Graphene oxide enhanced ozonation of 5-chloro-2-methyl-4-isothiazolin-3-one: Kinetics, degradation pathway, and toxicity

Kathon is among the most common non-oxidative biocides, containing 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and methylisothiazolone (MIT) as the active ingredients. In our previous work, MIT was shown to be efficiently removed by ozonation. In this work, we found that ozonation didn't readily degrade CMIT. Rate constants [Formula: see text] and k_·OH,CMIT, determined to be 6.43 L mol^-1 s^-1 and 7.8 × 10⁹ L mol^-1 s^-1, indicated that hydroxyl radicals played a more important role than ozone molecule in the CMIT ozonation which was also proved by the significant inhibition (55.7 %) when adding t-butanol (TBA). Graphene oxide (GO) greatly enhanced the CMIT ozonation, and degradation efficiency raised from 15 % to 100 % after 10 min through the increased production of hydroxyl radical. Basic conditions benefited the CMIT degradation compared with acidic and neutral conditions by promoting ozone decomposition and hydroxyl radical generation, while high carbonate and humic acid concentrations had slight influence on the CMIT degradation. In spite of the complex water matrix, CMIT degradation by GO enhanced ozonation was applicable in reverse osmosis concentrate (ROC). Based on the identification of the inorganic and organic products, a possible CMIT degradation pathway was proposed. However, CMIT transformation products still showed toxicity to Photobacterium phosphoreum and Daphnia magna even after a longer ozonation time.