A new kind of microplasma for nitrogen-fixation multifunctional nanoparticle synthesis towards selected applications

N-doped carbon quantum dot (NCQDs) is an emerging material in the carbon family, which possess many advantageous qualities such as low toxicity, good compatibility with living cells, stability in chemical reactions, strong photoluminescence, photocatalysis, and efficient transfer of electrons when exposed to light. These properties make CDs a highly promising material to mitigate the current challenges in pest control, environmental treatment and theranostic medicine. This thesis study carried out a comprehensive literature review on the potential applications of these materials in pest control. Although a tremendous benefit from NCQDs has been revealed, generating these materials in large-scale production in a green and sustainable manner is still challenging. Therefore, a comprehensive assessment of all available large-scale production of NCQDs in terms of sustainability is significant. It has been revealed that non-thermal nitrogen fixation microplasma is a potential large-scale synthesis method in terms of sustainability while lacking mass efficiency. Therefore, it is crucial to overcome the improvement of mass efficiency of the non-thermal nitrogen fixation microplasma method. In addition, most of these CD synthesis strategies are classified as the trial-and-error approach. It is a time-consuming journey with cost- and process inefficiency to create CDs with a suitable structure and properties available for a specific application. For this reason, it is also urgent to develop a rational design strategy for synthesising NCQDs towards selected applications (pest control, environmental treatment and theranostic medicine), which are emerging issues mentioned above. It has been revealed that the photoluminescence of the as-prepared NCQD increases by 18.4% in the presence of metal flakes as catalysts. However, the role of plasma-liquid-catalyst interaction in the production of NCQDs is still unclear. Therefore, it is also significant to have a deep understanding of the plasma-liquid-catalyst mechanism in the reaction to control the large-scale production of NCQDs better. Finally, it has also been important to have an insight into the reaction rate in the production of NCQDs and to determine factors (viscosity and liquid surface area) that affect the reaction rate. The primary aim of this thesis is to develop a new kind of microplasma to address the challenges associated with the large-scale production of N-fixation multifunctional N-doped carbon quantum dots (NCQD) for selected applications. The objectives of this thesis are organised into 8 chapters that will be presented in the form of a collection of published and submitted papers, which are the research outcomes. In addition, a literature review has been provided to establish the background of microplasma-assisted synthesis of NCQDs and highlight the potential applications of this material in agriculture. Overall, this thesis's main contributions to developing a new kind of microplasma-assisted synthesis process are discovering, investigating, understanding, designing, fabricating, and improving the concept of using the non-thermal nitrogen fixation microplasma process to generate high-quality NCQDs for selected applications. The main contributions are summarised in the following chapters: • • Chapter 2. Literature review: Perspectives on the plasma-assisted synthesis of N-doped nanoparticles as nanopesticides for crop pest control (Published paper 1). • • Chapter 3. Sustainability assessment of large-scale synthesis processes of NCQDs (Published paper 2). • • Chapter 4. Process intensification for gram-scale synthesis of NCQDs (Published Paper 3). • • Chapter 5. Rationally designed microplasma synthesis of NCQDs for targeted applications (Published paper 4). • • Chapter 6. Insight into plasma-catalysis in triphasic microplasma synthesis for NCQDs (Ready manuscript 5). • • Chapter 7. Stagnant Liquid Layer as “Microreaction System” in Submerged Plasma Micro-Jet for Formation of Carbon Quantum Dots (Submitted)