For the application of advanced hydrogel-based artificial muscle systems, conventional polymeric hydrogels usually suffer from various limitations such as structural inhomogeneity and poor mechanical strengths. Thus, improving the mechanical strength of a specific hydrogel system while maintaining its other useful properties become increasingly important. In this project, three different approaches were employed to improve the mechanical properties of hydrogels though microstructural control, including physical cross-links, copolymerisation, and interpenetrating systems. Analytical tools such as FTIR and XRD were used to confirm the success of sample preparation. Morphological SEM characterisations were applied to reveal direct graphic information on hydrogels microstructures. Equilibrium water swelling tests as well as uniaxial compression measurements were conducted to evaluate the influences of various experimental parameters on the hydrogels water-holding and mechanical properties. The physical cross-linker approach was proved to be successful since comparable swelling capacities and dramatically enhanced mechanical strength were achieved in nanocomposite systems in comparison with conventional chemically cross-linked gel systems, due to the presence of flexible cross-linking points and the multifunctional cross-linker role played by clay. The copolymerisation approach, both between two neutral monomers and between one neutral and the other ionic monomer, was unsuccessful in terms of mechanical property enhancement due to the low cross-linking density as a result of the dominate competition of copolymerisation rather than cross-lining kinetics. The interpenetrating approach was concluded as successful since hugely improved mechanical toughness and slightly reduced swelling capacities were observed in most IPN gel systems.

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Utilizing biomass such as lignin, bamboo, soybean, corn stalk, rice husk, etc., as a carbon source to produce graphene-based nanomaterials has been reported recently. However, the potential of using such nanomaterials for engineering and environmental applications has not been realized. This dissertation investigates the use of graphene-based nanomaterials synthesized from using biomass as a carbon source for water remediation and cement-based composites’ (CBCs) property enhancement. The first chapter introduces graphene and graphene-based nanomaterials, as well as the synthesis and application of graphene-based nanomaterials for removing heavy metals in an aqueous solution and for property enhancement in CBCs. The experimental investigation on the pyrolytic synthesis of graphene-encapsulated iron nanoparticles from biochar (BC) as the carbon source (BC-G@Fe0) was covered in the second chapter. Two synthetic routes for producing BC-G@Fe0, i.e., impregnation-carbonization (route-I) and pyrolysis-impregnation-carbonization (route-II) processes, were investigated experimentally using different characterization techniques and heavy metal removal methods. The third chapter reports the experimental performances of the heavy metal removal of Pb2+, Cu2+, and Ag+ from an aqueous solution using BC-G@Fe0. The effectivenesses of various adsorption benchmarks, such as pH, kinetics, and isotherms were assessed. Additionally, the removal efficiency of BC-G@Fe0 was evaluated. BC-G@Fe0 sample made from route II, in particular, FeCl2-impregnated-BC with 15% wt% iron loading carbonized at 1000 ℃ for 1h showed promising Pb2+, Cu2+, and Ag+ removal capacities of 0.30, 1.58, and 1.91 mmol/g, respectively. The fourth chapter experimentally investigated the reinforcement effect of commercially sourced, industrial graphene nanoplates (IG) on the mechanical properties of CBCs. This investigation was based on a hypothesis that the uniform dispersion of IG would significantly enhance the compressive strength of CBC. The main outcome of this research was that, while the wet dispersion mixing process of IG into CBC did not consistently yield significant increases in the composite compressive strength, but the newly proposed dry dispersion process demonstrated significant increases (22%) in the composite compressive strength. Chapter Five investigated the synthesis of lignin-based graphene nanoplatelets (LG) and their application in CBC reinforcement. The main findings were that LG did not show impressive increases compared to IG, even when dry dispersion was introduced. This was attributed to LG's lack of effective surface area compared to IG. Finally, a general conclusion and outlook for the future of research into biomass-based graphene nanomaterials were discussed in chapter six.

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