Theoretical and experimental study of charge transfer processes in photocatalysis on anatase-TiO2

我们对光催化的基本认识相当有限，因为假设的反应途径大多缺乏直接证实。例如，通常不知道分子在接受光激发载体后是被吸附还是被解吸。除了光催化之外，固气之间的电荷转移也具有重要的意义，但缺乏适当的理论和实验技术来研究它。本提案旨在发展这些方法，并将其应用于具有实际意义的案例研究。理论通常应用周期模型，由于人为重复电荷之间的相互作用，需要修正。气固界面的电荷校正仍然是一个挑战，因为电荷可以位于任一相。到目前为止，解决方案要么是对电荷的位置进行假设，要么是不自洽的。我们建议在不同复杂程度下，为带电1D、2D和3D系统中的超级单体计算开发一种通用且自一致的校正方案，并将其实现到标准电子结构包（VASP）中。考虑到问题的复杂性，简单的收敛性检验是不够的。由于我们不知道任何理论方法，其中避免电荷校正问题不是在权衡大小收敛问题，唯一可接受的测试是实验。隔离表面上的反应可以通过原子力显微镜（AFM）进行原子分辨。然而，表面物种电荷强度变化的分配主要是推测性的，因为它不能直接观察到。我们将开发一种基于电荷敏感开尔文探针力显微镜（KPFM）的方法，结合原子尺度上的非接触原子力显微镜，用于明确识别表面物质的电荷状态。TiO2可能是最著名的光催化剂，但在绝大多数情况下，金红石被使用，而锐钛矿形式在光催化方面被认为是优越的。因此，这里开发的理论和实验工具将在锐钛矿- tio2上进行测试，根据我们的初步理论结果，锐钛矿- tio2表现出与金红石不同的化学途径。在用原子力显微镜对锐钛矿表面进行原子尺度的表征以及原子尺度KPFM的必要方法发展之后，我们将集中研究CO和NO转化为不危害健康和环境的化合物。在这些情况下，跨界面的电荷传输起着特别重要的作用。

Our basic understanding of photocatalysis is quite limited, because the assumed reaction pathways mostly lack direct confirmation. E.g., it is often not known, whether a molecule gets adsorbed or desorbed after receiving the photo-excited carrier. Charge transfer between the solid and the gas phase is of great importance also beyond photocatalysis, however, appropriate theoretical and experimental techniques to study it are lacking. This proposal aims to develop such methods and to apply them in case studies of practical significance. Theory often applies periodic models which require corrections because of the interaction between artificially repeated charges. Charge correction at a gas/solid interfaces, where the charge can be located in either phase, remain a challenge. Solutions so far are either making assumptions on the location of the charge, or are not self-consistent. We propose here to develop a general and self-consistent correction scheme, at various levels of complexity, for supercell calculations in charged 1D, 2D and 3D systems, and implement it into a standard electronic structure package (VASP). Considering the complexity of the problem, simple convergence tests are insufficient. Since we are not aware of any theoretical method where the avoidance of the charge correction problem is not in a trade-off for size-convergence problems, the only acceptable test is experiment.Reactions on isolating surfaces can be followed by atomic resolution using atomic force microscopy (AFM). The assignment of intensity changes to the charging of surface species is, however, mostly speculative, because it cannot be observed directly. We will develop a method based on the charge sensitive Kelvin-probe force microscopy (KPFM), in conjunction with non-contact atomic force microscopy on the atomic scale, for unambiguous identification of the charge state of surface species. TiO2 is probably the best know photocatalyst but, in the overwhelming majority of the cases, rutile was used, while the anatase form is known to be superior in photocatalysis. Therefore, the theoretical and experimental tools, developed here, will be tested on anatase-TiO2, which, according to our preliminary theoretical results, shows chemical pathways different form rutile. After an atomic scale characterization of the anatase surface by AFM, and the necessary method developments in atomic scale KPFM, we will concentrate on the transformation of CO and NO into compounds without health and environmental hazards. In these cases, charge transport across the interface plays a particularly important role.