Recognizing the dual ability of the nitride ligand to react as a nucleophile or an electrophile – depending on the metal and other supporting ligands – is a key to their broad-range reactivity; thus, three DFT studies were initiated to investigate these two factors effects (the metal and supporting ligands) for tuning nitride ligand reactivity for C-H and N-H bond activation/functionalization. We focused on studying these factors effects from both a kinetic and thermodynamic perspective in order to delineate new principles that explain the outcomes of TMN reactions. Chapter 2 reports a kinetic study of C–H amination of toluene to produce a new Csp3–N (benzylamine) or Csp2–N (para-toluidine) bond activated by diruthenium nitride intermediate. Studying three different mechanisms highlighted the excellent ability of diruthenium nitride to transform a C-H bond to a new C-N bond. These results also revealed that nitride basicity played an important role in determining C–H bond activating ability. Chapter 3 thus reports a thermodynamic study to map basicity trends of more than a one hundred TMN complexes of the 3d and 4d metals. TMN pKb(N) values were calculated in acetonitrile. Basicity trends decreased from left to right across the 3d and 4d rows and increases from 3d metals to their 4d congeners. Metal and supporting ligands effects were evaluated to determine their impacts on TMNs basicity. In Chapter 4 we sought correlations among basicity, nucleophilicity and enhanced reactivity for N–H bond activation. Three different mechanisms for ammonia decomposition reaction (ADR) were tested: 1,2-addition, nitridyl insertion and hydrogen atom transfer (HAT). Evaluating nitride reactivity for the aforementioned mechanisms revealed factors related to the metal and its attached ligands on TMNs for tuning nitride basicity and ammonia N–H activation barriers.

Les composites carbone/carbone présentent de propriétés thermomécaniques à hautes températures qui les rendent particulièrement adaptés à l’ablation ou à la friction. Leur sensibilité à l’oxydation dès 400°C a conduit à envisager leur dopage en éléments réfractaires inoxydables ou à température d’oxydation élevée. Le procédé sol-gel a permis d’introduire environ 1 % volumique d’oxyde ou de nitrure de titane ou d’aluminium dans leur matrice. Les nitrures sont obtenus par nitruration carbothermique des films d’oxydes. Deux types de sols ont été utilisés : des sols « standard » et des sols enrichis en saccharose. Le saccharose est ajouté pour prévenir la consommation du pyrocarbone lors de la nitruration. Il a par ailleurs une influence sur l’avancement de la nitruration. Les composites chargés sont ensuite densifiés par voie gazeuse, ce qui induit des transformations de phases prévues par la thermodynamique : les films de nitrure de titane sont partiellement carburés (formation de carbonitrure), et les films d’oxyde de titane sont réduits (formation d’oxycarbure). Les dépôts à base d’aluminium sont plus stables et ne subissent aucune transformation. La diffusivité thermique des composites réalisés est faiblement impactée par les charges introduites, alors que les résistances en traction/compression sont sensiblement augmentées. Par ailleurs, une rigidification des composites est observée. Leur cinétique d’oxydation est ralentie. Les composites enrichis en alumine et nitrure d’aluminium présentent des vitesses de perte de masse divisées par 2 par rapport à la référence C/C. Toutes ces propriétés sont liées directement ou non à la composition des sols, et plus particulièrement à sa teneur en saccharose. Il a en effet été montré que les sols qui en contiennent ont tendance à gélifier en surface du composite, ce qui gêne la diffusion des gaz précurseurs au cœur du composite lors de la densification. La porosité finale s’en trouve modifiée. Cette dernière a une influence non négligeable sur le comportement en compression, la diffusivité thermique et la cinétique d’oxydation des composites élaborés. / Carbon/carbon composites exhibit excellent mechanical and thermal properties at high temperature that make them espe-cially suitable for ablation or friction pieces. Their sensitivity toward oxidation above 400°C has lead to the will of doping them with refractory ceramics that are nonoxidizable or with a high oxidation temperature. The sol-gel process allowed to introduce 1 % in volume of titanium or aluminum oxide or nitride in the matrix. Nitrides are obtained by carbothermal nitridation of the oxide films. Two types of sols were used: the “standard” ones and those with extra sucrose. Sucrose is added to prevent pyrocarbon consumption during the nitridation. Furthermore, it was shown that it has an impact on the nitridation rate. Charged composites are then densified by Chemical Vapor Infiltration, which induces phases transforma-tions that were predicted by thermodynamics: titanium nitride films are partially carburized (formation of titanium carbonitride) and titanium dioxide films are reduced (formation of titanium oxycarbide). Aluminum-based films are more stable and don’t undergo any transformation. Thermal diffusivity of the as-synthesized composites is not much modified by the addition of these ceramics while the tensile and compressive strength are slightly increased. By the way, composites are hardened. Their oxidation kinetics is slowed down. Aluminum-rich composites exhibit a weight loss divided by two compared to the C/C reference. All those properties are directly, or not, linked to the composition of the sols, in particular to their sucrose content. Indeed, it was shown that sucrose-containing sols rather jellify on the surface of the composite, thus preventing the diffusion of precursor gases to the heart of the pieces. The final porosity is then modified. The porosity has an important impact on the compressive strength, thermal diffusivity and oxidation kinetics of the synthesized composites.

Finding economical and environmentally friendly processes to recover heavy metals (HMs) from spent batteries is a research priority to move toward sustainability. Adsorption seems an acceptable procedure to replace the current separation/purification stage of hydrometallurgical techniques. Chitosan is an efficient adsorbent for HM uptake from aqueous solutions. Nevertheless, in practice, chitosan modification is unavoidable to improve its physicochemical properties. Sodium tripolyphosphate is an environmentally benign crosslinker that can be used for chitosan modification. In addition, ion-imprinting technique could potentially enhance the adsorption efficiency and selectivity of crosslinked chitosan. Considering the above, the primary purposes of this research were: investigating the adsorption efficiency of chitosan for heavy metals uptake from synthetic solutions; modifying chitosan by crosslinking alone and combined with ion-imprinting techniques to improve the physicochemical properties as well as adsorption capacity and selectivity of chitosan; evaluating and comparing the adsorption efficiency of modified chitosan beads for the adsorption of Cd(II), Ni(II) and Co(II) in single and multicomponent batch adsorption systems. Chitosan and sodium tripolyphosphate crosslinked chitosan beads were prepared to remove Cd(II) from aqueous solution in the first phase. FTIR and XRD of the synthesized beads showed partial consumption of chitosan amine groups and a decrease in crystallinity of chitosan structure over crosslinking reaction. The isotherm and thermodynamic studies showed that Langmuir isotherm was the best fit to the experimental data of Cd(II) adsorption on crosslinked chitosan and all the adsorption reactions were endothermic and spontaneous. A reduced quadratic model, constructed by the Response Surface Methodology (RSM), indicated that the Cd(II) adsorption uptake of 99.87 (mg/g) was achieved at 55 °C and 2.92 % (w/v) crosslinking degree. Then, chitosan and crosslinked chitosan beads by sodium tripolyphosphate were used for Ni(II) adsorption from aqueous media in the second phase. The BET characterization showed that increasing the crosslinking degree reduced the chitosan beads' surface area and their total pore volume. The Langmuir model described the experimental results best and showed that the maximum adsorption capacity of chitosan (80.00 mg/g) decreased after crosslinking (52.36 mg/g). In addition, a reduced quadratic model with a correlation coefficient of 0.96 was established to correlate the adsorption uptake of Ni(II) with pH and crosslinking degree. In the third phase, the adsorption of Ni(II) and Cd(II) ions from single and binary metal ions solutions onto chitosan and crosslinked chitosan beads was studied. The extended Freundlich model fitted the adsorption equilibrium data in the binary system, implying the existence of preference in the order of Ni(II) > Cd(II). Desorption studies with a mixture of NaCl and H2SO4 were also conducted during this phase, demonstrating a desorption efficiency of greater than 85 %. In the fourth phase, the removal of cadmium from aqueous solution was examined using a novel Cd(II)-imprinted crosslinked chitosan. SEM, FTIR, TGA, and BET characterizations revealed that the ion-imprinted chitosan beads had better physicochemical properties than chitosan beads and superior potential adsorption properties than non-imprinted crosslinked chitosan beads. The isotherm and thermodynamic studies revealed that the Langmuir isotherm fitted the Cd(II) experimental data the best, and the adsorption reactions were spontaneous and endothermic. The kinetics data were also best fitted by the pseudo-second-order equation. Finally, the ion-imprinted crosslinked chitosan beads were employed for the selective adsorption of Cd(II) in a competitive adsorption system of Cd(II)-Ni(II)-Co(II) in phase five. The characterization of the prepared adsorbents was performed using XRD and BET, showing a higher surface area of ion-imprinted crosslinked chitosan than non-imprinted crosslinked chitosan beads. The Extended Langmuir model fitted the experimental results obtained from the multi-component system, indicating that ion-imprinted crosslinked chitosan had a higher total metal uptake with better selectivity toward Cd(II) uptake compared to non-imprinted crosslinked chitosan. Studying the adsorption mechanism in a ternary system showed that the adsorption was governed by chemical binding and ion exchange mechanisms in the ternary system. In conclusion, crosslinking by sodium tripolyphosphate improved chitosan physiochemical properties; however, it resulted in a decrease in HM adsorption uptake. The RSM was used to assess the effect of pH, temperature, and crosslinking degree and optimize the adsorption uptake of chitosan. Also, ion-imprinting was effective in enhancing the adsorption capacity and selectivity of crosslinked chitosan for the ion used as a template (Cd(II)) in preparing ion-imprinted crosslinked chitosan.