Hansong Yu
Advisor: Prof. Younan Xia

Co-advisor: Prof. Mark D. Losego

will defend a doctoral thesis entitled,

Steady-State Synthesis of Noble-Metal Hollow Nanostructures by Templating with Silver Nanocubes

On

Wednesday, Dec 3rd at 3:00 p.m.

Virtually via Zoom

https://gatech.zoom.us/j/94479883434?pwd=bQCmnyPg6ApIcyjHoiELXyClJpeHFW.1

Committee

Prof. Younan Xia – School of Chemistry and Biochemistry (advisor)

Prof. Mark D. Losego– School of Materials Science and Engineering (co-advisor)

Prof. Meilin Liu – School of Materials Science and Engineering

Dr. Yong Ding – School of Materials Science and Engineering

Prof. Nian Liu – School of Chemical and Biomolecular Engineering

Abstract
Noble-metal hollow nanostructures are emerging as a class of advanced catalytic materials for a wide range of applications. Most of them have been synthesized using a combination of dropwise addition and seed-mediated growth or galvanic replacement, with Ag nanocrystals serving as the templates. In these syntheses, dropwise addition plays a critical role in achieving steady-state kinetics for the production of hollow nanostructures with controllable properties. As a major drawback, the experimental setup of dropwise addition makes it impractical for large-scale synthesis in continuous flow reactors due to the necessity of continuous injection. In addition to further advancing dropwise addition, there is a pressing need to develop alternative strategies to achieve steady-state kinetics in the setting of one-shot injection.

In the first project, I developed a facile method for the synthesis of Ru nanoboxes by adding Ru(acac)3 precursor dropwise into a reaction mixture containing EG, PVP, and Ag nanocubes at an elevated temperature. After selective removal of the Ag templates, Ru-based nanoboxes characterized by an hcp structure were obtained. They were evaluated using the reduction of 4-nitrophenol by NaBH₄ to demonstrate enhanced catalytic performance relative to several other noble-metal nanocrystals. In the second project, I demonstrated a new method for achieving steady-state kinetics via one-shot injection of a metal complex to synthesize Pd–Ag alloy nanoframes. During the synthesis, a Pd(II) complex was injected into an aqueous suspension of PVP and Ag nanocubes in one shot. The Pd(II) complex features a slower reduction kinetics than the traditional Pd(II) precursor, offering a steady source of slowly released Pd(II) and thereby leading to the controlled deposition of Pd atoms on the corners and edges. Upon selective removal of the Ag cores, Pd–Ag alloy nanoframes were obtained, which potentially feature high catalytic activity due to the high utilization efficiency of atoms. I also adapted the synthesis to a continuous flow reactor, demonstrating the feasibility of high-throughput production of Pd–Ag nanoframes. In the last project, I developed a novel strategy to synthesize Pd–Ag alloy nanoframes comprised of hollow ridges using an insoluble precursor based on PdBr2. The low dissolution and slow dissociation of the insoluble powders enabled the slow and constant release of Pd(II), resulting in a steady state for the deposition of Pd atoms on corners and edges while carving out Ag atoms from the side faces. As the reaction proceeded, through holes connecting opposite side faces were formed, leading to the formation of cage cubes. With the diffusion of Pd atoms and continuous dealloying of the Pd skin, the ridges were hollowed out, transforming the nanostructures into Pd–Ag alloy nanoframes comprised of hollow ridges. Taken together, this dissertation covers research on both traditional dropwise addition and new strategies for the synthesis of noble-metal hollow nanostructures, contributing to the development of noble-metal nanocrystals for catalytic applications.