Engineering

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Now showing 1 - 10 of 26
  • (2021) Liu, Huabo
    Thesis
    Due to the large variety and unique physiochemical properties, such as high electrical conductivity, adjustable interlayer spacing, intercalation chemistry and so on, two-dimensional (2D) materials have attracted tremendous attention for their suitability in the development of high-performing supercapacitors. Despite that great progress has been made, there is still no single 2D material that can perfectly meet all the requirements to replace the existing material, mainly activated carbon, used in commercial supercapacitors. Therefore, continuing efforts for exploring novel, high-performing 2D materials with low cost are desirable. In this dissertation, the prior studies on the development of 2D materials ranging from layered inorganic materials to organic-inorganic hybrids for supercapacitors are first reviewed. As an emerging type of 2D material, layered organic-inorganic hybrids start to show promising results to be used to fabricate high-density, nonporous, and thick electrodes for compact capacitive energy storage. However, the studies in this area are still lacking. Thus, the goal here is to explore the opportunities of 2D organic-inorganic hybrids for applications in supercapacitors. The relevant techniques and methods used throughout the study are then outlined. Next, three research chapters supporting the main findings of the investigation are included. The first research chapter describes a facile mechanical strategy to improve the kinetics and rate performance of 2D organic-inorganic hybrid electrodes at ultrahigh mass loadings (up to 30 mg cm-2). The second research chapter reports the synthesis of a new layered organic-inorganic hybrid material with excellent volumetric and areal capacitances even at mass loadings reaching 50 mg cm-2, highlighting the good electrode kinetics. The third research chapter presents the wafer-scale electrochemical deposition synthesis of 2D organic-inorganic composite films with controlled size and thickness, which are promising for the development of flexible and transparent electrochemical energy storage devices. Finally, conclusions and recommendations are given at the end of this dissertation.

  • (2021) Li, Zhiwei
    Thesis
    Cataracts are responsible for almost half of worldwide blindness, making it one of the biggest health challenges in this era. Cataracts are irreversible because of their pathology, which is controlled by the aging and biochemical change of eye tissues. As a result cataract surgery is currently the only effective treatment. The general procedure of cataract surgery includes separation and removal of the failed lens tissue from the surrounding soft tissue in the eye, followed by artificial lens implantation. Lens removal requires successful separation of lens tissues as a critical step that determines surgical success. However key parts of cataract separation affected by fluid mechanics and rheology are uncharacterised. This project aims to explain the behaviors of such separation phenomena and connect fundamentals with possible explanations and enhancements. A multi-layer bio-polymer injection model is developed to mimic the separation process in cataract surgeries. The separation can be considered peeling of a soft elastic tissue by a pressure-driven fluid flow, whose performance is closely related to properties such as flow rate and velocity as well as fluid viscosity, normal stress and yield stress. In our project, the separation physics is studied as a hydraulic fracture problem. Theories are proposed to discuss the effectiveness and safety of hydraulic fracture with different flow and fluid parameters. It is found both higher flow rate and viscosity will cause tissue to be deformed more, which may increase the risks of tissue damage. Yield stress fluids with significant elasticity are not suitable as in most cases they rupture the tissue. Normal stress fluids have the potential to provide safe and effective separation. It is found that with a small scale separation, however, the separation effectiveness is mainly affected by the flow rate, and the fluid properties play a more minor role. General ideas and potential improvements according to our results and theories are also proposed for cataract surgeries, which we hope will contribute to easier and safer separation.

  • (2021) Ismail, Nor Akma
    Thesis
    Rice bran is a major, underutilised by-product of the rice industry and the high proportion (~90%) of insoluble fibre is the main reason limiting its applications in foods. This thesis is aimed at modifying the physicochemical properties of rice bran by physical (ultrasound and steam explosion) and enzymatic treatments, thereby improving its technological and health properties. Purified (starch and protein removed) and un-purified defatted rice brans were treated by ultrasound and steam explosion under different intensities (amplitude, time, steam pressure), followed by enzymatic hydrolysis using ShearzymePlus. Changes in physicochemical properties of the bran were determined. The physical treatments strongly impacted on the physicochemical properties, which were affected by both treatment intensity and bran purity. For purified bran, increasing treatment intensity generally led to decreases in particle size and bulk density, and increases in porosity, swelling, water and oil binding capacities, as well as the increased yield of soluble fibre. The greatest changes in these properties were generally achieved with ultrasound treatment at 60% amplitude for 20 min, where the highest yield of soluble fibre (35.2g/100g) was obtained. For un-purified rice bran, the presence of starch and proteins complicated the efficacy of the treatments. The steam explosion was found to be less effective than ultrasound in modifying the physicochemical properties of rice bran. Soluble fibre produced from both physical treatments mainly contained oligosaccharides with MW <25kDa, which showed good prebiotic potentials in promoting the growth of L. acidophilus and B. Bifidum with the highest MW fraction (~17kDa) being the most effective. Shearzyme Plus hydrolysed the insoluble fibre into the soluble fibre; however, the hydrolysis was more effective on untreated than physically treated bran. Incorporation of ultrasound and enzymatically treated rice bran to flour (15%) caused minimum deterioration in bread volume, texture and colour compared to untreated bran. The enrichment significantly improved the glucose adsorption capacity and glucose dialysis retardation, reduced glucose diffusion and glycaemic index (GI), and greatly increased the sodium cholate binding capacity of the bread. Overall, this thesis demonstrated that ultrasound and enzymatic treatment is a feasible method to modify rice bran with significantly enhanced technological and health functional properties.

  • (2021) Guo, Ziyi
    Thesis
    Artificial micro/nanomotors (MNMs), inspired by mobile biomolecular entities, have demonstrated great potential as miniaturized robots performing diverse tasks from environmental remediation to biological treatment owing to their great mobility and versatility. The reported MNMs can be propelled using various power sources, including magnetic field, electric field, ultrasound, light, and chemical reaction. MNMs that operate on chemical reactions are usually equipped with higher velocity due to the superior energy conversion efficiency, which dominantly present as bubble propelled systems. However, the majority of the bubble propelled MNMs utilize bubble ejection and detachment force, which result in swarming and linear motion for Janus and tubular motors, respectively. It is still challenging for chemical propelled MNMs to have absolute control in direction without external field. A crafty design to circumvent this limitation is to develop biocatalytic MNMs with bubble buoyancy propulsion. This thesis focuses on the design, fabrication, and applications of submarine-like buoyancy-propelled MNMs that move in the vertical direction. I fabricated buoyancy propelled nanomotors with one-pot synthesis and provided the first work characterizing detailed motion behavior with electrochemistry. With coupled biocatalytic cascade reaction converting glucose as the fuel to oxygen bubbles, the nanomotor was propelled by buoyancy, which dominated the initiative collision at the electrode surface. Four representative electrical impact signals were observed and corresponded to four types of motion patterns. The corresponding relationship was confirmed with a numerical simulation. The integration of MNMs and electrochemistry provided a new dimension to characterize and understand the complex dynamics of the self-propelled nanoparticles. I further investigated the buoyancy propelled MNMs in biomedical applications. The pH-sensitive polymer incorporated micromotor exhibited regulated vertical motion via hydrophilic/hydrophobic phase shifting in different pH environments, and the system was proved to be applicable for anti-cancer drug delivery in a proof-of-concept three-dimensional cell culture. The proposed micromotor opens up new avenues in autonomous robotic fabrication for in vivo drug delivery in complex media. I also investigated the buoyancy propelled MNMs in water remediation. The buoyancy propelled nanomotor exhibited reversible vertical motion in low concentrations of H2O2, which induced the convection of the micro-environment and increased the pollutants to get in contact with the absorbents. The proposed nanomotor showed efficient removal of both inorganic heavy metal ions and organic per- and poly-fluoroalkyl substances (PFAS) in complex environments. At last, the buoyancy propelled MNMs were studied for the vertically spatial separation of targeted cancer cells in mixed samples. With the aid of antibody surface modification, the buoyancy-propelled nanomotors can autonomously attach to the targeted cells and endow the cancer cells with vertical motion. With a customized glass tube, the floated cells can be easily separated. The proposed nanomotor exhibited great isolating efficiency with facile operations, which broadened the development of cell separation methods towards biocompatible nanostructures. The findings presented in this thesis open up new avenues for the development of buoyancy propelled MNMs in diverse applications.

  • (2021) Ullah, Sana
    Thesis
    In recent years, there has been an increased interest in utilising light and heat from the sun to produce solar fuels. Photo-assisted conversion of CO2 to CH4 is an effective and straightforward approach to produce solar fuels. The role of light, coupled with heat, for the methanation of carbon dioxide was investigated using different transition metal catalysts. The synergistic effect of heat and light was probed for the methanation of CO2 using Co, Cu and Ni supported on CeO2 and Al2O3. The role of light was explored using different wavelengths and intensities. Illuminating Co/CeO2 and Ni/CeO2 catalysts with blue light (450-460 nm) improved catalytic activity and selectivity. This improvement was attributed to the direct photoactivation of reaction intermediates on the catalyst surface by photogenerated hot electrons and the presence of intrinsic oxygen vacancies on CeO2. The absence of considerable light enhancement for Co/Al2O3 validated the importance of surface oxygen vacancies in accessing light enhancement. Based on the findings from the Co-based catalysis study, a detailed understanding of the reaction system was then developed by probing the role of surface basicity under light for CO2 methanation. The modification of commercial TiO2 with different loadings of La was investigated for a Co/La-TiO2-based catalyst. It was shown that homogeneously dispersing lanthanum on the surface of the TiO2 support boosted the catalytic performance of Co deposits under both non-illuminated (dark) and illuminated conditions. It was revealed that La promotion increased the surface basicity which facilitated CO2 adsorption and activation and allowed access to light enhancement. Subsequently, to gain further insights into the support properties which enable light enhancement during CO2 methanation, a Co/Al2O3 catalyst was modified with La and Pd via a double flame spray pyrolysis synthesis approach. La addition to the Al2O3 support played a crucial role, introducing actives site for CO2 adsorption and its potential transformation into an intermediate product which is more responsive under visible light illumination. In accompaniment to its plasmonic behavior, Pd metal addition to the Co/La-Al2O3 system facilitated H2 activation and provided further enhancement to the activity and CH4 yield. Overall, the research has demonstrated that through the rational design of transition metals loaded on a suitably active support the benefits of visible light illumination can be harnessed and can reduce the activation energy for thermal catalytic reactions.

  • (2020) Lian, Boyue
    Thesis
    This thesis used experimental observations, coupled with numerical techniques, to provide new insights on the inter-relationship between environmental conditions, interlayer (d-) spacing and water transport through Graphene Oxide (GO) laminates. In situ X-ray diffraction measurements during the drying of hydrated GO laminates captured the coexistence of two d-spacings at 1.16 nm and 0.87 nm, indicating that environmental conditions can affect the phase of water in GO. Molecular dynamic (MD) simulations showed diffusion and pore flow transport behaviours of water at these two GO d-spacings respectively. The slip length obtained from the velocity profile of the water pore flow in GO was found to range from 0.44 nm to 79 nm and was highly dependent on the distribution of hydroxyl functional groups on the pristine carbon. During the filtration of a 5 g L-1 NaCl solution, a non-incremental change in rejection from 5% to 99% was observed at feed temperatures between 30 degree C and 34 degree C indicating a mechanistic change of water transport from pore flow to diffusion. By modifying GO with alkylamines with different carbon chain lengths, the precise GO d-spacing at which the water phase change occurred was narrowed down to between 1.06nm to 1.16nm. Modifications of the Hagen-Poiseuille equation to include a slip length of approximately 60 to 70 nm, determined by molecular dynamic simulation, coupled with an estimate for laminate tortuosity of 11.3, determined by fitting Knudsen equation to experimental observation, enables a good agreement between theory and experiment. These studies distinguished the different water transport mechanisms for GO at varying environmental conditions and examined the viability of conventional transport theories, which can guide future theory development. Applying this knowledge, GO laminates were tested in a desiccation application and showed high water adsorption capacity of 0.58 g g-1 with a low regeneration temperature of 40 degree C and a water adsorption rate five times higher than silica gel. In a novel solar-driven pervaporation process, utilising the solar adsorption capacity and the fast pervaporation water transport rate, GO laminates produced 6.45 kg m-2 day-1 of distilled water from a 35 g L-1 NaCl solution at a Gain Output Ratio of 0.63, which are both higher than a conventional solar still system..

  • (2021) Liu, Yiran
    Thesis
    The implementation of innovative fuels is considered as an imperative and essential countermeasure for sustainable ironmaking. Biomass and hydrogen are regarded as promising renewable fuels to mitigate CO2 emission, and low-rank coal is regarded as flexible fuel to maintain the supply chain. Pulverised coal injection (PCI) technology has the readiness to accommodate these innovative fuels in ironmaking blast furnaces (BFs). However, the in-furnace phenomena of innovative fuels injection are not clear yet. In this thesis, several computational fluid dynamics (CFD) models are developed and applied to simulate the combustion of innovative fuels under real BF conditions. Firstly, a 3D CFD model is developed to simulate the flow and thermochemical behaviours of the pulverised biomass injection (PBI), and applied to pilot-scale and then industrial-scale simulations. The model features hollow cylindrical biomass particles and modified sub-models of biomass chemical reactions. It was validated against coal combustion in a commercial BF and biomass combustion in a pilot-scale PCI test rig. The key phenomena of the selected PBI were found to be comparable with two typical PCI coals. The model is finally used to investigate the influence of key PCI operation variables and biomass pretreatment schemes. Secondly, a 3D industrial-scale CFD model is developed to study the feasibility of semicoke (upgraded low-rank coal), in collaboration with lab-experiments and plant-tests. The simulation results show that, by optimisation, similar combustion profiles of semicoke with coal can be achieved. Also, the effect of the blending ratio is studied. The plant test with a blending ratio of 0–20% indicates that ironmaking indices remain stable, confirming the practical feasibility of semicoke co-injection operation. Finally, a 3D industrial-scale CFD model is developed for the co-injection of H2-PCI. The H2-PCI model features chemical reactions of hydrogen/H2O and H2-coal interactions. The model was validated based on coal injection in a commercial BF and co-injection in a pilot-scale test rig. Several injection schemes of H2-PCI were designed based on the constant bosh gas volume. The typical in-furnace phenomena and effects of blending ratios on combustion performance were investigated. The CFD models developed provides a cost-effective tool for understanding the combustion behaviour of innovative fuels and operation optimisation for sustainable ironmaking.

  • (2021) Chua, Stephanie
    Thesis
    Improvements in liquid lithium-ion battery electrolytes using of metal organic frameworks (MOFs) as a functional decoration on polymer membrane separators were investigated using a combination of experimental and theoretical methods. Zirconium-based MOF UiO-66 was introduced to the polymer support using the mixed matrix membrane (MMM) method. The method allowed the one-step manufacture of a robust, mechanically pliable polymer-MOF membrane composite of high MOF loading. MOF-MMMs imparted improved electrochemical behaviours such as a widened potential operating window, near-unity transference number, and increased presence of solid electrolyte interphase (SEI) components crucial to battery performance. Density functional theory (DFT) calculations were also performed to provide insights regarding electrolyte solvation in the presence of MOF. A simple dip-coating technique was utilised to modify the surface of the MOF-MMMs with polydopamine (PDA) for further improvement of the electrochemical properties. Increased transference numbers, as well as stability during rate cycling, were observed with the resulting PDA-MMM owing to the improved electrode/electrolyte interface. However, surface analyses using x-ray photoelectron spectroscopy (XPS) showed that there are reduced amounts vital SEI components compared to the original MOF-MMM support. The last section further explores the versatility of UiO-66 and tackled the preparation of gel polymer electrolytes (GPEs) decorated with UiO-66 via phase inversion technique. Using the phase inversion method, the fabricated GPE contained pores from both polymer substrate and the intrinsic pores of the 3D nanomaterial for improvement of electrochemical properties. It was demonstrated in this work that the MOF GPE is equally inert and suitable in ether or carbonate-based electrolytes. Overall, this study demonstrated the versatility of UiO-66 metal organic frameworks for use as a functional nanofiller for electrolyte membranes. With the use of inexpensive membrane fabrication methods, the composites obtained are viable for lithium-metal battery applications. Similarly, insights drawn can provide a springboard towards future study of MOF-based electrolytes.

  • (2022) Arbita, Ariestya Arlene
    Thesis
    The production of cheese involves milk coagulation as an essential step. Current milk coagulants still have various drawbacks and the search for alternatives is necessary. Marine macroalgae (seaweed) are a potential source of milk clotting enzymes that have not been well explored. This thesis investigates the extraction, characterisation and application of milk-clotting enzymes from seaweed for cheese making. Among seven species of algae studied, Gracilaria edulis was found to contain proteases with significant caseinolytic and milk-clotting activities. Optimum conditions for extracting and purifying the proteases were then determined. The proteases demonstrated optimum caseinolytic activity at 60°C and a pH range of 6–8 and were identified as serine and metalloprotease with MW of 44 and 108 kDa. The enzymes cleaved κ-casein at four main sites, one of which being the same as that of calf rennet. Amino acids sequencing showed greater than 80% matching with those from members of the bacteria kingdom, indicating that the proteases could be a novel enzyme or existing zymogen. The algal extracts were used successfully as the coagulant in making Cheddar and Feta style cheese, at a different coagulation temperature (50°C) than the usual temperature for calf rennet (37°C). The algal protease gave a higher cheese yield and moisture content but lower total solids compared to calf rennet. After aging for 6 months, proteins of the Cheddar style cheese made with algal protease were mostly digested, and the peptide profiles showed a large number of small peaks, demonstrating stronger proteolysis of the algal protease compared with calf rennet. The colour of algal cheese was lighter and less yellow, and the microstructure was similar to calf rennet cheese. Most of the textural properties of the algal cheese differed significantly (P<0.05) from the calf rennet cheese, but the hardness of both cheeses was similar (P>0.05). Sensory analysis showed that the fresh Feta algal cheese was less acidic than calf rennet cheese (P<0.05), but the two cheeses had similar texture, bitterness, and overall liking scores (P>0.05). Aged Cheddar algal cheese had similar score of texture, overall flavour, acidity (P>0.05) but higher bitterness, and lower overall liking score than aged Cheddar calf rennet cheese (P<0.05). This thesis demonstrates that the proteases from Gracilaria edulis have the potential for application in making fresh cheeses but not cheeses that require aging.

  • (2022) Xie, Zhouzun
    Thesis
    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.