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Title: Graphene and triptycene based porous materials for adsorption applications
Author: Gonciaruk, Aleksandra
ISNI:       0000 0004 6056 596X
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2016
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There were three main driving forces behind this thesis: global concern over climate change mainly due to uncontrolled carbon dioxide (CO2) emissions, the excitement over the discovery of graphene and its versatile potential, and the potential to design three-dimensional (3D) or two-dimensional (2D) structures, in our case using unique triptycene molecule. We examined two polymeric materials for CO2 adsorption and suggested simple design of disordered carbons suitable for gas adsorption studies. The approach in each task was to examine structural and adsorption properties of materials using detailed atomistic modelling employing Monte Carlo and Molecular Dynamics techniques and where possible provide experimental measurements to validate the simulations. The thesis is presented as a collection of papers and the work can be divided into three independent projects. The aim of the first project is to utilize graphene as an additive in polymer composites in order to increase separation between the polymer chains increasing available surface area. The matrix used is a polymer of intrinsic microporosity (PIM-1), which possess large surface area and narrow nano-sized ( > 2nm) pore distribution attractive for gas separation membrane applications. Adding a filler can reduce aging of the polymer, and enhance permeability across the membrane, often to the expense of loosing selectivity. Therefore, we investigated the packing of PIM-1 chains in presence of discrete 2D graphene platelets and 3D graphene-derived structures and its effect on composite structure and adsorption properties. We found that additives do not alter structural polymer properties at the molecular level preserving the same adsorption capacity and affinity. Potential permeability increase would benefit from the retention of selectivity in the material. Building on design philosophy of materials with intrinsic microporosity we continued further investigation of 3D graphene-derived structures. The idea is that highly concave molecules or polymer chains pack inefficiently creating microporous materials with sufficient surface area for gas adsorption. 3D propeller-like structures were derived from graphene arms connected through the rigid triptycene and other types of cores. The resulting structures created a large amount of micropores and showed similar CO2/CH4 selectivity to activated carbons reported in the literature. It was shown that rigid triptycene core leads to more open structures. The model was also applied to model commercially available activated carbon to predict n- perfluorohexane adsorption. The fitting to experimental structural information proved to be challenging due to trial and error nature of the approach. Nevertheless, the simple packing procedure and diverse structure design have a great potential to serve as a virtual model for porous carbons that possess pore complexity and does not require any previous experimental data to be build on. The last project concerns CO2 adsorption and selectivity over CH4 and N2 in recently reported triptycene-based polymer. The triptycene shape polymer can form a porous 2D network that can be exfoliated into free-standing sheets and potentially used as a membrane. Sheets stack in the bulk material forming anisotropic channel pores. Additionally it contains fluoro- functional groups, which are known to have a high CO2 affinity. We explored pore structure and chemistry of stacked material for gas adsorption and predicted comparable capacity and CO2 selectivity to other microporous covalent materials such as activated carbons and PIMs. The CH4/N2 selectivity was similar to currently most selective material belonging to MOF family. We showed that fluoro-group have a positive effect on CO2 affinity, however predictions are sensitive to the charges of fluorine atoms assigned by different methods.
Supervisor: Siperstein, Flor ; Carbone, Paola Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: PIM ; graphene ; adsorption ; molecular simulations ; carbon dioxide ; triptycene ; polymer of intrinsic microporosity ; separation ; gravimetric ; membrane ; gas ; selectivity ; microporosity ; methane ; nitrogen ; three-dimensional ; composite ; monte carlo ; molecular dynamics ; surface area ; PSD