Synthesis and photocatalytic activity of BiOBr nanosheets with tunable crystal facets and sizes

Abstract

Crystal facet engineering is one of the most important ways to enhance the photoactivity of photocatalysts, but it remains challenging so far. In addition, the effects of exposed facets and crystallite sizes on the photoactivity of BiOX (X = Cl, Br, or I) nanosheets have been widely investigated. However, it is still unclear which one between the exposed facets and the crystallite sizes is more important for the photoactivity of the BiOX nanosheets. In this work, a series of BiOBr nanosheets with tunable exposed facets and crystallite sizes were solvothermally synthesized in a mixed solvent of n-propanol, water, and acetic acid. The regulation of the exposed facets and crystallite sizes was achieved simply by changing the n-propanol/water volume ratios (R_p/w, 0/30 to 30/0) of the mixed solvent. At low n-propanol contents (R_p/w < 15/15), the obtained BiOBr nanosheets expose dominantly (001) facets, while at high n-propanol contents (R_p/w > 20/10), they expose dominantly (010) facets. With increasing R_p/w, the lateral size and thickness of the BiOBr nanosheets all decrease, from 1700 to 174 nm and from 156 to 17 nm, respectively. The effects of exposed facets and thicknesses of BiOBr nanosheets on the photocatalytic activity, evaluated by degradation of salicylic acid and rhodamine B under visible-light irradiation, were investigated. The exposed facet and thickness of BiOBr nanosheets are both important for their photocatalytic performance. The (001) facets exhibit a higher photocatalytic activity than the (010) facets. For the BiOBr nanosheets with the same (001) or (010) exposed facets, the photocatalytic activity increases with a decrease in their thickness. This study provides a new facile way to adjust the exposed facets and crystallite sizes of BiOX, and the findings may provide guidance for crystal facet engineering of other photocatalysts.