School of Chemistry - Theses

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Synthesis, structure and reactivity of ligand stabilized coinage metal nanoclusters

Zavras, Athanasios ( 2013)

The coinage metal nanoclusters (CMNCs), defined as copper, silver or gold, constitute an intermediate state of matter that exist between molecules and bulk material. The properties of CMNCs differs to that of molecules and bulk material due to quantum confinement effects. These nanostructured materials have attracted significant attention owing to their fundamentally interesting architectures, and unique properties with applications in areas such as catalysis, optical materials, medical imaging, models for hydrogen storage. Tailoring the properties of such promising materials has proven challenging and requires a fundamental understanding of their assembly, structure and reactivity. The aim of this thesis is: (i) the primary application of mass spectrometric techniques to monitor the formation of CMNCs which result from the addition of sodium borohydride to a solution consisting of a coinage metal salt and the bidentate ligand, bis(diphenylphsphino)methane (dppm) under various synthetic conditions; (ii) to apply this information in developing synthetic approaches to optimize clusters of interest and apply a mass spectrometry (MS) directed synthesis leading to the isolation of crystalline material suitable for structural characterization by X-ray crystallography (iii) apply MS based analysis methods to provide information on the reactivity of CMNCs in solution and the reactivity and structure of mass selected CMNCs in the gas phase. Electrospray ionization mass spectrometry (ESI-MS) and UV-Vis spectroscopy were used to monitor the formation of gold nanocluster cations in the condensed phase via the sodium borohydride (NaBH4) reduction of methanolic solutions containing AuClPPh3 and dppm. ESI-MS highlights the formation of complexes prior to the addition of NaBH4 as [Au2(dppm)2]2+, [Au(PPh3)2]+, [Au2(dppm)3]2+, [Au(dppm)2]+,[Au2Cl(dppm)2]+. The cationic complex product distribution can be monitored over a range of metal to ligand ratios to minimize the colloid precursor [Au(PPh3)2]+. The addition of NaBH4 where the optimized metal to ligand ratio was determined as AuClPPh3:dppm is 1:2 results in the formation of the following types of gold nanoclusters [Au9(dppm)4]3+, [Au9(dppm)5]3+, [Au5(dppm)3(dppm-H+)]2+, [Au10(dppm)4]2+, [Au11(dppm)5]3+, [Au11(dppm)6]3+, [Au13(dppm)6]3+ and [Au14(dppm)6(Ph2PCHPPh2)]3+. The gas phase unimolecular chemistry of these cations was examined by (i) collision induced dissociation (CID) and electron capture dissociation resulting in the gas phase synthesis of the novel clusters [Aux(dppm)y]z+ (x = 2,3 , 6–13; y = 1–6 and z = 1–3) and [Aux(dppm)y(dppm-H+)]z+ (x = 5,14; y= 2,5; z = 2,3) via ligand loss and core fission fragmentation channels. (ii) electron capture dissociation (ECD) of mass selected multiply charged gold cluster cations where an additional fragmentation channel arises due to C-P bond activation. ESI-MS was also applied to study the reactivity that results from silver salts in the presence of dppm, that are treated with sodium borohydride. It was observed by ESI-MS that no all metallic silver clusters had formed. Instead there existed abundant and relatively monodisperse trinuclear silver(I) hydride clusters. The synthesis could be refined by careful MS based analysis to result in the isolation of crystalline material of (i) [Ag3(μ3-H)(μ3-Cl)(dppm)3]BF4, and (ii) [Ag3(μ3-H)(dppm)3](BF4)2. These clusters could be mass selected to generate novel gas phase clusters in the gas phase. The multiply charged cation [Ag3(μ3-H)(dppm)3]2+ was also investigated by ECD and EID. The silver hydride cluster cation [Ag10H8(dppm)6]2+ was observed during the synthesis of trinuclear silver clusters. This cluster has yet to be isolated.
Ultrasonic synthesis and characterization of multifunctional nano/microcapsules

CAVALIERI, FRANCESCA ( 2013)

Liquid and air-filled nano/microcapsules have potential applications in diagnostic and therapeutic medicine. Air and liquid cores are generally coated by a protein, lipid or polymer shell. Air-filled nano- and microcapsules, commonly referred to as nano- and microbubbles (NBs and MBs), are ultrasound responsive colloidal particles with a strong potential to become theranostic agents, combining the contrast and therapeutic functionalities. In the last decades, they have played a significant role as ultrasound contrast agents in diagnostic imaging. Similarly, liquid and solid encapsulated nano/ microcapsules have potential applications in targeted drug delivery in medicine. This thesis investigates the use of high energy ultrasound processing (batch and flow-through) to synthesise nano- and microcapsules using proteins and biocompatible polymers (e.g., polymethacrylic acid) in aqueous solutions. The ultrasound-assisted self-assembly and cross-linking of lysozyme at water–air and water–perfluorohexane interfaces are shown to produce lysozyme-shelled hollow microbubbles (LSMBs) and microcapsules (LSMCs), respectively. The arrangement of lysozyme at the air–liquid or oil–liquid interfaces is accompanied by changes in the bioactivity and conformational state of the protein. A comprehensive study of the microspheres (LSMBs and LSMCs) size distribution, degradability, mechanical and surface properties, acoustic response and biofunctional properties has been performed. A novel flow-through sonication technique for synthesizing stable and monodispersed nano- and micrometer-sized bubbles has been developed. It has been demonstrated that the size and size distribution of the bubbles are controlled by the active cavitation zone generated by ultrasound. The cytoxicity of LSMBs and LSMCs on adherent cell line derived from a human breast adenocarcinoma cells (SKBR3) has been evaluated. SKBR3 shows capability to phagocyte LSMBs and LSMCs in vitro. In addition, a one-pot ultrasonic procedure has been developed as a versatile route for synthesizing polymerv coated microspheres, PMASH MB, that have potential application as drug delivery vehicles. The use of biocompatible thiolated poly(methacrylic acid) as the shell material offers control over size, morphology and functionality of the microspheres. LSMBs and PMASH MBs are shown to possess echogenic properties and can be used for loading oligonucleotides. Finally, LSMBs were engineered as a support for the immobilization of gold nanoparticles and an enzyme, alkaline phosphatase, in order to develop micro-antimicrobial and biosensing devices.
Synthesis and X-ray crystallographic studies of novel radioprotectors derived from Hoechst 33258

Wee, Jing-Yi Wyvette ( 2013)

Hoechst 33258 is a fluorescent bibenzimidazole that has been shown to bind in AT-rich regions of the minor groove of B-DNA by X-ray, footprinting, NMR and other biophysical studies. An analogue of Hoechst 33258, methylproamine, was a radioprotector developed by the Peter MacCallum Cancer Institute and the White Group (initially David Kelly’s Group) at the School of Chemistry, University of Melbourne. Methylproamine was shown to be 100-fold more potent than the classical aminothiol radioprotector WR1065 in protecting cells against radiation damage. However, studies also revealed that it was toxic to cells at high concentrations, hence limiting its potential as a radioprotector. Nine novel radioprotectors based on Hoechst 33258 and methylproamine had been designed in an attempt to improve radioprotective activity. These compounds included low molecular weight analogues (41, 42, 60 and 73), selenium-containing (93–95) and tetrathiafulvalene-containing bibenzimidazoles (110 and 117). They were synthesised via a linear synthetic approach and their structures were determined by 1H, 13C, DEPT-135, gHSQC and gHMBC NMR, and mass spectrometry. Cyclic voltammetry experiments were conducted for the tetrathiafulvalene compounds and showed that they could undergo reversible oxidation and reduction reactions, which suggested that they might be recycled under biological conditions. The pharmacological properties of the bibenzimidazoles were investigated using in vitro biological and biochemical assays. DNA binding affinity was assessed by spectrophotometric titration, while cytotoxicity and radioprotective activity were evaluated using clonogenic survival assays. Preliminary results showed that the novel compounds were weaker binders than methylproamine. The low molecular weight bibenzimidazoles (except compound 73), selenium- (except compound 95) and tetrathiafulvalene-containing compounds had lower toxicity than methylproamine. Although the cytotoxicity property for most of the novel compounds had improved, they did not show a better radioprotection as hypothesised. Among the new analogues, only the low molecular weight compound, 60, demonstrated a significant radioprotective activity with low toxicity. Crystallographic studies of novel Hoechst 33258 analogues (42, 60, 110; and 59, 125, 126 and 127) complexed with dodecamers d(CGCAAATTTGCG)2 and d(CGCGAATTCGCG)2 showed that they also bind in the AT-rich region of the minor groove. The compounds adapted to the irregular curve of the minor groove by adjusting the torsion angles between the aromatic systems. Numerous intermolecular interactions, such as van der Waals, electrostatic and hydrogen bonding played vital roles in stabilising the ligand/DNA structures. For all of the DNA complexes, the nitrogen atoms (N3′ and N3′′) of the ligand benzimidazole groups formed bifurcated hydrogen bonds with the hydrogen bond acceptors of the DNA molecule.
Assessment of perylene-based profluorescent nitroxides for monitoring polyester degradation upon weathering

SYLVESTER, PAUL ( 2013)

A profluorescent nitroxide possessing an isoindoline nitroxide moiety linked to a perylene fluorophore was developed to monitor radical mediated degradation of melamine-formaldehyde crosslinked polyester coil coatings in an industry standard accelerated weathering tester. Trapping of polyester derived radicals (most likely C-radicals) that are generated during polymer degradation leads to fluorescent closed-shell alkoxy amines. Time-dependent degradation profiles were generated to assess the relative stability of different polyesters towards weathering. The nitroxide probe couples excellent thermal stability and satisfactory photostability with high sensitivity and enables detection of free radical damage in polyesters under conditions that mimic exposure to the environment on a time scale of hours rather than months or years required by other testing methods. There are indications that the profluorescent nitroxide undergoes partial photodegradation in the absence of polymer derived radicals. It was also found that UV-induced fragmentation of the NO-C bond in closed-shell alkoxy amines leads to regeneration of the profluorescent nitroxide and the respective C-radical. The maximum fluorescence intensity that could be achieved with a given probe concentration is therefore not only determined by the amount of polyester radicals formed during accelerated weathering, but also by the light-driven side reactions of the profluorescent nitroxide and the corresponding alkoxy amine radical trapping products. Studies to determine the optimum probe concentration in the polymer matrix revealed that aggregation and reabsorption effects lowered the fluorescence intensity at higher concentrations of the profluorescent nitroxide, but lower probe concentrations, where these effects would be avoided, were not sufficient to trap the amount of polyester radicals formed upon weathering. The optimized experimental conditions were used to assess the impact of temperature and UV irradiance on polymer degradation during accelerated weathering.
Ultrafast photochemistry of photosynthetic reaction centre mimics

Robotham, Benjamin Edward ( 2013)

In this work the photoinduced electron transfer (ET) behaviour of several photosynthetic reaction centre (RC) mimics was investigated. Particular attention was given to the decay pathways following excitation of the porphyrin S2 state. The systems studied are linked either by covalent or supramolecular means or a combination of both. The redox-active chromophores include zinc(II) tetraphenylporphyrin (ZnTPP), tin(IV) tetraphenylporphyrin (SnTPP), buckminsterfullerene (C60 ), an amino-substituted naphthalene diimide (ANDI) and several N-substituted naphthalene diimides (NDIs). A boron dipyrromethene (BODIPY) is employed as an energy transfer (EnT) partner. The time scales of the investigated processes required the use of ultrafast transient absorption (TA) measurements. The design and construction of the first implementation of a multichannel broadband detection TA instrument using a high repetition rate (94 kHz) amplified laser source is described. A hybrid global target analysis method, which allows TA data to be fitted by both sequential and branched decay scheme models, is also presented. In non-covalently bound ZnTPP:C60 complexes ET originating directly from the porphyrin S2 state is observed. Rapid charge recombination partially reforms both the ZnTPP S1 state as well as the ground state species. In a covalently linked ZnTPP-ANDI dyad a very similar behaviour is observed, although in this case charge recombination returns the ZnTPP S1 state near quantitatively. In both cases a non-thermalised charge separated state can be inferred. If a further thermalised charge separated state is energetically accessible from the porphyrin S1 state, a second ET step to the same acceptor can occur. In supramolecular complexes of ZnTPP with either dipyridine naphthalene diimide (pyrNDI) or diisoquinoline naphthalene diimide (isoquinNDI), ET commencing from the former’s S1 state to the NDI acceptors is observed. Isoquinoline coordination to the porphyrin metal centre, as it occurs in the ZnTPP:isoquinNDI complex, has not been previously reported as an assembly method for RC mimics. In this system the possibility of a very similar higher excited state behaviour as in the ZnTPP-ANDI dyad, i.e. ET from the porphyrin S2 state followed by charge recombination to itsS1 state, is inferred. ET from the porphyrin S2 state does not require a covalent link to the employed acceptor, although a small chromophore separation and the proximity of the frontier orbitals thereby ensured are a necessity. Finally, the photophysics of an NDI2-SnTPP:(OPh-BODIPY)2 array and several related model systems was investigated. In the NDI2-SnTPP:(OH)2 triad, ET from SnTPP to an NDI moiety is exclusively observed for porphyrin S2-excitation. The product of subsequent charge recombination, either the porphyrin S1 state or the ground state species, is strongly dependent on the solvent polarity. In the arrays containing both SnTPP and BODIPY the former’s S2 state can undergo EnT to the latter’s S1 state. However, rapid ET from the interlocated phenolate linker moiety to SnTPP is the dominant quenching process of the S2 state in these arrays.
Donor-acceptor block copolymers for photovoltaic applications

Bicciocchi, Erika ( 2013)

The performance of an organic photovoltaic (OPV) cell depends on the properties of the active layer, which usually consists of a blend of electron donor and acceptor materials. The donor (D) is often a π-conjugated polymer that also acts as the light absorbing medium, while the acceptor (A) is commonly a soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Since both donor and acceptor materials tend to phase separate on a macroscopic scale, the control of the morphology of this active layer is of utmost importance. The aim of this research is to explore the potential of rod-coil block to acts as blend compatibilizers for modifying OPV material morphology. A novel and widely applicable synthetic approach for donor-acceptor (D-A) rod-coil block copolymers has been developed that combines polycondensation techniques, such as Suzuki and Stille coupling, with radical addition fragmentation chain transfer (RAFT) polymerization. Suzuki and Stille couplings are the synthetic methods of choice for obtaining conjugated polymers with suitable electro-optical properties, while RAFT polymerization allows the synthesis of well-defined functional coil polymers with suitable end-groups able to end-cap the conjugated polymers. Two different series of rod-coil block copolymers have been prepared. The first series is based on a combination of Suzuki and RAFT, while the second series employs Stille and RAFT polymerization. The two rod-coil block copolymers obtained by Suzuki and RAFT polymerization techniques were based on the well-known conjugated polymer poly(9,9-dihexylfluorene-alt-bithiophene) (F6T2). In this series different ways to functionalize the coil block with the acceptor moieties were investigated and two new synthetic protocols were developed. The first one describes the successful synthesis of D A rod coil block copolymers through the cycloaddition of tosylhydrazone-functionalized polystyrene with fullerene (C60). The second methodology utilizes an acid chloride of the widely used electron acceptor [6’6]-phenyl-C61-butyric acid methyl ester (PCBM) in conjunction with an amine-containing coil block. In particular the latter protocol appears very suitable as it ensures the functionalization of the coil block without cross-linking. In order to develop a generic methodology for rod-coil block copolymers obtained by Stille and RAFT polymerizations, a new alternating D-A conjugated polymer was designed and synthesized. The building blocks for the Stille coupling were based on the well-known N-octylthieno[3,4-c]pyrrole-4,6-dione as well as a newly designed 2,3-bis(2-ethylhexyl)thiophenylethynyl substituted benzodithiophene. The introduction of electron rich thiophene units raised the HOMO level of the conjugated polymer and thus reduced the band gap for enhanced light absorption. This modification also introduces sterically less-demanding triple bonds, potentially providing better molecular interaction and an extra dimension of conjugation perpendicular to the main polymer chain. The properties of this new conjugated polymer have been evaluated by UV-vis, fluorescence, photoelectron spectroscopy in air (PESA) and density functional theory (DFT) calculations. The polymer absorbs broadly in solution and solid state in the region 300 nm to 680 nm. A HOMO and LUMO level of -5.38 eV and –3.56 eV, respectively were estimated, corresponding to a band gap of 1.82 eV. In order to derive the D-A rod-coil block copolymer the conjugated block was directly end-capped with the C60-containing coil polymer. The newly synthesized rod-coil block copolymers were characterized by NMR, GPC, AFM, steady-state (UV-vis and fluorescence) as well as time-resolved spectroscopy methods. The characterization results confirmed the successful synthesis of the rod-coil block copolymers and highlighted the improved thermal stability of the copolymers compared to blends of their components. The series of rod-coil block copolymers based on F6T2 have been utilized as compatibilizers in bulk heterojunction solar cells and it has been demonstrated that they extend the operational stability of the devices. While the photophysical properties of the new benzodithiophene-based conjugated copolymer suggested that the new material was an excellent candidate to be tested in an OPV device, the unexpectedly low efficiencies of this material precluded studies of the D-A rod-coil block copolymer additive as a compatibilizer. Photo-CELIV studies indicate low charge mobility combined with a strong tendency for charge recombination are the reasons for the low efficiency observed.
Ultrasonics as a new platform technology in dairy processing

Koh, Li Ling Apple ( 2013)

It has been shown recently that the use of ultrasound (US) on dairy whey systems can lead to a reduction in the size of whey protein aggregates and a consequent reduction in viscosity. Further, application of ultrasound after heat treatment can lead to a heat stable dairy product. However, a number of unanswered questions remain regarding this approach and this thesis attempts to answer some of these questions. Prior to commercialisation, a comparison with other physical shear and high pressure processes is required to determine the viability of US in the dairy industry. The thesis shows that at identical energy density of 153 J/ml, both sonication at 20 kHz and homogenisation at 80 bar of a 5 wt% whey protein concentrate (WPC80) solution provided similar reductions in whey protein aggregate size and viscosity. Smaller reductions were observed in samples subjected to high shear mixing at the same energy density, which may be the result of excessive foaming. The work shows that free radicals are absent in both the high shear mixing and homogenisation processes, implying that high shear forces is responsible for the observed changes, rather than acoustic collapse events. In addition, heat stability was achieved in all systems, with the best results again obtained for both homogenisation and sonication. Hence, the combination of a heat treatment followed by any suitable high shear process is capable of producing a low viscosity, heat stable product. A further concern was whether ultrasound impacted only the aggregate size or whether there were more subtle changes to the secondary structure of the protein. In this thesis, the changes in aggregation and secondary structure of the individual whey proteins and their mixtures upon sonication and the combination of heat and sonication were studied. No structural changes were observed in any native protein solution upon sonication at 31 J/mL using a 20 kHz sonicator. Prolonged sonication led to minor structural changes in pure β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) solutions, as shown using fourier transform infrared spectroscopy (FTIR) analysis, but these proteins remained predominantly in their native β-sheet and α-helical structure respectively. None of the heated and sonicated protein samples showed any large increases in β-sheet content. Hence, with the conditions performed for heat and US treatments in this thesis, no drastic alteration in the secondary structure of the protein were observed in US of dairy whey solutions. In the dairy industry, membrane ultrafiltration (UF) is used for the concentration of whey to produce whey protein concentrate. A further aim of the thesis was to determine the impact of ultrasound if applied upstream of the UF unit to reduce membrane fouling and increase productivity. In addition, the combination of heat and US pre treatment is investigated as it is a promising approach to produce heat stable powders while alleviating membrane fouling. The use of sonication on 5 to 10 wt% WPC80 solutions had a small but significant effect on membrane fouling – for the 10 wt% solution, the cake growth factor fell from 0.66 to 0.44 × 10 11 m/kg and the steady state flux increased from 16.8 to 17.7 L/m2.h. Similar subtle effects were observed with fresh whey, with the cake growth factor falling from 3.7 to 3.0 × 10 11 m/kg. This may reflect the low solids concentration used in these experiments and the use of more concentrated protein solutions might lead to more positive results. Conversely, a pronounced effect was observed in the heat-treated feeds: with increasing solids concentration, both pore blockage and cake growth grew for all heat-treated feeds but these two parameters remained low for the pre-heated and sonicated feed. Sonication was also found to delay the ‘gelling’ of proteins as indicated by the higher gel concentration obtained in the pre heated and sonicated feed (27 wt%) relative to a solution exposed only to heat (21 wt%). However, 100% flux recoveries upon cleaning were not achievable in heat treated feeds and surface charge measurements indicated that protein deposit remained attached to the membrane surface. This may be due to the inability of the chemical cleaning agents to break down large, denatured protein aggregates formed during heating. microfiltration (MF) of skim milk on its selectivity and productivity was also investigated. In skim milk MF, the best selectivity was obtained at the lowest TMP of 55 kPa. A pre heated and sonicated feed provided the lowest whey protein and highest casein rejections, with values of 85.8 and 97.9 % respectively, and the greatest absolute flux of approximately 10 L/m2.h. However, the selectivity and flux obtained were considerably lower than that generally observed with the use of ceramic membranes.
Nanostructured nanoparticulate contrast agent for medical imaging

Tse, Nicholas Man Kei ( 2013)

Magnetic resonance imaging (MRI) is one of the most common and non-invasive medical diagnostics technique used in modern medicine. The contrast of the MRI image generated may be greatly improved with the use of contrast agents which are entities that facilitates the relaxation of nuclear magnetic resonance energy. Paramagnetic elements such as gadolinium have been traditionally employed to enhance the contrast of longitudinal (T1) weighted MRI images. The performance (relaxivity) of these gadolinium based contrast agents are governed by parameters which include the degree of hydration, the molecular tumbling rate and the localised gadolinium (and dopant) concentration. This thesis examined the postulate of improved MRI contrast ability by including the MRI active species, gadolinium, into a porous nanoparticulate matrix. The porous nanoparticles matrix were predominately mesoporous silicate based frameworks. To investigate this multivariate problem, high throughput combinatorial synthesis and characterisation techniques were employed. Using a robotic setup, a library of porous silicates incorporated with gadolinium were synthesised and subsequently structurally characterised using the small and wide angle X-ray scattering beamline at the Australian Synchrotron. The performance of the materials were subsequently characterised using a clinical MRI scanner at the Royal Melbourne Hospital. The gadolinium doped silicates were found to be better performing than the commercially available gadolinium based contrast agent. The synthetic and characterisation techniques were demonstrated to be applicable in examining the effect of co-dopants (aluminium, europium and terbium) has on the relaxivity. Using this approach, additional libraries of silicate nanoparticles with mixed dopant were synthesised and characterised for their MRI activities. The MRI performance was found to be significantly modified in the presence of the additive dopant. Materials with the additional lanthanides incorporated exhibited luminescence responses, enabling the MRI contrast agents to function as bimodal (MRI and luminescence) medical imaging probes. To further investigate the effect porosity has on the MRI activities of these nanoparticlular frameworks, a range of silicate samples with varying pore sizes and pore orderings were synthesised using a low-throughput methodology. The MRI performance was found to be dependent on pore size and pore ordering of the template silicate framework. The MRI performance was significantly dependent on both the gadolinium loading and the type of porous network for materials with pore-pore connectivity. This may be due to the increased hydration of the pore walls within the porous network. The dependency between the relaxivity and the porosity was not observed for a different type of porous framework. The MRI activity of analogous ordered porous framework generated from self-assembled amphiphiles were found to be independent of the ordering of the porosity. The dependency of MRI activity on the porosity of the host framework may be governed by the type porous framework and the mode of interaction between the paramagnetic species and the surrounding water protons.
Removal of thiocyanate and cyanide from gold mine tailings water using a polymer inclusion membrane

Cho, Youngsoo ( 2013)

Gold mine tailings water has been considered for recycling so that fresh water consumption can be reduced. However, the tailings water contains, along with a small amount of free cyanide, a high concentration of thiocyanate that can decrease the efficiency of the flotation of the sulfide minerals containing gold. Therefore, the possibility of using polymer inclusion membranes has been explored to remove thiocyanate and cyanide from tailings water. A polymer inclusion membrane containing 70% (m/m) poly(vinyl chloride) (PVC), 20% (m/m) Aliquat 336 and 10% (m/m) 1-tetradecanol was selected after a number of membrane screening experiments and found to successfully extract thiocyanate from a solution with pH in the range of 7-10 and the extracted thiocyanate in the membrane was efficiently back-extracted using 1 M NaNO3 solution. A mathematical model of thiocyanate extraction was developed and provided excellent agreement with the experimental data, thus allowing both the membrane extraction constant (18.9) and the diffusion coefficient (2.4x10-13 m2 s-1) of thiocyanate within the membrane to be successfully determined. The transport of thiocyanate from the feed to the receiving solution was investigated by varying the membrane thickness (46.1, 78.6, 108.5, 125.7 um) and the temperature (25, 35, 45, 65 °C) and the rate was found to increase with decrease the membrane thickness and with increase in the temperature. A laboratory scale pilot system has been designed to provide a large surface area (61.5 cm2) of flat sheet membrane in contact with both the feed (1000 mg L-1 SCN-) and receiving (1 M NaNO3) solutions. Thiocyanate was completely transported for over 135 days using a slow flow rate (0.028 mL min-1) and excellent stability of the flat sheet PIM used in the system was observed. The receiving solution was recirculated in the system to limit the consumption of the receiving solution and the removal of thiocyanate from the receiving solution was essential to maintain high transport efficiency. This was achieved by the approach of precipitation of thiocyanate as CuSCN. A study of cyanide extraction and oxidation in the membrane was also carried out to explore the possibility of using PIMs for cyanide clean-up of tailings water.
Protic ionic liquids as solvents for amphiphile self-assembly and the preparation of nano-structured inorganic materials

CHEN, ZHENGFEI ( 2013)

The aims of this PhD project are: 1) to investigate the amphiphile self-assembly in protic ionic liquids and establish the phase diagrams of these systems; 2) to utilise protic ionic liquids (PILs) to synthesize nanostructured metal oxide materials, including TiO2, SiO2. The first stage is to have a careful selection of the PILs available in the literature so that suitable PILs can be chosen for the synthesis of inorganic materials. Those PILs that promote amphiphiles will be particularly of interest to create structured materials. Two key issues need to be addressed during this stage. First, a new synthetic approach needs to be developed as the synthesis of inorganic materials in PILs has not been reported in the literature up to date. However, the approaches for producing inorganic materials in aprotic ionic liquids may be used as a reference approach. Second, it has already been reported that many PILs are capable of promoting self-assembly of amphiphiles and structures such as lamellar, hexagonal and cubic phases have been observed in PILs. However, whether or not these structures can be retained after introducing an inorganic network into the system needs be investigated. TiO2 and SiO2 materials will be synthesized from the selected surfactant-PIL systems and these materials will be characterized using various analytical techniques such as BET, SAXS, and TEM. On the conclusion of the project, a comprehensive understanding of the phase formation of surfactants in PILs has been established. Two ionic and two non-ionic amphiphiles (hexadecyltrimethyl ammonium chloride (CTAC), hexadecylpyridinium bromide, HDPB), polyoxyethylene (10) oleyl ether, Brij 97 and Pluronic block copolymer, P123) were studied in three selected PILs (ethylammonium nitrate, EAN, ethanolammonium nitrate, EOAN and diethanolammonium formate, DEOAF) with different structures. The phase behaviour of these amphiphiles has been explored in these PILs in comparison with water using the small angle X-ray scattering technique. More diverse phases could be formed by the amphiphiles in EOAN and DEOAF compared to those in EAN due to the structure change of the PIL. Micelles formed by amphiphiles in a protic ionic liquid, ethylammonium nitrate (EAN), and water were analysed using various models (spherical, core-shell and cylindrical). The amphiphiles used were cationic CTAC and HDPB, non-ionic Brij 97 and P123. Spherical micelles were preferentially formed at low amphiphile concentrations, and no structure factor for intermicellar interactions was required. The micelles formed by the two cationic amphiphiles were similar in EAN and water, though different models were used due to the ionic nature of EAN. However, for the two non-ionic amphiphiles, the micelles contain a shell of ethylene oxide groups (EO) which was significantly thicker in water than in EAN, though the core radii were similar for the two solvents. At high concentrations (above 10 wt%), there was a preference for cylindrical micelles for CTAC, HDPB and Brij 97, however, the P123 micelles still remained as spheres at such concentrations. The cosolvent effects (water and methanol) on the structures formed by P123 in EAN have been investigated and two ternary phase diagrams have been established. The addition of water did not have much effect on the phase behaviour of P123 in EAN as only slightly change of the lattice spacing of the phase was observed. However, the introduction of methanol into the system changed the phase behaviour significantly. There no phases were present above 20 wt% of methanol. Interestingly, a bicontinuous cubic phase was induced with a small amount of methanol in the system. Finally, mesoporous silica materials have been synthesised using a P123-EAN template. These silica materials have ordered mesopores with disordered micropores. The amount of inorganic network could greatly affect the final structure. A sufficient amount of inorganic silica network was required to retain the structure (hexagonal) of the template. However, the preformed structure in the template could be disrupted if the silica amount was too high. The fabrication of TiO2 materials has also been attempted by using the same template. However, ordered structures were not obtained due to the crystallisation of TiO2 during the calcination process. Thus, a potential application of these PIL/amphiphile systems is the synthesis of mesoporous inorganic materials, in particular for inorganic precursors with slow hydrolysis rates.

School of Chemistry - Theses

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