Vortex-Induced Photo-Contact Electrification Synthesis of Func6onal Metal Nanomaterials

Abstract

Metal nanomaterials with precise control over their shape, morphology, and size (ranging from nanometers to micrometers), have gain significant interest due to the unique chemical, physical, thermal, op5cal, mechanical, and conduc5ve proper5es. These materials hold an immense poten5al for a wide range of applica5ons par5cularly in catalysis. Over the years, various synthesis methods have been developed including boAom-up and top-down. A notable progress has been occurred using these methods, for controlling the synthesis of zero-dimensional (0D), onedimensional (1D) and two-dimensional (2D) nanostructures. However, there are several limita5ons and challenges that s5ll to be address, including the necessity of using high amounts of reagents, long processing 5me, the use of chemical stabilisers, the high cost of the associated complex processing, and scalability issue. This dissertation focuses on creating a paradigm shift in metal nanomaterials synthesis to overcome its limitation, by using the Vortex Fluidic Device (VFD) which is a continuous flow reactor utilizing rotating liquid tubes to generate a dynamic thin film. This can enhance chemical reactions through increased mass transfer, micro-mixing, and shear stress applied to the dynamic thin film of liquid. Thin film microfluidics offer numerous benefits in chemical processing due to their large surface-to-volume ratios, resulting in reduced reaction times, precise control over residence time and temperature, enhanced safety measures, and crucially enable scalability considerations from the initial stages of research. This contribute significantly to the development of environmentally sustainable processes that are also economically feasible. My PhD research aimed at utilizing a cutting-edge VFD to establish an unprecedented method of generating pristine gold (Au), silver (Ag), and rhenium(Re) nanoparticles and gold@graphene oxide (Au@GO) nanocomposite, where the size and morphology of nanoparticles can be controlled in water and in the absence of added reducing agents or other excipients such as surfactants. This involves UV irradiation of an aqueous metal source in a thin film of liquid generated in the VFD within a rapidly rotating quartz tube, resulted in a charge transfer between dielectric surfaces during contact and separation known as Contact Electrification (CE). The CE phenomena occur at the solid (tube surface)-liquid interface, forming reactive oxygen species present, competing with CE reduction of metal on the surface of the tube coupled with the photo-induced oxidation of water. The findings establish a paradigm for VFD processing in water under such UV irradiation involving photo-induced CE, which allows access to different nanoparticles crystallization of 1D, 2D, 3D structures and composite materials beyond what is possible using traditional batch processing strategies, with the surfaces pristine and the overall processing having beneficial green chemistry metrics. These metal nanomaterials show promising potential for catalysis applications along with other possible uses currently under investigation. The VFD offers the advantage of synthesising nanomaterials by employing simple one-step methods that eliminate the use of chemical stabilizers and surfactants, while maintaining scalability.