Understanding Competing Reaction Pathways in Nanoparticle Cation Exchange Processes Using the Tyndall Effect
Open Access
- Author:
- Di Domizio, Gabriella
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 12, 2020
- Committee Members:
- Raymond Edward Schaak, Thesis Advisor/Co-Advisor
Lauren Dell Zarzar, Committee Member
Benjamin James Lear, Committee Member
Philip C Bevilacqua, Program Head/Chair - Keywords:
- Tyndall effect
Cation Exchange
Structure-Selective
Nanoparticle
Manganese Sulfide
MnS
Digenite - Abstract:
- Nanochemistry has evolved into capturing the imagination and attention of scientists that are interested in synthesizing materials with unique properties for a variety of applications, such as in medicine, electronics, and renewable energy. Solution-based colloidal reactions are a common approach to achieving nanoscale products with diverse compositions, shapes, and crystal structures as these materials can be synthesized affordably at lower temperatures, and in a potentially scalable manner. However, such bottom-up methods require careful tuning of subtle reaction conditions to gain control over the product outcome, which is frequently not trivial to accomplish. As one of the many foundational goals of materials chemistry is having the ability to predictably access a product of interest, nanoscale cation exchange has provided such an opportunity as a postsynthetic modification technique where complex nanomaterials can be obtained through stepwise construction. As with many other solution-based protocols, cation exchange also requires a delicate balance of reaction conditions as the integrity of the nanoparticles being postsynthetically modified plays a crucial role in its successful execution. Typically, cation exchanges are performed under mild conditions where they are the dominant reaction pathway, and thereby enabling kinetic control and allowing the anion sublattice to remain rigid. Conversely, some cation exchanges may utilize higher temperatures and/or may not proceed in a topotactic manner. As a result, it is important to recognize the potential emergence of competing reaction pathways, such as a dissolution and reprecipitation process, as temperature increases to correctly understand how specific products are truly obtained in solution. In the research reported herein, the structure-selective cation exchange from digenite Cu1.8S to zincblende MnS will serve as a model system undergoing increased injection temperatures (100°C, 200°C, and 300°C) of the starting material, digenite Cu1.8S, dispersed in tri-n-octylphosphine (TOP). To monitor the state of the reactions in real-time, the Tyndall effect will be applied, upon injection, to probe the state of colloidal dispersions in an effort to correlate the persistence, or disappearance and then reappearance, of the visible light beam to a particular reaction pathway. As probing cation exchange reactions in-situ can be challenging, it is beneficial to utilize a simple, and inexpensive method, such as the Tyndall effect, as a complementary characterization tool to other spectroscopic, diffraction, and microscopy techniques commonly used to investigate cation exchange.