Engineering composition-tunable 3D hierarchical bismuth oxyiodides heterojunctions: Ionic liquid-assisted fabrication with strong adsorption ability and enhanced photocatalytic properties

In this work, we report the fabrication of composition-tunable heterostructured bismuth oxyiodides photo catalysts using a facile ionic liquid-assisted precipitation method at room temperature. Through elaborately governing the reaction parameters, two groups of bismuth oxyiodide hybrids (Group 1: BiOI/Bi4O5I2, and Group 2: Bi4O5I2/Bi5O7I) with different components were prepared. The DRS spectra shows that the absorption edges of the hybrids were gradually tuned from 550 to 660 nm, which was in accordance with the color gradient from light yellow (Bi5O7I) to brick red (BiOI), The SEM images show that the products mainly exhibited 3D hierarchical architecture, which was beneficial for the adsorption of contaminants over the catalyst's surface. The two groups of heterojunction photocatalysts all exhibited remarkably improved photocatalytic activity in decomposing o-phenylphenol (OPP) and 4-tert-butylphenol (PTBP) under visible light irradiation respect to single phase photocatalyst (BiOI, Bi4O5I2, or Bi5O7I). For BiOI/Bi4O5I2 hybrids, the 55 sample exhibited the optimal activity, which was approximately 5.35 and 1.85 times higher than that of pristine BiOI and Bi4O5I2, respectively. For the second group of Bi4O5I2/Bi5O7I, the optimal activity was observed for 59 hybrid, which was approximately 2.43 and 2.12 times higher than that of bare Bi4O5I2 and Bi5O7I under identical conditions. This activity enhancement should be attributed to the balanced band levels of the components, which facilitates the fast interfacial charge transmigration of photo-generated carriers, resulting in highly promoted charge separation efficiency. This deduction was proved by the photocurrent, electrochemical impedance spectroscopy, and photoluminescence measurements. The possible degradation mechanisms for BiOI/Bi4O5I2 and Bi4O5I2/Bi5O7I hybrids were proposed based on the band potentials and trapping experiment results.