- Near-quantitative mineralization of two refractory triazines under hydrothermal-supercritical aqueous conditions assisted by ozone and UV/ozone
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Refractory atrazine and cyanuric acid were degraded under hydrothermal and supercritical aqueous media (HY-SC) conditions, as well as in the presence of ozone (HY-SC/O3) and UV-illuminated ozone (HY-SC/UV/O3) to assess whether the efficacy of the decomposition process could be enhanced using a single-pass flow-through treatment device under a constant pressure of 23 MPa. The progress of the degradation was evidenced by the extent of removal of total organic carbon (TOC) in solution, by UV absorption spectroscopy (opening of the atrazine and cyanuric acid heterorings), and by the extent of deamination (formation of NH4+) and dechlorination (release of Cl- ions) of the two compounds. Loss of atrazine was confirmed by LC-MSD techniques in the positive ion mode. Formation of various intermediates from the degradation of atrazine was substantiated by positive and negative ion mode MSD analyses. Dechlorination of atrazine occurred around 100°C under hydrothermal conditions for the HY-SC and HY-SC/O3 processes but not for HY-SC/UV/O3; it did increase rapidly at higher temperatures (beginning at ca. 220-230°C) for all three methods: HY-SC through HY-SC/UV/O3. Deamination, removal of TOC, and loss of atrazine mass spectral features began around 260-280°C in hydrothermal aqueous media. Degradation of cyanuric acid showed a similar behavior. For the treated effluent solution in the collector reservoir, ozonation enhanced somewhat both dechlorination and mineralization, but had no significant effect on the deamination of either atrazine or cyanuric acid.
- Horikoshi, Satoshi,Wada, Yoshinori,Watanabe, Natsuko,Hidaka, Hisao,Serpone, Nick
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- Integrated photocatalytic-biological treatment of triazine-containing pollutants
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The degradation of triazine-containing pollutants including simazine, Irgarol 1051 and Reactive Brilliant Red K-2G (K-2G) by photocatalytic treatment was investigated. The effects of titanium dioxide (TiO2) concentration, initial pH of reaction mixture, irradiation time and ultraviolet (UV) intensity on photocatalytic treatment efficiency were examined. Complete decolorization of K-2G was observed at 60 min photodegradation while only 15 min were required to completely degrade simazine and Irgarol 1051 under respective optimized conditions. High-performance liquid chromatography (HPLC), gas chromatography/mass spectrometry (GC/MS) and ion chromatography (IC) were employed to identify the photocatalytic degradation intermediates and products. Dealkylated intermediates of simazine, deisopropylatrazine and deethyldeisopropylatrazine, and Irgarol 1051 were detected by GC/MS in the initial phase of degradation. Complete mineralization could not be achieved for all triazine-containing pollutants even after prolonged (>72 h) UV irradiation due to the presence of a photocatalysis-resistant end product, cyanuric acid (CA). The toxicities of different compounds before and after photocatalytic treatment were also monitored by three bioassays. To further treat the photocatalysis-resistant end product, a CA-degrading bacterium was isolated from polluted marine sediment and further identified as Klebsiella pneumoniae by comparing the substrate utilization pattern (Biolog microplate), fatty acid composition and 16S rRNA gene sequencing. K. pneumoniae efficiently utilized CA from 1 to 2000 mg/L as a good nitrogen source and complete mineralization of CA was observed within 24 h of incubation. This study demonstrates that the biodegradability of triazine-containing pollutants was significantly improved by the photocatalytic pre-treatment, and this proposed photocatalytic-biological integrated system can effectively treat various classes of triazine-containing pollutants.
- Chan, Cho Yin,Chan, Ho Shing,Wong, Po Keung
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p. 371 - 380
(2019/02/07)
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- A proof of the direct hole transfer in photocatalysis: The case of melamine
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The photoinduced transformation of 2,4,6-triamino-1,3,5-triazine (melamine) was studied by using different advanced oxidation technologies under a variety of experimental conditions. The systems involving homogeneous hydroxyl radicals, as generated by H2O2/hν, Fenton reagent, and sonocatalysis are ineffective. However, melamine is degraded under photocatalytic conditions or by SO4- (S2O82-/hν). The time evolution of long-living intermediates, such as 2,4-diamino-6-hydroxy-1,3,5-triazine (ammeline) and 2-amino-4,6-dihydroxy-1,3,5-triazine (ammelide), has been followed, being 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid) the final stable product. During both photocatalytic and S2O82-/hν experiments, in the early steps, a fairly stable intermediate evolving to ammelide is observed in a large extent. This intermediate was identified as 2,4-diamino-6-nitro-1,3,5-triazine. This indicates that the primary photocatalytic event is the oxidation of the amino-group to nitro-group through several consecutive fast oxidation steps, and that a hydrolytic step leads to the release of nitrite in solution. To elucidate the nature of the oxidant species hole scavengers such as methanol and bromide ions were added to the irradiated TiO2. They completely stop the degradation, whereas chloride and fluoride ions decrease the degradation rate. The study of the photocatalytic degradation rate of melamine at increasing concentrations using two different commercial titanium dioxides, such as P25 and Merck TiO2, showed an intriguing behavior. A drastic abatement of the melamine transformation rate was observed when coagulation of the P25 slurry occurs due both to the pH change and melamine concentration effect that increase melamine adsorption. In the presence of TiO2 (Merck) the melamine initial degradation rates are significantly lower than those observed in the presence of P25 but are not depressed at larger concentrations. The experimental evidences (e.g.; absence of melamine adsorption onto TiO2 surface at low concentrations or at acidic pH or due to the catalyst surface texture, and the lack of reactivity toward OH free and bound) suggest that the effective photocatalytic mechanism is based on an outer sphere direct hole transfer to the melamine. Its formal potential lies in the range 1.9-2.3 V vs NHE. Then, the photodegradation of melamine is an efficient tool to evaluate the direct hole transfer ability of a photocatalyst.
- Maurino, Valter,Minella, Marco,Sordello, Fabrizio,Minero, Claudio
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- Photocatalytic degradation of the herbicide terbuthylazine: Preparation, characterization and photoactivity of the immobilized thin layer of TiO2/chitosan
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The aim of this study was to immobilize a photocatalytic TiO2 layer on a suitable support material for potential use in a variety of photoreactor designs. The immobilized TiO2/chitosan thin film was used for the photocatalytic treatment of a triazine herbicide, terbuthylazine as representative agrochemical pollutant in the wastewater. The method of preparation was based on the use of a chitosan as binder and glass fiber woven roving material as a support. The employed method was found to be very simple, low cost and quite effective. Several methods of the photocatalyst characterization, such as FE-SEM/EDX, AAS, ICP-MS, TOC and nitrogen adsorption/desorption at 77 K were employed to correlate structural and morphological properties of immobilized TiO2-chitosan/glass fiber woven roving and its photocatalytic properties under UV irradiation. Reaction was performed in a self-constructed batch mode and annular type of the photoreactor. Comparison of thermal, photolytic and photocatalytical degradation of treated terbuthylazine at different reaction conditions was performed in order to get more insight into the photocatalytic performance and reaction mechanism. It was observed that there is no decay in photocatalytic efficiency over a long period of reaction time using for the photocatalytic degradation of terbuthylazine.
- Le Cunff, Jér?me,Toma?i?, Vesna,Wittine, Ozren
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- METHOD FOR THE TREATMENT OF TRIAZINE-CONTAINING WATER OF A MELAMINE PLANT
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The invention relates to a method for treating triazine-containing water of a melamine plant. Said method is characterized in that the water containing ionic and non-ionic triazines in a dissolved form is fed to at least one membrane filtration unit (MF), the water is separated into an ionic triazine-rich fraction and a non-ionic triazine-rich fraction in the membrane filtration unit (MF), whereupon the ionic triazine-rich fraction is discharged and the non-ionic triazine-rich fraction is redirected into the melamine plant. The inventive method allows a great portion of the melamine contained in the triazine-containing water to be redirected into the process while the yield is increased along the entire melamine process. Furthermore, the need for fresh water in the wet part of the melamine plant is decreased. The disclosed method can be carried out continuously and in liquid phase.
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Page/Page column 10-14
(2008/06/13)
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- Microwave assisted pyrolysis of urea supported on graphite under solvent-free conditions
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The coupling of graphite (support) with microwaves (energy source) is responsible for a high temperature gradient leading to increased reaction rates as compared to conventional procedures. A rapid one-pot preparation of cyanuric acid is described that proceeds from urea by pyrolysis using microwave heating in the absence of water and organic solvents.
- Chemat, Farid,Poux, Martine
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p. 3693 - 3695
(2007/10/03)
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- Studies of Cyanamide Derivatives. Part 110. A facile Synthesis of 2,4,6-Triureido-1,3,5-triazine and 2-Amino-4,6-diureido-1,3,5-triazine
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2,4,6-Triureido-1,3,5-triazine and 2-amino-4,6-diureido-1,3,5-triazine were readily synthetized in high yields, 94 and 85percent respectively, by the alcoholysis of 2,4,6-tris(cyanoamino)-1,3,5-triazine and 2-amino-4,6-bis(cyanoamino)-1,3,5-triazine in the presence of hydrogen chloride
- Iio, Kokoro,Ichikawa, Eiichi
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p. 2009 - 2010
(2007/10/02)
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