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

• Formation of many anisotropic shapes of AuNP after oxidative etching with KMnO4.
• Hydrodynamic diameter of Au nanospheres (∼41 nm) decreased to ∼4 nm after etching.
• Au nanorods gradually converted to spherical particles (∼34 nm) with KMnO4 etching.
• Etched AuNP always exhibit higher catalytic activity than as-prepared AuNP.
• An anodic peak at -0.90 V for etched AuNP indicate the formation of Au0/Au+3 couple.

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 527 nm) and Au nanorods (679 to 532 nm) 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 (∼4-7 nm), low aspect ratio rods (2.6) and spheroids (∼13 nm) of narrow size distribution after KMnO4 etching. As a result, the hydrodynamic diameter of Au nanospheres (∼41 nm) and Au nanorods (∼109 nm) were reduced to ∼4 nm and ∼34 nm, 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+) = -0.90 V 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.

The oxidative etching of Au nanostructures with KMnO4 resulted in the formation of smaller size anisotropic particles due to the gradual dissolution of surface exposed Au atom to Au + 3 ions as confirmed by the cyclic voltammetry and potentiometric titration study. The Tem and DLS particle size analysis indicates that the Au nanospheres (∼41 nm) and nanorods (∼109 nm) are reduced to ∼ 4 nm and ∼ 34 nm, respectively, that significantly improved (∼2 times) the catalytic activity for the reduction of p-nitrophenol and p-nitrobenzoic acid relative to unetched Au nanoparticles.Figure optionsDownload as PowerPoint slide