Enhanced visible light photocatalytic activity of bismuth oxybromide lamellas with decreasing lamella thicknesses

BiOBr lamellas were synthesized at different reaction pH values via a hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy and N-2 sorption measurements were used to characterize the BiOBr samples. BiOBr samples have the same lamella structures and band gaps but different lamella sizes and thicknesses. Adjusting the pH of the reaction system tunes the BiOBr lamella thickness from 42 to 21 nm. The photodegradation efficiencies of the BiOBr lamellas for rhodamine B (RhB) and methylene blue (MB) in aqueous solution were examined. The degradation efficiency for RhB is much higher than that for MB. The decrease in BiOBr lamella thickness significantly enhances the photocatalytic activity for dye degradation, despite the decrease in exposed photoactive (001) facet percentage. Decreasing the lamella thickness from 42 to 21 nm yields a more than fourfold enhancement in photodegradation efficiency of BiOBr samples for RhB. The most important factor influencing the photocatalytic activity of the BiOBr samples is their lamella thickness, rather than the exposed (001) facet percentage. Thus, even for flaky semiconductors with high exposed photoactive facet contents, the influence of lamella thickness on photocatalytic activity should be preferentially considered.