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Item Adsorption of NH3 and NO2 molecules on sn-doped and undoped ZnO (101) surfaces using density functional theory(2022) Dima, Ratshilumela S; Tshwane, David M; Shingange, Katekani; Modiba, Rosinah; Maluta, NE; Maphanga, Rapela RThe adsorption and interaction mechanisms of gaseous molecules on ZnO surfaces have received considerable attention because of their technological applications in gas sensing. The adsorption behavior of NH3 and NO2 molecules on undoped and Sn-doped ZnO (101) surfaces was investigated using density functional theory. The current findings revealed that both molecules adsorb via chemisorption rather than physisorption, with all the adsorption energy values found to be negative. The calculated adsorption energy revealed that the adsorption of the NH3 molecule on the bare ZnO surface is more energetically favorable than the adsorption of the NO2 molecule. However, a stable adsorption configuration was discovered for the NO2 molecule on the surface of the Sn-doped ZnO surface. Furthermore, the adsorption on the undoped surface increased the work function, while the adsorption on the doped surface decreased. The charge density redistribution showed charge accumulation and depletion on both adsorbent and adsorbate. In addition, the density of states and band structures were studied to investigate the electronic behavior of NH3 and NO2 molecules adsorbed on undoped and Sn-doped ZnO (101) surfaces.Item Anti-mycobacterial peroxides: A new class of agents for development against tuberculosis(2020) Van der Westhuyzen, Christiaan W; Haynes, J; Panayides, Jenny-Lee; Wiid, I; Parkinson, CBackground: With few exceptions, existing tuberculosis drugs were developed many years ago and resistance profiles have emerged. This has created a need for new drugs with discrete modes of action. There is evidence that tuberculosis (like other bacteria) is susceptible to oxidative pressure and this has yet to be properly utilised as a therapeutic approach in a manner similar to that which has proven highly successful in malaria therapy. Objective: To develop an alternative approach to the incorporation of bacterial siderophores that results in the creation of antitubercular peroxidic leads for subsequent development as novel agents against tuberculosis. Methods: Eight novel peroxides were prepared and the antitubercular activity (H37Rv) was compared to existing artemisinin derivatives in vitro. The potential for toxicity was evaluated against the L6 rat skeletal myoblast and HeLa cervical cancer lines in vitro. Results: The addition of a pyrimidinyl residue to an artemisinin or, preferably, a tetraoxane peroxidic structure results in antitubercular activity in vitro. The same effect is not observed in the absence of the pyrimidine or with other heteroaromatic substituents. Conclusion: The incorporation of a pyrimidinyl residue adjacent to the peroxidic function in an organic peroxide results in anti-tubercular activity in an otherwise inactive peroxidic compound. This will be a useful approach for creating oxidative drugs to target tuberculosis.Item Antibiotic 3D printed Materials for healthcare applications(Elsevier Inc, 2020-05) Mokhena, Teboho C; John, Maya J; Mochane, MJ; Sadiku, ER; Motsoeneng, TS; Mtibe, Asanda; Tsipa, PC; Kokkarachedu, V; Kanikireddy, V; Sadiku, RSince its introduction in the past 25 years, three-dimensional (3D) printing has been a major research topic owing to its potential to overcome the limitations of conventional 3D manufacturing techniques, that is, to control the overall architecture toward various applications. In the third (2013–present) decade, 3D printing enters a new phase in which researchers fabricate clinical constructs that benefit the current society. In this chapter, we briefly discuss the recent progress of 3D printing and challenges related to the antibiotic materials and manufacturing process for biomedical applications.Item Application of electrospun materials in oil–water separations(Scrivener Publishing LLC, 2020-04) Mokhena, Teboho C; John, Maya J; Mochane, MJ; Tsipa, PC; Boddula, RI; Ahamed, MI; Asiri, AMThere has been ever-increasing pressure to come up with novel strategies for oily wastewater treatment since it affect the available water sources, crop production, aquatic life and human health. Electrospun nanofibrous materials with attractive attributes, such as interconnected porous structure, large surface-to-area ratio, malleable mechanical properties, tuneable wettability, and porosity have a huge potential for oily wastewater treatment. In this chapter, the recent progress of oil/ water separation using electrospun nanofibrous materials is reviewed. The challenges and future prospects of this new field are also described.Item Assessing a sustainable manufacturing route to lapatinib(2022-08) Stark, RT; Rye, DR; Newton, OJ; Deadman, BJ; Miller, PW; Panayides, Jenny-Lee; Riley, Darren L; Helldardt, K; Hii, KKA synthetic route to an anti-cancer drug, lapatinib, was devised to support the development of a sustainable manufacturing process in South Africa. Quantitative metrics were employed to evaluate the sustainability of the key steps of the reaction.Item Beneficiation of eucalyptus tree barks in the context of an integrated biorefinery – Optimisation of accelerated solvent extraction (ASE) of polyphenolic compounds using response surface methodology(2020-12) Andrew, Jerome E; Masetlwa, J; Tesfaye, T; Sithole, Bishop BBark from trees obtained from sustainably managed plantations used in the production of timber, pulp and paper is an under-utilised waste in many countries across the world. However, in the context of an integrated biorefinery, they may serve as a valuable feedstock for the production of high-value products for increased revenue generation and mitigation of environmental impacts for the ailing forestry, timber, pulp and paper industry. In this study, optimum accelerated solvent extraction conditions were established for the recovery of total polyphenolic compounds (TPC) and total extractive content (TEC) from barks obtained from four Eucalyptus tree species (E.dunnii, E.grandis, E.smithii and E.nitens). Using a response surface methodology and Box-Behnken experimental design, optimum extraction conditions found were an extraction temperature of 117 °C, three extraction cycles, and a milled bark particle size class of 500–850 μm. E. smithii showed the highest TEC at 21.9% and the highest TPC at 4.7 g/100 g gallic acid equivalents (GAE).Item Beneficiation of wood sawdust into cellulose nanocrystals for application as a bio-binder in the manufacture of particleboard(2021-10) Fagbemi, Olajumoke D; Andrew, Jerome E; Sithole, Bishop BThis study reports on the beneficiation of wood sawdust into cellulose nanocrystals (CNC) for application as a binder in the manufacture of particleboard. The cellulose nanocrystal from wood sawdust was extracted using acid hydrolysis and an oxidizing agent. This was used as it is for particleboard fabrication, likewise, after cross-linking with several cross-linking agents, viz., CNC-glyoxal, CNC-hexamine, CNC-polyamide–epichlorohydrin, and CNC-polyethylene to make cross-linked binders. The tensile strength performances of the particleboard panels were determined by modulus of rupture (MOR) and elasticity (MOE). The characterization of the CNC by Fourier transform infrared spectroscopy (FTIR) confirmed cellulose functional structures in the CNC. X-ray diffraction (XRD) analysis indicated high crystallinity index (78%) of the CNC and typical nano-dimensions of 2.1–10 nm for diameter and 150–350 nm for length as revealed by the transmission electron microscope (TEM). Thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) analyze high thermal stability (250–400 ℃) of the CNC. Significant mechanical strength performances of the particleboard panels were evident in the modulus of rupture (MOR) and the modulus of elasticity (MOE) values that were determined. The panels met grade 1-L-1 specification of the American National Standards Institute A208.1. The incorporation of cross-linking agents enhanced the static bending and bonding strength properties of the formulated bio-binders. It can be concluded that cellulose nanocrystals extracted from waste wood sawdust could be considered for use as a binder to produce environmentally friendly wood composites bio-adhesives and particleboard panel fabrication.Item Binding pose analysis of hydroxyethylamine based ß-secretase inhibitors and application thereof to the design and synthesis of novel indeno[1,2-b]indole based inhibitors(2020-11) Van der Westhuizen, CJ; Van Greunen, DG; Cordier, W; Nell, M; Steenkamp, V; Stander, A; Panayides, Jenny-Lee; Riley, DLß-Secretase (BACE1) is recognised as a target for the treatment of Alzheimer’s disease, and transition-state isosteres such as hydroxyethylamines have shown promise when incorporated into BACE1 inhibitors. A computational investigation of previously reported carbazole-based hydroxylethylamines with contradictory binding poses was undertaken using molecular dynamic simulations to rationalise the ligands preferred binding preference. Visual inspection of the confirmed binding pocket showed unoccupied space surrounding the carbazole moiety which was probed through the synthesis of seventeen ligands wherein the carbazole ring system was replaced with an indeno[1,2-b]indole ring system. The most active compound, rac-1- [benzyl(methyl)amino]-3-(indeno[1,2-b]indol-5(10H)-yl)propan-2-ol, indicated an inhibition of 91% at 10 µM against ß-secretase with a cytotoxicity IC50 value of 10.51 ± 1.11 µM against the SH-SY5Y cell line.Item Biodegradable behaviour of waste wool and their recycled polyster preforms in aqueous and soil conditions(2021-01) Muniyasamy, Sudhakar; Patnaik, AsisPresent study deals with the biodegradable behavior of individual components and their preforms of nonwoven biocomposites developed from waste wool fibers including coring wool (CW), dorper wool (DW) and recycled polyester fibers (RPET). A respirometric technique was employed to estimate the production of CO2 during the biodegradation experiments under soil and aqueous media conditions. Functional groups of test samples before and after biodegradation were analyzed using Fourier transform infrared spectroscopy (FTIR). Leaching chemicals such as formaldehyde (hydrolyzed) and Chromium VI (Cr VI) was also measured. The CO2 emission in wool fibers CW and DW indicated 90% and 60% biodegradation in soil burial and aqueous media conditions respectively, for 100 days incubation. RPET fibers, 20% and 10% biodegradation in soil burial and aqueous media conditions was measured respectively while the preforms of waste wool and RPET reflected 30% and 25% biodegradation in soil burial and aqueous media conditions, respectively. The degradation of end functional groups such as carbonyl (keto and ester), aldehyde and hydroxyl were also confirmed by FTIR. The DW and CW wool fibers showed higher Cr(VI) concentration as compared to the RPET. The released formaldehyde results showed higher concentration for RPET preforms as compared to waste wool preforms. These results suggest that waste wool preforms are extremely environment friendly as compared to RPET preforms. Thus, waste wool preforms it can be potentially utilized for preparing biocomposite materials and associated biobased products.Item Biodegradation of petroleum hydrocarbon waste using consortia of Bacillus sp(2020-12) Masika, Wendy S; Moonsamy, Ghaneshree; Mandree, Prisha; Ramchuran, Santosh O; Lalloo, Rajesh; Kudanga, TPetroleum hydrocarbons are toxic to all forms of life; therefore, environmental pollution caused by petroleum is of great concern. Bio-based environmentally friendly strategies are preferred for the remediation of these contaminated sites. This study investigated the potential of consortia of Bacillus spp for the removal of petroleum hydrocarbons from synthetic media and industrial effluents. Of the 115 isolates, the top three performing isolates, designated as GPA 11.2, GPA 7.1, GPA 3.5, were selected and identified using 16 s rDNA as Bacillus subtilis (GPA 11.2), Bacillus methylotrophicus (GPA 3.5), and Bacillus amyloliquefaciens (GPA 7.1). The three strains were combined to produce three different consortia designated as prototype 1, prototype 2, and prototype 3. The bioremediation potential of each consortium was evaluated by Gas Chromatography (GC) using industrial effluents that contained hydrocarbons. Results indicated that the bulk of the contaminants were removed during the first 48 h; and removal (%) did not increase significantly after 72h. The total petroleum hydrocarbons (TPH) (C8–C28) removal rates from synthetic effluent after 48h of treatment using prototype 1, prototype 2, and prototype 3 were 64.9%, 30.0%, and 79.8%, respectively. The TPH (C8–C28) removal rate from true effluents after 48h of treatment using prototype 1, prototype 2, and prototype 3 consortia were 64.5%, 53.6%, and 52.7%, respectively. The results showed that the best performing consortium was prototype 1. This study has demonstrated the potential application of Bacillus consortia as bioremediation agents for the treatment of hydrocarbon-contaminated sites.Item Biodiesel production potential of an indigenous South African microalga, Acutodesmus bajacalifornicus(2021-09) Grobler, J; Harding, KG; Smit, Monique; Ramchuran, Santosh O; Durand, P; Low, MIn this study, a South African indigenous microalga Acutodesmus bajacalifornicus was evaluated in different cultivation media. Eleven potential cultivation media were identified and tested on A. bajacalifornicus, a potential source for biodiesel production. A. bajacalifornicus had the highest growth rate in the JG medium (in-house formulation), with a competitive average specific growth rate of 0.47 d-1. The highest biomass productivity was in the Hase medium, but with relatively low productivity of 53.1 mg.L-1.d-1. Analysis of the biomass lipid content and profile of each cell culture, using fatty acid methyl ester (FAME) gas chromatography (GC) showed that the lipid content varied between cultivation media, with minimum lipid content of 20% (w/w) and an average close to 47% (w/w). Utilising biodiesel property predictive formulas, and the lipid profiles obtained in this study, it was possible to predict the properties of biodiesel that could be generated from A. bajacalifornicus. It was found that biomass from eight of the media adhered to South African summer grade biodiesel standards. As such, A. bajacalifornicus is a potential candidate for microalgal biodiesel production in South Africa. However, the bioenergy yield rate would need to be improved to have a similar attractiveness to other studies.Item Bioelectricity generation by natural microflora of septic tank wastewater (STWW) and biodegradation of persistent petrogenic pollutants by basidiomycetes fungi: An integrated microbial fuel cell system(2021-01) Thulasinathan, B; Jayabalan, T; Sethupathi, M; Kim, W; Muniyasamy, Sudhakar; Sengottuvelan, N; Nainamohamed, S; Ponnuchamy, K; Alagarsamy, AThe microbial fuel cell is a unique advantageous technology for the scientific community with the simultaneous generation of green energy along with bioelectroremediation of persistent hazardous materials. In this work, a novel approach of integrated system with bioelectricity generation from septic tank wastewater by native microflora in the anode chamber, while Psathyrella candolleana with higher ligninolytic enzyme activity was employed at cathode chamber for the biodegradation of polycyclic aromatic hydrocarbons (PAHs). Six MFC systems designated as MFC1, MFC2, MFC3, MFC4, MFC5, and MFC6 were experimented with different conditions. MFC1 system using natural microflora of STWW (100%) at anode chamber and K3[Fe(CN)6] as cathode buffer showed a power density and current density of 110 ± 10 mW/m2 and 90 ± 10 mA/m2 respectively. In the other five MFC systems 100% STWW was used at the anode and basidiomycetes fungi in the presence or absence of individual PAHs (naphthalene, acenaphthene, fluorene, and anthracene) at the cathode. MFC2, MFC3, MFC4, MFC5, and MFC6 had showed power density of 132 ± 17 mW/m2, 138 ± 20 mW/m2, 139 ± 25 mW/m2, and 147 ± 10 mW/m2 respectively. MFC2, MFC3, MFC4, MFC5, and MFC6 had showed current density of 497 ± 17 mA/m2, 519 ± 10 mA/m2, 522 ± 21 mA/m2 and 525 ± 20 mA/m2 respectively. In all the MFC systems, the electrochemical activity of anode biofilm was evaluated by cyclic voltammetry analysis and biofilms on all the MFC systems electrode surface were visualized by confocal laser scanning microscope. Biodegradation of PAHs during MFC experimentations in the cathode chamber was estimated by UV-Vis spectrophotometer. Overall, MFC6 system achieved maximum power density production of 525 ± 20 mA/m2 with 77% of chemical oxygen demand removal and 54% of coulombic efficiency at the anode chamber and higher anthracene biodegradation (62 ± 1.13%) at the cathode chamber by the selected Psathyrella candolleana at 14th day. The present natural microflora - basidiomycetes fungal coupled MFC system offers excellent opening towards the simultaneous generation of green electricity and PAHs bioelectroremediation.Item Bioremediation of polycyclic aromatic hydrocarbons from industry contaminated soil using indigenous bacillus spp.(2021-09) Mandree, Prisha; Masika, Wendy S; Naicker, Justin; Moonsamy, Ghaneshree; Ramchuran, Santosh O; Lalloo, RajeshPolycyclic aromatic hydrocarbons (PAHs) are reportedly toxic, ubiquitous and organic compounds that can persist in the environment and are released largely due to the incomplete combustion of fossil fuel. There is a range of microorganisms that are capable of degrading low molecular weight PAHs, such as naphthalene; however, fewer were reported to degrade higher molecular weight PAHs. Bacillus spp. has shown to be effective in neutralizing polluted streams containing hydrocarbons. Following the growing regulatory requirement to meet the PAH specification upon disposal of contaminated soil, the following study aimed to identify potential Bacillus strains that could effectively remediate low and high molecular weight PAHs from the soil. Six potential hydrocarbon-degrading strains were formulated into two prototypes and tested for the ability to remove PAHs from industry-contaminated soil. Following the dosing of each respective soil system with prototypes 1 and 2, the samples were analyzed for PAH concentration over 11 weeks against an un-augmented control system. After 11 weeks, the control system indicated the presence of naphthalene (3.11 µg·kg-1), phenanthrene (24.47 µg·kg-1), fluoranthene (17.80 µg·kg-1) and pyrene (28.92 µg·kg-1), which illustrated the recalcitrant nature of aromatic hydrocarbons. The soil system dosed with prototype 2 was capable of completely degrading (100%) naphthalene, phenanthrene and pyrene over the experimental period. However, the accumulation of PAHs, namely phenanthrene, fluoranthene and pyrene, were observed using prototype 1. The results showed that prototype 2, consisting of a combination of Bacillus cereus and Bacillus subtilis strains, was more effective in the biodegradation of PAHs and intermediate products. Furthermore, the bio-augmented system dosed with prototype 2 showed an improvement in the overall degradation (10–50%) of PAHs, naphthalene, phenanthrene and pyrene, over the un-augmented control system. The following study demonstrates the potential of using Bacillus spp. in a bioremediation solution for sites contaminated with PAHs and informs the use of biological additives for large-scale environmental remediation.Item Cellulose nanocrystals-based composites(Scrivener Publishing LLC, 2020-01) Mokhena, Teboho C; John, Maya J; Mochane, MJ; Mtibe, Asanda; Motsoeneng, TS; Mokhothu, TH; Tshifularo, CA; Jamil, N; Kumar, P; Batool, RCellulose nanocrystals and cellulose nanocrystals-based composites with their unique features, such as abundance, renewability, high strength and stiffness, eco-friendliness, and relatively low density received unprecedented interest from both academia and industries as replacement of conventional petroleum-based materials, since conventional petroleum-based materials create ecological threats such as global warming and pollution. In this chapter, critical factors in the manufacturing of cellulose nanocrystals-based composites with regard to preparation methods, morphology, barrier and mechanical behaviour are comprehensively discussed. It concludes with the recent developments and future trends of cellulose nanocrystals reinforced biopolymers.Item Cellulose nanomaterials: New generation materials for solving global issues(2020-02) Mokhena, Teboho C; John, Maya JThis review describes the recent advances in the production and application of cellulose nanomaterials. Cellulose nanomaterials (CNMs), especially cellulose nanocrystals and cellulose nanofibers, can be produced using different preparation processes resulting in materials with unique structures and physicochemical properties that are exploited in different fields such as, biomedical, sensors, in wastewater treatment, paper and board/packaging industry. These materials possess attractive properties such as large surface area, high tensile strength and stiffness, surface tailor-ability via hydroxyl groups and are renewable. This has been a driving force to produce these materials in industrial scale with several companies producing CNMs at tons-per-day scale. The recent developments in their production rate and their applications in various fields such as medical sector, environmental protection, energy harvesting/storage are comprehensively discussed in this review. We emphasize on the current trends and future remarks based on the production and applications of cellulose nanomaterials.Item Characterisation of engineered nanomaterials in nano-enabled products exhibiting priority environmental exposure(2021-03) Lehutso, Raisibe F; Tancu, Yolanda; Maity, Arjun; Thwala, MelusiAnalytical limitations have constrained the determination of nanopollution character from real-world sources such as nano-enabled products (NEPs), thus hindering the development of environmental safety guidelines for engineered nanomaterials (ENMs). This study examined the properties of ENMs in 18 commercial products: sunscreens, personal care products, clothing, and paints—products exhibiting medium to a high potential for environmental nanopollution. It was found that 17 of the products contained ENMs; 9, 3, 3, and 2 were incorporated with nTiO2, nAg, binaries of nZnO + nTiO2, and nTiO2 + nAg, respectively. Commonly, the nTiO2 were elongated or angular, whereas nAg and nZnO were near-spherical and angular in morphology, respectively. The size ranges (width × length) were 7–48 × 14–200, 34–35 × 37–38, and 18–28 nm for nTiO2, nZnO, and nAg respectively. All ENMs were negatively charged. The total concentration of Ti, Zn, and Ag in the NEPs were 2.3 × 10-4–4.3%, 3.4–4.3%, and 1.0 × 10-4–11.3 × 10-3%, respectively. The study determined some key ENM characteristics required for environmental risk assessment; however, challenges persist regarding the accurate determination of the concentration in NEPs. Overall, the study confirmed NEPs as actual sources of nanopollution; hence, scenario-specific efforts are recommended to quantify their loads into water resources.Item Characterisation of pulp and paper mill sludge for beneficiation(2022-05) Jele, TB; Sithole, Bishop B; Lekha, Prabashni; Andrew, Jerome EIn this study, three different pulp and paper mill sludge (PPMS) samples collected from different South African mills were chemically and physically characterised to investigate their suitability for various beneficiation pathways. The overall objective was to identify the most suitable beneficiation opportunities for each PPMS sample based on characteristics. The potential beneficiation pathways (identified) were biofuels, building materials (cement and brick), biopolymer/composites, cellulose nanomaterials, composting, land application, and thermal processing (energy). Each of the beneficiation pathways was more suitable for one type of PPMS due to the varying characteristics of the PPMS. The characteristics of PPMS were influenced by the pulping technique employed at each mill, the raw material and the type of effluent treatment employed. Proximate analysis revealed that the calorific values of all PPMS samples studied were too low for energy harvesting (thermal processing). The high ash content of PPMS A and PPMS C was suitable for biocomposites whose strength could be enhanced by fillers present in PPMS. The higher glucose content in PPMS B compared to PPMS A and PPMS C was favourable for bioethanol and bio-oil production. The high cellulose and low ash content of PPMS B were found suitable for the production of nanocellulose.Item Co-pelletization of a zirconium-based metalorganic framework (UiO-66) with polymer nanofibers for improved useable capacity in hydrogen storage(2020-12) Bambalaza, Sonwabo E; Langmi, HW; Mokaya, R; Musyoka, Nicholas M; Khotseng, LEWe report on a concept of co-pelletization using mechanically robust hydroxylated UiO-66 to develop a metal-organic framework (MOF) monolith that contains 5 wt% electrospun polymer nanofibers, and consists of an architecture with alternating layers of MOF and nanofiber mats. The polymers of choice were the microporous Polymer of Intrinsic Microporosity (PIM-1) and non-porous polyacrylonitrile (PAN). Co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths retain no less than 85% of the porosity obtained in pristine powder and pelletized UiO-66. The composition of the pore size distribution in co-pelletized UiO-66/PIM-1 and UiO-66/PAN monoliths is significantly different to that of pristine UiO-66 forms, with pristine UiO-66 forms showing 90% of the pore apertures in the micropore region and both UiO-66/nanofiber monoliths showing a composite micro-mesoporous pore size distribution. The co-pelletized UiO-66/nanofiber monoliths obtained improved useable H2 capacities in comparison to pristine UiO-66 forms, under isothermal pressure swing conditions. The UiO-66/PIM-1 monolith constitutes the highest gravimetric (and volumetric) useable capacities at 2.3 wt% (32 g L−1) in comparison to 1.8 wt% (12 g L−1) and 1.9 wt% (29 g L−1) obtainable in pristine UiO-66 powder and UiO-66 pellet, respectively. The co-pelletized UiO-66/PAN monolith, however, shows a significantly reduced surface area by up to 50% less in comparison to pristine UiO-66, but its pore volume only 13% less in comparison to pristine UiO-66. As a result, total gravimetric H2 capacity of the co-pelletized UiO-66/PAN monolith is 50% less in comparison to that of pristine UiO-66, but crucially the useable volumetric H2 capacity is 50% higher for the UiO-66/PAN monolith in comparison to pristine UiO-66 powder. The co-pelletization strategy provides a simple method for generating hierarchical porosity into an initially highly microporous MOF without changing the structure of the MOF through complex chemical modifications. The UiO-66/nanofiber monoliths offer improvements to the typically low H2 useable capacities in highly microporous MOFs, and open new opportunities towards achieving system-level H2 storage targets.Item Colour tuning from violet to blue emission stimulated by various nickel oxide nanostructures: Influence of bias voltage towards volatile organic compounds vapours(2021-03) Mokoena, Teboho P; Swart, HC; Hillie, Kenneth T; Motaung, DEPropanol and benzene, toluene, ethylenebenzene and xylene (BTEX) vapours are within the volatile organic compounds (VOCs) family and are utilized in industrial and petroleum goods, are greatly toxic in human health and environment. Therefore, it is desired to fabricate the gas sensor that is sensitive and selective towards VOCs at relatively low temperature. Thus, herein, p-type NiO with various morphologies were synthesized using hydrothermal method, using different base precursors. Surface morphology analyses displayed NiO with platelets, nanoblocks, microspheres and nanorods structures, while Brunauer-Emmett-Teller surface area analyses showed surface areas of 79.19, 117.21, 70.47, and 20.98 m2/g, respectively. The colour changing from violet to blue emission with the transformation in morphology was observed from the Commission Internationale de I’Eclairage diagram. The deficiency in a material, such as nickel interstitials and nickel and/or oxygen vacancies were confirmed from photoluminescence and X-ray photoelectron spectroscopy. The performance of various NiO based sensors was evaluated in the presence of different vapours, at various bias voltages (0.25–2 V) and operating temperatures (25–150 °C). The NiO microsphere based sensor showed the best sensing characteristics towards propanol at an optimized applied bias voltage of 1 V and operating temperature of 150 °C. The NiO sensor derived from porous microspheres showed relatively maximum response values of 40 and 64% towards 60 ppm toluene and propanol vapours and rapid response/recovery times of 20 s/54 s (toluene) and 29 s/86 s (propanol) at the functional temperature of 150 °C. These findings showed that NiO sensors can be regarded as promising candidates for the identification of toluene and propanol vapours at relatively low operating temperatures with fast response/recovery times.Item Comparative study of graphene-polypyrrole and borophene-polypyrrole composites: Molecular dynamics modeling approach(2021) Folorunso, Oladipo; Hamam, Y; Sadiku, R; Ray, Suprakas S; Adekoya, GJIn the search for the solution to energy storage problems, this study investigates the interfacial energy interaction and temperature stability of the composites made of polypyrrole-graphene-borophene (PPy-Gr-Bon) by using molecular dynamics simulations. From the calculated thermodynamics and interfacial energies of the system, comparisons between the ternary and the binary-binary systems were made. The materials in the entity show a good degree of temperature stability to a dynamic process at 300, 350, 400, and 450 K. Moreso, at 300 K, the interaction energy of PPy-Gr, PPy-Bon, and PPy-Gr-Bon are: -5.621e3 kcal/mol, -26.094e3 kcal/mol, and -28.206e3 kcal/mol respectively. The temperature stability of the systems is in the order of: PPy-Gr-Bon > PPy-Bon > PPy-Gr. The effect of temperature on the interaction energy of the systems was also investigated. The ternary system showed higher stability as the temperature increased. In addition, the radial distribution function computed for the three systems revealed that there is a strong, but non-chemical bonding interaction between PPy-Gr-Bon, Bon-PPy, and Gr-PPy. By considering the excellent mechanical properties of PPy-Gr-Bon and the already established high electrical conductivity and chemical stability of Gr, Bon and PPy, their composite is therefore suggested to be considered for the manufacturing of electrochemical electrodes.