pH-dependent synthesis of iodine-deficient bismuth oxyiodide microstructures: Visible-light photocatalytic activity

Bismuth oxyiodides have exhibited high potential for applications in visible-light photocatalytic environmental remediation and solar energy conversion. In this work, a series of iodine-deficient bismuth oxyiodides (Bi₄O₅I₂, Bi₇O₉I₃, Bi₅O₇I) can be simply prepared through a pH-dependent aqueous procedure with feeding Bi/I ratio of 2:1. The compositions of the Bi-based oxyiodides are closely related to acid-base circumstances, with Bi₄O₅I₂ formed in weakly acidic medium (pH = 5) and Bi₇O₉I₃, Bi₅O₇I in basic medium (pH = 8 and 11). Morphology differences of nanosheet-assembled Bi₄O₅I₂, Bi₇O₉I₃ architectures and rod-like Bi₅O₇I microstructures demonstrate different crystalline characters and construction of Bi-based oxyiodide crystals. UV-vis DRS results revealed good visible-light absorptions of Bi₄O₅I₂ and Bi₇O₉I₃ architectures and appropriate band structures for photocatalytic reactions, on comparison to Bi₅O₇I microrods. Low electrochemical impedance of Bi₇O₉I₃ microflowers with sheet-like units further facilitated the separation of e^--h⁺ carriers in the degradation process. Accordingly, among the bismuth oxyiodide samples, Bi₇O₉I₃ displayed prominent visible-light degradation performance for colorless bisphenol-A (BPA) due to the direct photoexcitation process.