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Plasma engineering of advanced functional materials for photocatalytic wastewater treatment
Semiconductor metal oxide photocatalyst with favourable light absorption and charge transport characteristics have been widely used as a photocatalyst in various applications, to name a few, energy harvesting and storage, environmental remediation and air pollution. Energy harvesting which comprises the full utilisation of the wide solar light (wavelength) spectrum has become a central point of research in the field of materials science and engineering. Hence, the development of sustainable materials from environmentally sustainable techniques which can absorb majority of the solar light spectrum has become a huge challenge. For efficient utilisation of solar energy in catalytic applications, it is important to create photocatalyst that can absorb the full solar spectrum involving ultraviolet (UV), visible (VIS) and near infrared (NIR) wavelengths. More than three decades, TiO2 and its composites have been widely researched academically and used industrially as a low-cost material for photocatalytic applications. However, the large bandgap of TiO2 limits its photocatalytic activity to the UV region which is just 3-5% of sunlight on Earth’s atmosphere. TiO2 also suffers from rapid recombination of photogenerated carriers (i.e., holes and electrons) thereby affecting its photocatalytic efficiency. Over the years, there has been active research in altering the chemistries of TiO2 to overcome these aforementioned shortcomings. The most recent advantage is the use of two dimensional (2D) materials because of its layered structure One of the unexplored and interesting layered structure is MXene. The aim of this thesis is to modify the chemical structure of Ti2C MXene to produce TiO2 as an efficient photocatalyst for absorbing solar energy especially in the UV and visible regions. As a compound of titanium and carbon, Ti2C MXene could facilitate the creation of TiO2 and carbonaceous materials hereby improving the photocatalytic performance. The abundance of surface terminal groups on Ti2C MXene allow for ease of surface modification and functionalisation. In this thesis, for the first time, the functionalisation of TiO2 from Ti2C MXene using a dry and low powered system, atmospheric pressure plasma jet (APPJ) is reported. This process involved using Ti2C nano colloidal ink with highly reactive oxygen plasma source which can tune the electronic properties (engineering bandgap) of Ti2C MXene in-situ while simultaneously printing on to a substrate. X-ray/Ultraviolet Photoelectron spectroscopy showed an additional density of states (DOS) close to valence band edge and changes to the Ti, O core level spectra due to the oxygen plasma functionalisation. Density functional Theory calculation suggests that the changes in the electron structure might be due to the influence of oxygen vacancies and hence the increase in efficiency of catalytic process. Also, time dependent oxygen plasma functionalisation studies reveal the morphology and size of the in-situ generated TiO2 nanoparticles varied from 5-8 nm with exceptionally high photocatalytic performance.
The second aim of the thesis is to create a heterostructure of Ti2C MXene with low cost and earth abundant graphitic carbon nitride, g-C3N4 (GCN) with visible light properties. For the first time, a lower power APPJ method was reported to produce a ternary in-situ TiO2/Ti2C/GCN heterostructure. In this thesis, GCN nanosheets were used as a semiconducting photocatalyst that could efficiently harvest the energy from visible light. Ti2C MXene nanosheets acted as an excellent electron sink while providing enhanced surface area which could facilitate the interfacial charge carriers. Structural studies show the formation of heterostructure formation between Ti2C MXene and GCN. Influence of morphology and hence changes to the optical properties were discussed. The synthesized ternary in-situ TiO2/Ti2C/GCN nanosheets showed enhancement in photocatalytic performance.
The third aim of my research was to integrate TiO2 onto earth abundant natural cellulose fibres. Utilising the power of low power atmospheric pressure plasma (APPJ) to in-situ anchor TiO2 onto cellulose fibres to prevent the thermal degradation and chemical instability leading to leaching of the oxides from the cellulose fibres. APPJ in the presence of highly oxidised species caused an increase in COO- bonds which provided a strong linkage between TiO2 and cellulose materials. Also, structural studies revealed polymorphic changes in the structure of cellulose materials that improved its crystallinity and surface area for photocatalytic applications. APPJ is also able to create oxygen vacancies in the TiO2 which further reduced the bandgap of as synthesized TiO2/cellulose nanocomposites that enhanced photocatalytic applications. Toxicity studies showed that TiO2 was not cytotoxic.
This plasma modified surfaces (of all the samples) show exceptional degradation of wastewater with ternary in-situ TiO2/Ti2C/GCN showing two times more improvement in methylene blue degradation (84% degradation) as compared to in-situ TiO2/Ti2C MXene (42% degradation). Also, TiO2/cellulose bionanocomposite showed excellent adsorptive-photocatalytic performance in degrading industrial waste dye providing a clear route as nanocomposites from research into industrialisation
Design aspects and characterization of hydrogel-based bioinks for extrusion-based bioprinting
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Evaluating the sustainability and resiliency of local food systems
With an ever-rising global population and looming environmental challenges such as climate change and soil degradation, it is imperative to increase the sustainability of food production. The drastic rise in food insecurity during the COVID-19 pandemic has further shown a pressing need to increase the resiliency of food systems. One strategy to reduce the dependence on complex, vulnerable global supply chains is to strengthen local food systems, such as by producing more food in cities. This thesis uses an interdisciplinary, food systems approach to explore aspects of sustainability and resiliency within local food systems.
Lifecycle assessment (LCA) was used to evaluate how farm scale, distance to consumer, and management practices influence environmental impacts for different local agriculture models in two case study locations: Georgia, USA and England, UK. Farms were grouped based on urbanisation level and management practices, including: urban organic, peri-urban organic, rural organic, and rural conventional. A total of 25 farms and 40 crop lifecycles were evaluated, focusing on two crops (kale and tomatoes) and including impacts from seedling production through final distribution to the point of sale. Results were extremely sensitive to the allocation of composting burdens (decomposition emissions), with impact variation between organic farms driven mainly by levels of compost use. When composting burdens were attributed to compost inputs, the rural conventional category in the U.S. and the rural organic category in the UK had the lowest average impacts per kg sellable crop produced, including the lowest global warming potential (GWP). However, when subtracting avoided burdens from the municipal waste stream from compost inputs, trends reversed entirely, with urban or peri-urban farm categories having the lowest impacts (often negative) for GWP and marine eutrophication. Overall, farm management practices were the most important factor driving environmental impacts from local food supply chains.
A soil health assessment was then performed on a subset of the UK farms to provide insight to ecosystem services that are not captured within LCA frameworks. Better soil health was observed in organically-farmed and uncultivated soils compared to conventionally farmed soils, suggesting higher ecosystem service provisioning as related to improved soil structure, flood mitigation, erosion control, and carbon storage. However, relatively high heavy metal concentrations were seen on urban and peri-urban farms, as well as those located in areas with previous mining activity. This implies that there are important services and disservices on farms that are not captured by LCAs.
Zooming out from a focus on food production, a qualitative methodology was used to explore experiences of food insecurity and related health and social challenges during the COVID-19 pandemic. Fourteen individuals receiving emergency food parcels from a community food project in Sheffield, UK were interviewed. Results showed that maintaining food security in times of crisis requires a diverse set of individual, household, social, and place-based resources, which were largely diminished or strained during the pandemic. Drawing upon social capital and community support was essential to cope with a multiplicity of hardship, highlighting a need to develop community food infrastructure that supports ideals of mutual aid and builds connections throughout the food supply chain. Overall, this thesis shows that a range of context-specific solutions are required to build sustainable and resilient food systems. This can be supported by increasing local control of food systems and designing strategies to meet specific community needs, whilst still acknowledging a shared global responsibility to protect ecosystem, human, and planetary health
2017 GREAT Day Program
SUNY Geneseo’s Eleventh Annual GREAT Day.https://knightscholar.geneseo.edu/program-2007/1011/thumbnail.jp
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
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