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.