RATIONAL DESIGN OF COMPLEX NANOMATERIALS VIA CATION EXCHANGE, CRYSTAL PHASE TUNING, AND SURFACE REACTIVITY

Open Access
- Author:
- Butterfield, Auston Glen
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 28, 2021
- Committee Members:
- Robert Hickey, Outside Unit & Field Member
Elizabeth Elacqua, Major Field Member
Christine Keating, Major Field Member
Raymond Schaak, Chair & Dissertation Advisor
Philip Bevilacqua, Program Head/Chair - Keywords:
- Cation exchange
copper sulfide
stacking faults
crystal phase tuning
nanoparticle surface chemistry
morphology control
composition tuning
nanomaterials
zinc sulfide
cadmium sulfide
crystal structure retention
cobalt sulfide
defect density tuning
manganese doping
copper sulfide etching - Abstract:
- Nanoparticles are a unique class of materials because they exhibit properties that differ from their bulk counterparts and are dependent on their size, shape, composition, and crystal structure. To realize their potential in applications, scalable synthetic strategies that produce highly uniform particles are needed. While great progress has been made in direct growth methods, these procedures are often empirically optimized and are material specific. To overcome these limitations, post-synthetic modification techniques have emerged as powerful strategies for targeting specific property defining features and enabling rational synthesis. While a vast number of post-synthetic modification techniques exist, this thesis will focus on cation exchange, material selective etching, and surface modification, with an emphasis on cation exchange. Cation exchange enables the decoupling of nanomaterial composition from size and shape by using mild reaction conditions to replace the cations from a pre-synthesized template material with cations from solution. Through careful selection of template crystal structure, cation exchange can also be leveraged to target specific crystal structures, including metastable structures. While great progress has been made in this field to enable rational cation exchange synthesis, including to synthesize heterostructured materials that contain multiple distinct material domains, there is still much to learn. In this dissertation, I leverage known cation exchange behaviors to rationally produce complex nanomaterials, while investigating fundamental concepts that underpin their formation and transformation. These include defect formation, the role of morphology on crystal structure, and the influence of surface chemistry. The findings in this dissertation pave the way for rationally navigating cation exchange reactions in more complex material systems, and open avenues for further investigation. I begin by leveraging known behaviors in partial cation exchange and chemical etching for achieving heterostructured nanomaterials with higher degrees of morphological complexity than were previously achievable. In doing so, I demonstrate a rational synthetic approach for producing nanomaterials with anisotropic morphologies inaccessible via direct synthesis routes. Through my use of partial cation exchange reactions, I recognized unexpected planar defects forming in the exchanged regions. Accordingly, I transition into investigating these planar crystal defects, which were found to be the formation of stacking faults. These findings challenged oversimplified assumptions within the field of cation exchange and demonstrated that the anion sublattice is more dynamic than previously assumed. Building on this dynamic nature I developed cation exchange conditions that enable stacking fault density to be readily tuned during cation exchange. Next, I further probe the concept of a dynamic anion sublattice in more complex material systems by investigating cation exchange with Co2+ to form cobalt sulfide, which has a rich phase diagram. Here, I demonstrate the first report establishing that the morphology of the template particle can influence anion sublattice rearrangement, ultimately affecting the crystal phase of the resulting product. Lastly, I close by investigating how the reaction conditions commonly used in cation exchange can inadvertently modify the surface reactivity of copper sulfide template materials. These findings demonstrate new capabilities in cation exchange reactions and call to action the need for careful consideration of factors previously assumed to be noninfluential.