Graduation date: 1999

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

In this work, we studied the possibility of synthesizing nanocrystalline germanium (Ge) via dry and wet oxidation of both amorphous and polycrystalline Si₀.₅₄Ge₀.₄₆ films. In dry oxidation, Ge was rejected from the growing SiO₂ forming a Ge-rich polycrystalline layer. As for wet oxidation, Ge was incorporated into the oxide, forming a layer of mixed oxide, SixGe₁₋xOy. Formation of nanocrystalline Ge was observed when the layer of SixGe₁₋xOy was annealed in a N₂ ambient. We have fabricated a metal-insulator-semiconductor structure with nanocrystalline Ge embedded within the insulator layer to study its feasibility as a memory device. / Singapore-MIT Alliance (SMA)

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

This work takes a closer look at ceria catalyst synthesis through micelle self-assembly. We compare surfactants, precursors, solvent systems, and doping. The surfactants are the building blocks upon which the ceria can crystallize. The samples are calcinated to test their thermal stability. Characterization is performed using pXRD as well as physisorption. The samples that exhibited a higher thermal stability were characterized to have a high surface area as well as low fluctuations in crystallite size, pore volume, and pore size. Ceria synthesized with cerium (III) nitrate hexahydrate and CTAB in a water:ethanol mixture using sodium hydroxide showed to be the most effective at providing a thermally stable product. Doping the catalyst with titanium increased the thermal stability significantly. Select samples were run in a variety of fuel to oxygen ratios to determine the best conditions in which we could perform partial methane oxidation to recuperate hydrogen gas. Most of the experiments show oxygen depletion with minor changes in other gas levels indicating that there is no oxidation occurring. Curiously the oxygen levels do decrease. There is a possibility that there is a reaction occurring initially at room temperature and being exacerbated with further temperature increase.

In the past few decades, several aqueous oxidants have been employed (e.g., permanganate, persulfate) to remediate petroleum hydrocarbons. However, the majority of the research in this field has been focused primarily on the use of oxidants in treating fresh water at low groundwater temperature. In this study, bench experiments were carried out to investigate the effectiveness of persulfate (PS) as an oxidant to remediate petroleum hydrocarbons in alternative settings (saline environments at high groundwater temperature). Benzene, Toluene, Ethylbenzene, Xylenes (BTEX), Trimethylbenzenes (TMBs), and Naphthalene were the target organic compounds investigated. Three important aspects were examined during this laboratory study: 1) the evaluation of (alkaline activated and non-activated) persulfate as a chemical oxidation agent; 2) the investigation of the effect of different temperatures (10°C versus 30°C); and 3) the examination of the effect of different persulfate concentration (20 versus 100 g/L) on the reactivity of persulfate. The results showed the high potential of persulfate to remediate the target contaminants under certain conditions. In general, alkaline-activated persulfate showed a higher potential than the non-activated persulfate. However, precipitations of calcium hydroxide were observed due to the reaction between sodium hydroxide and the high concentration of calcium which will limit the use of alkaline-activated persulfate in this particular groundwater setting The results also showed that the initial concentration of persulfate and the system temperature can play important roles in enhancing the effectiveness of PS to oxidize the target contaminants. For instance, the oxidation rate of the target contaminants was seen to be dramatically increased by increasing the persulfate addition from 20 to 100 g/L as well as with increasing the system temperature from 10°C to 30°C. However, increasing both factors (temperature and concentration) accelerated the decomposition rate of PS. Lowering the system pH was tremendously successful in order to enhance the oxidation rate of all compounds. Moreover, the expected effect of the radicals scavenging at acidic pH by Cl- and Br – ,which was reported in the literatures (e.g., Pignatello et al., 2006; Grebel et al., 2010; Suri et al., 2010), was not observed in this study which might be attributed to the contribution of the produced halogen radicals to the contaminant oxidation.

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In this study, a two-bed electrically-heated regenerative thermal oxidizer (RTO) was used to test NOx formation characteristics from burning air-laden N, N-dimethyl formamide (DMF) and air-laden DMF mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m ¡Ñ 0.14 m ¡Ñ 1.0 m (L ¡Ñ W ¡Ñ H) beds both packed with gravel particles of around 1.11 cm in average diameter to a height of 1.0 m, and the packed section had a void fraction of 0.416. Performances on the thermal destructions of DMF and MEK, the thermal recovery efficiency, as well as the gas pressure drop over the regenerative beds were investigated. Experimental results indicate that, with a valve shifting time (ts) of 1.5 min, gas superficial velocities (Ug) of 0.39-0.78 m/s (evaluated at an influent air temperature of around 30oC), and set maximum destruction temperatures (Tset) of 750-950 oC, there was no NOx in the effluent gas from the RTO with no DMF in the influent air. With only DMF in the influent gas, its destruction efficiencies were 96.3 (750oC), 97.4 (850oC) and 97.9 % (950oC), and increased with increasing influent DMF concentration from 100-250 ppm. Mole ratios of ¡§NOx-N formation/DMF destruction¡¨ were found to be in the range of 0.84-1.20, and the ratio decreased with increasing influent DMF concentration within the experimental range. With both DMF and MEK in the influent gas, no significant influence was found in the NOx formation ratio and the DMF destruction efficiency with influent MEK/DMF ratios of 50/100 - 1500/100 (ppm/ppm) and the set temperatures. The NOx formation ratios were in the range of 0.85-1.07. The Ergun equation was adequate for the estimation of the pressure drop for the gas flowing over the packed regenerative beds in the Ug range of 37-0.74 m/s. It was also found that the thermal recovery efficiency was decreasing with the increasing Ug and invariant with Tset.