Bismuth oxyiodide-oxychloride mixed phase nanocomposites: synthesis, adsorption capacity, and photocatalytic activity under visible light

The synthesis of bismuth oxyiodide-oxychloride mixed phase (BiO-I_xCl_y) nanocomposites is reported. Their adsorption capacity and photocatalytic activity were evaluated in the removal of RhB dye from water under visible light illumination as a model system. The microstructure and optical properties of the obtained materials were studied in detail using several characterization techniques. It was found that the phase composition and resulting morphology depend on the nominal I:Cl molar ratio. The adsorption capacity/photocatalytic activity of the BiO-I_xCl_y nanocomposites tends to increase with the iodide/chloride content. Adsorption efficiencies as large as 80.0% were achieved for those nanocomposites with significant Bi₅O₇I content; however, their photocatalytic activity is moderate (>70%). The nanocomposite with intermediate chloride content showed the highest photocatalytic efficiency (89.3%). It is ascribed to a large active phase (Bi₃O₄Cl) content and the formation of in-built electric fields at Bi₅O₇I-Bi₃O₄Cl heterojunctions. The synergy of photocatalytic activity and moderate adsorption capacity allows Bi₅O₇I-Bi₃O₄Cl nanocomposites to achieve a total removal efficiency as high as 96.4%. Possible physicochemical mechanisms are proposed.