Metallic nanoparticles (NPs) which are ultra-small in size are widely used for catalytic and sensing applications. The structural stability of the metal NPs is a key point to maintain their reactivity towards applications. In particular, coarsening (either by Smoluchowski or Ostwald ripening) that directly leads to a decrease of the surface area-to-volume ratio of the catalyst is undesirable. In general, dissolution of small particles and redeposition of dissolved ions/species on the surface of bigger sized particles is called Ostwald ripening. The main driving force between this coarsening of particles is the chemical potential difference between small sized and bigger-sized particles, which drives them to oxidize and redeposit on bigger-sized particles. Here, we describe the size dependent electrochemical Ostwald ripening of 2, 4 and 15 nm Au NPs attached to the 3-aminopropyl triethoxysilane (APTES) modified glass ITO electrode. For better understand the effect of NPs size towards electrochemically induced Ostwald ripening we keep similar coverage (amount) of 2, 4 and 15 nm Au NPs on the electrode surface. We applied constant potential (0.0, 0.3 and 0.45 V vs Ag/AgCl) for 35, 70, 105 and 140 min in 10 mM KBr plus 0.1 M HClO4. This potential was not sufficient to completely oxidized Au NPs but Br- starts partially oxidized Au atoms from NPs surface. We measure surface area (cyclic voltammetry coverage in acid electrolyte) and total volume (linear sweep stripping voltammetry coverage in Br-) and plot surface area over volume as a function of time. Since surface area over volume ratio is different for different size particles and its decrease with the increase of particles size, so we measured surface area and volume after each time (0, 35, 70, 105, 140 min) and plot as a function of time. We found that with the increase of applied potential and time NPs SA/V were decreased. By analyzing the slope for three different sized particles, we found that rate of NPs size transformation in the increasing order of 15&lt; 4 &lt;2 nm. This is because small size particles are less stable and more prone to oxidized as compared to bigger size particles. Also, the rate of mixture of two different sized NPs were found to be higher than the individual NPs. The mechanism of ripening was further confirmed by the size determine by SEM and size histogram before and after Ostwald ripening.

Understanding the metal nanoparticles size effect for electrochemically induced ostwald ripening: A case study with Au nanoparticles

2019 Spring National Meeting

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