Characterization of Charge Separation in Visible Light-Sensitive TiO_2 by In-Situ ESR Spectroscopy

在77 K下，利用ESR原位研究了部分还原TiO_2和萘酚吸附TiO_2在可见光照射下产生的顺磁性捕获电子和电子注，并探讨了它们在可见光照射下的转移过程。对于部分还原的纯金红石和金红石颗粒，由于Ti^<3+>（俘获电子）而产生的宽单重态ESR谱在可见光照射下强度降低，然后在黑暗中恢复到初始强度。而对于TiO_2（P25）颗粒，信号恢复到原来的2.5-3倍。通过对谱线形状的分析，发现在还原态TiO_2（P25）中，电子是通过光激发从金红石颗粒转移到金红石颗粒上的.对于在部分还原的TiO_2纳米颗粒上形成的O_2 ~+，在可见光照射下，O_2和表面Ti^<3+>信号增加了2-3倍，而在室温退火后，O_2和表面Ti^<3+>信号降低到初始值。在 ...更多信息 黑暗假设Ti^&lt;4+&gt;-O_2^<2->-Ti^&lt;4+&gt;和Ti^&lt;4+&gt;-O_2^- + Ti^&lt;3+&gt;之间存在可逆的电子转移反应，并根据O_2^-的捕获位置对光响应进行了动力学分析.在可见光照射下，1-萘酚吸附的TiO_2在异丙醇悬浮液中，电子从与表面结合的萘酚电荷转移络合物转移到TiO_2表面，被捕获为内层Ti^&lt;3+&gt;。Ti^&lt;3+&gt;的信号强度反映了光敏化的效率，而光敏化的效率与吸附分子的结构和照射的光子能量密切相关。光响应动力学分析表明，界面电荷转移过程涉及表面Ti^&lt;3+&gt;的电子俘获，ESR谱可用于评价可见光敏感TiO_2的电荷分离效率，为深入理解电荷转移过程提供了有趣而重要的结果。少

In-situ ESR studies were curried out to characterize paramagnetic species as the trapped electrons and notes generated and explore their transfer processes under visible light illumination in partially reduced TiO_2 and naphthol-adsorbed TiO_2 at 77 K.1. For the partially reduced pure anatase and rutile particles, a broad singlet ESR spectra due to Ti^<3+> (trapped electron) decreased in intensity upon visible light illumination, and then restored to the initial intensity in the dark. For the TiO_2 (P25) particles, however, the signal restored up to 2.5-3 times greater than before. Through the analysis of the spectral line shape, it was found that the electrons are transferred from the anatase to the rutile particles by photoexcitation in reduced TiO_2(P25).2. For O_2^- formed on partially reduced TiO_2 nanoparticles, the O2 and the surface Ti^<3+> signals were increased by 2-3 times upon illumination with visible light and reduced to the initial one by annealing the sample to r.t. in … More the dark. Assuming a reversible electron transfer reaction between Ti^<4+>-O_2^<2->-Ti^<4+> and Ti^<4+>-O_2^- + Ti^<3+>, the photoresponse was kinetically analyzed in terms of the trapping site of the O_2^- species.3. For 1-naphthol-adsorbed TiO_2 in 2-propanol suspension, electrons were transferred from the charge-transfer complex of the naphthol bound to the TiO_2 surface to be trapped as inner Ti^<3+> under visible light illumination. The signal intensity of Ti^<3+> reflected the efficiency of the photosensitization, which depended significantly on the structure of adsorbed molecules and photon energies illuminated. The kinetic analysis of the photoresponse suggested that electron trapping as surface Ti^<3+> is involved in the interfacial charge transfer process.The study demonstrated that ESR spectroscopy is useful in evaluating the charge-separation efficiency in visible light-sensitive TiO_2 and presented interesting and fundamentally important results for deepening understandings of the charge transfer processes. Less