Physical Chemistry Commons^™

Synthesis And Study Of High-Spin Stable Organic Radicals For Electrical Conductors And Mannosamine Nitroxide For Mri Contrast Agents, Shuyang Zhang

Department of Chemistry: Dissertations, Theses, and Student Research

In the first project, we describe the synthesis of an ambient stable high spin organic diradical 4 based on the Blatter moiety. The high-spin (S = 1) organic diradical 4, which consists of two Blatter radical moieties in a conjugated structure, exhibits a nearly exclusive population (88%) on triplet ground state at room temperature as a consequence of a large single-triplet energy gap (ΔEST = 0.5 kcal/mol). The target diradical molecule is synthesized over five steps with structural confirmation by single-crystal X-ray diffraction. The thermogravimetric analysis (TGA) shows the onset of decomposition at ~264 oC, indicating the diradical molecule has …

Halide Exchange And Transport In Halide Perovskite Lattices, Temban Acha Billy

Department of Chemistry: Dissertations, Theses, and Student Research

In recent years, metal-halide perovskites (MHPs) have risen quickly to prominence as promising materials across a variety of fields, from photovoltaics to optoelectronics in general. We show here a facile solution growth for creating a variety of mixed halide MAPbBr_3-xI_x crystals, which we will use to study halide exchange and transport in halide perovskites. We generated a calibration curve between the optical response and chemical composition in mixed Br/I MHPs at room temperature. All mixed Br/I MHP crystals were subjected to measurements of photoluminescence (PL) and Raman spectroscopy. A subset of mixed-halide MHP crystals exhibited multiple emission …

Diffractive Imaging Of Laser Induced Molecular Reactions With Kiloelectron-Volt Ultrafast Electron Diffraction, Yanwei Xiong

Department of Physics and Astronomy: Dissertations, Theses, and Student Research

Capturing the structural changes during a molecular reaction with ultrafast electron diffraction (UED) requires a high spatiotemporal resolution and sufficiently high signal-to-noise to record the signals with high fidelity. In this dissertation, I have focused on the development of a tabletop gas phase keV-UED setup with a femtosecond temporal resolution. A DC electron gun was employed to generate electron pulses with a high repetition rate of 5 kHz. The space charge effect in the electron pulse was ameliorated by compressing the 90 keV electron pulse longitudinally with a time varying electric field in an RF cavity. The velocity mismatch between …

Two-Dimensional Monolayer Salt Nanostructures Can Spontaneously Aggregate Rather Than Dissolve In Dilute Aqueous Solutions, Wenhui Zhao, Yunxiang Sun, Weiduo Zhu, Jian Jiang, Xiaorong Zhao, Dongdong Lin, Wenwu Xu, Xiangmei Duan, Joseph S. Francisco, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal …

Multiple Wetting−Dewetting States Of A Water Droplet On Dual- Scale Hierarchical Structured Surfaces, Yurui Gao, Yuan Liu, Jian Jiang, Chongqin Zhu, Craig Zuhlke, Dennis Alexander, Joseph S. Francisco, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Surfaces with microscale roughness can entail dualscale hierarchical structures such as the recently reported nano/ microstructured surfaces produced in the laboratory (Wang et al. Nature 2020, 582, 55−57). However, how the dual-scale hierarchical structured surface affects the apparent wetting/ dewetting states of a water droplet, and the transitions between the states are still largely unexplored. Here, we report a systematic large-scale molecular dynamics (MD) simulation study on the wetting/dewetting states of water droplets on various dual-scale nano/near-submicrometer structured surfaces. To this end, we devise slab-water/slab-substrate model systems with a variety of dual-scale surface structures and with different degrees of intrinsic …

Molecular Design Of Three-Dimensional Metal-Free A(Nh4)X3 Perovskites For Photovoltaic Applications, Jie Bie, Dai-Bei Yang, Ming-Gang Ju, Qiang Pan, Yu-Meng You, Wei Fa, Xiao Cheng Zeng, Shuang Chen

Xiao Cheng Zeng Publications

The intense research activities on the hybrid organic−inorganic perovskites (HOIPs) have led to the greatly improved light absorbers for solar cells with high power conversion efficiency (PCE). However, it is still challenging to find an alternative lead-free perovskite to replace the organohalide lead perovskites to achieve high PCE. This is because both previous experimental and theoretical investigations have shown that the Pb²⁺ cations play a dominating role in contributing the desirable frontier electronic bands of the HOIPs for light absorbing. Recent advances in the chemical synthesis of three-dimensional (3D) metal-free perovskites, by replacing Pb²⁺ with NH₄^{+ …}

Oxygen Binding Thermodynamics Of Human Hemoglobin In The Red Blood Cell, Kyle K. Hill

Department of Chemistry: Dissertations, Theses, and Student Research

We report for the first time the binding constants and Hill numbers for oxygen in the red blood cell under physiological conditions. When compared to our results for hemoglobin in solution, our results show conclusively that hemoglobin binds oxygen more tightly and with lower co-operativity when packed in the red blood cell. At 18°C, these differences are striking: the respective half-saturation values are 15.57 µM (in red blood cells) and 18.83 µM (in solution), with corresponding Hill numbers of 2.475 (in red blood cells) and 2.949 (in solution). The optical complications that arise from high turbidity of red blood cell …

How Oxygen-Binding Affects Structural Evolution Of Even-Sized Gold Anion Clusters. (Size Range 20 To 34), David Brunken-Deibert

Department of Chemistry: Dissertations, Theses, and Student Research

We report a joint anion photoelectron spectroscopy (PES) and theoretical study to investigate the effect of O₂-binding on the mid-sized even-numbered gold clusters, Au_n− (n = 20−34), a special size region of bare gold clusters that entail rich forms of structural evolution and transformation. Specifically, within this size range, bare Au₂₀₋ is a highly-symmetric pyramidal cluster, bare Au_21-25− are flat-planar or hollow-tubular clusters, bare Au₂₆₋ is the smallest core-shell gold cluster, while bare Au₃₄₋ is a magic-number/fluxional core-shell cluster with the high-symmetry tetrahedral Au₄ core. In light of the strong …

A Possible Unaccounted Source Of Atmospheric Sulfate Formation: Amine-Promoted Hydrolysis And Non-Radical Oxidation Of Sulfur Dioxide, Shixian Wang, Xiao Cheng Zeng, Hui Li, Joseph S. Francisco

Xiao Cheng Zeng Publications

Numerous field and laboratory studies have shown that amines, especially dimethylamine (DMA), are crucial to atmospheric particulate nucleation. However, the molecular mechanism by which amines lead to atmospheric particulate formation is still not fully understood. Herein, we show that DMA molecules can also promote the conversion of atmospheric SO₂ to sulfate. Based on ab initio simulations, we find that in the presence of DMA, the originally endothermic and kinetically unfavourable hydrolysis reaction between gaseous SO₂ and water vapour can become both exothermic and kinetically favourable. The resulting product, bisulfite NH₂(CH₃)₂⁺ ∙ HSO …

Resolving The Puzzle Of Single-Atom Silver Dispersion On Nanosized Γ-Al2O3 Surface For High Catalytic Performance, Fei Wang, Jinzhu Ma, Shaohui Xin, Qiang Wang, Jun Xu, Changbin Zhang, Hong He, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Ag/γ-Al₂O₃ is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al₂O₃ remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al₂O₃ are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al₂O₃ can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al₂O₃. Density-functional-theory calculations confirm that Ag atom is mainly …

Computational Studies Of Thermal Properties And Desalination Performance Of Low-Dimensional Materials, Yang Hong

Department of Chemistry: Dissertations, Theses, and Student Research

During the last 30 years, microelectronic devices have been continuously designed and developed with smaller size and yet more functionalities. Today, hundreds of millions of transistors and complementary metal-oxide-semiconductor cells can be designed and integrated on a single microchip through 3D packaging and chip stacking technology. A large amount of heat will be generated in a limited space during the operation of microchips. Moreover, there is a high possibility of hot spots due to non-uniform integrated circuit design patterns as some core parts of a microchip work harder than other memory parts. This issue becomes acute as stacked microchips get …

Quantum Chemical Calculations Applied To Somo-Homo Conversion And Vibrationally Averaged Nmr Shielding Parameters, Erik Johnson

Department of Chemistry: Dissertations, Theses, and Student Research

The inversion of frontier orbitals of free radicals was studied using density functional theory calculations in Gaussian 09. Comparisons of images of orbitals in GaussView was used to assess the relative positions of singly occupied and doubly occupied orbitals and to determine which was the highest in energy. A variety of organic free radicals were studied including several radical anions and also a neutral radical. It was found that cross-conjugation appears to be a factor in whether or not molecules show SOMO-HOMO conversion. Cross-conjugation is when two unsaturated groups are conjugated to a third unsaturated group but are not conjugated …

Monolayer Triphosphates Mp3 (M = Sn, Ge) With Excellent Basal Catalytic Activity For Hydrogen Evolution Reaction, Hong-Hui Wu, He Huang, Jie Zhong, Song Yu, Qiaobao Zhang, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Atomically thin two-dimensional (2D) materials have received intense research interest due to their novel properties and promising applications in nanodevices. By using density functional theory (DFT) calculations, we investigate catalytic activities of several newly predicted two-dimensional (2D) triphosphides GeP₃, SnP₃ and InP₃ monolayers for hydrogen evolution reaction (HER). The calculation results show that GeP₃ and SnP₃ monolayers are active catalysts for HER with suitable free energy of hydrogen adsorption in the basal plane. In particular, the Gibbs free energy of hydrogen adsorption (ΔG_H*) of GeP₃ is 0.024 eV, a value even …

Slips-Teng: Robust Triboelectric Nanogenerator With Optical And Charge Transparency Using A Slippery Interface, Wanghuai Xu, Xiaofeng Zhou, Chonglei Hao, Huanxi Zheng, Yuan Liu, Xiantong Yan, Zhengbao Yang, Michael Leung, Xiao Cheng Zeng, Ronald X. Xu, Zuankai Wang

Xiao Cheng Zeng Publications

Energy harvesting devices that prosper in harsh environments are highly demanded in a wide range of applications ranging from wearable and biomedical devices to self-powered and intelligent systems. Particularly, over the past several years, the innovation of triboelectric nanogenerators (TENGs) that efficiently convert ambient kinetic energy of water droplets or wave power to electricity has received growing attention. One of the main bottlenecks for the practical implications of such devices originates from the fast degradation of the physiochemical properties of interfacial materials under harsh environments. To overcome these challenges, here we report the design of a novel slippery lubricant-impregnated porous …

Diisopropylammonium Bromide Based Two-Dimensional Ferroelectric Monolayer Molecular Crystal With Large In-Plane Spontaneous Polarization, Liang Ma, Yinglu Jia, Stephen Ducharme, Jinlan Wang, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

In light of their easy processing, light weight and mechanical flexibility, ferroelectric molecular crystal with large spontaneous polarization (P_s) is highly desired for many advanced applications. Herein, we report the first theoretical study of two-dimensional (2D) ferroelectric molecular crystals via ab initio calculations. Specifically, we show that diisopropylammonium bromide (DIPAB) based 2D ferroelectric monolayer molecular crystal with large in-plane P_s of ∼1.5 × 10⁻⁶ μC cm⁻¹ can be achieved by slicing the bulk DIPAB along a specific plane while keeping the space group unchanged. The important roles of hydrogen bonds are …

Au60–: The Smallest Gold Cluster With The High-Symmetry Icosahedral Core Au13, Seema Pande, Xingao Gong, Lai-Sheng Wang, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Among coinage metal nanoclusters with 55 atoms, only Ag₅₅^– and Cu₅₅^– are the geometric magic-number clusters, as both exhibit icosahedral symmetry. Au₅₅^–, however, exhibits much lower symmetry due largely to the strong relativistic bonding effect. In this study, we collect a much larger population (>10,000 isomers) of low-energy isomers of Au₅₅^– to Au₆₀^– by using the combined density-functional theory and basin-hopping global optimization method. We also include the spin−orbit effect in the density-functional theory computation to achieve simulated photoelectron spectra in quantitative fashion. Remarkably, we uncover that the …

Reaction Mechanism Between Small-Sized Ce Clusters And Water Molecules: An Ab Initio Investigation On CeN+H2O, Rulong Zhou, Yang Yang, Seema Pande, Bingyan Qu, Dongdong Li, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

Reactions of small-sized cerium clusters Ce_n (n = 1–3) with a single water molecule are systematically investigated theoretically. The ground state structures of the Ce_n/H₂O complex and the reaction pathways between Ce_n + H₂O are predicted. Our results show the size-dependent reactivity of small-sized Ce clusters. The calculated reaction energies and reaction barriers indicate that the reactivity between Ce_n and water becomes higher with increasing cluster size. The predicted reaction pathways show that the single Ce atom and the Ce₂ and Ce₃ clusters can all easily react with H …

Synthesis, Characterization, And Catalytic Activity Of Copper Palladium Oxide Solid Solutions., Gregory L. Christensen

Department of Chemistry: Dissertations, Theses, and Student Research

Cu_xPd_1-xO forms a homogeneous solid solution over the wide range of 0 ≤ x ≤ 0.725 in which compositional variation can be correlated with structural and chemical environmental changes. After a small lag at low Cu²⁺ concentrations, where the lattice cell parameters are pinned to that of the pure PdO structure, Cu_xPd_1-xO lattice parameters follow Vegard’s law in which the cell volume decreases linearly with x, indicating a homogenous solution in which Cu²⁺ randomly replaces the larger Pd²⁺ cation. The crystal structure also undergoes an increase in the c/a …

Global Minimum Search And Carbon Monoxide Binding Studies Of Novel Gold Nanoclusters, Navneet S. Khetrapal

Department of Chemistry: Dissertations, Theses, and Student Research

In bulk form, gold is a well-known noble metal. However, gold nanoparticles exhibit remarkable catalytic behavior towards various types of chemical reactions. These catalytic properties are highly dependent upon the size and shape and therefore knowledge of the geometries of these nanoparticles is of prime importance. The main goal of this dissertation is, therefore, going to be towards the elucidation of the structures of novel gold clusters using a combined experimental and theoretical approach and subsequent modeling to explore the binding of simple substrates like carbon monoxide with gold clusters. The theoretical method used to study the structural evolution of …

Abnormal Phase Transition Between Two-Dimensional High-Density Liquid Crystal And Low-Density Crystalline Solid Phases, Wenbin Li, Longjuan Kong, Baojie Feng, Huixia Fu, Hui Li, Xiao Cheng Zeng, Kehui Wu, Lan Chen

Xiao Cheng Zeng Publications

Some two-dimensional liquid systems are theoretically predicted to have an anomalous phase transition due to unique intermolecular interactions, for example the first-order transition between two-dimensional high-density water and low-density amorphous ice. However, it has never been experimentally observed, to the best of our knowledge. Here we report an entropy-driven phase transition between a high-density liquid crystal and low-density crystalline solid, directly observed by scanning tunneling microscope in carbon monoxide adsorbed on Cu(111). Combined with first principle calculations, we find that repulsive dipole–dipole interactions between carbon monoxide molecules lead to unconventional thermodynamics. This finding of unconventional thermodynamics in two-dimensional carbon monoxide …

Structural Evolution Of Gold-Doped Bismuth Clusters AubiN– (N = 4−8), Seema Pande, Tian Jian, Navneet S. Khetrapal, Lai-Sheng Wang, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

The structures of gold-doped bismuth clusters, AuBi_n⁻ (n = 4−8), are investigated through a joint photoelectron spectroscopy and density functional theory (DFT) study. Well-resolved photoelectron spectra are obtained at several photon energies. Global minimum searches coupled with DFT calculations yield low-lying structures, whose relative energies are further evaluated by single-point energy calculations at the CCSD(T) level of theory. Vertical detachment energies are calculated with the inclusion of spin−orbit effects to compare with the experimental data. Three-dimensional structures are found to be dominant in this size range, while a planar low-lying isomer is observed only for AuBi_{4 …}

Distinct Ice Patterns On Solid Surfaces With Various Wettabilities, Jie Liu, Chongqin Zhu, Kai Liu, Ying Jiang, Yanlin Song, Joseph S. Francisco, Xiao Cheng Zeng, Jianjun Wang

Xiao Cheng Zeng Publications

No relationship has been established between surface wettability and ice growth patterns, although ice often forms on top of solid surfaces. Here, we report experimental observations obtained using a process specially designed to avoid the influence of nucleation and describe the wettability-dependent ice morphology on solid surfaces under atmospheric conditions and the discovery of two growth modes of ice crystals: along-surface and off-surface growth modes. Using atomistic molecular dynamics simulation analysis, we show that these distinct ice growth phenomena are attributable to the presence (or absence) of bilayer ice on solid surfaces with different wettability; that is, the formation of …

Ion-Specific Ice Recrystallization Provides A Facile Approach For The Fabrication Of Porous Materials, Shuwang Wu, Chongqin Zhu, Zhiyuan He, Han Xue, Qingrui Fan, Yanlin Song, Joseph S. Francisco, Xiao Cheng Zeng, Jianjun Wang

Xiao Cheng Zeng Publications

Ice recrystallization is of great importance to both fundamental research and practical applications, however understanding and controlling ice recrystallization processes remains challenging. Here, we report the discovery of an ion-specific effect on ice recrystallization. By simply changing the initial type and concentration of ions in an aqueous solution, the size of ice grains after recrystallization can be tuned from 27.4±4.1 to 277.5±30.9 mm. Molecular dynamics simulations show that the ability of the ion to be incorporated into the ice phase plays a key role in the ultimate size of the ice grains after recrystallization. Moreover, by using recrystallized ice crystals …

In Situ Electron Microscopy Of Plasmon-Mediated Nanocrystal Synthesis, Peter Sutter, Ying Li, Christos Argyropoulos, Eli A. Sutter

Department of Electrical and Computer Engineering: Faculty Publications

Chemical processes driven by nonthermal energy (e.g., visible light) are attractive for future approaches to energy conversion, synthesis, photocatalysis, and so forth. The growth of anisotropic metal nanostructures mediated by excitation of a localized surface plasmon resonance (LSPR) is a prototype example of such a reaction. Important aspects, notably the growth mechanism and a possible role of plasmonic “hot spots” within the metal nanostructures, remain poorly understood. Here, we use in situ electron microscopy to stimulate and image the plasmon-mediated growth of triangular Ag nanoprisms in solution. The quantification of the time-dependent evolution of the lateral size and thickness of …

Criegee Intermediate-Hydrogen Sulfide Chemistry At The Air/Water Interface, Manoj Kumar, Jie Zhong, Joseph S. Francisco, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

We carry out Born–Oppenheimer molecular dynamic simulations to show that the reaction between the smallest Criegee intermediate, CH₂OO, and hydrogen sulfide (H₂S) at the air/water interface can be observed within few picoseconds. The reaction follows both concerted and stepwise mechanisms with former being the dominant reaction pathway. The concerted reaction proceeds with or without the involvement of one or two nearby water molecules. An important implication of the simulation results is that the Criegee-H₂S reaction can provide a novel non-photochemical pathway for the formation of a C–S linkage in clouds and could be a …

Probing The Structural Evolution Of Gold−Aluminum Bimetallic Clusters (Au2AlN−, N = 3−11) Using Photoelectron Spectroscopy And Theoretical Calculations, Navneet S. Khetrapal, Tian Jian, Gary V. Lopez, Seema Pande, Lai-Sheng Wang, Xiao Cheng Zeng

Xiao Cheng Zeng Publications

We report a combined photoelectron spectroscopy and theoretical study of the structural evolution of aluminum cluster anions doped with two gold atoms, Au₂Al_n^– (n = 3−11). Well-resolved photoelectron spectra have been obtained at several photon energies and are used to compare with theoretical calculations to elucidate the structures of the bimetallic clusters. Global minima of the Au₂Al_n^– clusters were searched using the basin-hopping method combined with density functional theory calculations. Vertical detachment energies were computed for the low-lying isomers with the inclusion of spin−orbit effects and were used to generate simulated …

Reply To ‘On The Bonding In Ligand-Protected Gold Clusters’, Wen Wu Xu, Xiao Cheng Zeng, Yi Gao

Xiao Cheng Zeng Publications

In the recent Correspondence, Professor Henrik Grönbeck made several comments on the recently developed grand unified model (GUM), in particular using the ligand-protected gold cluster [Au₂₅(SR)₁₈]¹⁻ as an example. We noted that the latter cluster can be viewed as belonging to a special group of ligand-protected gold clusters that contain one or several icosahedral Au₁₃ motifs. For this group of clusters, a secondary block Au₁₃(8e) has been identified as a more convenient way to describe their structure anatomy and evolution. Another extension of the GUM is the identification of the new elementary …

A Grand Unified Model For Liganded Gold Clusters, Wen Wu Xu, Beien Zhu, Xiao Cheng Zeng, Yi Gao

Xiao Cheng Zeng Publications

A grand unified model (GUM) is developed to achieve fundamental understanding of rich structures of all 71 liganded gold clusters reported to date. Inspired by the quark model by which composite particles (for example, protons and neutrons) are formed by combining three quarks (or flavours), here gold atoms are assigned three ‘flavours’ (namely, bottom, middle and top) to represent three possible valence states. The ‘composite particles’ in GUM are categorized into two groups: variants of triangular elementary block Au₃(2e) and tetrahedral elementary block Au₄(2e), all satisfying the duet rule (2e) of the valence shell, akin to …

Synthesis And Applications Of Lanthanide Sulfides And Oxides, Christopher Marin

Department of Chemistry: Dissertations, Theses, and Student Research

This dissertation focuses on two of the key fields where lanthanides find ready application: as optically active materials with a focus on the lanthanide sulfides, and as catalytic materials with a focus on cerium oxide.

The lanthanide sulfides have attracted considerable interest for their potential as solar energy conversion materials, pigments, infrared window materials, and phosphor host media. However, applications of these materials remain limited due to their synthetic difficulty along with their not well understood properties compounded by both their difficulty in manufacturing as well as in simulating largely due to the need to take into account f-shell electrons. …

Binding Of Oxygen To Human Hemoglobin Within The Erythrocyte Using Icam Spectrophotometry, Kyle K. Hill

Department of Chemistry: Dissertations, Theses, and Student Research

Many of the spectrophotometric techniques used to determine the properties of intracellular human hemoglobin cannot be utilized due to the turbidity of erythrocyte suspensions. An Integrating Cavity Absorption Meter, or ICAM, allows for absorption measurements of strongly scattering samples in the visible-light region of the spectrum. The spectrum of oxygenated hemoglobin within erythrocytes is significantly different from the absorption spectrum of oxygenated hemoglobin in solution. Studies of the oxygen binding to hemoglobin in erythrocytes allowed the four sequential binding constants (Adair constants) to be determined and compared with those of hemoglobin in solution. The Adair constants for hemoglobin in solution …