科研之友
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摘要
Investigation of charge carrier recombination dynamics is central to understanding and further enhancing the photocatalytic activity of water splitting and other photochemical reactions catalyzed by TiO2. In this study, we carried out nonadiabatic molecular dynamics calculations combined with real-time time-dependent density functional theory to investigate the effects of size and shape on charge recombination in TiO2 nanoparticles (NPs). Using the Wulff construction method, we considered both octahedral (10, 35, and 84 TiO2 units) and cuboctahedral (29, 78, and 97 TiO2 units) nanoclusters with size varying from 1 to 3 nm. Generally, the recombination rates decreased with increasing NP size. We rationalized the trend in terms of average transition energy, exciton binding energy (Delta E-ex), nonadiabatic coupling (NAC), and pure-dephasing time. The relaxation times increased with increasing NP size, as the NAC and Delta E-ex decreased. The cuboctahedral clusters showed smaller Delta E-ex compared to the octahedral clusters. For the octahedral clusters, the smaller NAC and shorter dephasing time contributed to longer relaxation, despite smaller transition energy, as the size increased. However, the influence of the NAC, transition energy, and dephasing time were intertwined for the cuboctahedral clusters. The smaller NAC of the 97-unit cluster rationalized its longer relaxation time compared to the 29-unit cluster, but the presence of a singly coordinated oxygen atom greatly reduced the transition energy, thus leading to a shorter relaxation time compared to the 78-unit cluster. Our results provide a detailed understanding on the effects of size and shape on the charge carrier dynamics in TiO2 nanoclusters, separating these effects from other factors, such as presence of defects, dopants, and adsorbates that are hard to control precisely in experiments.
- 出版日期2018-3-8
