Publication Search Results

Now showing 1 - 9 of 9
  • (2022) Xie, Zhouzun
    The polydisperse solid-liquid system has been practised in many chemical engineering applications. A fundamental understanding of complex multi-phase flow with a wide particle size distribution (PSD) in the system is beneficial for process control and reactor optimisation, yet the currently existing numerical models, including conventional computational fluid dynamics - discrete element method (CFD-DEM), fail to capture the cross-scale inter-phase/particle interactions. Accordingly, multi-resolution models are developed in this thesis for the high-fidelity simulation of polydisperse solid-liquid systems. 1) A smoothed volume distribution model (SVDM) is first developed based on the unresolved CFD-DEM framework, with the capability of simulating the polydisperse solid-liquid system with a coarse-to-fine particle size ratio of up to 20. Via studying the migration of fine particles in suspension flow through a packed bed of coarse particles, the migration mechanism of fine particles is proposed and the inherent fundamental of clusters are elucidated. Via investigating the bed hydrodynamics in a bi-disperse solid-liquid fluidised bed (SLFB), the segregation and mixing mechanisms of particles in solid-liquid systems are illuminated. Via quantifying the solid transportation behaviours during the rapid filtration of dual-media filters, a probabilistic model is derived and verified for predicting clogging performance. This work establishes an effective framework to handle complex polydisperse solid-liquid systems. 2) Two acceleration methods (i.e., coarse-grained method and machine learning method) are studied, with the capability of simulating solid-liquid systems with improved computational efficiency at spatial and temporal scales, respectively. The coarse-grained method is employed to simulate large-scale particulate systems for unveiling the sedimentation mechanism of particles in water. The machine learning method is used to predict mixing and segregation behaviours in a solid-liquid system. This work provides an efficient method to predict granular flow behaviours in solid-liquid systems. 3) Further, a hybrid CFD-DEM model combining the resolved and unresolved CFD-DEM frameworks is originally developed, with the capability of simulating the polydisperse solid-liquid system with unlimited coarse-to-fine particle size ratios, for the first time. A resolved part obtains the fluid details around each coarse particle without extra models using fine grids (i.e., grid size to particle diameter ratio, lm/dp < 1/10), an unresolved part describes the fluid-fine particle interactions with empirical correlations using coarse grids (lm/dp > 3), and a semi-resolved part denotes the medium particle behaviours with a kernel-based approximation using medium grids (1/10 < lm/dp < 3). This work delivers a novel idea for modelling cross-scale solid-liquid flow and has the potential application to any polydisperse solid-liquid systems. This thesis represents collection of a suite of innovative numerical works of polydisperse particulate flows in solid-liquid systems and provides a range of numerical tools for understanding and optimising polydisperse solid-liquid flow systems.

  • (2022) Zulkifli, Muhammad Yazid Bin
    Zinc-azole-based metal organic frameworks (MOFs) have been demonstrated to exist in a wide variety of structural states, with applications in different fields such as gas separation. In this dissertation, we explore the phase control and dynamics of zinc-azolebased MOFs in crystalline, liquid, and glassy states. We first study ZIF-7 phase control using mechanochemical synthesis. Ammonium nitrate was found to be a good catalyst in mechanochemical ZIF formation, with the usage of DMF and H2O favouring ZIF-7-I and ZIF-7-III formation, respectively. New phases of ZIF-7 variations not accessible using the solvothermal method were also obtained mechanochemically indicating the possibility of a new mechanochemical synthesis route. The mechanochemical ZIF-7 mixed matrix membrane (MMM) demonstrates good CO2- based selectivity improvements. Next, we demonstrate the formation of a new meltable zinc-azole framework (ZnCP) with liquid crystal behaviour by the addition of orthophosphate. ZnCP was able to melt at a low temperature while retaining and orienting its crystallinity into transparent liquid, thus showing promising use in optical-based applications. This material can also be obtained using a top-down approach by adding phosphoric acid to ZIF-7. Controlling phosphoric acid incorporation results in different melted ZnCP particle ratios, which was explored as a gas separation membrane. We then explore the effect of silver (Ag) composite presence on the thermal dynamics of another zinc-azole framework (ZIF-62). The benzimidazole amount within the Ag-doped ZIF-62 structure affects its thermal conversion, forming either Ag-doped ZIF-zni or Agdoped ZIF glass. The thermal dynamics of Ag-doped structures were explored using both in-situ (thermal) and ex-situ techniques. Both Ag-doped phases were demonstrated to have good MMM separation improvements for CO2 and light hydrocarbon, indicating the accessibility of the silver composite. Lastly, a quick demonstration of new methods (dip and spin coating) to process ZIF-62 and ZIF-62 composite successfully forms continuous particle dispersion, allowing the formation of a continuous glass layer. Different compositions such as sandwiched structure and layer by layer were explored, with advantages outlined. The novelty of this dissertation lies within the exploration of new synthetic methods and thermal dynamics to form structurally diverse zinc-azole MOFs which will be beneficial in the understanding of phase transformations in MOFs

  • (2022) Wang, Shuangyue
    Two-dimensional transition metal dichalcogenide (TMD) nanocrystals (NCs) exhibit unique optical and electrocatalytic properties. However, the growth of uniform and high-quality NCs of monolayer TMD remains a challenge. Until now, most of them are synthesized via solution-based hydrothermal process or ultrasonic exfoliation method, in which the capping ligands introduced from organic solution often quench the optical and electrocatalytic properties of TMD NCs. Moreover, it is difficult to homogeneously disperse the solution-based TMD NCs on a substrate for device fabrication since the dispersed NCs can easily aggregate. Here, we put forward a novel CVD method to grow closely-spaced TMD NCs and explored the growth mechanism and attempts on the size control. Their applications acting as electrocatalysts and adhesion layer for Au film deposition have been also well displayed. Through the whole chapters of this thesis, the following aspects are highlighted: 1. MoS2 and other TMD nanocrystals have been grown on the c-plane sapphire. The surface oxygen vacancies determine the density of TMD nanocrystals. The MoS2 nanocrystals demonstrate excellent hydrogen evolution reaction and surface-enhanced Raman scattering performance owing to the abundant edges. 2. Deep insights into the growth of MoS2 nanograins have been explored. The surface step edges and lattice structures of the underlying sapphire substrates have a significant influence on the growth behaviors. The step edges could modulate the aggregation of MoS2 nanograins to form unidirectional triangular islands. The Raman spectra of MoS2 demonstrate a linear relationship with the crystal size of MoS2. 3. The orientation of sapphire substrate has an of importance effect on the critical size of MoS2 nanocrystals. The MoS2 nanocrystals have the smallest size on the r-plane sapphire, besides, the MoS2 on r-plane sapphire demonstrates the sintering-resistance feature, which is attributed to the edge-pinning effect when MoS2 edges are anchored on the sapphire surface. 4. The MoS2 nanocrystalline layer was utilized as the adhesion layer for Au film depositing on a sapphire substrate. The Au films on MoS2 displayed superior transmittance and electrical conductivity as well as outstanding thermal stability, which lay in the strong binding of Au film with MoS2 nanocrystalline layer.

  • (2022) ZHANG, Qianyi
    To improve the imaging specificity for accurate diagnosis, nanoparticle-based contrast agents have been developed for magnetic bioimaging modalities including magnetic resonance imaging (MRI) and magnetic particle imaging (MPI). MPI, providing positive contrast, low tissue background (high signal-to-noise ratio) and unlimited tissue penetration depth, has great promise to become clinical imaging tool. Constructing the nanoprobe tailored for MPI based on its inherent properties is critical to achieve its potential. Tumour-targeted delivery of imaging nanoprobes also provides a versatile approach for precision diagnosis of diseases. MRI, owing to its excellent soft tissue sensitivity, high spatial resolution, and lack of ionizing radiation, has been considered as one of the imaging modalities to explore the imaging specificity. Our group has previously developed a tumour microenvironment-sensitive MRI contrast agent that can be further improved by increasing tumour cell targeting and tumour tissue penetration. Surface engineering of nanoparticles offers a critical strategy to improve tumour-targeting capacities of nanoprobes. Improvements to the efficacy of targeted nanoprobes have been intensively explored and much of this work centres on developing reliable and efficient surface functionalization strategies. Herein, in this thesis, various nanoparticles and surface modification approaches have been developed to improve imaging specificity for precision imaging diagnosis. Developing novel and promising nanoprobes based on their inherent properties and different surface modification strategies highlighting on nanoparticle engineering and emerging coating techniques has been described and discussed in this work.

  • (2022) Salman, Saad
    One of the biggest challenges of implementing the future hydrogen (H2) economy is H2 storage with high density, compactness, and safety. Borohydrides have been extensively investigated as promising candidates for H2 storage; however, the high thermodynamic stability, sluggish H2 release kinetics, and limited H2 reversibility have hampered their practical use. Nanosizing is an attractive technique for improving the H2 release/uptake of borohydrides owing to the shorter H2 diffusion paths, new surface states, and/or high surface areas. The nanoconfinement of borohydrides in porous hosts (e.g. carbon, SiO2, and/or MOFs) has shown the possibility of improving their H2 release/uptake properties; however, this technique is impractical because of the hydroxyl/oxygen species, dead mass, and/or laborious synthetic procedures of the host materials. Alternatively, scalable synthesis of size and shape-controlled borohydrides as freestanding core-shell structures has surfaced as an appealing approach to enable H2 release/uptake at low temperatures. Through this technique, it is hypothesised that the shell would limit the loss of active species (e.g. boron), recrystallisation, side-reactions, and facilitate the H2 release/uptake from the borohydride core. However, the widespread implementation of this technique remains limited because of the lack of effective methods for controlling the borohydride nanoarchitectures. This work aims to synthesise controlled borohydride nanoarchitectures and explain their structure-H2 release/uptake relationships. Specifically, this work aims to (i) understand the paths to synthesise various NaBH4 nanoarchitectures (e.g. spheres, cubes, or bars) and potential nanostructure/H2 property interdependencies, (ii) rationalise the fabrication of core-shell NaBH4@Ni using wet-chemistry approaches to confine NaBH4 for reversible H2 storage, (iii) improve the H2 release of structurally controlled NaBH4 using catalysts in the core-shell framework, (iv) rationalise the fabrication of core-shell NaBH4@Ni nanoarchitectures using solvent-free approaches and their H2 release/uptake properties, and (v) understand the effect of the core-shell structure to mitigate the B2H6 release from NaZn(BH4)3. This work shows the effectiveness of wet-chemistry and solvent-free methods for designing core-shell borohydrides with improved H2 release/uptake properties. These methods will serve as a guide for designing practical storage materials with H2 release/uptake close to ambient conditions.

  • (2022) Hadinata Lie, William
    Electrochemical upgrading of biomass compounds to value-added platform chemicals is a sustainable route towards reducing reliance on fossil fuels and greenhouse gas emissions. When powered by renewable electricity, the electrochemical upgrading of biomass can be used to generate green hydrogen cost-efficiently. 5-Hydroxymethyl furfural (HMF), derived from acid-catalysed dehydration of sugars, is a representative biomass compound capable of yielding several useful platform chemicals. 2,5-Furandicarboxylic acid (FDCA) generated from the alkaline electrooxidation of HMF (HMFOR) has been studied extensively as a renewable building block that can substitute petroleum for making monomers, medicine, agrochemicals, and specialty chemicals. For these reasons, there have been considerable efforts in researching active electrocatalyst materials for HMFOR. This thesis focuses on application of Prussian blue analogues (PBAs) as an HMFOR electrocatalyst material. PBAs are a class of porous coordination polymers with branching applications in bio-sensing, gas adsorption, energy storage, and electrocatalysis. These materials are ideal electrocatalyst materials due to their easy synthesis, tuneable structure, large concentration of metal sites, and porous structure which allows for the easy diffusion of electrolyte species. In alkaline solutions, they transform into oxide/hydroxide structures with superior electrocatalytic activity to their conventional counterparts due to the presence of defects. Despite these advantages, the catalytic performance of PBA-derived electrocatalysts is still limited by their relatively poor conductivity. This limitation is largely due to the conventional wet precipitation methods used to synthesise PBAs, which limit the amount of active site exposure and interfacial adhesion with the anode current collector. Utilising binder-free synthesis methods like electrodeposition can potentially overcome these limitations and maximise the electrochemical activity of these materials.

  • (2022) Luo, Jeff
    Nitric oxide (NO) plays pivotal roles in various physiological systems and has immense therapeutic potential. NO, however, has a short half-life (<5 s) and a short diffusion distance of ~160 μm in vivo, and its physiological functions are highly dependent on its concentrations. Current NO delivery strategies can be generally categorized into non-catalytic and catalytic (enzymatic) approaches. For the former, the longevity of the NO delivery systems principally relies on the finite NO donor reservoir, while the latter is limited by the low stability of natural enzymes. Another important challenge in NO delivery is the difficulty in accurately detecting circulating NO reservoir in blood. To address these challenges, this thesis focuses on the design, synthesis, and applications of nano-biomaterials to enable sustained NO delivery and accurate detection of endogenous circulating NO reservoir. This thesis revealed ceria nanoparticles as a new class of nanomaterials with the unique ability to catalyze NO generation from NO donors. The therapeutic activity of ceria-induced NO was demonstrated to inhibit cancer cell proliferation. This unique NO-generating feature stood in contrast to the well-established understanding of ceria to scavenge NO. This study provided deeper insights into the bio-functions of ceria nanoparticles and broadened their biomedical applications. Then this thesis reported the first catalytic polymers that generate NO, in particular amine-containing polymers, e.g., polyethyleneimine (PEI). These polymers can be easily integrated into a suite of biomaterials (e.g. hydrogels) to equip them with NO delivery capability. The therapeutic application of polymer-induced NO was demonstrated to prevent the formation of Pseudomonas aeruginosa biofilm. Finally, the thesis tackled the demand for rapid and accurate detection of human serum albumin (HSA, the most abundant circulating NO reservoir in blood) by developing a fluorescent paper-based sensor. This sensing platform allowed sensitive (detection limit of 0.91 g/L) and rapid (20 minutes) point-of-care detection of HSA and HSA-related disease diagnosis by visible color change, and could be extended to the detection of a spectrum of biomarkers. Collectively, these findings open new routes to produce next generation nano-biomaterials for the diverse biomedical applications of NO such as anticancer, antibacterial, and sensing applications.

  • (2022) Oudone, Phetdala
    Dissolved organic carbon is stored and processed in groundwater in three ways. It is stored on minerals by adsorption, it is biologically processed through biodegradation, and it also undergoes a process to return to groundwater called desorption. This biophysiochemical research shows that the groundwater system is therefore a vital part of the global carbon cycle and carbon sink. This research fills a gap in the existing understanding of how to calculate the global carbon budget, as does not yet include the dissolved organic carbon that is stored in groundwater. This thesis exclusively explores processes determining dissolved organic carbon character and concentration in groundwater in different geological environments. This is new, useful knowledge to describe the biophysiochemical process. This research did not examine human interference in adding carbon to groundwater. This research found how dissolved organic carbon is stored and processed in groundwater due to biodegradation and desorption, and how it is adsorbed onto sediment surface. This research explored the characteristics and concentration of Dissolved organic carbon in groundwater by using Liquid Chromatography-Organic Carbon Detection, and other techniques, to examine dissolved organic carbon in terms of its fractions: humic substances, hydrophobic organic carbon, biopolymers, building blocks (BB), low molecular weight neutrals and low molecular weight acids. There were several key findings. First, the results showed that both semi-arid inland low sedimentary organic carbon environments – i.e., Maules Creek and Wellington – were a carbon source; while the high rainfall temperate coastal peatland environment of Anna Bay was a carbon sink. Secondly, another key finding was that dissolved organic carbon was not processed as a whole chemical compound, but it was processed by its fractions where each fraction was processed distinctly. For example, humic substances were only adsorbed/desorbed in groundwater; while low molecular weight neutrals were only consumed by microbes in the biodegradation process in groundwater.

  • (2022) Huang, Feng
    Structural composite supercapacitors have been investigated as a promising weight-saving technology for electrical vehicles (EV), electric aircraft, and mobile robots. The main objective is to maintain excellent (ideally the same as the existing structure of the same weight) mechanical properties while storing adequate electrical energy. This thesis aims to develop structural composite supercapacitors with both outstanding mechanical properties and electrical energy storage performance. The main findings and contributions of my research presented in this thesis are: (1) A novel structural electrolyte made of carbon nanofibers, epoxy, and ionic liquid (IL) that offers ionic conduction properties as well as mechanical stiffness and rigidity. The incorporation of carbon nanofibres (CNFs) into epoxy-ionic liquid-based electrolytes creates pathways for ion migration, resulting in a 40-fold boost in the ionic conductivity for the resulting electrolytes. The tensile strength and Young’s modulus of the resulting electrolytes exhibit only a slight drop. Therefore, the new solid epoxy-based electrolyte offers great potential for use in energy storage structures, for example structural composite supercapacitors and/or batteries; (2) A structural composite supercapacitor consisting of the high-performance electrodes made by grafting manganese dioxide onto carbon fibre fabrics and the epoxy-ionic liquid electrolyte. Mixing 40 wt.% of IL and 60 wt.% of epoxy (denoted as the 40IL electrolyte) yields the best combination of ionic conductivity and tensile properties. A structural composite supercapacitor has been fabricated using a 40IL electrolyte with high-capacity manganese dioxide coated carbon fibre electrodes. The resulting composite supercapacitors demonstrate excellent mechanical and electrochemical performance compared to the literature data. (3) A novel silane treatment method to enhance the ionic conduction between the electrolyte and the electrodes. The results show that the silane treatment enables the composite supercapacitors to achieve a 3-fold increase in areal capacitance without deterioration of the mechanical properties. Finally, potential opportunities for future studies of the structural composite supercapacitors are discussed.