Kevin Pachuta defends doctoral dissertation
On Nov. 23, Kevin Pachuta successfully defended his doctoral dissertation, “Accessing Controlled Nanostructures from Lithium Cobalt Oxide.”
Pachuta, who grew up in Farmington Hills, Mich., decided to focus his defense on cobalt oxide nanosheets, a material that is “underexplored in the literature and has great potential for future applications.” He has completed numerous soft-chemical treatments on layered transition metal oxides studying their structure, morphology, and properties of the materials as functions of processing conditions. “I believe that the nanoscale still offers untapped opportunities to manipulate existing and discover new materials' properties,” said Pachuta. “Through both chemistry and materials science fundamentals these properties can be accessed and are of interest to me.”
When he started his graduate studies at CWRU in 2016, Pachuta wasn’t new to the Cleveland area, having earned his Bachelor of Science in chemistry from John Carroll University. It was during his time at John Carroll that he was first introduced to materials science while taking an elective course. “Once I heard of nanoscale materials I wanted to learn more.”
In 2018, Pachuta received his Master of Science in materials science and engineering from CWRU. Looking back at his time at CWRU, he is most appreciative of the relationships he has built, whether they be friends he made in research groups, conferences or collaborations. He described the guidance of his advisors, Associate Professor Alp Sehirlioglu and Associate Professor Emily Pentzer (from Texas A&M University) as “immeasurable.”
After graduation, Pachuta hopes to make an impact in the field of sustainable energy sources. He is currently seeking a postdoc position or a position in industry in the field of renewable energy.
In addition to being an engineer, Pachuta is an athlete, musician, and baker. He was a member of John Carroll’s soccer team as an undergraduate and rides with CWRU’s VeloSano team. He also enjoys volleyball, tennis, golf, running, and biking, and competed in a triathlon in 2018. He plays the guitar and opened and closed his dissertation practices by performing some songs for the members of his research group. Additionally, he enjoys baking bread and pizza for himself and others and runs a baking-dedicated Instagram account.
The exfoliation of lithium cobalt oxide, a layered transition metal oxide, using a two-step soft-chemical method to access cobalt oxide nanostructures was investigated extensively in this work. The first soft-chemical treatment step involves hydrochloric acid treatment of lithium cobalt oxide and results in cobalt dissolution, incomplete lithium-ion extraction, incomplete proton replacement of lithium, full unit-cell dissolution of the structure, slight changes in the lattice parameters, and significant etching and changes in morphology. This was examined using inductively coupled plasma – mass spectrometry, ultraviolet-visible spectroscopy, time of flight – secondary ion mass spectrometry, mass loss analysis, scanning electron microscopy, X‑ray nanotomography, and X‑ray diffraction. Additional acid treatments with sulfuric acid, nitric acid, and phosphoric acid were completed to analyze the effects of varying acid identity. The second soft-chemical treatment step involves the swelling and exfoliation of protic lithium cobalt oxide through tetraalkylammonium hydroxide treatment. Varying reaction conditions (e.g., solvents, conjugate bases, proton concentration in protic lithium cobalt oxide, tetraalkylammonium ion concentration, tetraalkylammonium ion ionic size, powder aging, reaction time, stir rate, and loading concentration) were studied in-depth using UV‑Vis spectroscopy to determine the effect they had on the exfoliation yield of protic lithium cobalt oxide. Reaction conditions that produced suspensions of cobalt oxide nanosheets were then analyzed with respect to aging time and their optical band gap was determined. These findings led to methods for controlling and understanding cobalt oxide nanosheets. First, the exfoliation of large and ultrathin cobalt oxide nanosheets in pH neutral solutions, the stability of cobalt oxide nanosheets in multiple solvents, and the production of high concentration cobalt oxide nanosheets solutions are presented and examined using UV-Vis spectroscopy, optical images, atomic force microscopy, and transmission electron microscopy. Next, the effects of mechanical work, such as sonication and centrifugation, applied to cobalt oxide nanosheets were investigated through UV-Vis spectroscopy. Finally, kelvin probe force microscopy and piezoresponse force microscopy were used to examine the fundamental electronic, optoelectronic, and electromechanical properties of cobalt oxide nanosheets. This is followed by the investigation of the catalytic performance (e.g. photocatalytic dye degradation and carbon monoxide oxidation) of lithium cobalt oxide and chemically treated lithium cobalt oxide powders. By manipulating the morphology and defect structure of lithium cobalt oxide, the catalytic performance was significantly enhanced. These changes were examined using scanning electron microscopy, surface area analysis, and X-ray photoelectron spectroscopy. The catalytic performance of these powders was investigated through photocatalytic dye degradation and the catalytic oxidation of carbon monoxide. In summary, this work has demonstrated a significant step forward in understanding the structure-property-processing relationships of the exfoliation of lithium cobalt oxide forming cobalt oxide nanosheets advancing these materials towards technological and industrial relevance.