Ultrahigh Charge Separation Achieved by Selective Growth of Bi4O5I2 Nanoplates on Electron-Accumulating Facets of Bi5O7I Nanobelts.

Ultrahigh charge separation was observed in Bi4O5I2/Bi5O7I two-dimensional (2D)/one-dimensional (1D) hierarchical structures (HSs) constructed by selective growth of 2D monocrystalline Bi4O5I2 nanoplates on the electron-accumulating (100) facet of 1D monocrystalline Bi5O7I nanobelts. In addition to the presence of type-II heterojunction between Bi4O5I2 and Bi5O7I elementary entities in 2D/1D HSs, the type-II (100)/(001) surface heterojunction in Bi5O7I nanobelt substrates was also confirmed by means of density functional theory (DFT) calculations and selective photoreduction/oxidation deposition experiments. The synergistic effect of two kinds of heterojunctions in Bi4O5I2/Bi5O7I 2D/1D HSs endowed them with ultrahigh charge carrier separation and transfer characteristics. In contrast with the control sample (BB40-C) constructed by growing Bi4O5I2 nanoplates on whole four sides of Bi5O7I nanobelts, Bi4O5I2/Bi5O7I 2D/1D HSs demonstrated significantly enhanced charge transfer between Bi5O7I nanobelt substrates and Bi4O5I2 nanoplates, owing to respective electron and hole accumulations on (100) and (001) facets of Bi5O7I substrates caused by (100)/(001) surface heterojunction. The enhanced separation behavior was successfully verified by steady/transient-state photoluminescence, electrochemical techniques, and photocatalytic degradation experiments. Based on the above effective charge separation of Bi4O5I2/Bi5O7I 2D/1D HSs as well as the routine advantages for 2D/1D HSs, such as the excellent charge transport in monocrystalline elementary entities, much higher specific surface area, and enhanced light absorption by multiple reflections, the optimal BB40 HSs demonstrated ultrahigh photocatalytic performance than the control samples, whose apparent rates for Rhodamine B [or tetracycline hydrochloride (TC)] degradation were 7.1 (2.9 for TC), 10.3 (4.7 for TC), and 2.2 (1.7 for TC) times those of pristine Bi5O7I nanobelts, Bi4O5I2 nanoplates, and BB40-C, respectively. It is hoped that this crystal facet selection during the heterostructure construction in this work could provide a new strategy or some enlightenment for the exploration of highly active 2D/1D HSs or other-dimensional heterostructure nanomaterials applied in the fields of photocatalysts, solar cells, sensors, and others.