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(2019)ThesisDue to the severe environment pollution and critical energy issues around the world, fossil fuel is being replaced by new energy sources, e.g. solar power, wind power, etc. To enhance the efficiency of those new energies, electrochemical energy systems (EESs), including lithium-ion battery (LIB), supercapacitor (SC) and lithium-ion capacitor (LIC) are widely used in our daily life. Combining the advantages of LIB and SC, LIC seems to be the most competitive candidate for the next generation EESs. The similarities and differences between three of them are discussed in chapter 1. Also, evaluation methods, device design principles, together with configurations are summarized. By reviewing the development status of LIC, it’s worth to pointing out that pre-lithiation step is necessary in almost all the device design. Moreover, to further enhance the energy density of the device, there is also the call for new cathode material with wide operational voltage and large capacity. Lastly, symmetric LIC design is not popular because the lack of suitable active materials. Aiming to build up a high performance symmetric LIC, 2-dimensional tungstate acid-link polyaniline (TALP), which has a wide working potential range from 0.01V to 4.5V versus Li/ Li+, is used as active material in this thesis. Solvent exchange effect in TALP is observed and confirmed. Water, NMP and electrolyte could diffuse in the interlayer to form the nanoconfined fluid and replace the former existed solution. Plus, as spotted by XPS, not just Li+, but also PF6- is able to intercalate/ de-intercalate into/ from TALP interlayer, thanks to the large interlayer spacing, resulting in a high areal capacity of 39 mAh cm-3 under a large current of 2000 mA g-1. As anode, getting use of the solvent exchange effect and layered structure, interlayer SEI is formed for pre-lithiaiton. The modified sample (5FEC-SEI-TALP) exhibits 4 times higher initial columbic efficiency than the fresh sample. Later, symmetric LIC is produced with TALP as cathode and 5FEC-SEI TALP as anode, which demonstrates a high energy density of 102.63 Wh kg-1 under a power density of 224.5 W kg-1, which is superior to the AC-based symmetric LIC.
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(2019)ThesisRadio frequency electric field treatment (RFEF) is a non-thermal method of food preservation that utilizes high intensity oscillating electric field to inactivate bacteria. Past studies reported that RFEF operated at lower frequencies resulted in a higher inactivation rate of bacteria. However, the electrode may corrode at lower frequencies, especially at frequencies lower than 20 kHz, which could potentially degrade the quality of the processed liquid food. This research studied on the electrode corrosion occurred during the high intensity RFEF operated under 20 kHz, also called the audio frequency electric field treatment (AFEF), and it proposed a novel method to reduce the corrosion rate of electrodes. Inspired by the electrical double layer (EDL) and its equivalent electrical circuit, applying a high permittivity coating on the surface of electrodes was proposed to reduce the corrosion rate. Three coatings composed of titanium dioxide, barium titanate, and CCTO, having low, moderate, and high permittivities, respectively, were selected as the coatings applied on the surface of electrodes to explore how the permittivity of the coatings affect the corrosion rate. Mathematical modeling and experiments were conducted to test whether the three coatings could mitigate the electrode corrosion. In mathematical modeling, an equivalent electrical circuit of the coating-solution system was employed to calculate the phase angle and voltage drop across the three coatings and the solution (saline water). After that, the experiment of the electrode corrosion, with/without applying the three coatings on electrodes during the high intensity AFEF treatment, was conducted. Furthermore, the electrical impedance, atomic and molecular structures, surface morphology, and elemental analysis of the three coatings were conducted. Finally, the concentration of the metallic ions in the AFEF-processed saline water was measured. In conclusion, the corrosion rate generally increased with the increase of the electric field strength and the conductivity and the reduction in frequency, respectively. The CCTO coating performed the best on the reduction of the electrode corrosion among the three proactive coatings, while the titanium dioxide coating marginally reduced the electrode corrosion. However, calcium ions were detected in the processed saline water when the CCTO coating was applied, although the concentration was deficient. As a novel study in this area, this research contributes to the effective mitigation of electrode corrosion, during the electric field treatment, thereby increasing the Industrial applicability of the electric field treatments.
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(2014)ThesisMethane emitted by coal mine ventilation air (MVA) is a significant greenhouse gas. A mitigation strategy is the oxidation of methane to carbon dioxide, which is approximately twenty-one times less effective at global warming than methane on a mass-basis. The low non-combustible methane concentrations at high MVA flow rates call for a catalytic strategy of oxidation. A biofiltration technology was proposed as a promising solution to reduce/eliminate methane emissions from coal MVA. Unlike conventional CH4 removal technology, biofiltration is relatively cheap to build and operate as it works at ambient temperature and pressure. The challenge in developing biofilter system for MVA remains as high gas flow rate (> 50 m3 s-1) coupled with low methane concentrations (⠤ 1% (v/v) in air) require an improved biofilter performance to be applied for MVA applications. Several steps have been taken in this project including identification and isolation of methanotrophs (methane-oxidising microorganisms) from coal mine site which might be able to adapt better to MVA environments, investigation to seek optimum methane oxidation activity and microbial growth using pure culture of Methylosinus sporium (M. sporium) by batch experiments, and a lab-scale biofiltration study using inoculated (with M. sporium) and non-inoculated coal as packing material in a simulated MVA conditions. A laboratory-scale coal-packed biofilter was designed and partially removed methane from humidified air at flow rates between 0.2 and 2.4 L min-1. From the biofilter operation, the most abundant member of methane-oxidising microorganisms had been identified by 16S rRNA gene sequence as belonging to the methanotrophic genus Methylocystis. The greatest level of methane removal of 27.2 ± 0.66 gmethane m-3 empty bed h-1 was attained for the non-inoculated system, which was equivalent to removing 19.7 ± 2.9 % methane from an inlet concentration of 1% (v/v) at an inlet gas flow rate of 1.6 L min-1(2.4 min empty bed residence time). These results show that low-cost coal packing biofilter holds promising potential as a methane removal technology in MVA.
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(2017)ThesisA new concept based on the use of magnetic iron sand for harvesting and extracting the cellular content of microalgae was investigated herein. By employing iron sand, a natural occurring magnetic material, as a filter media in sand filtration and as a heat in AC Magnetic induction heating, previously separate algal harvesting and processing step can potential be carried within the same unit operation, resulting in significant saving in energy and labour cost. Elucidation of the algal capture mechanisms and the heat generating properties of iron sand, as well as the cell content extraction mechanism was required as a proof of concept. A series of advanced characterisation techniques, including Small Angle Light Scattering, Inductively Coupled Plasma Mass Spectrometry, X-Ray Diffraction, Laser Doppler Micro-Electrophoresis and Vibrating Sample Magnetometery was used to characterise the physical and chemical properties of iron sand. The performance of iron sand as a thermal source in magnetic induction heating was shown to be dependent on the magnetic properties of iron sand, which in turn was dependent on the particle size, composition and magnetic domain characteristics. When iron sand was used as a filter media, harvesting efficiencies between 48% and 82% can be achieved. Iron sand in the smaller size range (<150 μm) produced a higher separation effectiveness, but the retention time was high (approximately 275 s over 10 bed volume). The high separation effectiveness and high retention time were due to the cake deposition being the main capture mechanism. Iron sand in the larger size range of 150 μm to 180 μm was able to reduce the retention time remarkably, albeit at a much lower separation effectiveness of 54% over 10 bed volume; this was due to straining filtration being the main capture mechanism. Chromatographic and fluorescence techniques were then used to determine differences in the organic and lipid characteristic of the algal cell extract. It was found that when iron sand was used as a thermal source for the heat induced extraction of algal cell content, a high level of cell rupture and algal organic matter release were observed using flow cytometry when the algal cells were exposed to temperatures between 125 °C to 185 °C. However, high temperature was also shown to decompose cell component such as lipids, and the lipids detected per cell by magnetic induction heating decreased sharply from 155 °C to 185 °C. Whilst direct comparison (e.g. efficiency, recovery rate etc.) with existing algal harvesting and processing technique is not possible due to the bench scale nature of this study, these findings suggest the use of iron sand for a combined algal harvesting and processing process is viable and warrant further investigations.
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(2015)ThesisCashew nut (Anacardium occidentale L.) as a nutritious and popular snack is also a potent allergenic food which could elicit severe or even life-threatening allergic reactions in sensitive individuals. The only recommended management option is the strict avoidance of offending cashew nut, and to achieve this, reliable and accurate food labelling is essential. Cashew allergen Ana o 3 (2S albumin), due to its compact and stable structure, is more stable after thermal processing and is potentially a good biomarker for ELISA development. This study aims to develop a sensitive sandwich ELISA specific to Ana o 3, which is less influenced by food processing conditions or protein composition of cashew nut cultivars so to detect traces of cashew residues in pre-packed food products more reliably. Ana o 3 was purified from raw and roasted cashew nut kernels and used as an immunogen to raise polyclonal antibodies. Four sandwich ELISAs differing in their capture-detection antibody pairs were developed and compared for their performance. The CAS–ELISA–1 developed for crude protein presented a sensitivity of 0.58 mg protein kg-1 (57.1 ± 10.8 g L-1). The other three ELISAs, CAS–ELISA–2, Ano3–ELISA–1 and Ano3–ELISA–2, by using anti-Ana o 3 antibody to detect thermally stable cashew nut allergen, offered LODs of 0.04 mg protein kg-1 (4.1 ± 0.02 μg L-1), 0.06 mg protein kg-1 (0.6 ± 0.1 μg L-1) and 0.13 mg protein kg-1 (1.3 ± 0.4 μg L-1), respectively. The assay provided less variation in detecting cashew nut (protein) in different cultivars in raw and roasted form, indicating Ana o 3 was an ideal biomarker for ELISA. The ELISAs were highly specific to cashew nut only showing very low cross-reactivity with pistachio, pecan, almond, peanut and hazelnut. Two cashew nut ELISAs were validated by spiking cashew nut into model biscuits and chocolate. The biscuit extracts significantly interfered with assay performance, resulting in lower recovery of 40.2–44.9% with CAS–ELISA–2 and 25.2–79.8% with Ano3–ELISA–1 in the model biscuits for CAS–ELISA–2 and Ano3–ELISA–1 and a limit of quantitation (LOQ) of 40 mg protein kg-1 for both assays. Chocolate provided less matrix interference than biscuit. CAS–ELISA–2 and Ano3–ELISA–1 provided LOQs of 4 mg protein kg-1 and 0.4 mg protein kg-1 in chocolate with an acceptable recovery of 74.0–87.7% (CAS–ELISA–2) and 43.8–136.2% (Ano3–ELISA–1). Therefore, they are valuable tools for detecting cashew nut residues under the recommended VITAL action level.
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(2016)ThesisIn this thesis, two types of supercapacitors based on the functionalised carbon nanotube (CNT) electrodes that were decorated with different amounts of oxygen-containing groups were assembled. The as-purchased CNTs were functionalised by using improved Hummer’s method, which was adjusted to introduce different amounts of oxygen functional groups. These oxygen functional groups changed the surface structures of the CNTs and hence their electrochemical performances, because the oxygen groups are redox active. On the other side, the quantity of the oxygen groups also reduces the electrical conductivity of CNTs, thereby impairing the electrode performance. Therefore, as the first part of this thesis we studied the correlation of structures with electrochemical performances of those functionalised CNTs with different oxygen contents. In the second part, an asymmetric zinc ion capacitor (ZIC) was constructed, which was composed of a zinc anode, a low-level oxidised CNT cathode and a zinc sulphate-based liquid or gel electrolyte. The low-level oxidised CNTs were characterised by the abundant surface oxygen-containing groups and the intact graphitic inner tubes that maintained the electrical conductivity. These oxygen functional groups provided a large pseudo-capacitance, due to the electrochemical adsorption/desorption of Zn2+ ions as well as improved the electrode wettability, giving rise to a higher capacitance than that of the ZIC with an as-purchased CNT cathode. In the last part of this work, a symmetric solid-state supercapacitor was fabricated, which used the mildly oxidised CNT electrodes and sulfuric acid/poly(vinyl alcohol) gel electrolyte. The CNTs oxidised in a mild condition showed a hybrid geometrical structure with both closed tubes and unzipped tubes. The unzipped tubes enriched with oxygen-containing groups could provide electrochemical active sites for improving the capacitance while the closed tubes that preserved mostly the sp2 bonding network could endow the electrode with a good electrical conductivity. This hybrid structure rendered a good electrochemical performance in the solid-state device.
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(2013)ThesisHydrocarbon reforming using CO2, a greenhouse gas, as a feedstock has attracted increasing attention due to the benefits of chemical valorisation of natural gas and CO2, which have an adverse impact on the environment. For hydrocarbon dry reforming, where the product stream H2: CO ratio is less than 3, synfuel production is more amenable for downstream methanol and other oxygenated synthesis. Dry reforming of propane has attracted much interest because of the associated lower reforming temperature and lower vapour pressure of propane compared with methane at ambient temperature, which makes it more favourable for fuel cell cars with internal reforming. However, the formation of carbon on Ni catalysts is well known, thus the addition of Mo to Ni would help in mitigating carbon deposition through possible conversion of the Mo oxide to a Mo carbide phase. Several authors reported high activity, stability and carbon resilience of the Mo-Ni catalyst during methane steam and dry reforming. Furthermore, it has been shown that potassium promotion also retards the nucleation of carbon. As a result, the present project investigates both reactor operation and the performance of Mo-Ni/Al2O3 catalyst as well as the effect of K-promotion on propane dry reforming at temperatures of 773 -973 K . The catalysts were prepared using wetness co-impregnation method. Alumina supported bimetallic 5(wt%)Mo-10(wt%)Ni was doped with 2.5 (wt%) K. Various characterization techniques were employed to measure the physicochemical properties of the catalysts. Specifically, N2-physisorption, H2-chemisorption, temperature-programmed calcination (TPC), temperature-programmed reduction (TPR), NH3 and CO2- temperature-programmed desorption (TPD), X-ray diffraction (XRD) and Total organic carbon (TOC) analyses were performed. K-promotion enhanced the BET surface area, pore volume, metal dispersion and metal surface area. XRD analysis of calcined catalysts confirmed the presence of metal oxides. TPD experiments revealed the acid : basic site ratio of 8.3 for Mo-Ni , while K-promotion decreased the value to 7.5 ,suggesting that basicity of the catalyst was improved by K addition. Catalytic reaction studies were carried out in a stainless-steel quartz fixed-bed reactor (ID = 15 mm ID) co-axially placed within a temperature-controlled tubular furnace and loaded with 0.5g of catalyst. Both Mo-Ni and K-containing catalysts were found to be promising for dry reforming of propane due to their high activity and stability under different operating conditions.
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(2015)ThesisMicro-structured devices have attracted increasing interest in intensifying manufacturing processes in recent years. In fact, various miniaturized and micro-devices have been used for continuous production of pharmaceuticals, nanomaterials and organic compounds, and multiple functions of chemical analysis, for instance, the paper-based analytical devices (μPADs). However, these tools were only very recently made compatible for high pressure or high temperature processes. Supercritical fluids (SCFs) find useful application in performing green chemistry and engineering, especially in pharmaceutical industry. The concern for sustainable environment was the main impetus for using SCFs. The unique properties of some SCFs have enabled the possibility of replacing toxic organic solvents. In this study, the hypothesis that dense gas based microfluidic processes can be developed as an intensified and effective technique to micronize drug particles was tested using two poorly water-soluble pharmaceuticals: copper indomethacin and budesonide. Carbon dioxide was used as an antisolvent to conduct precipitation of the drugs within a microfluidic system under supercritical conditions. The experiments were designed with the aim to optimize the process; the effects of operating parameters, namely temperature, pressure, flow rates of drug solution and carbon dioxide were manipulated to reduce particle size and improve product yield. The Taguchi Method (TM) and Response Surface Methodology (RSM) were introduced to improve operating conditions and run statistical analysis. In the study of synthesis and micronisation of copper indomethacin, particles of diameter less than 5μm were produced at a yield of 80% and the purity of the product was upwards of 95%. The results from the particle size distribution analysis indicated that 90% of the product consisted of particles that were less than 8μm in diameter. The statistical analysis results also demonstrated that temperature and pressure were two significant factors affecting product yield while the flow rates of carbon dioxide and solution had minor impact. To extend the application of microfluidic processes, budesonide was processed in a dense gas assisted microfluidic system. The experiments were conducted under the optimal conditions computed by the Taguchi Method; a yield of budesonide particles of 71.1% was achieved. A particle size distribution study showed that 10% by volume of precipitate produced had diameter smaller than 4μm, and 90% of them having diameters under 10μm. Working under the dense gas or supercritical conditions at micro-scale combines the advantage of size reduction provided by micro-devices to the unique properties of the dense gas or supercritical fluids. Therefore, a dense gas based microfluidic process addresses the limitations of both macro-scale supercritical fluids reactors and conventional liquid microfluidic systems, and brings benefits to particle engineering.
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(2015)ThesisBanana pseudostems are crop waste, which cause economic loss and environment issues after harvest. However, pseudostems are rich in dietary fibre and have health benefits. This study explored the chemical composition (proximates, minerals, vitamins) as well as the digestibility and functionality of the carbohydrates. Dietary fibre was estimated using three methods namely the established AOAC method, Gas Chromatography and Nuclear Magnetic Resonance. As fresh banana pseudostems have limited shelf life, drying the stems using cabinet dryer using several conditions such as, drying at 40 °C and 50°C with/ without blanching, were compared with regard to drying time, colour as well as quality of the dried product in terms of the retention of nutrients. Drying at 50 °C without blanching provided the whitest colour and shortest drying time. Thus the optimum condition for drying was established at 50 °C without blanching based on nutrient retention. Musa balbisiana and Musa acuminata banana pseudostems were used in this study. There was no significant difference between protein, fat and carbohydrate content of banana pseudostems dried under different conditions. Moisture content was significantly higher in banana pseudostems dried at 40 °C without blanching; ash content was significantly higher in pseudostems dried at 50 °C without blanching. According to the percentage of total dietary fibre and resistant starch, pseudostem dried at 40 °C with blanching had the lowest digestibility. The neutral sugars in the non-starch polysaccharides were studied and compared with commercially available natural dietary fibre supplements sold in Australia. Pseudostems had higher ratio of soluble dietary fibre to insoluble dietary fibre, as compared to the commercial supplements. The main neutral sugars in the pseudostems were glucose, mannose and xylose, while those in the commercial supplements were xylose, arabinose and mannose, which had different functionality compared to pseudostem fibre. This study is the first to demonstrate that banana pseudostem is a potential dietary fibre supplement, which may bring health benefits to consumers and economic profits to the banana growers.
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(2019)ThesisAustralian native plants have a long history of being used for nutritional and medicinal purposes; however, the scientific foundation of such uses is not well established. In this thesis, three native Australian plants, namely samphire (Sarcocornia quinqueflora), saltbush (Atriplex nummularia) and sea parsley (Apium prostratum), were investigated for their phenolic compositions, antioxidant capacities and inhibitory activities on four enzymes: α-glucosidase, α-amylase, pancreatic lipase and hyaluronidase, for the first time. These enzymes are closely related to disorders such diabetes, overweight, obesity and inflammation. Furthermore, the phenolic compounds in sea parsley were identified and quantified by a combination of high-performance liquid chromatography (HPLC) and liquid chromatography-high resolution mass spectrometry (LC-HDMS) analyses. Phenolic compounds in the plants were extracted with methanol 80% (v/v) and purified with XAD-7 Amberlite® resin. The three plants contained relatively high levels of phenolic compounds and antioxidant capacities as well as enzyme-inhibition activities that are comparable with other Australian native plants. Of the three plants, sea parsley had the highest total phenolic content, exhibited the largest ABTS and DPPH free-radical scavenging capacities, and was the most potent inhibitor of α-glucosidase, α-amylase and pancreatic lipase. Samphire had the highest ferric reducing antioxidant power (FRAP) and was the most potent inhibitor of hyaluronidase while saltbush had the lowest phenolic content, displayed the lowest antioxidant capacity and was the least potent inhibitor of all the enzymes. Purification of the extracts resulted in a significant concentration of the phenolic compounds (1.43-2.67 times) with corresponding increases in the bioactivities. Seven phenolic compounds were identified in sea parsley, with the main ones being apiin (48.2%), apigenin (24.8%), caffeic acid (6%) and ferulic acid (2%), while the minor compounds were ρ-coumaric acid, luteolin and catechin which were present at trace levels (<1%). Significantly, catechin was identified for the first time in the Apium genus. The high levels of health-related bioactivities and the presence of several phenolic compounds known to have disease-preventing effects indicate that the consumption of these native Australian plants could bring significant health benefits to the consumer.