Synergetic decomposition performance and mechanism of perfluorooctanoic acid in dielectric barrier discharge plasma system with Fe3O4@SiO2-BiOBr magnetic photocatalyst

Dielectric Barrier Discharge (DBD) enhanced Fenton process for landfill leachate nanofiltration: Organic matter removal and membrane fouling alleviation

This study investigated a sustainable approach through dielectric barrier discharge (DBD) enhanced Fenton technology coupling nanofiltration (NF) process for landfill leachate treatment. The DBD/Fe(II)/H2O2 system exhibited significant synergistic effects, removing 55.07 % of TOC and 53.79 % of UV254 within 60 min, respectively. Additionally, the DBD/Fe(II)/H2O2 system demonstrated exceptional performance in removing fluorescent substances and large molecular organic compounds, thereby reducing the formation of cake layer on the nanofiltration membrane. Moreover, membrane flux increased by 2.34 times, with reversible and irreversible resistances decreasing by 75.79 % and 81.55 %, respectively. Quenching experiments revealed ·OH as the primary active species for perfluorooctanoic acid (PFOA) degradation in the DBD/Fe(II)/H2O2 process. The degradation pathway of PFOA was also elucidated via capillary electrophoresis-quadrupole time-of-flight mass spectrometry analysis. Correlation analysis indicated that TOC and EEM were the primary fouling factors. Lastly, through an assessment of energy consumption, economic costs, and carbon dioxide emissions, the advantages and practical application potential of the DBD/Fe(II)/H2O2 system were demonstrated. In summary, the DBD/Fe(II)/H2O2 system emerges as a feasible strategy for NF pretreatment, holding immense potential for treating landfill leachate.

Fabrication of novel magnetic Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite synthesized by a simple ultrasonic-assisted route for organic dye removal using Fenton-like reaction

Fenton-like degradation of contaminants is considered to be a feasible method for eliminating environmental pollution. In this study, a novel ternary Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite was fabricated using a novel ultrasonic-assisted technique, and investigated as a Fenton-like catalyst for the removal of tartrazine (TRZ) dye. The nanocomposite was synthesized by first coating the SiO2 shell around the Mg0.8Cu0.2Fe2O4 core via a Stöber-like process to form Mg0.8Cu0.2Fe2O4/SiO2. Then, a simple ultrasonic-assisted route was used to synthesize Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite. This approach provides a simple and environmentally friendly way to produce this material without the use of any additional reductants or organic surfactants. The fabricated sample demonstrated excellent Fenton-like activity. The efficiency of Mg0.8Cu0.2Fe2O4 was significantly enhanced by the incorporation of SiO2 and CeO2, and complete removal of TRZ (30 mg/L) was achieved within 120 min using 0.2 g/L of Mg0.8Cu0.2Fe2O4/SiO2/CeO2. The scavenger test shows that the main active species is the strong oxidizing of hydroxyl radicals (HO•). Consequently, the Fenton-like mechanism of Mg0.8Cu0.2Fe2O4/SiO2/CeO2 is explained based on the coexistence of Fe3+/Fe2+, Cu2+/Cu+, and Ce4+/Ce3+ redox couples. The removal efficiency of TRZ dye remained around 85% after the third recycling run, revealing that the nanocomposite could be employed to eliminate organic contaminants in water treatment. This research opened up a new avenue for expanding the practical application of new-generation Fenton-like catalysts.

Recent trends in magnetic spinel ferrites and their composites as heterogeneous Fenton-like catalysts: A review

In recent years, there has been a growing interest in utilizing spinel ferrite and their nanocomposites as Fenton-like catalysts. The use of these materials offers numerous advantages, including ability to efficiently degrade pollutants and potential for long-term and repeated use facilitated by their magnetic properties that make them easily recoverable. The remarkable catalytic properties, stability, and reusability of these materials make them highly attractive for researchers. This paper encompasses a comprehensive review of various aspects related to the Fenton process and the utilization of spinel ferrite and their composites in catalytic applications. Firstly, it provides an overview of the background, principles, mechanisms, and key parameters governing the Fenton reaction, along with the role of physical field assistance in enhancing the process. Secondly, it delves into the advantages and mechanisms of H2O2 activation induced by different spinel ferrite and their composites for the removal of organic pollutants, shedding light on their efficacy in environmental remediation. Thirdly, the paper explores the application of these materials in various Fenton-like processes, including Fenon-like, photo-Fenton-like, sono-Fenton-like, and electro-Fenton-like, for the effective removal of different types of contaminants. Furthermore, it addresses important considerations such as the toxicity, recovery, and reuse of these materials. Finally, the paper presents the challenges associated with H2O2 activation by these materials, along with proposed directions for future improvements.

Recent advances in the application of magnetic materials for the management of perfluoroalkyl substances in aqueous phases

Perfluoroalkyl substances (PFASs) are a class of artificially synthesised organic compounds extensively used in both industrial and consumer products owing to their unique characteristics. However, their persistence in the environment and potential risk to health have raised serious global concerns. Therefore, developing effective techniques to identify, eliminate, and degrade these pollutants in water are crucial. Owing to their high surface area, magnetic responsiveness, redox sensitivity, and ease of separation, magnetic materials have been considered for the treatment of PFASs from water in recent years. This review provides a comprehensive overview of the recent use of magnetic materials for the detection, removal, and degradation of PFASs in aqueous solutions. First, the use of magnetic materials for sensitive and precise detection of PFASs is addressed. Second, the adsorption of PFASs using magnetic materials is discussed. Several magnetic materials, including iron oxides, ferrites, and magnetic carbon composites, have been explored as efficient adsorbents for PFASs removal from water. Surface modification, functionalization, and composite fabrication have been employed to improve the adsorption effectiveness and selectivity of magnetic materials for PFASs. The final section of this review focuses on the advanced oxidation for PFASs using magnetic materials. This review suggests that magnetic materials have demonstrated considerable potential for use in various environmental remediation applications, as well as in the treatment of PFASs-contaminated water.

Subnanoscale spatially confined heterogeneous Fenton reaction enables mineralization of perfluorooctanoic acid

Superoxide radical (•O2-) is capable of degrading perfluorinated compounds that are persistent in nature and cannot be removed by biological or advanced oxidation treatments, but the inherent drawback is the negligible reactivity of •O2-in aqueous phases due to the hydration effect. Here, we explored an innovative way to make use of •O2- by modulating a partial hydration state through spatial confinement control. We demonstrated this idea by conducting heterogeneous Fenton reaction with layered iron oxychloride (FeOCl) catalyst, wherein •O2-radicals produced and confined within the catalyst structure (interlayer spacing of 7.92 Å) showed defluorination effect dealing with perfluorooctanoic acid (PFOA) as model compound. The defluorination combined with advanced oxidation achieved mineralization. Mechanism study revealed that the confinement frustrated the hydration shell of •O2-with coordination number reduced from 3.3 (for bulk phase) to 1.89, and thereby changed its orbital electron properties and enhanced the nucleophilic ability. We further demonstrated a compact FeOCl membrane reactor with highly efficient degradation of PFOA (kobs up to 1.2 min-1) and cost-effective mineralization (2 × 10-6 $ per mgC), operated under ultrafiltration reaction mode. Our findings highlight the great interest of developing spatial confinement technology to modulate •O2--based reactions, as well as the feasibility of combining confinement catalyst structures with heterogeneous Fenton reaction to achieve the mineralization treatment goal.

Recent Advances of Emerging Organic Pollutants Degradation in Environment by Non-Thermal Plasma Technology: A Review

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a novel advanced oxidation process, which combines the effects of free radical oxidation, ozone oxidation, ultraviolet radiation, shockwave, etc. This paper summarized and discussed the research progress of non-thermal plasma remediation of EOPs-contaminated water and soil. In addition, the reactive species in the process of non-thermal plasma degradation of EOPs were summarized, and the degradation pathways and degradation mechanisms of EOPs were evaluated of selected EOPs for different study cases. At the same time, the effect of non-thermal plasma in synergy with other techniques on the degradation of EOPs in the environment was evaluated. Finally, the bottleneck problems of non-thermal plasma technology are summarized, and some suggestions for the future development of non-thermal plasma technology in the environmental remediation were presented. This review contributes to our better understanding of non-thermal plasma technology for remediation of EOPs-contaminated water and soil, hoping to provide reference for relevant practitioners.

Theoretical and experimental insights into the mechanisms of C6/C6 PFPiA degradation by dielectric barrier discharge plasma

As an emerging alternative legacy perfluoroalkyl substance, C6/C6 PFPiA (perfluoroalkyl phosphinic acids) has been detected in aquatic environments and causes potential risks to human health. The degradation mechanisms of C6/C6 PFPiA in a dielectric barrier discharge (DBD) plasma system were explored using validated experimental data and density functional theory (DFT) calculations. Approximately 94.5% of C6/C6 PFPiA was degraded by plasma treatment within 15 min at 18 kV. A relatively higher discharge voltage and alkaline conditions favored its degradation. C6/C6 PFPiA degradation was attributed to attacks of •OH, •O₂^-, and ¹O₂. Besides PFHxPA and C2 -C6 shorter-chain perfluorocarboxylic acids, several other major intermediates including C4/C6 PFPiA, C4/C4 PFPiA, and C3/C3 PFPiA were identified. According to DFT calculations, the potential energy surface was proposed for possible reactions during C6/C6 PFPiA degradation in the discharge plasma system. Integrating the identified intermediates and DFT results, C6/C6 PFPiA degradation was deduced to occur by stepwise losing CF₂, free radical polymerization, and C-C bond cleavage. Furthermore, the DBD plasma treatment process decreased the toxicity of C6/C6 PFPiA to some extent. This study provides a comprehensive understanding of C6/C6 PFPiA degradation by plasma advanced oxidation.

Reactive Nitrogen Species Generated by Gas-Liquid Dielectric Barrier Discharge for Efficient Degradation of Perfluorooctanoic Acid from Water

Perfluorooctanoic acid (PFOA) poses a serious threat to the ecological environment and biological health because of its ubiquitous distribution, extreme persistence, and high toxicity. In this study, we designed a novel gas-liquid dielectric barrier discharge (GLDBD) reactor which could efficiently destruct PFOA. PFOA removal efficiencies can be obtained in various water matrices, which were higher than 98.0% within 50 min, with energy yields higher than 114.5 mg·kWh^-1. It was confirmed that the reactive species including e^-, ONOOH, •NO₂, and hydroxyl radicals (•OH) were responsible for PFOA removal. Especially, this study first revealed the crucial role of reactive nitrogen species (RNS) for PFOA degradation in the plasma system. Due to the generation of a large amount of RNS, the designed GLDBD reactor proved to be less sensitive to various water matrices, which meant a broader promising practical application. Moreover, influential factors including high concentration of various ions and humic acid (HA), were investigated. The possible PFOA degradation pathways were proposed based on liquid chromatograph-mass spectrometer (LC-MS) results and density functional theory (DFT) calculation, which further confirmed the feasibility of PFOA removal with RNS. This research, therefore, provides an effective and versatile alternative for PFOA removal from various water matrices.

Dielectric barrier discharge plasma coupled with WO3 for bisphenol A degradation

Based on the difficulty of the refractory organic compounds degradation in water by the traditional wastewater treatment methods, the research relies on the technology of the dielectric barrier discharge plasma (DBDP) and the catalysis of the nano WO₃, investigating the bisphenol A (BPA) degradation in the synergistic system of DBDP/WO₃. The coupled degradation percentage of the BPA under different amounts of WO₃ addition, different initial solution pH and carrier gas were investigated to confirm the catalysis of the WO₃ in the DBDP system. It was obtained from the experimental results that the optimal additive amount of the WO₃ was 175 mg L^-1 and change of the solution pH value and the carrier gas variety could not change the catalysis of the WO₃. The BPA degradation percentage could reach 100% after treating 30 min in the DBDP/WO₃ system with 0.5 L min^-1 O₂ as the carrier gas. The WO₃ still had a better catalysis after four times usage and the discharge had little effect on the microstructure of the WO₃. The existence of the WO₃ in the DBDP system could result in the reduction of the O₃ concentration and the enhancement of the H₂O₂ concentration, which improve the catalysis of the WO₃ in the DBDP system, while the experiments on the scavengers' addition verified the major role of the OH on the BPA degradation. The catalytic mechanism of the WO₃ as well as the BPA degradation pathway was also speculated in the research.

Decomposition of highly persistent perfluorooctanoic acid by hollow Bi/BiOI1-xFx: Synergistic effects of surface plasmon resonance and modified band structures

Perfluorooctanoic acid (PFOA) is highly stable due to the strong CF bond and extremely difficult to be removed by conventional photocatalysts. In this study, Bi doped BiOI_1-xF_x solid solutions with hollow microsphere structure were prepared through a facile one-step hydrothermal method. Compared with pure BiOI and BiOF, the band gap of the Bi/BiOI_1-xF_x solid solutions was significantly reduced, thus promoting the visible light absorbance. The cavity structure of the BiOI_1-xF_x solid solutions enhanced the surface areas and active sites for reaction. The local electromagnetic field dominated by surface plasmon resonance (SPR) effect of Bi metal on the surface favored the separation of the photoinduced charge pairs. As a consequence, Bi/BiOI_0.8F_0.2 (x = 0.20, the doping amount of fluorine was 20 %) composite displayed the best photocatalytic performance for decomposing PFOA, and 40 mg/L PFOA could be removed within 2 h illumination. The degradation rate constant (k = 0.0375 min^-1) of PFOA by Bi/BiOI_0.8F_0.2 was about tenfold of that by pure BiOI and BiOF. Superoxide radical (·O₂-) predominated in the degradation of PFOA by Bi/BiOI_0.8F_0.2, and the possible degradation pathway of PFOA by Bi/BiOI_0.8F_0.2 was proposed. This work provides a highly efficient catalyst for the practical application in removal of highly persistent PFOA.

Advanced Filtration Membranes for the Removal of Perfluoroalkyl Species from Water

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two perfluoroalkyl substances that have been shown to result in several adverse health effects, including birth defects, kidney/testicular cancer, as well as liver and thyroid damage. The surfactant nature of PFOS and PFOA in water makes these compounds extremely difficult to remove from drinking water. In this paper, an efficient method to remove PFOS and PFOA from drinking water using linear fluorinated silane-functionalized aluminum oxide hydroxide (γ-AlOOH) nanowhiskers was developed. Filters functionalized with linear fluorinated silanes containing 13-17 fluorine atoms were able to remove >90% of the PFOS/PFOA at a very high flux of 1223 L/m²·h. However, due to the hydrophobicity of these linear fluorinated silanes, high pressure drop was also noted across the membrane thickness during the filtration process. To reduce the back-pressure drop, linear fluorinated silanes with appended hydrophilic poly(ethylene glycol) units were synthesized, and it was further demonstrated that the new hydrophilic linear fluorinated silane dramatically reduced the pressure drop of the γ-AlOOH filter while maintaining 99.9% PFOS and PFOA reduction. Adsorption tests were performed to understand the removal mechanism.