偶氮类化合物在纳米TiO_2表面光降解的UV-Vis光谱示踪研究(Ⅰ)——中间体的发现及动力学行为

UV\|Vis Adsorption Spectra Tracing on Photodegradation of Azo Compounds on the Surface of Titanium Dioxide(Ⅰ) The Discovery and Kinetic Behaviors Researching of Intermadiates

用ＵＶ－Ｖｉｓ吸收光谱和差谱考察了以ＤＢＣ－偶氮羧为主的５ 种偶氮化合物在纳米ＴｉＯ２ 表面光降解的动力学行为和电子转移历程， 载荷子的捕获经历一个中间过程， 最终矿化为无机物． 按误差补偿理论拟合的中间体峰形曲线和实验ｃ～ｔ图平行吻合， 获得了相应的动力学参数．

The kinetics and electron transfer of the photo degradation procedure of five azo compounds, mainly DBC carboxyazo, on the surface of titanium dioxide were studied by using UV\|Vis absorption and differential spectra. An intermediate with rather long life( t 1/2 =8 86 min) formed and then destructed during the procedure of the capture of the photo induced charge carrier. The theoretically fit peak shape curve of the intermediate with error compensated algorithm parallel accorded with the experimental c^t curve. Thus we have got the rate constants of DBC carboxyazo and TBC CPA at 25 ℃, being 0 170( k 1/min -1 ) and 2 96×10 -2 ( k 2/min -1 ) as well as 0 104( k 1/min -1 ) and 9 56×10 -2 ( k 2/min -1 ), respectively. The effect of the initial pH value on the photo degradation rate was tested. pH 3—7 was found to be the optimal pH range for the photo degradation. In addition, the reaction solution without being buffered was found to tend to be weak acidic. The sensitization mechanism of TiO 2 by azo was discussed. That is, electrons transferred from the excited azo to the conductive band of semiconductor TiO 2, which made the bandgap energy match the energy of visible light. The degradation course was presumed as that, after the electron injection and the self oxidaiton of azo, the intermediate naphthoquinone was oxidized by O ·- 2 to produce phthalic acid, followed by the final mineralization of the phthalic acid to yield CO 2, H 2O and other inorganic compounds.