Thesis (M.Sc. (Physics)) -- University of Limpopo, 2022 / 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
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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. / University of Limpopo (UL)
Mintek
Council for Scientific and Industrial Research (CSIR)
Center for High Performance Computing (CHPC)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/4128 |
| Date | January 2022 |
| Creators | Kekana, Magopa Tshepho Mcdonald |
| Contributors | Mosuang, T. E., Sikhwavhilu, L.M., Mahladisa, M. A. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xviii, 171 leaves |
| Relation |
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