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Opaline silica (opal-A) is thermodynamically unstable at surface conditions and readily transitions into opal-CT and at higher temperatures and pressures, quartz. Past work has used the temperature dependency of this phase transition for paleothermometry in opal-bearing sedimentary rocks. Those works determined that bulk concentrations of silica, organic material, and detrital minerals influenced the phase transition temperature. However, previous work only addressed the influence of these impurities on a macroscale and ignore potential microtextural interactions of silica and organic material. In this thesis, I present a set of experiments designed to characterize the effect of organic matter distribution on the opal-A to opal-CT transition in siliceous sedimentary rocks. Silica, humic acid, and mock seawater solution were loaded into Parr hydrothermal vessels as bulk sediments or in defined physical configurations (stratified or intermixed) and were heated at 200°C for up to 14 weeks. The solid products of these experiments were analyzed using X-Ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. In organic-free experiments, the broad opal-A diffraction peak at 22° 2θ narrowed over the course of 14 weeks, suggesting increased internal ordering. FT-IR spectra showed changes in the position of the Si-O-Si stretching mode peak at 1060 cm-1 with silica diagenesis. Opal-CT may have been observed to occur sporadically in some stratified experiments and associated controls, but apparently did not occur in intermixed configurations. In stratified experiments, no correlation was observed between opal-A full-width half maximum and proximity to the humic acid layer. Similarly, no trend was observed between FT-IR peak positions and proximity to humic acid. These results suggest that the presence of organic matter does play a role in inhibiting the internal ordering of opal; however, the configuration might not be a primary factor in this transition. The results of this study may be applicable to the Monterey Formation and other hydrocarbon-bearing siliceous sedimentary formations. Our results suggest that the maturation of oil reservoirs in the Monterey Formation may be constrained solely on the silica phases present. / Geology

In this dissertation the gas permeation process within four hybrid inorganic-organic membranes is modeled at the micro level using molecular dynamics (MD) and at the meso scale level using a diffusion mechanism. The predicted permeances and relative selectivity of CO₂ and CH₄ are compared with the experimental results. In the MD simulation a single-pore silica crystal framework model with and without inserted phenyl groups are used to define two membrane structures. We designate the two cases as PSPM and SPM respectively. To mimic the diffusion of gas across the membrane, a three-region system with a repulsive wall potential on the edge is employed. Results from the SPM model indicate that the pore size affects the permeance but not the selectivity. In the PSPM model the permeance decreases significantly when the pore size is below a critical value. The extent of decrease varies with the type of gas and this is reflected in the large selectivity in the PSPM model. When the initial diameter is 0.4 nm the model shows a selectivity of 17.3, which is very close to experimental results. At this selectivity the CO₂ permeance is 2.87 Ã 10^-4 mol m⁻²s⁻¹Pa⁻¹ and the CH₄ permeance is 1.66 Ã 10⁻⁵ mol m⁻²s⁻¹Pa⁻¹. For different gases we also studied the motions of the phenyl groups in the pore during the permeation process. The results show that in CO₂ diffusion the phenyl groups moves in a larger range than in CH₄ diffusion. The density profile of gas molecules that the phenyl groups see is analyzed using double layer phenyl groups . The results show that the number of phenyl groups cannot affect the permeation. In the meso scale study a mixed mechanism model with a grid framework is developed to model the permeation process. In the model the membrane is assumed to consist of various grids which follow three major diffusion mechanisms. Models with different grid sizes are employed for the four membranes. Parameters in each model are estimated from the permeance results of the two gases. By comparing the estimated parameters in the surface diffusion mechanism with the reported values, the acceptable grid models are determined and the models with the minimum number of grids are studied. The diffusion is dominated by the activated Knudsen diffusion mechanism at lower temperatures and follows the surface diffusion mechanism when the temperature is above a critical value. In the diffusion of both gases within the four membranes the surface diffusion portion is very close but the activated Knudsen diffusion portion is not. This explains why the permeation with high selectivity occurs at lower temperatures. By comparing the results it shows the two studies can validate each other. On the other hand the two methods can be complementary as the diffusion model is able to predict the permeance within the right range and the MD model is able to predict the selectivity more accurately. / Ph. D.

The adsorption of several homopolymer polypeptides on Al2O3 and SiO2 particles and surfaces was investigated to identify possible anchor and tail blocks for brush-forming block copolypeptides. Poly-L-(glutamic acid) (GLU) and poly-L-(aspartic acid) (ASP) were found to adsorb on positively charged and nearly neutral Al2O3, while the GLU did not adsorb on negatively charged SiO2. Poly-L-proline (PRO) adsorbed only slightly on the alumina, but showed high affinity adsorption on silica. These results are useful in designing a brush forming block copolymer with the GLU acting as the anchor block and the PRO as the tail block. An important finding in this work is that these unstructured polypeptides, or proteins that only have primary and secondary structure, have adsorption behavior that is similar to that of synthetic polymers. The complexation between a random copolymer of two amino acids, glutamic acid and tyrosine, and poly(ethylene oxide) (PEO) was studied using an in-situ adsorption experiment. It was shown that the adsorption of the random copolymer greatly increased the adsorption of PEO. It was found that the conformation of the copolymer on the surface was controlled by the ionic strength, and the conformation of the adsorbed PEO was controlled by the PEO molecular weight. Both of these factors affected the molar complexation ratio between the PEO and the tyrosine repeat units. The adsorption of two novel triblock copolymers, with PEO tails and anionic hydrophobic center blocks, was studied on alumina and silica surfaces. On silica the adsorption was due to the PEO tails, resulting in low adsorbed amounts. The adsorption was much greater on alumina, indicating either brush formation on the surface or the adsorption of micelles, which are present in solution. The effect of adsorbed polymer on the steric stabilization of alumina particles was studied using sedimentation and electrophoretic mobility experiments. These results do not show conclusively that the triblock copolymer adsorption led to particle stabilization. It is possible that better colloid stabilization of the alumina may be realized by changing the triblock composition to get greater extension and higher packing of the PEO tails. / Ph. D.

Yes / We present here a quantification of the sorption process and molecular conformation involved in the attachment of bacterial cell wall lipopolysaccharides (LPSs), extracted from Escherichia coli, to silica (SiO2) and alumina (Al2O3) particles. We propose that interfacial forces govern the physicochemical interactions of the bacterial cell wall with minerals in the natural environment, and the molecular conformation of LPS cell wall components depends on both the local charge at the point of binding and hydrogen bonding potential. This has an effect on bacterial adaptation to the host environment through adhesion, growth, function, and ability to form biofilms. Photophysical techniques were used to investigate adsorption of fluorescently labeled LPS onto mineral surfaces as model systems for bacterial attachment. Adsorption of macromolecules in dilute solutions was studied as a function of pH and ionic strength in the presence of alumina and silica via fluorescence, potentiometric, and mass spectrometry techniques. The effect of silica and alumina particles on bacterial growth as a function of pH was also investigated using spectrophotometry. The alumina and silica particles were used to mimic active sites on the surface of clay and soil particles, which serve as a point of attachment of bacteria in natural systems. It was found that LPS had a high adsorption affinity for Al2O3 while adsorbing weakly to SiO2 surfaces. Strong adsorption was observed at low pH for both minerals and varied with both pH and mineral concentration, likely in part due to conformational rearrangement of the LPS macromolecules. Bacterial growth was also enhanced in the presence of the particles at low pH values. This demonstrates that at a molecular level, bacterial cell wall components are able to adapt their conformation, depending on the solution pH, in order to maximize attachment to substrates and guarantee community survival. / The authors thank the Libyan Ministry of Education for financial support during the experimental study. We thank the EPSRC funded consortium “Hard-soft matter interfaces: from understanding to engineering” (EP/I001514/1) for financial support. Emily Caseley, who assisted in the preparation and characterization of AmNS-LPS particles as an MRC Confidence in Concept funded postdoctoral researcher at the University of Bradford, (MC_PC_16038).

In this dissertation, mesoporous silica thin films with tunable features at the nanoscale were fabricated using the triblock copolymer template pathway, with the aim of specifically harvesting the low molecular weight peptides and proteins from human serum, which has been regarded as a potential source of diagnostic biomarkers for the early detection of disease. The superior properties of mesoporous silica have been demonstrated in applications which include chemical sensing, filtration, catalysis, drug-delivery and selective biomolecular uptake. These properties depend on the architectural, physical and chemical properties of the materials, which in turn are determined by the processing parameters in evaporation-induced self-assembly (EISA). Using the different polymer templates and polymer concentration in the precursor solution, various pore size distributions, pore structures and surface hydrophilicities were obtained and applied for nanotexture-selective recovery of low mass proteins. With the assistance of mass spectrometry and statistic analysis, we demonstrated the correlation between the nanophase characteristics of the mesoporous silica thin film and the specificity and efficacy of low mass proteome harvesting. In addition, to overcome the limitations of the pre-functionalization method in polymer selection, plasma ashing was used for the first time for the treatment of the mesoporous silica surface prior to chemical modification. Opposite surface charges due to the different functional groups used, resulted in a distinctive selectivity of the low molecular weight proteins from the serum sample. The mesoporous silica chips operate with extraordinary rapidity, high reproducibility, no sample pre-processing, and substantial independence from sample acquisition and storage temperature.In conclusion our study demonstrates that the ability to tune the physicochemical properties of mesoporous silica surfaces has the potential to promote the use of this material as a tool for the selective separation and concentration of the low molecular weight proteome from complex biological fluids. / text

ABSTRACT Nanostructured silica materials were synthesised by the sol-gel process using simple hydroxyacids as template precursors, and these materials were employed as supports for a low temperature iron Fischer-Tropsch (FT) catalyst. Thus, this thesis is divided into two parts: (I) the synthesis of nanostructured silica gels, and (II) their use as catalyst supports in the FT reaction. PART I The effects of synthesis conditions, acidic and basic template precursors and their amounts, synthesis temperature, duration of hydrolysis and ageing, solvent concentration, organic co-solvent, and the synthesis procedure used on the morphology of the silica materials were studied. The synthesised silica gels were characterised by TEM, SEM, BET, TGA, and XRD. Mixtures of different morphologies were obtained with all the hydroxyacids used and the studies revealed that the morphology of the resultant silica gels was largely determined by the type of the hydroxyacid used. The use of oxalic acid produced materials with 4-9 % micropores and a mixture of meso- and macropores mainly consisting of hollow tubes and hollow spheres; the use of D-gluconic and L-tartaric acids produced mesoporous materials mainly consisting of hollow spheres and sheets with folds, respectively; while the use of stearic and cinammic acids produced macroporous materials mainly consisting of solid spheres and undeveloped particles, respectively. The silica gels formed were found to be amorphous in nature, despite the different morphologies that existed in them, and were also thermally stable.Studies involving the use of oxalic and D-gluconic acids showed that the key to the shape of the resultant morphologies resided in the shape of the template crystals formed in solution under specific synthesis conditions. The template shape depended on the type of the template precursor (i.e. both the acid and the base) and its amount. It was also observed that under certain conditions, both at elevated temperatures (≥ 55 oC) and at high water concentrations (> 50 %), the template dissolved and this led to low yields of shaped morphologies (i.e. hollow spheres and tubes). The solvent concentration to produce a maximum tube yield (in the case of oxalic acid) and hollow sphere yield (in the case of D-gluconic acid) was found to require about 25- 50 % water. Very well-developed tubes were also obtained at this concentration (i.e. with oxalic acid). Long hydrolysis and ageing times (i.e. > 2 h) of the sols and gels, respectively, resulted in the formation of surface attached colloidal particles and of tubes and hollow spheres with decreased wall thicknesses. Pre-formation of the template prior to addition of TEOS produced materials with lower surface areas, higher tube yields and bigger tube sizes when compared with materials synthesised by forming the template together with the silica gel. PART II Two types of silica gels were used as supports for an iron FT catalyst; the nanostructured silica gels (tubes with surface area 109 m2/g and spheres with surface area 245 m2/g ) and a commercial silica gel (Davisil silica, surface area 273 m2/g - consisting of undeveloped particles). The effect of varying the potassium promotion levels and of the support morphology on the catalyst activity and selectivity in the FT reaction was studied at 250 oC, in a slurry operated CSTR.It was observed that an increase in the potassium loading up to 0.5 wt % in the Davisil silica catalyst led to a decrease in the catalyst FT and water gas shift (WGS) activity, and methane selectivity. However, the efficiency of the catalyst to produce hydrocarbons increased with an increase in potassium loading up to 0.5 wt %. Increasing the potassium level up to 0.9 wt % led to a slight increase in both the catalyst activity and methane selectivity, and a decrease in the catalyst efficiency. For the silica tubes catalyst, increasing the potassium loading to 0.5 wt % led to an increase in the catalyst activity and methane selectivity, while increasing the potassium level up to 0.9 wt % led to a decrease in the catalyst activity. For both supports, increasing the potassium loading led to an increase in the selectivity towards high molecular weight hydrocarbons, olefins (relative to paraffins) and terminal olefins (relative to internal olefins). While the Davisil silica and the silica tube catalysts remained more or less stable throughout the reaction, the activity of the silica spheres catalyst declined rapidly with time. The nanostructured silica gel supported catalysts both showed higher activities and methane selectivities, but lower efficiencies when compared to the Davisil silica catalyst. Although the selectivity of all three catalysts towards olefins were similar, their selectivity towards high molecular weight hydrocarbons decreased in the order Davisil silica > silica spheres > silica tubes. Elongated needlelike Fe nanoparticles (NPs) were obtained in the silica tubes catalyst, semi hexagonal Fe NPs were formed in the silica spheres catalyst, while the Fe NPs could not be distinguished from the support in the Davisil silica catalyst. After the reaction, the surface areas of all three catalysts were found to have decreased and the catalysts to have sintered. The nanostructured silica supported catalysts showed the presence of Fe nanozones surrounded by a layer of amorphous carbon, while only agglomerated particles of Fe and some carbon rich regions were observed in the Davisil silica catalyst. No evidence of alteration of the morphology of the nanostructured silica supports was observed after the reaction.

The synthesis of mesoporous silica thin films using surfactant templating typically leads to an inaccessible pore orientation, making these films not suitable for membrane applications. Recent advances in thin film synthesis provide for the alignment of hexagonal pores in a direction orthogonal to the surface when templated on chemically neutral surfaces. In this work, orthogonal thin film silica membranes are synthesized on alumina supports using block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as the template. The orthogonal pore structure is achieved by sandwiching membranes between two chemically neutral surfaces, resulting in 90 nm thick films. Solvent flux of ethanol through the membrane demonstrates pore accessibility and suggests a silica pore size of approximately 10 nm. The permeability of ions and fluorescently tagged solutes (ranging from 4,000 to 70,000 Da) is used to demonstrate the membrane’s size selectivity characteristics. A size cut off occurs at 69,000 Da for the model protein BSA. By functionalizing the silica surface with a long chained alkyl group using n-decyltriethoxysilane (D-TEOS), the transport properties of the membranes can be altered. Contact angle measurements and FTIR results show the surface to be very hydrophobic after functionalization. Solvent flux of ethanol through the silica thin film membrane is similar before and after functionalization, but water flux decreases. Thin film silica membranes show much promise for applications in catalysis, bio-sensing, and affinity separations.

Throughout this body of work, three classes of sorbent materials were created and optimized, each designed to selectively capture organics or desired metals from natural water sources. These target species included toxic heavy metals, uranium, rare earths, and simple organics, such as benzene. Each class of sorbent materials is functionalized nanostructured silicas, created by the development of several functionalization methods: utilizing thiol-ene click chemistry, aromatic interactions, and the formation of inclusion complexes. Thiol-ene click surface modification gave rise to sorbent materials with impressive affinities for both soft metals, such as gold, and harder metals, such as uranium and rare earth elements. Applications of these materials for aqueous mining of uranium and rare earth elements from various natural water sources are presented. Two classes of materials based on supramolecular functionalization methods were prepared. In the first class, aromatic interactions allowed for surface functionalization with thiol containing aryl ligands. These materials proved to have an excellent affinity for heavy metals from natural waters, and hold promise for regenerable nanostructured silica sorbents. The second class of materials utilizes the ability of β-cyclodextins to form inclusion complexes with small molecule organics, such as benzene. The formation of inclusion complexes drove both surface functionalization and the capture of small molecule organics from aqueous solutions. This work serves to inspire the development of novel functionalized nanostructured sorbents for trace collection of toxic organics from aqueous streams. These supramolecular methods for surface medication can be expanded to nanomaterials at large. This dissertation includes both previously published/unpublished and co-authored material. / 10000-01-01