Directed surface overgrowth and functionalization of polyhedral gold nanocrystals

Abstract

In Part I, the shape and size of gold nanocrystals are controlled simultaneously through directed surface overgrowth from spherical seeds with different sizes. In this overgrowth approach, the structure of gold nanocrystals was dependent on the concentrations of the gold precursor and the seeds in the reaction mixture. The resulting cubes, cuboctahedrons, and octahedrons have the size range of 70~230 nm. The clear XRD patterns inform that each structure has a uniform shape and revealed that Au^{3+} addition enhance the growth of {100} face. In Part II, we present the convenient and facile one-pot synthesis for well-defined hydroxyl-functionalized gold nanocrystals using poly(vinyl pyrrolidone-ran-vinyl acetate) without ligand exchange process. The pyrrolidone units act as a regulating surfactant of the gold nanocrystals and acetate units serve the hydroxyl functionality. Both size and shape of the gold nanocrystals were successfully controlled. The number of hydroxyl groups on the gold nanoparticle surface was estimated by FT-IR spectroscopy and TGA. These Functionalized-gold nanocrystals show thermal and chemical stability. We also confirmed that the hydroxyl groups are reactive with various functional groups. In Part III, carboxyl functionality is introduced to the surface of gold nanocrystals by using poly(N,N-dimethyl acrylamide) and poly(dimethyl aminoethyl methacrylate). Both polymers are able to not only regulate the metal surface effectively but also provide faceted edges of the gold nanocrystals. The carboxyl groups are effectively generated on the surface of gold nanocrystals through hydrolysis of amide or ester units of polymers. The resulting carboxyl-functionalized gold nanocrystals display a high pH sensitivity, which is induced by the hydrogen bond interaction between gold nanocrystals.