycles. Non-radical pathway represented by 1O2 served as the main contributor to TC degradation besides radicals (i.e., SO4−, OH, and O2−). Density functional theory (DFT) calculations unveiled the synergistic interaction of Co@GCNs, where 2D GCNs as electron mediators promoted the Co3+/Co2+ cycle. Based on the LC-MS analysis, three main degradation pathways of TC including fourteen possible intermediates were proposed based on different ROS reactions. This work provides a facilely prepared and promising 2D metal-based carbonous catalyst to activate PMS for the efficient degradation of TC.

Goethite and lepidocrocite catalyzing different double-oxidant systems to degrade chlorophenol.

Goethite and lepidocrocite, as the main compositions of pipe deposits in the water distribution network, could be used as a catalyst for advanced oxidation processes (AOPs). This research utilizes them to activate PDS/H2O2 and PMS/H2O2 degrading the 2,4,6-trichlorophenol, respectively. To describe the incomplete degradation of pollutants and reflect the induction period, a modified first-order model has been proposed and used to analyze degradation differences under several key affecting factors. The results revealed that the PDS/H2O2 system has a synergy effect in the 2,4,6-trichlorophenol degradation process. The possible degradation pathways and intermediate products were confirmed by gas chromatograph-mass spectrometry (GC-MS). The paper provides a new idea for the effective use of pipe deposits to remove chlorophenols from drinking water, which is of great significance to ensure water quality safety.

Hierarchical porous N-doped carbon encapsulated CoFe2O4-CoO nanoparticles derived from layered double hydroxide/chitosan biocomposite for the enhanced degradation of tetracycline

Developing a sustainable, efficient, and cost-effective heterogeneous catalyst for advanced oxidation processes is challenging in wastewater remediation. Herein, chitosan intercalated CoFe-layered double hydroxide was first employed as a precursor to fabricate a novel CoFe2O4-CoO/N-doped carbon composite (CoFe-LDO/NC) via a simple “in-situ coprecipitation-calcination” method. The resulting CoFe-LDO/NC was carefully characterized and employed to degrade tetracycline (TC) with the assistance of peroxymonosulfate (PMS). Under the optimum conditions (30 mg L−1 TC, 0.4 g L−1 catalyst, 0.4 g L−1 PMS, pH = 5), the degradation efficiency and mineralization degree reached 97.6% and 60.7% within 30 min, respectively. The superior activity of CoFe-LDO/NC was ascribed to its well-dispersed metal nanoparticles, large specific surface area (230.7 m2 g−1), hierarchical porous structure, and intensified electron transfer efficiency. The quenching test revealed that both the sulfate radicals and singlet oxygen were the dominant active species in the system. The degradation mechanism and TC evolution route were speculated by X-ray photoelectron spectroscopy and liquid chromatography-mass spectrometry. Escherichia coli growth inhibition test exhibited remarkable detoxification of TC solution after degradation. Moreover, CoFe-LDO/NC could be easily collected by magnetism, and 94.3% of its original activity was retained after five cycles. This work offers a green and scalable approach for the rational design of heterogeneous Co-based catalysts for degradation.