LU|ZONE|UL Collection: 2019-12-13T20:05:10Z Surface modification of biodegradable magnesium implant materials for controlled biodegradation Title: Surface modification of biodegradable magnesium implant materials for controlled biodegradation Authors: Hegy, Afrah Al Abstract: Magnesium and its alloys are promising candidates to be employed as a new generation of biodegradable metals in orthopaedic applications. However, the rapid degradation rate of magnesium alloys in the physiological environment has prevented their widespread application in medicine. The main objective of this thesis was to develop surface modification strategies that control the degradation rate of magnesium alloys in physiological environments and to provide an accurate assessment and evaluation of their biocompatibility in vitro. The overall thesis is composed of three individual projects. The first project was to develop an accurate method to test the in vitro biocompatibility of magnesium alloys. In this study, the CyQUANT assay was used to quantitatively evaluate the in vitro biocompatibility of Mg AZ31 alloy by both direct and indirect methods. The results demonstrated that the CyQUANT assay provides a more complete assessment of the overall in vitro biocompatibility of biodegradable metals by combining both direct and indirect analyses. In the second project, a multilayer coating consisting of a sol-gel silica layer followed by a mesoporous silica layer and finally a layer of calcium phosphate was developed. Surface characterization showed that a uniform and stable multilayer coating was successfully deposited on the Mg AZ31 alloy. In vitro characterization of the coatings confirmed this surface modification strategy significantly decreases the degradation rate of the magnesium alloy and that it is not cytotoxic. Superhydrophobic surfaces decrease the corrosion rate of magnesium alloys, however, cell adhesion is inhibited. In the third project, a superhydrophobic magnesium alloy surface was modified with the cell adhesive molecule, MAPTrix-F-RGD and the influence of this surface modification on cell adhesion was studied. The results demonstrate that although the MAPTrixF-RGD molecule was successfully immobilized to the superhydrophobic magnesium alloy surface, cell adhesion was not improved. The complex surface topography of the superhydrophobic Mg AZ31 surface may be responsible for the observed cell behavior. This thesis demonstrates that surface modification can be used to simultaneously control both the biodegradation rate and the biocompatibility of magnesium and its alloys, making these materials promising candidates for orthopaedic applications. In addition, it has been demonstrated that cell quantification assays based on the fluorescence of cyanine dyes are an excellent method for in vitro testing of these materials in direct contact with cells. 2019-06-18T00:00:00Z Utilization of coal fly ash and grape waste to remove toxic metal ions in mining waste waters Title: Utilization of coal fly ash and grape waste to remove toxic metal ions in mining waste waters Authors: Appiah-Hagan, Emmanuel Abstract: In recent years, the studies of a variety of inexpensive adsorbents as alternative to the expensive activated carbon have received a lot of attention. The purpose of my research was primarily focused on the modification of Thunder Bay coal fly ash, the characterization of the pristine and modified fly ash and the application of modified fly ash for removal of metal ions from mine wastewater. Adsorption by grape wine material (GWM) was also investigated though not completed. Modification at low and elevated temperatures with 2.0 M NaOH yielded improvement in surface area, pore volume and cation exchange capacity. However, low-temperature modification was pursued leading to very efficient adsorbents named TBRM and TBFZ compared to the original fly ash named TB. The modified and unmodified fly ash was characterized using different techniques including ICP-OES, X-ray diffraction, specific surface analysis (Brunauer-Emmet- Teller), particle size distribution analysis and scanning electron microscopy. Surface area analysis revealed an increase of specific surface area from 1.24 (TB) to 64.34 (TBRM) and 68.98 (TBFZ) m2/g, respectively. Likewise, porosity was also induced in the modified fly ash. Cation exchange capacities were determined as 1.94, 23.48 and 29.23 meq/g for TB, TBRM and TBFZ, respectively. SEM-EDS and XPS were employed to confirm the adsorption of metal cations on the surface of the adsorbents. The performance of TBRM and TBFZ for the removal of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2+ from a synthetic cocktail solution (SCS) and tailing pond water (TPW) was compared to that of TB. Results indicated TBRM and TBFZ were more efficient in both SCS and TPW. A batch method was used to study the influential parameters of the adsorption process including contact time, pH effect, and kinetics and adsorption isotherms. Column studies were done to compliment the batch mode approach. Regeneration of TBFZ revealed a possible 3-cycle application. The equilibrium data were generally modeled by the Langmuir and Freundlich models. Also, the pseudo-second order model was found to explain the adsorption kinetics most effectively. Thermodynamic studies of Ni2+ and Cu2+ with TBFZ in SCS revealed that the adsorption process was spontaneous although endothermic with a decrease in entropy. The most efficient adsorbent TBFZ was converted into innovative concrete foam composite material TBFZ:FA:BA 0.22:0.33:0.45, for adsorption studies. Preliminary studies revealed a removal of more than 95 % of Cu2+, Pb2+, Ni2+, Cr3+, Co2+ and Cd2 in both SCS and TPW after 6 h of contact. However, the regeneration of TBFZ:FA:BA 0.22:0.33:0.45 was inefficient and further investigation ought to be carried out. Overall, the results indicate a significant potential of the modified Thunder Bay fly ash as an inexpensive and effective adsorbent for the removal of toxic metals from mine wastewater. 2017-09-15T00:00:00Z Synthesis and characterization of novel ethylene copolymers by palladium-diimine catalysts Title: Synthesis and characterization of novel ethylene copolymers by palladium-diimine catalysts Authors: Xiang, Peng Abstract: Late transition metal catalysts, especially Pd-diimine catalysts, have been extensive studied for olefin polymerization. The unique characteristics of Pd–diimine catalysts, including chain walking mechanism, highly electrophilic cationic metal center with reduced oxophilicity, the capability of initiating and catalyzing olefin "living" polymerization, and the sterically tunable–diimine ligands, allow the synthesis of a range of polyolefins and olefin copolymers with special pedant functionalities and unique microstructures. The main objective of this thesis research is to synthesize different new types of polymers and polymer-grafted nanoparticles with Pd–diimine catalysts by utilizing above unique characteristics. A broad class of low-polydispersity ethylene–norbornene (E–NB) copolymers having various controllable comonomer composition distributions, including gradient, alternating, diblock, triblock, and block-gradient, was synthesized through “living”/quasi-living E–NB copolymerization facilitated with a single Pd–diimine catalyst. This synthesis benefits from two remarkable features of the Pd–diimine catalyst, its high capability in NB incorporation and high versatility in rendering E–NB “living” copolymerization at various NB feed concentrations ([NB]0) while under an ethylene pressure of 1 atm and at 15 C. A class of hyperbranched polyethylene ionomers containing positively charged tetralkylammonium ions and different counter anions were first synthesized by direct iv one-pot copolymerization of ethylene with tetralkylammonium-containing acrylate-type ionic liquid comonomers. The use of a Pd–diimine catalyst, which shows excellent stability towards the highly polar ionic group, is key to the direct synthesis. The resulting ionomers properties including structural, thermal, and melt rheological properties have also been demonstrated. In a further study, HBPE ionomers encapsulating self-supported Pd(0) nanoparticles (NPs) as efficient and recyclable supported Pd catalysts were synthesized with a Pd–diimine catalyst. The Pd(0) NPs were immobilized on the ionomer matrix through ionic interaction directly during the copolymerization of ethylene with polymerizable ionic liquid comonomer. The resulting ionomer supported Pd(0) nanocatalysts have been utilized to catalyze carbon-carbon cross coupling reactions (Suzuki and Heck reactions) and semi-hydrogenation of alkynes. Moreover, the successful tuning of structural parameters of PE brushes in surface-initiated ethylene “living” polymerization from two types of silica nanoparticles were studied. The brush parameters that are controlled herein include brush length, density, and topology. The PE-grafted silicas with varying brush density and length are also used as nanofillers to construct polymer nanocomposites with an elastomeric ethylene-olefin copolymer (EOC) as the matrix polymer. The effects of brush length and density on the nanofiller dispersion, rheological properties, and tensile properties of the composites are examined (The preparation and characterization of the nanocomposites were carried out by K. Petrie and M. Kontopoulou at Queen’s University). 2015-09-24T00:00:00Z An investigation into bioleaching of uranium and rare earth elements from quartz-pebble conglomerate ores from Elliot Lake, Ontario Title: An investigation into bioleaching of uranium and rare earth elements from quartz-pebble conglomerate ores from Elliot Lake, Ontario Authors: Williamson, Aimee Lynn Abstract: Biogeochemical mineral dissolution, the microbial-assisted dissolution of minerals, is an effective method for economically promoting the release of metals of interest from ores and mine waste materials. As the low-grade ores of the Elliot Lake region may be suitable for development of a sustainable heap-leach method for the extraction of U and REEs from the low-grade host mineralization, this thesis is focused on the geochemical and biological process simulation monitoring of the biogeochemical release of elements to the leaching solutions. The response of the retired heap material to a variety of passive closure strategies is also addressed. A series of biogeochemical mineral dissolution experiments have provided a detailed understanding of the biogeochemical mineral dissolution process, with the investigation of passive approaches to prepare for decommissioning to determine suitability to the ore materials from the study site. The chemical analyses of effluents collected throughout the experimentation, coupled with mineralogical and geochemical analyses of the feed and residual mineral material has enabled an understanding of the chemical controls of the overall biogeochemical mineral dissolution process for Fe, U, and Th, together with the preferential leaching release patterns for REEs, to be obtained. A mechanism describing U retention in secondary coatings has been proposed, with a passive approach to closure using inhibition and encapsulation methods being demonstrated, along with a determination of the potential for ongoing radionuclide release from a simulated heap upon decommissioning. The laboratory research in this study has shown that biogeochemical mineral dissolution, followed by waste material encapsulation, can be successfully applied to heap-leach pads potentially, enabling the economic recovery of U, Th, and selected REEs to solution for subsequent metallurgical collection. The studies strongly support the concept of sustainable development for heap-leach operations in the Elliot Lake region. 2014-08-29T00:00:00Z