[CCoE Notice] Dissertation Announcement: Haley Keister, "Novel Counterflow Reactor for Continuous Templated Synthesis of Semiconductor Nanocrystals"

[Greenwell, Stephen J]

[Dissertation Defense Announcement at the Cullen College of Engineering]
Novel Counterflow Reactor for Continuous Templated Synthesis of Semiconductor Nanocrystals

Haley Keister

April 29, 2025; 1 p.m. to 3 p.m.
Location: Engineering Building 1, Room S234

Committee Chair:
Triantafillos J. Mountziaris, Ph.D.
Committee Members:
Jeffrey Rimer, Ph.D. | Alamgir Karim, Ph.D. | Richa Chandra, Ph.D. |
Birol Dindoruk, Ph.D.
Abstract
          Semiconductor nanocrystals, also referred to as quantum dots, are an exciting class of materials exhibiting size-dependent and tunable optical and electronic properties.  This allows QDs to have many different applicational usages such as display devices, photovoltaics, catalysis, and biological sensing and imaging.  The commercial development of these nanocrystals requires the advancement of synthesis techniques that are scalable, as well as being both economical and environmentally friendly; at the same time allow for the specific control of all the tunable features of the nanocrystals such as size, shape, and the size distribution.  There are many ways to synthesize nanocrystals with either a top-down or bottom-up methods, most of the synthesis techniques involve small batch reactors.  The most well-known technique is the hot injection method which involves rapid injection of an organometallic precursor into a hot coordinating solvent where the nanocrystals grow as a function of time. Trying to commercialize the hot injection method has many limitations such as the incomplete mixing of the precursors, high cost, the flammability, and toxicity of the reactants as well it is an operator intensive process.
          Templated synthesis of nanocrystals has distinct advantages over other methods, including the ability to have precise control over the nanoparticle features such as the particle size, shape, and size distribution.  The templated synthesis method as is has been used in small batch reactors, but because of the reactants used it allows for an easier model to scale up.  The template consists of a stable microemulsion formed by the self-assembly of an amphiphilic block copolymer in the presence of both a polar and non-polar solvent.  This microemulsion contains a group-II salt in the dispersed phase which is then contacted with a group-VI hydride gas reactant inside the nanodomains of the microemulsion.  To precisely control the size, the metal salt composition and concentration can be adjusted.  This technique is easily scalable to a continuous synthesis by building a counter-current flow, packed-bed reactor.   In this design the gas phase reactant enters from the bottom of the reactor while the microemulsion is fed from the top of the reactor which causes a concentration gradient allowing for the most efficient and cost-effective use of the reactants.   The development of this reactor is explored as well as the optimization of the process by exploring different packing sizes, gas flow rates, as well as the start-up conditions for the reactor.  To increase the optical properties of the nanoparticles synthesized with this technique a post-processing technique involving both extraction from the microemulsion and functionalizing the nanocrystals surface was developed.

[Engineered For What's Next]


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