AgBr Nanocrystals from Plates to Cubes and Their Photocatalytic Properties



AgBr nanocrystals, evolving from plates through truncated cubes and finally to regular cubes, corresponding to a progressive shrinkage of exposed {1 1 1} facets and enlargement of exposed {1 0 0} facets, were successfully prepared by facile ion-exchange reactions under the synergistic effects of polyvinylpyrrolidone and NH3 H2O. An investigation of the growth mechanism revealed that polyvinylpyrrolidone can selectively adsorb on the {1 1 1} facets of AgBr nanocrystals, whereas NH3H2O not only forms a [Ag(NH3)2]+ complex that slows the rates of ion-exchange reactions, but may also prefer to adsorb on {1 0 0} facets. Studies of their photocatalytic properties showed that the as-prepared AgBr nanocrystals exhibited facet-dependent photocatalytic properties. The {1 1 1}-dominated AgBr nanoplates exhibited the highest photocatalytic activities, and the photodegradation rate of methyl orange dyes over them was 3 times faster than over AgBr nanocubes that expose {1 0 0} facets. Surface atomic models and DFT calculations indicate that the {1 1 1} facets have more dangling bonds and a higher surface energy than the {1 0 0} facets, which substantiate the facet-dependent photocatalytic properties. Therefore, our work not only provides a novel method to prepare regular AgBr nanocrystals, but also demonstrates that the shape and exposed facets have important influence on their photocatalytic activities.