Influence of Oxidative Etching of Au Nanostructures by KMnO4 on its Surface Morphology, Electro-kinetic Properties and Improved Catalytic Activity

Abstract

This paper reports the impact of oxidative etching of Au nanospheres and nanorods by KMnO4 on their surface morphology, electro-kinetic properties and catalytic activity. A significant blue-shift of the surface plasmon bands for Au nanospheres (536 to 527nm) and Au nanorods (679 to 532nm) were observed, due to their size and shape alterations after oxidative dissolution. TEM analysis also revealed the formation of various irregular Au nano-morphologies such as spheres (∼4-7nm), low aspect ratio rods (2.6) and spheroids (∼13nm) of narrow size distribution after KMnO4 etching. As a result, the hydrodynamic diameter of Au nanospheres (∼41nm) and Au nanorods (∼109nm) were reduced to ∼4nm and ∼34nm, respectively. The oxidative dissolution of Au0 by KMnO4 occurred via its oxidation to Au3+ ions as confirmed by the measured electrode potential, E0(Au0/Au3+)=-0.90V by cyclic voltammetry with significant increase in the zeta potential and conductance values. The etched Au nanoparticles being smaller in size and of higher surface to volume ratio resulted in ∼ 2 fold higher catalytic activities for the reduction of p-nitrophenol and p-nitrobenzoic acid as compared to bare unetched Au nanostructures.