Formation of Refractory Ring-Expanded Triazine Intermediates during the Photocatalyzed Mineralization of the Endocrine Disruntor Amitrole and Related Triazole Derivatives at UV-lrradiated TiO_2/H_20 Interfaces

摘要

Amitrole(ATz,3-amino-1H-1,2,4-triazole)is a widely employed herbicide with strong estrogenic activity that can lead to abnormalities of the thyroid gland and can cause mutations.The photocatalytic transformation of ATz was carried out at the UV-irradiated TiO_2/H_20 interface,along with the triazole derivatives Tz(1H-1,2,4-triazole)and DaTz(3,5-diamino-1 H-1,2,4-triazole)to assess the decomposition of these herbicides,to identify intermediates,and to elucidate some mechanistic details of the ATz degradation.Conversion of the nitrogens of these triazoles to NH_4~+ and/ or NO_3~- ions occurs competitively and depends on the number of amine functions on the five-membered triazole rings.Photomineralization of the substrates in terms of loss of nitrogen to NH_4~+/NO_3~- was rather low(ca.25-40%)for each of the triazoles,whereas evolution of CO_2(loss of TOC)was more significant(60-70%),indicating considerable retention of nitrogen in the intermediate products.UV-Vis spectroscopy,TOC assays,FT-IR spectroscopy,proton NMR spectrometry,electrospray LC-MS,and molecular orbital calculations were brought to bear in assessing the temporal course of the photocatalyzed process(es).Results show that after cleavage of the triazole ring,the various intermediate fragments recombine to yield ring-expanded six-memberedtriazine intermediates,which slowly degrade to give the refractory cyanuric acid under the conditions used.