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.

Les composés organiques volatiles (COVs) sont produits de façon massive chaque jour, et contribuent fortement à la dégradation de la qualité de vie. Pour cette raison, de nombreuses techniques ont été développées pour leur destruction. Parmi celles-ci, l'adsorption présente l'avantage d'être simple et de revaloriser les composés capturés. Elle est industriellement réalisée sur les charbons actifs ou les zéolites. Dans cette thèse, nous étudions les Metal Organic Frameworks (MOFs) comme possibles matériaux adsorbants. Les MOFs sont des matériaux à la fois constitués de parties organiques et inorganiques dont on peut moduler la structure à souhait par un processus de design. L'objectif principal de cette thèse est de dégager les interactions microscopiques gouvernant les phénomènes d'adsorption des COVs dans les MOFs. Pour cela, nous avons utilisé une approche à la fois théorique (DFT+D, Monte-Carlo classique) et expérimentale (gravimétrie, DRIFT, DRUV, adsorption d'azote, DRX).La première partie a montré le comportement des alcanes linéaires adsorbés dans trois MOFs différents (MIL-47, MIL-125 et UiO-66), ainsi que dans ces MOFs fonctionnalisés. Dans le cadre de l'adsorption d'alcanes interagissant exclusivement par interactions vdW, la forme et la taille des pores du MOF sont des facteurs gouvernant l'adsorption. Toutefois, les alcanes sont des molécules flexibles qui peuvent se replier sous contrainte du confinement au sein des MOFs. Ce repliement est un phénomène primordial pour mieux comprendre l'adsorption des alcanes. Selon le milieu, les alcanes peuvent être linéaires ou repliés, et ainsi montrer des différences dans les quantités adsorbées et les sites d'adsorption préférentiels (et donc de leur enthalpie d'adsorption). Ce repliement est basé sur le compromis énergétique entre le coût lié au repliement, et au gain d'énergie apporté par ce repliement. Les alcanes interagissent faiblement avec les structures, mais cette faible énergie pourrait être suffisante pour modifier très légèrement la structure du MOF. La deuxième partie a montré le comportement de l'adsorption d'acétone dans le Cu-BTC. Le Cu-BTC est un MOF particulier qui peut présenter des sites acides de Lewis après activation thermique. Dans ce cas, l'acétone étant une molécule polaire, elle peut établir à la fois des interactions électroniques et de vdW. L'étude IR in-situ couplée à une approche quantique ont permis de relier les fréquences de vibrations du C=O de l'acétone avec leur position dans le Cu-BTC en termes de site d'adsorption. De plus, cette étude a montré que le site préférentiel de l'acétone représente un cas limite, entre les interactions purement vdW et les interactions électroniques. / Volatile Organic compounds (VOCs) are massively produced each day, and contribute strongly to a degradation of quality of life. For this purpose, several techniques were developed for their removal. Among these, adsorption has the advantage to be simple and allow further re-use of captured compounds. Industrially, adsorption is made on activated carbons or zeolites. In this thesis, we investigated the possibility of taking Metal Organic Frameworks (MOFs) as adsorbents. MOFs are materials constituted by both organic and inorganic which can be precisely modulated through a design process. The main objective of this work is to give insights about microscopic interactions controlling adsorption phenomena between VOCs and MOFs. Consequently, we used an approach based both on theoretical (DFT+D, classic Monte-Carlo) and experimental (gravimetric, DRIFT, DRUV, azote adsorption, XRD) aspects.The first part shows the behavior of linear alkanes inside three different MOFs (MIL-47, MIL-125 et UiO-66) in their pure and functionalized forms. Alkanes adsorption is mainly driven by vdW forces, thus, shape and pore size are the most important factors to be taken into account. However, alkanes are flexible molecules which can be folded under constraint of confinement effect within MOFs. This folding is a phenomenon of prime importance while considering study of alkanes. Depending on the environment, alkanes can be linear or folded, and subsequently show differences for quantity adsorbed or preferential adsorption sites (and their isosteric heat of adsorption). This folding is based on an energetic compromise between cost associated to folding and the gain consequent of this folding. Moreover, alkanes interact weakly with MOF, but this energy could be sufficient to modify slightly MOF structure. The second part shows the behavior of acetone adsorption inside Cu-BTC. Cu-BTC is a particular MOF which reveals Lewis acid sites upon thermal activation. In this case, acetone is a polar molecule which can interact with MOF via electronic and vdW interactions. The in situ IR study, compared to quantum approach, allows to make a link between the frequency of C=O stretching of acetone and the position of acetone inside Cu-BTC. Moreover, acetone adsorption appears to be a limit case between a preferential adsorption driven by electronic forces at Lewis acid site and by vdW forces inside a small cage.

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The theme of this work is the observation and understanding of the effects of pore functionalization on adsorption properties of stable Metal-Organic Frameworks (MOFs). Over the first two sections of this work, sets of materials with representative pore sizes and functional groups are studied for adsorption properties. Observed trends are used to identify the best pore properties achievable via functionalization for adsorption systems. The third section of this work provides perspective on MOF materials and proposes target pore features for an efficient adsorbent for carbon dioxide capture from flue gas. First, the highly stable UiO-66 series of materials was selected for a pure-component adsorption study. The selectivity and capacity for CO2 can be best enhanced with the smallest, most polar functional group, such as an amino group, but significantly enhance water adsorption. Large, non-polar groups do not yield a completely hydrophobic material, but may be useful for humid gas separations as pore filling with water is inhibited. Next, a breakthrough study was conducted using CO2:CH4 and CO2:N2 mixtures on a set of stable MOFs. UiO-66-NH2 and UiO-66-DM, where DM=dimethyl, outperform predictions based on published isotherms and have dynamic CO2:CH4 selectivity comparable to zeolite NaY. UiO-66-DM may be a good candidate for further study due to the combination of partial hydrophobicity and good selectivity. Finally, by combining a review of literature with observations made in this work, a perspective on MOFs as efficient humid gas separation materials is provided. The presence of water vapor prevents use of current high performance adsorbents, but several MOF pore features show promise for these separations. The designable nature of MOFs allows for targeted design of size-matched pores and single-molecule traps which can selectively or cooperatively adsorb CO2 in the presence of water. Also, many MOF materials would be well suited for advanced pressure swing adsorption cycles and engineered sorbents, which enables greater material utilization and system efficiency.

Call number: LD2668 .T4 1965 J25 / Master of Science

<p>The polyelectrolyte titration method has been developed overthe years in order to determine the surface charge ofcellulosic fibers. The conditions have been varied depending onthe author. This work has been aimed at resolving theappropriate conditions for measuring the charge, such aselectrolyte concentration and molecular mass of thepolyelectrolyte. The charge ratio of variously treated pulpswas also investigated.</p><p>The polyelectrolyte titration technique is based on a 1:1adsorption stoichiometry between fiber and polyelectrolytecharges. Adsorption of polydiallyldimethylammonium chloride(poly-DADMAC) was first performed at various electrolyteconcentrations and then with various molecular masses. ESCA(Electron Spectroscopy for Chemical Analysis) was used toindependently validate the polyelectrolyte titrationmethod.</p><p>Results showed that stoichiometry prevailsat lowelectrolyte concentrations. Increasing the electrolyteconcentration screens the fiber charges, initially enhancingthe adsorption and causing a deviation from stoichiometry.Further increases in electrolyte concentration eventuallydecrease the adsorption. Deviation from stoichiometry occurredat higher electrolyte concentrations for higher charge densitypulps. ESCA-measurements showed that high and low molecularmass cationic polyelectrolyte adsorb to the same extent on thefiber surface, confirming stoichiometry. There was a goodagreement between the two techniques, hence, thepolyelectrolyte titration technique is a good method to measuresurface charges. Comparing the charge ratio between differentkind of pulps and treatments, it was found that mechanicalpulps have a higher surface charge than chemical pulps. Thecharge ratio of chemical pulps was, however, practicallyunchanged when comparing different types of wood and bleachingsequences.</p><p><b>KEYWORDS:</b>Adsorption, electrolyte, polyelectrolyte,polyelectrolyte titration, charge stoichiometry, charge ratio,diffuse electric double layer, Debye length, poly-DADMAC,cellulosic fibers, ESCA.</p>

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