Dynamics of photogenerated charges in the phosphate modified TiO2 and the enhanced activity for photoelectrochemical water splitting
Dynamics of photogenerated charges in the phosphate modified TiO2 and the enhanced activity for photoelectrochemical water splitting
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磷酸盐修饰TiO2中光生电荷的动态及其光电化学分解水活性的增强
DOI：
10.1039/c2ee03383f
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发表时间：
2012-04-01
影响因子：
32.5
通讯作者：
Fu, Honggang
中科院分区：
文献类型：
--
作者：
Jing, Liqiang;Zhou, Jia;Fu, Honggang
采用刀刃法制备了磷酸盐修饰的纳米二氧化钛薄膜，然后用单金属正磷酸钠溶液进行后处理。用暂态吸收光谱(TAS)研究了纳米二氧化钛薄膜光生电荷的动态过程。结果表明，在pH为7的无氧水中，未改性纳米二氧化钛薄膜的光生空穴与其光生电子具有相同的动态衰减过程，但磷酸盐改性薄膜的光生空穴动态衰减过程略快于其光生电子的动态衰减过程，且改性后薄膜的光生电荷寿命比未改性薄膜的长得多。这些差异是由磷酸基团(-Ti-O-P-O-−)引起的纳米二氧化钛表面负电荷造成的。有趣的是，光电化学(PEC)实验表明，在中性电解液中，在0V的电压下，适量的磷酸盐修饰可以使纳米二氧化钛薄膜电极的光电流密度提高约2倍。通过对未改性和磷酸盐改性纳米二氧化钛薄膜在不同条件下的TAS和PEC测量表明，光生电荷寿命的延长可以归因于表层形成的负静电场。这也是PEC分解水的活性增加和报告的污染物光催化降解的原因。所提出的机理同样适用于其他氧化物半导体光催化剂以及其他无机阴离子的修饰。
Phosphate modified nanocrystalline TiO2 (nc-TiO2) films were prepared by a doctor blade method, followed by post-treatment with monometallic sodium orthophosphate solution. The dynamic processes of the photogenerated charges from the resulting nc-TiO2 films were thoroughly investigated by means of transient absorption spectroscopy (TAS). It is shown that photogenerated holes in the un-modified TiO2 film exhibit the same dynamic decay process as its photogenerated electrons, in oxygen-free water of pH 7. However, photogenerated holes in the phosphate modified film display a slightly faster dynamic decay process than its photogenerated electrons, and photogenerated charges of the modified film have a much longer lifetime than those of the un-modified film. These differences are attributed to the surface-carried negative charges of nc-TiO2 resulting from the phosphate groups (–Ti–O–P–O−). Interestingly, the photoelectrochemical (PEC) experiments show that modification with an appropriate amount of phosphate could improve the photocurrent density of the nc-TiO2 film electrode by about 2 times, at a voltage of 0 V in the neutral electrolyte. Based on the TAS and PEC measurements of un-modified and phosphate modified nc-TiO2 films, with different conditions, it is suggested that the prolonged lifetime of photogenerated charges can be attributed to the negative electrostatic field formed in the surface layers. It is also responsible for the increase in activity for PEC water splitting and for the reported photocatalytic degradation of pollutants. The suggested mechanism would be applicable to other oxide semiconductor photocatalysts and to modification with other inorganic anions.