Discovery and Design of Heterostructured and Solid Solutioned Nanoparticles
Restricted (Penn State Only)
- Author:
- Mc Cormick, Connor
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 08, 2023
- Committee Members:
- Benjamin Lear, Major Field Member
Christine Keating, Major Field Member
Raymond Schaak, Chair & Dissertation Advisor
Philip Bevilacqua, Program Head/Chair
Ismaila Dabo, Outside Unit & Field Member - Keywords:
- Nanoparticles
High Entropy
Sulfide
Phosphide
heterostructure
Cation exchange - Abstract:
- Synthetic strategies to develop increasingly more complex nanoparticle materials have grown in relevance in recent decades as nanoparticle-based technologies have developed. Specifically, in applications of optics, photocatalysis, thermoelectrics, and medical fields, where having multiple nanomaterials combined in a single nanoparticle, a heterostructure, allows access to multiple functionalities within a single construct. In addition to these additive strategies, precision in physical outcome has been achieved in solid solution nanoparticles, which are alloys of two distinct materials. Designing scalable and solution processable methods to access such materials is far from optimized. Many methods of discovery and design rely on non-scalable methodologies, minimizing their impacts as a basis for retrosynthesis of complex nanoparticles. Colloidal chemistry offers an avenue for fundamentally scalable and solution processable syntheses, but insights into synthetic outcomes can be obscured by the multitude of variables synthesis to synthesis. Specifically, cation exchange is leveraged to generate these heterostructures and solid solutions. Cation exchange is chemical transformation that replaces the host cations in a template material with guest cations from solution. This chemistry has been utilized to generate robust chemistry to design heterostructures and solid solutions. This dissertation contains works that further the goal of developing syntheses to target complex heterostructure and solid solution constructs. Specifically, in chapter 2 I utilize simultaneous multi-cation exchange to generate products with a high number of products. Then through trends in compositions and interfacial arrangement, I iterate different synthetic conditions and re-evaluate product outcomes to determine which product features are targetable and synthetically achievable. Then, these observations of small populations are used to develop syntheses for high-yield targeted syntheses of previously unattainable products. Specifically, high yield syntheses of a (Ni,Co)xS solid solution and two isomers, ZnS − Cu1.8S − (Ni,Co)xS and ZnS − (Ni,Co)xS − Cu1.8S, are realized. The isomers are generated through a different sequence of cation injections. This work serves as a template of how to do exploratory syntheses to discover new and achievable products. Then, building on the observations in chapter 2, I investigate the formation of a high entropy metal sulfide, wurtzite-type Zn0.25Co0.22Cu0.28In0.16Ga0.11S in chapter 3. The formation of a high entropy material was surprising, as typical high entropy material syntheses rely on high temperatures and rapid quenches to trap the high entropy phase. I, however, use cation exchange which leaves the anion scaffolding unaltered and allows for the incoming cations to react with the copper sites to form the solid solution. It is shown that the reaction is not generalizable to make any solid solution but does allow for compositional tuning. Overall, the formation of the high entropy material through cation exchange is revealed to behave similarly to the formation of single cation metal sulfides made through cation exchange. Returning to observations in chapter 2, I investigate the formation of a zinc cobalt sulfide, CoxZn1-xS, solid solution in chapter 4. This solid solution phase is verified to be a metastable phase through DFT modelling in collaboration with Ismaila Dabo and Steven Baksa. Synthetically, the formation of the solid solution is observed across three morphologies (spheres, plates, and rods) of Cu1.8S used as the template material. However, targeting larger amounts of cobalt in the CoxZn1-xS in the nanorods and nanoplates resulted in phase segregation. On Cu1.8S spheres, the full composition range (0 ≤ x ≤ 1) was achieved. The key to the success of the reaction was the balancing of the Zn2+ and Co2+ cation exchange reactivities, demonstrated by the formation of cobalt sulfide in reactions where the total concentration of Co2+ was higher than it would be in a synthesis that generated a solid solution. Finally, the x ≤ 0.5 solid solutions were shown to be semiconductors and were integrated in the retrosynthetic design of heterostructured nanorods. Pulling from observations in chapter 2 for a final time, the formation of (Ni,Co)xS through sequential and simultaneous cation exchange is studied in chapter 5. Sequential Ni2+ then Co2+ cation exchanges on Cu1.8S rods result in a solid solution, (Ni,Co)xS, emanating from the established Ni9S8 domain. In sequential Co2+ then Ni2+ cation exchanges on Cu1.8S rods, a solid solution domain appears to form in the established CoxS domain. Importantly, these cation exchange reactions are exchanging Co2+ or Ni2+ for Cu+ exclusively, as a CoxS or Ni9S8 rod will not convert to the solid solution. Exposed CoxS-Cu1.8S or Ni9S8-Cu1.8S interfaces are critical for the formation of the solid solution. Aspects like temperature and domain size were probed, showing domain size had little importance in reaction outcome, while temperature had a large impact on the formation of solid solution through sequential exchange reactions. Finally, using simultaneous Ni2+/Co2+ generates homogeneous NixCo9-xS8 rods, with a pentlandite crystal structure. The key to making compositionally tunable NixCo9-xS8 rods is slow injecting the Ni2+/Co2+ cation solution into the reaction, to mitigate the higher reactivity of Co2+. Finally, work targeting the formation of a high entropy phosphide was carried out in chapter 6. Syntheses targeting (Ni,Co,Fe)2P solid solutions serve as the model system to incorporate more metals into the nanoparticle product. Specifically, I used metal carbonyls to make amorphous metal phosphide intermediates at intermediate temperatures which then at higher temperatures crystalize. This strategy showed success at integrating chromium, molybdenum, and tungsten into the (Ni,Co,Fe)2P nanoparticle synthesis framework. Generally, this strategy of making amorphous metal phosphides with all metals of interest mixed followed by annealing builds on chemical strategies targeting intermediates that can be converted into high entropy materials. These strategies circumvent the traditional high temperature and quench methodologies typically required to prepare high entropy materials.