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dc.contributor.advisor Mosuang, T. E. Kekana, Magopa Tshepho Mcdonald
dc.contributor.other Sikhwavhilu, L.M.
dc.contributor.other Mahladisa, M. A. 2023-03-27T14:03:32Z 2023-03-27T14:03:32Z 2022
dc.description Thesis (M.Sc. (Physics)) -- University of Limpopo, 2022 en_US
dc.description.abstract The gas sensing performance of two-dimensional (2D) hexagonal boron nitride nanosheets (h-BNNSs) has being studied by means of computational and experimental methods. The structural, stability and vacancies properties of both defect free and defected 2D h-BNNSs were studied using the classical molecular dynamics (MD) approach. The calculations were performed in the NVT Evans and NPT hoover ensembles using the Tersoff potentials with the Verlet leapfrog algorithm to obtain reliable structural properties and energies for defect free, boron (B) and nitrogen (N) vacancies. B and N defect energies were calculated relative to the bulk defect free total energies, and the results suggest that N vacancy is the most stable vacancy as compared to the B vacancy. The radial distribution functions and structure factors were used to predict the most probable structural form. Mean square displacements suggests the mobility of B and N atoms in the system is increasing with an increase in the surface area of the nanosheets. Results obtained are compared with the bulk defect free h-BNNSs. Experimentally, 2D h-BNNSs were synthesised using the wet chemical reaction method through chemical vapour deposition (CVD) catalyst free approach. The X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RM), UV-visible Spectroscopy (UV-VIS), dynamic light scattering (DLS), Energy Dispersion Spectroscopy (EDS) and Brunauer-Emmett Teller (BET) were adopted to attain the structural properties of the nanosheets. Each spectroscopic technique affirmed unique features about the surface morphology of h BNNSs. The crystallinity of the nanosheets with the stacking of the B and N vii honeycomb lattice was validated by the XRD, while the TEM disclosed the specimen orientations and chemical compositions of phases with the number of layers of a planar honeycomb BN sheet, the EDS express the atoms present in the samples and BET validated the surface area of the materials. The FTIR, RM, DLS and the UV-vis expressed the formation of the in-plane, out-of-plane h-BN vibrations and, the nature of the surface with the thickness, particles stability together with the optical properties of the nanosheets. From TEM, FTIR, RS and BET the material fabricated at 800°C showed different morphologies, large number of disordering together with high surface area, which enhances the sensing properties of the nanosheets. However, with an increase in temperature the sensitivity of the nanosheets was found to decrease. Additionally, the UV-vis results, confirmed a lower energy band gap of 4.79, 4.55 and 4.70 eV for materials fabricated at 800, 900 and 1000 °C, that improved the semiconducting properties of the materials, which in return enhanced the sensing properties of the nanosheets. The gas sensing properties of the 2D h BNNSs were also investigated on hydrogen sulphide (H2S) and carbon monoxide (CO). The fabricated sensor based on 800 – 900 °C h-BNNSs showed good sensitivity towards ppm of H2S at 250 °C. The excellent gas sensing properties could be attributed to high surface area, small crystallite size, defect/disordering of h BNNSs. Overall, the h-BNNSs were found to be more sensitive to H2S over CO. en_US
dc.description.sponsorship University of Limpopo (UL) Mintek Council for Scientific and Industrial Research (CSIR) Center for High Performance Computing (CHPC) en_US
dc.format.extent xviii, 171 leaves en_US
dc.language.iso en en_US
dc.relation.requires PDF en_US
dc.subject Molecular Dynamics en_US
dc.subject Defect free energies en_US
dc.subject Defects energies en_US
dc.subject Radial Distribution Functions en_US
dc.subject Structure Factors en_US
dc.subject Mean Square Displacement en_US
dc.subject 2D h-BNNSs en_US
dc.subject Chemical Vapour Deposition en_US
dc.subject Nanosheets en_US
dc.subject Gas Sensing en_US
dc.subject H2S en_US
dc.subject CO and Defects/Dislocations en_US
dc.subject.lcsh Boron nitride en_US
dc.subject.lcsh Gas detectors en_US
dc.subject.lcsh Carbon monoxide detectors en_US
dc.title Synthesis, characterisation and modelling of two-dimensional hexagonal boron nitride nanosheets for gas sensing en_US
dc.type Thesis en_US

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