Design and Synthesis of Inorganic Nanoparticle Heterostructures Using Cation Exchange Transformations

Open Access
- Author:
- Steimle, Benjamin Colby
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 09, 2021
- Committee Members:
- Robert Rioux, Outside Unit & Field Member
John Asbury, Major Field Member
Raymond Schaak, Chair & Dissertation Advisor
Philip Bevilacqua, Program Head/Chair
Benjamin Lear, Major Field Member - Keywords:
- Colloidal synthesis
Nanoparticles
Cation exchange
Solid-state interfaces
Inorganic materials - Abstract:
- The properties of nanoscale materials are influenced by their morphology, composition, and crystal structure. These properties can be further modified or improved by forming solid-state interfaces between discrete nanoscale materials. In many cases, the property-defining features of relatively simple, single component nanomaterials can be well controlled, but limited synthetic approaches exist to controllably form interfaces between dissimilar materials. Many of the existing strategies to synthesize such multicomponent nanomaterials, often referred to as heterostructures, rely on multiple known and unknown variables to achieve a desired reaction outcome. Nanoscale cation exchange offers a means to circumvent some of these synthetic limitations. This topotactic process transforms a reactive, preformed nanoparticle template into a product with a targeted composition while preserving the original size, shape, and, often, crystallographic features of the starting material. Arresting cation exchange reactions prior to completion enables the synthesis of heterostructures while still benefiting from the morphology and crystallographic feature preservation intrinsic to these transformations. In this dissertation, I expand upon existing knowledge of partial cation exchange to develop synthetic design guidelines based on simple material and crystallographic parameters. I use these insights in generalized reaction pathways to create some of the most complex heterostructured nanomaterials ever observed. I show preliminary evidence for the use of these heterostructures as precursors in the formation of alloyed metal sulfides and speculate that similar crystallographic insights in different template nanoparticles could enable the synthesis of even more diverse heterostructured nanoparticles. I first explore the use of roxbyite copper(I) sulfide nanoparticles as reactive synthons in two related cation exchange reaction pathways with tractable synthetic steps. In both pathways, partial cation exchange transformations on the template(s) introduced one or more new material segments embedded within chemically addressable copper(I) sulfide regions. In the first reaction pathway (Chapter 2), reactive copper(I) sulfide regions were selectively targeted for post-synthetic modifications that included cation exchange, etching, or deposition to produce 47 heterostructured products. I expanded on these capabilities to generate the second reaction pathway (Chapter 3) by developing extended synthetic design rules based on crystallographic relationships and interfacial reactivity. This modular reaction pathway included up to seven distinct reaction steps using up to five different metal cations. We experimentally observed 113 unique heterostructured nanorods and predict that over 65,000 different heterostructured nanorods are accessible using this reaction pathway. I describe in detail the important nuances of both reaction pathways (Chapter 4), with the goal of making these reactions approachable to a broader community. The heterostructures synthesized through both reaction pathways contained multiple material segments within a continuous sulfur sublattice, making them ideal targets to investigate cation mobility in solid-state nanoscale materials. I present preliminary evidence for the formation of solid-solutions of metal chalcogenides using both thermally- and exchange-induced cation migration (Chapter 5). I show evidence of cation migration during a newly reported alloy-forming cation exchange reaction. In both thermally- and exchange-induced reaction conditions, there is the potential for the discovery of new phases of metal sulfides and alloys with new compositions. Finally, I transition to investigation of partial cation exchange behavior of digenite copper(I) sulfide nanoparticles, which is structurally distinct from roxbyite copper(I) sulfide. I discovered that a previously unknown reaction intermediate forms under standard cation exchange reaction conditions (Chapter 6). I used the crystallography of this intermediate to rationalize partial cation exchange products that contain up to four segments of the same material and present preliminary evidence for size- and shape-controlled synthesis of digenite (Chapter 7). Further development of this phase as template for partial cation exchange could enable the synthesis of even more diverse classes of heterostructured metal sulfides and provide an opportunity to develop new design principles to this system.