Hansong Yu
Advisor: Prof. Younan Xia

Co-advisor: Prof. Mark D. Losego

will propose a doctoral thesis entitled,

Steady-State Synthesis and High-Throughput Production of Noble-Metal Hollow Nanostructures by Templating with Silver Nanocubes

On

Friday, Nov 1st at 11:00 a.m.
MoSE Room 3121

and

Virtually via Zoom

https://gatech.zoom.us/j/98686367351?pwd=bX219uRwuQglieZMkZorwGfMqlljHz.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
Over the past two decades, numerous methods have been developed to produce colloidal metal nanocrystals with uniform sizes and shapes. These nanocrystals not only provide a well-defined system to investigate the structure-property relationship, but also offer opportunities for a variety of applications in catalysis, plasmonics, and medicine. In particular, bi-metallic nanocrystals, synthesized through seed-mediated growth on nanocrystal templates, provided more possibilities for precise control over the surface structures, leading to enhanced catalytic capabilities. By etching away the templates, one could obtain hollow nanostructures, such as nanoframes and nanocages featuring more active sites and higher specific surface areas than their solid counterparts. As a major advantage over conventional catalysts based on solid nanoparticles, hollow nanostructures offer a viable means to optimize their catalytic performance by maximizing the effective surface area and atom utilization.

Despite the remarkable progress, synthesis of bi-metallic nanocrystal is still far from reaching the ultimate goal of robust, reproducible, and scalable production. In many published works, dropwise addition has emerged as a powerful tool for a number of synthetic tasks. However, this approach is unsuitable for high-throughput or scale-up production because of the necessity to continuously add precursors into the reaction system throughout a synthesis. Therefore, there is a pressing need to develop new methods capable of achieving the steady-state kinetics characteristic of dropwise addition while introducing the precursor through one-shot methods. Such new methods hold the key to the deterministic, reliable, and scalable production of colloidal metal nanocrystals with well-controlled properties.

In this thesis, I will develop and validate three approaches to realize nanocrystal synthesis under both steady-state kinetics and one-shot injection. In the first approach, I will substitute the precursor featuring fast reduction kinetics to one with a slower reduction kinetics, in order to slow down the exponential decay of the concentration of the precursor to achieve a near steady-state reduction. In the second approach, I will switch from a soluble to an insoluble precursor to ensure that the metal ion in the reaction solution will stay at a constant level controlled by temperature and the concentration of free counterion until all the solid precursor is consumed. When the reductant is used in large excess relative to the precursor, the reduction will undergo steady-state kinetics from the beginning of a synthesis. In the third approach, I will borrow the concept of controlled release from drug delivery by loading a soluble precursor in micro- or nanoscale polymer carriers. In the case of zero-order release, the precursor can be maintained at a low and constant concentration because it will be immediately reduced as soon as it has diffused out from the carrier. Again, the reduction will follow steady-state kinetics if the reductant is used in large excess. Once the conditions for achieving steady-state kinetics at different levels have been established for one-shot injection, I will employ them for scale-up production by switching from a batch to a continuous flow reactor. Along with experimental inquiries, computational studies will be conducted to achieve a better understanding of the dissolution of solid precursors, as well as reduction and growth mechanisms.