Search

The research presented in this thesis started with the idea to study alcohols as modifiers and dopants in differential ion mobility spectrometry (d-IMS) to produce complicated chemical signatures to explore a concept of chemical labels for product security application. D-IMS is a gas phase atmospheric pressure separation and detection technique which distinguishes compounds based on differences in their ions mobility as their travel under a low and high electric field. The hypothesis was that alcohols will form typical d-IMS products such as protonated monomers and proton bound cluster ions. However, the very first experiments revealed unexpected phenomena which included changes in the mobility of ions over a narrow range of concentrations that could not be explained by existing theory. Another observation was the apparent regeneration of reactant ions. It became evident that the observed phenomena had not been described in the open literature and that addressing the research-questions that were being raised would be essential for the determination of alcohols by d-IMS and its use in medical applications for toxicity screening and monitoring of alcohols. The above discovery shifted the research objective towards a fundamental and comprehensive study on the behaviour of alcohols in d-IMS. This thesis describes designed experiments and constructed systems allowing the efficient study of effect of concentration, electric field and temperature on the d-IMS responses of alcohols. The results of those studies demonstate: extensive fragmentation of alcohols, including previously undescribed fragmentation patterns with regeneration of the hydrated proton; new phenomena of adduct ion formation within the d-IMS drift tube, observed in the case of methanol within a narrow range of concentration; and self-modification of the alpha function of alcohols. This knowledge was exploited by developing an non-invasive analytical method for recovery, separation and detection of toxins from human saliva (including alcohols, diols and GHB) using TD-GC-d-IMS (thermal desorption - gas chromatography d-IMS) within a full range of toxicological concentration levels.

At present, more than 80% of the world’s energy consumption and production of chemicals is originated from the use of fossil resources. There is a tremendous growing interest in utilising biomass molecules for energy provision due to their carbon neutrality. Lower alcohols such as methanol and ethanol if produced from biomass as transportation fuels as well as platform chemicals, can become strategically important for many energy/chemically starved countries. Currently, they are synthesised by indirect and inefficient processes. We show for the first time in this thesis study that ethylene glycol, the simplest representative of biomass-derived polyols, can be directly converted to these two lower alcohols by selective hydrogenolysis over modified Raney Ni and Cu catalysts in hydrogen atmosphere. This work provides essential information that may lead to the development of new catalysts for carbohydrate activation to methanol, a novel but important reaction concerning the important biomass conversion to transportable form of energy. Modification of electronic structure and the adsorption properties of Raney catalysts have therefore been achieved by blending with second metal(s). It is found that the activity and selectivity of this reaction can be significantly affected by this approach. In contrast, there is no subtle effect on methanol selectivity despite a great variation in the d-band centre positions of metal catalysts which show a distinctive effect on other products. Our result suggests that methanol is produced on specific surface sites independent from the other sites at an intrinsic rate and will not be converted to other products by the d-band alteration. On the other hand, it is reported in this thesis that a dramatic improvement in the combined selectivity to methanol/ethanol reaching 80% can be obtained over a Pd/Fe3O4 catalyst under relatively milder conditions (20 bar and 195 oC). This direct production of the non-enzymatic bio-alcohols is established over a carefully prepared co-precipitated Pd/Fe3O4 catalyst which gives a metallic phase of unexpectedly high dispersion ranging from small clusters to individual metal adatoms on defective iron oxide to give the required metal-support interaction for the novel synthesis. It is demonstrated that the small PdFe clusters on iron oxide surface provide the active species responsible for methanol production. In addition, a related Rh/Fe3O4 catalyst synthesised by co-precipitation is also shown to be selective for CO2 and H2 production from a direct methane-oxygen oxidation reaction. As a result, 2.7% conversion of methane with selectivity ratio of CO2/H2 = 4 in a mixed gas feed stream of CH2/O2 = 30 at 300 oC is obtained. The reaction is operated in a kinetically controlled regime at 300oC, where the CO formation from reverse water gas shift reaction is greatly suppressed. It is evident that the Rh/Fe3O4 acts as an interesting bifunctional catalyst for this reaction. This catalyst firstly gives a high dispersion of Rh which is expected to deliver a higher surface energy with enhanced activity. The Rh metal surface provides catalytically active sites for dissociation of methane to adsorbed hydrogen and carbon atoms effectively, and active oxygen on metal surface readily catalyses the carbon atoms to CO. Following these elementary reactions, the surface oxygen from Fe3O4 subsequently converts it to CO2 selectively at the metal-support interface. As a result, the novel study of catalytic biomass conversion and the discoveries of new catalysts are reported in this thesis.

The aim of this thesis is the study of protein resistant oligo(ethylene glycol) (OEG) self-assembled monolayers (SAMs) using in situ techniques, such as neutron reflectivity (NR), polarisation modulation infrared spectroscopy (PMIR) and small-angle x-ray scattering (SAXS). In order to elucidate the mechanisms that lead to the nonfouling properties of these SAMs, the SAM-water, protein-protein and protein-SAM interactions have been studied separately. NR measurements, focused on the solid-liquid interface between OEG SAMs and water, show clear evidence of an extended layer with reduced density water. The reduction in density is up to 10% compared to the bulk value, and extends up to 5 nm into the bulk. The effective area (density reduction x length) of this reduced density water layer did not significantly change when the temperature was reduced to 5°C. In a complementary study, the interaction of water with protein-resistant HS(CHV2)11(OCH2CH2)3OMe monolayers was examined using in and ex situ PMIR. In particular, shifts in the position of the characteristic C-O-C stretching vibration were observed after the monolayers had been exposed to water. The shift in frequency increased when the SAM was observed in direct contact with a thin layer of water. It was found that the magnitude of the shift also depended on the surface coverage of the SAM. These results suggest a rather strong interaction of oligo(ethylene glycol) SAMs with water and indicate the penetration of water into the upper region of the monolayer. These findings indicate the presence of a tightly bound water layer at the SAM-water interface. Further NR studies of the interface between OEG SAMs and a highly concentrated protein solution revealed an oscillating protein density profile. A protein depleted region of about 4-5 nm close to the SAM was followed by a more densely populated region of 5-6 nm. These oscillations were then rapidly damped out until the bulk value was reached. The influence of temperature and salt concentration on the protein density profile was small, indicating a rather minor contribution of electrostatic interactions to the protein repulsive force. SAXS measurements of OEG coated gold colloids mixed with proteins in solution did also not show any pronounced salt concentration dependence of the colloid-protein interaction. The strong association of water with the SAM and the layer of tightly bound water, together with the lack of electrostatic repulsion, suggest that the adsorption of proteins is energetically hindered by the presence of a strongly bound hydration layer.

Direct alcohol fuel cells are a viable alternative to the traditional hydrogen PEM fuel cell. Fuel versatility, integration with existing distribution networks, and increased safety when handling these fuels increases their appeal for portable power applications. In order to maximize their utility, the liquid fuel must be fully oxidized to CO2 so as to harvest the full amount of energy. Methanol and ethanol are widely researched as potential fuels to power these devices, but methanol is a toxic substance, and ethanol has a much lower energy density than other liquids such as gasoline or glucose. Oxidation of complex fuels is difficult to realize, due to difficulty in breaking carbon-carbon bonding and poisoning of the catalysts by oxidative byproducts. In order to achieve the highest efficiency, an anode needs to be engineered in such a way as to maximize activity while minimizing poisoning effects of reaction byproducts. We have engineered an anode that uses platinum-based catalysts that is capable of completely oxidizing ethylene glycol and glycerol in neutral and alkaline media with little evidence of CO poisoning. We have constructed a hybrid anode consisting of a nano-structured PtRu electrocatalyst with an NAD-dependent alcohol dehydrogenase for improved oxidation of complex molecules. A nano-structured PtRu catalyst was used to oxidize ethylene glycol and glycerol in neutral media. In situ infrared spectroscopy was used to verify complete oxidation via CO2 generation.,There was no evidence of poisoning by CO species. A pH study was performed to determine the effect of pH on oxidative current. The peak currents did not trend at 60 mV/pH unit as would be expected from the Nernst equation, suggesting that adsorption of fuel to the surface of the electrode is not an electron-transfer step. We synthesized nano-structured PtRu, PtSn, and PtRuSn catalysts for oxidation of ethylene glycol and glycerol in alkaline media. The PtRu electrocatalyst gave the highest oxidative currents and highest stability compared to a nano-structured platinum, PtSn, and PtRuSn catalyst. In situ infrared spectroscopy showed complete oxidation of each fuel occurred by the presence of CO2, with very little poisoning CO species present. In order to increase oxidative performance in neutral media, a hybrid anode based on nano-structured PtRu and a NAD-dependent alcohol dehydrogenase for the oxidation of ethanol and ethylene glycol was developed. Steady state polarization showed that the hybrid anode had higher current densities than the enzyme or the PtRu electrocatalyst alone. The hybrid anode had higher current densities at concentrations up to 3 M while oxidizing ethanol and ethylene glycol. The catalyst synthesis, characterization, and experimental results demonstrate the feasibility of fuel cells that can oxidize higher order fuels that platinum based catalysts or enzymes cannot oxidize alone. The cooperative mechanism from co-catalysis using inorganic and organic catalysts will allow for deep oxidation and improved power generation.

This dissertation focuses on the characterization of two surfaces: mixed self-assembled monolayers (SAMs) of hexa(ethylene glycol) and alkyl thiolates (mixed SAM) and poly(N-isopropylacrylamide) (PNIPAAm). The synthesis of hexa(ethylene gylcol) alkyl thiol (C11EG6OH) is presented along with the mass spectrometry and nuclear magnetic resonance results. The mixed SAM surface was confirmed to be thermally responsive by contact angle goniometry, 35° at 28 °C and 55° at 40 °C. In addition, the mixed SAM surfaces were confirmed to be thermally responsive for various aqueous mediums by tensiometry. Factors such as oxygen, age, and surface mole fraction and how they affect the thermal response of the mixed SAM are discussed. Lastly, rat fibroblasts were grown on the mixed SAM and imaged by phase contrast microscopy to show inhibition of attachment at temperatures below the molecular transition. Qualitative and quantitative measurements of the fibroblast adhesion data are provided that support the hypothesis of the mixed SAM exhibiting a dominantly non-fouling molecular conformation at 25 °C whereas it exhibits a dominantly fouling molecular conformation at 40 °C. The adhesion of six model proteins: bovine serum albumin, collagen, pyruvate kinase, cholera toxin subunit B, ribonuclease, and lysozyme to the model thermally responsive mixed SAM were examined using AFM. All six proteins demonstrated adhesion to the pure component alkyl thiol, and in contrast demonstrated no adhesion to the pure component C11EG6OH SAM at both temperatures examined, 25 and 40 °C. The protein adhesion data to the mixed SAM also supports the hypothesis that the mixed SAM displays a non-fouling molecular conformation at 25 °C whereas it displays a dominantly fouling molecular conformation at 40 °C. PNIPAAm brushes grown on a silicon substrate by atom-transfer radical polymerization (ATRP) were imaged by AFM and characterized by XPS. The height of the resulting brushes could be controlled from 5 to 55 nm by reaction time. A thermal response was observed for polymer brushes with a length greater than 20 nm. For polymer brush lengths greater than 20 nm, the static contact angle at 22 °C was 35° and varied from 60 to 80° at 40 °C. The thermal response was also observed using the captive bubble method. Force-distance curves of the PNIPAAm brushes were taken with an unmodified silicon nitride AFM cantilever at incremental temperature steps. At room temperature the force-distance data was fit to the Alexander-de Gennes model resulting in a hydrated polymer length of 235 nm. The Youngs modulus was calculated using the Hertz model and changed from 80 MPa at 26 °C to 350 MPa at 40 °C. The solvent condition of the Alexander-de Gennes model was set to the case of good solvent and showed close match to the force-distance data at 26 °C. The match was not as close when the solvent condition was set to theta solvent condition and compared to the force-distance data at 40 °C.'

Carbon-carbon bond forming carbonylation reactions were investigated as candidates to replace ethene epoxidation as the major source of ethylene glycol production. This work was motivated by the potentially lower cost of carbon derived from synthesis gas as compared to ethylene. Synthesis gas can be produced from relatively abundant and cheap natural gas, coal, and biomass resources whereas ethylene is derived from increasingly scarce and expensive crude oil. From synthesis gas, a range of C1 compounds containing no C-C bonds, such as methanol, formaldehyde and its closely related acetals such as dimethoxymethane (DMM), can be readily obtained. Formaldehyde carbonylation was once used commercially to produce precursors to ethylene glycol. Previous investigations of this reaction were carried out in the liquid phase, and required high carbon monoxide pressures (tens to hundreds of atmospheres) to overcome the low solubility of carbon monoxide. At lower carbon monoxide pressures, the reaction of formaldehyde with itself, the Cannizzaro disproportionation reaction, becomes the dominant process. The focus of this work was to carry out the carbonylation of formaldehyde and DMM with high selectivity and activity towards ethylene glycol precursors without requiring harsh conditions. Formaldehyde carbonylation was investigated in the liquid-phase using methyl formate (MF) as the source of CO using silicotungstic acid and other heteropoly acids as the catalyst. Methyl glycolate (MG) and methyl methoxyacetate (MMAc), both precursors to ethylene glycol, were formed along with DMM and dimethyl ether (DME), the primary byproducts. Using MF as the CO source avoided the need to pressurize the headspace with high pressures of CO gas. The effects of formaldehyde source, reaction temperature, reaction time, and catalyst were investigated. Methoxymethanol, paraformaldehyde, 1,3,5-trioxane, and DMM were examined as sources of formaldehyde. The highest yields of methyl glycolate and methyl methoxyacetate were obtained using 1,3,5-trioxane as the source of formaldehyde. Release of carbon monoxide from MF was found to be slow and limited the rate of carbonylation. Of the heteropoly acids investigated, silicotungstic acid produced the highest yields of MG and MMAc, whereas methanesulfonic acid did not produce these products at similar acid loading. The difference in the effectiveness of heteropoly acids and methanesulfonic acid is ascribed to the role of the anion of the heteropoly acid, a soft base, in stabilizing the reactive intermediates involved in the carbonylation of formaldehyde. While using MF as the CO source provided milder conditions, the selectivity to ethylene glycol precursors was still low. To achieve high selectivity under mild conditions, a novel vapor-phase process was developed. By carrying out the reaction in the vapor phase, the need for high pressure to dissolve CO in a liquid was avoided, and by using the dimethyl acetal of formaldehyde, DMM, the need for water or alcohol was avoided. Using an acid zeolite, Faujasite (FAU), as the catalyst it was possible to produce MMAc with a selectivity of up to 79% and a yield of up to 20% based on DMM at 3 atm of CO pressure. The disproportionation of DMM to produce DME and MF was the only competing process observed. The rate of disproportionation was minimized by operating at high CO to dimethoxymethane feed ratios. By selecting zeolites of different frameworks and Si/Al ratios, the effects of pore size and connectivity and the proximity of acid sites on the carbonylation of dimethoxymethane to produce methyl methoxyacetate were revealed. FAU, ZSM-5 (MFI), Mordenite (MOR), and Beta (BEA) showed very similar activity for DMM carbonylation. However, FAU had the highest selectivity compared to the other zeolites because of its very low activity towards disproportionation. The higher rate of DMM disproportionation observed for MFI, MOR, and BEA is ascribed to the small pores of these zeolites, which facilitate the initial and critical step in the formation of dimethyl ether and methyl formate. Ferrierite showed very low activity for both carbonylation and disproportionation. Increasing the Si/Al ratio for both FAU and MFI led to an increase in the turnover frequency for DMM carbonylation. The low rate of MMAc formation found at low Si/Al ratios was proposed to be due to repulsive interactions occurring between adsorbed species located within the same supercage of FAU or channel intersection of MFI. Mechanisms were proposed for both DMM carbonylation and disproportionation reactions over acid zeolites and were evaluated using in situ infrared spectroscopy. Surface intermediates for both carbonylation and disproportionation reactions were observed spectroscopically, and their responses to changes in reaction conditions were consistent with steady-state kinetic experiments and the predictions of density functional theory (DFT) calculations. For DMM carbonylation, the solvation of the carbocationic transition state of the CO insertion step was observed when gaseous nucleophiles promoted the formation of the CO insertion product, a methoxyacetyl surface species. The surface concentration of the methoxyacetyl species at steady state, as measured by infrared spectroscopy, was 10 times smaller on zeolite FAU than on MFI, despite the higher rate of DMM carbonylation on FAU. This was supported by DFT calculations, which predicted a very small barrier for the reaction of the methoxyacetyl species over FAU, but a substantial barrier over MFI, leading respectively to smaller and larger concentrations of this species. The rate expression derived from the proposed mechanisms was used in a plug-flow reactor model to predict the rates of carbonylation and disproportionation over FAU as functions of reaction temperature and DMM and CO partial pressures. The results showed good agreement with steady-state rate measurements.

Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.

Advances in surface broad bandwidth sum frequency generation (BBSFG) spectroscopy and investigations of liquid surfaces are discussed in this dissertation. The technique implemented uses a double amplifier ultrafast laser system to produce a narrow bandwidth visible beam and a broad bandwidth infrared beam. The two beams are overlapped in time and space on a liquid surface to produce a broad bandwidth sum frequency signal. The double amplifier system allows for higher peak powers resulting in a stronger sum frequency generation response from characteristically low signal liquid surfaces. Several organic liquids are investigated using BBSFG spectroscopy and Raman spectroscopy to investigate the surface structure and the bulk liquids, respectively. The series of liquids selected are applicable to atmospheric aerosol processing. Initially, a surrogate hydrophilic compound ethylene glycol was investigated. In addition to ethylene glycol, several aromatic compounds were probed at their air-liquid interfaces. The aromatic compounds studied were benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, and mesitylene. The final aromatic compound to be studied was 1-methyl naphthalene. The surface of the neat 1-methyl naphthalene liquid is dramatically altered upon the addition of small amounts of water into the bulk liquid.

Results disclosed in this thesis indicate that a microencapsulated octacosane phase-change material fluid is well suited for large scale electronic cooling applications. The fluid was successfully circulated in a liquid pumped loop heat exchanger system resembling the cooling system of an electric vehicle. Little or no particle breakdown occurred to the polymer encapsulated spheres. The high melting point, Tmelt ∼60°C, of octacosane PCM make it ideal for cooling electronics. The microPCM fluid is controllable by using a pump at all times. To achieve optimum performance from the microPCM fluid, the concentration of solid PCM particles and the mass flow rate must be tailored to the amount of energy that needs to be transferred and the maximum surface temperature at which this can be accomplished. For the 0.0138 meter internal diameter, smooth copper tube used in the experiments, the microPCM fluid produced lower exit surface temperatures than the 50/50 ethylene-glycol/water baseline fluid for mass flow rates less than 0.035 kg/s. This flow value is independent of the applied heat rate so long as some un-melted PCM particles remain at the exit of the heated section. MicroPCM fluids should be considered as a working fluid for liquid heat transfer systems when pumping power limitations, low surface temperature or surface temperature uniformity are design requirements. When operated at the correct conditions, the enhanced heat capacity of octacosane microPCM fluid will provide lower and more constant surface temperatures, and require less pumping power than conventional coolants.