Date of Award
Fall 2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemical and Environmental Engineering (ENAS)
First Advisor
Plata, Desirée
Abstract
Nanotechnology’s perceived maturity motivated the assessment of the environmental impacts of the industry in anticipation of the large-scale production of engineered nanomaterial (ENM). However, the relatively early evaluation of ENM risks posed the challenge of discerning relevant use and release scenarios of emerging materials. Further, early evaluation of nanomaterial production efficiencies estimated that nanomaterial syntheses have exceptionally high waste-to-product ratios compared to other materials (e.g., bulk and fine chemicals and pharmaceuticals). Identifying industrially relevant ENMs and their specific synthetic constraints offers an opportunity to influence the manufacturing process to minimize environmental impacts. The first part of this dissertation (Chapter 2) surveyed twenty-five ENMs to assess the status and scale of nanotechnologies from a bird’s eye view. The industrial relevance of ENMs was evaluated based on the following metrics: technology readiness level, annual global production volumes, synthetic efficiencies, and projected annual market growth rates. Further, global ENM production volumes were placed in the context of global anthropogenic element cycles for the first time. Considering the nanomaterial space en masse, graphene emerged with a unique industrial profile, i.e., high global past and projected production growth rates, diverse applications and corresponding exposure routes, and low synthetic/material efficiencies. Next, this dissertation focused on the investigation of graphene production via chemical vapor deposition (CVD). The widely recognized potential of catalytic CVD as the most promising scalable manufacturing approach for the controlled growth of large-area, high-quality graphene has yet to be fully realized in the absence of a comprehensive understanding of the formation mechanism. Notably, limited knowledge of the gas-phase dynamics, confined mostly to theoretical studies, precludes complete mechanistic insight, efficient resource utilization, and hazardous by-product emissions mitigation. We characterized the gas-phase dynamics of graphene CVD growth (Chapter 3) across a set of low-carbon and low-hydrogen conditions. Experiments were carried out at ambient pressures using a custom-built reactor, which enabled (1) the decoupling of pressure regimes between the annealing and growth phases, and (2) fast-cooling via mobile furnace. Analysis of the gas-phase compositions indicates that C2 and C3 species are important intermediates in the formation of graphene. Environmental impacts of the growth phase were quantified, including hazardous emissions, carbon conversion efficiencies, and E-factors (waste-to-product ratios). Contributions of this chapter to the fundamental understanding of graphene formation can inform the rational design of synthetic strategies with the potential to enhance material and environmental performance (e.g., controllable synthesis, increased carbon conversion efficiency, decreased energy demand, and reduced hazardous emissions) by delivering relevant precursors. Finally, we recognized that a well-known industrial occupational hazard poses a pronounced risk in lab-scale CVD operations via exposure to refractory ceramic fibers released from the furnace lining (Chapter 4). We designed, built, and implemented an effective engineering control, which eliminated operator exposure to these hazardous fibers at low cost. The principal contribution of this dissertation is to the fundamental knowledge of the graphene formation reaction mechanism. Ultimately, exploiting these mechanistic insights to advance the synthetic approach will enable material design at the atomic level, i.e., the controlled production of graphene with tailored material properties and improved environmental performance. Importantly, insights into the environmental impacts of graphene production (Chapter 3) (1) can inform graphene synthetic design schemes with the potential to enhance our ability to manipulate material properties (Chapter 5), and (2) may enable the further upscaling of production. Thus, serving as an example of the alignment and convergence of environmental objectives with functional performance to implement “best chemistries” at scale.
Recommended Citation
Janković, Nina Zoran, "Graphene Formation via Catalytic Chemical Vapor Deposition: Environmental Implications of Synthetic Design" (2022). Yale Graduate School of Arts and Sciences Dissertations. 743.
https://elischolar.library.yale.edu/gsas_dissertations/743
