Ultrathin BiOX (X = Cl, Br, I) Nanosheets with Exposed {001} Facets for Photocatalysis

As a family of semiconductor photocatalysts, Sillén-type bismuth oxyhalides (BiOX, X = Cl, Br, I) have attracted widespread interest due to their excellent photocatalytic activity and photoconductivity. However, most current strategies on synthesizing ultrathin 2D BiOX nanosheets (NSs) rely on high temperature and pressure and complex procedures, which seriously confine their large-scale applications. Herein, we develop a simple and facile two-phase method for the synthesis of ultrathin 2D BiOX NSs with highly exposed {001} facets. On the basis of systematically studying the effects of various reaction parameters on the size, thickness, morphology, and composition of the products, the growth mechanism of ultrathin 2D BiOX NSs is presented, which indicates that the suppression of Bi3+ hydrolysis is required for the growth of 2D BiOX NSs with highly exposed {001} facets. The acidic condition prefers the growth of BiOX NSs with ultrathin structure and high crystallinity along the [001] zone axis. By using BiOBr NSs as the example, the photocatalytic activities of ultrathin 2D BiOX NSs are evaluated upon photodegradation of organic compounds and photocatalytic water oxidation. The results show that the organic compound photodegradation is mainly determined by the specific surface area of BiOBr NSs, while the O2 evolution rate of BiOBr NSs for water oxidation is dependent on their photogenerated charge separation efficiency. Because of the larger specific surface area and higher photogenerated charge separation efficiency, BiOBr-acid-0.5 ultrathin 2D NSs exhibits the fastest organic compound photodegradation rate and O2 evolution rate of 445.6 μmol g–1 h–1.