School of Chemistry and Biochemistry, Thapar University, Patiala, 147-004, Punjab, India.
Environ Sci Pollut Res Int. 2013 Jun;20(6):3956-64. doi: 10.1007/s11356-012-1313-2. Epub 2012 Nov 28.
This study demonstrates the influences of position, number of nitrogen (N) atoms and -C-N- or -N=N- linkage present in the six membered heterocyclic compounds such as pyridine, pyrazine, and pyridazine on their photocatalytic degradation by Au, Ag, and Fe(+2) deposited TiO(2) photocatalyst. The photodegradation rate of these heterocyclic compounds follow the order pyridine > pyrazine > pyridazine due to the different extent of hydroxylation and difference in position and number of N atoms in the aromatic moiety. The Au photodeposition significantly improved the TiO(2) photoactivity as compared to Ag and Fe(+2) loading. The presence of two N atoms in pyrazine and pyridazine as compared to one N atom in pyridine hamper the nucleophilc attack of OH radicals in comparison to easy hydroxylation of pyridine ring. There is 1 N atom, 4C-C, 1C-N and 1C=N bond in pyridine, 2 N atoms in the 1 and 4 positions, 2C-C, 2C-N bonds and 2C=N bonds in pyrazine, and pyridazine ring contains 2 N atoms in the 1 and 2 positions, 3C-C, 1N-N bond and 2C=N bonds. The bond strength/energy decreases gradually as: C=N- (615 KJ/mol) > -N=N- (418 KJ/mol) > -C-C- (347 KJ/mol) > -C-N- (305 KJ/mol) > -N-N- (163 KJ/mol). As pyridine has 1C-N, 1C=N, and no N-N bond, it photodegrades easily as compared to 1 N-N and 2C=N bonds of pyridazine of lowest photodecomposition rate. The improved photoactivity of Au-TiO(2) is explained on the basis of its favorable redox potential, work function, and electron-capturing capacity, etc.
本研究表明,在六元杂环化合物如吡啶、吡嗪和哒嗪中,氮(N)原子的位置、数量以及 -C-N- 或 -N=N- 键的存在对金、银和 Fe(+2)沉积 TiO(2)光催化剂的光催化降解有影响。由于芳香部分中 N 原子的位置和数量不同,以及程度不同的羟基化作用,这些杂环化合物的光降解速率顺序为吡啶 > 吡嗪 > 哒嗪。与负载 Ag 和 Fe(+2)相比,Au 光沉积显著提高了 TiO(2)的光活性。与吡啶环的易羟基化作用相比,吡嗪和哒嗪中存在两个 N 原子,而吡啶中存在一个 N 原子,这阻碍了 OH 自由基的亲核攻击。吡啶环中存在 1 个 N 原子、4 个 C-C、1 个 C-N 和 1 个 C=N 键,1 位和 4 位有 2 个 N 原子,2 个 C-C、2 个 C-N 键和 2 个 C=N 键,哒嗪环中 1 位和 2 位有 2 个 N 原子,3 个 C-C、1 个 N-N 键和 2 个 C=N 键。键强度/能量逐渐降低:C=N-(615 KJ/mol)> -N=N-(418 KJ/mol)> -C-C-(347 KJ/mol)> -C-N-(305 KJ/mol)> -N-N-(163 KJ/mol)。由于吡啶具有 1C-N、1C=N 和没有 N-N 键,因此与光降解率最低的哒嗪中的 1 个 N-N 和 2 个 C=N 键相比,它容易光降解。Au-TiO(2)的光活性提高是基于其有利的氧化还原电位、功函数和电子俘获能力等。