Size Determination of Metal Nanoparticles Based on Electrochemically Measured Surface-Area-to-Volume Ratios

Here we report the electrochemical determination of the surface-area-to-volume ratio (SA/<i>V</i>) of Au nanospheres (NSs) attached to electrode surfaces for size analysis. The SA is determined by electrochemically measuring the number of coulombs of charge passed during the reduction of surface Au₂O₃ following Au NS oxidation in HClO₄, whereas <i>V</i> is determined by electrochemically measuring the coulombs of charge passed during the complete oxidative dissolution of all of the Au in the Au NSs in the presence of Br^– to form aqueous soluble AuBr₄^–. Assuming a spherical geometry and taking into account the total number of Au NSs on the electrode surface, the SA/<i>V</i> is theoretically equal to 3/radius. A plot of the electrochemically measured SA/<i>V</i> versus 1/radius for five different-sized Au NSs is linear with a slope of 1.8 instead of the expected value of 3. Following attachment of the Au NSs to the electrode and ozone treatment, the plot of SA/<i>V</i> versus 1/radius is linear with a slope of 3.5, and the size based on electrochemistry matches very closely with those measured by scanning electron microscopy. We believe the ozone cleans the Au NS surface, allowing a more accurate measurement of the SA