Philosophiae Doctor - PhD / The application of porous materials into industrial hydrogen (H2) storage systems is based on their use in combination with high-pressure cylinders. The processing of metal-organic frameworks (MOF) powders into shaped forms is therefore imperative in order to counteract the adverse effects of poor packing of powders in cylinders. The fabrication of shaped MOFs has, however, been shown to be accompanied by compromised properties such as surface areas, gravimetric and volumetric H2 capacities, and also the working/deliverable H2 capacities in comparison to MOF powders.

Nanotechnology as a field has the potential to answer some of the major challenges that mankind faces in regards to environmental sustainability, energy generation and health care. Though, solutions to these concerns can not necessarily rely on our current knowhow. Instead, it is reasonable to expect that humanity must adapt and learn to develop new materials and methods to overcome the adversities that we are facing. This master thesis has involved developing novel materials, serving as a small step in the continuous march towards a bright future where this is possible. More specifically, this work sought to combine mesoporous magnesium carbonate with various metal-organic frameworks to utilize the beneficial aspects from each of these constituents. The ambition was that these could be joined to render combined micro-/mesoporous core-shell structures, with high surface areas and many active sites whilst maintaining a good permeability. Numerous different synthesis routes were developed and explored in the pursuit of viable routes to design novel materials with potential future applications within for instance drug delivery, water harvesting from air and gas adsorption. Coreshell structures of the hydrophilic mesoporous magnesium carbonate covered with the hydrophobic zeolitic imidazole framework ZIF-8 was successfully synthesized for the first time, and practical studies demonstrated a dramatically enhanced water stability, which is perceived to have an impact on further research on these materials. ZIF-67 was also combined with mesoporous magnesium carbonate in a similar manner. Further, Mg-MOF-74 was grown directly from mesoporous magnesium carbonate, where the latter acted as a partially self-sacrificing template, with the aim of rendering a porous hierarchical structure with contributions from the micro- and mesoporous ranges. The outcomes of all these syntheses were characterized using several analyzing methods such as scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and nitrogen sorption analysis.

No description available.

No description available.

Conventional primary Li/CFx batteries employ graphite and polyvinylidene fluoride additives in the cathodes. These additives usher in some un-desired side-effects, such as lower battery capacities (mAh/g) and smaller current densities (mA/g). An innovative pretreatment was developed in this research in which CFx was subject to a “solvated electron” reduction to obtain a thin layer graphitic carbon coating on the CFx particle surfaces. Resistivity tests revealed that these partially reduced CFx particles have a higher conductivity at comparable graphitic carbon contents. Electrochemical discharge reactions demonstrated that batteries made from the reduced CFx were superior to the conventional batteries with higher current densities and higher capacities achieved. Impedance spectroscopy (EIS) studies found out that the reduced CFx particles have smaller cell reaction resistances, smaller double layer/intercalation capacitances and smaller mass transport resistances. It appears that use of reduced CFx has the potential to replace the conventional CFx plus additives as a cathode material in Li/CFx batteries.

<p>    </p> <p>Surface functionalization of metallic nanoparticles is an attractive route to tailor the ensemble geometry and redox properties of active sites in heterogeneous catalysts. However, it is challenging to generate well-defined interfaces through conventional impregnation and one-pot colloidal synthesis methods. In this work, we utilize ligand exchange reactions for post synthetic surface modification of colloidal nanoparticles to generate unique core-shell and surface alloy structures. We use halometallate and metal chalcogenide complexes to create surface sites that are active for electrocatalytic hydrogen evolution reaction (HER). </p> <p>We synthesize a self-limiting monolayer of metal chalcogenides on colloidal Au nanoparticles through biphasic ligand exchange reaction between ammonium tetrathiomolybdate (NH₄)₂MoS₄ complex and Au nanoparticles. Through a combination of spectroscopy techniques and computational methods, we show that strong Au-S interactions introduce electronic and geometric distortion to the geometry and bond metrics of MoS₄^2-complex. Moreover, proximal MoS₄ units adsorbed on the Au surface interlink to form small MoSx oligomers with highly active bridging disulfide sites. Consequently, these core-shell AuMoS₄ nanoparticles exhibit significantly higher HER activity than MoS₄^2- supported on non-interacting carbon supports under highly acidic electrolyte conditions. Although post catalysis characterization reveals partial hydrolysis of surface adsorbed MoSx species, stable HER activity under bulk electrolysis condition indicates that active sites remain persistent. </p> <p>In an effort to extend these ligand exchange reactions to create metal/metal interfaces on other coinage metal nanoparticles such as Ag, we design metal-ligand coordination complexes to mitigate undesired galvanic replacement reactions. By varying the strength and number of coordinating ligands, we fine-tune the redox potential of oxidized noble metal precursors and confine the deposition of noble metals to a few surface layers of the Ag nanoparticles. We utilize organic amine and phosphine ligands to generate Ag@AgM core-shell nanoparticles, where M = Pd, Pt, and Au. Surface alloy or pure metal shells of Pd and Pt on Ag nanoparticles generated through this ligand-based strategy exhibited high precious metal atom utilization in electrocatalytic hydrogen evolution reaction. </p>

No description available.

Industries’ interest in nanomaterials is tremendous and catalysis is one of their applications. Catalysts allow reactions to occur under milder conditions, avoiding committing excessive heat or pressure to foster reactions. The discovery of Frustrated Lewis Pairs (FLP) in 2006 led to a new concept of homogeneous catalysis: metal-free acids and bases preventing from forming an Lewis adduct because their bulkiness create an active clamp that is able to cleave dihydrogen and other small molecules at room temperature. Transferring the FLP concept to the “nano”-world which is more relevant for industrial applications, requires well-designed nanoparticles and rationalization of their interaction with ligands aiming at forming a FLP between nanoparticles and ligands. The following project conducted at LCMCP (Laboratoire de Chimie de la Matière Condensée de Paris) under the supervision of Sophie Carenco aimed at studying the insertion of phosphorus in metallic nanoparticles in order to tune their catalytic activity and demonstrate Frustrated-Lewis Pair catalytic behaviours. To that end, copper nanoparticles and bimetallic core-shell nickel-cobalt nanoparticles were synthesized in colloidal solution. The phosphidation of both nanoparticles was investigated with trioctylphosphine (TOP) as the phosphorous source. Nanoparticles were characterized by X-Ray Diffraction, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. Starting from the failure to reproduce a published procedure of copper phosphide nanoparticles synthesis, conditions of the reaction and the washing procedure were successively improved aiming the obtention of copper phosphide nanoparticles. The one-pot synthesis with hot-injection of TOP at the second step (320°C, 1h), allowed to isolate copper phosphide nanoparticles but a longer reaction time did not result in enhanced phosphorus doping. Further work would need to examine the reproducibility problems faced and investigate harsher reaction conditions (eg. higher temperature). Cu3P nanoparticles would be interesting to test as catalysts for hydrosilylation of benzaldehyde or CO2, a model reaction for CO2 hydrogenation. The synthesis of core-shell nickel-cobalt nanoparticles has been previously rationalized by Sophie Carenco’s team. Phosphidation was attempted from this optimized procedure. We started with harsh conditions (&gt; 250°C, &gt; 1h30) which caused reconstruction of the nanoparticles after leaching of the cobalt shell. In such conditions, the core-shell structure is not retained and a NiCoP alloy is obtained. Milder conditions allowed to retain the structure but further studies are required to characterize and locate the phosphorus insertion in the core-shell nanoparticles. NiCoP alloy and phosphidized core-shell Ni@Co will be of great interest to apply in catalysis for water splitting and hydrogenation of nitriles, respectively.

This work focuses on improving the quality of carbon-based core-shell materials for high performance liquid chromatography (HPLC) via the characterization of the core materials, and also the development of chromatographic methods (separations) for them. In the early part of this work, I applied organic synthesis to make uniform, spherical poly(divinylbenzene) (PDVB) microspheres, and then carbonized them to prepare carbon core materials for core-shell particle synthesis. Here, I studied in detail the surface and material properties of these particles with multiple instruments, which allowed me to describe the physical and chemical changes that took place during each treatment. The uniform, spherical carbon core materials greatly improved the efficiency of the previously developed carbon-based core-shell HPLC columns from ca. 70,000 plates per meter (N/m) to ca. 110,000 N/m for various alkyl benzenes. Later, I focused on generating application notes to showcase these mixed-mode HPLC columns. Here, liquid chromatography mass spectrometry (LC-MS) was used for the detection of analytes that lack chromophores for UV detection. In this dissertation, Chapter 1 contains a historical background and theory of HPLC along with a review of the use of carbon-based core-shell materials for elevated pH and temperature applications. Chapter 2 describes the improvement of the efficiency of carbon-based materials for HPLC using carbonized PDVB microspheres as the carbon core material. Chapter 3 is a study on the characterization of carbonized PDVB microspheres with multiple instruments. Chapter 4 describes the separation of cannabinoids using three types of carbon-based mixed-mode HPLC columns. Chapter 5 consists of (i) guidelines for the retention mechanism of the core-shell particles that have been commercialized for chromatography by Diamond Analytics, a US Synthetic Company in Orem, Utah, and (ii) application notes for these columns. Finally, Chapter 6 discusses possible future work.

The primary focus of my work was to chemically functionalize diamond as normal and reversed phases for solid phase extraction (SPE) and high performance liquid chromatography (HPLC). Diamond was functionalized with -NH2 groups via self-limiting adsorption of an amine-containing polymer, polyallylamine (PAAm), onto oxidized diamond particles. The chemical stability of these particles was improved by thermal curing or chemical crosslinking with 1,2,5,6-diepoxycyclooctane. The reversed phase material for SPE was synthesized by reacting amine-functionalized diamond particles with long chain alkyl and a perfluorinated isocyanate. Unlike commercially available silica, functionalized diamond particles were stable under extreme pH conditions (pH 0-14). Functionalized diamond particles were used for SPE, although their lack of porosity resulted in poor analyte capacity. To create materials with greater surface area, core-shell diamond particles were synthesized via layer-by-layer deposition of PAAm and nanodiamond onto solid microdiamond. These particles had higher surface areas than solid diamond particles, and their application in SPE and HPLC was demonstrated. As a related project, I demonstrated microlens array patterning (MAP) for selective adsorption of PAAm during microarray fabrication. Initially, alkyl monolayer terminated silicon surfaces were photopatterned with thousands of wells using a microlens array. PAAm was then deposited in the presence of a cationic surfactant to limit nonspecific adsorption of PAAm. Finally, reactions of selectively adsorbed PAAm were shown with glutaric anhydride, phenylenediisothiocyanate, biotin NHS-ester and an oligonucleotide (DNA). My third project concerned the synthesis of an abrasion resistant hydrophobic coating on the surface of nylon and silicon oxide substrates using chemical vapor deposition (CVD) of two silanes. The synthesis consists of four steps: 1) plasma oxidation of the substrate, 2) treatment with 3-isocyanatopropyltrimethoxysilane, 3) exposure of the treated surfaces to water vapors, and 4) treatment with a perfluorinated silane to make the surfaces hydrophobic. The coating is not visible to the eye and does not change the feel of the surface. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, contact angle goniometry, scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) were used to characterize the resulting materials.