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•Magnetic MnFe2O4 along with H2O2 was tested for catalytic oxidation of norfloxacin.•Norfloxacin could be removed efficiently at neutral pH.•Surface OH played a key role on ...norfloxacin removal.•Degradation intermediates were identified, and three degradation pathways were proposed.
Magnetic MnFe2O4 particles were prepared by sol-gel method and used to activate H2O2 for norfloxacin removal from water. The results of hydrodynamic particle size distribution and Zeta potential analyses show that the particle size ranged from 100 nm to 500 nm, and Zeta potential from −76 mV to −25 mV at pHintial = 7.0. The MnFe2O4/H2O2 system was able to remove 90.6% of norfloxacin at neutral pH, and the spent material can be reused in multiple cycles of operations. Fluorescence detection and DMPO capture analyses indicated that OH was the main free radicals, which played a primary role in degradation of norfloxacin. The valence variations of Mn and Fe were analyzed by XPS, and the results showed that coupled transformations of Mn2+/Mn3+ and Fe2+/Fe3+ were involved in generation of OH. Moreover, the removal rate in the MnFe2O4/H2O2 system showed a positive correlation with the adsorption efficiency of NOR by MnFe2O4. Eight degradation intermediates were detected by LC-QToF-MS/MS, and consequently, three degradation pathways were proposed, including defluorination, piperazinyl ring opening, and quinolone transformation. Further analyses of F−, NH4+, NO3− and NO2− before and after the reaction showed that defluorination process was the main degradation pathway. The MnFe2O4/H2O2 system may offer an efficient alterative for degradation of emerging persistent contaminants.
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•Tea polyphenols was firstly used as accelerators in the Fenton reaction to degrade antibiotics.•Chelation and reduction of tea polyphenols are the key to improve the efficiency of ...Fe3+/Fe2+ cycle.•The pH values is the decisive factor for chelation or reduction of tea polyphenols.
Tea polyphenols (TP) are natural green organic compounds with chelating and reducing properties, which can promote the catalytic reaction, but the mechanism of promotion is still uncertain. In this paper, the chelation and reduction of TP were used to promote the degradation of lincomycin (LCM) by zero-valent iron Fenton-like reaction, and the mechanism of the two properties of TP was analyzed. The results showed that in the Fe0/H2O2 system, the degradation rate of the reaction system was increased from 27% to 100% in two hours after the addition of TP, and the reaction rate was increased about 26 times. Moreover, the parameters of pH, Fe2+, ·OH, oxidation reduction potential (ORP) and so forth indicating that the chelating structure of TP and iron ions was formed under pH = 4–9, which obviously promoted the mutual conversion of Fe3+/Fe2+. It is propitious to the proper amount of iron dissolution in order to facilitate the continuous and efficient Fenton reaction. Under acidic conditions, the TP are more reductive due to the destruction of the chelate structure, which promotes the conversion of Fe3+ to Fe2+ or even zero-valent iron, significantly improves the Fe3+/Fe2+ cycle capacity and increases the amount of OH produced.
Mechanochemistry has been proved to be an effective method to remediation of organic-contaminated sites. However, the high ball-to-powder mass ratio (CR) limits the large-scale application of ...mechanochemistry. In this study, co-milling additives were introduced to enhance the mechanochemical degradation of decabromodiphenyl ether (BDE209)-contaminated soil under the condition of low CR. Based on additive screening experiments, sodium borohydride was selected as the ideal additive to assist the mechanochemical degradation of BDE209, and the resulting removal efficiency was approximately 100% with 2 h of ball milling at a rotational speed of 550 rpm. The main degradation intermediates and degradation pathway of BDE209 were identified using gas chromatography-tandem mass spectrometry. It was proposed that the degradation of BDE209 by sodium borohydride-assisted mechanochemistry was a concurrent process of stepwise and multistage debromination. Meanwhile, the meta-bromine atom in BDE209 was more susceptible to debromination than those at the para and ortho positions. The evolution of the concentration of Br− was monitored by ion chromatography, which revealed that reduction and oxidation both occurred in the removal of BDE209. This paper provides a new perspective for reducing the CR in the mechanochemical remediation of BDE209-contaminated soil.
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•BDE209 could be completely removed by mechanochemical with the assistance of NaBH4.•Stepwise and multistage debromination occurred in the removal of BDE209.•Meta-bromine in BDE209 was more susceptible to debromination.•Reduction and oxidation were responsible for the removal of BDE209.
Iron-based catalysts (GFe0.5) were successfully prepared from tea polyphenols (TP) and ferric trichloride and used as a heterogeneous Fenton-like catalyst for the degradation of lincomycin (LCM). The ...results showed that a GFe0.5 dosage of 0.01 g/L could completely degrade a 20 mg/L concentration of LCM in 90 min, and assessment of the toxicity to luminous bacteria showed that the GFe0.5/H2O2 system effectively reduced the toxicity risk posed by this pollutant. The results of transmission electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and other characterisations showed that the synthetic material had a triangular structure similar to that of nonacarbonyldiiron, with Fe2+, Fe3+ and organic groups attached to the triangular structure's surface. That is, the present environment-friendly synthesis produces an Fe-based material resembling a mixture of nonacarbonyldiiron and ferrous chloride. Free-radical capture and electron spin resonance experiments confirmed that ·OH was the main active free radical in the degradation mechanism of the iron-based material. Cyclic experiments, inductively coupled plasma and XRD characterisation of the materials after the reaction showed that the loss of free iron was the main reason for the decrease of activity. The free iron in the Fe-based material becomes bound during the reaction, which effectively avoids the excessive consumption of Fe2+ in the prophase of the Fenton-like reaction, and is the key to both the efficient Fenton-like catalytic ability of GFe0.5, and to preventing the production of iron sludge.
•A efficient Fenton-like catalyst was prepared by mixing TP and ferric.•The GFe0.5 transformed free iron into bound iron avoiding excessive waste of iron.•The toxicity test proved that the GFe0.5 was truly eco-friendly catalyst.
