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(2022)ThesisConverting natural resources or greenhouse gases into value-added species with low carbon footprint, is essential for the development and sustainability of modern society. However, the goal for sustainable and cost-effective conversion by using many current technologies, including photo-, electro- and thermal-based catalytic reaction systems, has been largely underachieved. Hence, it is a necessity to explore and develop new approaches to fulfill this objective. In this thesis, three hybrid catalytic systems, containing liquid gallium (Ga) and solid materials as co-catalysts, are demonstrated, which realize the gaseous and liquid feedstocks conversion through nano-tribo-electrochemical reaction pathways. In the first stage of this PhD thesis, the author reports a green carbon capture and conversion technology for mitigating CO2 emissions. The technology uses suspensions of Ga liquid metal to reduce CO2 into solid carbonaceous products and O2 at near room temperature. The solid co-contributor of silver-Ga rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano dimensional triboelectrochemical reactions. In the next stage, for the gaseous feedstock conversion, the author demonstrates an approach based on Ga liquid metal droplets and Ni(OH)2 co-catalysts for CH4 conversion into H2 and carbon. Mainly driven by the triboelectric voltage, originating from the joint contributions of the co-catalysts during agitation, CH4 is converted at the Ga and Ni(OH)2 interfaces. The efficiency of the system is enhanced when the reaction is performed at an increased pressure. The dehydrogenation of other non-gaseous hydrocarbons using this approach is also demonstrated. In the final stage, the author explores and realizes the liquid biofuels conversion, including canola oil and other liquid hydrocarbons, with H2 and C2H4 as the main products by employing Ga and nickel particles as the co-catalysts and mechanical energy as the stimulus. Altogether, the work of this PhD research offers novel pathways for low energy and green conversion of gaseous and liquid feedstocks that can be implemented in large scale conversion systems of the future.
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(2022)ThesisLiquid metals (LMs) are a class of metals and their alloys which have low melting points near or below room temperature, and they are mainly composed of post-transition elements. The low melting points of LMs make them easily stay in a liquid state and readily be broken into tens or hundreds of nanometers, which are called LM nanoparticles (LMNPs). In this thesis, the author investigates LMNPs for three exciting applications of creating conductive polymer-LMNPs compositions and explores the potential utilization of LMNPs in biological applications. In the first phase of this research, the author develops nanocomposites of Ga-based LMNPs (EGaIn NPs) with conductive polymer polyaniline (PANI). This work reports a method of growing PANI nanofibers on the EGaIn NPs by firstly providing initial functionalization sites at the interfaces for the formation of PANI nanofibrous network. The nanocomposites provide synergistic effects of PANI nanofibers and EGaIn NPs for the applications of environmental sensing and molecular separation. In the second phase of the research, the author focused on the exploration of LMNPs for their anti-inflammatory applications. Considering that Ga ions (Ga3+), have been historically utilized as anti-inflammatory agents by interfering with the Fe homeostasis of immune cells. The study presents the anti-inflammatory effects of Ga by delivering Ga nanoparticles (Ga NPs) into lipopolysaccharide-induced macrophages. The Ga NPs show a selective anti-inflammatory effect by modulating nitric oxide production without disturbing other pro-inflammatory mediators. This work reveals the different anti-inflammatory effects between Ga NPs and Ga3+ come from their different endocytic pathways: transferrin receptor independent and dependent endocytosis for Ga NPs and Ga3+, respectively. In the final phase, the author studies the interactions between LMNPs and macrophages at a light microscopic level. The mechanistic responses of macrophages to LMNPs with different densities were observed, in comparison to some other commonly studied nanoparticles. This work discovers the mobility of macrophages is very much density-dependent. This thesis comprehensively studies the interactions between LMNPs and polymeric and biological systems, at both molecular and microscopic levels, which provides a basis and road map for utilizing LMNPs in various fields such as electronics and biomedical engineering.
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(2023)ThesisLow melting point post-transition metals and alloys, dubbed as liquid metals (LMs), have emerged as group of soft yet conductive materials with remarkable physical and chemical properties. The enigmatic features of LMs originate from their deformable and electron-rich core as well as their atomically smooth and chemically active interface. These features can offer opportunities for designing novel electrochemical systems with improved performance and applicability. Despite the great potential, LM-based electrochemical modules are at nascent stage and the fundamental knowledge regarding electric field-induced events at LMs/electrolyte interfaces is still elusive. The present thesis focuses on the incorporation of LMs and LM-based materials in different electrochemical set-ups. The outcomes showcase the capability of LMs for materials synthesis, biosensing, and alloy processing via electrochemical routes. In chapter 3 of this thesis, the author focuses on the exploitation of autogenous interfacial potential generated on gallium and indium eutectic alloy, EGaIn, to drive a galvanic reduction reaction (GRR). It is revealed that EGaIn could effectively reduce graphene oxide (GO) in different configurations to produce monolayers and thick membranes of reduced GO (rGO) as well as LM droplets covered with a shell of rGO flakes. In chapter 4, the core-shell structures of LM-rGO, synthesized via GRR, were electrochemically characterized through their incorporation as a modifier to electrochemical interfaces. The author revealed that incorporation of the LM-based modifier results in improved charge transfer kinetics, higher electroactive surface area, and lower resistance. The remarkable electrochemical performance of LM-rGO particles were exploited for selective biosensing of dopamine using both paper-based devices and conventional electrochemical set-ups. In chapter 5, droplets of a gallium- and an indium-based LM eutectic alloys were electrochemically diagnosed to explore interfacial events occurring at LM/electrolyte interface. The author showed that upon surface perturbation by a cathodic voltage, solute elements tend to segregate at the interface according to their energy levels. The electrolyte solution was observed to have a substantial effect on the composition of segregated domains. Collectively, this PhD research demonstrates opportunities for designing novel electrochemical systems based on LMs and provides valuable insights into voltage-dependent behaviour of LMs, which can potentially contribute to the advancement of scientific fields such as materials processing, energy, and sensors.
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(2023)ThesisProteins are natural biopolymers composed of amino acids, holding significant roles in both industry and medicine towing to their high efficiency and selectivity. Conjugating synthetic polymers to proteins results in novel hybrid macromolecular structures, which synergistically combine the benefits of each component. Consequently, these novel conjugates often display enhanced solubility, stability, in vivo half-life, and reduced immunogenicity, thereby expanding the application scope for proteins. In the late 1970s, Davis’s pioneering work on the PEGylation of proteins marked the beginning of an era of protein-polymer conjugation for the preparation of therapeutic agents. However, early methods for protein-polymer conjugation often involved complex polymer modifications, leading to low yields and posing purification challenges. The development of controlled/living radical polymerization (CLRP) techniques (or also known as reversible-deactivation radical polymerization, RDRP) has been emerging since 1990’s to address these issues and refine the process. Notably, the recent advancements in photochemistry, such as photo-RDRP or photo-CLRP, has revolutionized the protein-polymer conjugation process. These developments enable the establishment of robust and biocompatible reaction conditions, including ambient temperature and aqueous systems, when employing photo-mediated CLRP for bioconjugation. The successful integration of Photo-initiated Reversible Addition-Fragmentation Chain-Transfer Polymerization (Photo-RAFT) and Photo-induced Atom Transfer Radical Polymerization (Photo-ATRP) into the protein-polymer conjugation process, allows for the synthesis of bioconjugates with exceptional performance characteristics, including well-defined polymers and enhanced enzymatic activity. Herein, taking advantage of these properties of Photo-CLRP, this thesis focuses on developing novel visible light mediated CLRP, enabling the synthesis of protein-polymer conjugates for therapeutics application. In the first part, this thesis describes a biocompatible vitamin-based photo initiating system for conducting aqueous Photo-RAFT polymerization under mild, presenting great promise for biological application. In a following chapter, an EY/TEOA-initiated Photo-RAFT system is introduced with excellent oxygen tolerance, allowing high-bioactivity protein-polymer conjugates to be synthesized under mild, aerobic conditions while maintaining protein structure and function. The synthesized protein-polymer conjugates were employed as antimicrobial agents that exhibit enhanced antimicrobial activity against both Gram-positive and Gram-negative bacteria. By introducing an N-terminus modified Lysozyme-Polycation conjugate via Photo-ATRP, a new protein-conjugation method is reported, which results in the production of protein-polymer conjugates with enhanced proteolytic and thermal stability as well as superior therapeutic efficacy compared to the native protein.