Liquid metal facilitated synthesis of low dimensional materials
Creators: name: Grant, Ryan
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 400499
subject: Chemical engineering not elsewhere classified

description: The field of two dimensional (2D) materials has gained much attention and interest in recent years. Due to their varied nature, numerous families of 2D materials have been explored for their application in a wide range of applications. Despite growing interest, challenges remain particularly in the synthesis of large area, homogenous sheets of 2D materials, as well as in the synthesis of nonlayered 2D materials, with their layered counterparts gaining much of the focus of researchers. These nonlayered materials have been identified to hold much promise in numerous future applications when synthesised into a 2D morphology. Liquid metals have been identified, and shown remarkable promise, in the synthesis of nonlayered 2D materials. Gallium and its alloys have been shown to be strong candidates for the synthesis of 2D materials due to their features including their low melting temperatures, as well as their ability to undergo and facilitate a Cabrera-Mott oxidation process in air, resulting in the formation of an oxide layer on the surface of the metal. This, in conjunction with their corrosive nature to other metals, has been identified to support the synthesis of various complex metal compounds. For the purpose of this Master's thesis, 2D aluminium phosphate (AlPO4) has been synthesised through a Cabrera-Mott based synthesis method. This Master's thesis aims to document the research process into the synthesis of 2D AlPO4 via a liquid metal synthesis pathway. The synthesised 2D AlPO4 will then undergo qualitative and structural analysis, after which it will be characterised via advanced techniques to determine piezoelectric characteristics, as well as the exploration of the ability of the synthesised material to absorb heavy metals.

The first objective of this thesis was to use a liquid metal synthesis pathway to facilitate the synthesis, then the characterisation, of 2D AlPO4Galinstan was identified as being a strong candidate for the facilitation of the initial synthesis of aluminium hydroxide (Al(OH)3) due to its corrosive nature to other metals and it being liquid at room temperature. This initial synthesis was undertaken in an oxygen free environment. A freeze drying process was introduced after the sample had rested to facilitate long term, stable storage of the sample.  Characterisation confirmed the synthesised material to be Al(OH)3 through the positioning of the O1s peak at ~532 eV in the XPS data, the presence of characteristic peaks for Al(OH)3 in XRD data, the presence of a peak due to the OH bond in FTIR analysis, the 2D sheet-like morphology in TEM data, and the amorphous nature of the sample through SAED analysis. Once the sample was identified, a phosphatisation process was conducted to convert the sample to AlPO4.  Further XPS analysis of the final product confirmed the presence of a P2p peak due to the presence of phosphorus, as well as loss of the AlOx constituent in the O1s peak. XRD confirmed the presence of peaks associated with the crystal plans of cubic AlPO4. FTIR showed the loss of the peak due to the OH bon, as well as the gaining of peaks due to the P-O and P=O bonds. TEM showed a now crystalline structure which, along with SAED agreed with the XRD analysis of the sample being cubic AlPO4. EDS confirmed the elemental breakdown to be aligned with that of AlPO4. TGA suggested a complete conversion of the sample to AlPO4 by the lack of loss of sample in the heating process. AFM confirmed the 2D nature of the material with a measured thickness of ~5 nm.
 
Advanced AFM characterisation techniques were employed for further sample analysis. These techniques included piezoresponse force microscopy (PFM) to investigate the piezoelectric nature of the synthesised sample, and Nano Fourier transform infrared spectroscopy (NanoFTIR) to further characterise the sample's structure and to analyse homogeneity of the synthesised material. AlPO4 was identified as a strong candidate for piezoelectric analysis via PFM due to its similar chemical structure to other, previously determined, piezoelectric materials. The piezoelectric coefficient of the synthesised 2D AlPO4 in the normal direction was measured to be 114.06 pm/V and the piezoelectric coefficient in the lateral direction was measured to be 3.92 pm/V. NanoFTIR analysis of the sample was able to, through the two dimensional line scan, confirm the presence of characteristic peaks due to P-O and P=O bonds. Additionally, via three dimensional hyperscan, homogeneity of the sample was determined and confirmed.
 
The health impact due to heavy metal pollution is a still present challenge the world faces. Numerous methods are used to remediate this issue including chemical precipitation, ion exchange, and adsorption. 2D AlPO4 synthesised in this thesis has been identified as a strong candidate for the purpose of absorbing heavy metal waste. The capabilities of 2D AlPO4 to absorb heavy metal waste have been analysed by mixing ~0.02 g of 2D AlPO4 with samples of lead chloride (PbCl2) in molar ratios of 1:1, 1:0.1, 1:0.01, and 1:0.001. Samples were then measured via atomic absorption spectroscopy (AAS). Absorption rates of lead in the samples were measured to be up to 97.8%, showing 2D AlPO4 to be a strong candidate for the absorption of heavy metal waste.
 
Overall, the outcomes presented herein will contribute to the advancement of the field of 2D materials and their synthesis. Additionally, the work presented in this thesis is believed to have great applications in the realm of absorbing and cleaning heavy metal waste, thus mitigating the dangerous health and environmental effects involved with those heavy metals.