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

通过原位ESR研究，对部分还原TiO_2和naphthore -吸附TiO_2在77 K.1的可见光照射下产生的捕获电子和注释进行了表征，并探索了它们的转移过程。对于部分还原的纯锐钛矿和金红石颗粒，由于Ti^<3+>（捕获电子）的作用，宽单线态ESR光谱在可见光照射下强度下降，然后在黑暗中恢复到初始强度。然而，对于TiO_2 （P25）颗粒，信号恢复到以前的2.5-3倍。通过谱线形状分析，发现在还原TiO_2（P25）中，电子通过光激发从锐钛矿转移到金红石颗粒上。对于在部分还原TiO_2纳米颗粒上形成的O_2^-，在可见光照射下O2和表面Ti^<3+>信号增加了2-3倍，在黑暗中退火至室温后，O2和表面Ti^<3+>信号降低到初始水平。假设Ti^<4+>-O_2^<2->-Ti^<4+>和Ti^<4+>-O_2^- + Ti^<3+>之间存在可逆电子转移反应，从O_2^-的俘获位置出发，对其光响应进行动力学分析。对于2-丙醇悬浮液中1-萘酚吸附的TiO_2，在可见光照射下，电子从萘酚的电荷转移配合物转移到TiO_2表面，并以Ti^<3+>的形式被捕获。Ti^<3+>的信号强度反映了光敏化的效率，这主要取决于被吸附分子的结构和照射的光子能量。光响应的动力学分析表明，表面Ti^<3+>的电子捕获参与了界面电荷转移过程。该研究表明，ESR光谱可用于评价可见光敏感TiO_2的电荷分离效率，并为加深对电荷转移过程的理解提供了有趣且具有根本意义的结果。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