Peroxydisulfate activation by in-situ synthesized Fe3O4 nanoparticles for degradation of atrazine: Performance and mechanism

Instant and efficient greenly silver nanoparticles for remediating atrazine and methylene blue from contaminated water

In an attempt to create economically feasible and sustainable wastewater treatment "green" techniques, Malva parviflora leaf water extract was used for biosynthesizing silver nanoparticles (Malva-AgNPs). Fourier transform infrared, ultraviolet-visible (UV-Vis), scanning electron microscopy, and dynamic light scattering (DLS) were used for the characterization of Malva-AgNPs. UV-Vis and DLS analysis revealed the stability of the Malva-AgNPs at a wavelength of 420 nm and an average size of 100 nm ± 1 nm. A zeta potential of - 26.4 mV provides additional support for the stability of the material. The removal studies were conducted using atrazine and methylene blue (MB) in a single or mixed liquid state. The adsorbent dose, pH, incubation time, and pollutant concentration in the adsorption process were investigated. The optimal removal for 500 mg L-1 of atrazine and MB at the adsorbent dosage of 450 mg, when incubated for 5 min, was found to be 99.5% and 82.03% for atrazine and MB, respectively. Also, Malva-AgNPs eliminated more than 95% and 50% of the atrazine and MB mixture, respectively, in 5 min. The kinetics study showed that the pseudo-second-order kinetics model was a better fit for explaining the experimental adsorption experiments for atrazine and MB. The obtained equilibrium adsorption data were examined using the Langmuir and Freundlich isotherm models, which indicate that atrazine and MB have maximum adsorption capacities of 434.78 mg g-1 and 400 mg g-1, respectively.

Low-coordinated Mn-N2 sites in graphene oxide induce peroxydisulfate activation for tetracycline degradation: Process optimization and theoretical calculation

Atom-dispersed low-coordinated transition metal-Nx catalysts exhibit excellent efficiency in activating peroxydisulfate (PDS) for environmental remediation. However, their catalytic performance is limited due to metal-N coordination number and single-atom loading amount. In this study, low-coordinated nitrogen-doped graphene oxide (GO) confined single-atom Mn catalyst (Mn-SA/NGO) was synthesized by molten salt-assisted pyrolysis and coupled to PDS for degradation of tetracycline (TC) in water. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and X-ray absorption fine structure spectroscopy (XAFS) analysis showed the successful doping of single-atom Mn (weight percentage 1.6%) onto GO and the formation of low-coordinated Mn-N2 sites. The optimized parameters obtained by Box-Behnken Design achieved 100% TC removal in both prediction and experimental results. The Mn-SA/NGO + PDS system had strong anti-interference ability for TC removal in the presence of anions. Besides, Mn-SA/NGO possessed good reusability and stability. O2•-, •OH, and 1O2 were the main active species for TC degradation, and the TC mineralization reached 85.1%. Density functional theory (DFT) calculations confirmed that the introduction of single atoms Mn could effectively enhance adsorption and activation of PDS. The findings provide a reference for the synthesis of high-performance single-atom catalysts for effective removal of antibiotics.

Facile Synthesis of Novel Magnetic Janus Graphene Oxide for Efficient and Recyclable Demulsification of Crude Oil-in-Water Emulsion

Nanoparticles have been widely applied to treat emulsion-containing wastewater in the form of chemical demulsifiers, such as SiO2, Fe3O4, and graphene oxide (GO). Owing to their asymmetric structures and selective adsorption, Janus nanoparticles show greater application potential in many fields. In the present work, the novel magnetic Janus graphene oxide (MJGO) nanoparticle was successfully prepared by grafting magnetic Fe3O4 to the surface of the JGO, and its demulsifying ability to treat a crude oil-in-water emulsion was evaluated. The MJGO structure and its magnetic intensity were verified by Fourier-transform infrared spectra (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), and magnetization saturation (MS) tests. Compared with GO and JGO, MJGO displayed the superior efficiency (>96%) to demulsify the crude oil-in-water emulsion, which can be attributed to the reduced electrostatic repulsion between MJGO and the emulsion droplets. Furthermore, the effects of pH and temperature on the demulsification performance of MJGO were also studied. Lastly, the recyclability of MJGO largely reduced the cost of demulsifiers in separating crude oil and water. The current research presents an efficient and recyclable demulsifier, which provides a new perspective for the structural design of nanomaterials and their application in the field of demulsification.

Investigation of the Persistence, Toxicological Effects, and Ecological Issues of S-Triazine Herbicides and Their Biodegradation Using Emerging Technologies: A Review

S-triazines are a group of herbicides that are extensively applied to control broadleaf weeds and grasses in agricultural production. They are mainly taken up through plant roots and are transformed by xylem tissues throughout the plant system. They are highly persistent and have a long half-life in the environment. Due to imprudent use, their toxic residues have enormously increased in the last few years and are frequently detected in food commodities, which causes chronic diseases in humans and mammals. However, for the safety of the environment and the diversity of living organisms, the removal of s-triazine herbicides has received widespread attention. In this review, the degradation of s-triazine herbicides and their intermediates by indigenous microbial species, genes, enzymes, plants, and nanoparticles are systematically investigated. The hydrolytic degradation of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is further metabolized into ammonia and carbon dioxide. Microbial-free cells efficiently degrade s-triazine herbicides in laboratory as well as field trials. Additionally, the combinatorial approach of nanomaterials with indigenous microbes has vast potential and considered sustainable for removing toxic residues in the agroecosystem. Due to their smaller size and unique properties, they are equally distributed in sediments, soil, water bodies, and even small crevices. Finally, this paper highlights the implementation of bioinformatics and molecular tools, which provide a myriad of new methods to monitor the biodegradation of s-triazine herbicides and help to identify the diverse number of microbial communities that actively participate in the biodegradation process.

Waste self-heating bag derived iron-based composite with abundant oxygen vacancies for highly efficient Fenton-like degradation of micropollutants

In this study, iron-rich waste self-heating bag was reutilized as the raw material to prepare oxygen vacancies (OV) functionalized iron-based composite (iron oxide (Fe₃O₄)-carbon-vermiculite, viz. OV-ICV), which exhibited excellent performance in the Fenton-like degradation of micropollutants via peroxydisulfate (PDS) activation. Above 95% of 1.0 mg/L carbaryl (CB) was efficiently eliminated in the presence of 0.1 g/L of OV-ICV and 0.5 mmol/L of PDS over a wide pH range of 3-10 within 30 min. Besides, OV-ICV also showed acceptable adaptability, stability, and renewability. Imbedding OV into Fe₃O₄ structure significantly generated more active iron sites and localized electrons, promoted the charge transfer ability, and assisted the redox cycle of ≡Fe(III)/≡Fe(II) for PDS activation. Mechanism investigation demonstrated that superoxide radicals (O₂^•-) derived from the activation of molecular oxygen mediated the generation of H₂O₂, and both of them further enhanced the formation of more sulfate radicals (SO₄^•-) and hydroxyl radicals (^•OH), which led to the efficient degradation and mineralization of CB. Furthermore, the degradation pathways of CB were proposed based on the intermediates identification. This work lays a foundation for the rational reutilization of iron-containing wastes modified with defect engineering in heterogeneous Fenton-like catalysis for the remediation of micropollutants wastewater.

Degradation of atrazine by electroactivation of persulfate using FeCuO@C modified composite cathode: Synergistic activation mechanism

In sulfate radical-based advanced oxidation processes (SR-AOPs), high-efficiency and perdurable materials have drawn considerable interest for use as cathodes, which can effectively degrade refractory organic contaminants through the synergistic electro-activation and transition metal activation of persulfate (PS). Here, the FeCuO@C modified composite cathode (FeCuO@C/AGF) was synthesized via the solvothermal and thermal treatment method based on the CuFe-MOF-74 structure, and the electro-activation PS process (EC/FeCuO@C/AGF/PS) was developed to effectively remove atrazine (ATZ). The surface morphology, electrochemical characteristics, chemical composition, crystal structure, and electrode surface wettability of FeCuO@C/AGF were investigated. It was found that the proposed EC/FeCuO@C/AGF/PS process can successfully remove 100% of ATZ in 20 min at a low current density (2 mA cm^-2) and a low PS concentration (0.4 mM), and PS is successfully activated by combining the electrical and transition metal synergistic activation. The FeCuO@C/AGF cathode exhibits outstanding catalytic functionality over a broad pH range (2-9) and remains stable over five successive cycles. Additionally, the active species involved in the reaction as well as the potential ATZ degradation reaction mechanisms and pathways are discussed. Electrochemical oxidation is a process in which both radicals (SO₄^·-, ·OH, and O₂^·-) and non-radical (¹O₂) participate in the degradation of ATZ. The intermediates of the ATZ degradation process were studied upon the toxicity changing, and the toxicity of the intermediates was found to be reduced during degradation. These results present a novel approach toward the establishment of an effective and reliable electrode in SR-AOPs that can efficiently treat pesticide wastewater.

A self-circulating electro-fenton-like process over Fe3O4-CaO2 cathode for highly efficient degradation of levofloxacin

Electro-Fenton reaction was limited by the generation of H₂O₂ and the circulation of Fe(Ⅱ)/Fe(Ⅲ). Herein, an efficient electro-Fenton-like process was constructed based on Fe₃O₄-CaO₂ cathode promoted by peroxymonosulfate (PMS). Levofloxacin (LEV) could be efficiently degraded (92.1%) and mineralized with the TOC removal of 74.5% in this self-circulating process. More importantly, the Fe₃O₄-CaO₂ exhibited good stability in the recycles due that CaO₂ was covered by Fe₃O₄, which inhibited the rapid release of H₂O₂. Mechanism analysis indicated that CaO₂ could not only replace H₂O₂ to accelerate the oxidation of Fe(Ⅱ) to Fe(Ⅲ), but also could form complexes with Fe(Ⅲ) and PMS to transfer electrons from ligands to metals, thereby enhancing the reduction of Fe(Ⅲ) to Fe(Ⅱ). As a result, the electrical consumption was significantly reduced, which was only 5.0% of the Fe₃O₄ in electro-Fenton reaction. Meanwhile, the hydrolyzed product of Ca(OH)₂ reacted with Fe(Ⅲ) in the presence of H₂O₂ and converted into CaO₂. Thus, the self-circulation of CaO₂/Ca(OH)₂ and Fe(Ⅲ)/Fe(Ⅱ) was realized, which accelerated the generation of active species, such as, ·OH, O₂·^- and ¹O₂. This work first proposed a self-circulating electro-Fenton-like system and demonstrated the potential application of Fe₃O₄-CaO₂ in the treatment of wastewater.

Electrochemiluminescence Systems for the Detection of Biomarkers: Strategical and Technological Advances

Electrochemiluminescence (ECL)-based sensing systems rely on light emissions from luminophores, which are generated by high-energy electron transfer reactions between electrogenerated species on an electrode. ECL systems have been widely used in the detection and monitoring of diverse, disease-related biomarkers due to their high selectivity and fast response times, as well as their spatial and temporal control of luminance, high controllability, and a wide detection range. This review focuses on the recent strategic and technological advances in ECL-based biomarker detection systems. We introduce several sensing systems for medical applications that are classified according to the reactions that drive ECL signal emissions. We also provide recent examples of sensing strategies and technologies based on factors that enhance sensitivity and multiplexing abilities as well as simplify sensing procedures. This review also discusses the potential strategies and technologies for the development of ECL systems with an enhanced detection ability.

Effect of dielectric barrier discharge plasma on persulfate activation for rapid degradation of atrazine: Optimization, mechanism and energy consumption

Dielectric barrier discharge plasma (DBDP) is an emerging and promising advanced oxidation process (AOP) for wastewater treatment. After investigating the effect of input voltage, O₃ (generated by dielectric barrier discharge), and peroxydisulfate (PDS) dosage, the DBDP_O3/PDS system was established. With the assistance of PDS, the atrazine (ATZ) removal efficiency increased from 69.67% to 82.46% within 25 min. Synergistic effect calculation suggests that there were markedly synergies between DBDP, O_3, and PDS. Under the effect of SO₄^-•, the total organic carbon (TOC) removal and dechlorination efficiency were significantly improved. In addition, the DBDP_O3/PDS system maintained the ATZ removal efficiency at a high level over a wide range of initial pH values. According to quenching experiments and electron paramagnetic resonance (EPR) detection, the dominant radical for ATZ degradation in the DBDP_O3/PDS system was HO^•. A possible degradation pathway of ATZ was proposed based on density functional theory (DFT) analysis, quadrupole-time of flight-liquid chromatography/mass spectrometry (Q-TOF-LC/MS) results, and related literature. The acute toxicity to aquatic minnows and the developmental toxicity of intermediate products prediction confirmed that the DBDP_O3/PDS system could effectively reduce ATZ toxicity. The electrical energy per order (E_EO) was 7.10 kWh m^-3 order^-1 illustrating that the DBDP_O3/PDS was a more energy-economic system than other energy-intensive processing technologies.

Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

The degradation of emerging contaminant coumarin was separately investigated in anodic, electro-Fenton and subcritical water oxidation processes. With respect to the anodic and electro-Fenton oxidation, the influence of constant current, treatment time and initial concentration of coumarin was studied. Regarding subcritical water oxidation, the effect of the oxidant concentration, temperature, treatment time and initial coumarin concentration was investigated. In anodic and electro-Fenton oxidation processes, coumarin degradation proceeded in a similar manner, achieving 99% degradation, after 180 min at a constant current of 200 mA. In both set-ups, further increasing the applied current lowered the degradation efficiency due to the formation of by-products and the increasing occurrence of side-reactions. The highest degradation of 88% was achieved in subcritical conditions, specifically at 200 °C, using 150 mM H₂O₂ and after 37.5 min of treatment. Under subcritical conditions, temperature was the most prominent parameter, followed by the H₂O₂ concentration. Under all methodologies, increasing treatment time had a small positive effect on coumarin degradation, indicating that time is not the most influential parameter. A comparison of the three methodologies in terms of performance as well as energy consumption and simplicity of operation highlighted the advantages of subcritical water oxidation.

Efficient degradation of organic dyes using peroxymonosulfate activated by magnetic graphene oxide

Magnetic graphene oxide (MGO) was prepared and used as a catalyst to activate peroxymonosulfate (PMS) for degradation of Coomassie brilliant blue G250 (CBB). The effects of operation conditions including MGO dosage, PMS dosage and initial concentration of CBB were studied. CBB removal could reach 99.5% under optimum conditions, and high removals of 98.4–99.9% were also achieved for other organic dyes with varied structures, verifying the high efficiency and wide applicability of the MGO/PMS catalytic system. The effects of environmental factors including solution pH, inorganic ions and water matrices were also investigated. Reusability test showed that CBB removals maintained above 90% in five consecutive runs, indicating the acceptable recyclability of MGO. Based on quenching experiments, solvent exchange (H₂O to D₂O) and in situ open circuit potential (OCP) test, it was found that ˙OH, SO₄˙⁻ and high-valent iron species were responsible for the efficient degradation of CBB in the MGO/PMS system, while the contributions of O₂˙⁻, ¹O₂ and the non-radical electron-transfer pathway were limited. Furthermore, the plausible degradation pathway of CBB was proposed based on density functional theory (DFT) calculations and liquid chromatography-mass spectrometry (LC-MS) results, and toxicity variation in the degradation process was evaluated by computerized structure–activity relationships (SARs) using green algae, daphnia, and fish as indicator species.

Efficient degradation of organic dyes with PMS and magnetic graphene oxide.

l-cysteine-modified Fe3 O4 nanoparticles as a novel heterogeneous catalyst for persulfate activation on BTEX removal

l-cysteine-modified Fe₃ O₄ nanoparticles (l-cys@nFe₃ O₄ ) were synthesized successfully and used as catalyst to activate persulfate (PS) for benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation. The composite was fully characterized, and the l-cys@nFe₃ O₄ had more protrusions and l-cys was combined on the surface of nFe₃ O₄ . The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/l-cys@nFe₃ O₄ system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe₃ O₄ chelated with l-cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/l-cys@nFe₃ O₄ system. The synergistic mechanisms of BTEX degradation in PS/l-cys@nFe₃ O₄ system were investigated by electron paramagnetic resonance (EPR), benzoic acid (BA) probe and X-ray photoelectron spectroscopy (XPS) tests. SFe bond in l-cys-Fe complexes promoted the electron transfer between nFe₃ O₄ core and the solution, iron and iron at the interface, thereby promoting the Fe³⁺ /Fe²⁺ cycle and the catalytic capacity of nFe₃ O₄ . The optimal pH of PS/l-cys@nFe₃ O₄ system was 3, while HCO₃ ^- and Cl^- exhibited negative influences on BTEX degradation. Only 14.2%, 15.5%, 15.9%, and 15.6% BTEX had been removed in the presence of 0.12-M PS and 8.0 g/L l-cys@nFe₃ O₄ under the actual groundwater condition. However, expanding the dosage of PS and l-cys@nFe₃ O₄ was an effective strategy to overcome the adverse effect. PRACTITIONER POINTS: L-cys@nFe₃ O₄ were synthesized successfully and used as catalyst to activate PS for BTEX degradation. Four successive cycles of BTEX degradation were completed in PS/L-cys@nFe₃ O₄ system. lS-Fe bond in L-cys@nFe₃ O₄ promoted the electron transfer between PS and nFe₃ O₄ core.

Fe3O4 nanoparticles three-dimensional electro-peroxydisulfate for improving tetracycline degradation

In this work, Fe₃O₄ nanoparticle employed as the three-dimensional electrode, were introduced into the electro-oxidation system with peroxydisulfate to improve the tetracycline (TC) degradation. The coprecipitation method prepared Fe₃O₄ was proved to be the irregular sphere-like form through the characterizations of XRD, SEM, N₂ adsorption isotherms, and XPS. By the contrast experiments, the EO-Fe₃O₄-PDS exhibited the outstanding TC degradation capability, which achieved 86.53% after 60 min treatment with current intensity of 20 mA cm^-2, Fe₃O₄ dose of 0.2 g L^-1, PDS amount of 2 mmol L^-1, initial pH 4.5, and TC concentration of 25 mg L^-1. Besides, the influence of current intensity, Fe₃O₄ dosage, PDS concentration, and beginning pH on the TC degradation was investigated systemically. The consecutive five recycles of Fe₃O₄ demonstrated that a favorable stability for the coupling process. The EO-Fe₃O₄-PDS could improve the PDS decomposition and H₂O₂ production. The sulfate and hydroxyl radicals both took charge of the antibiotic degradation as certified by scavenger test. The TC degradation evolution was presented based on the HPLC-MS analyses of degradation byproducts.

A synergistic promotion strategy remarkably accelerated electrochemiluminescence of SnO2 QDs for MicroRNA detection using 3D DNA walker amplification

Developing low-cost and efficient methods to enhance the electrochemiluminescence (ECL) intensity of luminophores is highly desirable and challenging. Herein, we develop a synergistic promotion strategy based on three types of co-reaction accelerators to achieve an efficient SnO2 quantum dots (SnO2 QDs)-based ternary ECL system. Specifically, the MnO2 nanoflowers (MnO2 NFs), Ag nanoparticles (Ag NPs) and hemin/G-quadruplex were rationally selected as co-reaction accelerators. Owing to the synergistic effect, the deft integration of three types of co-reaction accelerators enabled better structural stability, more exposed catalytic active sites, and faster charge transfer, thus more effectively facilitating the reduction of co-reactant (S2O82-) compared with that of the single co-reaction accelerator. To demonstrate the practical utility of this principle, an "on-off-super on" ECL biosensor was constructed in combination with a 3D DNA walker, which showed a superior linear range (10 aM-100 pM) and a low detection limit (2.9 aM) for the highly-sensitive miRNA-21 detection. In general, this work firstly reported that three types of co-reaction accelerators were deftly integrated to remarkably amplify the ECL emission of SnO2 QDs, and provided brand-new perspectives for research on the ingenious design of the structure and component of highly efficient co-reaction accelerators.