3,310 research outputs found

    Thermochemistry of Species in Gas-Phase Thermal Oxidation of C<sub>2</sub> to C<sub>8</sub> Perfluorinated Carboxylic Acids

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    New thermochemical properties, Cp°(T), H°(T), S°(T), and G°(T), are predicted for 123 species involved in the thermal destruction of perfluorinated carboxylic acids (PFCAs) using computational quantum chemistry and ideal-gas statistical mechanics. Relevant species were identified from the development of mechanisms for the pyrolysis and oxidation of PFCAs of C2 to C8 in length. Partition functions were obtained from the results of calculations at the G4 level for species up to C4 in length and M06-2X-D3(0)/def2-QZVPP for species C5 to C8 in length. The 1D hindered-rotor approximation was used to correct for torsional modes in the larger species. Ideal-gas thermochemistry was computed and fitted to 7-parameter NASA polynomials over a 200–2500 K temperature range, and the data are provided in standardized format. To gauge the effects of both method and basis set choice, enthalpies of formation at 0 K are calculated from various other density functionals (including B3LYP and ωB97XD), basis sets, and composite model chemistries (CBS-QB3). They are benchmarked against data from the Active Thermochemical Tables, high-level ANL0 calculations from the literature, and G4 calculations from this work. The effects of internal rotations and other anharmonicities are discussed, and bond dissociation energies and reaction equilibria provide mechanistic insights

    Reactivity of [Cp*Fe(η⁔ ‐As₅)] towards Carbenes, Silylenes and Germylenes

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    The reaction behavior of [Cp*Fe(η5-As5)] (I) (Cp*=C5Me5) towards carbenes and their heavier analogs was investigated. The reaction of I with NHCs (NHCs=N-heterocyclic carbenes) results in the first substitution products of polyarsenic ligand complexes by NHCs [Cp*Fe(η4-As5NHC)] (1 a: NHC=IMe=1,3,4,5-tetramethylimidazolin-2-ylidene, 1 b: NHC=IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene). In contrast, the reaction of I with EtCAAC (EtCAAC=2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene) leads to a fragmentation and the formation of an unprecedented As6-sawhorse-type compound [As2(AsEtCAAC)4] (2). The reaction of (LE)2 (L=PhC(NtBu)2; E=Si, Ge) with I resulted in a rearrangement and an insertion of LE fragments, forming unique silicon- (4: [Cp*Fe(η4-As4SiL)], 5 a: [Cp*Fe(η4-As6SiL)) and germanium-containing (5 b: [Cp*Fe(η4-As6GeL)) cyclic polyarsenic ligand complexes

    Activating Methane and Other Small Molecules: Computational study of Zeolites and Actinides

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    Exploring the catalytic properties and reactivity of actinide complexes towards activation of small molecules is important as human activities have led to the increased distribution of these species in nature. Toward this end, it is important to have a computational protocol for studying these species, in this thesis we provide details on the performance of multiconfigurational pair-density functional theory (MC-PDFT) in actinide chemistry. MC-PDFT and Kohn-Sham Density Functional Theory (KS-DFT) perform well for these species with indications that the former can be used for species with even greater static electron correlation effect. In addition, we study the activity of organometallic trans-uranium complexes towards the electrocatalytic reduction of water. We conclude that, with a guided choice of ligand, neptunium complexes can provide similar reactivity when compared to organometallic uranium complexes.Conversion of methane to methanol has been a major focus of research interest over the years. This is largely due to the abundance of natural gas, of which methane is the major constituent. Copper-exchanged zeolites have been shown to be able to kinetically trap activated methane as strongly-bound methoxy groups, preventing over-oxidation to CO2, CO and HCOOH. In this stepwise process, there are three cycles; an initial activation step to form the copper oxo active site, methane C-H activation and lastly simultaneous desorption of methanol and re -activation of the active site.. We provide detailed description of the pathway for the formation of over oxidation products. It is observed that to ensure high selectivity to methanol and prevent further hydrogen atom abstraction by extra-framework species, the methyl group must be stabilized from the copper-oxo active sites. There is a temperature gradient between the steps in the methane-to-methanol conversion cycle which is an impediment to industrial adoption of this approach for methane-to-methanol conversion. To mitigate this, we have investigated the impact of heterometallic extra-framework motifs on the temperature gradients of each step. Using periodic DFT, we provide detailed descriptions of the mechanistic pathways for each of the three steps. We were subsequently able to design motif(s) with great methane C-H activities as well as the abilities to be formed and regenerated at nearly the same temperatures. We found [Cu-O-Ag] and [Cu-O-Pd] to be potential candidates for isothermal or near-isothermal operations of the methane-to-methanol conversion cycle. Finally, we provide insights to the changes in optical spectra of activated copper-exchanged zeolites, gaining an understanding of the evolution of these systems on a molecular level will provide opportunities to achieve improved reactivity

    AIEgen orthopalladated hybrid polymers for efficient inactivation of the total coliforms in urban wastewater

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    Monitorable AIE polymers with a bioactive pattern are employed in advanced biomedical applications such as functional coatings, theranostic probes, and implants. After the global COVID-19 pandemic, interest in developing surfaces with superior antimicrobial, antiproliferative, and antiviral activities dramatically increased. Many formulations for biocide surfaces are based on hybrid organic/inorganic materials. Palladium (II) complexes display relevant activity against common bacteria, even higher when compared to their uncoordinated ligands. This article reports the design and synthesis of two series of orthopalladated polymers obtained by grafting a cyclopalladated fragment on two diferent O, N chelating Schif base polymers. Diferent grafting percentages were examined and compared for each organic polymer. The fuorescence emission in the solid state was explored on organic matrixes and grafted polymers. DFT analysis provided a rationale for the role of the coordination core. The antibacterial response of the two series of hybrid polymers was tested against the total coliform group of untreated urban wastewater, revealing excellent inactivation abilit

    Bismuth Cations: Fluoride Ion Abstraction, Isocyanide Coordination, and Impact of Steric Bulk on Lewis Acidity

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    The molecular compound [BiDipp2(SbF6)], containing the bulky, donor-free bismuth cation [BiDipp2]+ has been synthesized and fully characterized (Dipp=2,6-iPr2-C6H3). Using its methyl analog [BiMe2(SbF6)] as a second reference point, the impact of steric bulk on bismuth-based Lewis acidity was investigated in a combined experimental (Gutmann-Beckett and modified Gutmann-Beckett methods) and theoretical approach (DFT calculations). Reactivity studies of the bismuth cations towards [PF6]− and neutral Lewis bases such as isocyanides C≡NR’ revealed facile fluoride ion abstraction and straightforward Lewis pair formation, respectively. The first examples of compounds featuring bismuth-bound isocyanides have been isolated and fully characterized

    Combination of natural betanidin dye with synthetic organic sensitiser towards dye-sensitised solar cell application

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    A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Materials Science and Engineering of the Nelson Mandela African Institution of Science and TechnologyBetanidins belong to natural red-purple pigments betacyanins, which experimentally demonstrated good light adsorption in a visible range and might be suitable for the dye sensitised solar cell (DSSCs). Instability is a well-known drawback of natural dyes, which impedes their use for DSSCs. A thermodynamic approach helps to understand the betanidin (Bd) instability which occurs due to spontaneous decarboxylation reaction with decarboxylated betanidin (dBd) formation. The study considers the improvement of the sensitiser’s functionality via combination of natural Bd/dBd dyes and synthetic 4- (Diphenylamino)phenylcyanoacrylic acid (L0) dye. Novel complex D–π–A organic dyes, L0–Bd and L0–dBd with structural isomers, have been designed via esterification reactions. The DFT/B3LYP5/6‒31G(d,p) approach has been used to compute geometry, vibrational spectra and thermodynamic characteristics of the individual isomers and their complexes with L0. Implementation of TD–DFT method aids in obtaining optoelectronic properties. The broader coverage of the solar spectrum with greater light-harvesting efficiency was achieved for the complexes compared to individual dyes. The dyes attachment to the semiconductor TiO2 was simulated in terms of different adsorption modes to hydrogenated (TiO2)6 cluster. Binding energies and electronic spectra of the dye@TiO2 systems were computed, and electron density distributions over frontier molecular orbitals analysed. Binding energy magnitudes varied within 15‒21 eV for the dye@TiO2 systems

    Über die Darstellung 2,6-Di-iso-propylphenyl substituierter Bismutverbindungen und neuer bismuthaltiger Interpnictogenverbindungen

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    Ziel der vorliegenden Dissertation war die Darstellung neuer Interpnictogenverbindungen mit terminalen Diarylbismut-Einheiten. Die Darstellung erfolgte aus Verbindungen der Form Ar2BiX (X = F, Cl, Br), wobei als Aromaten Phenyl-, Mesityl und 2,6-Di-iso-propylphenyl-Substituenten eingesetzt wurden, um den Einfluss des sterischen Anspruchs auf die StabilitĂ€t der Verbindungen zu untersuchen. Arylhalidobismutane mit Phenyl- und Mesityl-Substituenten sind weitestgehend in der Literatur beschrieben. Dagegen wurde der Dipp-Substituent im Rahmen dieser Arbeit in die Bismut-Chemie eingefĂŒhrt. Weiterhin wurde der Aufbau neuer bismuthaltiger Interpnictogenverbindungen mit Bi-N, -P, -As und -Sb Einfachbindung untersucht und deren ReaktivitĂ€t evaluiert

    Functionalization and Subsequent Chemical Reactions of Polypnictogen Ligand Complexes

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    In summary, this dissertation deals with the synthesis and functionalization of polypnictogen ligand complexes. Besides the successful realization of the latter with organic nucleophiles and electrophiles, a conceptually new way for the preparation of phosphines could be found. For the first time, a functionalized phosphorus atom could be removed from the coordination sphere of a transition metal. This finding was transferred to other substituents and the versatility of this method was demonstrated

    Rétention du tritium dans les parois en béryllium d'ITER : modélisation ab initio de son insertion dans l'oxyde et aux joints de grains

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    L’installation ITER a pour finalitĂ© de dĂ©montrer la maĂźtrise de la production d’énergie par fusion thermonuclĂ©aire Ă  partir d’un plasma de tritium-deutĂ©rium, deux isotopes de l’hydrogĂšne. La rĂ©action de fusion est produite dans une chambre Ă  vide autour de laquelle des aimants supraconducteurs permettent de confiner le plasma. Le tritium Ă©tant radioactif, du point de vue de l’analyse de sĂ»retĂ©, il est nĂ©cessaire d’étudier ses interactions avec les diffĂ©rents matĂ©riaux constitutifs de la chambre Ă  vide. En l’occurrence, la premiĂšre paroi de la chambre Ă  vide est en bĂ©ryllium, matĂ©riaux choisis pour sa faible absorption du tritium et sa grande affinitĂ© vis-Ă -vis de l’oxygĂšne permettant de purifier la chambre vide. L’étude de l’interaction du tritium avec le bĂ©ryllium va permettre d’évaluer l’efficacitĂ© des mĂ©thodes mises en place par l’exploitant afin de quantifier l’inventaire en tritium dans la chambre, les mĂ©thodes d’étuvage de la premiĂšre paroi pour la dĂ©sorption du tritium et minimiser les rejets dans l’environnement en cas de perte de confinement de la chambre Ă  vide. De prĂ©cĂ©dant travaux ont permis d’analyser l’interaction du tritium avec le bĂ©ryllium et ses dĂ©fauts intrinsĂšques, ce travail a donc pour but d’étendre l’étude aux dĂ©fauts plus complexes. Le bĂ©ryllium en s’associant Ă  l’oxygĂšne va former de l’oxyde de bĂ©ryllium. En fonctionnement normal, il va donc se former une couche d’oxyde de bĂ©ryllium au niveau de la paroi en bĂ©ryllium. La comprĂ©hension de l’interaction du tritium avec la premiĂšre paroi passe donc Ă©galement par la comprĂ©hension du comportement du tritium avec l’oxyde de bĂ©ryllium. Une premiĂšre partie de ce travail de thĂšse est donc consacrĂ©e Ă  l’évaluation de la solubilitĂ© et de la diffusivitĂ© du tritium dans l’oxyde de bĂ©ryllium. La premiĂšre paroi Ă©tant formĂ©e de bĂ©ryllium polycristallin, la seconde partie est donc consacrĂ©e Ă  l’étude des joints de grain, interface entre deux cristaux. Le nombre de configurations possibles pour les joints de grain Ă©tant trĂšs important, il est nĂ©cessaire dans un premier temps de modĂ©liser les diffĂ©rents joints de grains du bĂ©ryllium pour dĂ©terminer ceux qui sont Ă©nergĂ©tiquement les plus favorables. Pour ensuite pouvoir y Ă©tudier la sĂ©grĂ©gation du tritium, en l’occurrence dĂ©terminer si ces joints de grain peuvent avoir un effet de type "chemin de fuite" augmentant ainsi la diffusion, ou de type "rĂ©servoir" formant des poches qui piĂšgent le tritium
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