叶绿素敏化二氧化钛纳米管电极光电性能及其增强机理

为了研究叶绿素的敏化机理,本文以菠菜叶片叶绿素的乙醇浸提液敏化纳米管TiO_2电极,在Na2SO4水溶液电解液中测定其光电性能。敏化电极的光电流响应曲线显示,叶绿素浸提液敏化纳米管TiO_2电极时会显著改变电极的光电流值,而敏化Ti电极时则产生光电流极小。电极的循环伏安曲线则表明,叶绿素浸提液使电极上的氧化反应更容易发生。测定不同浓度的叶绿素浸提液敏化纳米管TiO_2电极的单色光光电转化效率(IPCE)图谱,结果表明,合适的叶绿素浓度(7.123~71.23μg/L)使电极IPCE平均增加2倍以上,但浓度增大至7123μg/L时,其敏化电极IPCE则明显降低;同时发现叶绿素的敏化作用未明显改变TiO_2电极IPCE图谱的特征谱峰位置。根据实验数据和结果,得出在水溶液中叶绿素改变纳米管TiO_2光电性能的机理,主要是通过叶绿素分子与TiO_2电极中的光生空穴发生反应,进而减少光生电子与空穴的复合,使电极有效光生电子数量增加,光电流密度增大,最终提高TiO_2电极的IPCE。

Photoelectric Activity and Enhancing Mechanism of TiO2 Electrodes Coated with Nature Plant Pigments

In order to study the sensitization mechanism of chlorophyll, ethanol extract of spinach chlorophyll served as sensitizers of TiO₂ nanotubes electrodes, and the aqueous solution of Na₂SO₄ was used as electrolyte to measure the photocurrent activity of the as-obtained electrodes. Photocurrent response results show that the TiO₂ nanotubes electrode changes its photocurrent value after sensitizing, while the pristine Ti electrode has weak photocurrent response. Cyclic voltammetry curves indicate that the oxidation of sensitized TiO₂ electrodes is more reactive than unsensitized ones. The incident photocurrent conversion efficiency(IPCE) of TiO₂ electrodes sensitized by extracts from different chlorophyll concentrations was tested. The result shows that, at optimized concentration(7.123~71.23 μg/L), sensitizers can increase the IPCE value of electrodes over 2 times than that before sensitizing, while at high concentration(7123 μg/L), the IPCE value decreases obviously. It is found that the characteristic peak positions of the IPCE spectra change very little between sensitized and unsensitized electrodes. The absorption spectrum of spinach pigment and the sensitization efficiency(SE_λ) spectra reveal the mechanism of the enhancement of photoelectric activity as chlorophyll molecules react with photo-generated hole of TiO₂ and reduce the rate of electron-hole recombination, resulting in an increased IPCE value of TiO₂ nanotube electrodes.