In-Situ Study of Heterogeneous Crystal Growth of Gold Nanoparticles on Hematite Facets

Abstract

Although significant research has been conducted on metal nanoparticles, a notable gap persists in understanding the fundamental principles governing their crystallization and stability, particularly when deposited on heterogeneous supports. Most current studies focus on specific systems, such as single nanocrystalline facet, which limits the broader understanding of how these processes are influenced by various factors, such as interactions with the facet-dependent crystalline supports. Gaining deeper insights into these mechanisms could lead to the development of more robust and efficient catalytic systems, sensors, and nanomaterials for other advanced applications across various industries. To address this gap, our study focuses on the in-depth examination of the crystallization process of gold (Au) nanoparticles on hematite (104) and (001) facets through in situ transmission electron microscopy (TEM) observation. Our findings reveal the existence of three distinct crystal growth pathways in hematite-supported Au nanoparticles: Ostwald ripening, particle coalescence, and disordered intermediate-phase-mediated growth where particle coalescence plays a dominant role in the sintering process. Furthermore, analysis of crystal growth kinetics on different facets of hematite substrate highlights a facet-dependent behavior. Hematite (001) effectively stabilizes Au nanoparticles and suppresses their sintering more effectively than (104) facets. This enhanced stabilization is attributed to the lower surface energy and stronger interaction between Au and the hematite (001) facet. Density functional theory (DFT) calculations, in conjunction with molecular dynamics (MD) simulations, provide valuable insight into heterogeneous coarsening of Au nanoparticles on hematite. Our research significantly contributes to the understanding of facet-dependent growth of metal nanoparticles on hematite nanocrystals and offers guidelines for selecting hematite-supported heterogeneous catalysts.