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ItemEngineering High-Efficiency Adsorption Contactors via 3D Printing of Microporous Polymers(Georgia Institute of Technology, 2019-12-10) Zhang, FengyiAdsorption is a promising energy-efficient separation process, which selectively removes one or several components from a mixture by transporting a fluid through a mass transfer contactor. The most traditional mass transfer contactor design is a packed bed of adsorbent pellets, which suffers from high pressure drop, low mass transfer rate, difficulty in heat integration, etc. State-of-the-art structured mass transfer contactors have been developed to address these problems. For instance, hollow fiber sorbents can achieve rapid temperature manipulation by flowing heat-exchange media through the bore channels, and monoliths provide uniform fluid channels to minimize pressure drop. However, limited by manufacturing techniques, existing structured mass transfer contactors struggle to address all of the aforementioned problems with one structural design. 3D printing techniques can fabricate complex architectures without molding-based approaches, which is suitable for rapid prototyping of novel mass transfer contactor designs. The overarching goal of this thesis is to engineer high-efficiency adsorption contactors via 3D printing of microporous polymers. To achieve this goal, three objectives were established: (1) develop 3D printing techniques that can process adsorptive materials and generate hierarchical porosity, (2) prototype scalable mass transfer contactors with optimized energy efficiency, (3) perform proof-of-concept adsorption experiments to demonstrate the advantages of 3D printing in mass transfer contactor fabrication.
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ItemThe PH dependent mechanisms of peptide bond cleavage(Georgia Institute of Technology, 2019-12-09) Sun, YiThe origin of life under prebiotic conditions has been an unsolved mystery for decades. Amino acids were available under prebiotic conditions, and different approaches of amino acids condensation into proto-polypeptides have been well designed, giving rise to a prebiotic soup with various peptide sequences. The emergence of functional biopolymers involves not only polymerization into longer species, but also the selective process with some species being protected and enriched over time. In this project, we treated peptide bond cleavage as the driving force for the selection process, by reshuffling peptide sequences and thus increasing the rate of search through sequence space. As a result, understanding the reaction mechanisms and quantifying the degradation kinetics of various peptide species is necessary to design a prebiotically plausible system that can demonstrate chemical evolution. In this project, we conducted fundamental research studies to understand the impact of pH on the peptide degradation reaction kinetics and mechanisms. The degradation rate of the amide bonds in oligopeptides in aqueous solution is pH-dependent and is suggested to involve two distinct mechanism: direct hydrolysis (herein termed “scission”) and backbiting. While amide degradation was studied previously using various peptides, no systematic study has been reported addressing the separate rates of amide bond degradation over a wide pH range via these two mechanisms. In this study, the degradation kinetics of several short oligopeptides, specifically the glycine dimer, trimer, and cyclic dimer, as well as the alanine trimer, were measured at 95oC over a range of pH conditions using 1H NMR. The rate constants were obtained by solving the differential equations based on mechanistic models and elucidate the favored reaction pathway under acidic, neutral, and basic pH conditions. The degradation rate of the glycine trimer is much faster than the dimer under the acidic and neutral pH conditions. The glycine dimer degradation rate is highest under acidic and basic conditions, while the glycine trimer degradation rate is highest under neutral pH conditions. The results suggest that while the glycine dimer undergoes ring opening purely through a scission reaction mechanism, the glycine trimer is degraded through both backbiting and scission reaction mechanisms. At an acidic pH of 3, both mechanisms are active, while at neutral pH backbiting is dominant. In contrast, at a basic pH of 10, scission dominates.
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ItemComputational Modeling of Adsorption of Complex Molecules in Metal-Organic Frameworks(Georgia Institute of Technology, 2019-11-01) Agrawal, MayankMetal-organic frameworks (MOFs) are nanoporous materials that have organic parts connected to metal nodes constructing a crystalline structures. MOFs are intrinsically flexible in nature, however, general practices in computational studies of MOFs assume the structure to be rigid during simulations. In this thesis, we focus on the effects of framework flexibility in MOFs on their adsorption properties. We first divided the flexibility in MOFs into two categories: flexibility with constant volume (ΔV=0) and flexibility with volume change (ΔV≠0). We then demonstrated that flexibility with ΔV=0 in MOFs can affect their adsorption at dilute loadings and multicomponent adsorption significantly but have negligible effects on the single component adsorption at high loadings. Following this work, we studied MIL-53, a MOF that show the flexibility ΔV≠0 and concluded that the flexibility with ΔV≠0 can significantly affect even the single component adsorption in MOFs. In the second half of the thesis, we focused on the adsorption and diffusion properties of chemical warfare agents (CWAs) and their simulants in MOFs. We compared the Henry constants of two CWAs, sarin and soman, with their simulants to study whether the available simulants are accurately able to mimic the CWAs’ adsorption properties. We then extended this study to calculate diffusion coefficients of CWAs and simulants. Our results showed that dimethyl-methylphosphonate (DMMP) is the best simulant available to mimic adsorption and diffusion properties of sarin while dimethyl nitrophenylphosphonate (DMNP) is the closest simulant to predit soman’s adsorption properties. Finally, we performed a literature meta-analysis to assess the frequency of replicate materials synthesis and found that less than 12% of MOFs have been replicated in a published report. The methodology and the findings of this thesis advance the scientific knowledge on adsorption and diffusion in nanoporous materials and suggest ways how the research community can improve replicability of these materials.
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ItemElectrokinetics, Transport and Stability of Metal/Electrolyte Interfaces in Secondary Batteries(Georgia Institute of Technology, 2019-10-30) Archer, Lynden A.
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ItemAtomistic characterization of metal-organic frameworks for sub-ambient pressure swing adsorption of post-combustion CO2 capture and separation(Georgia Institute of Technology, 2019-10-28) Park, JongwooDeveloping cost-effective and less energy-intensive carbon capture processes for dilute CO2 sources is of high interest. Adsorption-based CO2 capture such as pressure swing adsorption (PSA) is one promising approach to this challenge. PSA and other cyclic adsorption processes are materials-enabled separations that use porous adsorbents, including metal-organic frameworks (MOFs). This thesis examines post-combustion carbon capture in sub-ambient PSA, a potential route to an effective adsorption process, using MOF materials via molecular modeling. We first estimated the reproducibility of CO2 adsorption isotherm measurements in MOFs via literature meta-analysis. This chapter provides a comprehensive summary of the state of knowledge regarding CO2 adsorption in MOFs and its implications for molecular modeling of adsorption in MOFs. We then examined the upper bounds on CO2 swing capacity in sub-ambient PSA by Grand Canonical Monte Carlo (GCMC) simulation of an extensive collection of MOFs. A wide variety of MOFs was found to have swing capacity exceeding 10 mol/kg at sub-ambient temperatures provided that MOFs are appropriately selected based on their physical properties. We also assessed the capability of simple proxies for adsorbent performance and approximate models of cyclic adsorption to predict the outcomes of detailed process models of adsorption-based CO2 capture processes. To this end, we discuss the correlations between predictions from the simpler models and detailed process models. As a separate contribution, molecular modeling of chemical warfare agents (CWAs) adsorption in MOFs was analyzed. Molecular models of adsorption of CO2, CWAs or other molecules typically employ a rigid framework approximation for computational convenience. All real frameworks including MOFs, however, have intrinsic flexibility due to thermal vibrations. We examine the implications of this simple observation for quantitative predictions of the properties of adsorbed CWAs.
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ItemShape-Selective Growth of Nanoscale Materials: Insights From Multi-Scale Theory and Simulation(Georgia Institute of Technology, 2019-10-16) Fichthorn, KristenMetal nanocrystals have gained tremendous attention due to their superior performance in various applications, ranging from selective catalysis to electronic devices to plasmonic applications, such as photovoltaics and sensing. The properties of nanocrystals are highly sensitive to their size and shape. To this end, solution-phase synthetic protocols have been highly successful at producing a variety of nanocrystal structures. However, great challenges remain in achieving high selectivity to particular nanostructures. A significant difficulty lies in understanding and controlling shape evolution in these systems. A deep, fundamental understanding of the phenomena that promote selective growth in these syntheses would enable tight control of nanostructure morphologies in next-generation techniques. I will discuss our efforts to understand the workings of PVP, a polymer capping molecule that facilitates the formation of selective Ag nanoparticle shapes. In these studies, we use first-principles density-functional theory (DFT) to characterize the binding of PVP repeat units to Ag(100) and Ag(111) surfaces. To understand the solution-phase binding of PVP to these Ag surfaces, we develop a new metal-organic many-body force field with high fidelity to DFT. We implement this force field into molecular-dynamics (MD) simulations to characterize the potential of mean force and the mean first-passage times for solution-phase Ag atoms to reach PVP-covered Ag facets. Using these mean first-passage times, we predict kinetic shapes of large Ag nanocrystals (around 100 nm) and show that these should be {100}-faceted cubes. We also use MD simulations to characterize the interfacial free energies of PVP-covered Ag facets in solution. The thermodynamic shapes that we predict in these calculations are truncated octahedra, with a predominance of {111} facets. These findings are consistent with experimental observations that sufficiently small Ag nanocrystals tend to have shapes with a predominance of {111} facets and larger nanocrystals become {100}-faceted during solution-phase growth in the presence of PVP. Though our studies are consistent with experiments that demonstrate nanocube growth can be directed by PVP alone, many studies have demonstrated that more robust nanocube syntheses can be achieved in the presence of halide additives. We use DFT-based ab initio thermodynamics calculations to probe the influence of chloride on Ag nanoshapes. Consistent with experiment, these calculations indicate that chloride adsorption alone can lead to truncated Ag cubes. “Late breaking” calculations indicate there is a synergistic interaction between Cl and PVP, whereby the combination of these two additives can lead to “pointy” Ag cubes.
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ItemMultiscale Modeling of Tissues, Treatments, and Toxicology(Georgia Institute of Technology, 2019-10-09) Ford Versypt, Ashlee N.The Systems Biomedicine and Pharmaceutics research lab at Oklahoma State University led by Dr. Ford Versypt focuses on developing and utilizing multiscale systems engineering approaches including mathematical and computational modeling to determine and understand the mechanisms governing physiological effects of various chemicals, e.g., pharmaceutical drugs, toxins, metabolites, and hormones, on human and animal tissues. We specialize in modeling the transport processes and chemical interactions related to both natural and engineered biomedical and pharmaceutical systems. We also develop and refine the computational software elements to support multiscale modeling of such systems. We draw from an interdisciplinary skillset in chemical engineering, pharmaceutics, physiology, applied mathematics, and computational science. In this seminar, vignettes of recently published work from the lab in four different lines of research will be highlighted including (1) the immune system interplay with tuberculosis granulomas, (2) metastatic cancer spread, (3) bumblebee behaviors in response to chronic exposure to pesticides, and (4) glucose-stimulated damage to kidney cells in diabetes and preventative pharmaceutical treatments. The latter area has recently been funded by an NSF CAREER award and exemplifies the integration of teaching, research, and outreach.
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ItemWhy Are There So Few Female Faculty Members in Several STEM Fields? What Needs To Be Done?(Georgia Institute of Technology, 2019-09-11) Kuck, ValerieSince 2009 women have received a majority of the doctoral degrees granted by U.S. institutions.In several scientific fields women have made great strides, whereas in a number of STEM areas the progress has been substantially slower.ln 2017 women received 53% of the doctorates in Biological and Agricultural Sciences and 70% in the Health and Medical Sciences.In contrast, women earned only 23% of the doctorates in engineering, 25% in mathematics and computer sciences, and 34% in the physical and earth sciences.Over the years, the percentage of tenure-line female faculty members in the physical sciences, engineering and mathematics has remained low. Findings from an analysis of the responses to surveys and site visit discussions that involved over 1200 administrators, chemistry and chemical engineering faculty members, graduate students and post-doctoral fellows will be discussed.The hiring rate of female faculty members and factors contributing to their career choices will also be addressed.
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ItemWorld’s First Commercial CO2 to Methanol Plant(Georgia Institute of Technology, 2019-08-28) Richter, ChristaanThe George Olah CO2 to methanol plant, commissioned in April 2012, currently produces ~ 5 million liters/year renewable methanol and capture and convert up to ~ 5600 ton CO2/year [Lim 2016, Nature, 526(630)]. This Carbon Recycling International (CRI) plant is located in Svartsengi, near Grindavik, Iceland. The process was originally developed by a small CRI team in Reykjavik, and has undergone several iterations to arrive at the present state of technology and functionality. Taking the process from pilot scale to industrial scale was not trivial. Several difficulties encountered along the way were resolved to arrive at the current robust version of the technology. The high purity renewable methanol currently produced is sold as gasoline additive, similar to ethanol in the USA. Perhaps the most consequential lesson learned from this enterprise is that producing methanol from CO2 need not be as expensive as most experts estimated; the production cost of the ‘green methanol’ produced at the George Olah plant is only approximately twice that of natural gas derived methanol. A second interesting lesson involves the optimal process configuration: There exist two viable catalytic routes to convert CO2 to methanol. The most familiar option is to first reduce CO2 to CO through the RWGS reaction and then reduce CO with H2 to methanol in a second step or reactor. The CRI process instead implements the direct hydrogenation of CO2 with H2 over a mixed metal oxide catalyst. The presentation will include a brief history of the R&D and early development of the process, followed by a discussion of selected process features. Currently two world-wide implementation opportunities are actively pursued, namely the transformation of stranded H2 into a liquid commodity and a combined CCU and energy storage option for intermittent renewables. The presentation will conclude with a motivation for the ongoing research addressing the main barriers to bringing renewable CO2-derived methanol even closer to becoming cost competitive with refinery CH4-derived methanol.
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ItemThe Use of Selective Polymerization of Poly(Methyl Methacrylate) for Area-Selective Masking of Nanoscale Semiconductors(Georgia Institute of Technology, 2019-08) Weiss, TrentNanowire transistor research has intensified in the past two decades due to the need for a novel idea to improve upon shortcomings associated with the modern transistor. A prevailing shortcoming in conventional transistor fabrication is limited throughput due to top-down fabrication steps such as lithography. One solution of interest is the nanowire heterostructure transistor which is fabricated in a bottom-up approach and leverages selective surface chemistry to controllably mask specific segments of the structure. The purpose of this work is to use polymers for selective surface chemical treatment on semiconductors enabling selective deposition or annealing of a dielectric by masking specific substrate chemistries. This occurs in a bottom-up fabrication process. The dielectric will act as the gate oxide for a nanowire transistor. Prior research has indicated that polymers can prevent various molecules from reaching a substrate surface due to their dense network. In this study, atom transfer radical polymerization is utilized to create a soft mask that is selective to silicon. The polymer of interest, poly(methyl methacrylate), is grown on initiating groups anchored to a silicon surface to attain a desired thickness. The intermediate steps are optimized for the best possible performance. The polymer is then subjected to atomic layer deposition with aluminum oxide to determine the stability of the polymer and its practicality as a mask for oxide deposition. These experiments may elucidate a method for gate oxide formation on a nanowire heterostructure. Success could have significant impact on this field and would be the next step to attaining functioning nanowire transistors for use in everyday devices.