In this study, the effects of an inorganic ligand tetrapolyphosphate on the molecular oxygen activation and the subsequent aerobic atrazine degradation by Fe@Fe2O3 core-shell nanowires were investigated systematically at a circumneutral to alkaline pH range (pH 6.0-9.0). We interestingly found that the addition of tetrapolyphosphate could enhance the aerobic atrazine degradation rate 955 times, which was even 10 times that of the traditional organic ligand ethylenediamine tetraacetate. This tetrapolyphosphate induced dramatic aerobic atrazine degradation enhancement could be attributed to two factors. One was that the presence of tetrapolyphosphate strongly suppressed hydrogen evolution from the reduction of proton by Fe@Fe2O3 core-shell nanowires through proton confinement, leaving over more electrons for the reduction of Fe(III) to Fe(II) and the subsequent molecular oxygen activation. The other was that the complexation of tetrapolyphosphate with ferrous ions not only guaranteed enough soluble Fe(II) for Fenton reaction, but also provided another route to produce more •OH in the solution via the single-electron molecular oxygen reduction pathway. We employed gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry to identify the atrazine degradation intermediates and proposed a possible aerobic atrazine degradation pathway. This study not only sheds light on the promotion effects of ligands on the molecular oxygen activation by nanoscale zerovalent iron, but also offers a facile and green iron-based method for the oxidative atrazine removal.
In this study, a novel electro-Fenton (EF) system was developed with iron wire, activated carbon fiber, and sodium tetrapolyphosphate (Na6TPP) as the anode, cathode, and electrolyte, respectively. This Na6TPP-EF system could efficiently degrade atrazine in a wide pH range of 4.0-10.2. The utilization of Na6TPP instead of Na2SO4 as the electrolyte enhanced the atrazine degradation rate by 130 times at an initial pH of 8.0. This dramatic enhancement was attributed to the formation of ferrous-tetrapolyphosphate (Fe(II)-TPP) complex from the electrochemical corrosion (ECC) and chemical corrosion (CC) of iron electrode in the presence of Na6TPP. The Fe(II)-TPP complex could provide an additional molecular oxygen activation pathway to produce more H2O2 and (•)OH via a series single-electron transfer processes, producing the Fe(III)-TPP complex. The cycle of Fe(II)/Fe(III) was easily realized through the electrochemical reduction (ECR) process on the cathode. More interestingly, we found that the presence of Na6TPP could prevent the iron electrode from excessive corrosion via phosphorization in the later stage of the Na6TPP-EF process, avoiding the generation of iron sludge. Gas chromatograph-mass spectrometry, liquid chromatography-mass spectrometry, and ion chromatography were used to investigate the degradation intermediates to propose a possible atrazine oxidation pathway in the Na6TPP-EF system. These interesting findings provide some new insight on the development of a low-cost and highly efficient EF system for wastewater treatment in a wide pH range.
The effects of different concentrations of copper (0-800 µmol) on growth, protein contents, peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and phenylalanine ammonia-lyase (PAL) in Jatropha curcas L. seedlings were assessed by means of pot experiments. Results suggested that increased copper concentrations lead to decreased shoot elongation and seedling biomass. Protein content in the leaves and roots reached their highest levels at the copper concentrations of 400 µmol, while the highest protein content in the stem was observed at 800 µmol copper. POD activity in leaves and stems was unaffected at low copper concentrations, but showed a considerable variation at high copper concentrations. In roots, the highest POD activity was observed at 200 µmol copper. Under copper stress, SOD activity in leaves increased concomitantly with increasing copper up to 400 µmol, and SOD activity in stems and roots showed a slight increase. Catalase activity significantly elevated in leaves and roots but showed no significant changes in stems of the seedlings exposed to copper. A gradual increase of PAL activity in leaves and roots at the copper concentration of 400 and 200 µmol was observed, while PAL activity remained unchanged in stems.
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