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Photocatalytic ozonation of clopyralid, picloram and triclopyr. Kinetics, toxicity and influence of operational parameters
Author(s) -
Solís Rafael R,
Rivas F Javier,
Gimeno Olga,
PérezBote José Luis
Publication year - 2016
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.4542
Subject(s) - clopyralid , triclopyr , picloram , photocatalysis , chemistry , reaction rate constant , ozone , chloride , mineralization (soil science) , dicamba , chloramine , environmental chemistry , photochemistry , catalysis , kinetics , chlorine , organic chemistry , glyphosate , botany , nitrogen , weed control , agronomy , physics , biology , quantum mechanics
BACKGROUND Photolysis, photocatalysis, ozonation and photocatalytic ozonation in the presence of titania have been applied to the elimination of three pyridine carboxylic acids herbicides (clopyralid, picloram and triclopyr) in water. RESULTS Photocatalytic ozonation led to the best results in terms of herbicide elimination rate and mineralization. The herbicides were relatively recalcitrant to direct ozonation (rate constants: 20 M −1 min −1 for clopyralid and triclopyr, and 105 M −1 min −1 in the case of picloram). Herbicides degradation proceeds by hydroxyl radicals attack (rate constants: 0.73, 3.80 and 1.73 × 10 9 M −1 s −1 for clopyralid, picloram and triclopyr, respectively). Monitoring of chloride and nitrates suggests dechlorination as the primary stage in the process. Further ring opening led to the accumulation of nitrates and the appearance of some low weight carboxylic acids. Toxicity decreased at the end of the process. CONCLUSION Tested herbicides slowly react with ozone. Photocatalytic ozonation shows different degrees of synergism, leading to 80% mineralization in less than 1 h. Small amounts of TiO 2 (i.e. 0.005 g L −1 ) maintains the efficiency of the photocatalytic ozonation. Quantitative free chloride and nitrates rapidly appear in the O 3 / UVA / TiO 2 system. First intermediates in the photocatalytic ozonation of clopyralid show higher toxicity than the parent compound. © 2014 Society of Chemical Industry