Bimetallic iron-nickel phosphide as efficient peroxymonosulfate activator for tetracycline hydrochloride degradation: Performance and mechanism

Sulfate radical-based advanced oxidation processes with (SR-AOPs) are widely employed to degrade organic pollutants due to their high efficiency, cost-effectiveness and safety. In this study, a highly active and stable FeNiP was successfully prepared by reduction and heat treatment. FeNiP exhibited high performance of peroxymonosulfate (PMS) activation for tetracycline hydrochloride (TC) removal. Over a wide pH range, an impressive TC degaradation efficiency 97.86% was achieved within 60 min employing 0.1 g/L FeNiP and 0.2 g/L PMS at room temperature. Both free radicals of SO4·-, ·OH, ·O2- and non-free radicals of 1O2 participated the TC degradation in the FeNiP/PMS system. The PMS activation ability was greatly enhanced by the cycling between Ni and Fe bimetal, and the active site regeneration was achieved due to the existence of the negatively charged Pn-. Moreover, the FeNiP/PMS system exhibited substantial TC degradation levels in both simulated real-world disturbance scenarios and practical water tests. Cycling experiments further affirmed the robust stability of FeNiP catalyst, demonstrating sustained degradation efficiency of approximately 80% even after four cycles. These findings illuminate its promising potential across natural water bodies, presenting an innovative catalyst construction approach for PMS activation in the degradation of antibiotic pollutants.

Fe3O4/biochar modified with molecularly imprinted polymer as efficient persulfate activator for salicylic acid removal from wastewater: Performance and specific recognition mechanism

In this study, a novel Fe3O4-based biochar coupled surface-imprinted polymer was constructed via simple hydrothermal route for salicylic acid recognition and degradation in advanced oxidation processes. The material exhibited excellent adsorption capability, up to 118.23 mg g-1, and efficient degradation performance, 87.44% removal rate within 240 min, based on integrating the advantages of both huge specific surface area as well as abundant functional groups from biochars and specific recognition sites from imprinted cavities. Moreover, high selectivity coefficient (11.67) showed stable recognition in single and binary systems. SO4•- and •OH were confirmed as reactive oxygen species in catalytic reaction according to quenching experiments and EPR analysis. The degradation mechanism and pathway were unraveled by DFT calculations and LC-MS. Furthermore, the results of toxicity evaluation, stability and reusability demonstrated application potential in the field of water environment restoration. This study confirmed that molecular imprinting provided a promising solution to targeted removal of emerging environmental pollutants by degrading after the enrichment of pollutants to the composites surface.

Effect of interaction between dissolved organic matter and iron/manganese (hydrogen) oxides on the degradation of organic pollutants by in-situ advanced oxidation techniques

Iron and manganese (hydrogen) oxides (IMHOs) exhibit excellent redox capabilities for environmental pollutants and are commonly used in situ chemical oxidation (ISCO) technologies for the degradation of organic pollutants. However, the coexisting dissolved organic matter (DOMs) in surface environments would influence the degradation behavior and fate of organic pollutants in IMHOs-based ISCO. This review has summarized the interactions and mechanisms between DOMs and IMHOs, as well as the properties of DOM-IMHOs complexes. Importantly, the promotion or inhibition impact of DOM was discussed from three perspectives. First, the presence of DOMs may hinder the accessibility of active sites on IMHOs, thus reducing their efficiency in degrading organic pollutants. The formation of compounds between DOMs and IMHOs alters their stability and activity in the degradation process. Second, the presence of DOMs may also affect the generation and transport of active species, thereby influencing the oxidative degradation process of organic pollutants. Third, specific components within DOMs also participate and affect the degradation pathways and rates. A comprehensive understanding of the interaction between DOMs and IMHOs helps to better understand and predict the degradation process of organic pollutants mediated by IMHOs in real environmental conditions and contributes to the further development and application of IMHO-mediated ISCO technology.

Feasibility and mechanism of removing Microcystis aeruginosa and degrading microcystin-LR by dielectric barrier discharge plasma

Harmful cyanobacterial bloom is one of the serious environmental problems worldwide. Microcystis aeruginosa is a representative harmful alga in cyanobacteria bloom. It is of great significance to develop new technologies for the removal of Microcystis aeruginosa and microcystins. The feasibility and mechanism of removing microcystis aeruginosa and degrading microcystins by dielectric barrier discharge (DBD) plasma were studied. The suitable DBD parameters obtained in this study are DBD (41.5 W, 40 min) and DBD (41.5 W, 50 min), resulting in algae removal efficiency of 77.4% and 80.4%, respectively; scanning electron microscope and LIVE-DEATH analysis demonstrate that DBD treatment can disrupt cell structure and lead to cell death; analysis of elemental composition and chemical state indicated that there are traces of oxidation of organic nitrogen and organic carbon in microcystis aeruginosa; further intracellular ROS concentration and antioxidant enzyme activity analysis confirm that DBD damage microcystis aeruginosa through oxidation. Meanwhile, DBD can effectively degrade the microcystin-LR released after cell lysis, the extracellular microcystin-LR concentration in the DBD (41.5 W) group decreased by 88.7% at 60 min compared to the highest concentration at 20 min; further toxicity analysis of degradation intermediates indicated that DBD can reduce the toxicity of microcystin-LR. The contribution of active substances to the inactivation of microcystis aeruginosa is eaq- > •OH > H2O2 > O3 > 1O2 > •O2- > ONOO-, while on the degradation of microcystin-LR is eaq- > •OH > H2O2 > O3 > •O2- > 1O2 > ONOO-. The application of DBD plasma technology in microcystis aeruginosa algae removal and detoxification has certain prospects for promotion and application.

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq- > •OH > 1O2 > •O2- > ONOO-, while the contribution order to microcystin-LR degradation was eaq- > •OH > •O2- > 1O2 > ONOO-. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

The fates of antibiotic resistance genes and their association with cell membrane permeability in response to peroxydisulfate during composting

The aims of this study were to use metagenomics to reveal the fates of antibiotic resistance genes (ARGs) during composting under the regulation of peroxydisulfate and clarify the relationship between ARGs and cell membrane permeability. Results showed that peroxydisulfate increased cell membrane permeability by effectively regulating the expression of outer membrane protein and lipopolysaccharide related genes. Besides, it reduced polysaccharides and proteins in extracellular polymer substances by 36% and 58%, respectively, making it easier for intracellular ARGs (i-ARGs) to reach the extracellular environment, among which the absolute intracellular abundance of mphK, Erm(31), and tet(44) decreased to 1.2, 1.0, and 0.89 fold of the control, respectively. Finally, variation partitioning analysis showed that i-ARGs dominated the removal of ARGs. These results revealed that the removal of i-ARGs by activated peroxydisulfate was the key to the removal of ARGs and increased cell membrane permeability played a key role for peroxydisulfate to remove i-ARGs during composting.

The removal performances and evaluation of heavy metals, antibiotics, and resistomes driven by peroxydisulfate amendment during composting

This study aimed to explore the effect of peroxydisulfate on the removal of heavy metals, antibiotics, heavy metal resistance genes (HMRGs), and antibiotic resistance genes (ARGs) during composting. The results showed that peroxydisulfate achieved the passivation of Fe, Mn, Zn, and Cu by promoting their speciation variations, thus reducing their bioavailability. And the residual antibiotics were better degraded by peroxydisulfate. In addition, metagenomics analysis indicated that the relative abundance of most HMRGs, ARGs, and MGEs was more effectively down-regulated by peroxydisulfate. Network analysis confirmed Thermobifida and Streptomyces were dominant potential host bacteria of HMRGs and ARGs, whose relative abundance was also effectively down-regulated by peroxydisulfate. Finally, mantel test showed the significant effect of the evolution of microbial communities and strong oxidation of peroxydisulfate on the removal of pollutants. These results suggested that heavy metals, antibiotics, HMRGs, and ARGs shared a joint fate of being removed driven by peroxydisulfate during composting.

Performances of antibiotic resistance genes profile upon the action of biochar-activated peroxydisulfate in composting

In this study, the amendment of biochar-activated peroxydisulfate during composting to remove antibiotic resistance genes (ARGs) by direct (microbial community succession) and indirect methods (physicochemical factors) was analyzed. When implementing indirect methods, the synergistic effect of peroxydisulfate with biochar optimized the physicochemical habitat of compost, maintaining its moisture within a range of 62.95%-65.71%, and a pH of 6.87-7.73, and causing the compost to mature 18 days earlier than the control groups. The direct methods caused the optimized physicochemical habitat to adjust the microbial communities and reduce the abundance of most of the ARG host bacteria (Thermopolyspora, Thermobifida, and Saccharomonospora), thus inhibiting this substance's amplification. Heatmap analysis confirmed the necessary connection between physicochemical factors, microbial communities, and ARGs. Moreover, a mantel test confirmed the direct significant effect of the microbial communities on ARGs and the indirect significant effect of physicochemical factors on ARGs. The results showed that the abundance of more ARGs was down-regulated at the end of composting and regulated by biochar-activated peroxydisulfate, especially for the abundance of AbaF, tet(44), golS, and mryA, which was significantly decreased by 0.87-1.07 fold. These results provide new insights into the removal of ARGs during composting.

Revelation of contributing mechanism of reactive oxygen species in photocatalytic ozonation heterocyclization of gaseous hexane isomers

The reactive oxygen species (ROS) involved photocatalytic ozonation of gaseous n-hexane to heterocyclic compounds has been recently reported. However, whether such heterocyclization reaction happens on other alkanes and what is the contributing mechanism of ROS to the heterocyclic compound formation are still unclear. In present study, photocatalytic ozonation of three n-hexane's isomers (i.e. 2-methypentane, 3-methylpentane and 2,3-dimethylbutane) on Cu₂O-CuO/TiO₂-foam ceramic was investigated. Within reaction period, 2-methylpentane and 3-methylpentane not only showed higher average degradation efficiency than 2,3-dimethylbutane, but also separately converted to interfacial heterocyclic compounds of 5,5-dimethyldihydro-2(3H)-furanone and 4,5-dimethyl-4,5-dihydro-2(3H)-furanone. Enough reaction time, optimum experimental atmosphere and shorter light wavelength benefited the formation of heterocyclization products. None of O₃, ¹O₂, electron and hole directly contributed to the heterocyclic compound formation. While ^•O₂^- dominated the production of the heterocyclic compound under the dry reaction atmosphere and ^•OH showed more important role than ^•O₂^- in the heterocyclic compound formation under the moist reaction atmosphere. Theoretical calculation confirmed that ^•OH or ^•O₂^- induced heterocyclization reaction of alkane was exothermic, while the former reaction released 0.47 eV higher energy than the later reaction. The findings provide a comprehensive understanding of contributing roles of ROS in heterocyclization reaction of alkanes, and are helpful for effective elimination of industrial alkanes by advanced oxidation methods.

Mechanism of dielectric barrier plasma technology to improve the quantity and quality of short chain fatty acids in anaerobic fermentation of cyanobacteria

The recycling of high value carbon resources from cyanobacteria has become a research hotspot. This work investigated the possibility of dielectric barrier discharge (DBD) plasma pretreatment to improve the anaerobic fermentation performance of cyanobacteria. The maximum accumulations of short-chain fatty acids (SCFAs) and acetic acid in DBD group were 3.30 and 1.49 times of that in control group. The physical effects of DBD plasma and the oxidative stress response of cyanobacteria cells could improve the solubilization of cyanobacteria polymer. The destruction of humus by DBD plasma can reduce the negative impact of humus on the early stage of anaerobic fermentation, thus facilitating the rapid start of anaerobic fermentation. The contents of Bacteroidetes, Firmicutes and Chloroflexi in DBD group were higher than those in control group, while the content of Proteobacteria was on the contrary, which was conducive to the hydrolysis and acidification process. The decrease of Methanosaeta sp. and Methanosarcina sp. abundance in DBD group might be another reason for the increase of acetic acid ratio. Under the joint action of plasma chemical oxidation and microbial degradation, the degradation effect of microcystin-LR in the anaerobic fermentation supernatant of DBD group was better than that of the control group, which was conducive to the recycling of cyanobacteria anaerobic fermentation supernatant. Therefore, DBD pretreatment was conductive to recycling valuable carbon source from cyanobacteria and can be further developed as a potential new pretreatment technology.

Construction lamellar BaFe12O19/Bi3.64Mo0.36O6.55 photocatalyst for enhanced photocatalytic activity via a photo-Fenton-like Mo6+/Mo4+redox cycle

The novel BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 composite materials were constructed as magnetically recyclable photo-Fenton-like degradation systems. The composite catalyst not only promoted the effective transfer of photo-generated electrons and improved the Mo⁶⁺/Mo⁴⁺ cycle consequent, but also activated hydrogen peroxide to generate oxidizing free radicals. BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55-0.25 exhibited an outstanding degradation performance for tetracycline hydrochloride it is 1.3 times to Bi_3.64Mo_0.36O_6.55. The thermal catalytic performance of the Bi_3.64Mo_0.36O_6.55 monomer is similar to that of the BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 material without light. However, the removal rate of BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 material reaches 84.5% after 60 min with light, far exceeding that of Bi_3.64Mo_0.36O_6.55 material. By way of the contrast experiment with light and without light, it is further demonstrated that interfacial interaction between BaFe₁₂O₁₉ and Bi_3.64Mo_0.36O_6.55 acted a key role in the photocatalytic reaction system. It is also a good advantage that pollutants can be efficiently degraded without adjusting the pH. The characterization of photocurrent and X-ray photoelectron spectroscopy (XPS) also further proved the synergy between the two materials, which is useful to the separation of electrons and holes. The synergy ultimately improves the degradation performance. Besides, BaFe₁₂O₁₉/Bi_3.64Mo_0.36O_6.55 can be easily separated by an external magnetic field after the photocatalytic activity reaction owing to BaFe₁₂O₁₉'s magnetic properties. It provides a new research idea for the construction and iron-based heterogeneous Fenton-like system for magnetic degradation of antibiotics.

Highly efficient removal of oxytetracycline using activated magnetic MIL-101(Fe)/γ-Fe2O3 heterojunction catalyst

A novel magnetic nanocomposite MIL-101(Fe)/γ-Fe₂O₃ was synthesized by hydrothermal method. The physical structure and chemical property of the as-obtained magnetic nanocomposite was characterized. The ability of MIL-101(Fe)/γ-Fe₂O₃ to promote photo-assisted peroxydisulfate (PDS) activation was investigated by using oxytetracycline (OTC) as the target pollutant. The results showed that the composite with a FeCl₃•6H₂O: γ-Fe₂O₃ mass ratio of 10:1 exhibited the highest degradation efficiency (up to 91.2%). Influencing factors such as pH, catalyst dosage, PDS concentration and OTC concentration on the catalytic performance of MIL-101(Fe)/γ-Fe₂O₃ were also investigated to determine the optimum conditions. More importantly, the MIL-101(Fe)/γ-Fe₂O₃ can be magnetically recovered and reused for 4 cycles. Based on radical quenching and electron spin resonance (ESR), the possible degradation mechanism of OTC in photo-assisted PDS activation (PPA) system was proposed. This research provided novel insights for the design and preparation of a new type of magnetic Fe-MOFs for environmental remediation.

Modulated construction of Fe-based MOF via formic acid modulator for enhanced degradation of sulfamethoxazole：Design, degradation pathways, and mechanism

Metal-organic frameworks (MOFs) have attracted more attention because of their excellent environmental catalytic capabilities. Modulation approach as an advanced assistant strategy is vital essential to enhancing the performance of MOFs. In this study, the modulated method was used to successfully synthesize a group of Fe-based MOFs, with formic acid as the modulator on the synthesis mixture. The most modulated sample Fe-MOFs-2 exhibit high specific surface areas and higher catalytic activity, which could effectively degrade SMX via PS activation, with almost 95% removal efficiency within 120 min. The results revealed that the % RSE of modulated Fe-MOFs-2 increased from 2.31 to 3.27 when compared with the origin Fe-MOFs. This may be due to the addition of formic acid induces the formation of more coordinatively unsaturated metal sites in the catalyst, resulting in structural defects. In addition, the quenching experiment and EPR analysis verified SO₄^-·and·OH as the major active free radicals in the degradation process. Modulated Fe-MOFs-2 demonstrated good reusability and stability under fifth cycles. Finally, four possible degradation pathways and catalytic mechanism of Fe-MOFs-2 was tentatively proposed. Our work provides insights into the rational design of modulated Fe-MOFs as promising heterogeneous catalysts for advanced wastewater treatment.

Critical review of perovskite-based materials in advanced oxidation system for wastewater treatment: Design, applications and mechanisms

Perovskite has been widely concerned in the field of modern environmental catalysis due to its low price, high stability, excellent catalytic activity, diverse structure and strong conversion adaptability. In recent years, people have been working on the coupling of perovskite catalysts and advanced oxidation processes (AOPs) on the removal of organic pollutants from wastewater. In this review, we classified perovskites of different designs and summarized the application and basic reaction mechanisms of each perovskite in different AOPs. This review helps scientists selecting and designing more effective perovskite catalysts for AOPs by summarizing the applications and reaction mechanisms of perovskite in AOPs. At the end of the review, the challenges and future directions of perovskite in removing organic pollutants from wastewater are discussed.

Fe@C activated peroxymonosulfate system for effectively degrading emerging contaminants: Analysis of the formation and activation mechanism of Fe coordinately unsaturated metal sites

Carbon-encapsulated Fe nanocomposites (Fe@C), obtained by pyrolysis of metal-organic frameworks (MOFs), can activate peroxymonosulfate (PMS) to remove emerging contaminants (ECs). Unfortunately, the current MOFs-derived catalysts always inevitably produce more iron-oxide compounds that unfavorable for PMS activation. In this work, according to the thermogravimetric curve of Fe(II)-MOF-74, to discuss the role of pyrolysis temperature on the structural characteristics of Fe@C. The results demonstrated that Fe@C-4 could obtain abundant coordinately unsaturated metal sites and exhibited the best activation performance. Radical-quenching experiments and EPR measurements confirm that the generated sulfate radical (SO₄^-˙) and singlet oxygen (¹O₂) only degraded approximately 35% of TBBPA. Meanwhile, negatively charged complex intermediates formed by the weak interaction between Fe@C-4 and PMS was proposed as the dominant reactive species, and approximately 65% of TBBPA was degraded. This work optimizes the synthesis strategy and mechanism of Fe@C and provides a methodological reference for the design of Fe-based catalysts.

Review on application of perylene diimide (PDI)-based materials in environment: Pollutant detection and degradation

Environment pollution is getting serious and various poisonous contaminants with chemical durability, biotoxicity and bioaccumulation have been widespreadly discovered in municipal wastewaters and surface water. The detection and removal of pollutants show great significance for the protection of human health and other organisms. Due to its distinctive physical and chemical properties, perylene diimide (PDI) has received widespread attention from different research fields, especially in the area of environment. In this review, a comprehensive summary of the development of PDI-based materials in fluorescence detection and advanced oxidation technology for environment was introduced. Firstly, we chiefly presented the recent progress about the synthesis of PDI and PDI-based nanomaterials. Then, their application in fluorescence detection for environment was presented and categorized, principally including the detection of heavy metal ions, harmful anions and organic contaminants in the environment. In addition, the application of PDI and PDI-based materials in different advanced oxidation technologies for environment, such as photocatalysis, photoelectrocatalysis, Fenton and Fenton-like reaction and persulfate activation, was also summarized. At last, the challenges and future prospects of PDI-based materials in environmental applications were discussed. This review focuses on presenting the practical applications of PDI and PDI-based materials as fluorescent probes or catalysts (especially photocatalysts) in the detection of hazardous substances or catalytic elimination of organic contaminants. The contents are aimed at supplying the researchers with a deeper understanding of PDI and PDI-based materials and encouraging their further development in environmental applications.

Fabrication of Bi1.81MnNbO6.72/sulfite system for efficient degradation of chlortetracycline

The design of eco-friendly Bi_1.81MnNbO_6.72/sulfite system for efficient degradation of chlortetracycline was achieved. The feasibility of synthesizing Bi_1.81MnNbO_6.72 by hydrothermal method was determined by X-ray diffraction. The magnetic test suggested that Bi_1.81MnNbO_6.72 possessed paramagnetic properties, indicating unpaired electrons were present. Scanning electron microscope and transmission electron microscopy images revealed that Bi_1.81MnNbO_6.72 octahedra exhibited exposed [1,1,1] crystal plane containing high density of Bi, Mn and Nb metal atoms. Large numbers of metal atoms will facilitate heterogeneous catalytic process. In a batch system with aeration, Bi_1.81MnNbO_6.72 could be used as sulfite activator for the disposal of chlortetracycline. The reaction kinetics of the degradation process conformed to the pseudo-second-order kinetic model. In Bi_1.81MnNbO_6.72/sulfite process, initial pH, Bi_1.81MnNbO_6.72 dosage, sulfite and chlortetracycline concentrations, as well as inorganic salt ions had great effect on chlortetracycline degradation. Under optimal conditions, the efficiency of Bi_1.81MnNbO_6.72/sulfite system for degradation of chlortetracycline could reach 76.2%. Moreover, Mn (II) plays a key role in the initiation of the catalytic reaction in Bi_1.81MnNbO_6.72/sulfite process. Generated SO₃^●‒ could act as main reactive species in Bi_1.81MnNbO_6.72/sulfite process, while HO^● was also involved. Three new degradation products were detected by UHPLC/MS/MS and the possible degradation pathways in this system were proposed. Based on this, we believe that Bi_1.81MnNbO_6.72/sulfite is a type of process for degradation of organic contaminants with research significance and application prospects.

Efficient degradation of tetracycline by CoFeLa-layered double hydroxides catalyzed peroxymonosulfate: Synergistic effect of radical and nonradical pathways

Advanced oxidation technologies based on peroxymonosulfate (PMS) have attracted increasing attention because of their high reactivity and selectivity. Herein, we reported a novel CoFeLa-LDH catalyst, which exhibited excellent performance to activate PMS for tetracycline (TC) elimination. The influence of extra addition, simulation wastewater tests and the reusability experiments were investigated in detail. Remarkably, the quenching experiments and the results of EPR demonstrated the synergistic effect of radical and nonradical pathways in the TC degradation. Free radicals (SO₄- and HO) played predominant roles in the first 1 min, and then both free and non-free radicals (¹O₂) interacted with TC. The possible TC degradation pathways were proposed on basis of the intermediates, which were analyzed by UPLC-QTOF-MS/MS. Finally, the reaction mechanisms of TC degradation in CoFeLa-LDH₂/PMS system were proposed according to the comprehensive analysis.

ZSM-5-(C@Fe) activated peroxymonosulfate for effectively degrading ciprofloxacin: In-depth analysis of degradation mode and degradation path

In this work, ZSM-5-(C@Fe), as a peroxymonosulfate (PMS) heterogeneous activator, was synthesized, characterized, and evaluated for activating PMS to degrade ciprofloxacin (CIP) in wastewater. Zeolite Socony Mobil-5 (ZSM-5) was utilized to enhance structural stability and provided a scaffold to graft Fe doping C nanocomposites activator. Pyrolytic metal-organic frameworks (MOFs) can use crystal structure to construct stable carbon-encapsulated Fe nanocomposites. The formation of C-O-Si, C-O-Al and C-Fe was the key to the stability of catalysts. Fe doping in ZSM-5-(C@Fe) formed non-radical degradation pathway was the key to improve the degradation efficiency. The experimental data indicated ZSM-5-(C@Fe) could completely remove 20 mg L^-1 CIP within 15 min and achieve good results in the experiments of treating actual wastewater, which could reduce 40% COD of the paper mill aerobic pond effluent. The Fukui function calculation and UHPL C-H RMS/MS analysis elucidated that the ¹O₂-dominated electrophilic reaction and the ZSM-5-(C@Fe) complex PMS-dominated nucleophilic reaction were the main pathways for CIP degradation and the radical degradation pathway (·OH and SO₄^-˙) plays auxiliary role. In addition, two new degradation pathways of the N29 and C27 in quinolone ring and the N22 in piperazine ring were discovered. This finding had important implications for the removal of N from organic pollutants.

Formation of odorous aldehydes, nitriles and N-chloroaldimines from combined leucine in short oligopeptides during chlorination

Previous studies have focused on investigating the formation of odorous by-products during the chlorination of free amino acids (AAs). However, studies on the formation of odorous by-products during the chlorination of combined AAs, which are much more abundant in natural waters than free AAs, are very limited. In this study, the generation of odorous aldehyde, nitrile and N-chloroaldimine from short oligopeptides containing combined Leucine (Leu) (a typical precursor of odorous by-products), including glycylleucine (Gly-Leu), leucylglycine (Leu-Gly), and trileucine (Leu-Leu-Leu), was investigated. The reaction mechanisms were then proposed based on Acquity UPLC-qTOF mass spectrometer measurement and kinetic studies modelled with Kintecus. The results indicated that a series of sequential reactions, including substitution, dehydrohalogenation, β-elimination, hydrolysis and decarboxylation reactions, occurred during the chlorination of short oligopeptides. The chlorination of Gly-Leu and Leu-Leu-Leu formed free Leu, which continued to react with chlorine, producing isovaleraldehyde, isovaleronitrile and N-chloroisovaleraldimine. Compared with Gly-Leu, Leu-Leu-Leu produced less free Leu, and therefore, a smaller amount of Leu-derived odorous by-products was generated. Leu-Gly produced free Gly, which was not a precursor of odorous by-products. Thus, neither isovaleraldehyde nor N-chloroisovaleraldimine was formed. Notably, isovaleronitriles can be formed directly from a β-elimination reaction during chlorination of Leu-Gly and Leu-Leu-Leu, and thus high yields of isovaleronitriles were observed after chlorination. The yields of odorous by-products during chlorination of short oligopeptides increased with increasing Cl/N ratios (the molar ratio of chlorine to nitrogen in the AAs) and reached their maximum at Cl/N = 2.4, except the yield of isovaleraldehyde formed from Gly-Leu reached its maximum at Cl/N = 1.6. UV and UV/H₂O₂ pre-treatments decreased odorous by-product formation during subsequent chlorination through non-peptide bond breaking of short oligopeptides. This study facilitates the identification of the causes of off-flavour problems in drinking water and the development of ways to control these problems.

Activation of persulfate by stability-enhanced magnetic graphene oxide for the removal of 2,4-dichlorophenol

A stability-enhanced magnetic catalyst, composed of α-Fe₂O₃@Fe₃O₄ shell-core magnetic nanoparticles and graphene oxide (MGO), was prepared and characterized by scanning electron micrope (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). Catalyst synthesis was used to efficiently activate persulfate for the removal of 2,4-dichlorophenol (2,4-DCP). A magnetic nanoparticle:GO mass ratio of 5 (MGO-5) exhibited a better catalytic efficiency and could be effectively reused four times. The influences of the pollutant, catalyst, and oxidant concentrations were investigated, and the intrinsic relationships among these factors and the degradation kinetic constant were evaluated by a fitting method. It was found that the catalytic degradation process in the MGO-5-persulfate-2,4-DCP system was most likely dominated by an interfacial catalytic reaction, with an activation energy of 13.88 kJ/mol. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis indicated that both sulfate radicals (SO₄^-) and hydroxyl radicals (OH) were responsible for 2,4-DCP removal, but surface-bounded SO₄^- played a greater role. Chloride ions at a concentration of 0-60 mg/L had no effect on 2,4-DCP removal. The proposed advanced oxidation technology has potential applications for the practical removal of aqueous organic pollutants.

Facile construction of highly reactive and stable defective iron-based metal organic frameworks for efficient degradation of Tetrabromobisphenol A via persulfate activation

Achieving large pore size, high catalytic performance with stable structure is critical for metal-organic frameworks (MOFs) to have more hopeful prospects in catalytic applications. Herein, we had reported a method to synthesize highly reactive yet stable defective iron-based Metal organic frameworks by using different monocarboxylic acids with varying lengths as a modulator. The physical-chemical characterization illustrating that modulators could improve the crystallinity, enlarge pore size and enhance catalytic performance and octanoic acid (OA) was screened to be the suitable choice. The catalytic performance of catalysts was detected through persulfate (PS) activation for degrading Tetrabromobisphenol A (TBBPA). The study demonstrated that the highest degradation efficiency for 0.018 mmol L^-1 TBBPA was that 97.79% in the conditions of the 1.0 g L^-1 Fe(BDC)(DMF,F)-OA-30 dosage and TBBPA:PS = 200:1. In addition, there was observed that no obvious change of the crystal structure, little the leachable iron concentration in the solutions and no significant loss of catalytic activities of Fe(BDC)(DMF,F)-OA-30 after 5th cycles. The iron valence state of Fe(BDC)(DMF,F)-OA-30 before and after degradation and electrochemical properties reveal that the partial substitution of organic ligands by octanoic acid, when removing OA and forming defects by heat and vacuum treatment to generate coordinatively unsaturated metal sites and accelerate the original transmission of electronic, leading to enhance the activity of persulfate activation for efficient removal TBBPA.

Carbon-based magnetic nanocomposite as catalyst for persulfate activation: a critical review

The activation of persulfate to produce active radicals has been attracting wide attention in environmental remediation fields. Among various catalysts, non-metal carbocatalysts and carbon-based composites have shown attractive prospects given that they are environmental-friendly, highly efficient, abundant, and diverse. In this paper, the use of carbon-based magnetic nanocomposites as catalysts for persulfate activation was reviewed and discussed. The preparation methods of carbon-based magnetic nanocomposites were first briefly summarized. Subsequently, the use of activated carbon, carbon nanotubes, graphene oxide, biochar, and nanodiamond-based magnetic composites to activate persulfate was discussed, respectively. A synergetic effect between carbon materials and magnetic nanoparticles facilitated the activation process because of the increased electron transfer capacity, good dispersity of magnetic nanoparticles, and good repeatability and separability. Both radical and non-radical pathways were detected in the activation processes, but the specific mechanisms were greatly influenced by the components of the catalyst and solution conditions. And fundamental studies were needed to clarify the inner mechanisms of the process. In the end, strategies for enhancing the catalytic performances of carbon-based magnetic nanocomposites were suggested. It is expected that this review will provide some inspirations for developing highly efficient and green catalyst, as well as sulfate radical-based advanced oxidation technology for the remediation water environment.

Formation of odorous by-products during chlorination of major amino acids in East Taihu Lake: Impacts of UV, UV/PS and UV/H2O2 pre-treatments

Certain amino acids (AAs) can form odorous aldehydes, nitriles and N-chloroaldimines during chlorination. Ultraviolet (UV) photolysis, ultraviolet/persulfate (UV/PS) and ultraviolet/hydrogen peroxide (UV/H₂O₂) treatments have been reported to decrease trace organic contaminants in drinking water. In this study, 20 common AAs in East Taihu (ET) Lake (the main drinking water source for the surrounding cities) were determined during one year (four seasons). The impacts of UV photolysis alone and two UV-advanced oxidation process (AOP) pre-treatments on the formation of aldehydes, nitriles and N-chloroaldimines during post-chlorination of water containing three of the most detected AAs (i.e. valine (Val), leucine (Leu) and isoleucine (Ile)) in ET Lake were investigated. Results showed that the two UV-AOPs significantly decreased the odorous by-product formation from AAs compared with UV photolysis alone. The formation of N-chloroaldimines was more easily controlled than that of aldehyde and nitrile. Furthermore, UV/H₂O₂ was more effective than UV/PS at pH = 5 and 7. At pH = 9, the two UV-AOPs had similar effects and did not perform very well. In addition, the UV-AOPs controlled the formation of odorous by-products effectively at Cl/AA (molar ratio of chlorine to amino acid) ratios of 2.4 and 3.0 but increased their formation at Cl/AA ratios of 0.8 and 1.2. Experiments in real water showed that UV/H₂O₂ was more suitable for controlling the off-flavor problem caused by chlorination of AAs in ET Lake.

Ferrous metal-organic frameworks with stronger coordinatively unsaturated metal sites for persulfate activation to effectively degrade dibutyl phthalate in wastewater

In the advanced oxidation system (AOPs) of persulfate (PS) activated by iron-based metal-organic frameworks (MOFs), aim at solving the problem on the treatment difficulty of wastewater with low concentration persistent organic pollutants (POPs), a new type of ferrous metal-organic frameworks (Fe(Ⅱ)-MOFs) with stronger coordinatively unsaturated metal sites (CUS) was successfully synthesized by different methods. The catalytic performance of Fe(Ⅱ)-MOFs was were obtained by the experiment of degrading dibutyl phthalate (DBP) through persulfate activation. It was found that the degradation efficiency of 0.018 mmol L^-1 DBP was 86.73% under the conditions of 0.40 g L^-1 and 2.70 mmol L^-1 persulfate at a wide pH range. At the same time, the crystal structure and surface morphology of Fe(Ⅱ)-MOFs did not change significantly after reaction and it could still maintain the removal rate of 75.44% of the target pollutants in the fifth cycle. Furthermore, in the consideration of iron valence state of MOFs before and after reaction, and combined with the analysis of electrochemical properties, the possible mechanism of PS activation was proposed, namely the metastable electron layer inside ferrous ions produced the internal power to accelerate the electron transfer in CUS, leading to improve the activity of the catalyst.

Effect of Co60 irradiation on the degradation and mineralization of sulfonated aromatic compounds in aqueous solutions

As sulfonated aromatic compounds are widely used in industry, they have frequently been detected in aquatic environments. This study evaluated the degradation and mineralization of 2,6-naphthalenedisulfonic acid disodium salt (2,6-NS), sodium 2-naphthalenesulfonate (2-NS), benzenesulfonic acid sodium salt (BS), and 4-vinylbenzene sulfonate sodium (4-VBS) by exposing aqueous solutions of these compounds to Co60 irradiation. The radiolytic degradation of these pollutants was found to follow pseudo-first-order kinetics. The dose required to achieve 90% degradation (D90) of these four sulfonated compounds was 0.480 (2,6-NS), 0.390 (2-NS), 0.194 (BS), and 0.280 kGy (4-VBS). The chemical radiolytic yield (G_value) decreased as the absorbed dose increased; moreover, the chemical structures of these compounds affected their radiolytic efficacy. No significant reduction in radiolytic degradation was observed in the presence of inorganic anions (SO₄^2-, Cl^-). The radiolytic degradation efficiency was higher when hydrogen peroxide (H₂O₂, a hydroxyl radical (OH) promoter) was added. The results also showed that combining H₂O₂, persulfate anions (S₂O₈^2-, a sulfate radical anion (SO₄^-) promoter), or N₂O gas (a OH radical promoter) with the sulfonated compounds enhanced the radiolytic mineralization yield and process by reducing the required irradiation energy. In terms of the Co60/O₂ system, at an absorbed dose of 12 kGy, the total organic carbon (TOC) removal efficiency was almost 70%, resulting in the observed release of SO₄^2- anions. In addition, the concentration of dissolved oxygen decreased and the pH was lowered. Based on these results, irradiation with Co60 was found to be a useful tool to remedy wastewater containing sulfonated aromatic compounds.

Detailed study of water radiolysis-based degradation of chloroorganic pollutants in aqueous solutions

Water radiolysis-induced destruction, dechlorination and mineralization of harmful chlorophenols, i.e., 2,4,6-trichlorophenol (2,4,6-tCPH), 4-chlorophenol (4-CPH) and 4-chlorocatechol (4-CC), using radioactive Co-60 have been investigated as individual and combination methods (2,4,6-tCPH+4-CPH+4-CC) with an initial concentration of 100 μM of each pollutant. The kinetic efficiencies of chlorophenol destruction were compared. The individual destruction percentages of 2,4,6-tCPH, 4-CPH and 4-CC reached at least 99% with absorbed doses (D_99%) of 1.44, 1.73 and 1.85 kGy, respectively. Substantially higher absorbed doses were required to destroy each chlorophenol when they were all present in the treated. HCO₃- anions inhibit the elimination efficiency of chlorophenols. The effects of S₂O₈^2- anions, N₂O and N₂ on destruction and mineralization were elaborated. O₂ was crucial for the mineralization. Except for the γ-ray/N₂ system, full mineralization was achieved for both individual and combined chlorophenols. The results indicate that hydrated electrons (e_aq^-) do not have a direct effect on the destruction of these chlorophenols. The study main goals were to show the successful application of ionizing radiation as a useful tool for environmental remediation, to continue scientific research on ionizing radiation as an advanced oxidation technology (AOT) and to provide a new, economic, practical and efficient solution to remove pollutants from aqueous media.

Preparation and application of magnetic nitrogen-doped rGO for persulfate activation

A heterogeneous catalyst (M-N-rGO) composed of stability enhanced magnetic iron oxide nanoparticles and nitrogen-doped reduced graphene oxide was synthesized and characterized by SEM, XRD, BET, and XPS. It showed excellent catalytic degradation properties in advanced oxidation technology. In the presence of 200 mg/L catalyst and 135 mg/L persulfate at pH 5, 95% of 10-20 mg/L methylene blue could be degraded in 90 min with the TOC removal efficiency of 50%. The rate constant based on pseudo-first-order kinetics ranged from 0.0227 to 0.0488/min in the temperature range of 15 to 32 °C, and the activation energy was 32.5 kJ/mol. Under the optimal operation conditions, 20 mg/L of 2,4-dichlorophneol (2,4-DCP) could be removed almost completely. EPR analysis showed that sulfate and hydroxyl radicals were responsible for degradation of pollutants, and radical quenching experiments indicated that nonradical pathway also played a role in pollutant removal. And a mechanism for M-N-rGO and persulfate system was elucidated. This catalyst was easy for preparation, low-cost, highly effective, convenient for separation, and could be used effectively for four times through 0.1 mol/L H₂SO₄ regeneration. It provided a choice for wastewater treatment in practice.

ZIF-8 derived nitrogen-doped porous carbon as metal-free catalyst of peroxymonosulfate activation

Nitrogen-doped porous carbon (NPC) is synthesized through a direct pyrolysis of zeolitic imidazolate framework (ZIF)-8 under N₂ flow followed by acid washing process. It is found that NPC-800 pyrolyzed at 800 °C can inherit the perfect rhombic dodecahedron morphology of ZIF-8 crystals and achieve the considerable nitrogen-doping content of 15.20%. When NPC-800 is applied as the heterogeneous catalyst in peroxymonosulfate (PMS) activation for the degradation of Rhodamine B (RhB) and phenol, NPC-800 will exhibit its better performance than some conventional transition metal-based oxides and common carbon materials. The active sites can be primarily ascribed to nitrogen modification and sp ²-hybridized carbon frameworks. Besides, the influence of several parameters such as the dosage of catalyst, the concentration of oxidant, and reaction temperature is conducted systematically. More importantly, NPC-800 can maintain its considerable degradation in the presence of some anions and natural organic matters, even under some actual water background conditions. Although NPC-800 displays mild deactivation in repeated experiments, its catalytic performance can be easily recovered through heat treatment at 350 °C in air. Radical quenching tests reveal that both sulfate and hydroxyl radicals are responsible for the removal of organic pollutants. This research may provide a new way for the application of novel metal-free carbocatalysts in terms of PMS activation.

Enhanced photocatalytic degradation of tetracycline and real pharmaceutical wastewater using MWCNT/TiO2 nano-composite

Photocatalytic degradation of tetracycline using MWCNT/TiO₂nanocomposite was investigated under UVC irradiation. The effective operational parameters included pH, irradiation time, photocatalyst dosage, weight ratio of MWCNT to TiO₂ and tetracycline concentration and were studied consecutively. Complete removal of tetracycline concentrations of up to 10 mg/L was obtained at MWCNT to TiO₂ ratio of 1.5 (w/w%), pH 5, photocatalyst dosage of 0.2 g/L. Pseudo-first order kinetic model was best fitted with the experimental results (R²: 0.91-0.98 for different tetracycline concentrations). Based on TOC analysis, mineralization was 37% in the same reaction conditions for initial tetracycline concentration of 10 mg/L and reached to 83% after 300 min. In the case of real pharmaceutical wastewater, the COD concentration of 2267 mg/L decreased to 342 mg/L after 240 min in the same operational conditions.

Bacterial-fungal interactions enhance power generation in microbial fuel cells and drive dye decolourisation by an ex situ and in situ electro-Fenton process

In this work, the potential for sustainable energy production from wastes has been exploited using a combination fungus-bacterium in microbial fuel cell (MFC) and electro-Fenton technology. The fungus Trametes versicolor was grown with Shewanella oneidensis so that the bacterium would use the networks of the fungus to transport the electrons to the anode. This system generated stable electricity that was enhanced when the electro-Fenton reactions occurred in the cathode chamber. This configuration reached a stable voltage of approximately 1000 mV. Thus, the dual benefits of the in situ-designed MFC electro-Fenton, the simultaneous dye decolourisation and the electricity generation, were demonstrated. Moreover, the generated power was effectively used to drive an ex situ electro-Fenton process in batch and continuous mode. This newly developed MFC fungus-bacterium with an in situ electro-Fenton system can ensure a high power output and a continuous degradation of organic pollutants.

Dark ambient degradation of Bisphenol A and Acid Orange 8 as organic pollutants by perovskite SrFeO₃-δ metal oxide

Current advanced oxidation processes (AOPs) are chemically and energetically intensive processes, which are undesirable for cost-effective and large-scale system water treatment and wastewater recycling. This study explored the Strontium Ferrite (SFO) metal oxide on the degradation of highly concentrated organic pollutants under dark ambient condition without any external stimulants. The SFO particles with single perovskite structure were successfully synthesized with a combined high temperature and high-energy ball milling process. An endocrine disruptor, Bisphenol A (BPA) and an azo dye, Acid Orange 8 (AO8) were used as probe organic pollutants. BPA was completely degraded with 83% of mineralization in 24 h while rapid decoloration of AO8 was achieved in 60 min and complete breakdown into primary intermediates and aliphatic acids occurred in 24 h under the treatment of dispersed SFO metal oxide in water. Such efficient degradation could be attributed to the enhanced adsorption of these anionic pollutants on positively charged ball-milled SFO metal oxide surface, resulted in higher degradation activity. Preliminary degradation mechanisms of BPA and AO8 under the action of SFO metal oxide were proposed. These results showed that the SFO metal oxide could be an efficient alternative material as novel advanced oxidation technology for low cost water treatment.