Ionic liquid [BMIM][BF4] as an interesting solvent for galvanic replacement mediated shape transformation of Ag nanospheres into Ag-Au dendritic nanostructures

Gold nanostructures exhibiting an interesting dendrite-like growth have been synthesized for the first time in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] using a galvanic replacement approach, wherein silver nanospheres were used as a precursor sacrificial template in the presence of a gold salt as an etchant. To understand the effect of unique physico-chemical properties of the (IL) such as viscosity and ionicity, comparative experiments were simultaneously performed in aqueous solutions. This study highlights the significantly different replacement reaction kinetics in [BMIM][BF4] than that seen in aqueous solutions, thereby leading to markedly different reaction products in these two solvent systems. In water, hollow Au-Ag nanoshells were observed after galvanic replacement, however a remarkable growth and shape transformation from nanospheres to hierarchical dendritic nanostructures is achieved in the ionic liquid. The improved performance of dendritic structures synthesized in IL over hollow nanostructures synthesized in water has been demonstrated for hydrazine and formaldehyde oxidation reaction, which are important reactions for liquid fuel cell applications. It is envisaged that the use of designed solvents like ionic liquids during galvanic replacement reactions may in future lay the groundwork for better control over shape anisotropy, leading to structures with multiple applications including optics, catalysis, sensing and biomedicine.