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Nanomaterials are widely used in a variety of applications such as opto-electronics, energy production and storage, and bio-medical applications due to their unique optical, catalytic, electronic, and mechanical properties. Most of the nanomaterials offer a plethora of modifications in their structure, composition, morphology, and dimensionality that can lead to the manipulation of their physiochemical properties. Thus, this dissertation presents insight into two types of compelling nanomaterials: carbon nanodots (CNDs) and transition metal dichalcogenides (TMDs), investigating their optical and electrocatalytic properties respectively.   Carbon nanodots (CNDs) are a promising class of photoluminescent nanomaterials that hold a significant potential in many optoelectronic applications. The photoluminescence behavior of CNDs highly depends on their structure and chemical composition. The complexity of the structure and chemical composition of CNDs makes it difficult to uncover the origin and behavior of the photoluminescence of these materials. Hence, this work first provides fundamental insight into the photoluminescence of low-oxygen-content CNDs derived from polycyclic aromatic hydrocarbon pyrene. In this study, the formation of bright emitting molecular fluorophore was identified through a rigorous separation scheme using column chromatography and solvent-induced extraction. Further, the distinct structure and optical properties of the molecular fluorophore  and CNDs were identified using different structural and morphological characterization techniques and bulk fluorescence measurements.  Transition metal dichalcogenides (TMDs) are another intriguing class of nanomaterials that are abundant and cost-effective alternatives to expensive and precious electrocatalysts for various electrochemical reactions. 

TMDs can be modified by changing their phase and dimensionality, and their layered nature makes them suitable for heterostructures. Consequently, TMD nanostructures have gained attention as electrocatalysts for hydrogen evolution reactions (HER) due to the increasing demand for low-cost green hydrogen production. Thus, secondly, a greener and reliable top-down synthesis approach for producing highly exfoliated ultrathin crystalline WS2 nanosheets using a modified liquid phase exfoliation is presented in this work. The ultrathin pristine WS2 nanosheets showed a promising electrochemical activity for HER, and the correlation between the structure and the electrocatalytic activity was carried out through Operando Raman spectro-electrochemical measurements. Further, TMD nanostructures are excellent candidates to use as support materials for metal single atom catalysis (SACs). Pt single atom catalysts (SACs) supported on transition metal dichalcogenides (TMDs) are promising electrocatalysts in the green hydrogen production by proton exchange membrane (PEM) water electrolysis. Hence, thirdly this study presents a novel and a convenient synthesis of Pt SACs and clusters supported on WS2 (Pt/WS2) using photonic curing, with improved efficiency for hydrogen evolution reaction (HER). This catalyst design constitutes enhanced atomic utilization, higher number of accessible active sites and catalytic activity modulation of Pt through electronic metal support interactions (EMSI). This work as a whole provides insight on the fundamental aspects of intricate properties of two types of nanomaterials in unveiling the correlation between structure, properties, and application.

The increasing atmospheric CO₂ concentration causes significant concern about global warming and its environmental impact. Industrial sectors, including power generation, transportation, and production factories, contribute most of the anthropogenic sources of CO₂ emissions. Researchers search for methods to mitigate these CO₂ emissions without compromising the benefits of industrial processes, including CO₂ capture, utilization, and sequestration (CCUS). Post-combustion carbon capture (PCCC) by amine scrubbing is the most technology ready CCUS, with various pilot-scale projects worldwide showing small-scale to fully operational plants. While researchers have made significant progress in amine scrubbing, they strive to improve the efficiency and economics of these plants. One challenge they face includes solvent degradation due to flue gas constituents and temperature effects. 

            This dissertation focuses on the degradation byproducts' impact on the parent amine solvent. It explores knowledge about degradation byproducts in amine solvents used in carbon capture, including what degradation products, how much, how they form, and what impact these products have on the capture process. The dissertation splits into three sections where the first focuses on three thermal degradation byproducts of ethanolamine (MEA): oxazolidine-2-one (OZD), N-(2-hydroxyethyl)-ethylenediamine (HEEDA), and N-(2-hydroxyethyl)-imidazoline-2-one (HEIA) interactions in the solvent. The second focuses on O₂ solubility and the role O₂ plays in oxidative degradation. The final section discusses some initial degradation results of a new class of amine carbon capture solvents called water-lean (WL) solvents. 

            The discussion of the thermal degradation byproducts began by describing thermal degradation byproducts that react with CO₂ with and without the parent amine present. The species found were explored further at the liquid-vapor barrier to explain how the species interact with each other. The degradation byproducts with unhindered primary or secondary amines, such as HEEDA, create a pseudo-blended solvent that could improve the solvent's capture performance as it improves the CO₂ solubility in the amine solvents. In contrast, hindered structures like HEIA and OZD will minimally impact the speciation in the amine solvents. However, these species revert to the carbamate at lower CO₂ concentrations or higher temperatures and further react with CO₂ concentrations. 

            The discussion on O₂ solubility in the different amine solvents and the role O₂ plays in oxidative degradation began by validating a dissolved oxygen (DO) electrochemical probe by redox titrations following the Winkler method. The validated probe then measured the DO or O₂ solubility in different amine solutions under various conditions found in CO₂ capture. It also explored how additives used in advanced amine solvents impact the O₂ solubility in the solution. The redox titration measured the DO slightly higher than the probe, validating the electrochemical probe for amine solvents. However, solvents with transition metals that can oxidize iodine cannot use this method to measure the DO in the solvents. In the amine solvents, the diamines measured higher O₂ solubility than the alkanolamines, and the alkanolamines measured higher O₂ solubility than the amine diols. In addition, as the number of hydrogens bonded to nitrogen decreased, the O₂ solubility decreased. The ionic effect on O₂ was also demonstrated, where the DO decreased with increased CO₂ loading. However, there was still DO, indicating that the solvents will undergo oxidative degradation at high loadings. Furthermore, the solvents minimally impacted the O₂ solubility except those that can react with CO₂. The additive 2-mercaptobenzathiazole (MBT) decreased the DO concentration until it exhausted its capacity to react with O_2, and then the DO rose back to the levels at equilibrium. The additive sodium metavanadate increased the DO concentration because metavanadate can react with O₂, increasing the oxidative potential in the solution. The final section described the initial findings of degradation byproducts of WL solvents and what the organic cosolvent does in the system, including some initial discussions on how the organic cosolvent impacts an amine solvent, how the solvent phase separates at higher loadings due to an ionic effect in the cosolvent, and what compounds were found during oxidative degradation experiments.

KEYWORDS: Carbon Capture, Amine Scrubbing, Degradation, Amine Oxidative Degradation, Amine Thermal Degradation, Water Lean Solvents

The long-anticipated implementation of using renewable sources such as solar and wind to meet the world’s energy demand is still limited by not having appropriate grid-level energy storage systems on a global scale. When considering grid-scale energy storage solutions, environmental concerns, and techno-economic viability play a crucial role in the practical implementation of such technology. To address this, redox-active organic molecules (ROMs) have been explored for many uses including serving as redox-active molecules in redox flow batteries (RFBs) and providing overcharge protection in lithium-ion batteries (LIBs). Nevertheless, in order to be a major player in electrochemical energy storage, further optimization of ROMs with respect to performance and stability is required. Achieving optimum performance and stability mandates a molecular-level understanding of the interactions between chemical compounds, solvent molecules, and any other supporting solutes in the medium. Hence we approached this research question in the context of redox-active organic molecules for non-aqueous redox-flow batteries (NARFBs) by narrowing down the chemical space to a few classes of molecules. Herein, we extensively studied it from multiple perspectives such as; (1) Examining the correlation of molecular structure of redox-active organic molecules (ROMs) to solubility at different states of charge using quantitative structure-property relationships (QSPR), (2) Investigating the effect of electrolytes (counter-anions) on the solubility of ROMs using molecular dynamics (MD) simulations interfacing with experiments and multiple linear regression, (3) Exploring the concentration dependence of electrolytes with MD to explain experimental behavior at very high concentrations and to identify optimum concentration ranges for NARFBs, and (4) Probing Bulk and Interfacial Interactions of ROMs in complex solutions under an applied potential using classical MD simulations. This multi-approach endeavor has informed us of the strengths and limitations of predictive modeling in non-trivial molecular systems with limited data and high variability and boundaries related to improving the solubility of ROMs using structural modifications. Thus, in our continued efforts, we discovered that the solubility of these ROMs can be dramatically improved up to three-fold by switching the counter-anion due to the flexibility and size of the counter-anions. Our exploration of high-concentrated electrolytes implies that changes to supporting electrolyte concentration are significantly more impactful to the solution’s transport properties with the crowding of electrolytes leading to non-Newtonian fluid-like regimes. Expanding classical MD simulations to capture bulk and interfacial properties opens up a new paradigm of using computationally less-expensive methods for high-throughput simulations. To address the limitations we encountered in this effort, we also developed systems to automate similar MD simulations and analyses with the goal of producing large datasets that may pave the path to generating machine-learning models to predict different performance matrices efficiently in the future. In summary, the results and theoretical insights gained through these collective efforts would set the foundations for optimizing the performance and stability of ROMs thus helping experimentalists design better materials for electrochemical energy storage.

Conjugated polymers (CPs) are an emerging class of materials that are attractive for many applications due to their low cost, flexibility, and ease of processing. Both chemical and electrochemical doping of CPs is done to alter important properties such as their electrical conductivities and optical absorbances. This ability to tune their properties allows for their use in devices such as organic electrochemical transistors (OECTs) for biosensing and bioelectronics, electrochromic devices for color changing windows, as well as wearable thermoelectrics to use body heat to power wearable electronics. There are several factors that can influence the properties of doped CPs including doping level, film morphology, and the dopant or counterion used in the process. One disputed topic is what influence the ion size within the electrolyte has on the properties of electrochemically doped CPs. These ions balance the positive or negative charges on the backbones of doped CPs and their size can influence their interactions with the charge carriers and the overall morphologies of the films, therefore influencing their optical and electronic properties. This dissertation focuses primarily on understanding the influence of anion size on the properties of doped CPs as a function of their respective doping level. 

            The work presented here first focuses on the electrochemical doping ability of two benchmark CPs regioregular and regiorandom poly(3-hexylthiophene), rr- and rra-P3HT respectively, in electrolytes with anions of different sizes. Films of rr-P3HT are semicrystalline while those for rra-P3HT are amorphous allowing us to probe anion size as a function of CP morphology. Measured oxidation potentials and UV-vis data suggest that the larger anions are positioned further from the backbone of the polymer with two distinct polaron/bipolaron transitions apparent for rr-P3HT and only one for rra-P3HT. Further investigation into these materials as a function of doping level shows two distinct regimes that are important to consider. In the low doping regime, Coulombic interactions with the CP backbone and counterion largely contribute to the film’s properties with the larger anion having a higher electrical conductivity and lower Seebeck coefficient than the smaller and more Coulombically bound anion. Alternatively, in the high doping regime all charges are essentially “free” and CP morphology has the largest impact on film properties. In this case, the larger anion is more disruptive to the film morphology granting a lower electrical conductivity but higher Seebeck coefficient. At all measured doping levels, the films with the larger anions display higher thermoelectric power factors, proving that counterion size is an important consideration for these devices. 

According to the center for disease control (CDC), an estimated 1.7 to 2.2 million persons die from waterborne diseases annually. The majority of individuals dying from diseases resulting from unsafe drinking water, such as diarrhea and gastroenteritis, are children. This has in turn created a global water crisis. Different methods have been developed to treat contaminated water in response to the global water crisis such as adsorption, filtration, ozonolysis, catalysis, etc. Of the methods available, filtration via polymeric membranes has been one of the most successfully applied. A membrane is a thin semi-permeable barrier (often made of a polymer) used to separate differing phases in a media under pressure. Membrane filtration is ideal for water treatment due to high rejection and throughput, as well as ease of integration into other water treatment systems. Unlike other methods of water treatment, membrane filtration can be easily tuned to target specified contaminant at different size and pressure levels.

Syed Joy will be presenting his doctoral thesis, "Understanding of Processing Additives Influence in Tin Halide Perovskites: ����vlog�ٷ����, Defect, and Photovoltaic Performance."

Perovskites have emerged as a promising candidate for low-cost production of solar cells. However, the most critical barrier for commercialization of perovskite solar cells (PSCs) is the inadequate stability of the organic metal halide perovskites (OMHPs). The degradation of OMHPs is induced by light, heat, air, and electrical bias. The known degradation pathways involve the oxidation of I^- and Sn²⁺, dissolution of perovskites by moisture, irreversible reactions with water, ion migration, and ion segregation. To improve the stability of OMHPs various methods are adopted, such as additive engineering, perovskite surface treatment, and composition engineering. Surface ligands are used on top of perovskite thin films to passivate the undercoordinated ions leading to improved charge collection efficiency and stability of PSCs. However, not all surface ligands stay at the surface of the perovskite. Some of them penetrate the perovskite layer forming reduced dimensional phases at the surface. This kind of behavior not only alters the electronic nature at the interface, but also negatively affects the stability of the OMHPs compared to surface ligands that remain only at the surface. On the other hand, additives are commonly used to reduce defects in bulk of the perovskites and thus improve their stability. They improve the stability of OMHPs by controlling the morphology of OMHP thin films, improving the thermodynamic stability of Sn²⁺ and I^-, and lowering the ion migration and ion segregation. The stability of OMHPs is also significantly improved by incorporating bulky organic cations into the perovskite composition. Although these routes for improving the stability are optimistic, it is not clear how the surface chemistry of OMHPs and chemical nature of additives or organic cations affects stability.

Surface chemistry of OMHPs can be tuned to control the extent of ligand penetration by changing the composition and processing conditions of OMHPs. To this end, it is important to find out what affects the extent of ligand penetration. We find that the perovskite compositions used in this study have little or no effect on ligand penetration. However, the perovskite film processing conditions have a greater effect on ligand penetration. Using a family of phenethylammonium iodide (PEAI) with different substituents on the benzene ring, we show that the ligand penetration can be affected by type of substituents as well. Stabilizing the perovskite precursors is also important as degraded precursors lead to defective perovskites with poor stability. Here, we show that additives influence the thermodynamic stability of Sn²⁺ and I^- by changing the acidity of the precursor solutions. Using additives with a range of pKa we find that additives with higher pKa provide a more stabilizing chemical environment for Sn²⁺ and I^-. 

It is known that bulky organic cations improve the stability of OMHPs by shielding the metal-halide octahedra from air. However, how the structure of the organic cations affect the air, oxygen, and moisture stability of the OMHPs is not well understood. Using twelve different organic cations we show that the stronger the attractive interactions between the organic cations in two dimensional (2D) OMHPs the higher is the stability. The stability of 2D-OMHP thin films decreases as the orientation of the 2D sheets deviates from planarity with respect to the substrate plane.

Abstract: Over the years, nanomaterials research has advanced towards discovering versatile and readily accessible materials tailored for a diverse range of applications. A comprehensive understanding of materials’ phases and their transformations are integral to this effect to enable better synthetic control as well as the functionalization of nanomaterial properties. Among advanced characterization techniques, the transmission electron microscope (TEM) is a powerful tool that provides direct access to the nanoscale and, therefore, an indispensable tool in studying fundamental materials problems. This dissertation discusses several nanomaterial systems where TEM tools and techniques are utilized to gain a deep understanding of their chemistry. 

This dissertation focuses on structural and phase transformations of nanomaterials using in situ heating in the TEM, which allows direct observation of these dynamic processes. Reported here are studies of the phase transformation and stabilization of the mackinawite phase of iron(II) sulfide nanoplatelets, the structural transformation of gold-catalyzed tin(IV) oxide nanowires into gold core/tin(IV) oxide shell nanowire heterostructures, and finally the interaction between aluminum oxide and lead (at. 17%) lithium alloy proposed for use as a coolant in nuclear fusion reactors. These studies showcase the significance of knowledge of the mechanistic details of phase transformations, with the eventual goal of being able to determine and control structure-property relationships. 

KEYWORDS: phase transformations, nanomaterials, transmission electron microscopy (TEM), in situ TEM

Abstract: Compared to ubiquitous functional groups such as alcohols, carboxylic acids, amines, and amides, which serve as central “actors” in most organic reactions, sulfamates, phosphoramidates, and di-tert-butyl silanols have historically been viewed as “extras”. Largely considered functional group curiosities rather than launchpoints of vital reactivity, the chemistry of these moieties is underdeveloped. Our research program has uncovered new facets of reactivity of each of these functional groups, and we are optimistic that the chemistry of these fascinating molecules can be developed into truly general transformations, useful for chemists across multiple disciplines. In the ensuing sections, I will describe our efforts to develop new reactions with these “unusual” functional groups, namely sulfamates, phosphoramidates, and di-tert-butyl silanols.

Abstract: Low-dimensional (LD) organic-inorganic hybrids have recently emerged as exciting electrocatalytic nanomaterials in which the 0D-1D, 1D-2D or 2D-2D electrochemical interfaces can be finely tuned to generate unprecedented features that are not perceived in the individual counterparts (Scheme 1). 

Low-dimensional interfaces have shown incredible advantages in regulating electron transfer, charge polarization, bonding energy and the adsorption energy of intermediates, thus markedly boosting crucial electrocatalytic parameters such as current density, onset overpotential and faradaic efficiency in many relevant energy conversion reactions including oxygen reduction (ORR), oxygen evolution (OER), and CO₂ electroreduction (CO₂RR). In this seminar, key learning points about the chemical aspects that govern the interfacial effects of low-dimensional hybrids in crucial electrocatalytic reactions will be provided based on both experimental and theoretical findings. The discussion will also cover an in-depth understanding of the heterointerface-electrocatalytic performance relationships as well as their impact for the fabrication of future energy-related devices.

Bio: Alain R. Puente Santiago received his Ph.D. degree in Physical-����vlog�ٷ���� with distinction (July 2017) from the University of Cordoba, Spain. He has worked as a Research Fellow in Prof. Goodenough’s group (Nobel Prize in ����vlog�ٷ���� 2019) at the University of Texas at Austin in the development of nanocluster-based electrocatalytic materials. Currently, he is working as a Postdoctoral Associate in the Department of ����vlog�ٷ���� at the Florida International University. He has published 67 articles in very prestigious journals such as Journal of the American Chemical Society (7), ACS Sustainable ����vlog�ٷ���� and Engineering (5), Journal of Materials ����vlog�ٷ���� A (5), Angewandte Chemie (3), Nanoscale (3), ACS Applied Materials and Interfaces (2), Green ����vlog�ٷ���� (2), Chemical Society Reviews (2), Advanced Energy Materials (1) and Journal of Catalysis (1).Dr. Santiago’s articles have reached more than 2500 citations and an H index of 27 in the last 5 years. His research interests tackle the development of low-dimensional heterostructures for electrocatalytic, sensing, and energy storage applications.