Graduate School of Engineering Science and Technology, National Yunlin University of Science and Technology (YunTech), Douliou, Yunlin, Taiwan.
Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology (YunTech), Douliou, Yunlin, Taiwan.
J Hazard Mater. 2014 Jun 15;274:420-7. doi: 10.1016/j.jhazmat.2014.04.042. Epub 2014 Apr 26.
When hexavalent chromium (Cr(VI)) is added to a TiO2 photocatalytic reaction, the decolorization and mineralization efficiencies of azo dyes Acid Orange 7 (AO7) are enhanced even though the mechanism is unclear. This study used 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the scavenger and the analysis of Electron Spin Resonance (ESR) to investigate this enhancement effect by observing the hydroxyl radical (OH) generation of the Cr(VI)/TiO2 system under UV and visible light (Vis) irradiation. With Cr(VI), the decolorization efficiencies were approximately 95% and 62% under UV and Vis, and those efficiencies were 25% less in the absence of Cr(VI). The phenomena of the DMPO-OH signals during the ESR analysis under Vis 405 and 550 nm irradiation were obviously the enhancement effects of Cr(VI) in aerobic conditions. In anoxic conditions, the catalytic effects of Cr(VI) could not be achieved due to the lack of a redox reaction between Cr(VI) and the adsorbed oxygen at the oxygen vacancy sites on the TiO2 surfaces. The results suggest that by introducing the agents of redox reactions such as chromate ions, we could lower the photoenergy of TiO2 needed and allow Vis irradiation to activate photocatalysis.
当六价铬（Cr(VI)）被添加到 TiO2 光催化反应中时，偶氮染料酸性橙 7（AO7）的脱色和矿化效率得到了提高，尽管其机制尚不清楚。本研究使用 5,5-二甲基-l-吡咯啉-N-氧化物（DMPO）作为清除剂，并通过分析电子自旋共振（ESR），在 UV 和可见光（Vis）照射下观察 Cr(VI)/TiO2 体系中羟基自由基（OH）的生成，来研究这种增强效应。在 Cr(VI)存在的情况下，在 UV 和 Vis 下的脱色效率分别约为 95%和 62%，而在没有 Cr(VI)的情况下，效率降低了 25%。在 Vis 405 和 550nm 照射下的 ESR 分析中，DMPO-OH 信号的现象显然是 Cr(VI)在有氧条件下的增强效应。在缺氧条件下，由于 Cr(VI)和 TiO2 表面氧空位吸附氧之间缺乏氧化还原反应，Cr(VI)的催化作用无法实现。结果表明，通过引入氧化还原反应的试剂，如铬酸盐离子，可以降低 TiO2 所需的光能，并允许 Vis 光激发光催化。
