Dissertations / Theses on the topic 'Molecular adsorption'
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Wallace, William Todd. "Selective molecular adsorption on gold clusters." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/27045.
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Heslop, Mark J. "Binary gas adsorption in molecular sieves." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/6861.
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This thesis is concerned with the development of sorption-effect chromatography as a rapid method for the determination of binary gas-mixture adsorption isotherms.There are many alternative non-chromatographic methods but these have inherent disadvantages the direct experimental methods require excessive equilibration times and the predictive methods require the respective pure-component isotherms and an ideal adsorbed phase. A computer simulation has shown that for an alternative chromatographic method, good results will only be obtained if both binary isotherms are close to linear. Sorption-effect chromatography is characterised by the flowrate retention time (TN) which measures the change in column inventory when a perturbation is made to the system. Along with the standard composition retention time (Tx), this extra measurement allows the gradient of each binary isotherm to be evaluated. Subsequent integration will give the respective mixture isotherm. Three gas systems (nitrogen-argon, nitrogen-helium and argon-helium) have been investigated over zeolite 5A at different temperatures. The results confirm that the adsorbed phase amounts decrease, with increasing temperature and that there are degrees of component interaction. Experimentally, thermal fluctuations in the oven will cause noise on the flowrate record making TN determination difficult. Isolation of the column from direct air flow was seen to reduce the noise level. Also, using a computer simulation model, the heat of adsorption for the above zeolite 5A systems will be easily dissipated preventing any unwanted gas temperature rises; the comparatively small column diameter was found to be a significant factor. The employment of delay lines (empty tubes) in various locations has been investigated. To directly determine TN it is necessary to used delay lines downstream of the column. Also, the chromatographic method has been extended to determine mixture isotherms by considering the change in average column pressure rather than the motion of a composition front through the column. Delay lines situated upstream of the column are able to separate these two effects, and preliminary results are satisfactory. However, the use of delay lines anywhere in the system changes the measured retention times and the theory has to be adjusted to account for this.
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Torres, Melissa Christine. "Copper adsorption on functionalized molecular sieves." Thesis, University of Iowa, 2011. https://ir.uiowa.edu/etd/1096.
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Naser, Md Abu. "Molecular dynamics simulation of protein adsorption." Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2187.
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Apolonatos, Georgia. "Gas adsorption with molecular sieve zeolites." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5907.
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Adsorption kinetics and equilibrium of CH$\sb4$, CO and N$\sb2$ gases were studied on various molecular sieve zeolites. Ethylyne was also tested, yet was found to be incompatible with the molecular sieves under consideration. The gas chromatographic technique was chosen as the method of studying the adsorption by which equilibrium and kinetic parameters are derived by matching the response peak to appropriate mathematical models. It was found that the synthetic zeolites (H-Mordenite, 4A zeolite, 5A zeolite) rather than naturally occurring Chabazite had a higher capacity for the adsorption of all three gases. Pure and binary gas isotherms of CH$\sb4$ and CO with molecular sieve 5A were also studied for the separation of these gases. These isotherms indicated that under the present conditions CO is preferentially adsorbed on the 5A zeolite and the adsorption capacity of the sieve increases with decreased temperature.
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Åkesson, Patrik. "Molecular Dynamics of the Adsorption of Organic Molecules on Organic Substrates." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-103688.
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A great interest has been shown for self-assembled organic nano-structures that can be used in a variety of optoelectronic applications, from element detection to home electronics. It is known from experimental research that sexiphenyl (6P) grown on muscovite mica substrate form uniaxially self-assembled nanofibers which together with sexithiophene (6T) deposited on top gives the possibility to tune their polarized emission. A key to continue develop and explore the full potential of this technique is to understand the mechanisms behind the growth. This thesis investigate the initial growth of 6P and 6T on a 6PProject P25154-N20 "Hetero-epitaxy of organic-organic nanofibers"
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Nesbitt, Alan. "A molecular beam investigation of adsorption dynamics." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333567.
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Gore, B. L. "Picosecond adsorption spectroscopy of molecular excited states." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47081.
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Dourado, Eduardo Manuel de Azevedo. "Computer simulations of adsorption and molecular recognition phenomena in molecularly imprinted polymers." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5680.
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Molecularly imprinted polymers (MIPs) are a novel, promising family of porous materials with potential applications ranging from separations, chemical sensing and catalysis to drug delivery and artificial immunoassays. The unique feature of these materials is their biomimetic molecular recognition functionality. Molecular recognition is the biological phenomenon of specific, selective and strong association between a substrate and a ligand. In man made MIPs this functionality is implemented via templated synthesis protocol. MIPs are synthesized in the presence of additional template molecules which form complexes with functional monomers in the pre‐polymerization mixture. After polymerization, the template is removed, leaving cavities in the structure which are complementary in shape and interaction patterns to the template molecules. These cavities act as mimics of biological receptors and are able to recognize and rebind template molecules. Although the imprinting concept is simple in principle, synthesis of MIPs with precisely controlled characteristics and performance remains a challenging task. Composition, polymerization conditions, template removal process and application conditions all affect the properties of MIPs. The material is affected at different scales, but crucially at the microscopic level, the number, fidelity and accessibility of binding sites are dependent on all the factors mentioned. The full potential of these materials can only be achieved if researchers can control and optimize the properties of MIPs through detailed understanding of adsorption and molecular recognition processes in these materials. The objective of this work is to, using computer simulations and statistical mechanics; develop a fundamental description of MIP formation and function, and to link morphological features of the model materials to their molecular recognition capabilities. In general, molecular simulations employed in this study should allow easier and more efficient exploration of a vast number of factors influencing the behaviour of MIPs. At the heart of the approach developed in this thesis is a computational strategy that imitates all the stages of MIP formation and function. First, the model simulates the pre‐polymerization mixture, allowing the formation of template‐functional monomer complexes. (This stage is implemented via canonical Monte Carlo simulation). Complexes can have different structures, depending on the chemical nature of template and functional monomer; therefore complexes can have a range of association constants. The distribution of template‐functional monomer complexes also translates into a distribution of binding sites of different specificity after template removal. In the second stage of the process, adsorption simulations (grand canonical Monte Carlo) are performed for a variety of model MIPs prepared to assess the role of various processing conditions such as composition, density and binding sites degeneration. This strategy was first applied to a simplified description of MIP species in order to identify the minimal model capable of molecular recognition and thus shed the light on the very nature of this phenomenon. In the developed model, the molecular species are constructed from hard spheres, featuring small interaction sites on their surfaces. The bond between two interaction sites has the strength and topological features of a typical hydrogen bond. The model exhibits molecular recognition, being able to preferentially adsorb template molecules. The associations between template and functional monomers were analyzed and classified to describe the distribution of binding sites and their heterogeneity. Using this model, several experimental trends typically observed in MIP studies could be explained, such as maximum in the selectivity as a function of monomer concentration. Using this model, we were also able to explore hypothetical, alternative protocols for MIP synthesis in order to improve their performance. These include the use of alternative templates and the post‐synthetic surface modifications of MIPs. The general strategy to modelling MIP, employed in this thesis, was then applied to a more detailed description of MIPs with realistic force field potentials for all the species involved. This more elaborate model is simulated with a combination of molecular dynamics (MD) and Monte Carlo techniques. This detailed model provided a wealth of information on various types of complexes observed in the pre‐polymerization mixture. Specifically, it revealed the relative weight of different interactions in the complex and their role in the binding energy of adsorbates. These simulations also provided the comparison of the relative contribution of different types of interactions (van der Waals, Coulombic) involved in a molecular recognition process. We believe the insights gained in this work will contribute to the development of rational MIP design strategies. In the discussion of the results of the thesis we speculate on how these models can be further developed in order to generate quantitative predictions and what type of systems it would be interesting and important to investigate in the future.
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Brandani, Giovanni Bruno. "Molecular dynamics simulations of protein adsorption at interfaces." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20415.
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Proteins can often adsorb irreversibly at fluid/fluid interfaces; the understanding of the adsorption mechanism has relevance across a variety of industrial (e.g. the creation of stable emulsions) and biological (e.g. biofilm formation) processes. I performed molecular dynamics simulations of two surfactant proteins as they interact with air/water and oil/water interfaces, describing the origin of the surface activity, the adsorption dynamics and the conformational changes that these proteins undergo at the interface. BslA is an amphiphilic protein that forms a highly hydrophobic coat around B. subtilis biofilms, shielding the bacterial community from an external aqueous solution. By investigating the behaviour of BslA variants at oil/water interfaces via coarse-grained molecular dynamics, I show that BslA represents a biological example of an ellipsoidal Janus nanoparticle, whose surface interactions are controlled by a local conformational change. All-atom molecular dynamics simulations then reveal the details of the conformational change of the protein upon adsorption, and the self-assembly into a two-dimensional interfacial crystal. Ranaspumin-2 is one of the main components of the tungara frog foam nest. Contrary to most surfactant proteins, its structure lacks any sign of amphiphilicity. All-atom simulations show that the adsorption proceeds via a two-step mechanism where firstly the protein binds to the interface through its flexible N-terminal tail and then it undergoes a large conformational change in which the hydrophobic core becomes exposed to the oil phase. I then developed a simple structure-based coarse-grained model that highlights the same adsorption mechanism observed in all-atom simulations, and I used it to compare the dynamics of adsorption and the underlying free energy landscape of several mutants. These results agree with and are used to rationalise the observations from Langmuir trough and pendant drop experiments. Colloids can often be considered simpler versions of proteins that lack conformational changes. I performed coarse-grained simulations of the compression of interfacial monolayers formed by rod-like particles. These simulations show a rich behaviour characterised by the flipping of adsorbed rods, nematic ordering and bilayer formation. I report the series of transitions that take place as the rod aspect ratio is increased from 3 to 15.
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Haas, Ole-Erich, Jean-Marc Simon, and Signe Kjelstrup. "Adsorption-desorption kinetics of H 2 molecules on graphite: a molecular dynamics study." Diffusion fundamentals 11 (2009) 29, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13978.
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Jiang, Tingming. "Adsorption of chalcogen-based aromatic organic molecules on metal and dielectric surfaces by self-assembly and molecular beam expitaxy." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS581.
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Dans cette thèse, on a étudié la formation de monocouches auto-assemblées de différentes molécules de chalcogénure et de films minces de semiconducteurs organiques. Leurs caractéristiques électroniques et structurelles ont été étudiées principalement par la spectroscopie de photoélectron à rayons X à base de rayonnement synchrotron, la spectroscopie d’adsorption de rayons X à proximité de seuil, la microscopie à force atomique et la diffraction d'électrons à faible énergie. En outre, les caractéristiques d'adsorption du sélénium et du soufre ont été étudiées comme complément à l'étude des adsorptions des molécules comportant des atomes de chalcogène. Le XPS à haute résolution a été utilisé pour enquêter sur les monocouches auto-assemblées de benzèneselénol et de sélénophène sur Cu (111). L'étude détaillée des pics caractéristiques des niveaux du coeur a démontré l'existence de différents sites d'absorption des molécules et aussi avec les mesures NEXAFS l'apparition du clivage de la liaison Se-C. Ces conclusions sont étayées par l'étude de l’adsorption de sélénium atomique montrant également différents sites d'absorption pour le sélénium atomique avec différents environnements chimiques basés sur une étude XPS haute résolution des spectres caractéristiques Se3d, Se3p et l'imagerie LEED. On a étudié les adsorptions de molécules de polythiophène (nT, n = 1-4, 6) ainsi que pour le α, ω-diquaterthiophène (DH4T) et le dihexylsexithiophène (DH6T) sur les films Au (111) et films de Au sur le mica. Les résultats indiquent que les pics XPS S2p ont des contributions de molécules intactes sur différents sites d'adsorption et des molécules cassées. Ces conclusions sont étayées par les calculs DFT existants. La dissociation spontanée apparaît dans une mesure variable dans différents cas, ce qui pourrait être lié à différentes morphologies de surface, à l'existence de défauts et à la réactivité différentes liés a ces défauts. Des films ultra-minces d'α-sexithiophène (6T) ont été déposés sur des surfaces planes de CaF2 (111) / Si (111) et sur des surfaces striées de CaF2 (110) / Si (001) par épitaxie par faisceau moléculaire. L'image AFM de 6T sur CaF2 (111) montre de grandes îles avec des terrasses plates sans préférence dans le plan, tandis que des îlots étroits et allongés suivant l'ondulation du substrat sont formés pour 6T sur CaF2 (110). Les spectres XPS et NEXAFS indiquent que les interactions entre 6T et les surfaces sont négligeables et que les molécules s'alignent avec leur long axe perpendiculaire aux surfaces pour les deux casIn this thesis, formation of self-assembled monolayers of different chalcogenide molecules and organic semiconductor thin films was investigated. Their electronic and structural characteristics have been investigated primarily by synchrotron based X-ray photoelectron, near edge X-ray absorption fine structure spectroscopy, Atomic force microscopy and low energy electron diffraction. In addition, the adsorption characteristics of selenium and sulfur were studied as a complement to the study of adsorptions of chalcogen headgroup molecules. The high resolution XPS was employed to investigate the self assembled monolayers of benzeneselenol and selenophene on Cu(111). The detailed study of characteristic core level peaks demonstrated the existence of different absorption sites of the molecules and also along with NEXAFS measurements the occurrence of Se-C bond cleavage. These conclusions are supported by the study of atomic selenium adsorptions showing also different absorption sites for the atomic selenium with different chemical environments based on high resolution XPS study of characteristic Se3d, Se3p spectra and LEED imaging. The adsorptions of polythiophene molecules (nT, n=1-4, 6) as well as for α, ω-diquaterthiophene (DH4T) and dihexylsexithiophene (DH6T) on Au(111) and Au films grown on mica was studied. The results indicate that the XPS S2p peaks have contributions from intact molecules on different adsorption sites and broken molecules complemented. These conclusions are supported by existing DFT calculations. Spontaneous dissociation appears to a variable extent in different cases, which could be related to different surface morphologies, existence of defects and ensuing differences reactivity.α-Sexithiophene (6T) ultrathin films were grown on CaF2(111)/Si(111) planar surfaces and on CaF2(110)/Si(001) ridged surfaces by molecular beam epitaxy. The AFM image of 6T on CaF2(111) shows large islands with flat terraces without in-plane preference, while narrow and elongated islands following the substrate corrugation are formed for 6T on CaF2(110). XPS and NEXAFS spectra indicate that the interactions between 6T and surfaces are negligible, and the molecules align with their long axis perpendicular to the surfaces for both cases
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Zhang, Fei. "Adsorption of Small Molecules in Advanced Material Systems." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/89917.
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Adsorption is a ubiquitous phenomenon that plays key roles in numerous applications including molecule separation, energy storage, catalysis, and lubrications. Since adsorption is sensitive to molecular details of adsorbate molecule and adsorbent materials, it is often difficult to describe theoretically. Molecular modeling capable of resolving physical processes at atomistic scales is an effective method for studying adsorption. In this dissertation, the adsorption of small molecules in three emerging materials systems: porous liquids, room-temperature ionic liquids, and atomically sharp electrodes immersed in aqueous electrolytes, are investigated to understand the physics of adsorption as well as to help design and optimize these materials systems.
Thermodynamics and kinetics of gas storage in the recently synthesized porous liquids (crown-ether-substituted cage molecules dispersed in an organic solvent) were studied. Gas molecules were found to store differently in cage molecules with gas storage capacity per cage in the following order: CO2>CH4>N2. The cage molecules show selectivity of CO2 over CH4/N2 and demonstrate capability in gas separation. These studies suggest that porous liquids can be useful for CO2 capture from power plants and CH4 separation from shale gas.
The effect of adsorbed water on the three-dimensional structure of ionic liquids [BMIM][Tf2N] near mica surfaces was investigated. It was shown that water, as a dielectric solvent and a molecular liquid, can alter layering and ordering of ions near mica surfaces. A three-way coupling between the self-organization of ions, the adsorption of interfacial water, and the electrification of the solid surfaces was suggested to govern the structure of ionic liquid near solid surfaces.
The effects of electrode charge and surface curvature on adsorption of N2 molecules near electrodes immersed in water were studied. N2 molecules are enriched near neutral electrodes. Their enrichment is enhanced as the electrode becomes moderately charged but is reduced when the electrode becomes highly charged. Near highly charged electrodes, the amount of N2 molecules available for electrochemical reduction is an order of magnitude higher near spherical electrodes with radius ~1nm than near planar electrodes. The underlying molecular mechanisms are elucidated and their implications for development of electrodes for electrochemical reduction of N2 are discussed.Doctor of Philosophy
Adsorption is a ubiquitous phenomenon that plays key roles in numerous applications including molecule separation, energy storage, catalysis, and lubrications. Since adsorption is sensitive to molecular details of adsorbate molecule and adsorbent materials, it is often difficult to describe theoretically. Molecular modeling capable of resolving physical processes at atomistic scales is an effective method for studying adsorption. In this dissertation, the adsorption of small molecules in three emerging materials systems: porous liquids, room-temperature ionic liquids, and atomically sharp electrodes immersed in aqueous electrolytes, are investigated to understand the physics of adsorption as well as to help design and optimize these materials systems. Thermodynamics and kinetics of gas storage in the recently synthesized porous liquids (crown-ether-substituted cage molecules dispersed in an organic solvent) were studied. Gas molecules were found to store differently in cage molecules with gas storage capacity per cage in the following order: CO2>CH4>N2. The cage molecules show selectivity of CO2 over CH4/N2 and demonstrate capability in gas separation. These studies suggest that porous liquids can be useful for CO2 capture from power plants and CH4 separation from shale gas. The effect of adsorbed water on the three-dimensional structure of ionic liquids [BMIM][Tf2N] near mica surfaces was investigated. It was shown that water, as a dielectric solvent and a molecular liquid, can alter layering and ordering of ions near mica surfaces. vi A three-way coupling between the self-organization of ions, the adsorption of interfacial water, and the electrification of the solid surfaces was suggested to govern the structure of ionic liquid near solid surfaces. The effects of electrode charge and surface curvature on adsorption of N2 molecules near electrodes immersed in water were studied. N2 molecules are enriched near neutral electrodes. Their enrichment is enhanced as the electrode becomes moderately charged but is reduced when the electrode becomes highly charged. Near highly charged electrodes, the amount of N2 molecules available for electrochemical reduction is an order of magnitude higher near spherical electrodes with radius ~1nm than near planar electrodes. The underlying molecular mechanisms are elucidated and their implications for development of electrodes for electrochemical reduction of N2 are discussed.
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Vargas, fuentes Crisa. "Theoretical studies on molecular adsorption and selective hydrogenation catalysts." Doctoral thesis, Universitat Rovira i Virgili, 2013. http://hdl.handle.net/10803/454762.
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Esta tesis se divide básicamente en dos bloques principales desarrollados por medio de la Teoría del Funcional Densidad, a saber, Adsorción Molecular y Promotores en la Hidrogenación Selectiva de Alquinos en Mezclas. El primero describe un análisis del comportamiento de un número de moléculas orgánicas (C2H2, C2H4, CH2O, CHN, CH4O, y CO2H2) y fragmentos (CH3O, and CO2H) adsorbidas sobre cuatro caras diferentes, (100), (110), (111), y (211), de la estructura cristalográfica estable fcc de ocho sistemas monometálicos (Pd, Pt, Rh, Ir, Cu, Ni, Ag, and Au), además probando varios sitios de cada superficie. Los Promotores en la Hidrogenación Selectiva de Alquinos en Mezclas se han estudiado mediante la investigación de los papeles que juegan los diferentes componentes del mítico catalizador Lyndlar en primer lugar, y luego del paladio con otros posibles co-catalizadores además del plomo, haciendo comparaciones entre ellos y también con el catalizador paladio en solitario.This dissertation is basically divided in two main blocks performed by means of Density Functional Theory, i.e. Molecular Adsorption and Promoters in the Selective Hydrogenation of Alkynes in Mixtures. The former describes an analysis of the behaviour of a number of organic molecules (C2H2, C2H4, CH2O, CHN, CH4O, and CO2H2) and fragments (CH3O, and CO2H) adsorbed on four different facets, (100), (110), (111), and (211), of the stable fcc crystallographic structure of eight monometallic systems (Pd, Pt, Rh, Ir, Cu, Ni, Ag, and Au), moreover testing various sites on each surface. Promoters in the Selective Hydrogenation of Alkynes in Mixtures has been studied from the investigation of the roles of the different components in the legendary Lindlar catalyst in the first place, and then palladium with other possible co-catalysts besides lead, making a comparison between them and also with the clean palladium catalyst.
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Yazaydin, Ahmet Ozgur. "Molecular simulation of the adsorption of organics from water." Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-042507-023605/.
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Shapley, Thomas Victor. "Molecular adsorption and templating at the solid-water interface." Thesis, University of Bath, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607625.
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The aim of the thesis is to apply atomistic simulation techniques to investigate the factors controlling the adsorption of a range of organic compounds at mineral interfaces. The work broaches three main topics: the adsorption of persistent organic pollutants at remediative clay interfaces, the fate of illicit and pharmaceutical drug molecules in the environment and the adsorption of the organic template TPA at the surfaces of siliceous MFI. Chapter 1 introduces these three themes and outlines previous work, both experimental and computational, relevant to the research areas. Chapters 2 and 3 outline the computational methodologies used throughout the work. The quantum and potential based methods that define the forces and thus interaction between atoms are detailed in chapter two. Chapter three describes how these forces are utilised to find lowest energy structures, calculate free-energies and probe surface structures. The results begin in chapter 4 with an investigation of the interactions of the persistent organic pollutants polychlorinated dibenzo-p-dioxins with single and bilayers of clay minerals in the presence of water. It was found that the adsorption to hydrophilic clays was poor due to competition with water. Equally, it was found that the hydrophobic regions created by organoclays were able to adsorb the molecules to the same extent as a hydrophobic surface. Chapter 5 describes the challenges in modelling several drug molecules found in the environment, at a range of solvated mineral and organic surfaces. The simulations predict that the favourability of adsorption was strongly dependent on the charge of the molecule, and hence pH. Chapter 6 shows the influence of surface structure on the adsorption of the SDA TPA to the siliceous MFI zeolite. Furthermore, it is shown. how the surface interactions of TPA and water impact the morphology of MFI.
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Pugh, Steven. "First-principles simulation of molecular adsorption at oxide surfaces." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321407.
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Casagrande, Douglas. "Adsorção Atômica e Molecular de Cloro sobre a Superfície Livre de Silício." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-23052012-152952/.
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Realizamos dentro do formalismo ab-initio do funcional da densidade e pseudopotenciais com conservação da norma, estudos detalhados da geometria atômica e estrutura eletrônica das superfícies Si (001) com a deposição de Cl atômico sobre as reconstruções (2x1) e (4x2), e disposição de Cl molecular sobre a superfície (001) com reconstrução (2x1). Estudamos também a superfície Si (111) com reconstruções (1x1), (2x1) e (4x2) com a deposição de Cl atômico. A superfície Si (001)-(2x1) com deposição de CI molecular mostrou evidências da não desorção do composto SiCI2. Os resultados para a deposição de Cl atômico sobre as superfícies Si (001)-(2x1) e Si (001)-(4x2) foram os mesmos para a geometria atômica e energia total por átomo de superfície. Os átomos de CI posicionam-se a 19,5° em relação a normal com um comprimento de ligação de 2,08 A. As superfícies Si (111)-(2x1) e Si (111)-(4x2) utilizando o modelo de cadeias ? forneceram os mesmos resultados para a geometria atômica e energia total. Os átomos de Cl posicionam-se com ângulos de 24,2° e 25,2° em relação a normal e comprimento de ligação de 2,09 A. Um efeito de blindagem e observado para a superfície livre Si (111)-(1x1) originado pela presença de ligações ? entre orbitais pz dos átomos das duas primeiras camadas. Estes estados são mais ligados do que os estados de mesma natureza para os átomos da terceira e da quarta camada. Esta blindagem e removida após a deposição de CI ocorrendo uma troca em nível de energia entre estes estados. Para a superfície Si (111)- (1x1)CI os átomos de Cl posicionam-se normalmente à superfície com comprimento de ligação de 2,08 A. A geometria relaxada dos átomos de Si aproxima-se da geometria ideal. Em todos os casos, os estados apresentados na região do gap fundamental são temem removidos após a deposição de átomos de Cl. Estados puros de CI e estados ressonantes apresentam-se especialmente nas regiões dos gaps estômagos. Uma técnica para a separação de estados eletrônicos originários de uma determinada região do cristal é introduzida. Esta técnica mostrou-se eficiente num processo de identificação de estados eletrônicos, contribuindo como uma ferramenta importante na investigação rigorosa sobre a ocorrência de estados da mesma natureza na estrutura eletrônica do cristal.We have done within the ab-initio density-functional formalism and norm-conserved pseudo-potential, detailed studies for the atomic geometry and electronic structure of Si(001) covered with atomic chlorine on tlle (2x1) and (4x2) reconstructions, and molecular chlorine adsorption on the (2x1) reconstruction. The surface Si(111) with atomic chlorine adsorption on the (1x1), (2x1) and (4x2) reconstructions were performed as well. The Si(001)-(2x1) with molecular de-position have shown evidences of non-desorption of the SiCl2 compound. The results for ato-mic deposition of Cl on Si(001)-(2x1) and Si(001)-(4x2) surfaces were the same for the atomic geometry and total energy per surface atom. The CI atoms stay at 19.5° off normal and Si-CI bond-length is 2.08 A for the relaxed surface. The Si(111)-(2x1) and Si(111)-(4x2) surfaces with the 11\" model chain have shown the same results for atomic geometry and total energy. The CI atoms atop the Si atoms with 24.2° and 25.2° off normal each one and the bond-length is 2.09 A for both. We have found screening effects on the clean Si(111)-(1x1) surface. These effects are origina-ted by 11\" bonds of pz orbitals between the first and the second atom layer that are more energetically bonded than the similar states observed between the third and the fourth atom layer. The screening is removed after CI deposition observing the swap of energy levels betwe-en that states. For Si(111)-(1x1)Cl surface, the Cl atoms atop surface normally with bond-length 2.08 A. The relaxed geometry for the Si atoms approaches to the ideal geometry. The states that have been found in the gap region for all clean surfaces are completely remo-ved after Cl deposition. Pure Cl states and resonant states were found specially in the intern stomach gaps. We have introduced a technique to collect electronic states originated from one specific crys-tal region. This technique has shown to be very efficient for electronic state identification pro-cess, contributing as an important tool for rigorous analyses, conceming about electronic sta-tes of the same nature in the electronic structure.
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Giacomini, Mattia. "Pressure Swing Adsorption on Carbon Molecular Sieves for Nitrogen Production: Modelling and Simulation with Aspen Adsorption." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/9800/.
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L’azoto è uno dei prodotti principali dell’industria chimica, utilizzato principalmente per assicurare un sicuro stoccaggio di composti infiammabili. Generatori con sistemi PSA sono spesso più economici della tradizionale distillazione criogenica.
I processi PSA utilizzano una colonna a letto fisso, riempita con materiale adsorbente, che adsorbe selettivamente un componente da una miscela gassosa. L’ossigeno diffonde molto più velocemente dell'azoto nei pori di setacci molecolari carboniosi.
Oltre ad un ottimo materiale adsorbente, anche il design è fondamentale per la performance di un processo PSA. La fase di adsorbimento è seguita da una fase di desorbimento. Il materiale adsorbente può essere quindi riutilizzato nel ciclo seguente.
L’assenza di un simulatore di processo ha reso necessario l’uso di dati sperimentali per sviluppare nuovi processi. Un tale approccio è molto costoso e lungo. Una modellazione e simulazione matematica, che consideri tutti i fenomeni di trasporto, è richiesta per una migliore comprensione dell'adsorbente sia per l'ottimizzazione del processo.
La dinamica della colonna richiede la soluzione di insiemi di PDE distribuite nel tempo e nello spazio.
Questo lavoro è stato svolto presso l'Università di Scienze Applicate - Münster, Germania. Argomento di questa tesi è la modellazione e simulazione di un impianto PSA per la produzione di azoto con il simulatore di processo Aspen Adsorption con l’obiettivo di permettere in futuro ottimizzazioni di processo affidabili, attendibili ed economiche basate su computazioni numeriche. E' discussa l’ottimizzazione di parametri, dati cinetici, termodinamici e di equilibrio.
Il modello è affidabile, rigoroso e risponde adeguatamente a diverse condizioni al contorno. Tuttavia non è ancora pienamente soddisfacente poiché manca una rappresentazione adeguata della cinetica ovvero dei fenomeni di trasporto di materia.
La messa a punto del software permetterà in futuro di indagare velocemente nuove possibilità di operazione.
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Kang, Jie Hun. "Photoelectron diffraction studies of molecular adsorbates on transition metal surfaces." Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246787.
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Mormiche, Claire. "Direct and indirect channels to molecular dissociation at metal surfaces." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252173.
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Sharp, Peter. "Passivated silicon and diamond surfaces : mapping, modification and molecular adsorption." Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604336.
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The contrasting surface chemistry of passivated and unpassivated Group IV elemental semiconductor surfaces fund amentally affects both their electronic properties and the binding of adsorbates. Partially passivated surfaces offer a way to explore these different environments simultaneously. Control of the surface properties by selective passivation also allows a route to direct the adsorption of atoms and molecules. Herein, we investigate and attempt to manipulate the properties of hydrogen-passivated silicon and diamond surfaces, and subsequently study their interaction with fullerenes. Hydrogen-passivated silicon surfaces have been studied extensively over the past few decades and it is possible to control the passivation of individual silicon atoms via STM hydrogen lithography. Despite this, hardly any work has been done using AFM and there have been no reports of for ce-meditated lithography. We have studied the H:Si(100)(2 x 1) surface with both STM and frequency modulated dynamic AFM. AFM images exhibit both conventional and inverted contrast imaging modes, which we explain in terms of the termination of the probe apex by comparing force spectra to DFT calculations. We also demonstrate hydrogen lithography via voltage pulsing using a Plus sensor.
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Undin, Torgny. "Characterization of Molecular Adsorption Using Liquid Chromatography and Mass Spectrometry." Doctoral thesis, Uppsala universitet, Analytisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-249003.
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Molecular adsorption is a key feature in several disciplines of chemistry, covering as diverse fields as chromatographic separation to biomaterial development. This thesis aims at developing methods and techniques for the characterization of molecular adsorption at the liquid-solid interface. Two different experimental models were used, small molecular interaction characterization using liquid chromatography and complex protein adsorption on polymeric materials possible for biological sampling. Holistic approaches, where both detailed molecular interactions and identifications of trends, could improve the fundamental understanding of adsorption systems, were invariably part of the scientific process. The characterization of small molecular interactions on liquid chromatography stationary phases via adsorption isotherm determination used combined data from physical phase parameters i.e. carbon loading, linear-, and nonlinear-characterization methods. These experiments were conducted on high performance liquid chromatography systems, using both ordinary reversed phase stationary phases, and hybrid phases. The expansion of the improved elusion by characteristic point (ECP) for adsorption isotherm determination, led to that previous impossible isotherm types, having inflexion points, now could be determined by the method. It also reduced errors in isotherm parameters due to the elimination of inaccurate determined retention times where the mobile phase concentration was zero. The characterization of protein adsorption where performed in an unbiased way. Adsorbed proteins on different surfaces were identified using mass spectrometry (MS) and data dependent acquisition or a targeted method. Prior MS, an improved on surface enzymatic digestion (oSED) method was used to enable identification and quantitation of adsorbed protein originating from ventricular cerebrospinal fluid (vCSF). oSED was found to be able to experimentally determine large variations in protein adsorption characteristics between native and coated polycarbonate surfaces in contact with vCSF. The method was also confirmed being mechanistic in favor of enzymatic digestion of the proteins adsorbed on a surface, rather than a prior desorption into solution before digestion. An improvement of the overall understanding of adsorption systems was not only achieved with the oSED method as a promising tool for characterization of protein adsorption on arbitrary surfaces, but also the use of linear and nonlinear approaches in stationary phase characterization that strengthened drawn conclusions.
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Marnell, Lisa. "Adsorption of precursor molecular magnets on single crystal metal surfaces." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439490.
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Jensen, Craig Robert Carl. "Multicomponent adsorption equilibrium in microporous adsorbents : thermodynamics and molecular simulation." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387986.
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Tian, Jian Atwood J. L. "Molecular organic solids for gas adsorption and solid-gas interaction." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6882.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Jerry L. Atwood. Vita. Includes bibliographical references.
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LOPEZ, EVELINA DUNESKA ESTRADA. "MOLECULAR DYNAMICS OF PREDNISOLONE ADSORPTION ON A LUNG SURFACTANT MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34024@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
BOLSA NOTA 10
A simulação da adsorção da prednisolona em um modelo de surfactante pulmonar foi realizada com sucesso usando dinâmica molecular coarse grained a uma temperatura de 310 K. O modelo coarse grained da prednisolona foi parametrizado usando o modelo do colesterol e validado utilizando cálculos de coeficientes de partição octanol-água e coeficientes de difusão lateral. O coeficiente de partição octanol-água calculado para prednisolona a 298 K é 3,9 mais ou menos 1,6 que possui um acordo razoável com o valor experimental. O coeficiente de difusão lateral da prednisolona na monocamada mista de DPPC/POPC é estimado ser (6 mais ou menos 4) x10(-7) cm(2) s(-1) a 20 mN m(-1), o que está de acordo com o encontrado para o colesterol. A monocamada mista de DPPC/POPC foi utilizada como modelo de surfactante pulmonar onde moléculas de prednisolona foram adsorvidas formando nanoagregados. Os nanoagregados de prednisolona foram transferidos dentro da monocamada mista DPPC/POPC sendo espalhados na tensão superficial de 20 mN m(-1). A 0 e 10 mN m(-1) os nanoagregados de prednisolona induzem o colapso da monocamada mista DPPC/POPC formando bicamadas. A implicação deste trabalho é que a prednisolona pode apenas ser administrada com surfactante pulmonar utilizando baixas frações em massa de prednisolona por lipídio (menor que 10 por cento). Com frações elevadas, o colapso inativa as propriedades do surfactante pulmonar pela formação de uma bicamada. Os resultados desta pesquisa podem ser utilizados para o desenvolvimento de novos tratamentos clínicos de doenças como a síndrome da angústia respiratória do recém-nascido, asma e doença pulmonar obstrutiva crônica.
The simulation of prednisolone adsorption on a lung surfactant model was successfully performed using coarse grained molecular dynamics at 310 K (dynamics first performed). The coarse grained model for prednisolone was parameterized using a well-established cholesterol model and validated by using calculations of octanol–water partition coefficients and lateral diffusion coefficients. The calculated octanol–water partition coefficient of prednisolone at 298 K is 3.9 more or less 1.6, which is in reasonable agreement with experiment. The lateral diffusion coefficient of prednisolone in the DPPC/POPC mixed monolayer is estimated to be (6 more or less 4) x10(-7) cm(2) s(-1) at 20 mN m(-1), which is in agreement with that found for cholesterol. The DPPC/POPC mixed monolayer was used as lung surfactant model where prednisolone molecules were adsorbed forming nanoaggregates. The nanoaggregates of prednisolone were transferred into the DPPC/POPC mixed monolayer being spread at the surface tension of 20 mN m(-1). At 0 and 10 mN m(-1) , the prednisolone nanoaggregates induce the collapse of the DPPC/POPC mixed monolayer forming a bilayer. The implications of this work are that prednisolone may only be administered with lung surfactant by using low mass fractions of prednisolone per lipid (less than 10 percent). And, with high fractions, the collapse inactivates the properties of the lung surfactant by forming a bilayer. The results of this research can be used to develop new clinical treatments for diseases such as respiratory distress syndrome of the newborn, asthma and chronic obstructive pulmonary disease.
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Venkatakrishnan, Abishek. "Molecular Simulations Study of Adsorption of Polymers on Rough Surfaces." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427812323.
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Bowfield, Andrew. "Spectroscopic considerations on molecular adsorption at the solid/liquid interface." Thesis, University of Liverpool, 2009. http://livrepository.liverpool.ac.uk/1225/.
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This thesis mainly focuses on the adsorption behaviour of various molecules at the solid/liquid interface. The variation in adsorption kinetics are studied as a function of concentration, pH, applied electrode potential and surrounding environment by the surface sensitive analytical techniques of Reflection Anisotropy Spectroscopy and X-ray Photoelectron Spectroscopy. An electrochemical investigation into the surface reconstructions of Au(110) and their associated RA profiles is undertaken. The spectral profiles of Au(110) in 0.1 M H2SO4/Na2SO4, NaClO4/HClO4 and NaClO4 electrolytes were observed as a function of potential and spectral signatures of the different reconstructions are assigned. The adsorption of adenine and its monophosphate (AMP) on Au(110) was studied using RAS. It is shown that both molecules adsorb in a vertical orientation through sites common to the base through formation of base stacked layers. Application of a phenomenological Lorentzian transition model and rotations about the polarisation direction of the incident light suggest that the molecules align along the [1 0] principal axis of the substrate. Linear simulations show that the orientation of adenine at sub-saturation coverage is the same as that when a monolayer is adsorbed and that adenine does not adsorb on the surface at sufficiently alkaline pH. The attachment of thiolated ss DNA on a functionalised diamond surface and the subsequent detection of hybridisation are discussed. High resolution XPS spectra are used to characterise both the integrity and structure of the organic thin film and its modification to precipitate DNA adsorption. The sensitivity of RAS to the orientation of the alkyl backbone of decanethiol is displayed through alteration to the surrounding environment of the molecule. It is suggested that orientation of the hydrophobic backbone varies as the surrounding environment is changed from ethanol to air and finally to phosphate buffer.
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Chen, Linjiang. "Molecular simulations studies of gas adsorption in metal-organic frameworks." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9366.
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Using computational tools ranging from molecular simulations – including both Monte Carlo and molecular dynamics methods – to quantum mechanical (QM) calculations (primarily at density functional theory (DFT) level), this work focuses on addressing some of the challenges faced in molecular simulations of gas adsorption in metal–organic frameworks (MOFs). This work consists of two themes: one concerns gas adsorption in MOFs with coordinatively unsaturated metal sites (cus’s), and the other one deals with predicting and understanding the breathing behaviour of the flexible MOF MIL-53(Sc). It has been shown experimentally that incorporation of cus’s – also known as “open” metal sites or unsaturated metal centres – into MOFs significantly enhances the uptake of certain gases such as CO2 and CH4. As a result of the considerably enhanced, localized guest-molecule interactions with the cus’s, it, however, remains a challenge to predict correctly adsorption isotherms and/or mechanisms in MOFs with cus’s using grand-canonical Monte Carlo (GCMC) simulations based on generic classical force fields. To address this problem, two multi-scale modelling approaches – which combine GCMC simulations with QM calculations – have been proposed in this work. The first approach is based on the direct implementation of a fluid–framework potential energy surface, calculated by a hybrid DFT/ab initio method, in the GCMC simulations. The second approach involves parameterization of ab initio force fields for GCMC simulations of gas adsorption in MOFs with cus’s. This approach focuses on the generation of accurate ab initio reference data, selection of semiempirical model potentials, and force-field fitting through a multi-objective genetic algorithm approach. The multi-scale simulation strategy not only yields adsorption isotherms in very good agreement with experimental data but also correctly captures adsorption mechanisms, including the adsorption on the cus’s, observed experimentally but absent from GCMC simulations based on generic force fields. The second challenge that this work aims to address concerns the “breathing” phenomenon of MOFs, in which the framework structure adapts its pore opening to accommodate guest molecules, for example. The breathing effect gives rise to some exceptional properties of these MOFs and hence promising applications. However, framework flexibility often poses a challenge for computational studies of such MOFs, because suitable flexible force fields for frameworks are lacking and the effort involved in developing a new one is no less a challenge. Here, an alternative to the force-field-based approach is adopted. Ab initio molecular dynamics (AIMD) simulations – which combine classical molecular dynamics simulations with electronic-structure calculations “on the fly” – have been deployed to study structural changes of the breathing MOF MIL-53(Sc) in response to changes in temperature over the range 100–623 K and adsorption of CO2 at 0–0.9 bar at 196 K. AIMD simulations employing dispersion-corrected DFT accurately simulated the experimentally observed closure of MIL-53(Sc) upon solvent removal and the transition of the empty MOF from the closed-pore phase to the very-narrow-pore phase with increasing temperature. AIMD simulations were also used to mimic the CO2 adsorption of MIL-53(Sc) in silico by allowing the MIL-53(Sc) framework to evolve freely in response to CO2 loadings corresponding to the two steps in the experimental adsorption isotherm. The resulting structures enabled the structure determination of the two CO2-containing intermediate and large-pore phases observed by experimental synchrotron X-ray diffraction studies with increasing CO2 pressure; this would not have been possible for the intermediate structure via conventional methods because of diffraction peak broadening. Furthermore, the strong and anisotropic peak broadening observed for the intermediate structure could be explained in terms of fluctuations of the framework predicted by the AIMD simulations. Fundamental insights from the molecular-level interactions further revealed the origin of the breathing of MIL-53(Sc) upon temperature variation and CO2 adsorption. Both the multi-scale simulation strategy for gas adsorption in MOFs with cus’s and the AIMD study of the stimuli-responsive breathing behaviour of MIL-53(Sc) illustrate the power and promise of combining molecular simulations with quantum mechanical calculations for the prediction and understanding of MOFs.
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Pearce, Gordon Michael. "Synthesis, adsorption and catalysis of large pore metal phosphonates /." St Andrews, 2009. http://hdl.handle.net/10023/823.
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Garcia, Vidal Claudio Andres. "Molecular weight effects in guar gum adsorption and depression of talc." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44116.
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The effect of the molecular weight of guar gum on adsorption, talc depression, and stability of talc suspensions was studied. Four guar gum samples of different molecular weights in the range from 0.162 MDa to 1.4 MDa were used. It was also found that the intrinsic viscosities of the guar gum samples were independent of the type of background solution (NaCl, KCl, distilled water).
The adsorption density of the tested guar gum samples on talc was measured from the same background solutions at pH 9. The floatability of fine talc particles as well as their stability towards aggregation in the presence of guar gum were simultaneously determined so a direct relationship between talc depression and talc flocculation/dispersion by guar gum could be established. It was found that the effect of the molecular weight of guar gum on the adsorption density was negligible. No effect of the background electrolyte on guar gum adsorption was observed. All four guar gum samples were found to be equally strong depressants of talc flotation without any clear relationship with their molecular weights. It was determined that an adsorption density equal to about 20% of the complete surface coverage was sufficient to completely depress talc floatability. All guar gum samples also exhibited strong flocculating capabilities towards the talc particles at lower polymer dosages. As determined from turbidity data, higher molecular weight guar gum samples were more powerful flocculants than lower molecular samples. Most importantly, the strongest depression of talc flotation and the most pronounced flocculation of talc were found to occur at the same dosage. Higher doses of the polymers kept the talc particles completely depressed while simultaneously causing gradual steric redispersion of the mineral. The dispersing capabilities of the polymers were a function of the molecular weight, with the lower molecular weight samples bringing about stronger dispersion than higher molecular weight samples.
It was concluded that a high molecular weight guar gum would be the best depressant, since such a polymer would strongly depress the flotation of talc while minimizing talc dispersion and subsequent mechanical entrainment in the flotation concentrate.
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Campos, Diana Santiago. "Adsorption and diffusion characterizations of pillared clays and silicate molecular sieves." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ29978.pdf.
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Bhattacharya, Supriyo. "Molecular Models for Templated Mesoporous materials: Mimetic Simulation and Gas Adsorption." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-01062006-163437/.
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The complex structures of the Templated Mesoporous Materials (TMMs) are difficult to capture using experiments. On the other hand, detailed structural information is required in order to study the confinement effects and predict material properties. We therefore present a methodology to prepare realistic molecular models of the TMMs using molecular simulations. Mimetic simulations are used to simulate the synthesis of the TMMs resulting in mesoscale models of the materials. Using this technique, we have developed models for SBA-15 and the Mesostructured Cellular Foams (MCF). The mimetic simulations also allow us to study the phase diagrams of the surfactants involved in the synthesis. We have investigated the ternary phase diagrams (surfactant-oil-water and surfactant-silica-water) of model triblock surfactants and have highlighted the effects of oil on the ordered structures. The simulation results for the effect of oil are in partial agreement with the experiments. Next, we devise a technique to convert the mesoscale TMM models into atomistic ones. The method has been demonstrated by preparing atomistic models for SBA-15. The physical properties of the models (pore size distribution, surface area, TEM and AFM images) are compared to the experimental ones. The porosities and the surface areas of the models are in quantitative agreement with those of the experimental SBA-15, whereas the pore size distribution and TEM results agree qualitatively with the experiments. We also present new methods for characterizing model structures including a fast technique for computing pore size distributions. The results from our new technique show speed increases of several orders of magnitude compared to the existing method. Finally we simulate the adsorption of Argon inside the model SBA-15 using Grand canonical Monte Carlo simulations. The adsorption isotherm from the model is in semi-quantitative agreement with that of an experimental SBA-15. The adsorption behavior of several different pore models are investigated, which provides new light on the roles of surface roughness and micropores in determining adsorption properties. We conclude by saying that the pore models developed in this work may be used in studying phase transitions, adsorption, diffusion and reactions inside nanopores, and in preparing new mesoporous material models such as the CMK carbons.
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Lee, Seok-Won 1970. "Molecular adsorption at solid/liquid interfaces using self-assembled monolayer films." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/50552.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999.Includes bibliographical references.
Many areas of technology rely on interfacial events that are controlled by nanometer-level interactions present at solid/liquid interfaces. Properties of wetting, corrosion inhibition, and molecular recognition provide convenient examples. To investigate such interactions at the molecular level, self-assembled monolayers (SAMs) have been employed as a model system as they offer the ability to produce well-defined organic surfaces of controlled composition. This thesis addresses the development and characterization of such films for controlling the adsorptive properties of surfaces toward various surfactant-like molecules and for proteins. Adsorption is controlled to facilitate the organized assembly of molecular precursors, retard the non-specific adsorption of proteins, provide a specificity for the adsorption of select proteins, and the use of molecular adsorption to generate local surface energy gradients useful for directing self propelled drop movement. A common theme in these studies is the importance of controlling the energetics and compositions of surfaces at the molecular level to influence microscopic events that translate into macroscopically observable changes in behavior. The first part of this thesis details the formation of monolayer films by the solution-phase adsorption of n-alkyl-chained adsorbates [CH 3(CH2)~ Y] onto the polar surfaces of terminally substituted SAMs [Au/S(CH)mX]. The polar tail groups (X and Y) of the adsorbate and SAM included amine, carboxylic acid, and amide groups, and the formation of the adsorbed monomolecular films on the SAMs relied on non-covalent interactions between X and Y. Highly organized monomolecular adlayers could be produced that were as densely packed as the alkanethiolate SAMs on gold comprising the first layer. This thesis also used this molecular adsorption process to cause liquid drops to move spontaneously on surfaces by creating local changes in surface energy. The drops could be directed to move along specified paths using patterned substrates that contained inner tracks of polar functionality and exterior domains of oleophobic methyl groups. The adsorption process allowed sequential transport of two drops on a common track and also regeneration of the initial high energy surface for reuse. The developed system provides an experimental platform for examining reactive flow and offers a novel "pumpless" method for sequentially delivering multiple drops along surfaces and within microfluidic devices. The second part of this thesis discusses various oligo(ethylene glycol)-terminated alkyltrichlorosilanes [C13Si(CH2)11(OCH2CHnX; X = -OCH 3 or -O 2CCH 3, n= 2- 4] that can form robust films on glass and metal oxide surfaces and control the adsorption of proteins. The adsorption of the methyl-capped trichlorosilanes produces densely packed, oriented monolayer films that are 2-3 nm in thickness. The trichlorosilyl group anchors the molecules to the surface, and the resulting film exposes the ethylene glycol units at its surface, as noted by its moderate hydrophilicity. The films are robust with stabilities similar to those of other alkylsiloxane coatings. These oligo(ethylene glycol)-terminated silane reagents produce films that exhibit resistances against the non-specific adsorption of proteins and that are better than for films prepared from octadecyltrichlorosilane. These oligo(ethylene glycol)-siloxane coatings offer performance advantages and could easily provide a direct and superior replacement for protocols that presently use silane reagents to generate hydrophobic, "inert" surfaces. This thesis also discusses the development of an acetate-capped oligo(ethylene glycol)-terminated silane to produce a HO-terminated oligo(ethylene glycol)-based coating on glass and metal oxide surfaces. The HO-termini of these films provide sites for covalently grafting biomolecules to the parent surface. As a demonstration, biotin and mannose moieties were covalently attached to the HO-surfaces to provide a means to induce the specific adsorption of proteins. For these surfaces, the presence of oligo(ethylene glycol) groups reduces the nonspecific adsorption of other competing proteins. The results indicate that the developed systems could offer a strategy to arrange biomolecules selectively on glass and metal oxide surfaces.
by Seok-Won Lee.
Ph.D.
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Besharat, Zahra. "Adsorption of molecular thin films on metal and metal oxide surfaces." Doctoral thesis, KTH, Materialfysik, MF, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-195613.
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Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces. Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs. Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth. Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces.QC 20161107
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Ali, J. A. M. "Liquid-phase adsorption of n-paraffins on type 5A molecular sieves." Thesis, Aston University, 1987. http://publications.aston.ac.uk/9700/.
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As a basis for the commercial separation of normal paraffins a detailed study has been made of factors affecting the adsorption of binary liquid mixtures of high molecular weight normal paraffins (C12, C16, and C20) from isooctane on type 5A molecular sieves. The literature relating to molecular sieve properties and applications, and to liquid-phase adsorption of high molecular weight normal paraffin compounds by zeolites, was reviewed. Equilibrium isotherms were determined experimentally for the normal paraffins under investigation at temperatures of 303oK, 323oK and 343oK and showed a non-linear, favourable- type of isotherm. A higher equilibrium amount was adsorbed with lower molecular weight normal paraffins. An increase in adsorption temperature resulted in a decrease in the adsorption value. Kinetics of adsorption were investigated for the three normal paraffins at different temperatures. The effective diffusivity and the rate of adsorption of each normal paraffin increased with an increase in temperature in the range 303 to 343oK. The value of activation energy was between 2 and 4 kcal/mole. The dynamic properties of the three systems were investigated over a range of operating conditions (i.e. temperature, flow rate, feed concentration, and molecular sieve size in the range 0.032 x 10-3 to 2 x 10-3m) with a packed column. The heights of adsorption zones calculated by two independent equations (one based on a constant width, constant velocity and adsorption zone and the second on a solute material balance within the adsorption zone) agreed within 3% which confirmed the validity of using the mass transfer zone concept to provide a simple design procedure for the systems under study. The dynamic capacity of type 5A sieves for n-eicosane was lower than for n-hexadecane and n-dodecane corresponding to a lower equilibrium loading capacity and lower overall mass transfer coefficient. The values of individual external, internal, theoretical and experimental overall mass transfer coefficient were determined. The internal resistance was in all cases rate-controlling. A mathematical model for the prediction of dynamic breakthrough curves was developed analytically and solved from the equilibrium isotherm and the mass transfer rate equation. The experimental breakthrough curves were tested against both the proposed model and a graphical method developed by Treybal. The model produced the best fit with mean relative percent deviations of 26, 22, and 13% for the n-dodecane, n-hexadecane, and n-eicosane systems respectively.
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Syres, Karen Louise. "Molecular adsorption on TiO2 surfaces : modelling potential biomedical and photovoltaic devices." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/molecular-adsorption-on-tio2-surfaces-modelling-potential-biomedical-and-photovoltaic-devices(14c1f1a6-7650-43e2-b8cc-9c9e102f6923).html.
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This thesis describes molecular adsorption on single crystal anatase (101) and rutile (110) TiO2 surfaces and TiO2 nanoparticles using photoemission and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. DFT calculations were carried out in order to complement the experimental data. The adsorption of dopamine and pyrocatechol on single crystal TiO2 surfaces was investigated with photoemission and NEXAFS and indicates the molecules adsorb in a bidentate mode following deprotonation of the hydroxyl groups. NEXAFS analysis of pyrocatechol adsorption on the rutile (110) and anatase (101) TiO2 surfaces shows the plane of the aromatic ring to be oriented at 23˚±8˚ and 27˚±6˚ from the surface normal, respectively. Dopamine adsorbed on the anatase TiO2 (101) surface was found to adsorb with the plane of the ring approximately normal to the surface. Adsorption of pyrocatechol and dopamine on anatase TiO2 (101) gave rise to a feature below the main pi* peak, not observed when pyrocatechol was adsorbed on rutile TiO2 (110). This feature was replicated in DFT calculations of both dopamine and pyrocatechol adsorbed on an anatase TiO2 cluster, but was not present in calculations of the free molecules. The new states are found to be located on the TiO2 surface, which may allow direct charge-transfer from the molecule to the surface. Simulated NEXAFS spectra from the cluster showed good agreement with the experimental data in the pi* region for the molecule-anatase TiO2 (101) system. The rutile experimental data showed good agreement with calculations of the free molecule in terms of the pi* peak separation. Charge-transfer studies of pyrocatechol adsorbed on the rutile TiO2 (110) surface indicate that charge-transfer could be occurring from the LUMO, LUMO+1 and LUMO+2 in the pyrocatechol molecule. The charge transfer time for this system was found to be < 9.0 ± 2.0 fs. XPS results for functionalised TiO2 nanoparticles show that dopamine (DA) molecules adsorb intact and bond through both oxygen atoms. The attachment of PEG (polyethylene glycol) and Pluronic was investigated. PEGme-DA (terminated with methyl) and DA-PEG-DA showed attachment to the nanoparticles occurs through one end of the chain. DA-Pluronic-DA may attach through both DA molecules but this could not be proved conclusively. Adsorption of malonic acid on rutile TiO2 (110) showed that the molecule degraded under the synchrotron beam and formed acetate and/or formate. It was found that dipping this surface into a ruthenium di-2,2'-bipyridyl-4,4'-dicarboxylic acid diisocyanate-dye solution in air appeared to displace the adsorbed species, replacing them with the dye.
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Vieira, Linhares Alexandre Manual. "Molecular simulation of adsorption and diffusion in a microporous carbon membrane." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/14604.
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In this thesis, we have particular interest in the hydrogen recovery from a hydrogen/hydrocarbon refinery waste mixture. Hydrogen is one of the clean, affordable and environmentally friendly energy sources. However, the current industry is not focused on the production or use of hydrogen as an energy carrier or a fuel for energy generation. Membrane separations are an economic alternative to either pressure swing adsorption separations or cryogenic separations. Transport across thin membranes can produce chemical and physical separations at a relatively low price. Thus, the diffusion of fluid gas-mixtures inside a porous material is an important factor in membrane separations. This research involves the mathematical modelling of adsorption and diffusion in microporous carbon membranes and particularly the Selective Surface Flow (SSF) carbon membranes developed by Air Products and Chemicals, Inc. Molecular simulations are used to predict the performance of the SSF membranes for hydrogen/hydrocarbon mixture separation under realistic conditions of temperature pressure and bulk gas compositions. Non-Equilibrium Molecular Dynamics (NEMD) gives a fully rigorous account of the dynamics of adsorption and diffusion at an atomic level, by integrating the equations of motion of adsorbed molecules interacting with each other, and with the surface, according to specified intermolecular potentials. In the NEMD simulations performed, it is assumed that all the pores in the membranes are identical, unconnected and open to the surface. However, this single-pore assumption is unlikely to occur in a real material. A real membrane contains pores of different sizes, connected together in a pore network, allowing the possibility of connectivity effects that are not accommodated by a single-pore model. Thus, the fundamentals of critical path analysis (CPA) are used to characterise the pore network structure. The CPA shows that species are selectively transported essentially through distinct sub-networks within the pore network of the membrane. The simulation results are compared with experimental permeabilities obtained from the Air Products selective surface flow membrane for a mixture of hydrogen/methane, relevant to the e.g. recovery of hydrogen from catalytic reformer offgas.
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Ko, Xueying. "Molecular Simulations of Adsorption and Self-Assembly of Surfactants on MetallicSurfaces." Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1628088858550208.
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Lamonte, Kevin Anthony. "Modeling H2 adsorption in carbon-based structures." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2684.
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Ma, Yuan-Ron. "Adsorption and manipulation of Câ†6â†0 on silicon surfaces." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262962.
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Jullian, Christelle Francoise. "Self-Assembly of Matching Molecular Weight Linear and Star-Shaped Polyethylene glycol Molecules for Protein Adsorption Resistance." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29581.
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Fouling properties of materials such as polyethylene glycol (PEG) have been extensively studied over the past decades. Traditionally, the factors believed to result in protein adsorption resistance have included i) steric exclusion arising from the compression of longer chains and ii) grafting density contribution which may provide shielding from the underlying material.
Recent studies have suggested that PEG interaction with water may also play a role in its ability to resist protein adsorption suggesting that steric exclusion may not be the only mechanism occurring during PEG/protein interactions.
Star-shaped PEG polymers have been utilized in protein adsorption studies due to their high PEG segment concentration, which allows to increase the PEG chain grafting density compared to that achieved with linear PEG chains. Most studies that have investigated the interactions of tethered linear and star-shaped PEG layers with proteins have considered linear PEG molecules with molecular weights several orders of magnitude smaller than those considered for star-shaped PEG molecules (i.e. 10 000 g/mol vs. 200 000 g/mol, respectively). Additionally, the star-shaped PEG molecules which have been considered in the literature had up to ~70 arms and were therefore modeled by hard-sphere like structures and low chain densities near the surface due to steric hindrance. This resulted in some difficulties to achieve grafted PEG chain overlap for star molecules.
Here, triethoxysilane end-functionalized linear PEG molecules have been synthesized and utilized to form star-shaped PEG derivatives based on ethoxy hydrolysis and condensation reactions. This resulted in PEG stars with up to ~4 arms, which were found to result in grafted star-shaped PEG chains with significant chain overlap. Linear PEG derivatives were synthesized so that their molecular weight would match the overall molecular weight of the star-shaped PEG molecules. These 2 PEG molecular architectures were covalently self-assembled to hydroxylated silicon wafers and the thickness, grafting density, and conformation of these films were studied. The adsorption of human albumin (serum protein) on linear and star-shaped PEG films was compared to that obtained on control samples, i.e. uncoated silicon wafers. Both film architectures were found to significantly lower albumin adsorption.Ph. D.
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Zoroufchian, Moghadam Peyman. "Molecular simulation studies of gas adsorption and separation in metal-organic frameworks." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7595.
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Adsorption in porous materials plays a significant role in industrial separation processes. Here, the host-guest interaction and the pore shape influence the distribution of products. Metal-organic frameworks (MOFs) are promising materials for separation purposes as their diversity due to their building block synthesis from metal corners and organic linker gives rise to a wide range of porous structures. The selectivity differs from MOF to MOF as the size and shapes of their pores are tuneable by altering the organic linkers and thus changing the host-guest interactions in the pores. Using mainly molecular simulation techniques, this work focuses on three types of separations using MOFs. Firstly, the experimental incorporation of calix[4]arenes in MOFs as a linker to create additional adsorption sites is investigated. For a mixture of methane and hydrogen, it is shown that in the calix[4]arene-based MOFs, methane is adsorbed preferentially over hydrogen with much higher selectivities compared to other MOFs in the literature. Remarkably, it was shown that extra voids created by calix[4]arene-based linkers, were accessible to only hydrogen molecules. Secondly, the strong correlation between different pore sizes and shapes in MOFs and their capabilities to separate xylene isomers were investigated for a number of MOFs. Finally, the underlying molecular mechanism of enantioseparation behaviour in a homochiral MOF for a number of chiral diols is presented. The simulation results showed good agreement with experimental enantioselectivity values. It was observed that high enantioselectivity occurs only at high loadings and when a perfect match in terms of size and shape exists between the pore size and the adsorbates. Ultimately, the information obtained from molecular simulations will further our understanding of how network topology, pore size and shape in MOFs influence their performance as selective adsorbents for desired applications.
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Ngadi, Norzita. "Mechanisms of Molecular Brush Inhibition of Protein Adsorption onto Stainless Steel Surface." Thesis, University of Canterbury. Chemical and Process Engineering, 2009. http://hdl.handle.net/10092/4454.
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Protein-resistant ("non-fouling") surfaces are particularly important in many
fields such as medical engineering, dentistry, pharmaceutical processes,
bioprocessing, dairy and food manufacturing. Poly(ethylene glycol) (PEG)
immobilized onto surfaces has been shown to confer high resistance to protein
adsorption. The reasons for variable performance and optimal protein repellency of
PEG layers have been the subject of much discussion; however there remains no
general consensus on the molecular mechanisms underlying the protein resistance
achieved with PEG coatings.
The main objective of this study was to inhibit protein adsorption onto a
stainless steel surface. This objective requires an exploration of the mechanisms of
protein adsorption on a stainless steel surface and how these mechanisms are
modified when a surface inhibits the adsorption of proteins. The stainless steel
surface has been chosen as a substrate as it is a commonly used material in many
relevant applications such as in the dairy industry, in food processing and in clinical
uses.
In order to elucidate the mechanisms of protein-PEG interactions the
adsorption of lysozyme, β-casein, apo α-lactalbumin, holo α-lactalbumin and β-
lactoglobulin onto various PEG-grafted surfaces was explored. The adsorption was
conducted at room temperature and at 40 C. The modification of bare SS surfaces
and adsorption kinetics of proteins on unmodified and modified surfaces (i.e. bare
stainless steel and PEG surfaces) has been done in-situ and studied by means of a
quartz crystal microbalance with dissipation sensing (QCM-D). The merit of the
modification methods studied, compared to those of most published methods is that
the process of modification is simple and easy, being done simply by passing a
solution over the surface. The methods also do not involve any harmful or hazardous
chemicals and thus are safe to be used even in food processing plants.
The PEG coated surfaces prepared in this study were able to inhibit adsorption
of β-casein, α-lactalbumin (calcium enriched) and lysozyme proteins especially; the
lowest adsorption of these achieved as a percentage of that on bare stainless steel, β-
casein, 45 %, holo α-lactalbumin, 11 % and lysozyme, 1 %. By contrast, and
unexpectedly, PEG molecules enhanced the adsorption of apo α-lactalbumin (the
form without calcium). It is suggested that the PEG to apo α- lactalbumin
hydrophobic interaction plays a dominant role which leads to protein aggregation at
the surface, for this latter observation. The results have shown that protein stability
(i.e. whether it is a soft or a hard protein) greatly influenced the inhibition
performance of PEG surfaces. It is apparently more difficult to prevent the adsorption
of soft proteins than hard proteins. This appears to be because soft proteins tend to
denature regardless of the surface properties (i.e. hydrophilic or hydrophobic) and
attach more effectively in their unfolded state. The results also indicated that higher
PEG grafting density is not necessarily reflected in better protein inhibition.
At the end of the project, a novel method of surface modification was
developed. In this method, stainless steel surfaces were modified by coating the
surface with a protein layer (as a base) then followed by the attachment of PEG
molecules. Interestingly, the method developed showed an excellent potential for
preventing further protein adsorption at room and body temperatures. The adsorption
of β-casein, lysozyme, holo α-lactalbumin and β-lactoglobulin on the SS-lysozyme-
PEG surfaces was down to about 3, 1, 4 and 0.4 %, respectively compared to that on
the bare surface. More interestingly and surprisingly also, there was almost zero
adsorption on those surfaces of mixed protein and single protein solutions at the
concentration found in milk. The method is believed to have the potential to be
applied in the pharmaceutical industry, in the biosensor field and in artificial medical
implants with some modifications perhaps to suit the application.
The modelling results demonstrated negative free energy changes on
adsorption, consistent with the studied proteins being thermodynamically favoured to
adsorb on bare SS. The adsorption of proteins was an endothermic process. The
proteins also showed large positive entropy changes on adsorption, indicating
adsorption-induced denaturation mechanisms (especially apo α-lactalbumin protein).
At high temperatures and concentrations, the adsorption was governed first by
diffusion and later by surface kinetics, whereas under lower temperature (i.e. room
temperature) and low concentration conditions (i.e. 0.1 g / L) the adsorption was able
to be described solely by surface-reactions.
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Loganathan, Narasimhan. "Adsorption of protein bound uremic toxins in zeolites : a molecular simulation study." Aix-Marseille 1, 2010. http://www.theses.fr/2010AIX11120.
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Le paracrésol sous sa forme libre est une toxine urémique causant des dommages cellulaires très importants qui peuvent conduire E1 des arrêts cardiaques. Le traitement de l'insuffisance rénale repose principalement sur l‘utilisation de la dialyse. Il s'avère cependant que ce procédé ne permet pas une élimination efficace de la toxine. Une alternative serait d'utiliser des zéolithes afin de piéger la molécule pour ensuite l'éliminer. Ce travail de thèse présente une étude théorique de l‘adsorption du paracrésol et de l'eau dans les zéolithes silicalite-1 et faujasites NaY. Les simulations ont été réalisées par la technique Monte Carlo dans les ensembles grand-canonique et canonique à une température de 37°C (310 K). Les résultats montrent qu‘un effet coopératif interviendrait entre les deux molécules lors de la coadsorption dans la silicalite-1. L‘étude détaillée des interactions énergétiques intermoléculaires semble confirmer cette hypothèse. Les simulations montrent que le mécanisme d'adsorption dans la faujasite est quelque peu différentThe paracresol as a free molecule is a uremic toxin that may cause critical cell damages which can eventually lead to heart failures. The treatment of renal insufficiency is essentially based on the utilisation of the dialysis techniques. However, it appears that, this process does not allow the effective elimination of the molecule. A possible alternative would be to use zeolites to sequestrate the molecule in order to eliminate it. This PhD thesis presents a theoretical investigation of the adsorption of paracresol and water in the silicalite-1 and faujasite NaX and NaY zeolites. The computer simulations were performed using the Monte Carlo technique in both the grand-canonical and canonical ensembles at a temperature of 98. 6° (310 K). The results show that, a cooperative effect could appear between both molecules during the coadsorption in silicalite-1. The detailed study of the energetic intermolecular interactions seems to confirm this hypothesis. The simulations show that, the mechanism of adsorption in the faujasite zeolites is somewhat different
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Jorge, Miguel Angelo da Silva. "Molecular simulation of the adsorption of water/organic mixtures on activated carbon." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/12321.
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The adsorption of mixtures of polar and non-polar species is influenced by both the structure and the surface chemistry of the adsorbent. Several molecular simulation techniques have been employed to study the effect of these factors on the extent and mechanism of adsorption of water and light hydrocarbons. In particular, the effect of pore size as well as the concentration, distribution and type of polar surface groups have been examined in a detailed and systematic way. It is shown in this thesis that the presence of polar sites on the surface of the carbon enhances the affinity of the adsorbent towards water. However, in most situations of practical interest, the most important variable was seen to be the concentration of polar sites, with their distribution and type playing only a minor part. This fundamental study formed a basis for the development of a model for activated carbon that can be used in an industrial context. The model for activated carbon includes a representation of the structure of the adsorbent using a distribution of slit-shaped pores, and of the surface chemistry, using a distribution of polar sites. The adsorption in single pores was calculated by grand canonical Monte Carlo simulation. The pore size distribution was obtained from an analysis of pure-ethane adsorption isotherms, while the polar site distribution was calculated by analysing pure-water adsorption. The performance of the model was assessed by comparing the simulated results for binary water/ethane adsorption with experimental adsorption data on a commercial activated carbon. The sensitivity of the predictions to changes in the surface chemistry of the model was examined. The model proposed here was seen to perform much better than the more widely used classical methods, opening good prospects for its use in industrial applications.
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Barbetta, Aurelio. "Thermodynamics of water adsorption in model structured molecular systems including analogues of hemicelluloses, crystalline cellulose and lignin." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT171/document.
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Le bois est un matériau nanocomposite complexe, fortement anisotrope et hiérarchiquement organisé. La micro-structure à l'échelle nanométrique est caractérisée par des nanofibres rigides de cellulose cristalline parallèles les unes aux autres et noyées dans un matrice plus molle et moins anisotrope. Cette matrice est composée par hémicelluloses et lignine, avec une absorption contrôlée par l'entropie et les liaisons hydrogène entre hémicelluloses, lignine, et la surface de micro-cristaux de cellulose. La matrice est hygroscopique et se gonfle avec les changements de l'humidité relative, en fournissant une source de stress interne, tandis que les fibrilles de cellulose s'enroulent en spirale autour de la lumière centrale à un angle précis, qui est appellé AMF, angle des micro-fibrilles. Les micro-fibrilles se réorganisent passivement selon les contraintes osmotique appliquées. Selon l'AMF, le positionnement et les propriétés mécaniques des fibres de bois varient considérablement: le matériau rigide se rétrécit ou il s'allonge dans le sens de la longueur lors du gonflement, en générant de cette façon une grande déformation anisotrope.Une première forme d'équation d'état comprenant entropie et termes chimiques, colloïdaux (comme la force d'hydratation) et termes mécaniques macroscopiques a été établie et permet de prédire sans paramètres l'absorption d'eau en fonction de l'humidité relative du composite de bois pas traité.Le but de la thèse est d'étendre cette équation d'état au bois traité par absorption d'électrolytes en conditions hydrotermales, en intégrant l'équation avec des termes chimiques lié à la présence d'électrolytes. Les résultats du modèle sont comparés avec les données expérimentales de sorption d'électrolytes formulés en fonction de la balance entre chaotropes et cosmotropes de l'échelle de Hofmeister. Les données expérimentales sont produit à partir des isothermes de sorption et des mécanismes moteurs pour tester la prédiction de la théorie en explorant l'effet du soluté (introduit dans le bois par mise en équilibre avec une solution utilisée comme une réservoir osmotique) sur la structure et les dimensions du matériauThe so-called “wood material” is a complex, highly anisotropic and hierarchically organized nanocomposite. At the nanometric scale, it is characterised by stiff crystalline cellulose nanofibres parallel to each others embedded in a matrix of a much softer, less anisotropic, gel of hemicelluloses, lignin and water. This matrix is hygroscopic and the solvent uptake is controlled by molecular forces like entropy, H-bonding of polysaccharides to cellulose nano-crystals and hydration force. The swelling provides a source of internal stress for the cellulose fibrils that, winding with a spiral angle (the microfibril angle, MFA) around the central lumen, passively reorient following the osmotic stress applied to them. Depending on the MFA, wood fibres exhibit a wide range of behaviors and mechanical properties, being able to act as stiff material to bear load, or shrink or expand in the longitudinal direction upon swelling, generating in this way either large tensile or compressive stresses or large strains.For the first time, the equation of state including entropic, chemical, colloidal terms (as the hydration force) as well as the mechanical, macroscopic, term has been established and allows to predict with a parameterless analytical expression, the water absorption of untreated softwoods as a function of relative humidity changes.The aim of the thesis is to extend this first equation of state to describe wood treatments by electrolytes adsorption in hydrothermal conditions. The experimental part is performed using specific sorption devices as well as X-Ray scattering techniques. The theoretical part is developed extending the established master equation linking molecular level chemical forces, colloidal interactions and mechanics. The results of the model are tested against experimental data of electrolytes adsorption and compared with their chaotropic/cosmotropic character according to the Hofmeister series.Nowadays, several wood treatments have been developed to reduce the water uptake by wood, in order to confer higher resistance to moist to low-quality wood materials. The final aim of the project is to test the prediction of the model against these known treatments and to develop a general model to describe the behaviour of the wood under different chemical and physical environments. This way, new treatments can be conceptually designed and pre-existing treatments (as for instance the patented "woodprotect" one) improved
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Reeves, Christopher Thomas. "Kinetics and dynamics of adsorption on single crystal semiconductor and metal surfaces." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035962.
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Gee, Adam Timothy. "The role of steps in the dynamics of dissociative adsorption at surfaces." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310485.
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