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.

中文翻译：

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具有可调晶面和尺寸的BiOBr纳米片的合成和光催化活性†

晶体刻面工程是增强光催化剂光活性的最重要方法之一，但到目前为止，它仍然具有挑战性。另外，已经广泛研究了暴露的小平面和微晶尺寸对BiOX（X = Cl，Br或I）纳米片的光活性的影响。然而，对于BiOX纳米片的光活性，仍不清楚在暴露的小平面和微晶尺寸之间的哪一个更重要。在这项工作中，在正丙醇，水和乙酸的混合溶剂中溶剂热合成了一系列具有可调暴露面和微晶尺寸的BiOBr纳米片。只需通过改变正丙醇/水体积比（R _{p / w）}就可以实现裸露面和微晶尺寸的调节。（0/30至30/0）。在正丙醇含量低（R _{p / w} <15/15）时，获得的BiOBr纳米片主要暴露（001）面，而在正丙醇含量高（R _{p / w} > 20/10）时，它们显着暴露（001）。010）。随着R _{p / w的}增加，BiOBr纳米片的横向尺寸和厚度均从1700减小到174 nm，从156减小到17 nm。通过在可见光照射下水杨酸和若丹明B的降解来评估BiOBr纳米片的暴露面和厚度对光催化活性的影响。BiOBr纳米片的暴露面和厚度对于它们的光催化性能都很重要。（001）面比（010）面具有更高的光催化活性。对于具有相同（001）或（010）暴露面的BiOBr纳米片，光催化活性随其厚度的减小而增加。这项研究为调整BiOX的裸露面和微晶尺寸提供了一种新的简便方法，该发现可能为其他光催化剂的晶面工程化提供指导。