LAUSR

Abstract Three different aspect ratios (AR = rods length/rods width, AR = 2.8, 3.3, 3.8) of Au nanorods were synthesized and characterized by various measurements. We have evaluated the AR-dependent catalytic properties of Au nanorods using a model reaction based on the reduction of 4-nitrophenol (4-NP) by NaBH4. From the average reaction rate constants (k) at different temperatures, the activation energy (Ea) was determined. For different aspect ratios of Au nanorods, the larger AR owns the higher k, and the values of Ea increase with decreasing AR, meaning Au nanorods with the higher AR performed the higher catalytic activity. The thermodynamic parameters of entropy (ΔS), Gibbs free energy (ΔG) and activation enthalpy (ΔH) indicated that this catalytic reduction is a non-spontaneous process. The catalytic results of Au nanorods clearly showed that the larger aspect ratio the higher catalytic activity. This substantial difference in AR-dependent catalytic activity can be explained from three different points: The superior catalytic properties of Au nanorods with higher AR result from higher surface-to-volume ratios; Au nanorods with lower AR needs to cross the higher energy barriers; Au nanorods with a larger AR may have higher fractions of uncoordinated surface atoms because of their increased surface curvature.