Shape direction and size control of novel nanostructures: towards a fundamental understanding of growth

Abstract

Shape control of metal nanoparticles has had a great deal of attention in the past decade due to the enhanced catalytic properties based on structure and surface faceting. Numerous methods have been developed to synthesize various nanostructures that make more efficient use of the active surfaces by tuning porosity, shapes, sizes, and facets by adding foreign ions which promote or restrict growth on specific sites; however, a fundamental mechanistic understanding of how and why ions and other synthetic parameters direct growth resulting in specific shapes and porosity have only been hypothesized. Herein, we first demonstrate the importance of shaped metal nanoparticles in terms of active sites in Au icosahedra, which motivates a full literature review of shaped Pt nanostructures. The conclusions regarding need for understanding towards growth systems motivates the study of both direct (wet chemical reduction) and indirect (galvanic displacement) synthesis techniques, which is then followed by the probing of nanoparticle growth kinetics as well as mesopore expansion in silica. Synergistic capabilities of computationally-guided synthetic routes as proposed by the Materials Genome Initiative (MGI) are demonstrated by testing hypotheses, then utilizing experimental insight from platinum systems to predict the growth of faceted palladium nanocrystals. Mechanistic insight on growth kinetics can be elucidated by studying the role of directing ions during the growth process, thereby obtaining a general fundamental understanding of directed nanoparticle formation. The pore expansion mechanisms in mesoporous materials via hydrothermal treatments allows us to understand pore sizes as a function of solution etching, thus giving rise to size-dependent separation and sequestration applications. Understanding structure and activity relationships of our resulting products will assist in the synthesis of next generation materials with enhanced properties, thereby advancing the nanotechnology field from serendipitous materials discovery to intuitive materials design.