Does morphology of a metal nanoparticle play a role in Ostwald ripening processes?

Abstract

The Ostwald ripening theory is commonly adopted to rationalize the growth of large metal nanoparticles that are formed at the expense of small-sized nanoparticles of higher chemical potential energies. This classical theory did not describe whether the morphology of a metal nanoparticle plays a role in controlling the shape evolution in the ripening processes. Here we show the direct observation of shape evolution among Ag nanoparticles of different morphologies in solutions, and experimental measurements of the relative chemical potential energies (or the electrochemical oxidation potentials) of Ag NPs of different morphologies, including, nanocubes, nanospheres, triangular plates, and decahedral nanoparticles. Theoretical calculation shows that when the diameter of a metal NP is beyond 35 nm, the influence of particle sizes on the oxidation potentials becomes very small. Chemical etching of Ag NPs by Fe(NO3)3 results in preferential removal of atoms at sharp edges/corners, and negative shift in the oxidation potentials. The measured electrochemical oxidation potentials of Ag NPs are in following orders: nanocubes (43 nm in length, 346 mVAg/AgCl) > nanospheres (53 nm in diameter, 337 mVAg/AgCl) > penta-twinned decahedrons (86 nm in edge length, 315 mVAg/AgCl) > triangular nanoplates (127 nm in edge length and 11 nm in thickness, 293 mVAg/AgCl). © 2013 American Chemical Society.