Physical Chemistry Commons^™

Tunable Surface Interactions In Adsorbing Polymer Solutions, Sorour Hosseini

Open Access Theses & Dissertations

A simple formalism is suggested, to calculate the most likely configuration of a finite polymer, between two surfaces on which the monomers can adsorb. Grafted polymers typically enhance the stability of colloidal dispersions, via the long ranged steric repulsion due to the overlap of their polymer brushes, which can be thicker that the typical range of the DLVO interactions. However, if the polymers are adsorbing on the colloidal surfaces, there is the possibility of bridge formation between particles and therefore long-range attractions are induced (a procedure commonly used for the flocculation of colloidal suspensions). The two effects are competing and …

Computational Investigation Of Energetic Materials: Influence Of Intramolecular And Intermolecular Interactions On Sensitivity, Ashley Lauren Shoaf

Chemistry & Biochemistry Theses & Dissertations

The development of novel high energy density materials (HEDMs) with superior energetic properties depends on characterizing how and why detonation occurs. Detonation is highly energetic and a nearly instantaneous process, making experimental studies challenging; thus, computational modeling through density functional theory (DFT) and molecular dynamics (MD) can be used to propose weakened, or activated, bonds that break to initiate explosive decomposition, termed trigger bonds. Bond activation is characterized by the Wiberg bond index (WBI), a measure of interatomic electron density. Trigger bonds in HEDMs are commonly found in explosophores, functional groups that contribute to energetic potential such as X-NO_{2 …}

Laser Synthesis Of Nanomaterials Incorporated Within High Surface Area Materials: Applications For Heterogeneous Catalysis, Water Treatment, And Photothermal Energy Conversion, Julian A. Bobb

Theses and Dissertations

Chemical methods are generally used for the synthesis of active nanoparticles (metals, semi-metals, metal oxides, and etc) supported on high surface area materials. Chemical methods involve using strong solvents, harmful gases (H₂ & CO), and high temperature techniques such as high boiling solvents, calcination and pyrolysis. The main drawbacks of using this approach, is the prevalence of chemical agents on nanomaterials which tends to negate its applications. Alternatively, photochemical and photothermal methods are widely being considered for the synthesis and design of nanomaterials.

For these studies, the active nanomaterials incorporated within high surface area materials were prepared by the …

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 …

Fabrication Of Mnox/Mwcnts-Gc Nanocatalyst For Oxygen Evolution Reaction, Islam M. Al-Akraa Dr., Yaser M. Asal Mr, Amr M. Arafa Eng.

Chemical Engineering

Manganese oxide (MnOx) and multiwalled carbon nanotubes (MWCNTs) are intended to modify the GC electrode for oxygen evolution reaction (OER). Optimization of MnOx loading is carried out and the deposition of 55 cycles was sufficient to obtain the highest activity toward OER. The stability of the catalyst is enhanced by the addition of MWCNTs. As a result, an amount of 22 kWh/Kg of O2 of energy is saved. Several techniques including cyclic voltammetry, linear sweep voltammetry, chronoamperometry, chronopotentiometry, field-emission scanning electron microscopy, and energy dispersive X-ray spectroscopy will be combined to track the catalyst activity and to determine its morphology …

Assembling Of Niox/Mwcnts-Gc Anodic Nanocatalyst For Water Electrolysis Applications, Islam M. Al-Akraa Dr., Yaser M. Asal Mr, Saher D. Khamis Eng

Chemical Engineering

Glassy carbon (GC) electrode is intended to be modified with nickel oxide (NiOx) and multiwalled carbon nanotubes (MWCNTs) in the anodic reaction of water electrolysis. NiOx deposition time is optimized and a 5 min was enough to attain the maximum activity. A further modification of the catalyst with MWCNTs could greatly enhance its stability during continuous electrolysis. As an outcome, an energy amount of 21.7 kWh/KgO2 is minimized. Several electrochemical and materials characterization setups will be utilized to test the catalyst activity and to know its geometry and structure.

Fabrication Of Cuox-Pd Nanocatalyst Supported On A Glassy Carbon Electrode For Enhanced Formic Acid Electro-Oxidation, Islam M. Al-Akraa Dr., Ahmad M. Mohammad Prof, Mohamed S. El-Deab Prof, Bahgat E. El-Anadouli Prof

Chemical Engineering

Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of palladium nanoparticles (PdNPs) and copper oxide nanowires (CuOxNWs) and assembled onto a glassy carbon (GC) electrode. /e deposition sequence of PdNPs and CuOxNWs was properly adjusted in such a way that could improve the electrocatalytic activity and stability of the electrode toward FAO. Several techniques including cyclic voltammetry, chronoamperometry, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were all combined to report the catalyst’s activity and to evaluate its morphology, composition, and structure. /e highest catalytic activity and stability were obtained at the CuOx/Pd/GC …

Spectroscopy And Formation Of Lanthanum-Hydrocarbon Complexes, Wenjin Cao

Theses and Dissertations--Chemistry

Lanthanum-mediated bond activation reactions of small hydrocarbon molecules, including alkenes, alkynes, and alkadienes, were carried out in a laser vaporization metal cluster beam source. Time-of-flight mass spectrometry and mass-analyzed threshold ionization (MATI) spectroscopy, in combination with quantum chemical and multi-dimensional Franck-Condon factor calculations, were utilized to identify the reaction products and investigate their geometries, electronic structures, and formation mechanisms.

La-hydrocarbon association was only observed in the reaction of La with isoprene. C-H bond activation was observed in all reactions, hydrogen elimination was observed as the prominent reaction for the alkenes (2-butene, isobutene, 1-pentene, and 2-pentene), alkynes (1-butyne, 2-butyne, and 1-pentyne), …

Carbon Quantum Dots: Bridging The Gap Between Chemical Structure And Material Properties, Timothy J. Pillar-Little Jr.

Theses and Dissertations--Chemistry

Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs.

This …

Cappack Devices For The Evaluation Of Parameters And Pulse Performances In Liquid And Solid-State Nmr Spectroscopy, Lingyu Chi

Doctoral Dissertations

"NMR spectroscopy is a powerful analytical tool to obtain explicit information about molecular structures, conformations, dynamics, and functions. To extract the desired information most accurately, NMR reference standards and devices are needed for calibrating the spectrometer hardware, generating reference data for the NMR software, and testing the applicability of pulse sequences. In this dissertation, the CapPack (Capillary-tube Package) platform is introduced which provides well-defined external reference and calibration standards for liquid and solid-state NMR applications. CapPacks consist of one or more permanently sealed capillary tubes that, depending on the intended application, come arranged in different geometries such as side-by-side or …

Structural And Chemical Consequences Of High Oxygen Coverages On Rh(111), Rachael Gabrielle Farber

Dissertations

Partial oxidations of small molecules over metal surfaces are central to many heterogeneously catalyzed reactions. However, the identity of the actual surface species that promote or hinder these reactions has remained elusive for a variety of reasons. Recently, the understanding of the role of surface oxides in catalytic activity has changed. Instead of being thought of as poisons, they are now believed to be effective promoters of selective catalysis.

Rhodium (Rh) effectively promotes oxidation reactions and is a benchmark system for models of heterogeneously catalyzed chemistry. For this reason, Rh(111) was chosen as the model system for this dissertation work. …

Metal-Organic Frameworks And Graphene-Based Support Materials For Heterogeneous Catalysis, Andrew Lin

Theses and Dissertations

Nanoparticles are involved in a broad range of applications, including heterogeneous catalysis. Nanoparticles tend to quickly lose their well-defined shapes and facets due to aggregation under duress such as heat.

A series of highly studied materials are explored as support materials for nanoparticle supports. These supports include metal-organic frameworks (MOF), graphene oxide (GO), and a MOF-PRGO (partially reduced graphene oxide) hybrid. The inclusion of a support with the palladium increased lifespan of the catalyst by separation of nanoparticles. The choice of support material not only allowed for supporting of palladium nanoparticles, but allowed for rational catalyst synthesis in order to …

Water Dynamics And The Effect Of Static And Alternating Electric Fields, Mohammadmahdi Shafiei Alavijeh

Theses and Dissertations

Having a net dipole moment, water molecules tend to align with an external electric field. The re-orientation of water molecules to align with the field direction can result in structural and dynamic changes in liquid water. Studying these changes can help us to understand the role of an E-field in many biological systems, chemical reactions, and many technological advancements.

In short, the application of static electric fields causes molecules to stay aligned with the field, so, fewer hydrogen bonds break, and molecules have slower dynamics. This type of field can be used when the mobility of water molecules needs to …

The Investigation Of Oxidative Addition Reactions Of Metal Complexes In Cross-Coupling Catalytic Cycles Based On A Unique Methodology Of Coupled Ion/Ion-Ion/Molecule Reactions, Mariah L. Parker

Theses and Dissertations

Popular catalytic cycles, such as the Heck, Suzuki, and Negishi, utilize metal centers that oscillate between two oxidation states (II/0) during the three main steps of catalysis: reductive elimination, oxidative addition, and transmetallation. There has been a push to use less toxic, cheaper metal centers in catalytic cycles, leading to interest in first-row transition metals, such as nickel and cobalt. With these metals, the cycles can potentially pass through the +1 oxidation state, which acts as reactive intermediates, undergoing oxidative additions to form products, potentially with radical characteristics. The oxidative addition steps of catalytic cycles are critical to determining overall …

Development Of Photocatalysts Supported On Graphitic Carbon Nitride For The Degradation Of Organic Water Pollutants, Atanu Giri

Theses and Dissertations

Graphitic carbon nitride (g-C₃N₄) heterojunction composites with the semiconducting metal oxides, CeO₂, ZnO and TiO₂ are prepared in situ by co-calcination of the precursor materials or by a solvothermal method. The structural, morphological and the optical properties of the prepared materials are studied using various microscopy and spectroscopy techniques. The synthesized composite materials, CeO₂/g-C₃N₄, ZnO/g-C₃N₄ and TiO₂/g-C₃N₄ are more efficient in the photocatalytic degradation of the water pollutants indigo carmine (IC) and atrazine than the pure metal oxide, g-C …

Experimental Evaluation Of Uranyl Transport Into Mesoporous Silica Gel Using Fluorescence, Brandon M. Dodd

Theses and Dissertations

This research investigated parameters that can affect the use of nanoporous silica gel as a media for accumulating a detectable amount of uranium. The unique fluorescence of the Uranyl (UO₂²⁺) ion was used to evaluate the transport kinetics and accumulation within silica gel in a static fluid and under pressure driven flow. The addition of fluid flow decreased the time constant from on the order of an hour to approximately 2s with a very low fluid velocity of 0.36cm/s. The 0.36cm/s fluid velocity was found to be the critical velocity above which there was no gain in …

Physicochemical, Spectroscopic Properties, And Diffusion Mechanisms Of Small Hydrocarbon Molecules In Mof-74-Mg/Zn: A Quantum Chemical Investigation, Gemechis Degaga

Dissertations, Master's Theses and Master's Reports

In petroleum refining industries, the fracturing process allows for the cracking of long-chain hydrocarbons into a mixture of small olefin and paraffin molecules that are then separated via the energetically and monetarily demanding cryogenic distillation process. In an attempt to mitigate both energetic and capital consumptions, selective sorption of light hydrocarbons by tunable sorbents, such as metal-organic frameworks (MOFs), appears to be the most promising alternative for a more efficient gas separation process. MOFs are novel porous materials assembled from inorganic bricks connected by organic linkers. From a crystal engineering stand point, MOFs are advantageous in creating a range …

Preparation Of Nis2 Nanosheet And Its Application In Asymmetric Supercapacitor, Yuan-You Wang, Ya-Nan Liu, Dang-Qin Jin

Journal of Electrochemistry

In this work, the NiS₂ nanosheets have been synthesized using Ni(OH)₂  as a precursor through a sacrificial template method. The microstructure and chemical composition of as-prepared NiS₂ were characterized by XRD, EDS, BET, SEM and TEM techniques. The results showed that both Ni(OH)₂  and NiS₂  were composed of nanoplates. The electrochemical tests revealed that NiS₂ exhibited the high specific capacitance of 1067.3 F•g^-1 at a current density of 1 A•g^-1 and excellent rate performance. Furthermore, in order to evaluate the practical application of NiS₂, an asymmetric supercapacitor, NiS₂ as …

Electroactivities Of Pd/Fe3O4-C Catalysts For Electro-Oxidation Of Methanol, Ethanol And Propanol, Tao Zou, Qing-Feng Yi, Yuan-Yuan Zhang, Xiao-Ping Liu, Guo-Rong Xu, Hui-Dong Nie, Xiu-Lin Zhou

Journal of Electrochemistry

Development of palladium (Pd) catalysts with high electroactivity for alcohol oxidation is significant for alcohol fuel cells. In this work, Pd nanoparticles were formed by sodium borohydride (NaBH₄) reduction method and subsequently deposited on the surface of carbon supported ferriferrous oxide (Fe₃O₄/C) composites to obtain the Pd/Fe₃O₄-C catalysts with different Fe₃O₄ loadings. Their transmission electron microscopic (TEM) images show that the Pd nanoparticles were uniformly dispersed on the Fe₃O₄/C. Electroactivities of the prepared Pd/Fe₃O₄-C catalysts toward oxidations of C1-C3 …

Kinetics And Mechanism Toward Electrochemical Reductions Of Sodium Bromide And Methanol Over Iron Electrodes, Qun Liao, Shu-Feng Zhang, Wen-Hua Leng

Journal of Electrochemistry

It is of technological value and scientific interest to the electro-synthesis of ferrocene, conversion of carbon dioxide (CO₂) and organic electro-synthesis in non-aqueous solutions by investigating the kinetics and mechanism toward electrochemical reductions of sodium bromide (NaBr) and methanol over iron electrodes. However, few reports in the related researches are available. In this article, the kinetics and mechanism toward electrochemical reductions of NaBr and methanol over iron electrodes were examined in detail by carrying out the polarization curve and electrochemical impedance spectroscopic measurements. The results showed that methanol was the reactant, while Na⁺ ions were functioned only …

Effect Of Peg-Coating On Properties Of Lithium-Sulfur Battery Cathode Material Containing Carbon Fiber Conductive Agent, Jie-Cheng Tan, Yan-Hong Tian, Xue-Jun Zhang, Kai-Le Fan

Journal of Electrochemistry

The composite materials contained high modulus carbon fiber (HMCF) were successfully prepared by employing a ball-milling process based on the coating treatment of polyethylene glycol (PEG), and their structures and morphologies were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques．The influences of PEG content on sulfur cathode capacity, cycle stability and rate performance were systematically studied. It was found that by the pre-coating of PEG, the cathode exhibited the high initial discharge specific capacity of 1312.5 mAh⋅g^-1 at a current rate of 0.2C, and the reversible discharge capacity of 650 mAh⋅g …

Capacity Fading Analyses Of Lini0.5Co0.2Mn0.3O2And Lini0.5Co0.2Mn0.3O2/Lifepo4 Cathode Materials For Lithium-Ion Battery, Yi Hu, Xiang-Zhu He, Zhong-De Deng, Ling-Yong Kong, Wei-Li Shang

Journal of Electrochemistry

The LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP) composite cathode material for lithium-ion battery was prepared by wet ball-milling. The capacity fading behaviors of LiNi _0.5Co _0.2Mn _0.3O₂ (NMC532) and LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP) were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), charge/discharge and electrochemical impedance spectroscopy (EIS) tests. The results indicated that the capacity retention values of NMC532/LFP were 97.80% and 86.48%, respectively, after 50 cycles and 60℃ high temperature storage. The NMC532/LFP exhibited better cycle performance and high temperature storage performance. …

Cobalt-Based Nitrogen-Doped Carbon Non-Noble Metal Catalysts For Oxygen Reduction Reaction, Meng-Xiu Jiang, Jing Zhang, Yue-Hua Li, Rong Zhang

Journal of Electrochemistry

Transition metal-nitrogen co-doped carbon catalysts have attracted significant attention because of their reasonable activity and remarkable selectivity toward oxygen reduction reaction (ORR) as cathodic reaction in fuel cells. However, the role of transition metal in the active sites of the catalysts still is uncertain. In this work, the Co_x-N_y/C-T catalysts were prepared with BP2000 as a carbon source, urea (Ur) as a nitrogen source and Co(OAc)₂•4H₂O as a metal precursor by a simple chemical method. Meanwhile, in order to optimize the ORR activity, the catalysts were synthesized with different amounts of Co …

Electrochemical Behaviors Of Ce3+/Ce4+ Couple In A Mixed-Acid Medium Of Ch3So3H And H2So4, Zhao-Hua Li, Jiao-Long Xu, Ting Wu

Journal of Electrochemistry

In order to determine the optimum molar ratio between methanesulfonic acid (MSA) and sulfuric acid, linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behaviors of cerium (III)/cerium (IV) (Ce³⁺/Ce⁴⁺couple on a Pt electrode in a mixed acid solution. Various concentrations of sulfuric acid were considered in the experiments, while the concentration of MSA was fixed at 1.0 mol·L^-1. It was found that the optimum concentration of sulfuric acid was 0.8 mol·L^-1 since the current response was the highest in the control groups and …

Core-Shell Pd@Pt Ultrathin Nanowires As Durable Oxygen Reduction Electrocatalysts, Xin Wang, Yun-Jie Xiong, Liang-Liang Zou, Qing-Hong Huang, Zhi-Qing Zou, Hui Yang

Journal of Electrochemistry

This paper describes a simple CO-assisted reduction approach for the controllable synthesis of ultrathin Pd nanowires along the one-dimensional (1D) direction. Ultrathin Pt films from one to several atomic layers were successfully decorated onto ultrathin Pd nanowires by utilizing Cu UPD deposition, and followed by in-situ redox replacement reaction of UPD Cu by Pt. The core–shell structure and composition of the Pd@Pt ultrathin nanowires have been verified using transmission electron microscopy and energy dispersive X-ray spectrometry. The core–shell Pd@Pt ultrathin nanowires exhibited comparative electrocatalytic activity and improved durability for the oxygen reduction reaction in comparison with commercial Pt black. The …

Effect Of Allyl Thiourea On Nickel Electrodeposition From Solution Containing Ammonia And Chloride, Ya-Ning He, Liang Yuan, Zhi-Ying Ding, Shi-Jun Liu

Journal of Electrochemistry

The effects of allylthiourea (ATU) concentration on the cathodic polarization behaviour, nucleation and surface morphology of nickel electrodeposited on the glassy carbon electrode from ammonia-ammonium chloride-water (NH₃-NH₄Cl-H₂O) solutions were investigated by cyclic voltammogry, cathodic polarization and current transient methods. The results revealed that the addition of ATU inhibited nickel deposition, which was enhanced with an increase in ATU concentration from 5 to 50 mg•L^-1. The initial deposition kinetics corresponded to a model including instantaneous nucleation and diffusion controlled growth. In the presence of ATU, the initial nucleation of nickel electrocrystallisation remained unchanged. …

Effects Of Jet Milling And Classifying Process On The Performance Of Lifepo4/C In Full Batteries, Xing-Liang Liu, Mao-Ping Yang, Wei-Wei Wang, Yong Cao

Journal of Electrochemistry

The carbon coated lithium iron phosphate (LiFePO₄/C) composite cathode material was prepared by using iron phosphate process. The effects of jet milling and classifying process on the electrochemical performance of LiFePO₄/C cathode material in full batteries were investigted. Scanning electron microscopic analyses suggested that the globose secondary particles were crustily crushed during the jet milling and classifying process, which would further result in lower tap density and carbon content. The LiFeP₄/C composite cathode materials with different physical characteristics were further tested in full batteries to evaluate the electrochemical properties. The results showed no obvious …

Engineering The Electrochemical Capacitive Properties Of Activated Carbon By Correct Selection Of Ionic-Liquid Electrolytes, Qiu-Hong Zhang, Bao-Shou Shen, Song-Lin Zuo, Xin-Yu Wei

Journal of Electrochemistry

In order to improve the electrochemical capacitive properties and to apply coconut shell activated carbon (AC) serving as electrode materials in ionic liquid (IL)-based supercapacitor (SC), the coconut shell AC material was re-activated using a steam as an activating agent in this work, forming a secondary AC (W-AC). The results showed that the specific capacitance of the W-AC electrode was much larger than that of the raw activated carbon electrode (R-AC) in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF₄). The electrochemical techniques including cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) measurement, and electrochemical impedance spectroscopy (EIS) were used to systematically study the capacitive …

Applications Of N-Methyl-N-Butyl-Pyrrolidinium Bromide And N-Methyl-N-Ethyl-Pyrrolidinium Bromide In Zn-Br Flow Batteries, Qi Zhang, Miao-Miao Zhang, Lin Meng

Journal of Electrochemistry

It is extremely important for battery performance and safety in Zn-Br flow battery to use quaternary ammonium salts as complex agents for bromine. In this work, the effects of electrolyte compositions and concentrations on the electrode reactions and battery performances were studied in the absence and presences of N-methyl-N-ethyl-pyrrolidinium bromide (MEP) or N-methyl-N-butyl-pyrrolidinium bromide (MBP). The conductivities in the electrolytes containing different constitutions and concentrations were measured by EIS method. The charge-discharge performance for the battery and the complex ability for bromine in different electrolytes were also investigated. The results showed that the electrolyte containing MBP was better than that …

Effect Of Fe2+/Fe3+Interconvertion On Reduction Behavior Of Fe3+ In Acidic Electrolytes, Jian-Xin Qin, Feng Lin, Wen-Ping Liu, Chao Chen, Meng-De Ren

Journal of Electrochemistry

The influences of ferrous/ferric (Fe²⁺/Fe³⁺) interconvertion on electrochemical reduction and electrode reaction of Fe³⁺ were investigated by using linear sweep voltammetry, potentiostatic method and cyclic voltammetry (CV) in acidic electrolytes containing chloride ion (Cl^-) and sulfate ion (SO₄^2-). It was shown that the reduction process of Fe³⁺/Fe²⁺ would take place in two independent stages: (1) the reduction of Fe³⁺ to Fe²⁺ at E=0.35V and (2) the co-precipitation of Fe²⁺ by forming Fe(OH)₂ (E≤-0.3 V) instead of Fe. The major effect of Fe^{2+ …}