Browsing by Author "Brgoch, Jakoah"
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Item A low-cost smartphone-based platform for highly sensitive point-of-care testing with persistent luminescent phosphors(Lab on a Chip, 2018-03) Paterson, Andrew S.; Raja, Balakrishnan; Mandadi, Vinay; Townsend, Blane; Lee, Miles; Buell, Alex; Vu, Binh V.; Brgoch, Jakoah; Willson, Richard C.Through their computational power and connectivity, smartphones are poised to rapidly expand telemedicine and transform healthcare by enabling better personal health monitoring and rapid diagnostics. Recently, a variety of platforms have been developed to enable smartphone-based point-of-care testing using imaging-based readout with the smartphone camera as the detector. Fluorescent reporters have been shown to improve the sensitivity of assays over colorimetric labels, but fluorescence readout necessitates incorporating optical hardware into the detection system, adding to the cost and complexity of the device. Here we present a simple, low-cost smartphone-based detection platform for highly sensitive luminescence imaging readout of point-of-care tests run with persistent luminescent phosphors as reporters. The extremely bright and long-lived emission of persistent phosphors allows sensitive analyte detection with a smartphone by a facile time-gated imaging strategy. Phosphors are first briefly excited with the phone's camera flash, followed by switching off the flash, and subsequent imaging of phosphor luminescence with the camera. Using this approach, we demonstrate detection of human chorionic gonadotropin using a lateral flow assay and the smartphone platform with strontium aluminate nanoparticles as reporters, giving a detection limit of ?45 pg mL?1 (1.2 pM) in buffer. Time-gated imaging on a smartphone can be readily adapted for sensitive and potentially quantitative testing using other point-of-care formats, and is workable with a variety of persistent luminescent materials.Item AAg2(M'xM1-x)[VO4]2: Synthesis and Structure-Property Relationships(2015-08) Bratsch, Michaela 1988-; Guloy, Arnold M.; Moeller, Angela; Jacobson, Allan J.; Brgoch, Jakoah; Yang, Ding-ShyueThis dissertation focuses on the synthesis and characterization of the AAg2(M’1 xMx)[VO4]2 series of compounds. These compounds are modifications of the parent type of compound, AAg2M[VO4]2. We have investigated the following parameters: i) the charge and size of the spacer ion (A), ii) the charge, size, and spin of the magnetic cation (M), and iii) the ratio (M’:M) of the solid solution series. In this research we specifically targeted the honeycomb (1:2) and kagome (1:3) lattices for the solid solution series, AAg2(M’1-xMx)[VO4]2. This provides an opportunity to tune the magnetic lattices by varying the M-site cations. The M-site cations utilized in this research are non-magnetic cations, Mg2+, Zn2+, In3+, and the magnetic cations, Ni2+ (S = 1), Co2+ (S = 3/2), Mn2+ (S = 5/2), Fe3+ (S = 5/2), and Cr3+ (S = 3/2). These cations provided an opportunity to probe different magnetic interactions in the compounds. The A-site cations that have been studied in this research were: Rb+, K+, Ba2+, Sr2+, and Ag+. With decreasing ionic radius, from Rb+ to Ba2+ the crystal structure is P3, and for Sr2+ and Ag+ the crystal structure is C 2/c. The structure and phase purity of the compounds were confirmed by XRD measurements. SEM-EDX was used to investigate the chemical compositions, and confirm the ratio of the M’ and M cations (stoichiometry). Raman spectroscopy in combination with DFT calculations has been conducted as a local probe to monitor the environment of the [VO4]3- unit and confirms that the surrounding of the [VO4]3- is in either a 1:2 (honeycomb) or 1:3 (kagome) ratio of M’:M. The thermodynamic properties of this series were investigated. These confirmed that the cations Ni2+ and Co2+ are ferromagnetic and follow a mean field theory behavior and that Mn2+, Fe3+, and Cr3+ are antiferromagnetic. The physical properties measurements indicate the bulk magnetic properties of the compounds are in agreement with the chemical composition. Neutron diffraction measurements performed on RbAg2(In1/3Cr2/3)[VO4]2 and AgAg2Cr[VO4]2 provided further information about the magnetic behaviors of these compounds.Item Advancing the capabilities of plasmonic and semiconductor nanostructures for light-powered applications(2022-04) Ngo, Nhat Minh; Lee, T. Randall; Guloy, Arnold M.; Harth, Eva M.; Brgoch, Jakoah; Varghese, Oomman K.Light-powered applications are attracting increasing attention in the rapidly developing field of nanomaterials, especially in photocatalysis and biomedical technologies. Such progress requires effective designs and fabrication methods for high-performance nanoparticles. The fabrication of nano-sized particles significantly increases the surface-to-volume ratio, which leads to cost reductions. Wet chemistry synthesis of nanoparticles offers precise control over the size and morphology of nanoparticles, as well as good scalability for bulk applications. Many light-active nanostructures suffer from shortcomings that arise from limited properties inherent to the nature of their structures as well as the inability to utilize the high-intensity region of the solar spectrum. Rational designs of new plasmonic nanostructures can lead to remarkably unique optical properties that offer emergent applications. Doping metal oxide semiconductors can tune the bandgap and recombination rate of the semiconducting nanoparticles, making them more effective photocatalysts. On the other hand, noble metal-semiconductor hybridizations can offer unique synergies that are beneficial for the intended applications. Chapter 1 of this dissertation provides a detailed review of an important class of plasmonic nanoparticles know as "metal nanostars". Chater 2 describes the synthesis and characterization of an entirely new metal nanostar; namely, semi-hollow gold-silver nanostars (hAuAgNSts). This unique bimetallic plasmonic nanostructures offers a new operational window in the ultraviolet and visible regions of the electromagnetic spectrum for metal nanostars that is complementary to the existing optical windows of conventional silver nanostars (AgNSts) and gold nanostars (AuNSts). The capability to tune the localized surface plasmon resonance (LSPR) peak of hAuAgNSts in the visible region enables their usage in many solar-powered applications, such as photocatalysis or photovoltaics, and makes better use of the high-energy flux of this region of the solar spectrum. Importantly, the fabricated bimetallic nanostars exhibit greater stability than traditional AuNSts. Chapter 3 of this dissertation reports a quick and easy method to fabricate cuprous oxide-coated silver core-shell nanoparticles Ag@Cu2O. The method offers tunable shell thicknesses, leading to highly tunable extinction behavior of the core-shell nanoparticles in the center of the solar spectrum. This semiconductor-plasmonic combination significantly reduces the recombination rate of photogenerated electron-hole pairs in the composite core-shell nanostructures; moreover, the Ag@Cu2O hybrid particles showed significantly enhanced hydrogen generation rates in photocatalytic tests. Chapter 4 of this dissertation describes facile procedures for the syntheses of uniform, monodisperse titanium dioxide (TiO2) and doped titanium dioxide nanoparticles. The bandgap and electron-hole recombination rates of the doped particles were successfully reduced by doping separately with niobium and tantalum. Dually-doped NTTO nanoparticles exhibited an even larger bandgap reduction compared to both singly doped NTO or TTO nanoparticle analogs. The photocatalytic hydrogen evolution rates of the doped TiO2 nanoparticles were also enhanced when compared to pristine TiO2 nanoparticles and reached the highest rate in the dually doped NTTO nanoparticles.Item Computation and Data-Driven Methods Toward Superhard Materials Design(2022-08-02) Zhang, Ziyan; Brgoch, Jakoah; Halasyamani, P. Shiv; Hoffman, David M.; Xu, Shoujun; Grabow, Lars C.High hardness materials as measured through Vickers microindentation testing are indis- pensable for a myriad of industrial applications. The development of new high hardness ma- terials has traditionally relied on trial-and-error methods or empirically derived designing rules. This has significantly hindered the development of novel superhard materials. The complex relationship between crystal structure, composition, bonding, and hardness also remains difficult to elucidate and requires more insight. This contribution employs compu- tational methods to understand the fundamental mechanical properties of hard materials and machine learning methods to design predictive models that can capture the complex composition-structure-property relationship of high hardness materials. Moreover, an un- supervised learning model is designed to capture the underlying crystal-chemical patterns in existing data and provide new chemical knowledge from the learning process. First, the influence of chemical bonding is studied on the mechanical properties of earth-abundant transition metal borides through density functional theory. These results showed that bonding optimization through elemental substitution can effectively tailor a material’s mechanical properties. Then, a machine learning model is developed to map the complex relationship between chemical composition, applied load, and Vickers hard- ness (HV ). Large-scale screening is further enabled by this new method for high hardness materials by directly predicting HV at various applied loads. More than ten thermo- dynamically favorable compositions are identified to be superhard, proving the machine learning model’s ability to find previously unknown materials with outstanding hardness. Then, the influence of temperature on hardness is studied by adding the measurement temperature as an additional variable in a supervised learning model. The reported model showed excellent performance in estimating the hardness decrease at elevated tempera- ture, which is extremely useful for identifying thermally-robust hard materials. Finally, this work overcomes the main limitation of supervised learning–sparse and small training datasets. This is one of the main reasons machine learning struggles to find materials that outperform the state-of-the-art. Unsupervised learning in the form of an anomaly detection framework is developed using an autoencoder architecture. The model is trained on known crystal structure data learning to distinguish normal crystal-chemical patterns from anomalies. Further analyzing the structural factors that contribute to high anomaly scores revealed that due to the unexpectedly short bond lengths in superhard materials, they are statistically considered anomalies among all inorganic materials. Together this dissertation provided insights on chemical bonding of structural materials, demonstrated highly efficient and accurate predictive machine learning models that captured the complex relationship between external factors and hardness, and provided advanced unsupervised anomaly detection methodologies to further understand rare materials’ properties.Item Computational Modeling and Advanced Synthesis Techniques for the Improved Design of Zeolite Catalysts(2015-12) Ghorbanpour, Arian; Grabow, Lars C.; Rimer, Jeffrey D.; Harold, Michael P.; Epling, William S.; Brgoch, Jakoah; Konstantinov, Ivan A.Zeolites are the most widely used catalysts in industry due to a unique combination of features such as porous structure and high surface area, voids and channels of molecular dimensions, tunable active sites, and environmentally benign properties. To realize their great potential requires a thorough knowledge of structure-function relationships for rational zeolite design. Active sites in zeolites are created by Al substitution of framework Si atoms in crystallographically different positions on the exterior or in the interior of zeolite crystals. This leads to heterogeneous chemical/kinetic behavior of various active sites, which can be employed to tune the activity, selectivity, and lifetime of zeolites in catalytic processes. On the experimental side of this project, we enhance the shape selectivity of ZSM-5, an important zeolite catalyst in the petrochemical industry, by manipulating its active site distribution. Therefore, an advanced synthesis method was designed to passivate the external surface of ZSM-5 particles and suppress the reaction of bulky reactants over the exterior of the catalyst particles. The inert overlayer growth is performed at very low thicknesses and in an epitaxial structure so that the mass transfer limitations due to the added layer is minimized and the activity of internal active sites is not compromised. We continue our investigation of the impact of heterogeneous distribution of active sites through atomic-scale modeling. Our density functional theory (DFT) simulation of H-ZSM-5 internal active sites reveal a large variation in the acidity and adsorption characteristics of 12 distinct active sites. The modeling of a test reaction, the dehydration of methanol to dimethyl ether (DME), indicates that the pore confinement effects that vary among different H-ZSM-5 active site locations result in nonidentical kinetic behavior through different extents of transition state stabilization. This heterogeneous performance not only causes different rates of reaction, but also impacts the dominant reaction mechanism at typical reaction conditions. The distribution of H-ZSM-5 active sites in the form of paired acid sites, more likely to form in Al-rich zeolites, is also studied, which shows evidence for significant adsorption and kinetic variations compared to isolated active sites.Item Computational Screening of Bifunctional Catalysts for CO and CH4 oxidation(2015-12) Doan, Hieu; Grabow, Lars C.; Harold, Michael P.; Epling, William S.; Brankovic, Stanko R.; Brgoch, JakoahModern advances in density functional theory (DFT) and computing power have allowed us to investigate catalytic reaction at surfaces in great details and with reasonable chemical accuracy. Based on fundamental knowledge of reaction mechanism and key surface properties, new catalysts can be designed and further tuned for optimal performance. In the recent literature, several examples of catalysts that perform multiple site-specific functionalities under steady-state reaction conditions have been reported. The most common systems are bifunctional catalysts where each of the two distinct sites preferentially catalyzes different reaction steps independently. In this dissertation, DFT calculations were used in combination with microkinetic modeling to explore bifunctional catalyst design strategies for CO and CH4 oxidation. Preliminary study suggested that there are theoretical limits for the achievable activity improvement and bifunctional catalysts do not necessarily outperform single-site catalysts. For CO oxidation on bimetallic surfaces, it was found that the optimal activity is not significantly altered when bifunctional mechanism are considered, but equally active bifunctional catalysts may be tailored from less active and cheaper components. In particular, when CO oxidation was probed on the novel RuPt core-edge nanocluster catalyst, a bifunctional mechanism that involves the delivery of two reactants from two different spatial domains to a reacting interface was used to explain the significant activity improvement. In the special case of CO oxidation on Au/TiO2 system, a new mechanism was proposed and water was identified as a co-catalyst in the reaction. To investigate the importance of the material gap in computational catalyst screening, complete CH4 oxidation was evaluated on different representative models of Pd catalysts. It was observed that, although quantitative results may vary significantly, the trend in reactivity is the same across all surface models. Extensive promoter screening was also performed on PdO(101) surfaces, and calculated data for CH4 activation suggested that there exists an additive effect upon promoter substitution at two distinct Pd sites on PdO(101). Our efficient screening strategy has led to predictions of several promising promoters for Pd catalyst for complete CH4 oxidation on the basis of intrinsic activity and resistance toward water inhibition and sulfur poisoning.Item Controlled Hydrothermal Synthesis and Structure-Property Relationships of Transition Metal Vanadates(2014-12) Sun, Kewen 1987-; Möller, Angela; Guloy, Arnold M.; Xu, Shoujun; Meen, James K.; Brgoch, JakoahThis dissertation focuses on the synthesis and structure-property relationships of multi anionic transition metal vanadates. Hydrothermal synthesis methods have been optimized and used to obtain compounds with intriguing structural features. Ba2XCu(OH)[V2O7] with X = Cl, Br crystallizes in a new structure type (Pnma, a ≈ 15.1 Å, b ≈ 6.1 Å, c ≈ 9.6 Å) which features pseudo-honeycomb 2[Ba2X]3+ layers and isolated 1[CuO2/2(OH)2/2O2/1]5- chains. Two polymorphs of the M2(OH)[VO4] compound were obtained with M = Mn (Pnma, a = 14.911(1) Å, b = 6.1225(3) Å, c = 9.1635(5) Å) and M = Cu (P212121, a = 6.0564(1) Å, b = 8.5581(2) Å, c = 14.954(1) Å). These two structures are similar with respect to the M–O‒M connectivity, which results in corrugated layers. The M6+x(OH)3[VO4]4-2z[V2O7]z series of compounds with M = Mn, Co, Mg, and Fe crystallize in the acentric P63mc space group with lattice parameters a ≈ 12.9 - 13.2 Å, c ≈ 5.1 - 5.3 Å featuring a metal-based framework with isolated chains of face-sharing [MO6]-units. BaMn9[VO4]6(OH)2 crystallizes in the space group P213 with a = 12.8417(2) Å and has the unique structural feature of a chiral paddle-wheel. Further investigations of thermodynamic properties reveal for: i) Ba2XCu(OH)[V2O7] an antiferromagnetic quasi 1D S = 1/2 Heisenberg system; ii) Cu2(OH)[VO4] an antiferromagnetically coupled 2D lattice with ferrimagnetic long-range order; iii) M6+x(OH)3[VO4]4-2z[V2O7]z an antiferromagnetic framework ferrimagnetically coupled to the incorporated chains; iv) BaMn9[VO4]6(OH)2 a canted antiferromagnet due to geometrical frustration.Item Controlling Crystal Morphology and Polymorph Selection Using Molecular Additives(2019-08) Clark, Robert J.; Palmer, Jeremy C.; Conrad, Jacinta C.; Rimer, Jeffrey D.; Kulkarni, Yashashree; Brgoch, JakoahCrystallization is relevant to a variety of important applications ranging from chemical refinement and pharmaceutical formulation to the design of novel materials for electronics and photonics applications. In these applied settings, successful outcomes require the ability to produce the desired crystal polymorph or structure that exhibits the critical functional properties needed for a particular application. Additionally, in many scenarios, material performance is strongly affected by the size, shape, and morphology of the produced crystallites. Unfortunately, controlling polymorph selection and crystal size and shape is often very synthetically challenging, providing a significant barrier to designing materials with optimal performance characteristics for targeted applications. In this thesis, we show that computer simulation methods can be used to complement experiment and aid in the development of rational crystal design strategies based on the use of molecular additives. Specifically, we show several instances of how molecular simulation can be used to elucidate the mechanisms of molecular additives such as crystal growth modifiers and structure directing agents, which can be used to control crystal morphology and polymorph selection during synthesis, respectively. These insights provide fundamental understanding that can help with \emph{a prior} identification of effective additives to achieve desired synthesis outcomes. Moreover, they suggest promising future directions in applying these computational methods to screen large libraries of compounds to identify effective molecular additives and thereby accelerate material design.Item Cyclobenzoins for Energy Industries(2023-05-01) Robles, Alexandra; Miljanić, Ognjen Š.; Brgoch, Jakoah; Guloy, Arnold M.; Comito, Robert J.; Brankovic, Stanko R.Porous molecular crystals are an emerging class of porous materials with properties reaching and exceeding their polymeric counterparts, metal organic frameworks and covalent organic frameworks. They are composed of discrete molecules containing intrinsic voids or inefficiently packed to create extrinsic pores. Porous molecular crystals have been studied for a variety of applications from more traditional catalysis and gas separations to innovative utilizations in porous liquids and analytical sensing devices. Herein we focus on cyclotetrabenzoins, macrocycles synthesized through benzoin condensation cyclooligomerization of dialdehydes, for applications in energy industries. Chapter 1 introduces porous molecular crystals and discusses their studies in chemical separations, molecular sensing, catalysis, porous liquids, and proton conduction. Chapter 2 focuses on an esterified cyclotetrabenzoin for CO2/CO separation through pressure swing adsorption. Chapter 3 discusses a strategy to systematically expand the extrinsic porosity of cyclotetra(bisarylhydrazone)benzils and the utilization of their virtual pores for iodine capture in the solid state and from solutions. Chapter 4 presents two expanded cyclotetrabenzoins and their oxidation into redox-active cyclotetrabenzils which can be incorporated into organic cathode materials for lithium-ion batteries.Item Cyclometalated Iridium(III) Ratiometric Oxygen Sensors and Supramolecular Constructs(2023-04-07) Sutton, Gregory; Teets, Thomas S.; Brgoch, Jakoah; Bao, Jiming; Xu, Shoujun; Hoffman, David M.Hypoxia, or a lack of oxygen, is a key contributor to a vast number of diseases such as cancer, diabetes and COPD. A wide variety of oxygen partial pressures (pO2) ranging from 0.01–100 mmHg needs to be accurately detected in these diseases. Ratiometric oxygen sensing, a technique which utilizes dual-emissive materials with oxygen-insensitive fluorescence as an internal standard and oxygen-sensitive phosphorescence as a measuring tool, has been applied in recent years to improve the sensitivity and dynamic range of oxygen sensing while reducing the cost of optics and need for instrument calibration. Despite being photochemically robust, very few examples of cyclometalated iridium(III) as ratiometric oxygen sensors exist in the literature and require complicated synthetic procedures to produce. The primary aim presented here was to synthesize cyclometalated iridium(III) compounds using simple methods, adding to the existing library of ratiometric sensors for detection of varying ranges of pO2. Expanding on the group’s previous work with iridium BODIPY (boron dipyrromethene) structures, supramolecular complexes linking two phosphorescent iridium centers via a BODIPY fluorophore were designed. However, BODIPY fluorescence dominated the emission spectra, eliminating dual-emission. Subsequently, coumarin dyes were used to give well-resolved blue fluorescence and red iridium-centered phosphorescence. This spectral separation enabled Stern-Volmer quenching to be performed and it was determined that several of our coumarin-isocyanide and coumarin-chloride iridium complexes were useful ratiometric oxygen sensors in detecting pO2 levels ranging from small (0.3–11 mmHg), to medium (8–46 mmHg) and to large (27–160 mmHg) amounts of oxygen. The chloride-terminated complexes have enhanced quantum yields over the isocyanide sensors and include a BODIPY structure which shows the possibility of visible excitation in this design.Item Cyclometalated Platinum β-Diketiminate Complexes(2017-04-25) Islam, Mohammad Din 1986-; Teets, Thomas S.; Halasyamani, P. Shiv; Van Caemelbecke, Eric; Do, Loi H.; Brgoch, JakoahA series of cyclometalated platinum complexes with ancillary β-diketiminate (NacNac) ligands, prepared by a general synthetic route are described. Two different cyclometalating (C^N) ligands―2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (F2ppy)―are used in concert with two different fluorinated NacNac ligands (NacNacF6 and NacNacF18) ‒ to furnish a suite of complexes. The complexes were prepared by metathesis reactions of chloro-bridged dimers [Pt(C^N)(μ-Cl)]2 with lithium salts of the ancillary (LX) ligand. Two structure types can be accessed, depending on the reaction temperature. At lower temperature (ca. 80 °C) bimetallic structures with a bridging NacNac and bridging chloride were prepared, and when the temperature was increased (ca. 100 °C) monometallic Pt(C^N)2(NacNac) complexes formed. The complexes were characterized by X-ray crystallography, and were subjected to in-depth optical and electrochemical interrogation. Fluorination of these ligands by introducing CF3 substituents onto the ligand backbone and/or the N-aryl substituents lead to pronounced changes in the redox properties. All the complexes show a reversible redox couple that was sensitive to the degree of fluorination on the ancillary ligand. Introduction of CF3 groups at the 3- and 5- positions of the N-aryl substituents shifted the potential positive by ca. 50 – 110 mV, but the same substitution minimally perturbed the UV-Vis absorption spectra of the complexes.Item Design of Efficient Yellow to Near-infrared Bis-cyclometalated Iridium(III) Phosphors via Ancillary Ligand Modification(2020-05) Lai, Po-Ni; Teets, Thomas S.; Bao, Jiming; Brgoch, Jakoah; Daugulis, Olafs; Halasyamani, P. ShivLuminescent transition metal complexes, especially ones that contains iridium, have attracted considerable attention due to their unique photophysical properties and their applications in optoelectronic technology, photocatalysis, and phosphorescent probes in biological systems. Due to their continued development and implementation in applications, careful control and optimization of photophysical and electrochemical properties of these complexes are needed, motivating studies to understand structural-property relationships in order to design top performing molecular phosphors. While many iridium(III) complexes were designed, those emitting in the blue-green to yellow regions of the visible spectrum have already achieved near unity quantum yields. The luminescence quantum yields in the long wavelength regions (orange, red, and near-infrared) region tend to be intrinsically low for common structure types in this class. This dissertation is mainly focused on exploring ligand design strategies for new iridium(III) complexes. Chapter 1 introduces general photophysical principles of transition metal complexes with a brief overview of classes of cyclometalated iridium(III) complexes. In Chapters 2–4, various new designs of bis-cyclometalated iridium(III) complexes are presented and organized according to emission color ranging from green to yellow, red, and near-infrared regions with detailed studies of their electrochemistry and photophysical properties.Item Developing Rare-Earth Substituted Inorganic Phosphors through Machine Learning(2021-05) Zhuo, Ya; Brgoch, Jakoah; Halasyamani, P. Shiv; Hoffman, David M.; Xu, Shoujun; Bao, JimingReplacing incandescent and fluorescent light bulbs with LED-based, solid-state white lighting devices is one of the most accessible ways to reduce energy consumption around the world. Solid-state white lights have advantages such as high efficiency, a long lifespan, a small physical size, and environmentally benign components. The development of rare-earth substituted inorganic phosphors, which are the central component of solid-state white lighting devices, accelerates the complete switch to solid-state lights. Historically, the development of phosphors relies on chemical intuition or trial-and-error synthesis. These approaches require a significant amount of starting reagents and are usually highly time-consuming. Recently, the employment of machine learning methods has provided an alternative avenue to accelerate the development of phosphors. It not only enables the fast identification of candidates but also provides insights into the composition-structure-property relationships within these materials. This contribution employs machine learning algorithms to predict optical properties of phosphors. First principle calculations and experimental methods are also used to verify the machine learning predictions and investigate the properties of the synthesized materials. First, the bandgap of inorganic compounds was predicted with a two-stage machine learning model. Then, a regression model was developed to predict the Debye temperature (D) of inorganic compounds as D is a proxy for structural rigidity, which is closely related to photoluminescent quantum yield (PLQY) of phosphors. Using this model, a sorting diagram was created to evaluate D and bandgap simultaneously. The blue-emitting phosphor, NaBaB9O15:Eu2+, was highlighted and the subsequent synthesis and characterization confirmed its high PLQY. Moreover, changing the synthetic route of NaBaB9O15:Eu2+ yielded a green-emitting phosphor. DFT calculations and synchrotron data confirmed the origin of the green emission stems from Eu2+ substituting on the aliovent Na+ site rather than the energetically favorable Ba2+ site. The application of machine learning can also be expanded to predict the T50 of Eu3+-doped phosphors, which is a value corresponds to thermal stability. Finally, combining compositional descriptors with local geometry information made the centroid shift be successfully predicted. This dissertation provides new methodologies for phosphor discovery. The fast prediction of optical properties with machine learning can undoubtedly accelerate the advancement of phosphors.Item Development of Bidentate Phosphonic Acid Based Self-Assembled Monolayers on Silver(2021-12) Lee, Jiyoung; Lee, T. Randall; Miljanić, Ognjen Š.; Teets, Thomas S.; Brgoch, Jakoah; Hallmark, PawilaiSelf-assembled monolayers are a significant means to achieve a nanoscale modification in surface chemistry. Self-assembled monolayers have been applied to a wide range of scientific fields ranging from chemical processes, biomolecule embraced surfaces to microelectromechanical systems (MEMs). Various types of combinations of adsorbates and substrates for self-assembled monolayers have been proposed and research continues to introduce newly designed substances possessing unique properties. This thesis describes the development of bidentate phosphonic acid-based self-assembled monolayers on silver for the purpose of constructing surface patterns on silver-coated superconducting films. Chapter 1 describes the basic concepts of patterned self-assembled monolayers which fabricate sophisticated nanoscale architecture and many types of patterning strategies are reported. In addition, a variety of recent applications of the patterned self-assembled monolayers are introduced in this chapter. Based on the background studied in Chapter 1, Chapter 2 is a study of a newly designed, synthesized, and characterized perfluoroterminated aromatic bidentate phosphonic acid adsorbate and its corresponding self-assembled monolayer on silver-coated yttrium barium copper oxide superconducting tapes. Perfluoroterminated aromatic bidentate phosphonic acid creates a relatively well-ordered thin film on silver with high hydrophobicity that can potentially be used to pattern superconducting tapes.Item Development of Iridium Based Photosensitizer for Potent Photoreductants and Photocatalytic Application(2020-08) Shon, Jong Hwa; Teets, Thomas S.; Halasyamani, P. Shiv; Miljanić, Ognjen Š.; Brgoch, Jakoah; Bao, JimingThis dissertation describes the development of iridium based organometallic photosensitizers which function as potent photoreductants for photoredox catalysis. Chapter 1 describes the basic concepts of photosensitizers in photocatalysis and strategies to modify the photophysical and electrochemical properties via ligand modification with different types of photosensitizers. Chapter 2 describes the first generation of bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ligands. The photophysical and electrochemical properties were compared to fac-Ir(ppy)3, known to be a ‘the-state-of-the-art’ photoreductant, and the calculated excited-state potentials (ESPs) show that our complexes have more reductive potential than fac-Ir(ppy)3. Stern-Volmer quenching experiments also support that the new complexes have higher ESP and reducing ability. Chapter 3 describes an expanded photocatalyst library with further modified NacNac ligands. Based on results from Chapter 1, we have prepared a dozen photosensitizers for the photocatalytic hydrodebromination of bromide substrate and we have screened to find the best-optimized conditions to activate the carbon-bromine bond to replace with a hydrogen atom. Chapter 4 is a deeper study of the hydrodehalogenation reaction with candidate photosensitizers from Chapter 3. Under modified and optimized reaction conditions, alkyl and aryl halides (X = Br, Cl, F) are tolerated in hydrodehalogenation and functionalization reactions proceeding through a radical-mediated reaction mechanism. Finally, Chapter 5 describes the second ligand modification strategy to elevate the excited-state energy (ET1) with alternative cyclometalating ligands which have been used for blue-emitting compounds. Replacing the cyclometalating ligands that we previously used with triazole or NHC-derviced cyclometalating ligands results in a highly destabilized LUMO energy level and record-high excited-state potentials for cyclometalated iridium photosensitizers.Item Development of Sustainable Superhard Materials(2019-05) Mansouritehrani, Aria 1991-; Brgoch, Jakoah; Guloy, Arnold M.; Jacobson, Allan J.; Lubchenko, Vassiliy; Grabow, Lars C.Hard and superhard materials are essential for a myriad of scientific, biomedical, and industrial applications. Their ability to resist indentation stems from a complex relationship among the crystal structure, chemical composition, and microstructure. One of the main difficulties in modeling the mechanical properties is that hardness is influenced by many factors, which requires extensive calculations to account for the multiple length scales ranging from local atomic interactions to long length scales encompassing microstructure. Consequently, it is not possible to employ one single method to predict the hardness of inorganic solids for various chemical systems. As a result, most known superhard materials have either been discovered through trial-and-error or by following simple design rules limiting the development of the field. This contribution employs a combination of computational methods to identify hardness theories, machine learning techniques to screen for optimal materials, and experimental tools to verify theoretical predictions in route to developing new superhard materials. First, the influence of vacancies is explored on the mechanical behavior of ultraincompressible hard transition metal sub-nitrides through density functional theory. These studies show the synthetic conditions can be tuned to limit the occurrence of adverse vacancy softening mechanisms. Then, a methodology is developed to screen for hard materials based on high-throughput density functional theory calculations. Sustainability parameters have also been included to ensure the targeted compositions are sustainable. A machine learning method is further developed which allows the screening of more than 118,000 compounds for the highest possible hardness. The procedure highlighted two compounds, ReWC0.8 and Mo0.9W1.1BC, and their subsequent synthesis and characterization confirmed they are both ultraincompressible and nearly superhard. Further examining the solid-solution behavior of Mo2-xWxBC showed the variation of hardness and revealed a unique balance between hardness, ductility, and sustainability which can be tuned based on transition metal ratio. Finally, the mechanism of simultaneous ductility and hardness is explored in Mo2BC using first-principles stress-strain curves and monitoring the electronic perturbation along the deformation path. Together this dissertation provides insights on deformation mechanisms, pinpoints crystal chemical traits that generate high hardness, and provides methodologies to accelerate the advancement of hard and superhard materials.Item Direct Halogenation of TpRu(diene)Cl Preceding Ligand Exchange Reactions and Assessment of the Halogenated Complexes via Oxidation Potentials and Catalysis(2019-05) Hattori, Hiroyuki 1988-; May, Jeremy A.; Daugulis, Olafs; Do, Loi H.; Brgoch, Jakoah; Faler, Catherine A.The focus of this dissertation centers on the direct on-metal halogenation of trispyrazoyl borate ligand (Tp) in TpRu(diene)Cl. The first chapter begins with the preparation of TpRu(diene)Cl complexes and assessment of their stability under different conditions. TpRu(diene)Cl complexes were halogenated in one step using sulfuryl chloride, NBS, and iodine in the presence of mCPBA and H2O and then also functionalized through Sonogashira coupling reactions. Through this methodology, TpClRu(diene)Cl, TpBrRu(diene)Cl, TpIRu(nbd)Cl, and, TpC≡CHRu(nbd)Cl were synthesized via an unusual strategy. The next chapter encompasses the syntheses of simple di-phosphine complexes (dppm to dppb) and mono-phosphine complexes from the TpXRu(diene)Cl obtained in the previous chapter. By synthesizing the di-phosphine complexes of different P-P linker lengths, changes to the chemical properties of the complexes were investigated. Mono-phosphine complexes TpXPPh3Cl2 were synthesized via a reported reaction reported for TpRuPPh3Cl2, and other mono-phosphine complexes TpXRuPPh3(MeCN)Cl were derived from the counterpart TpXRuPPh3Cl2 with newly devised reaction conditions. These phosphine complexes, in addition to the new diene complexes, were analyzed with cyclic voltammetry. Lastly, the synthesized complexes were subject to evaluation of their catalysis. Two investigatory reactions used were (1) propargylic substitution and furan synthesis from epoxy alkynes. Propargylic substitution reactions gave a mixture of copious compounds from which the product was not isolated. Furan synthesis gave the expected furan, but in an unexpectedly low yield. Increasing the catalyst loading barely enabled a comparison between differently halogenated complexes. In TpXRuPPh3Cl2 catalysis, TpClRuPPh3Cl2 gave a slightly higher yield (17%) than the analogues (14%). On the other hand, TpRuPPh3(MeCN)Cl (26%) and TpIRuPPh3(MeCN)Cl (28%) gave slightly higher yield than the chlorinated (23%) and brominated (22%) complex.Item Discovering Intermetallics through Synthesis, Computation, and Data-Driven Analysis(2020-05) Lotfi, Sogol; Brgoch, Jakoah; Jacobson, Allan J.; Guloy, Arnold M.; Ren, Zhifeng; Yang, Ding-ShyueIntermetallics adopt an array of crystal structures, boast diverse chemical compositions, and possess exotic physical properties that have led to a wide range of applications from the biomedical to aerospace industries. Despite a long history of intermetallic synthesis and crystal structure analysis, identifying new intermetallic phases has remained challenging due to the prolonged nature of experimental phase space searching or the need for fortuitous discovery. New approaches with a specific focus on realizing novel intermetallics have been proposed that expand on traditional methods for materials synthesis and characterization. One of the most notable methods is to merge traditional intermetallic synthesis and characterization with computation and materials informatics, when combined, provide a new set of tools capable of advancing the discovery of metal-rich solids. Each chapter of this dissertation employs solid-state synthesis, first-principle calculations, and machine learning to modernize how intermetallics are discovered and to better understand their complex structures. For example, we combined exploratory solidstate synthesis with ab initio calculations to investigate gold’s polyanionic bonding in intermetallic phases. The application of density functional theory goes beyond merely studying the electronic structure and chemical bonding of intermetallics. We also utilized an ab initio approach coupled with a structure-search algorithm (CALYPSO) to predict the crystal structure of intermetallics under pressure. Our research revealed the existence of two binaries in the A-Ir (A = Rb, Cs) system over ~10 GPa. Further, a new approach merging experimental work, computation, and data-driven analysis to discover intermetallics was created. We developed a machine-learning model to predict the formation energy of metal-rich solid based only on the constituent elements followed by experimental validation through the subsequent synthesis of a novel compound, YAg0.65In1.35. Finally, exploratory synthesis was carried out on the ternary RE-Au-Ge (RE = La, Ce, Pr, Nd) phase system leading to the discovery of six novel compounds: La3Au3Ge, La2Au2Ge, and RE2AuGe3 (RE = La, Ce, Pr, Nd). The research results presented in this dissertation discuss the opportunities and challenges in the discovery of new intermetallic phases while new approaches that merge synthesis, computation, and data science to accelerate the realization of metal-rich materials are created.Item Electrochemical and Spectroelectrochemical Studies on Bis-porphyrins, Porphyrins with Charged Substituents and Water-soluble Porphyrazines(2015-08) Zeng, Lihan 1988-; Kadish, Karl M.; Bear, John L.; Baldelli, Steven; Brgoch, Jakoah; Van Caemelbecke, EricIn this thesis, the electrochemical and spectral properties of a series of bis-porphyrins, porphyrins with charged subsituents and water-soluble porphyrazines are investigated in aqueous or non-aqueous media. Bis-porphyrins containing a β,β'-fused pyrazino (Pz) linking group were examined by electrochemistry and thin-layer UV-visible spectroelectrochemistry in PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte. The investigated compounds are represented as M(TPP)-Pz-(TPP)M, where TPP is the dianion of tetraphenylporphyrin and M = ZnII, CuII or AgII. The effect of the linking Pz group on the redox potentials and UV-visible spectra of the neutral, electroreduced and electrooxidized bis-porphyrins is discussed. Electrochemical and spectral properties of a new class of water-soluble porphyrazine complexes are characterized in pyridine, DMSO, DMF and water media. The investigated compounds are represented as [{Pd(OAc)2}4LM] (L = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato dianion; M = MgII(H2O), ZnII, CuII, CoII, PdII, PtII) and bear four Pd(OAc)2 units, each externally coordinated at the vicinal pyridine N atoms of a single dipyridinopyrazine fragment of the porphyrazine macrocycle (“py-py” coordination). The electrochemistry and spectroelectrochemistry of a series of tetra-N-alkylpyridyl and tetrasulfonato manganese porphyrins are studied in DMSO and DMF. The mixture of tetra-N-alkylpyridyl and tetrasulfonato manganese porphyrins with 1:1 molar ratio in DMF solution is also studied by electrochemistry and spectroelectrochemistry and is described in this thesis.Item Evaluating the Hardness of Yttrium Ruthenium Borides(2022-04-14) Loloee, AryaHigh hardness materials are used for a multitude of applications, ranging from drill bits and saw blades to artificial joint replacement. Most of these materials are constructed out of simple binary phases, namely transition metal borides and carbides. Their simplicity makes them easy to produce but limits the ability to tune the mechanical properties through chemical substitution. As a result, we are investigating ternary borides that may have high hardness. The project started by preparing three yttrium ruthenium borides (YRu3B2, YRu4B4, YRuB4). The powders were mixed and pressed into pellets that were then melted into homogeneous ingots using an arc-melter under an argon atmosphere. After optimising the reaction conditions, the samples are ground, and the sample purity is checked using powder X-ray diffraction. The samples’ resistances to plastic deformation are measured with the Vickers hardness test under different loads. Density functional theory calculations were then used to understand how changes in electron density as a function of chemical composition could be used to maximise the mechanical properties. We are now using this information to develop new ternary high hardness materials with even better mechanical properties.
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