Crucial roles of oxygen and superoxide radical in bisulfite-activated persulfate oxidation of bisphenol AF: Mechanisms, kinetics and DFT studies

Synthesis of ZIF-67 composite lignin hydrogel and its catalytic degradation of naphthalene by PMS in wastewater

The incorporation of ZIF-67 into hydrogels for wastewater pollutant remediation has been widely studied, but the synthesis often requires organic solvents such as methanol or ethanol, which can result in the generation of toxic liquid waste. In this study, a novel hydrogel (ZIF-67@SL) was synthesized by integrating ZIF-67 into a dual-network system of sodium lignosulfonate (SL) and acrylamide (AM) using an in situ precipitation method in water. The material was characterized by XRD, FTIR, XPS, SEM, TEM, BET, and TGA analyses. ZIF-67@SL was used to activate peroxymonosulfate (PMS) for degrading naphthalene (NAP) in aqueous solutions. Results showed that ZIF-67@SL effectively activated PMS, achieving an 85.43 % removal rate of NAP within 60 min at 30 °C, with an initial NAP concentration of 10 mg·L-1, ZIF-67@SL dosage of 800 mg·L-1, PMS concentration of 1000 mg·L-1, and pH 7.0. The catalytic efficiency remained high after five recycling cycles. Quenching experiments and EPR spectra revealed that the degradation of NAP in the ZIF-67@SL/PMS system occurred through both free radical pathways (SO4•-, •OH, and O2•-) and a non-radical pathway (1O2). XPS analysis indicated that the activation of PMS and generation of radicals were influenced by Co2+, Co3+, Co0, nitrogen elements, and adsorbed oxygen in the ZIF-67@SL composite. Furthermore, the ZIF-67@SL/PMS system demonstrated strong resistance to low-concentration anions and humic acid (HA) interference and effectively removed multiple polycyclic aromatic hydrocarbons (PAHs) in mixed wastewater. Maximum removal rates for NAP, ACN, ACT, PHE, and FLU were 95.26 %, 99.9 %, 99.79 %, 99.04 %, and 75.69 %, respectively. This study provides an environmentally friendly strategy for wastewater treatment by synthesizing ZIF-67 hydrogel in water and utilizing it as an efficient catalyst.

Insight into Peroxymonosulfate Activation Catalyzed by Fe/Mn Bimetallic-Loaded In Situ Nitrogen-Doped Biochar: the Critical Role of Singlet Oxygen and Superoxide Radicals

Water pollution caused by emerging contaminants poses significant environmental and health risks, while the management of invasive algal biomass remains an underutilized resource. This study presents a novel Fe/Mn-modified in situ N-doped Enteromorpha prolifera-derived biochar catalyst (Fe/Mn/EP), addressing the dual challenges of efficient peroxymonosulfate (PMS) activation and utilization of invasive algal biomass. Through a straightforward one-step pyrolysis approach, the obtained catalyst integrated nitrogen functionalities and bimetallic active sites, enabling it to achieve an outstanding catalytic performance. It completely degraded carbamazepine (CBZ) in water samples within 30 min. The degradation process relied on the synergy between radical and nonradical pathways, primarily dominated by singlet oxygen (1O2) and superoxide radicals (·O2-). Specifically, in situ nitrogen doping, particularly involving pyrrole and graphite nitrogen, enhanced PMS activation by regulating the electronic properties and increasing the density of active sites. The degradation of CBZ significantly reduces the toxicity of the system by analysis prediction based on quantitative structure-activity relationship. The Fe/Mn/EP catalyst demonstrated broad adaptability across various emerging pollutants and real water matrices. This work highlights a sustainable strategy to transform problematic algae into high-performance biochar-based catalysts, offering a scalable solution for water pollution remediation.

Influence mechanism of anions on iron doping into swine bone char: Promoting non-radical oxidation of acetaminophen in a Fenton-like system

The application of iron-doped biochar in peroxymonosulfate (PMS) activation systems has gained increasing attention due to their effectiveness and environmental friendliness in addressing environmental issues. However, the behavioral mechanism of iron doping and the detailed 1O2 generation mechanism in PMS activation systems remain ambiguous. Here, we investigated the effects of three anions (Cl-, NO3-and SO42-) on the process of iron doping into bone char, leading to the synthesis of three iron-doped bone char (Fe-ClBC, Fe-NBC and Fe -SBC). These iron-doped bone char were used to catalyze PMS to degrade acetaminophen (APAP) and exhibited the following activity order: Fe-ClBC > Fe-NBC > Fe-SBC. Characterization results indicated that iron doping primarily occurred through the substitution of calcium in hydroxyapatite within BC. In the course of the impregnation, the binding of SO42- and Ca2+ hindered the exchange of iron ions, resulting in lower catalytic activity of Fe-SBC. The primary reactive oxygen species in the Fe-ClBC/PMS and Fe-NBC/PMS systems were both 1O2. 1O2 is produced through O2•- conversion and PMS self-dissociation, which involves the generation of metastable iron intermediates and electron transfer within iron species. The presence of oxygen vacancies and more carbon defects in the Fe-ClBC catalyst facilitates 1O2 generation, thereby enhancing APAP degradation within the Fe-ClBC/PMS system. This study is dedicated to in-depth exploration of the mechanisms underlying iron doping and defect materials in promoting 1O2 generation.

Degradation of Butylated Hydroxyanisole by the Combined Use of Peroxymonosulfate and Ferrate(VI): Reaction Kinetics, Mechanism and Toxicity Evaluation

Butylated hydroxyanisole (BHA), a synthetic phenolic antioxidant (SPA), is now widely present in natural waters. To improve the degradation efficiency of BHA and reduce product toxicity, a combination of peroxymonosulfate (PMS) and Ferrate(VI) (Fe(VI)) was used in this study. We systematically investigated the reaction kinetics, mechanism and product toxicity in the degradation of BHA through the combined use of PMS and Fe(VI). The results showed that PMS and Fe(VI) have synergistic effects on the degradation of BHA. The effects of operational factors, including PMS dosage, pH and coexisting ions (Cl-, SO42-, HCO3-, K+, NH4+ and Mg2+), and different water matrices were investigated through a series of kinetic experiments. When T = 25 °C, the initial pH was 8.0, the initial BHA concentration was 100 μM, the initial concentration ratio of [PMS]0:[Fe(VI)]0:[BHA]0 was 100:1:1 and the degradation rate could reach 92.4% within 30 min. Through liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) identification, it was determined that the oxidation pathway of BHA caused by PMS/Fe(VI) mainly includes hydroxylation, ring-opening and coupling reactions. Density functional theory (DFT) calculations indicated that •OH was most likely to attack BHA and generate hydroxylated products. The comprehensive comparison of product toxicity results showed that the PMS/Fe(VI) system can effectively reduce the environmental risk of a reaction. This study contributes to the development of PMS/Fe(VI) for water treatment applications.

Synergy between UV light and trichloroisocyanuric acid on methylisothiazolinone degradation: Performance, kinetics and degradation pathway

Methylisothiazolinone (MIT) is widely used in daily chemicals, fungicides, and other fields and its toxicity has posed a threat to water system and human health. In this study, ultraviolet (UV)/trichloroisocyanuric acid (TCCA), which belongs to advanced oxidation processes (AOP), was adopted to degrade MIT. Total chlorine attenuation detection proved that TCCA has medium UV absorption and a strong quantum yield (0.49 mol E-1). At a pH of 7.0, 93.5% of MIT had been decontaminated after 60 min in UV/TCCA system (kobs = 4.4 × 10-2 min-1, R2 = 0.978), which was much higher than that in the UV alone system and TCCA alone system, at 65% (1.7 × 10-2 min-1, R2 = 0.995) and 10% (1.8 × 10-3 s-1, R2 = 0.915), respectively. This system also behaved well in degrading other five kinds of contaminants. Tert-butanol (TBA) and carbonate (CO32-) were separately used in quenching experiments, and the degradation efficiency of MIT decreased by 39.5% and 46.5% respectively, which confirmed that HO• and reactive chlorine species (RCS) were dominant oxidants in UV/TCCA system. With TCCA dosage increasing in a relatively low concentration range (0.02-0.2 mM) and pH decreasing, the effectiveness of this AOP system would be strengthened. The influences of coexisting substances (Cl-, SO42-, CO32-, NO2- and NO3-) were explored. MIT degradation pathways were proposed and sulfur atom oxidation and carboxylation were considered as the dominant removal mechanisms of MIT. Frontier orbital theory and Fukui indexes of MIT were employed to further explore the degradation mechanism.

In-situ synthesis of magnetic iron-chitosan-derived biochar as an efficient persulfate activator for phenol degradation

Persulfate activation is a forceful method for eliminating organic pollutants from coal chemical wastewater. In this study, an in-situ synthesis method was used to fabricate an iron-chitosan-derived biochar (Fe-CS@BC) nanocomposite catalyst using chitosan as a template. Fe was successfully imprinted into the newly synthesized catalyst. The Fe-CS@BC can activate persulfate to effectively degrade phenol. This point was confirmed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The impact of various parameters on the removal rate was investigated in a single factor experiment. In Fe-CS@BC/PDS system, 95.96% of phenol (significantly higher than the original biochar of 34.33%) was removed within 45 min and 54.39% TOC within 2 h. The system showed superior efficiency over a broad pH value band from 3 to 9 and has a high degradation rate at ambient temperature. Free radical quenching experiment, EPR experiment and LSV experiment confirmed that multiple free radicals (including 1O2, SO4•-, O2•- and •OH) and electron transfer pathway combined to enhance phenol decomposition. Finally, the activation mechanism of persulfate by Fe-CS@BC was proposed to provide logical guidance on the treatment of organic pollutants in coal chemical wastewater.

Much Stronger Chemiluminescence of 9-Mesityl-10-methylacridinium Ion than Lucigenin at Neutral Conditions for Co2+ Detection

9-Mesityl-10-methylacridinium ion (Acr+-Mes) is a donor-acceptor molecule with a much longer lifetime and a higher energy electron transfer excited state than natural photosynthetic reaction centers. Unlike lucigenin with a coplanar geometry, Acr+-Mes has an orthogonal geometry. There is no π conjugation between Acr+ and Mes. Due to its special electron donor-acceptor structure, it does not rely on strong alkalinity to generate an electron transfer state like lucigenin, which makes it possible to achieve chemiluminescence (CL) under weakly alkaline or neutral conditions. In this study, we report Acr+-Mes CL for the first time. Acr+-Mes generates about 400 times stronger CL intensity than lucigenin under neutral conditions (pH = 7) using KHSO5 as the coreactant. Moreover, Co2+ can enhance Acr+-Mes/KHSO5 CL remarkably. Acr+-Mes/KHSO5 CL enables Co2+ detection with a linear range of 0.5-500 nM and a limit of detection of 28 pM (S/N = 3). This method was tested for the detection of Co2+ in lake water, and the standard recovery rate of 96.8-107% was achieved. This study provides a new way to develop efficient CL systems in neutral solutions.

Treatment of bisphenol pollutant in water by N,P-co-doped carbon nanosheet: Fast degradation, toxicity elimination and reaction mechanism investigation

Metal-free carbon catalysts perform well in peroxymonosulfate-based advanced oxidation process for the treatment of organic pollutant-containing wastewater. Herein, a natural biomolecule of adenosine triphosphate (ATP), containing abundant N and P elements, served as sole precursor to prepare N,P-co-doped carbon through one-step anoxic pyrolysis, which was applied as peroxymonosulfate activator to treat bisphenol-contaminated water. Owing to the endogenous N and P elements in ATP, in-situ doping was achieved for the prepared carbon material with excellent doping effect, such as high doping amount and numerous defects. During pyrolysis process, the generated gases facilitated the exfoliation of carbon structure, resulting in a nanosheet-like morphology with large specific surface area, e.g., 852.75 m² g^-1 for NPCN-900 sample obtained at 900 °C. Benefiting from the structural modulation brought by N,P co-doping, typical sample of NPCN-900 presented excellent catalytic performance towards bisphenol AF (BPAF) degradation through PMS activation. An apparent reaction rate constant of 0.4115 min^-1 was calculated under the investigated reaction conditions. Further studies indicated that ¹O₂, surface-bound •OH and SO₄^-• worked together in NPCN-900/PMS system for BPAF degradation. Graphitic N, pyrrolic N, CO groups, defect structure and the doped P atoms in NPCN-900 contributed to PMS activation. It was also important that the toxicity of BPAF solution could be preliminarily eliminated after treatment by NPCN-900/PMS system, which was verified by ecotoxicity assessments through ECOSAR program and green algae growth experiments.

Nanoconfinement-enhanced Fenton-like polymerization via hollow hetero-shell carbon for reducing carbon emissions in organic wastewater purification

Lower reaction speed and excessive oxidant inputs impede the removal of contaminants from water via the advanced oxidation processes based on peroxymonosulfate. Herein, we report a new confined catalysis paradigm via the hollow hetero-shell structured CN@C (H-CN@C), which permits effective decontamination through polymerization with faster reaction rates and lower oxidant dosage. The confined space structures regulated the CN and CO and electron density of the inner shell, which increased the electron transfer rate and mass transfer rate. As a result, CN in H-CN@C-10 reacted with peroxymonosulfate in preference to CO to generate singlet oxygen, improving the second-order reaction kinetics by 503 times. The identification of oxidation products implied that bisphenol AF could effectively remove by polymerization, which could reduce carbon dioxide emissions. These favorable properties make the nanoconfined catalytic polymerization of contaminants a remarkably promising nanocatalytic water purification technology.

Density Functional Theory and Machine Learning-Based Quantitative Structure-Activity Relationship Models Enabling Prediction of Contaminant Degradation Performance with Heterogeneous Peroxymonosulfate Treatments

Heterogeneous peroxymonosulfate (PMS) treatment is recognized as an effective advanced oxidation process (AOP) for the treatment of organic contaminants. Quantitative structure-activity relationship (QSAR) models have been applied to predict the oxidation reaction rates of contaminants in homogeneous PMS treatment systems but are seldom applied in heterogeneous treatment systems. Herein, we established QSAR models updated with density functional theory (DFT) and machine learning approaches to predict the degradation performance for a series of contaminants in heterogeneous PMS systems. We imported the characteristics of organic molecules calculated using constrained DFT as input descriptors and predicted the apparent degradation rate constants of contaminants as the output. The genetic algorithm and deep neural networks were used to improve the predictive accuracy. The qualitative and quantitative results from the QSAR model for the degradation of contaminants can be used to select the most appropriate treatment system. A strategy for selection of the optimum catalyst for PMS treatment of specific contaminants was also established according to the QSAR models. This work not only increases our understanding of contaminant degradation in PMS treatment systems but also highlights a novel QSAR model to predict the degradation performance in complicated heterogeneous AOPs.

Degradation of Bisphonel AF (BPAF) by zero-valent iron activated persulfate: Kinetics, mechanisms, theoretical calculations, and effect of co-existing chloride

The removal of Bisphonel AF (BPAF) by zero-valent iron activated persulfate (Fe⁰/PS) system was systematically evaluated in this work. 30.0 μM BPAF was removed by 94.4% in 60 min of treatment under optimal conditions of pH = 3.0 and [PS] = [Fe⁰] = 3.0 mM. Cl^- significantly accelerated the removal of BPAF, resulting from accelerated Fe²⁺ release and reactive chlorine species (RCS) formation. Liquid chromatography-time-of-flight-mass spectrometry identified thirteen degradation products, and bond breaking, coupling reactions, hydroxylation and sulfate addition were considered as the major transformation pathways. When Cl^- was present, six new chlorinated byproducts were also generated. Based on density functional theory (DFT) calculations, the occurrence of radical addition reactions was verified and the preferential reaction channels were determined. Significantly BPAF degradation products were less toxic, according to toxicity assessment by the ECOSAR program. Moreover, a high removal efficiency of BPAF (>90%) was also obtained in the three actual water matrixes. The present work demonstrates the feasibility of Fe⁰/PS system for treating BPAF, which could also provide new insights into the influence of coexisting Cl^- on the environmental fate of organic pollutants in sulfate radicals based advanced oxidation processes.

Synthesis and Applications of Dimensional SnS2 and SnS2/Carbon Nanomaterials

Dimensional nanomaterials can offer enhanced application properties benefiting from their sizes and morphological orientations. Tin disulfide (SnS₂) and carbon are typical sources of dimensional nanomaterials. SnS₂ is a semiconductor with visible light adsorption properties and has shown high energy density and long cycle life in energy storage processes. The integration of SnS₂ and carbon materials has shown enhanced visible light absorption and electron transmission efficiency. This helps to alleviate the volume expansion of SnS₂ which is a limitation during energy storage processes and provides a favorable bandgap in photocatalytic degradation. Several innovative approaches have been geared toward controlling the size, shape, and hybridization of SnS₂/Carbon composite nanostructures. However, dimensional nanomaterials of SnS₂ and SnS₂/Carbon have rarely been discussed. This review summarizes the synthesis methods of zero-, one-, two-, and three-dimensional SnS₂ and SnS₂/Carbon composite nanomaterials through wet and solid-state synthesis strategies. Moreover, the unique properties that promote their advances in photocatalysis and energy conversion and storage are discussed. Finally, some remarks and perspectives on the challenges and opportunities for exploring advanced SnS₂/Carbon nanomaterials are presented.

Simultaneous oxidation of trace organic contaminant and Mn(II) by Mn(VII): Accelerating role of dissolved oxygen

Permanganate (Mn(VII)) is a widely used oxidant in water treatment, which can oxidize trace organic contaminants (TrOCs) and Mn(II). Interestingly, this study found that presence of Mn(II) could accelerate the abatement of bisphenol A by Mn(VII) only under oxic condition. Herein, the effects of Mn(II) and dissolved oxygen (DO) on the abatement of TrOCs by Mn(VII) oxidation and the related mechanism were investigated. Results indicate that DO was involved in the Mn(VII)/Mn(II) reaction, with the reaction stoichiometry of Δ[Mn(VII)]:Δ[Mn(II)] determined to be 1:2 and 1:1.5 in the presence and absence of DO, respectively. Quenching and electron paramagnetic resonance tests verified that both superoxide radicals (O₂^•-) and reactive Mn species contributed to the accelerated abatement of TrOCs (bisphenol A, methyl phenyl sulfoxide, and methyl phenyl sulfone) in the Mn(VII)/Mn(II) process. Specifically, O₂^•- was produced through the one-electron reduction of DO and made an important contribution (32.4%-100%) to the abatement of selected TrOCs. This study reveals that Mn(II) could enhance TrOC abatement by Mn(VII) oxidation, and DO played a pivotal role in the Mn(VII)/Mn(II) process.

Superfast degradation of micropollutants in water by reactive species generated from the reaction between chlorine dioxide and sulfite

Chlorine dioxide (ClO₂) is used as an oxidant or disinfectant in (waste)water treatment, whereas sulfite is a prevalent reducing agent to quench the excess ClO₂. This study demonstrated that seven micropollutants with structural diversity could be rapidly degraded in the reaction between ClO₂ and sulfite under environmentally relevant conditions in synthetic and real drinking water. For example, carbamazepine, which is recalcitrant to standalone ClO₂ or sulfite, was degraded by 55%-80% in 10 s in the ClO₂/sulfite process at 30-µM ClO₂ and 30-µM sulfite concentrations within a pH range of 6.0-11.0. Results from experiments and a kinetic model supported that chlorine monoxide (ClO^·) and sulfate radicals (SO₄^·-) were generated in the ClO₂/sulfite process, while hydroxyl radical generation was insignificant. Apart from radicals, dichlorine trioxide (Cl₂O₃) was generated and largely contributed to micropollutant degradation, supported by experimental results using stopped-flow spectrometry and quantum chemical calculations. The impacts of pH, sulfite dosage, and water matrix components (chloride, bicarbonate, and natural organic matter) on micropollutant abatement in the ClO₂/sulfite process were evaluated and discussed. When treating the real potable water, the concentrations of organic (five regulated disinfection byproducts) and inorganic byproducts (chlorite and chlorate) formed in the ClO₂/sulfite process were all below the drinking water standards. This study disclosed fundamental knowledge advancements relevant to the reaction mechanisms between ClO₂ and sulfite, and highlighed a novel process to abate micropollutants in water and wastewater.

Overlooked environmental risks deriving from aqueous transformation of bisphenol alternatives: Integration of chemical and toxicological insights

Owing to the widespread prevalence and ecotoxicity of bisphenol alternatives such as bisphenol S, bisphenol F, and bisphenol AF, the past decade has witnessed the publication of a remarkable number of studies related to their transformation and remediation in natural waters. However, the reactivity, removal efficiency, transformation products (TPs), and mechanisms of such emerging pollutants by different treatment processes have not been well elucidated. Particularly, the transformation-driven environmental risks have been mostly overlooked. Therefore, we present a review to address these issues from chemical and toxicological viewpoints. Four degradation systems can be largely classified as catalytic persulfate (PS) oxidation, non-catalytic oxidation, photolysis and photocatalysis, and biodegradation. It was found that bisphenol alternatives possess distinct reactivities with different oxidizing species, with the highest performance for hydroxyl radicals. All systems exhibit superior elimination efficiency for these compounds. The inadequate mineralization suggests the formation of recalcitrant TPs, from which the overall reaction pathways are proposed. The combined experimental and in silico analysis indicates that many TPs have developmental toxicity, endocrine-disrupting effects, and genotoxicity. Notably, catalytic PS systems and non-catalytic oxidation result in the formation of coupling products as well as halogenated TPs with higher acute and chronic toxicity and lower biodegradability than the parent compounds. In contrast, photolysis and photocatalysis generate hydroxylated and bond-cleavage TPs with less toxicity. Overall, this review highlights the secondary environmental risks from the transformation of bisphenol alternatives by conventional and emerging treatment processes. Finally, future perspectives are recommended to address the knowledge gaps of these contaminants in aquatic ecosystems.

Pivotal roles of N-doped carbon shell and hollow structure in nanoreactor with spatial confined Co species in peroxymonosulfate activation: Obstructing metal leaching and enhancing catalytic stability

Metal leaching and catalytic stability are the key issues in Fenton-like reaction. Herein, a hollow yolk-shell nanoreactor (HYSCN) with shell confined Co species was fabricated for peroxymonosulfate (PMS) activation to degrade carbamazepine (CBZ). The uniform Co nanoparticles were completely anchored in a hollow void, further confined by a porous N-doped carbon shell. The unique construction significantly reduces Co species leaching in PMS activation and enhances catalytic stability. Co leaching came from HYSCN dropped by almost fourfold compared to CN-8 without shell confined (0.403 mg/L to 0.120 mg/L). The catalytic stability is also greatly improved, confirming the dominant role of heterogeneous catalysis in the HYSCN/PMS system. HYSCN exhibits excellent catalytic performance compared to a solid structure (SCSCN), demonstrating the significance of hollow structures. Mechanism study found that HO^•, SO₄^•- and ¹O₂ induced in HYSCN/PMS system and the relative contributions were distinguished and quantified by stoichiometric methods. The UPLC-Q-TOF-MS/MS was used to identify the CBZ degraded intermediate products and the possible degradation pathway was proposed. This study will provide theoretical guidance for reducing metal leaching and improving catalytic stability in the PMS activation.

Enhancing catalytic ozonation activity of MCM-41 via one-step incorporating fluorine and iron: The interfacial reaction induced by hydrophobic sites and Lewis acid sites

Fe-MCM-41 had been widely used as ozonation catalyst, however, the existence of large amount of hydrophilic silanol hindered its interfacial reaction with O₃ and pollutants. To solve this problem, F-Fe-MCM-41 was synthesized by co-doping F and Fe into the framework of MCM-41 to replace silanol with Si-F groups through a one-step hydrothermal method. F introduced hydrophobic sites which contributed to more ibuprofen (IBP) chemisorption on the surface of F-Fe-MCM-41. Moreover, doping F also enhanced the acidity, which accelerated O₃ decomposition into •OH. F-Fe-MCM-41/O₃ exhibited notably activity with 96.6% IBP removal efficiency within 120 min, while only 78.5% and 80.9% in O₃ alone and Fe-MCM-41/O₃, respectively. Surface Lewis acid sites and metal hydroxyl groups were considered as important factors for O₃ activation and •OH generation. F-Fe-MCM-41 exhibited excellent catalytic performance under acidic and alkaline conditions. Comparative experiments revealed that F doping improved the interfacial reaction, especially the interfacial electron transfer, which resulted in the high catalytic activity of F-Fe-MCM-41. F-Fe-MCM-41 possessed good stability and reusability, with only 5.7% decline for IBP removal in five successive cycles. Furthermore, the possible degradation path of IBP was proposed according to DFT calculation and GC-MS analysis.

Why the cooperation of radical and non-radical pathways in PMS system leads to a higher efficiency than a single pathway in tetracycline degradation

Current research focused on developing multiple active species in peroxymonosulfate (PMS) system to degrade contaminants, but deepening concern lacks over why cooperation of those active species facilitated a faster degradation. Here, we employed Co₃O₄, rGO and Co₃O₄@rGO composite to activate PMS for tetracycline (TC) degradation, and detected crucial factors toward highest performance of Co₃O₄@rGO/PMS system. Batch experiments exhibited a satisfactory TC degradation efficiency under Co₃O₄@rGO/PMS, complete degraded 50 mg/L TC within 20 min. Analytical tests discovered that radical active species generated by Co₃O₄/PMS and non-radical species by rGO/PMS were successfully co-existed in Co₃O₄@rGO/PMS system, significantly improving the performance of TC removal. Subsequently, a combination of density functional theory (DFT) calculation and intermediates analysis revealed that, in Co₃O₄@rGO/PMS system, the cooperation rather than independent effect of radical and non-radical active species expanded TC degradation pathways, enhancing the degradation performance. Furthermore, decent adaptability, stability, and recyclability toward affecting factors variation of Co₃O₄@rGO/PMS demonstrated it as a potent and economical system to degrade TC. Overall, this study developed a novel Co₃O₄@rGO/PMS system with a cooperative oxidation pathway for highly efficient TC removal, and managed to clarify why this oxidation pathway achieved high efficiency through a combination of theoretical and experimental method.

Persulfate adsorption and activation by carbon structure defects provided new insights into ofloxacin degradation by biochar

Cellulose and lignin derived biochars with significant differences in persistent free radicals (PFRs), oxygen-containing functional groups, and defective structure were prepared to explore the mechanism of biochar mediated persulfate (PS) activation. EPR spin trapping and quenching technique coupled with degradation experiments confirmed that the defective structures could activate PS to generate superoxide anions (O₂^•-), which was converted to singlet oxygen (¹O₂), especially in the acidic condition. ¹O₂ dominated the degradation of ofloxacin (OFL, a fluoroquinolone antibiotic). An improved iodometric measurement was applied for direct quantification of adsorbed PS on biochar. The amounts of adsorbed PS were consistent with the degradation of OFL and the measured electric current during the reaction indicated that PS adsorption was a prerequisite for PS activation, which may be neglected in previous studies. The results of this study highlighted the key roles of defective structure and adsorption of PS on biochar for the activation of PS.

Influence of anions on ozonation of bisphenol AF: Kinetics, reaction pathways, and toxicity assessment

In this article, the degradation of 4, 4'-(hexafluoroisopropylidene) diphenol (bisphenol AF, BPAF) by ozone was studied and toxicity of the degradation products was evaluated. Kinetic studies showed that acidic conditions were more conducive to the ozone degradation of BPAF than alkaline conditions. In the presence of common anions, Br^- and SO₄^2- promoted the degradation of BPAF, whereas NO₂^-, NO₃^-, HSO₃^- inhibited the degradation, and the other anions and cations had no significant effect. The degradation products were analyzed by mass spectrometry, and were mainly manifested in hydroxylation, carboxylation and cleavage of benzene ring. The addition of NO₂^-, HSO₃^- and Br^-produced the corresponding free radicals, resulting in the parent compound being attacked and affecting the degradation efficiency and pathways. The theoretical calculated results showed that the ortho-site of the BPAF phenolic hydroxyl group was more active than the meta-position, and it's more likely for free radicals to attack ortho-sites and initiate substitution reactions. Toxicity assessment of the products in the process of ozone degradation showed that toxicity of the products was reduced by benzene ring cleavage and a reduction in the F atomic number. However, the toxicity of nitro and brominated products of BPAF was increased. These findings provide some new insights into the role of common ions in ozonation process and product formation, and supplement the existing conclusions. The results of this study remind future researchers to concern that inorganic ions in real water may be converted into corresponding free radicals that affect the formation of ozone oxidation products.

Environmental occurrence and remediation of emerging organohalides: A review

As replacements for "old" organohalides, such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), "new" organohalides have been developed, including decabromodiphenyl ethane (DBDPE), short-chain chlorinated paraffins (SCCPs), and perfluorobutyrate (PFBA). In the past decade, these emerging organohalides (EOHs) have been extensively produced as industrial and consumer products, resulting in their widespread environmental distribution. This review comprehensively summarizes the environmental occurrence and remediation methods for typical EOHs. Based on the data collected from 2015 to 2021, these EOHs are widespread in both abiotic (e.g., dust, air, soil, sediment, and water) and biotic (e.g., bird, fish, and human serum) matrices. A significant positive correlation was found between the estimated annual production amounts of EOHs and their environmental contamination levels, suggesting the prohibition of both production and usage of EOHs as a critical pollution-source control strategy. The strengths and weaknesses, as well as the future prospects of up-to-date remediation techniques, such as photodegradation, chemical oxidation, and biodegradation, are critically discussed. Of these remediation techniques, microbial reductive dehalogenation represents a promising in situ remediation method for removal of EOHs, such as perfluoroalkyl and polyfluoroalkyl substances (PFASs) and halogenated flame retardants (HFRs).

Iron molydate catalyzed activation of peroxymonosulfate for bisphenol AF degradation via synergetic non-radical and radical pathways

Though molybdate oxides have been demonstrated as desirable catalysts for environmental remediation, the mechanism of catalytic activation of peroxymonosulfate (PMS) by iron (II) molybdate (FeMoO₄) remains unclear. In this study, FeMoO₄ was synthesized and applied for the activation of PMS to degrade bisphenol-AF (BPAF). FeMoO₄ showed excellent catalytic activity, high stability, and superior mineralization. The influence of operation parameters (i.e., FeMoO₄ dosage, PMS concentration, initial pH, co-existing anions, and temperature) on the removal of BPAF were also investigated in detail. Furthermore, the possible oxidation mechanism was proposed via the chemical quenching tests and electron spin resonance (ESR) analysis, which certified that both free radical (SO₄^-• and ^•OH) and non-radical (¹O₂) were the main reactive oxygen species for degrading BPAF. X-ray photoelectron spectroscopy (XPS) analysis indicated that the radicals were mainly generated via the continuous circulation of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁴⁺ redox cycles to enhance PMS activation. Finally, the degradation pathways of BPAF was proposed based on LC/MS results. This work showed the notable potential of the FeMoO₄/PMS system for degrading organic contaminants in the environment remediation and would promote the understanding of the mechanism of Fe-based molybdate in advanced oxidation.

Effective activation of peroxymonosulfate with natural manganese-containing minerals through a nonradical pathway and the application for the removal of bisphenols

Synthetic manganese oxides had been widely investigated to activate peroxymonosulfate (PMS) for contaminant removal in recent years. The generation of reactive oxygen species (ROS, e.g., radicals) was believed to be the primary PMS activation pathways. In this work, we report that natural manganese-containing minerals (NMMs) were also effective for PMS activation to degrade bisphenols in water. Moreover, a nonradical pathway different from literatures, was confirmed according to scavenging tests, electron paramagnetic resonance (EPR) characterization, chemical probing, solvent exchange, and Raman and electrochemical analysis. It was verified that PMS complexed with the mineral surface via inner-sphere interaction. This surface interaction improved its reactivity towards the probe compounds, bisphenols. Taking bisphenol AF (BPAF) as an example, its degradation rate was related to surface area and dosages of the mineral. Water constituents such as Cl^-, HCO₃^-, and NOM had negligible impact on BPAF removal. The activity of the mineral was kept in an 80-hour continuous flow test. The PMS/NMM coupled oxidation degraded BPAF through direct electron transfer, and the degradation intermediates further underwent hydroxylation, bond cleavage, H-atom substitution, aromatic ring-opening, and decarboxylation. Consequently, eco-toxicity of BPAF can be reduced during the oxidation.

Efficient activation of peroxydisulfate by g-C3N4/Bi2MoO6 nanocomposite for enhanced organic pollutants degradation through non-radical dominated oxidation processes

Persulfate-assisted photocatalysis technology is considered to be a promising method for the rapid and efficient degradation of organic pollutants in water environment remediation. In this study, a novel g-C₃N₄/Bi₂MoO₆/PDS (CN/BMO/PDS) system is constructed and applied in 2,4-dinitrophenylhydrazine (2,4-DPH) degradation under visible light irradiation. Compared with the CN/BMO system, the degradation rate of 2,4-DPH is significantly improved from 59.7% to 90.2% within 60 min in the combined CN/BMO/PDS system. The enhanced performance can be attributed to the superior synergetic effects of CN/BMO, PDS and visible light irradiation. More importantly, singlet oxygen (¹O₂) is determined as the main reactive species based on the radical scavenging experiments and electron paramagnetic resonance (EPR), which indicates that the combined system can achieve non-radical oxidative degradation of pollutants, instead of the traditional radical oxidation process. In addition, the active sites of the reaction during the non-radical ¹O₂ oxidation are calculated by density functional theory (DFT), and the stability and reusability of catalyst are also investigated. In brief, the CN/BMO/PDS system has great application potential for removing organic pollutants from wastewater.

Colloidal activated carbon as a highly efficient bifunctional catalyst for phenol degradation

A preparation of colloidal activated carbon (CAC) for phenol remediation from groundwater was introduced. The CAC prepared by a simple pulverization technique was an excellent metal-free catalyst for persulfate (PS) activation due to high contact surface area. The removal efficiency of phenol in the PS/CAC system (~100%) was higher than that in the PS/activated carbon (AC) system (90.1%) and was superior to the conventional PS/Fe²⁺ system (27.9%) within 30 min. The phenol removal reaction occurred both in bulk solution and at the surface of the CAC, as confirmed by Langmuir-Hinshelwood (L-H) kinetic model fitting, FT-IR, and electron spin resonance (ESR) analyses. The downsizing of particle size from AC to CAC played a critical role in the radical oxidation mechanism by leading to the formation of predominant superoxide radical (O₂^•-) species in the PS/CAC system. Anions NO₃^-, SO₄^2-, and Cl^- slightly inhibited the phenol removal efficiency, whereas CO₃^2-, HCO₃^- and PO₄3^- did not. Ferulic acid (C₁₀H₁₀O₄) was detected as an organic byproduct of phenol oxidation. The use of CAC as a metal-free bifunctional catalyst has an important implication in the PS activation for phenol degradation in groundwater.

Critical review of advanced oxidation processes in organic wastewater treatment

With the development of industrial society, organic wastewater produced by industrial manufacturing has caused many environmental problems. The vast majority of organic pollutants in water bodies are persistent in the environment, posing a threat to human and animal health. Therefore, efficient treatment methods for highly concentrated organic wastewater are urgently needed. Advanced oxidation processes (AOPs) are widely noticed in the area of treating organic wastewater. Compared with other chemical methods, AOPs have the characteristics of high oxidation efficiency and no secondary pollution. In this paper, the mechanisms, advantages, and limitations of AOPs are comprehensively reviewed. Besides, the basic principles of combining different AOPs to enhance the treatment efficiency are described. Furthermore, the applications of AOPs in various wastewater treatments, such as oily wastewater, dyeing wastewater, pharmaceutical wastewater, and landfill leachate, are also presented. Finally, we conclude that the main direction in the future of AOPs are the modification of catalysts and the optimization of operating parameters, with the challenges focusing on industrial applications.

A novel electrocatalytic filtration system with carbon nanotube supported nanoscale zerovalent copper toward ultrafast oxidation of organic pollutants

In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0-7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu²⁺/Cu⁺ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and ¹O₂via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu²⁺-O-O-SO₃^-), and then ¹O₂ will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.

Staged assessment for the involving mechanism of humic acid on enhancing water decontamination using H2O2-Fe(III) process

Humic acid (HA) as a natural coordinating agent was employed to modify the Fenton-like process by promoting the redox cycle of Fe(III)/Fe(II) and enhancing the pH tolerance. However, the roles of coordinating stages of HA-Fe(III) and the dynamic changes of iron species remain unclear. In this study, HA was introduced into the H₂O₂-Fe(III) process to investigate the accelerating roles of coordinating stages and systematically reveal the mechanism via the reactive oxygen species (ROS) identification, HA-Fe(III)/Fe(II) redox cycles tracking, electrochemical and kinetic analysis. Results suggested that two reaction stages were separated concerning the enhancement for HA in H₂O₂-Fe(III) process, including coordinating stage (slow rate) and promoting the redox stage (fast rate). HA-Fe(III) was identified as the major contributor, along with hydroxyl radical (·OH) and superoxide radical (·O₂^-) as the dominant ROS with formation rates calculated as 7.0 × 10^-9 and 2.1 × 10^-3 M s^-1 via the steady-state model. Based on the density-functional theory (DFT) calculations and HPLC-MS/MS analysis, three degradation pathways of 2,4-Dichlorophenol were proposed with ten intermediate products identified, and the ecotoxicity was evaluated through Ecological Structure Activity Relationships (ECOSAR) program. This study unveiled the mechanism of HA on enhancing water decontamination via H₂O₂-Fe(III) process in stages.

Enhancement of Removal of VOCs and Odors from Wood by Microwave-Activated Persulfate

Since traditional methods for removing volatile organic compounds (VOCs) from wood consume large amounts of energy and generate environmental pollution, it is desired to develop a convenient and green treatment method. Oxidation by microwave-activated persulfate (MW-PS) is a promising alternative method that has been used to eliminate VOCs from wood. The penetration of microwave energy can destroy the wood pit membranes and increase VOC emissions. The VOCs are further degraded by ·OH and SO₄ ^•-, which are generated via the activation of microwaves. This phenomenon can be detected by the electron paramagnetic resonance spectrometry. The 35 types of main VOCs of natural wood were determined, including alkanes/terpenes, alcohols/ethers, esters, aldehydes/ketones, and others. In the MW-PS system, 23 compounds were removed with an efficiency of 100%. Specifically, as one of the major compounds, the content of alkanes/terpenes was sharply decreased, and no alcohols/ethers and esters were detected. It was found that the optimal conditions of the MW-PS system for the minimum release of VOCs from wood were the microwave power of 462 W, irradiation time of 30 min, and PS dosage of 0.5 mmol/L.

Biosynthesized Schwertmannite@Biochar composite as a heterogeneous Fenton-like catalyst for the degradation of sulfanilamide antibiotics

Schwertmannite was successfully loaded onto biochar (Sch@BC) using a biosynthetic method. The physicochemical properties and structural morphology of Sch@BC were explored using XRD, SEM, BET, and XPS. The results showed that introducing biochar can effectively prevent the agglomeration of Sch. The catalytic activity of Sch@BC in the Fenton-like degradation of sulfamethoxazole (SMX) was also systematically investigated under different reaction conditions. Under optimum conditions ([SMX] = 10 mg L^-1, [H₂O₂] = 2.0 mM, Sch@BC = 1.0 g L^-1 and initial pH = 3.0), the removal efficiencies of the SMX and total organic carbon (TOC) were 100% and 45.9%, respectively, within 60 min of the reaction. The results of the radical scavenger effect and ESR studies suggested that the SMX degradation in the Sch@BC/H₂O₂ system was dominated by a heterogeneous Fenton-like reaction. The repeated use of Sch@BC for SMX degradation demonstrated its reusability and stability in Fenton-like reactions. There was also speculation about the degradation mechanism and pathways of SMX. Furthermore, under the same conditions, the removal efficiencies of sulfadiazine (SD) and sulfisoxazole (SIZ) under Fenton-like degradation in the Sch@BC system were 91% and 93%. The results provide a theoretical basis and practical guidance for the creation of a new catalyst using biochar as a support material for the degradation of sulfanilamide antibiotics.

Degradation of aqueous atrazine using persulfate activated by electrochemical plasma coupling with microbubbles: removal mechanisms and potential applications

Persulfate (PS) activated by dielectric barrier discharge (DBD) integrated with microbubbles (MBs) was designed to decompose atrazine (ATZ) from aqueous solutions. The degradation efficiency reached 89% at a discharge power of 85W, a PS concentration of 1mM, and a air flow rate of 30mL/min after 75min treatment. Heat caused by DBD favoured ATZ removal. Besides, the effect of PS dosage, discharge power and initial pH values on ATZ removal was evaluated. The calculated energy yield revealed that it was economical and promising to treat 1L of ATZ-wastewaters. The existence of SO₄^2-, Cl^-, CO₃^2- and HCO₃^- lead to negative effects, while positive effect was observed when the presence of MBs and humic acid. The identification results of radicals and degradation intermediates suggested that multiple synergistic effects (such as heat, e_aq^- and H•) activated PS, and ¹O₂/reactive nitrogen species, •OH and SO₄^-• with contributions of 18%, 26%, and 29%, were main species attacking ATZ. ATZ degradation pathways including olefination, alkylic-oxidation, dealkylation, and dechlorination were proposed. An environment-friendly and a novel method for enhancing the PS-activation and ATZ-decomposition was provided, which fully utilised the electric-chemical conversion of DBD and high mass transfer efficiency of MBs.

Heterogeneous catalytic oxidation degradation of BPAF by peroxymonosulfate active with manganic manganous oxide: Mineralization, mechanism and degradation pathways

In this study, the catalytic ability and mechanisms involved in activating peroxymonosulfate (PMS) with Mn₃O₄ and the degradation pathways of bisphenol-AF (BPAF) removal was investigated. SO₄^-• and ·OH which were explored by and scavenging tests were the major reactive radicals in the Mn₃O₄/PMS system. A simple simulation algorithm was also used to calculate the relative concentrations of SO₄^-• ([SO₄^-•]) and ·OH ([·OH]) which were 8.39 × 10 ^-15 M and 6.96 × 10 ^-13 M, respectively. The mechanism for the electron transfer between the Mn (II) and Mn (III) species was discussed. Three degradation pathways of BPAF were determined by the GC/MS and LC/MS technology, including chemical mechanism of oxidation, hydroxylation, electron transfer, polymerization, and ring-cleavage. In addition, the results suggested that the Mn₃O₄/PMS system had an efficient total organic carbon (TOC) removal rate and excellent environmental adaptability, the removal rate of TOC being as high as 73.2% in the control condition. Furthermore, the reuse experiments and the comparison on the structural and componential changes of Mn₃O₄ powder before and after reaction demonstrated that the Mn₃O₄ catalyst possessed excellent stability and reusability. Finally, a maximum BPAF degradation of approximately 90.0% was achieved on the optimal conditions for 500 mg/L Mn₃O₄ dosage, 4 mM PMS concentration, 7.0 ± 0.2 initial pH, and 5 mg/L BPAF concentration respectively. And the effect of the coexisting anions and natural environmental water quality were also considered. This study demonstrated the Mn₃O₄/PMS system can be considered as a green approach for the removal of environmental reluctant pollutants.