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

在77K.1的可见光照射下，用原位ESR研究了部分还原的二氧化钛和吸附在萘酚上的二氧化钛中顺磁性物种的电子和笔记的产生，并探讨了顺磁性物种的转移过程。对于部分还原的纯锐钛矿和金红石粒子，由于捕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。然而，对于二氧化钛(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，发现在还原的TiO2光激发下，电子从锐钛矿型向金红石型粒子转移。对于在部分还原的纳米二氧化钛上形成的O2^-，可见光照射下O2和表面的Ti^lt；3+&gt；信号增加了2-3倍，而通过将样品退火到R.T.在…中越黑越好。假定Ti^&lt；4+&gt；-O_2^&lt；2-&gt；-Ti^&lt；4+&gt；-O_2^-+Ti^&lt；3+&gt；之间发生了可逆的电子转移反应，根据O_2^-的捕获位置，对光响应进行了动力学分析。在异丙醇悬浮液中吸附了1-萘酚的二氧化钛，在可见光照射下，电子从与异丙醇结合的电荷转移络合物转移到二氧化钛表面，以钛离子的形式被捕获。Ti3+的信号强度反映了光敏化的效率，这在很大程度上取决于被吸附分子的结构和被照射的光子能量。光响应的动力学分析表明，界面电荷转移过程中参与了电子俘获。研究表明，ESR谱可用于评价可见光敏感的二氧化钛的电荷分离效率，为深化对电荷转移过程的理解提供了有趣而重要的结果。较少

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