title: A stochastic study of electron transfer kinetics in nano-particulate photocatalysis: a comparison of the quasi-equilibrium approximation with a random walking model.
abstract: In the photocatalysis of porous nano-crystalline materials, the transfer of electrons to O2plays an important role, which includes the electron transport to photocatalytic active centers and successive interfacial transfer to O2. The slowest of them will determine the overall speed of electron transfer in the photocatalysis reaction. Considering the photocatalysis of porous nano-crystalline TiO2as an example, although some experimental results have shown that the electron kinetics are limited by the interfacial transfer, we still lack the depth of understanding the microscopic mechanism from a theoretical viewpoint. In the present research, a stochastic quasi-equilibrium (QE) theoretical model and a stochastic random walking (RW) model were established to discuss the electron transport and electron interfacial transfer by taking the electron multi-trapping transport and electron interfacial transfer from the photocatalytic active centers to O2into consideration. By carefully investigating the effect of the electron Fermi level (EF) and the photocatalytic center number on electron transport, we showed that the time taken for an electron to transport to a photocatalytic center predicated by the stochastic RW model was much lower than that predicted by the stochastic QE model, indicating that the electrons cannot reach a QE state during their transport to photocatalytic centers. The stochastic QE model predicted that the electron kinetics of a real photocatalysis for porous nano-crystalline TiO2should be limited by electron transport, whereas the stochastic RW model showed that the electron kinetics of a real photocatalysis can be limited by the interfacial transfer. Our simulation results show that the stochastic RW model was more in line with the real electron kinetics that have been observed in experiments, therefore it is concluded that the photoinduced electrons cannot reach a QE state before transferring to O2.
authors.affiliation: State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan City, Hubei Province 430070, People's Republic of China. liubaoshun@126.com.
authors.forename: Baoshun
authors.initials: B
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan City, Hubei Province 430070, People's Republic of China. liubaoshun@126.com.
authors.forename: Xiujian
authors.identifier: http://orcid.org/0000-0002-2517-2605
authors.initials: X
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, People's Republic of China.
authors.forename: Jiaguo
authors.initials: J
authors.lastname: Yu
authors.affiliation: Research Institute for Science and Technology, Photocatalysis International Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Fujishima
authors.affiliation: Research Institute for Science and Technology, Photocatalysis International Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan and Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Nakata