Manipulating 0D, 1D and 2D nanomaterials by vortex fluidic device

Author: Ahmed Hussein Al-Antaki

Al-Antaki, Ahmed Hussein, 2021 Manipulating 0D, 1D and 2D nanomaterials by vortex fluidic device, Flinders University, College of Science and Engineering

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The focus of the research in this thesis is expanding the application of the vortex fluidic device (VFD), in both the top down and bottom up fabrication of nanomaterials. The VFD is a versatile thin film microfluidic platform which imparts mechanical energy in the liquid, and can operate under so called confined mode or continuous flow where scalability of any process is addressed early in the research. It has been used for exfoliating 2D materials, slicing 1D material, the in situ growth of metal oxides, and the fabrication of composites with other nanomaterials. In all studies, the operating parameters of the VFD were systematically varied in arriving at an optimised process. The operating parameters include, rotational speed of the glass tube, flow rate, tilt angle, and the concentration of reagents or feedstocks.

A process for exfoliating along with fragmenting 2D MXene (Ti2C) has been developed, down to a few sheets of the material and particles ca 68 nm in diameter, respectively. The process operates under an inert atmosphere to avoid oxidation, and avoids the need for auxiliary reagents or harsh chemicals, relying on the shear stress in the dynamic thin film of the VFD. In the presence of oxygen, oxidation to anatase (TiO2) occurs, facilitated by the high mass transfer of oxygen into the thin film. The oxidation can be controlled by carrying out the processing in 30% hydrogen peroxide, converting MXene (Ti2C) into a composite of anatase nanoparticles with the 2D material, TiO2 NPs/MXene, with selfassembled fragments of MXene and anatase organised into spheres approximately 2 μm± 0.5 μm in diameter. The TiO2 NPs anatase spheres decorate the surface of the exfoliated MXene sheets.

The VFD was effective also in exfoliating hexagonal-BN sheets (h-BN) down to a few sheets, or by changing the operating parameters of the device, the formation of h-BN scrolls, as a process high in green chemistry metrics, using water as the solvent. However, using the common 45o tilt angle of the tube in the VFD, which is the optimised tilt angle for a wide range of applications, there was a build-up of material in the rapidly rotating tube. This build up was avoided by operating the device with the tube tilted at -45o, as a paradigm shift in the operation of the VFD.

A simple and robust process has been developed for purifying as received boron nitride nanotubes (BNNTs). This was necessary to then develop a process in the VFD for disentangling and slicing BNNTs, in the absence of surfactants and harsh chemicals, relying on the mechanical energy in the dynamic thin film along with energy imparted from a NIR pulsed laser operating at 1064 nm. The ensuing optimised process highlights a utility of the VFD in being able to readily incorporate field effects around the rotating tube. The ability to slice BNNTs opens potential applications beyond those for entangled BNNTs, including vehicles for drug and protein delivery, with the payload inside the tubes, and boron neutron capture therapy.

In situ laser ablation was effective in decorating h-BN sheets with superparamagnetic magnetite nanoparticles in water, also as a green chemistry initiative. This involved irradiating a pure iron metal target inside the rapidly rotating tube in the VFD. The resulting composite material h-BN@magnetite was effective in removing phosphate from waste water. In the same vein, nanoparticles of dicopper oxide (Cu2O) can be generated in the VFD in water as a one step process under continuous flow, with the particles averaging 14

nm in diameter. These nanoparticles can be converted to slightly smaller nanoparticles of copper oxide (CuO), 11 nm in diameter, by mild heating of an aqueous suspension of the dicopper oxide nanoparticles in water.

The new chemistry and processing capabilities of the VFD reported in this thesis make a significant contribution to unlocking the full potential of the thin film microfluidic platform, filling this gap of research towards many industrial applications. This includes avoiding the use of reagents which can pose a threat to the environment, while making the process attractive to industry. Moreover, the materials prepared in the VFD are themselves high value-added functional nanomaterials.

Keywords: VFD (vortex fluidic device), MXene, Boron nitride nanotube, Boron nitride sheets, nanoparticles, copper oxide and dicopper oxide

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2021
School: College of Science and Engineering
Supervisor: Prof. Colin Raston