Controlling Nanoparticles with Atomic Precision – The Case of Gold

Controlling nanoparticles with atomic precision has long been a major goal in nanoscience. Gold nanoparticles are quite attractive due to their excellent stability and elegant optical properties. The synthesis of atomically precise gold nanoparticles, however, remains a major challenge, which hampers the pursuit of fundamental science of such nanoparticles and the development of their applications (e.g. catalysis). This talk will present a size-focusing methodology for synthesizing atomically precise gold nanoparticles protected by thiolates (referred to as Aun(SR)m, also called nanoclusters). Ultrasmall Aun(SR)m nanoparticles (e.g. n of a few dozens) exhibit distinct quantum confinement effects and interesting electronic and optical properties that are fundamentally different than their larger counterpartsfcc crystalline nanoparticles. A few representative, size-specific Aun(SR)m nanoparticles will be discussed in detail. Unlike fcc Au nanocrystals that possess translational symmetry, small Aun(SR)m nanoclusters do not adopt fcc structure; indeed, new types of non-crystallographic structures have been discovered in X-ray crystallographic analyses on Au25(SR)18 and Au38(SR)24 nanoclusters. Experiment and theory have revealed quantized electronic structure and intrinsic magnetism in such nanoclusters. The transition from the quantum-confined state to metallic state occurs with increasing size (n of a few hundreds). The Aun(SR)m nanoclusters have also been found to be excellent catalysts for some selective oxidation and hydrogenation processes. Correlation of Aun(SR)m catalytic properties with crystal structures will ultimately offer fundamental understanding on nanogold catalysis.