Chemistry

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Cadmium and lead thiosemicarbazide complexes : precursors for the synthesis of CdS nanorods and PbS nanoparticles
(2005) Mlondo, Sibusiso Nkosikhona; Revaprasadu, N.
This work reports the shape controlled synthesis of metal sulfide nanomaterials with varying morphologies using single source precursors based on the thiosemicarbazide ligand. The single crystal X-ray structures of [Cd(NH2CSNHNH2)CI2]n, [Cd(NH2CSNHNH2)2Cl2]n and [Pb(NH2CSNHNH2 )(N03)2] precursor complexes are reported and discussed. The non crystalline analogue of the cadmium complexes, [Cd(NH2CSNHNH2)2Cl2] was also synthesized and principally used to determine the effect of the precursor concentration and the growth temperature on the growth and final morphology of the CdS nanoparticles. The precursors were thermolysed in a hot co-ordinating solvent such as hexadecylamine (HDA) for CdS and tri-w-octylphosphine (TOPO) for PbS, using the "one-pot" single-molecule precursor route. The shape was found to move from short rods and dots to long rods at higher temperatures, where the growth is not easy to control. By contrast, at moderate temperatures the shape evolution was the opposite with the precursor concentration being the variation, as we moved from higher to lower concentrations. On the temperature variable's front, higher temperatures were found to favour the formation of shorter rods and dots whereas lower temperatures favour longer rods. By varying the important parameters such as precursor concentration and reaction temperature, various nanomaterials with a range of morphologies and sizes could be prepared. The effect of the nature of the precursor was also varied by synthesising nanoparticles from different crystalline complexes of the same metal (cadmium) and ligand (thiosemicarbazide) as precursors, which were found to give the nanoparticles of different crystallinity and aspect ratios. [Pb(NH2CSNHNH2 )(N03)2] was also used to synthesize PbS nanoparticles, in which determination shape control could not in be achieved. UV/Vis and photoluminescence spectra were used to study the materials optical properties of the material. The structural properties of the materials were studied by X-ray diffraction and TEM instruments.
Catalytic oxidation of cresols using molecular ozone
(University of Zululand, 2017) Ncanana, Zamani Siphephelo
Catalytic oxidation of cresols using molecular ozone. The environment, both in general and specifically our habitable segment is currently under threat from surfacing chemical pollutants that are generated mostly from pharmaceutical and industrial sectors. The extended use of cresols (meta-, ortho-, and para-cresol) in these sectors makes them potential pollutants and yet they are of hazardous nature to human, plants and animals. Therefore, the necessity to efficiently degrade these compounds is heightened and one of the reliable tools would be chemical oxidation, mainly advanced oxidation processes, which in this work refers to heterogeneously catalyzed oxidation of cresols using molecular ozone. The main objective of this study was to catalytically oxidize various cresol isomers using ozone. All oxidation reactions were studied as a function of time. Metal (Ni, Fe, Mn, V) loaded γ-Al2O3, SiO2 and V2O5 catalysts were synthesized by wet impregnation method. These catalysts were further calcined (300 oC) in air and characterized using powder X-ray diffraction (XRD), Fourier Transform-Infrared (FT-IR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) and Brunauer-Emmet-Teller (BET) surface area analyzer. These analytical techniques provided essential information about the catalysts, ranging from solid phase composition and purity, catalyst surface morphology, concentration of a loaded metal on a support to the specific surface area of the catalyst material. Prior to the application of these calcined catalysts in the oxidation of meta-, ortho- and para-cresol, a brief study of column mounted oxidation of cresols was done. A volume of 3.0 mL for each cresol isomer was adsorbed on pure γ-Al2O3 and SiO2, mounted on a vertical glass column and oxidized with O3 (0.123 mg/L) for 1, 3 and 5 h intervals. After each oxidation reaction, the samples were collected and dissolved in absolute ethanol. The resultant oxidation products were characterized using FT-IR and gas chromatography coupled with mass spectrometer (GC-MS), which separately provided data on functional groups that were introduced in the reaction and both percentage conversions & selectivities. Specific products that were identified include m-tolyl acetate (m-TA) and 2,3-dihydroxy toluene (2,3-DT) from m-cresol; o-tolyl acetate (o-TA) and 2,5-dihydroxy toluene (2,5-DT) from o-cresol; p-tolyl acetate (p-TA) and 3,4-dihydroxy toluene (3,4-DT) from p-cresol. Diethyl maleate (DM) and diethyl oxalate (DO) products were commonly found in all cresols oxidation. Column and reactor reactions yielded the same products of the respective cresol (m-, o-, p-cresol). Of all the products that were obtained, dihydroxy toluenes are the direct oxidation products of cresol whereas the rest are ethanol derivatised oxidation products. i.e. DM and DO were esterification products of maleic acid and oxalic acid, respectively. However, all products are termed „oxidation products‟ in this thesis for simplicity. Detection of these oxidation products laid preliminary grounds for the more traditional catalytic oxidation reactions. In a glass reactor (impinger), 25.0 mL of each cresol was ozonated in absence of a catalyst for 24 h and the obtained percentage conversions and selectivity results were used as reference data in catalyzed oxidations. The economically friendly pure activated charcoal was initially used as a catalyst (1% w/v charged) followed by pure supports viz. γ-Al2O3, SiO2 and V2O5 separately. Activated charcoal showed lowest efficiency than the pure supports and thus the attention was put on improving their activity by loading different metals on their surfaces. Catalytic activity of pure supports assumed the order of SiO2 > V2O5 > γ-Al2O3, with silica as the most active support. Moreover, the metal loaded catalysts were utilized in the oxidative degradation of cresols and 1% w/v of catalyst was used in all catalytic work. Of all γ-Al2O3 supported catalysts, Mn(2.5%)/γ-Al2O3 yielded highest conversion of m-cresol (70%) due to Mn species present on surface γ-Al2O3, whereas Ni(2.5%)/γ-Al2O3 showed highest percentage conversions of both o- (66%) and p-cresols (81%). Amongst metal loaded SiO2 catalysts, Fe(2.5%)/SiO2 was more active in the degradation of m- (81%) and o-cresol (70%) due to its relatively large surface area and presence of Fe in a form of catalytically active Fe2O3, while Ni(2.5%)/SiO2 degraded p-cresol (85%) the most. Mn(2.5%)/V2O5 catalyst converted most of m- (71%) and o-cresol (67%) to oxidation products whereas Fe(7.5%)/V2O5 relatively converted most of p-cresol (64%) to products which was promoted by Fe3O4 presence on V2O5 surface. The efficiency of metal loaded catalysts was decreased from SiO2 to V2O5 support. When supports (γ-Al2O3, SiO2, V2O5) were used as catalysts, there was an apparent improvement in product selectivity compared to uncatalyzed ozonation reactions. However, the use of metal (Ni, Fe, Mn, V) loaded supports as catalysts resulted in the decrease in product selectivities but significantly improved percentage conversions.
Chemical composition and biological potential of the volatile and non-volatile constituents of tarchonanthus camphoratus and tarchonanthus trilobus var galpinni of KwaZulu–Natal province.
(University of Zululand, 2013) Nanyonga, Sarah Kiwanuka; Oyedeji, O.A.; Opoku, A.R.; Lewu, F.B.
The chemical composition and the biological activities of the volatile extracts (essential oils) and non-volatile (solvent extracts) of the aerial parts Tarchonanthus camphoratus and Tarchonanthus trilobus var galpinni collected from Sangoyana and Ubombo respectively, in the Kwa-Zulu Natal province were investigated in this study. The essential oils were separately extracted from the fresh leaves, dry leaves and dry stem by hydro-distillation and their chemical constituents determined by Gas chromatography/mass spectrometry (GC/MS). The essential oils investigated were of the dry leaf of T. camphoratus harvested in 2009 and of the fresh leaf, dry leaf and dry stem of both T. camphoratus leaf and T. trilobus var galpinni harvested in 2010 and 2011. The compounds present in all the essential oils were categorised as monoterpene hydrocarbons, sesquiterpene hydrocarbons, oxygenated monoterpenes, oxygenated sesquiterpenes and others but they differed in the type and percentage composition. Sesquiterpene hydrocarbons dominated all the essential oils with β–caryophyllene and allo-aromadendrene present in all the essential oils either as minor or major compounds. The oxygenated monoterpene 1,8-cineole, which is suspected to be responsible for the camphor smell of T. camphoratus, was present in all the essential oils of the leaves and stem of T. camphoratus. δ-Cadinene, a sesquiterpene hydrocarbon, featured in all the essential oils except of the fresh and dry leaf of T. camphoratus harvested in 2011. The chemical constituents in the non volatile extracts were determined by Pyrolysis-Gas chromatography/mass spectrometry (Py-GC/MS). A variety of compounds categorised as hydrocarbons, tetraterpenes, triterpenoids, phenols, fatty acids, fatty alcohols, steroids and sterols among others were identified in the extracts. Phenols were identified in the aqueous, methanol, dichloromethane leaf extracts and the methanol bark extract of T. camphoratus and in the dichloromethane leaf and ethyl acetate leaf extracts of T. trilobus var galpinni. Steroids were identified in the bark extracts of T. camphoratus and in the methanol leaf extract of T. trilobus var galpinni. Hydrocarbons were identified in all the solvent/non volatile extracts but were more dominant in the dichloromethane bark extracts of both T. camphoratus and T. trilobus var galpinni. Triterpenoids were identified in the dichloromethane leaf extracts, ethyl acetate bark extracts of both species, in the methanol leaf of T. trilobus var galpinni and in the methanol bark extract of T. camphoratus. The preliminary phytochemical screening of the extracts also revealed the presence of phenols, flavonoids, saponins and tannins in some of the extracts. The volatile and non volatile extracts were screened for their antibacterial activity, antioxidant activity and cytotoxic activities and the volatile extracts were further screened for their insecticidal activities. The extracts were screened for antibacterial activity against 4 Gram positive and 5 Gram negative bacteria. The zones of inhibition of the fresh leaves, dry leaves and dry stem essential oils of T. camphoratus ranged from 7.3 – 14.0, 7.3 – 16.7 and 13.5 – 20.4 mm respectively and the zones of inhibition of the fresh leaf oil of T. trilobus var galpinni ranged from 8.2 – 21.8 mm. The volatile extracts exhibited higher percent inhibition than the non volatile extracts and the dry stem essential oil of T. camphoratus showed the highest antibacterial activity of all the extracts. The non volatile extracts exhibited significant antioxidant potential when tested by DPPH and ABTS•+ radical scavenging assays plus reducing power assay but showed poor nitric oxide inhibition and iron chelating ability. The volatile extracts generally showed poor antioxidant activity in all the antioxidant assays. The essential oils of both the dry leaf of T. camphoratus and fresh leaf of T. trilobus var galpinni showed the highest larval mortality of 100% which was observed at a concentration of 300 ppm after 24h whereas the lowest mortality after 24h was 20% at 25 ppm for T. camphoratus and 20% at 50 ppm for T. trilobus var galpinni. Insecticidal activity of the volatile extracts against stored product pests, S. zeamais and S. oryzae revealed a lack of contact and fumigation toxicity by essential oils of both plant species. The essential oil of the dry leaf of T. camphoratus, however, showed repellent activity of over 50% after 24h at all the concentrations used on both S. zeamais and S. oryzae. Cytotoxic investigation of the volatile and non volatile extracts revealed that the extracts generally had low toxicity. This study is the first to provide the chemical profiles and biological activities of the volatile and non volatile extracts of T. camphoratus and T. trilobus var galpinni from Kwa-Zulu Natal. The volatile extracts could be considered as potential alternatives, whether alone or in combination, to synthetic antibiotics, larvicides and repellents. The non volatile extracts on the other hand, could be potential sources of antioxidants that could have great importance as therapeutic agents.
Cobalt(III) complexes of a-w- diaminocarboxylic acids and chloroquine
(2001) Govender, kuvasani; Kolawole, G.A.; O'Brien, P.
a-w-Diaminocarboxylic acids, such as lysine and 2,3-diaminopropionic acid (2,3-DAPH), are trifunctional, and thus, when only two sites are available for coordination, an interesting question is posed as to which functional groups are utilised in chelation. A series of cobalt(III) complexes of the formulation [Co(en)2AA]2+, where en is ethylenediamine and AA represents lysine and DL-2,3-DAP, were prepared. In addition, complexes of the type [Co(AA)(AAH)Cl2] and [Co(AA)2]+, where AA is DL-2,3-DAP, have been synthesised. The compounds were characterised using elemental analysis, NMR, IR and electronic spectroscopy and mass spectrometry. The reaction of czs-[Co(en)2Cl2]Cl with lysine yielded two products notably, [Co(en)2(lys)]2+, within which lysine coordinates via the a-nitrogen and oxygen donor atoms, and [Co(en)3]3+. The reaction of c/s-[Co(en)2Cl2]Cl with DL-2,3-DAPH, however, yielded three products, viz. [Co(en)2(2,3-DAP)]2+, in which the glycinate portion of 2,3-DAP is involved in chelation, [Co(2,3-DAP)2]+ where 2,3-DAP acted as a tridentate ligand, and [Co(en)3]3+. In [Co(2,3-DAP)(2,3-DAPH)Cl2], one of the 2,3-DAP ligands coordinated via the two amino groups leaving the carboxylic acid group free whilst the second ligand coordinated via the glycinate portion leaving the terminal amino group free.
Coupling of single proton con_gurations to collective core excitations in 162Yb: the nucleus 161Tm.
(University of Zululand, 2017) Jongile, Sandile; Ntsh, S.S
There has been controversy over the past years as to whether deformed nu- clei are subject to quadrupole vibrations (gamma and _), particularly the _ vibrations. Pertaining the gamma K = 2+ vibrations, experimental evidence has been more or less consistent, confirming they indeed exist. On the other hand the situation remains complex for the _ vibrations which are charac- terized by the first low lying 0+2 excited state. Using a concept involving pairing it has been suggested that the K = 0+2 states are simply lowered into the pairing gap by configuration dependent pairing involving the [505]11=2􀀀 neutron orbital. In attempt to understand the true nature of the collective vibrations in relation to the \pairing theory" a suitable approach is studying nuclei in the N = 88 􀀀 90 region containing the [505]11=2􀀀 orbital. The current work seeks to get more insight on the microscopic nature of the aforementioned by studying the spectroscopy of 161Tm. The nucleus of interest 161Tm, was populated using the 152Sm(14N,5n)161Tm reaction with the aid of the AFRODITE array. The nucleus 161Tm is axially symmetric and it is a relatively good assumption that its core retains the same symmetry. As such the core will behave in a manner similar to that of a neighbouring even-even deformed nucleus. Therefore in this study we were searching for high K structures where the odd proton in 161Tm couples to collective excitations in 162Yb (the core) which has a very low lying K=2+ gamma band. The known level scheme of 161Tm has been extended at low spin with new transitions observed. Linear polarization measurements and Direct Correlations for Oriented states (DCO) ratios were performed to confirm the spin and parity assignments of old and new transitions. The semi-classical model together with alignments has been used to meaningfully describe the quantum behaviour of the collective structures observed in this work. Systematic comparisons have also been used to further understand the structural behaviour of band structures observed in this study. Furthermore experimental B(M1)/B(E2) values for bands involving the [505]11=2􀀀 orbital and other observed strong coupled bands were obtained to confirm quasi-particle configurations.
Deposition of CoxSy, NixSy MnS and CdS thin films from their alkylthiourea precursors using the Aerosol Assisted Chemical Vapour Desposition (AACVD) technique
(2008) Mgabi, Londiwe Patience; Revaprasadu, N.; Moloto, J.
Various complexes of Co (II), Ni (II), Mn (II) and Cd (II) thiourea and alkylthiourea have been successfully synthesized, using the 1:2 mole ratio metal salts of (NiCl^ C0CI2, MnCfe and CdCh) with their respective ligands. These complexes were characterized using melting points and elemental analysis to distinguish their monomelic character and confirm the purity of the complexes. Single X-ray crystal structures of [NiCl2(SC (NHC6Hn)2]2 and [MnCl2(CS(NH2)2)4] were obtained. Thermogravimetric studies on each complex were conducted to elucidate their volatility, for the deposition of thin films. Their decomposition patterns were found to yield predominantly a 2-stage TGA profiles with the resultant leading to the formation of the respective metal sulfide. Thin films were successfully deposited via the single source precursor method on glass and GaAs substrates by the Aerosol Assisted Chemical Vapour Deposition (AACVD) technique. Their lower volatility nature yielded less uniform deposition of thin films such that the substrate was changed as well the suspension of the substrate on the stubs with improved uniformity of the thin film. The respective metal chalcogenide thin films deposited were characterized by X-ray Diffraction (XRD) for their crystallinity, Scanning Electron Microscopy (SEM) for their morphological properties, Ultraviolet (UV) - Visible (Vis) spectra for their optical properties and Energy Dispersive X-ray (EDAX) for the composition of the films. Thin film measurement was performed using the Interferometer method. The X-ray diffraction pattern revealed different phases for the metal chalcogenide film, stoichiometric cobalt sulfide exhibited a mixture of cubic linnaeite C03S4 and cattierite C0S2, stoichiometric NiS, NiS2 (pyrite), |3- NiS (millerite), Ni3.xS2 and NiSi.97, Manganese sulfide revealed the presence of the a - alabandite phase and CdS showed the mixture of hexagonal and orthorhombic (300-350 C) and cubic phase at (400-450 C) respectively. Their morphological properties demonstrated the presence of mostly granulated spheres for the stoichiometric CoS, star-fish like rods for stoichiometric NiS, polycrystalline growth for the MnS films and mostly cubic and spore-like rods for CdS. Their absorption spectra revealed blue-shifted spectra with a mostly a higher optical band gap energy relative to that of bulk for all the metal chalcogenides. Thickness measurements showed that most thin films were deposited uniformly with minor contours and showed optimum adherence to the substrates.
Design, synthesis, and biological evaluation of Antimycobacterial agents from plant derived Betulinic acid, Oleanolic acid and their derivatives
(University of Zululand, 2015) Fadipe, Victor Olugbenga; Opoku, A.R.; Shode, O.O.O
Tuberculosis (TB) is a dangerous disease that has killed several millions of people globally in recent times. The available drugs for the treatment of the disease are not effective for complete cure and in most cases, usually come with side effects, as a result of which new set of potent drugs are needed. In a quest to develop potent hit/drug leads for TB, betulinic acid (BA) and oleanolic acid (OA) were isolated respectively from Curtisia dentata and Syzigum aromaticum. The 3-O- acetyl analogue of BA and OA were synthesized. The cinnamic acid conjugates at C-28 position of the four (4) synthesized compounds were all characterized using IR, MS and 1H and 13C NMR. Co-crystal compound synthesized from the isolated BA and OA with foremost first line antitubercular drug isoniazid (INH) was carried out for the first time. The co-crystal compounds were synthesized using three different conditions: I. Solvent evaporation method, II. Solvent drop method and III. Dry co-grinding method. The synthesized co-crystal compounds were characterized by P-XRD, TGA, and SEM. The isolated triterpenes and their synthesized derivatives were then evaluated for anti-mycobacterial activity (MABA test, against H37RV [ATCC27294] strain), cytotoxicity (MTT test using human embryonic kidney [HEK293] and human hepato-cellular carcinoma [HepG2] cell lines), and DNA polymerase β (pol β) inhibitor activity (with the POLB human ELISA kit). All the test compounds exhibited anti-TB activity, albeit to different levels of efficacy. The MIC values of the two pentacyclic triterpenes (BA and OA) against the mycobacterium ranged from >109.48 uM and 42.04 uM respectively. The acetylation of BA and OA at C-3 position did not observably improve their activity (MIC value of 39.70 uM and 100.26 uM) and neither did the cinnamic acid derivatives of BA and OA at C-28 position enhance the anti-TB activity (MIC value of >85.20 uM and 48.05 uM respectively). The di-substituted, 3-O-acetyl and 28- cinnamic acid ester of BA and OA however exhibited some enhanced anti-TB activity with MIC value of 17.88 uM. The co-crystallization of the triterpenes to INH drastically increased the efficacy of the triterpenes (MIC values in the range of 0.45 uM to 1.06 uM were obtained). The DNA polymerase β inhibitor activity of oleanolic acid and betulinic acid, their acetate derivatives, along with their cinnamic acid hybrid indicated that their inhibition of pol β was concentration dependent. The cytotoxicity of the test compounds to the two human cell lines (HEK293 and HepG2) was in the range of IC50 ≥ 300 μg, indicating low toxicity level. Conclusively, BA and OA may be explored as template for the syntheses of potent anti-TB drug hit/lead when combined with other compounds with known moderate anti-TB activity index.
Development of solvent extraction-gas chromatographic method for the identification and determination of polycyclic aromatic hydrocarbons and some related compounds in metallurgical factories
(1991.) Bache, Stewart Ian Richard; Weinert, C.S.
A method for the determination of polycyclic aromatic hydrocarbons (PAH) in carbonaceous materials and on particulate Batter produced in the atmosphere during the electrolytic reduction by various methods in the metallurgical industry is presented. The PAH are extracted into hexane with the aid of ultrasound, which is shown to be more efficient than the conventional Soxhlet thimble technique. Cyclohexane and hexane are shown to be more selective extractants for PAH than benzene or acetone. Hexane is preferred because it has a lower boiling point than cyclohexane. Three metnods of identification were investigated. These included thin-layer chromatography (TLCJ, gas chromatography (GO using retention times and indices and mass spectrometry (GC-MS). Hexane containing 2 % by volume of N.N -dimethylformaoide was used for the development of a thin-layer chromatograa. This resolved only ten of the twenty PAH investigated adequately. The non-polar OV-101 capillary column used in the GC-MS work did not resolve ten PAH well enough and the mass spectra did not assist in distinguishing overlapping peaks. The separation of individual PAH was optimised using a DB-5 wall-coated open tubular (WCOT) capillary column coupled to a flame ionisation detector. A splitless injection technique was used. Calculated retention indices normalised against four selected PAH. viz. naphthalene, phenanthrene. 1,2-benzophenanthrene and 1.2.6.7-dibenzan-thracene were used for the identification of unknown PAH and some related compounds. Problems encountered with this method of identification of some of the more strongly retained PAH are discussed. The program supplied by "DAPA Scientific (Pty) Ltd." was adapted for quantification of the identified PAH using 1.3,5-triphenylbenzene as internal standard. Suggestions for the adaption of the above analytical method to different matrices are presented.
Essential oil composition and some biological activities of tetradenia riparia
(University of Zululand, 2011) Khuzwayo, Joyce Khethiwe; Oyedeji, A.O.; Opoku, A.R.; Lewu, F.B.
This dissertation has a brief historical overview of medicinal plants, T. riparia and their traditional uses. The choice of the medicinal plant studied was based on the evidence in literature that oils of the species contain phenolic compounds and the herbs belonging to the family Lamiaceae was implicated in the management of chronic and infectious diseases. The study was designed to determine the secondary metabolites present in the plant through phytochemical screening of the plant material, establish the chemical profile of the isolated oils using GC-MS and evaluate the biological potential of both the crude extracts and the isolated oils which included; antioxidant, antibacterial and anti-ulcer activities. The essential oils were extracted from the dry stem and fresh leaves of T. riparia. Farnesol, caryophyllene oxide, -fenchyl acetate, and guaiol (12.3 - 7.1%) were the most prominent compounds identified in the dry stem oil collected from the botanic garden, Botany Department, University of Zululand (UZ). The analysis of the fresh leaf oil from the botanic garden collection had hexane as the major compound (60.9%), while -fenchyl acetate (6.7%), caryophyllene oxide (4.1%) and farnesol (2.5%) were other prominent components present in the oil. The dry stem oil from Maphumulo had farnesol (27.4%), humulene oxide (11.5%), -eudesmol (8.9%), caryophyllene oxide (3.8%) and terpinene-4-ol (3.35) as the main components, while the fresh leaf oil composition from Maphumulo was similar to that of botanic garden with hexane accounting for over 50% of the oil composition. Other prominent compounds identified in the GC-MS analysis of the fresh leaf oil were farnesol (6.3%) and a-thujone (3.6%). The chemical profiles of the T. riparia plant samples collected from two difference location within the KwaZulu-Natal suggest two distinct chemotypes of the plant species. Nonetheless, farnesol was found to be the major constituents of all the oils parts isolated. To the best of my literature knowledge and search, this is the first time that the chemical composition of the essential oils isolated from the leaf and stem of T. riparia is been reported. The phytochemical screening of the plant reveals saponins (23.3%), flavoinoids (3.7-4.9%) and tannins (4.1%) to be prominent secondary metabolites presence. These compounds are known to exhibit anti-ulcer activities. Indeed, a 65% inhibition of indomethacin-induced gastric ulceration was observed for the plants essential oil. The antibacterial activity studies indicated that the oil had moderate inhibitory effect on most of the bacteria. Zones of inhibition, from the disc diffusion assay of the essential oil, ranged from 6.3- 19.3 mm. The minimum inhibitory concentration (MIC) value of 0.157 mg/ml was recorded for the dry stem oil extracts from Maphumulo. The results from the biological assays showed that there is good correlation with the traditional usage of T. riparia. The results are explained fully in the body of the dissertation. The limitation for this work is that the isolation of essential oil compounds using Preparative GC was not possible as the equipment though available was not functional due to some technical unresolved issues.
Establishment of the relationship between the sediments mineral composition and groundwater quality of the primary aquifers in the Maputaland coastal plain
(2010) Mkhwanazi, Millicent N.; Kolawole, G.A; Kelbe, B.
The Maputaland coastal plain has the largest primary aquifers in South Africa. It has highly permeable sediments that promote rapid recharge to the aquifers and strong interactions with wetlands in the region. The hydrochemical study of the Richards Bay aquifers suggested that there is rising levels of dissolved minerals in the Science Center aquifer. This study was designed to determine the relationship between sediment mineral composition and the groundwater quality of the selected primary aquifers of the Maputaland coastal plain. The aquifers of interest were classified into Cretaceous, Miocene, Pleistocene and Holocene Units, depending principally on a specific type of rock Formation penetrated during the drilling process. The sediments of the aquifers were classified into the Kwambonambi, Sibaya, Kosi Bay, Port Durnford, Uloa and St Lucia Formations, according to the established lithological Units, using the grain size, texture and colours of the sediments. Water samples taken from the boreholes were assumed to represent all aquifers intersected during the drilling process. Maputaland aquifers are low in potassium, sulphate and magnesium ions. Sodium and chloride ions remain unevenly distributed throughout the entire selected Maputaland coastal plain aquifers. The Miocene Unit is characterized by two chemical signatures, calcium and bicarbonate ions dominance and sodium, calcium and bicarbonate ions dominance. The Pleistocene Unit is characterized by three chemical signatures, sodium and bicarbonate ions dominance, calcium and bicarbonate ions dominance and sodium and chloride ions dominance. The Holocene Unit is characterized by two chemical signatures, sodium and chloride ions dominance and calcium and bicarbonate ions dominance. The Richards Bay sediments of the shallow Units are predominantly acidic with high clay minerals, while the deep Units are mostly neutral or alkaline. It was concluded that the sediments in the shallow aquifers are acidic due to high rainfalls that leaches calcium and carbonate ions from the sediments resulting in weathering of the sediments to high clay minerals. Sodium and chloride ions were assumed to be contributed by marine sediment deposits, coastal-influence precipitation or direct recharge from surface water resources. These ions are exchanging sites with calcium and bicarbonate ions resulting in sodium and chloride ions dominance. Although the groundwater quality of the Maputaland region has elevated total dissolved solids with unevenly distributed sodium and chloride ions, low calcium and bicarbonate ions in the shallow aquifers, the chemical composition of the groundwater is still suitable for potable purposes, except in areas where the pH is low with elevated dissolved ferrous, fluoride, aluminium and manganese ions.
Extraction of cellulose from SCB and its applications in CNC/metal nanocomposites
(University of Zululand, 2018) Mzimela, Zimele N.T.; Revaprasadu, N.; Motaung, T.E.
The past few years have seen an increased interest in enforcing the principles of green chemistry in the scientific community. The aim of these principles is to reduce chemical related impacts on human health and virtually eliminate contamination of the environment through dedicated and sustainable prevention programs. In the present study, of the many (12) green chemistry principles, we have put into implementation waste prevention, the use of safer solvents and/ or auxiliaries in syntheses, and the use of less hazardous chemicals in syntheses by undertaking a project that makes use of sugarcane bagasse, which is an agricultural waste material obtained when sugarcane is crushed to extract its juices during the production of sugar. From bagasse, cellulose was extracted through five different methods. Through acid hydrolysis, cellulose nanocrystals were synthesised from the extracted cellulose and in turn used as a template, reducing- and stabilizing agent in the synthesis of cellulose nanocrystal/metal (silver and gold) nanocomposites. The fifth cellulose-extraction method yielded the most thermally stable and pure cellulose. This was shown by TGA and XRD analyses. As a result, the cellulose extracted through the fifth method was used to synthesize cellulose nanocrystals, which were then successfully used as a stabilizing and reducing agent in the formation of CNC/metal nanocomposites, as evident from FTIR, TGA, XRD, UV and TEM analyses.
A facile hybrid method to synthesize metal and metal chalcogenide nanoparticles using various capping groups
(2014) Mntungwa, Nhlakanipho; Revaprasadu, N.; Pullabhotla, V.S.R. Rajasekhar
The synthesis of bismuth (Bi), antimony (Sb) and tin (Sn) metal and metal chalcogenide nanoparticles is presented using a novel hybrid solution based high temperature method. Furthermore is the synthesis of zinc telluride (ZnTe) and cadmium telluride (CdTe) nanostructured materials also described. The nanomaterials are predominantly capped by organic ligands. The use of water soluble ligands such as triethanolamine (TEA) and cysteine is also reported. The synthetic method involves the reduction of a metal salt followed by the introduction of the chalcogenide source in the case of metal chalcogenide nanoparticle synthesis. The metal or metal chalcogenide prepared is thermolysed into a high boiling point ligand at high temperature. For the water soluble nanoparticles after reduction there is a simultaneous addition of a chalcogenide source and a ligand at room temperature. The Bi and Sb nanoparticles showed similar spherical morphology when capped with tri-noctylphosphine oxide (TOPO). Bismuth particles in the form of dots, branched nanorods and self assembled cubes were obtained at different reaction conditions. The cubed shaped Bi and Sb nanoparticles which appear to self-assemble were obtained when using oleylamine (OA) as a capping group. The Bi2S3, Bi2Se3 and Bi2Te3 nanoparticles were elongated when capped using alkylamines such as hexadecylamine (HDA) and OA, however at low temperature of 90oC they appeared to be close to spherical. The antimony chalcogenides, Sb2S3, Sb2Se3 and Sb2Te3 gave a similar rod shape morphology. The Sn nanoparticles appeared aggregated to some extent. A triangular shaped morphology is observed for the OA capped SnS nanoparticles. HDA capped ZnTe nanoparticles were synthesized using NaHTe and ZnCl2 as the tellurium and zinc sources respectively. The particles synthesized at reaction temperatures of 230 oC and 270 oC were spherical in shape. The blue shift in the absorption spectra confirms that the particles undergo quantum confinement. The photoluminescence studies show that the particles emit at a wavelengths close to their band edge. The water soluble cysteine and TEA capped ZnTe particles appear as nanorods which are aggregated. Finally water soluble CdTe nanoparticles were synthesized using TEA and cysteine as capping groups. The results showed that both cysteine and TEA are effective capping groups for water soluble CdTe nanoparticles. The optical properties of the particles synthesized in both capping groups revealed absorption features due to the Cd-ligand complex. The photoluminescence spectra showed reasonably narrow emission peaks. The cadmium salt was varied to study its effect on the morphology of the CdTe nanoparticles. The nitrate source gave well defined, crystalline, close to spherical nanoparticles. The FT-IR measurements confirmed the presence of the capping ligand on the surface of CdTe nanoparticles.
Indium-based thiospinels via solid-state pyrolysis of metal-organic precursors for water splitting and supercapacitance
(University of Zululand, 2023) Mzimela, Zimele N. T.; Revaprasadu, Neerish and Khan, Malik D.
The ever-increasing global energy demands emanating from population growth and technological advancements have propelled the research community into modelling plausible breakthroughs in the fabrication of electrochemical energy storage and conversion technologies with improved performances. As a result, the past few years have witnessed significant developments in the synthesis of electrode materials with refined electrochemical activities for water splitting and supercapacitance applications. The work outlined in this thesis focuses on the synthesis and evaluation of various indium-based thiospinel nanomaterials for enhanced electrochemical energy applications. Firstly, a comparative evaluation of the energy application capabilities of bare and oleylamine-capped NiIn2S4 nanosheets fabricated from dithiocarbamate and xanthate molecular precursors is outlined. Experimental results showed that the best energy storage activities were achieved with NiIn2S4 synthesized from the xanthate mixture through the colloidal route, which presented the highest Csp of 40 F/g at a current density of 0.5 A/g. In terms of electrocatalysis for water splitting, the highest performance was observed for NiIn2S4 synthesized from the xanthate mixture through the solventless thermolysis route, which presented an HER performance with an η of 138 mV at 10 mA/cm2 and a Tafel slope of 118 mV/dec. In terms of OER performance, an η of 382 mV at 10 mA/cm2 was obtained along with a Tafel slope of 145 mV/dec. Furthermore, the scalable fabrication of compositionally-tuned Ni1-xCoxIn2S4 solid solutions through the solventless thermolysis approach is outlined. All the alloyed nanomaterials outperformed the parent compounds in terms of both supercapacitance and water splitting applications. The best OER electrocatalytic performance was obtained when x = 0.6, which displayed an overpotential of 340 mV at 10 mA/cm2 along with a Tafel slope of 87 mV/dec. In terms of HER, the highest performance was obtained when x = 0.2, which reached an overpotential of 110 mV and a Tafel slope of 176 mV/dec. For supercapacitance applications, the nanoparticles synthesized at x = 0.8 yielded the highest specific capacitance of 118 F/g at 1 A/g, along with a maximum power density of 3450 W/kg at an energy density of 2.4 Wh/kg. The work also dwells into the amplification of the electrochemical properties of MnIn2S4 through the fabrication of Mn0.5M0.5In2S4 (where M= Ni/Co) solid solutions/alloys via the solventless thermolysis of compositionally-tuned xanthate precursors. Experimental results showed that the Ni2+ and Co2+-modified MnIn2S4 outperformed pure MnIn2S4 for both water splitting and supercapacitance applications. Overall, Mn0.5Co0.5In2S4 displayed the best electrocatalytic water splitting and supercapacitance activities amongst all the synthesized nanomaterials. We further describe the synthesis of Cd1-xZnxIn2S4 composites and their subsequent evaluation for electrochemical water splitting and supercapacitance applications. Structural analyses revealed the formation of cubic and hexagonal CdIn2S4 and ZnIn2S4 thiospinels with the Fd3m and P63mc spacegroups, respectively. Furthermore, a range of stoichiometric nanostructured composite materials, whose diffraction patterns are located between those of the two thiospinels were formed between x = 0.2 and x = 0.8. Morphological evaluation showed the formation of nanosheets. All alloyed materials displayed improved supercapacitive properties, with Cd0.2Zn0.8In2S4 achieving the best results. In terms of electrocatalytic hydrogen generation, the alloyed materials displayed lower capabilities than the parent compounds. Evidently, the ternary thiospinels, solid solutions and composite nanomaterials displayed improved performances for water splitting and supercapacitance applications. This is primarily due to the synergistic effects arising from the influence of different elements. Other factors, such as the morphology proved to play a significant role in the suitability of the materials for electrochemical water splitting and supercapacitance.
Investigation of chemical constituents, antimicrobial and antioxidant activities; and pharmacognostic characters of the leaves of momordica foetida and berkheya bergiana
(University of Zululand, 2010) Odeleye, Olukayode Michael; Opoku, A.R.; Oyedeji, O.A.
This research work was aimed at the isolation, structural elucidation and pharmacological evaluation of the chemical constituents of M. foetida (Cucurbitaceae) and B. bergiana (Asteraceae) and to determine the pharmacognotic profile of the plants. Phytochemical screening of the crude ethanol extract of Momordica foetida revealed the presence of alkaloids, flavonoids, terpenoids, steroids, saponins and tannins while that of B. bergiana had flavonoids, terpenoids, saponins and tannins as their major secondary metabolites. Six compounds were isolated from the various solvent extracts of the two plants, various chromatographic techniques were employed for the fractionation and purification of the isolates. Spectroscopic methods NMR, IR, MS were employed for the structural elucidation of the compounds. The NMR spectral pattern of four of the isolates suggests a triterpenoid based compound with the characteristics C30 carbon content. With the aid of the 1D and 2D NMR, MS and IR, these four compounds were identified as 3β,7β,25-trihydroxycucurbita-5,(23E)-dien-19-al; 3β,7β-dihydroxy-cucurbita-5(23E),23,25-triene-19-al; 3β-hydroxylup-20(29)-ene and lup-20(29)-en-3β-ol-1α-yl-acetate. The remaining 2 isolates were also identified with the help of full house NMR and Mass spectroscopy to be Kaempferol-3-O-β-D-glucopyranoside and 4-hydroxy-3-methoxy-benzaldehyde.Although Kaempferol-3-O-β-D-glucopyranoside has been reported isolated from Tephrosia calophylla and Clitoria ternatea, this is the first time that it is being reported and isolated from any Momordica species. Furthermore, the isolation of 3β,7β,25-trihydroxycucurbita-5,(23E)-dien-19-al and 3β,7β-dihydroxy-cucurbita-5(23E),23,25-triene-19-al is noteworthy because of the unique position of hydroxyl group at position 25 and the chromophore conjugation at position 23-25. These two compounds have not been reported isolate from M. foetida before. In-vitro antimicrobial activities of the crude extract and five solvent fractions were screened against 32 bacterial strains using disc diffusion and microplate dilution methods. Ethyl aceate fractions of M. foetida exhibited the highest broad spectrum antibacterial activity against the tested bacteria. The antibacterial activity followed the order: of ethyl acetate > butanol > chloroform > aqueous > hexane fraction at a 5.0 mg mL-1. The minimum inhibitory concentration (MIC) of M. foetida exhibited by the five fractions against the bacterial strains ranged between 0.156 and 5.0 mg mL-1. Chloroform extract of B. bergiana, exhibited the highest broad spectrum antibacterial activity against the tested bacteria and decreased in the order chloroform > ethyl acetate > butanol > hexane > aqueous extract at a concentration of 5.0 mg mL-1 while the minimum inhibitory concentration (MIC) of B. bergiana exhibited by successive extracts range between 0.078 mg mL-1 and 5.0 mg mL-1. Antioxidant activity of the extracts and fractions were investigated using four antioxidant assays namely DPPH, ABTS radical scavenging effect, reducing power and metal chelating effect on iron(II) ion. Total phenol, flavonoid and proanthocyanidin contents were also estimated. This study showed that M. foetida and B. bergiana possess substantial antibacterial and antioxidant potentials. They may be good potential drugs in the treatment of infection-related diseases because of their antibacterial activity. The antioxidant activity exhibited by the plants also provides a rationale for the ethnomedical use of the plants for the treatment of inflammation, neurodegenerative and cardiovascular disease conditions in traditional medicine.
Metal(ii) schiff base complexes and the insulin-mimetic Studies on the oxovanadium(iv) complexes
(2009) Nejo, Adeola Ayodeji; Kolawole, G.A.; Opoku, A.R.
Sixteen symmetrical and four unsymmetrical tetradentate Schiff bases with the N2O2 chromophore were isolated in pure form and fully characterized by elemental analyses, melting point, IR and 1H NMR. The appearance of two different peaks for each of the azomethine protons and phenolic protons confirm the asymmetry nature of the unsymmetrical Schiff bases. All the Schiff bases were successfully coordinated to oxovanadium (IV) ion to form the corresponding complexes. The unsymmetrical Schiff bases were also successfully coordinated to cobalt(II), nickel(II) and copper(II) ions to form their corresponding complexes. In all thirty-two metal(II) Schiff bases complexes were isolated. These complexes were characterized by elemental analyses, melting point, IR, EPR, cyclic voltammetry, magnetic susceptibility measurements, differential scanning calorimetry and electronic spectra. The isolation of the unsymmetrical tetradentate Schiff bases and their complexes as well as some of the symmetrical tetradentate Schiff bases and their complexes are considered to be novel. The purity and composition of both the Schiff bases and the metal (II) complexes were established by elemental analyses. The comparison of the IR spectra of the Schiff-bases and their metal complexes indicated that the Schiff bases acted as tetradentate ligands. The observed shifts in the stretching frequencies of (C=N) and (C¯O) are indicative of the formation of these complexes. Further conclusive evidence of the coordination of these Schiff-bases with the metal ions was shown by the appearance of new bands due to (M¯N) and (M¯O) in the metal complexes. Most of the oxovanadium (IV) complexes exhibit a strong band in the range 959−989 cm−1, which have been assigned to (V=O) in a monomeric square pyramidal coordination environme oxovanadium (IV) complexes with trimethylene bridge, in which their (V=O) appeared at 848−860 cm.1, have been assigned polymeric structure with [V=O∙∙∙•V=O] interactions, which afforded distorted octahedral coordination geometry. The electronic spectral and magnetic susceptibility measurements were used for assigning the stereochemistry of each metal complex. Electronic spectra indicate a square-planar geometry for all the cobalt(II), nickel(II) and copper(II) complexes. This was also corroborated by the effective magnetic moment of the complexes. The electronic spectra of the oxovanadium ( IV) complexes suggest a diversity of geometries. The electronic spectra indicate a square-pyramidal geometry for the fivecoordinate species and distorted octahedral geometry for the six-coordinate species. The room temperature magnetic moments of 1.6.1.8 BM are normal for V(IV) d1 configuration. The solution EPR spectra of the oxovanadium ( IV) are consistent with square pyramidal geometry. The cyclic voltammetry of the oxovanadium ( IV) complexes revealed only one quasi-reversible wave for each complex and they all showed redox couples with peak- to peak separation values ( Ep) ranging from 74 to 83 mV, indicating a single step one electron transfer process. In vitro glucose uptake was carried out on all the oxovanadium (IV) complexes using C2C12 cell line. All the complexes tested increased glucose utilization in C2C12 cells over basal values except two of the complexes whose percentage glucose uptake was lower than the basal glucose uptake (DMSO). Eighteen of the complexes significantly increased glucose uptake when compared to the basal glucose uptake of the solvent vehicle (DMSO). Cytotoxic test carried out on all the complexes using M at both low and high concentrations. Two of the complexes showed activities comparable or greater than that of insulin. Four unsymmetrical and five symmetrical Schiff base complexes of oxovanadium(IV) have been tested in vivo for their insulin mimetic activities. An acute oral administration of the four unsymmetrical Schiff base complexes of oxovanadium (IV) elicited a progressive reduction in plasma glucose over 6 h in STZ rats. Two of the unsymmetrical Schiff base complexes of oxovanadium( IV) induced a significant reduction in plasma glucose over a 6 h period. Oral administration of the five symmetrical complexes also elicited a progressive reduction in plasma glucose over 6hrs. Two of these complexes induced a significant reduction in plasma glucose during the 6 hour period.TT assay showed that the complexes were not toxic to the cells.
A new approach to the synthesis of selenium based nanoparticles
(2008) Oluwafemi, Samuel Oluwatobi; Revaprasadu, N.
We report the synthesis of high quality aqueous and organically soluble selenide nanoparticles by a novel greener, quick, facile, environmentally-benign and effective non-organometallic solution-based method. Briefly, the method involves the reduction of selenium powder to produce selenide ions which act as the selenide source, followed by the addition of MCI2 (M = Cd or Zn) or Zn(CH3COO)2. The nanoparticles were passivated with organic surfactants such as hexadecylamine (HDA) and tri-octylphosphine oxide (TOPO), for their solubility and stability in organic solvents, while passivation with biomolecules such as L-cysteine ethyl ester hydrochloride, methionine, ascorbic acid, starch, polyvinyl alcohol (PVA) and poly (vinylpyrroiidone) (PVP), rendered them water-soluble and aJso acted as an agent of stabilisation and facilitate conjugation with biomolecules. CdSe/ZnSe nano-composite and core-shell nanoparticles were also synthesised, using this new synthetic approach. The high quality of the as-synthesised nanoparticles was confirmed using absorption and photoluminescence spectroscopy (PL), Fourier transform infrared spectroscopy (FT-ER), powder x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area dififractometry (SAD) and energy dispersive spectroscopy (EDS). All measurements were performed without any post-preparative size separation of the nanoparticles. The thesis is divided into six chapters. Chapter one deals with the introduction and comprehensive review on previous works done on the synthesis of nanoparticies, VIII highlighting their advantages and disadvantages. The aim and objective of the study is also stated in this chapter. In chapter two, the systematic study of the effects of the capping group, growth time, temperature, reduction time and monomer concentration on the size, optical properties and morphology of the as-synthesized TOPO and HDA-capped CdSe nanoparticles was investigated. All the as-synthesised particles are blue-shifted in relation to the bulk band-gap of CdSe. The absorption and emission maxima are shifted to higher band-gap (lower wavelengths) as the reduction time increases from 2 to 6 hrs, indicating a decrease in particle size for the HDA-capped CdSe. The particle size ranges between, 2.3-3.2 (5-30 mins) 2.4-3.0 nm (5 -30 mins) and 2.5- 2.7 nm (15-30 mins) for the reduction time of 2,4 and 6 hrs respectively. At higher temperature (200 °C), particles with different shapes, i.e dot, rod and multi armed rods are produced. The presence of the elongated particles was attributed to the phenomenon of oriented attachment (self-assembly), due to dipole-dipole interactions between the highly charged surfaces of II-VI semiconductor nanocrystals. The synthesis of TOPO and HDA-capped ZnSe nanoparticles were investigated in chapter three. Increasing the monomer concentration and temperature, led to a faster growth rate, increase in particle sizes and narrowing of the size distribution. XRD analysis show phase transitions from sphalerite cubic to wurtzite hexagonal phase, on increasing the monomer concentration. The mean average particle diameters are, 3.71 ± 0.40 run 3.26 ± 0.37 nm and 2.95 ± 0.32 nm for the reduction time of 2. 4 and 6 hrs respectively. Chapter four describes the synthesis of water-soluble CdSe and ZnSe nanoparticles. The synthesis was carried-out at elevated and room temperatures, using biomolecules and polymers as passivating agents. A systematic study of the effects of parameters such as pH, reaction time, concentration, refluxing time, reactant ratio, passivating ligand and temperature on dispersibility, size, optical properties and morphology of the nanoparticles, was also investigated. At elevated temperature, the particle size decreases while the luminescence properties improve with increasing pH. Increasing the cadmium to cysteine ratio systematically from 1:10 to 1:60 at different pH, did not have any significant effect on the luminescence intensity of the nanoparticles. In contrast to the synthesis at higher temperature, particles with very sharp excitonic shoulders, absorption edges and high luminescence with narrower size distributions, are produced at room temperature. Particles with the first absorption peak at a wavelength as low as 415 nm, with a clearly resolved higher energy electronic transition, high luminescence without trap emission and particles size as small as 1.68 nm are obtained at pH 11. The synthesis and characterisation of highly monodispersed HDA-capped CdSe-ZnSe nanocomposites and CdSe/ZnSe core/shell nanoparticles were reported in chapter five. The study of the core/shell growth at different reaction times and the effect of temperature on the optical and structural properties, was also investigated. The absorption and emission maxima of the CdSe/ZnSe core/shell nanoparticles are red-shifted in relation to the core CdSe, with a visible second absorption band at higher temperature (250 °C). The emission spectra confirmed that separate ZnSe nanoparticles are not formed in the solution. XRD analysis indicates that the diffraction is predominantly due to the CdSe core. The average particle diameter of the CdSe/ZnSe are 3.99 ± 0.16 nm (230 °C) and 4.51 ± 0.27 run at 30 mins reaction time. The absorption and emission maxima of the CdSe-ZnSe nanocomposite are blue-shifted in relation to pure CdSe, with a small particle size (2.91 ± 0.20 nm) as compared to the core CdSe (3.00 ± 0.24 nm). The XRD analysis shows a phase transition from the hexagonal phase of the pure CdSe to the cubic phase. Chapter six gives a short description of the experimental details. Without any further post preparation, the qualities of the particles formed by this new method, are comparable to that of the best CdSe and ZnSe nanocrystals reported in literature, synthesised by the high temperature conventional organometallic methods. This new synthetic route is safe, inexpensive, involve the use of non-toxic chemicals, reproducible and can be readily used for large scale synthesis. We believe the knowledge gained from this work, will enable the direct green synthesis of functionalised organic and water-soluble selenide nanoparticles for large-scale production and commercial purposes, due to the economical and environmentally-benign nature of the synthetic method.
Nickel and cobalt sulfide nanomaterials for magnetic and energy applications
(University of Zululand, 2018) Gervas, Charles; Revaprasadu, N
This thesis reports the symthesis of five metal complexes, namely bis(piperidinylldithiocarbamato)nickel(II) (1), bis(tetrahydroquinolinyldithiocarbamato)nickel(II) (2), bis(N’-ethyl-N-piperazinyldithiocarbamato)nickel(II) (3), tris(morpholinodithiocarbamato)cobalt(III) (4) and tris(N’-ethyl-N-piperazinyldithiocarbamato)cobalt(III) (5). These heterocyclic dithiocarbamate complexes have been characterised using common techniques such as Fourier Transform Infrared spectroscopy, elemental analysis and nuclear magnetic resonance spectroscopy. Nuclear magnetic resonance spectroscopy measurements were not conducted for complexes, due to their paramagnetic behaviour which adversely interferes with the technique. Single-crystal X-ray diffraction was used instead, which aided in the accurate elucidation of novel chemical structures of the complexes. Three complexes were characterised using the technique; the chemical structures of the rest are already known in literature. Generally, dithiocarbamate complexes have been identified as compounds of technological importance, particularly as single-source molecular precursors for the fabrication of nanomaterials for widespread applications. However, interest has mainly been on alkyl derivatives. Thus, this thesis focuses on the use of heterocyclic dithiocarbamates complexes as single-source molecular precursors for the fabrication of the corresponding metal sulfide thin films and nanoparticles through thermal decomposition routes. Thermal decomposition of the complexes (1)-(5) produced Ni-S, Co-S and Ni-Co-S nanoparticles and thin films which exhibited interesting morphological and optoelectronic properties. The above-mentioned systems were particularly chosen for their increased interest in magnetism, as well as energy generation and storage applications. In this thesis, the nature of the complexes and other reaction parameters were demonstrated to have an influence on the particle size, morphology, and phase purity of the nanoparticles and thin films produced. These properties have a profound impact on the efficiency of the nanoparticles and thin films, towards specific applications. The work presented in chapter two aimed at establishing reactions protocols suitable to to produce good quality nanoparticles using the solvent thermolysis approach. The complexes (1), (2) and (3) afforded NixSy nanoparticles displaying various morphologies (spheres, rods, irregular tetrahedral, nanospheres and irregular shapes) which were identified mainly by the x transmission electron microscopy imaging technique. Furthermore, it was discovered that docecylamine and hexadecylamine capping agents produced phase pure Ni3S4 and Ni3S2, respectively; phase identification was conducted using the powder X-ray diffraction technique. On the contrary, oleylamine capping agent produced mixed phase NixSy nanoparticles from complexes (1) and (2) while complex (3) afforded phase-pure Ni3S2. Magnetic measurements identified Ni3S4 and Ni3S2 nanoparticles to possess ferromagnetic and paramagnetic behaviours, respectively. Chapter 3 reports the deposition of thin films using the same three complexes by the aerosol-assisted chemical vapour deposition method; NiS phase thin films were predominantly formed. The scanning electron microscopy imaging technique showed the films to display various morphologies. Chapter 4 focuses on the catalytic evaluation of Co3S4 nanoparticles (with minor CoS2 impurities) in the oxygen evolution reaction (OER), hydrogen evolution reaction reaction (HER) and supercapacitance applications. The nanoparticles were prepared from complex (4) by a facile olelylamine-mediated hot injection method. The OER catalytic performance of nanoparticles prepared at 230 ºC and 260 ºC showed the overpotential of 307 mV and 276 mV, respectively. The specific capacitance and specific stability for the nanoparticles prepared at 230 ºC are 298 F/g and 73%, respectively. Nanoparticles prepared at 260 ºC achieved 440 F/g and 97%. The efficiency was measured after 5000 cycles. These results indicated that the prepared materials are good candidates for efficient energy generation and energy storage devices. Chapter 5 reports the use of complexes (3) and (5) as dual precursors for the Ni-Co-S ternary material. Though thiospinels structure show interesting catalytic and energy storage applications, the cationic disorder can have major influence on the energy generation and/or energy storage applications. In this work, the effect of stoichiometric variation of metals in a thiospinel i.e. NixCo3-xS4 was examined on energy generation and storage properties. Nickel or cobalt-rich NixCo3-xS4 nanosheets were prepared by the oleylamine-mediated hot injection method. It was observed that nickel-rich and cobalt-rich nanosheet have different performances when tested for OER and HER, as well as supercapacitance performance. It was observed that the nickel-rich NixCo3-xS4 nanosheets have superior energy generation and storage properties.
Novel Precursors for the Synthesis of Metal Selenide Nanoparticles, Thin Films and Alloys
(University of Zululand, 2018) Khan, Malik Dilshas
Metal selenides are important semiconducting materials and are highly useful in various electronic and/or thermoelectric devices. Different synthetic protocols are available for preparation of metal selenide nanoparticles and/or thin films. Nonetheless, the use of single source precursors is usually advantageous, as they can be used for the synthesis of metal chalcogenide nanocrystals, and are equally suitable for the deposition of thin films. Furthermore, a better control over stoichiometry and phase can be achieved, due to preformed bonds between metal and chalcogen atom. Numerous sulfur based single source precursors have been used successfully for synthesis of variety of metal sulfide nanoparticles and/or deposition of thin films. However, the use of single source precursors with higher chalcogeno congeners, are not well explored. The prime reason is the difficulty in the synthesis of Se/Te based precursors. Only a limited starting material is available and that too are usually highly toxic, such as, phosphines and/or carbon disulfide. Hence, a facile synthetic route, using comparatively less toxic aterials, is highly desired for the synthesis of selenium containing molecular recursors. In this thesis, we have introduced a new one-pot synthesis of metal (Bi, Sn and Sb) selenobenzoate complexes and established their suitability for the synthesis of respective metal selenide nanoparticles, thin films and alloys. The thesis is divided into seven chapters, in which the first chapter gives a comprehensive literature review of all the selenium based single source precursors used until the present for the synthesis of metal selenide nanocrystals and/or thin films. The second chapter describes the synthesis of selenobenzoate ligand and its antimony complex i.e. tris(selenobenzoato)Sb(III) complex. The crystal structure of the complex was elucidated and the complex was used as a suitable single source precursor for the synthesis of Sb2Se3 nanorods by hot injection method and thin films were deposited by the aerosol assisted chemical vapor deposition (AACVD) method. The nanorods synthesized by colloidal method were used for water splitting application. In third chapter, the similar synthetic strategy was used to prepare tris(selenobenzoato)Bi(III) complex and the decomposition of the molecular precursor by hot injection method yields Bi2Se3 nanosheets. Thin films were also deposited at different temperatures on glass substrates and the water splitting efficiency of the oleylamine capped nanosheets was investigated. Both Sb2Se3 and Bi2Se3 shows p-type behavior as cathodic currents were observed for both materials. Similarly, the fourth chapter entails the detail about the use of bis(selenobenzoato)Sn(IV) for the deposition of SnSe thin films and nanosheets. The electrochemical studies indicate bifunctional behavior and the material can behave either as cathodic material and/or anodic material by changing the voltage. In chapter 5 and 6, thio- analogues of bis(selenobenzoato)Sn(IV) and tris(selenobenzoato)Sb(III) i.e. bis(thiobenzoato)Sn(IV) and tris(thiobenzoato)Sb(III) complexes were synthesized and mixture of both chalcogeno- complexes were used to prepare solid solutions (Sb2(SxSe1-x)3 and SnSxSe1-x) in entire range with excellent stoichiometric control. Sb2(SxSe1-x)3 was prepared by colloidal route using oleylamine as solvent and capping agent, band gap tuning was observed. For SnSxSe1-x solid solution, in addition to colloidal synthesis, solvent-less route was also used and the effect of both routes on structural behavior was investigated. Chapter 7 gives a brief summary of all the chapters and the potential future research plan.
Photochemical synthesis and characterization of mono- and bi-nuclear tungsen tetracarbonyl complexes of 2,2'-biquinoline and 2,3-bis(2- pyridyl) pyrazine
(2002) Musetha, Phumudzo Luvhengo; Kolawole, G.A.
The mononuclear and binuclear complexes of the type [W(CO)4JL] and [{W(CO)4}2]L, where L= 2,3-bis(2-pyridyl)pyrazine(BPPX 2,2' -biquinoline^QN), 2,2,-bipyrimidine(BPY]Vf)J and 2,2'-bipyidine(BPY), have been synthesized by direct photolysis of the metal hexacarbonyl and indirect route via THF substitution. In the second method, tungsten hexacarbonyl was first irradiated in THF to yield [W(CO)sTHF| and the THF was then replaced by the desired ligand. All complexes were characterised by a combination of infrared, UV-visible, *H NMR, mass spectroscopy and elemental analysis. Infrared spectra indicate that the complexes have approximately Cz* local symmetry. The absorption spectra of the complexes show intraligand band in the UV region and a broad metal-to-ligand charge-transfer (MLCT). The latter bands are red-shifted in the binuclear complexes. For comparison purposes, the properties of free ligands have also been studied. The complexes have electronic spectra dominated by intense MLCT transition in the visible region of the spectrum.
Physical, mechanical and durability properties of sugarcane ash enhanced compressed earth blocks stabilized with fly ash and lime powder
(University of Zululand, 2019) Mohomane, Samson Masulubanye
The construction sector is one of the principal component of anthropogenic activities and a major contributor of greenhouse gases (GHGs) emissions. Large quantities of solid wastes are being produced every year by industrial and agricultural industries which lead to environmental and health concerns such as flooding, air pollution and other public health scarce. These wastes have potential pozzolanic reactivity and may be used to develop cementitious materials that are sustainable, while maintaining requirements as affirmed in various standards. The sector is also an important economic sector that has a large environmental impact in terms of large quantities of construction and demolition wastes (C&DW) which are generated. These is mainly due to severe shortage of natural aggregates (NA) for the production of new concrete materials, and a boom in construction activities currently taking place worldwide. The utilization of recycled masonry and concrete (RCA) from C&DW will conserve the natural resources and reduce the environment impact of concrete manufacturing. Sugarcane bagasse ash (SCBA) is an industrial waste material obtained from sugar milling industry that can be used as pozzolanic material for the development of greenbricks. In this research, the application of various waste materials and the effects of fly ash and lime on the mechanical and durability properties of compressed earth bricks (CEBs) are investigated. Secondly, the applications of fly ash, recycled cement and masonry as industrial waste materials in construction industry are reviewed. Lastly, The SCBA greenbricks were developed using lime as a chemical stabilizer and tested for physical, mechanical and durability properties. In addition, several agricultural by-product such as sugar cane bagasse (SCB) and soft wood (SW) were treated as wastes until recent times when researchers considered incorporating them in polymeric matrices to mainly avoid environmental pollution and cost of a new synthesis. The properties of untreated sugarcane bagasse (SCB) and soft wood (SW), their respective celluloses, and corresponding composites and blends with thermoplastics (polypropylene and polyethylene) were analysed by DMA, SEM, XRD, FTIR, DSC and TGA. Three degradation models, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (OFW), and Kissinger (KGR) methods were employed to determine apparent activation energy values of untreated SCB and SW, and their respective celluloses. The apparent activation energy values obtained from OFW and KAS models vary with the degree of conversion, and showed similar trends. The activation energies TGA analysis shows that the untreated SCB and SW degrade earlier than their respective celluloses and the prolonged treatment affects the onset of main degradation. PP/SCB were least thermally stable compared to PP/SW composites. The addition of extracted cellulose decreased the thermal stability of PP/SCB composites at higher ﬁller content due to poor interfacial bonding as compared to PP/SW composites. Likewise, the cellulose containing blend composites were thermally stable compared to untreated fibre, and are less stable compared to neat PP/PE blend. DMA of both PP/SCB and PP/SW composites indicated improvement in the storage modulus compared with neat PP. Similar results were obtained for all blend composites, with the cellulose containing blend composites displaying higher values than untreated fibre. SEM results conﬁrmed a rough morphology and the presence of many voids resulting from ﬁbre pull-out in composites, especially for the ones with higher ﬁbre content. However, a stronger interaction between PP/PE/SW as compared to PP/PE/SCB took place in the blend composites. DSC analysis reveals that the introduction of SCB or SW did not significantly change the melting and crystallization behaviour of both the PE and PP.

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