IBN

CONTACT

EDUCATION

B.Eng., Materials Engineering, Nanyang Technological University, 2007

RESEARCH INTEREST

My research interest is to develop a rational approach to the design and synthesis of noble metal nanocrystals (NCs) in desired morphology as the physicochemical properties of NCs are strongly dependent on their shape and size. Two types of nanostructures are of particular interest: polyhedral NCs bound by high-index facets and hybrid metal NCs with complex but well-defined geometries.

1)        Synthesis of noble metal NCs with high-index facets by wet chemical methods.

High-index surface planes of noble metals denoted by a set of Miller indices {hkl} with at least one of the indices greater than unity are often catalytically more active than the close packed low-index planes of the same metal. The reason has been attributed to the presence of a high density of atomic steps and kinks. The lure and potential of enhanced catalytic performance has spurred the search for shape-controlled synthesis of noble metal NCs with high-index facets.

High quality polyhedral high-index NCs with customizable particle attributes such as size, crystallinity and exposed facets were synthesized by a seed-mediated growth method combined with kinetic control. Seed-mediated growth is a two-step synthesis in which NC seeds are prepared first and then added to a separate solution for growth. Such a strategy uses discrete steps to effectively separate seed formation from growth, which is particularly advantageous for the design of NC shapes through the optimization of the seed structure and growth conditions. The final shapes of the NCs are manipulated by the growth kinetics, i.e., the relative growth rates in different crystallographic directions, in the growth process. Specifically, monodisperse concave trisoctahedral gold NCs with high-index {hhl} facets are synthesized with tunable sizes. The crystallinity of the NCs could also be controlled, a new nanostructure–shield-like Au NCs with singly twinned structure and high-index {hhl} facets are formed. Using the concave Au TOH NCs as seeds, polyhedral Au@Pd NCs with customizable high-index Pd facets could be obtained including concave TOH, concave hexoctahedral and tetrahexahedral NCs with {hhl}, {hkl} and {hk0} facets respectively. The Miller indices of NCs are also modifiable.

Gold TOH NCs with tailorable sizes. 

Shield-like Au NCs with singly twinned structure.

Au@Pd polyhedral NCs with variable high-index Pd facets.

2)        Synthesis of hybrid noble metal NCs with exotic but designable morphologies.

Hybrid NCs are elaborate multi-component NCs consisting of two or more different materials that are integrated through chemically bonded interfaces. Hybrid NCs represent an effective means of integrating the properties of different materials to provide multifunctionality in applications. Besides, the close coupling of different components on the nanoscale may also generate synergistically enhanced properties.

A template growth process was used to prepare the hybrid NCs. The core NCs were prepared first where the shapes of the cores could be customized as a single component NC synthesis. Then the core NCs were employed as templates for the deposition of the secondary metals. The growth conditions were manipulated to control the deposition site and shape of the secondary metals. We have successfully prepared hybrid NCs with both core and secondary metals in well-defined shapes.

Core-shell Au@Pd NCs with both core and shell in well-defined shapes