Sieland Fabian, Schneider Jenny, Bahnemann Detlef W
Institute of Technical Chemistry, Leibniz University Hannover, Callinstr. 5, 30167 Hannover, Germany.
Phys Chem Chem Phys. 2018 Mar 28;20(12):8119-8132. doi: 10.1039/c8cp00398j. Epub 2018 Mar 8.
The effects of the particle size distribution on the charge carrier dynamics and the photocatalytic activity of mixed titanium dioxide (TiO) powder samples were investigated in this work. Instead of the synthesis of the small semiconductor particles, the binary particle size distributions of the powders were obtained by mixing commercially available TiO powders with different particle sizes. The pure anatase samples (average diameters: 7, 20, and 125 nm, respectively) were created via ultrasound treatment and discreet drying. The photocatalytic activity of the powder samples was assessed by the degradation of nitric oxide (NO) and acetaldehyde in the gas phase. Furthermore, the charge carrier kinetics was determined using transient absorption spectroscopy following pulsed laser excitation. Importantly, a recently published model based on fractal dimensions was used to fit the transient signals of the photo generated charge carriers in the TiO powder samples. The effects of the particle size on the acetaldehyde degradation could be explained by the formation of agglomerates, which reduce the available surface area of smaller particles. The fast oxidation of acetaldehyde on the surface of TiO by direct hole transfer was further independent of the observed charge carrier lifetimes on the microsecond time scale. The photocatalytic NO degradation, on the other hand, increased for samples containing larger amounts of small particles. The corresponding photonic efficiencies correlated well with the charge carrier lifetimes determined by the time-resolved studies. Hence, it was concluded that a long charge carrier lifetime generally leads to higher fractional conversions of NO. The employed fractal fit function was proved to be beneficial for the kinetic analysis of charge carrier recombination in TiO, in direct comparison with a second order fit function.
本工作研究了粒径分布对混合二氧化钛（TiO₂）粉末样品中电荷载流子动力学及光催化活性的影响。通过将不同粒径的市售TiO₂粉末混合，得到了粉末的二元粒径分布，而非合成小半导体颗粒。通过超声处理和谨慎干燥制备了纯锐钛矿样品（平均直径分别为7、20和125 nm）。通过气相中一氧化氮（NO）和乙醛的降解来评估粉末样品的光催化活性。此外，在脉冲激光激发后，使用瞬态吸收光谱法测定电荷载流子动力学。重要的是，基于分形维数的最近发表的模型用于拟合TiO₂粉末样品中光生电荷载流子的瞬态信号。粒径对乙醛降解的影响可以通过团聚体的形成来解释，团聚体会减小较小颗粒的可用表面积。乙醛在TiO₂表面通过直接空穴转移的快速氧化进一步与在微秒时间尺度上观察到的电荷载流子寿命无关。另一方面，对于含有大量小颗粒的样品，光催化NO降解增加。相应的光子效率与时间分辨研究确定的电荷载流子寿命密切相关。因此，可以得出结论，长电荷载流子寿命通常会导致NO的更高分数转化率。与二阶拟合函数直接比较，证明所采用的分形拟合函数有利于TiO₂中电荷载流子复合的动力学分析。
