Quantum dots (QDs) of II-VI semiconductors (CdS, CdSe, and CdTe) in the size range of 1~12 nm have attracted great interest in both fundamental research and technical applications in recent years. Due to their tunable size-dependent emission with high photoluminescence quantum yields, their broad excitation spectra and narrow emission bandwidths, the semiconductor QDs have been intensively investigated in versatile applications, including thin-film light emitting devices (LEDs), low-threshold lasers, optical amplifier media for telecommunication networks and biological labels. Thus, constructing and fabricating highly ordered QDs are of great importance in the field of nanotechnology. The surface chemistry behavior of the TOPO-CdSe QDs and TOPO-(CdSe)ZnS QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherms of the Langmuir monolayers of both types of QDs gave the average diameter which matched the value determined by TEM measurements. Topographic study of the Langmuir monolayers of both QDs revealed the 2D aggregation during the early stage of the compression process. The stability of the Langmuir monolayer of the TOPO-(CdSe)ZnS QDs was measured by the compression/decompression cycle and the kinetic measurements, both of which indicated that TOPO capped (CdSe)ZnS QDs can form stable Langmuir monolayers at the air-water interface. Langmuir-Blodgett (LB) film of the TOPO-(CdSe)ZnS QDs were prepared on quartz slides at different surface pressures and characterized by photoluminescence (PL) spectroscopy. The linear increase of the PL intensity with the increase of the number of layers deposited onto the quartz slide implied a homogeneous deposition of the Langmuir monolayer. The conjugates of 10, 12-pentacosadiynoic acid (PDA) and short chain peptide was used to modify the surface of (CdSe)ZnS core-shell QDs. The PDA-peptide capped QDs formed stable Langmuir monolayer. After the photopolymerization of PDA-peptide-QDs/PDA-peptide system at the air-water interface, a more uniform and robust Langmuir monolayer was constructed. The 3-mercaptopropyltrimethoxysilane (MPS) was linked to (CdSe)ZnS QDs by ligand exchange method. The sol-gel process of the MPS capped QDs Langmuir monolayer was studied under various subphases of pH and reaction time. The fast sol-gel process under a subphase of pH 12.0 led the formation of a more homogeneous Langmuir monolayer. A smooth MPS-QDs LB film deposited under pH 12.0 was also observed by AFM measurements. The imaging of the aggregates of lysozyme using lysozyme/(CdSe)ZnS QDs conjugate as a PL label was investigated. The amyloid fibrils formed by lysozyme/lysozyme-QDs conjugate were observed by epifluorescence microscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements. The emission intensity of the QDs labeled lysozyme was increased about 3 fold after formation of amyloid. This approach, for the first time, provided a convenience method to image the amyloid fibrils by epifluorescence microscopy.

With the increasing time people spend indoors, the indoor environment quality draws more and more attention. The concentration of indoor pollutants is usually much higher than outdoors, in which volatile organic compounds (VOCs) and mold/mildew are both major pollutants and cause many health problems to residents. Efforts devoted from academy and industry to protecting people from indoor environment problems are apparently not sufficient. Photocatalysts, such as TiO2, WO and ZnO, can absorb light photons and react with O2 and H2O to generate highly oxidative radicals, which can oxidize VOCs and disinfect microorganisms. Recently, this photocatalytic oxidation (PCO) technology has been intensively studied to reduce VOCs and disinfect bacteria in the indoor environment. Few papers address the indoor mold/mildew problem, and this research therefore endeavors to do so. The objectives are to evaluate the effectiveness of PCO technology to resist mold/mildew growth and prevent VOC emission from building materials under either UV or visible light irradiation. The models, including linear regression, logistic regression, and numerical model, are also built for interpreting experimental results and for predicting performance in application. The mold/mildew resistance of different PCO gels was examined using accelerated mold/mildew growth agar plate tests. These gels included TiO2 only and TiO2 in combination with H2O2 and with Ag. Without the application of PCO gels, no mold/mildew inhibition was observed from UV (365 nm) or visible light. Under UV light irradiation, the TiO2 gel achieved complete mold/mildew inhibition. Without light, a 12-day delay of mold growth was obtained using the Ag-TiO2/H2O2 gel. Under visible light irradiation, the Ag-TiO2/H2O2 gel was also the most effective PCO gel with a 8-day delay of mold growth, which, however, was shorter than the same gel in the condition of no light with a 10-day delay due to the light-induced deterioration of the Ag-TiO2. The reduction of VOC emission from PCO gel (TiO2 gel and Ag-TiO2/H2O2 gel) coated building materials under UV or visible light irradiation was also confirmed by small chamber tests (the Ag-TiO2/H2O2 gel with above 50% reduction of total VOC emission). A linear model was obtained for the Ag-TiO2/H2O2 gel in the condition of no light, with respect to the correlation between the delay of mold growth and the gel ingredients. A logistic model was created for predicting the probability of mold growth on different TiO2 gels with different UV light exposure time at different intensities. A numerical model was developed with better accuracy than the previous one for VOC emission from PCO gel coated building materials. This study showed that the PCO gel might be a promising multifunctional material in resisting mold/mildew growth and preventing VOC emission in the indoor environment (The TiO2 gel for complete mold/mildew inhibition and the Ag-TiO2/H2O2 gel for delay of mold growth in emergency situations and reduction of VOC emission from building materials). More stable Ag-TiO2 or other visible-light-driven photocatalysts are needed in future research because of the deterioration of the current one.

This dissertation presents the synthesis of a series of thermo- and pH-sensitive hydrophilic block copolymers and the study of their solution behavior in water. By incorporating a small amount of weak acid or base groups into the thermosensitive block(s) of a hydrophilic block copolymer, the LCST of the thermosensitive block(s) can be modified by changing the solution pH. Accordingly, the critical micellization temperature (CMT) and the sol-gel transition temperature (Tsol-gel) of the block copolymer in water can be tuned. Chapter 1 describes the synthesis of thermo- and pH-sensitive poly(methoxydi(ethylene glycol) methacrylate-co-methacrylic acid)-b-PEO-bpoly( methoxydi(ethylene glycol) methacrylate co-methacrylic acid) and the study of sol-gel transitions of its aqueous solutions at various pH values. The CMT of the 0.2 wt% solution and the Tsol-gel of the 12.0 wt% solution of this copolymer can be varied over a large temperature range. By judiciously controlling temperature and pH, multiple sol-gel-sol transitions were realized. Chapter 2 presents a systematic study of pH effect on rheological properties of micellar gels formed from 10.0 wt% aqueous solutions of thermo- and pH-sensitive poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid)-b-PEO-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid). With the increase of pH, the sol-gel transition became broader. The plateau moduli (GN) evaluated from frequency sweeps at T/Tsol-gel of 1.025, 1.032, and 1.039 decreased with the increase of pH from 3.00 to 5.40 with the largest drop observed at pH = ~ 4.7. The decrease in GN reflects the reduction of the number of bridging chains. The ionization of carboxylic acid introduced charges onto the thermosensitive blocks and made the polymer more hydrophilic, facilitating the formation of loops and dangling chains. Chapter 3 presents the synthesis of PEO-b-poly(methoxydi(ethylene glycol)methacrylate-co-2-(N-methyl-N-(4-pyridyl)amino)ethyl methacrylate) with the thermosensitive block containing a catalytic 4-N,N-dialkylaminopyridine and the study of the effect of thermo-induced micellization on its activity in the hydrolysis of pnitrophenyl acetate. The CMTs of this copolymer at pH of 7.06 and 7.56 were 40 and 37 °C, respectively. Below CMT, the logarithm of initial hydrolysis rate changed linearly with 1/T. Above CMT, the reaction rate leveled off, which is presumably because it was controlled by mass transport to the core of micelles above CMT.

Supramolecular copolymers have become of increasing interest in recent years for the search of new materials with tunable properties. In particular, metallo-supramolecular block copolymers have seen important progresses since the last five years. In this thesis, a library of metallo-supramolecular amphiphilic block copolymers containing a hydrophilic block, linked to a hydrophobic block, through a metal-ligand complex has been investigated. The micelles formed in water from these copolymers were characterized by AFM and TEM and exhibited a different behavior compared to their covalent counterpart. Furthermore, a novel strategy to control the formation of amphiphilic brushes from metallo-supramolecular block copolymers has been developed. Starting from a heteroleptic block copolymer, the initial low molecular weight counterions were exchanged for polymeric ones, leading to the formation of complex architectures. Another part of this thesis is dedicated to the use of metal-ligand interactions located at the extremity of micelles. Since ligands are located at the extremity of the coronal chains, they are available for complexation with metal ions. The effect of the addition of various metal ions to this system was studied in the dilute regime by dynamic light scattering, and different situations have been observed depending on the metal-to-ligand ratio and to the nature of the metal ions. In more concentrated solutions, a second hierarchical level is reached leading to the formation of a micellar gel, due to the formation of intermicellar bridges. Rheological measurements revealed that the characteristic behavior of those gels critically depends on the added metal ions. Finally, the self-assembly of a metallo-supramolecular block copolymer in thin films was investigated. Due to the presence of the charged complex at the junction of the two blocks, this copolymer could be considered as a triblock with a highly immiscible block that effects the orientation of the cylindrical microdomains and the lateral ordering.

The present work analyses the physicochemical phenomena responsible for the microstructure of Pd/SiO2 xerogel catalysts and of metal-free hybrid SiO2 xerogels synthesized by sol-gel process. The samples are synthesized by co-polymerizing tetraethoxysilane (TEOS) with 3-aminopropyltriethoxysilane or 3-(2-aminoethylamino)propyltrimethoxysilane in ethanol, the latter co-reactant possibly forming a complex with palladium. The analysis is conducted by following in situ the formation of the gels' nanostructure by Small-Angle X-ray Scattering (SAXS), by characterizing the microstructure of the final gels by beam-bending, and by analyzing the microstructure of the xerogels after desiccation, most notably by electron tomography. The in situ SAXS analysis shows that the nanometer structure of the gels forms via a reaction-induced phase separation. The microstructure of the hybrid xerogels is hierarchical, as assessed by electron microscopy, nitrogen adsorption and SAXS. Its structure is that of a microcellular foam at large scale, with pores a few hundred nanometers across, supported by elongated filaments, a few ten nanometers wide, each filament being made up by smaller structures, a few nanometers wide. The characteristics of the various structural levels depend on the nature and concentration of the co-reactant used. In the case of xerogel catalysts, electron tomography shows that Pd nanoparticles are regularly dispersed inside the silica, with distances between them comparable to the thickness of the skeleton. On the basis of the time-resolved SAXS and of the characterization of the xerogels, it is argued that a double phase separation process is responsible for the structuring of the gels, with a primary phase separation leading to the microcellular foam morphology, and a secondary phase separation being responsible for the substructure of the filaments. The large scale structure of the gels themselves, before desiccation, is analyzed by beam bending. This enables one to estimate the mechanical properties of the gels as well as the size of their largest pores. The microstructure of aerogels obtained by supercritical drying of the samples is also investigated. The comparison of the characterization data show that the nature and concentration of the co-reactant controls the amount of shrinkage that the gels undergo during desiccation, at the macroscopic scale as well as at the scale of the filaments.

Fuel cell technologies have developed high interest due to their ability to provide energy in an environmentally friendly method. Proton exchange membrane fuel cells (PEM-FCs) require a PEM for use, where the most accepted PEM used today is Nafion. Nafion is ideal due to its chemical durability and high proton conductivity however it is highly expensive and limited to 80˚C during operation. To target these issues two methods have been developed. One was to synthesize a new membrane material to replace Nafion based upon sulphonated polysiloxanes and the other was to improve Nafion by synthesizing a composite. Both of these methods involved the sulphonated silane 2-4-chlorosulphonylphenethyltrimethoxysilane. Methods to characterize membranes to observe their properties compared to Nafion were thermogravimetric analysis (TGA), Fourier transmission infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (used to determine proton conductivity) and fuel cell performance. / UOIT

Salmonella species continue to be commonly associated with cases of food-borne disease in developed countries. In the United States in 2001, the incidence per 100,000 people was highest for salmonellosis (15.1), followed by campylobacteriosis (13.8) and shigellosis (6.4). Enteric pathogens usually contaminate the surface of raw animal products during slaughter and primary processing (scalding, defeathering or dehiding, rinsing, cutting, mixing, and grinding, etc.) and can attach and/or reside in the regular and irregular surfaces of the skin, multiply and, thereafter, contaminate food preparation surfaces, hands and utensils. Trisodium phosphate (TSP) has been approved by the USDA as a sanitizer to reduce surface loads of Salmonella on chicken carcasses. A number of studies had demonstrated that TSP effectively removes surface contamination of carcasses by food-borne pathogens. However, very little scientific evidence is available which identifies the actual mechanisms of TSP antimicrobial activity and the response of food-borne pathogens exposed to TSP. This study examined both the physiological and molecular response of Salmonella enterica serovar Enteritidis to TSP treatment. The role of high pH during TSP treatment on its antimicrobial activity was examined. Adaptation of S. enterica serovar Enteritidis to TSP treatment was also examined by analyzing the proteome of serovar Enteritidis cells using two-dimensional gel electrophoresis and mass spectrometry. The role of high pH on the antimicrobial activity of TSP was examined using comparative studies involving treatment solutions containing different concentrations of TSP, treatment solutions adjusted to the equivalent pH as in each of the TSP treatments and TSP solutions pH adjusted to 7.0. Direct and indirect indices of cell survival, membrane damage, and cellular leakage were also employed to examine specific antimicrobial effects. Cell viability, loss of membrane integrity, cellular leakage, release of lipopolysaccharides and cell morphology were accordingly examined and quantified under the above treatment conditions. Exposure of serovar Enteritidis cells to TSP or equivalent alkaline pH made with NaOH resulted in the loss of cell viability and membrane integrity in a TSP concentration- or NaOH-alkaline pH-dependent manner. In contrast, cells treated with different concentrations of TSP whose pH was adjusted to 7.0 did not show any loss of cell viability or membrane integrity. These results indicate that TSP is a potent membrane-acting agent, and provide compelling evidence that high pH during TSP treatment was responsible for its antimicrobial activity. Adaptation of S. enterica serovar Enteritidis with a sublethal concentration of TSP resulted in the induction of the alkaline stress response. Alkaline stress response involves induced thermotolerance, resistance to higher concentrations of TSP, high pH and sensitivity to acid. Examination of the proteome of TSP-adapted cells revealed differential expression of a number of proteins but did not include the common heat shock proteins involved in thermotolerance. However, TSP adaptation caused a shift in the membrane fatty acid composition from unsaturated to a higher saturated and cyclic fatty acid. This shift in fatty acid composition increases the melting point of the cytoplasmic membrane so that it remains functional at high temperatures. Biofilm bacteria are more resistant to sanitizers, heat and antimicrobial agents than their planktonic counterparts. Examination of the proteome of TSP-adapted biofilm cell of S. enterica serovar Enteritidis revealed little overlap in the protein profile compared to TSP-adapted planktonic cells. Proteomic examination of planktonic and biofilm cells of S. enterica serovar Enteritidis revealed differential expression of a number of proteins involved in DNA replication, stress survival and transport of newly synthesized proteins. These results clearly indicate that changes in the expression of specific genes are involved in the biofilm mode of growth, which could play a significant role in resistance to antimicrobial agents. The results of the current study provide a better understanding of the mechanisms of antimicrobial action of TSP and also elucidate the response of S. enterica serovar Enteritidis to TSP and high pH adaptation. The study also raises new questions regarding stress tolerance of S. Enteritidis following TSP or alkaline pH adaptation with relevance to food safety.

Salmonella species continue to be commonly associated with cases of food-borne disease in developed countries. In the United States in 2001, the incidence per 100,000 people was highest for salmonellosis (15.1), followed by campylobacteriosis (13.8) and shigellosis (6.4). Enteric pathogens usually contaminate the surface of raw animal products during slaughter and primary processing (scalding, defeathering or dehiding, rinsing, cutting, mixing, and grinding, etc.) and can attach and/or reside in the regular and irregular surfaces of the skin, multiply and, thereafter, contaminate food preparation surfaces, hands and utensils. Trisodium phosphate (TSP) has been approved by the USDA as a sanitizer to reduce surface loads of Salmonella on chicken carcasses. A number of studies had demonstrated that TSP effectively removes surface contamination of carcasses by food-borne pathogens. However, very little scientific evidence is available which identifies the actual mechanisms of TSP antimicrobial activity and the response of food-borne pathogens exposed to TSP. This study examined both the physiological and molecular response of Salmonella enterica serovar Enteritidis to TSP treatment. The role of high pH during TSP treatment on its antimicrobial activity was examined. Adaptation of S. enterica serovar Enteritidis to TSP treatment was also examined by analyzing the proteome of serovar Enteritidis cells using two-dimensional gel electrophoresis and mass spectrometry. The role of high pH on the antimicrobial activity of TSP was examined using comparative studies involving treatment solutions containing different concentrations of TSP, treatment solutions adjusted to the equivalent pH as in each of the TSP treatments and TSP solutions pH adjusted to 7.0. Direct and indirect indices of cell survival, membrane damage, and cellular leakage were also employed to examine specific antimicrobial effects. Cell viability, loss of membrane integrity, cellular leakage, release of lipopolysaccharides and cell morphology were accordingly examined and quantified under the above treatment conditions. Exposure of serovar Enteritidis cells to TSP or equivalent alkaline pH made with NaOH resulted in the loss of cell viability and membrane integrity in a TSP concentration- or NaOH-alkaline pH-dependent manner. In contrast, cells treated with different concentrations of TSP whose pH was adjusted to 7.0 did not show any loss of cell viability or membrane integrity. These results indicate that TSP is a potent membrane-acting agent, and provide compelling evidence that high pH during TSP treatment was responsible for its antimicrobial activity. Adaptation of S. enterica serovar Enteritidis with a sublethal concentration of TSP resulted in the induction of the alkaline stress response. Alkaline stress response involves induced thermotolerance, resistance to higher concentrations of TSP, high pH and sensitivity to acid. Examination of the proteome of TSP-adapted cells revealed differential expression of a number of proteins but did not include the common heat shock proteins involved in thermotolerance. However, TSP adaptation caused a shift in the membrane fatty acid composition from unsaturated to a higher saturated and cyclic fatty acid. This shift in fatty acid composition increases the melting point of the cytoplasmic membrane so that it remains functional at high temperatures. Biofilm bacteria are more resistant to sanitizers, heat and antimicrobial agents than their planktonic counterparts. Examination of the proteome of TSP-adapted biofilm cell of S. enterica serovar Enteritidis revealed little overlap in the protein profile compared to TSP-adapted planktonic cells. Proteomic examination of planktonic and biofilm cells of S. enterica serovar Enteritidis revealed differential expression of a number of proteins involved in DNA replication, stress survival and transport of newly synthesized proteins. These results clearly indicate that changes in the expression of specific genes are involved in the biofilm mode of growth, which could play a significant role in resistance to antimicrobial agents. The results of the current study provide a better understanding of the mechanisms of antimicrobial action of TSP and also elucidate the response of S. enterica serovar Enteritidis to TSP and high pH adaptation. The study also raises new questions regarding stress tolerance of S. Enteritidis following TSP or alkaline pH adaptation with relevance to food safety.

Sol-gel (solution-gelation) method was used to prepare Ni-Ti and Ni-Ti-Al catalysts for reforming of methane with carbon dioxide. This method, after optimizing the parameters such as hydrolysis and acid/alkoxide ratio, is able to make a Ni-Ti catalyst with a surface area as high as 426m2/g when calcined at 473K; but calcination at higher temperature lead to dramatic decrease in surface area. XRD, XPS, TEM and SEM were used to understand this change. Using a packed bed reactor, the catalysts were evaluated with the reforming reaction. It was found that the activity of the Ni-Ti catalyst increases with the Ni loading in the range of 1-10wt%. The reduction temperature has strong effect on activity of the reduced catalyst. Up to 973K, the activity increases with the reduction temperature; but after 973K, the activity decreases and become 0 when the temperature is over 1023K. The Ni-Ti catalyst also deactivated as 15% after 4h of time on stream. The XRD analysis shows that Ti3O5 formed in the catalyst after higher-temperature reduction as well as after the reaction for a period of time. The formation of Ti3O5 may render the catalyst to loss its activity. However, further study is expected to understand the mechanism. TG/DTA analysis shows that both Ni-Ti and Ni-Ti-Al catalysts had carbon deposition; but the latter maintained higher activity in a longer period of time.

No description available.