摘要:
金雀异黄酮(genistein, Gs)在水体中频繁检出,其环境行为备受关注。为深入探讨水中溶解性有机质(DOM)激发三线态敏化Gs间接光降解的机理,以3-甲氧基苯乙酮(3-MAP)、亚甲基蓝(MB)、2-萘乙酮(2-AN)和2-苯甲酮(BP)模拟DOM引发三线态光敏化反应,阐明Gs发生间接光降解活性与敏化剂性质、pH值的关系。通过光化学实验结合密度泛函理论计算发现,激发态能量高的BP或3-MAP对Gs的敏化效率低,二者虽可与Gs发生能量或电子转移敏化,但对λ>290 nm的模拟太阳光吸收少,因此激发态产率低;激发态能量低的MB或2-AN对Gs的敏化效率高,且随pH升高而增强,因二者能吸收较多的模拟太阳光,激发态产率高。以MB为例,发现Gs分子形态几乎不能被光敏化降解(pH ≤ 5);Gs由一价阴离子逐渐解离成二、三价阴离子,kin增大102倍(pH 6~12),说明Gs不同解离形态的敏化光降解活性具有显著差异。因Gs阴离子更易发生敏化光降解,因此带正电荷的MB分子比中性分子态的2-AN更易与Gs阴离子结合,表现出更高的敏化能力,相同pH (9或12)条件下,敏化光降解速率相差25~47倍。敏化剂三线态性质及pH值对Gs光敏化降解的影响机理,对于深入认识化学组成复杂的环境DOM的光化学活性具有重要意义。
Abstract:
Genistein (Gs) was frequently detected in the waters, and its environmental behavior raised increasing concerns. To probe photosensitized mechanism of Gs by triplet dissolved organic matters (DOM), here, the correlation between the photodegradation reactivity of Gs with the properties of triplet sensitizers or the pH was investigated, by employing 3-methoxyacetophenone (3-MAP), methylene blue (MB), 2-acetonaphthone (2-AN) and 2-benzophenone (BP) as DOM analogs. According to the photochemical experimental and density functional theory calculation results, BP or 3-MAP showed low photosensitizing ability to Gs, though its high energy allowed the thermodynamically feasible triplet energy or electron transfer reaction with Gs. This was attributed to the weak absorption of the two sensitizers to the simulated sunlight of λ > 290 nm, and thus the inefficient formation of the triplet states. On the contrary, MB or 2-AN, of which the triplet state can only undergo electron transfer with Gs, initiated fast photodegradation of Gs, as both the sensitizers had strong absorption to the simulated sunlight and formed triplet states efficiently. The neutral Gs cannot be photosensitized by the triplet sensitizer taking MB+ as a case (pH ≤ 5), while mono-, di- and tri-valent anionic Gs showed significantly high reactivity in the photosensitization reaction, with the rate increasing 102 times from pH 6 to 12. As the anionic Gs was the species dominated in the photosensitization reaction, the positively charged MB+ exhibited higher photosensitizing ability than the neutral 2-AN, due to closer interaction with the anionic Gs. Thus, the correlation between the photodegradation reactivity of Gs and the properties of triplet sensitizers or the pH was unveiled, and was of significance to the understanding of the complex photosensitizing activity of the real DOM.
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