Chemistry

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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.
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.
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.
Synthesis and characterisation of ligand-bridged tungsten and chromium penta- and tetra-carbonyl complexes
(2002) Sinuka, Ludwe; Kolawole, G.A.
Ligand bridged metal carbonyl complexes of the form [5(CO)MLM(CO)5], [4(CO)MLM(CO)4] and [4(CO)ML], where M is either tungsten or chromium and L is either trans-l,2-(bis-4-pyridyl)ethylene(TBE) or 3,6-di-2-pyridyl-l,2,4,5-tetrazine (DPT) have been synthesised. They were characterised using IR, UV-Vis and NMR, MS, TLC and microanalysis. Electronic spectral studies showed that both the dinuclear, [4(CO)CrDPTCr(CO)4] and mononuclear, [4(CO)CrDPT] complexes have MLCT transitions at 900.88 nm and 652.52 nm respectively. The dinuclear MLCT is more intense and broad and is deemed to have overlapped with the d-d transitions observed in the mononuclear complex at 909.45 nm. However, intra-ligand transitions were observed at 279.97 nm, 303.53 nm and 382.75 nm for both mononuclear and dinuclear complexes. Photoluminescence spectra showed two emissions for [TBE{W(CO)5}2]; with the emission at 530 nm originating from an MLCT transition, and the one at 353 nm originating from an intra-ligand transition. For [4(CO)CrDPTCr(CO)4] and [4(CO)CrDPT], a single broad emission was observed at 523 nm and 460 nm respectively. A small peak at 400 nm in the dinuclear complex is observed and is tentatively attributed to an intra-ligand transition. A structure of distorted octahedron is proposed for pentacarbonyl/ro^-l^-(bis-4-pyridyl) emyIenetungsten.
Studies on semiconductor nanoparticles and polymer nanocomposites
(2002) Nair, P. Sreekumari; Revaprasadu, N; Kolawole, G.A.
Synthesis of nanometer-sized semiconductor materials using various synthetic methods has been an area of intense activity over the past decade. The emphasis has been mainly on the synthesis of semiconductor particles belonging to II-VI and III-V groups. These particles exhibit an increase in their electronic band gap with decreasing particle size, a property which is attributed to a strong quantum confinement effect. The ability to tune the physical properties of nanocrystallites makes them an important category of materials with potential use in a wide range of technological applications. This project deals with the synthesis, characterisation and investigation of the properties of semiconductor nanoparticles and semiconductor-polymer nanocomposites. The strategy for the synthesis of nanoparticles involves the use of various single-source precursors, which are thermolysed in a coordinating solvent, tri-w-octylphosphine oxide (TOPO). In the present study the focus has been mainly to prepare CdS nanoparticles using various single source precursors. Attempts have been made to correlate the precursor characteristics and the size, size distribution and morphology of the nanoparticles synthesised using these precursors. The other nanocrystallites studied in the present project include ZnS, Mn doped ZnS and Mn doped CdS. The single-source precursors used for the synthesis of CdS nanoparticles are cadmium(II) complexes of: Ethylxanthicacid; N,N' bis(thiocarbamoyl)hydrazine; N,N' -dioctyl thiourea; N,N'-diisopropyl thioureap; Thiocarbohydrazide; N,N' -dicyclohexyldithiooxamide; Thiosemicarbazide; 1 -(1 -carboxypropionyl)thiosemicarbazide; Glyoxalbis(thiosemicarbazone); 2,6-Diacetylpyridine bis(thiosemicarbazone); Zinc(H) complexes of: Ethylxanthicacid; N,N' -dioctyl thiourea; N.N; -bis(thiocarbamoyl)hydrazine The second part of the project involves the synthesis, characterisation and investigation of the properties of CdS, HgS and PbS nanoparticles in polymer matrices. Various synthetic methods have been used for the preparation of the polymer nanocomposites. The polymeric media that have been used include polyacrylamide, polystyrene and polyaniline. The structural characterisation of the composite materials confirm their nanosized nature. The thermal decomposition pattern of all precursors were studied by TGA. The optical properties of the nanoparticles and nanocomposites were investigated by UV-vis and photoluminescence (PL) spectroscopy. The structural properties were investigated by X-ray diffraction (XRD), energy dispersion analytical X-ray (EDAX), selected area electron diffraction (SAED), transmission electron microscopy (TEM) and electron paramagnetic resonance (EPR).
Synthesis and characterization of ruthenium and rhodium sulfide thin films and nanoparticles
(2004) Sosibo, Ndabenhle Mercury; Revaprasadu, N.; Compton, D.
The reaction of the metal salt (MClynH20) with the solution mixture of carbon disulfide (CS2), dialkylamine (R2NH) and sodium hydroxide (NaOH) yields a dithiocarbamate complex of formulation [M(S2CNR2)n], (M = Ru and Rh; R = alkyl group; n = 2 or 3). In this work, these complexes were synthesized and characterized, using such techniques as thermogravimetric analysis (TGA), infrared (IR), nuclear magnetic resonance (NMR), mass spectroscopy (MS) and elemental analysis. The complexes were then used as single-source molecular precursors for the synthesis of metal chalcogenide thin films and nanoparticles. The deposition of RI12S3 and RuS2 thin films was achieved by the decomposition of [Rh(S2CNEt2)2] and [Ru(S2CNEt2)3] dissolved in toluene using aerosol assisted chemical vapour deposition (AACVD) technique. The precursors gave good yields of high quality materials and pyrolyze cleanly to give the required films at reasonably high growth rates. Shiny, adherent thin films were deposited on glass substrates at 350-450 °C. The thin films were characterized using X-ray diffraction (XRD), UV-Vis absorption, ellipsometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). Metal chalcogenide nanoparticles were also synthesized using complexes [Ru(S2CNEt2)3] and [Rh(S2CNEt2}2] as single source molecular precursors. Both TOPO and HDA were used as capping agents for the nanoparticles. Materials of sizes up to 20 run were synthesized from the precursors. Characterization of the nanoparticles was done using UV-Vis absorption spectroscopy, TEM and photoluminescence (PL).
Synthesis and characterization of N-alkylthiourea and N, N -dialkylthiourea complexes of Cu, Cd and Pb, and their use as single source precursors for the synthesis of metal sulfide nanoparticles
(University of Zululand, 2005) Moloto, Makwena Justice; Revaprasadu, N.; Kolawole, G.A.
A number of complexes of various thiourea derivatives with different metals have been synthesized and characterized by a combination of spectroscopic studies, elemental analysis, melting points and X-ray crystallography. Infrared and NMR spectroscopy studies reveal the interaction between a metal and the ligands, thioureas, is mainly through bonding to sulfur. A series of cadmium(II) complexes with N-alkyl/aryl and N, N'-dialkyl/aryl thioureas (RNHCSNHR'; where R = R* = CH3, CH2CH3, CeHs and /or R' = H) have been synthesized and characterized. The structures of [CdCl3(CS(NH2)(NHCH3)3]n (I) and CdCl2(CS(NH2)NHCH2CH3)2 (II), CdCl2(CS(NH2)-NHCeHs^ (III) and CdCI2(CS(NH-CH3)2)2 (IV) were determined by single crystal X-ray methods. Complex I have a six coordinate polymeric chain with a CdCl3S3 core, which together with complex III (a monomer) gave a distorted octahedral geometry. Complexes II and IV are monomers with a distorted tetrahedral geometry around the cadmium(II) ion. The lH (nuclear magnetic resonance) NMR spectra in deuterated dimethyl sulfoxide (CD3SOCD3) at room temperature reveal the broadened NH peaks in the lower field region (6.0 - 10.0 ppm) and the presence of both syn and aw/z'-isomers for the N-alkylthioureas. All the spectral data obtained is consistent with the coordination of ligands by sulphur atom to the metal ion. Lead complexes were prepared in aqueous media to give white powder in a four coordinate form. Unlike cadmium and lead, copper gave multinuclear complexes resulting from the reduction of copper (II) to copper (I) by the thiourea ligands to form specifically tetranuclear copper complexes with thiourea behaving as the bridging ligands. Thermal behavior of these complexes both in air and under inert atmosphere gave residues after decomposition, which was predominantly metal sulfides, with little impurities. The presence of the metal sulfide was established by the XRD analysis of the residue from the thermo gravimetric analysis. These alkyl substituted thiourea complexes of Cd, Pb and Cu were easy to prepare, stable in air, inexpensive, obtained in good yields and decompose at temperatures about 200 -220 °C, which is convenient to thermal decomposition of precursors in the high boiling solvents or the suitable capping agents to prepare surface capped metal sulfide nanoparticles. Some of the complexes have been used as single-source molecular precursors in the preparation of copper sulfide, cadmium sulfide and lead sulfide nanoparticles by a process driven by thermal decomposition. Good crystalline particles were obtained from thermolysis of the precursors in tri-n-octylphosphine oxide (TOPO) as a solvent and capping agent, at different temperatures. All nanoparticles, CdS, PbS and CuxSy, were prepared from alkylthiourea complexes, cleanly decomposing to give average size ranges 4 - 26 nm at reasonably lower temperatures. The small size of these particles is a consistent property with the observed blue shift in the band edge of their optical spectra. Photoluminescence spectra of most samples were broadened with a red shift in relation to the band edge indicating the broad size distribution. Some relative quantity of bulk particles of copper sulfide and lead sulfide were obtained from the large yield of the products as insoluble particles in hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO). X-ray powder diffraction (powder XRD) patterns are consistent with predominantly hexagonal phase although copper sulfide showed evidence of various stoichiometric ratios. These phases were also confirmed by the images from the transmission electron microscope (TEM), although the CdS nanoparticles showed instability due to quick agglomeration in TOPO. Their patterns were confirmed by the XRD to be predominantly hexagonal. The morphology for most of the particles were close to those of thin needle-like plates, although the collapse is more of spheres which is a preferred mode of arrangement of the CdS particles when they settle on the carbon coated copper grids. High resolution transmission electron microscope (HRTEM) revealed the lattice fringes of all different types of nanoparticles including CdS, which tend to give agglomerates, hence it was difficult to determine particle sizes from the TEM images. All solution studies viz. ultraviolet-visible spectroscopy, photoluminescence and copper-coated grid-TEM were all consistent with particles in the nano-size regime. The copper and lead complexes of these thiourea derivatives have been used to prepare PbS and CuxSy, and gave crystalline, cubic or rod-shaped nanoparticles. CdS, PbS and CuxSy nanoparticles showed quantum confinement effects with a blue shift in their absorption spectra. The materials were further characterized by HRTEM images, XRD and selected area electron diffraction (SAED) patterns.
Synthesis, characterisation and in vitro studies of metal complexes of some selected antimalarial drugs
(University of Zululand, 2005) Ajibade, Peter Adewale.; Kalawole, G.A.
This project deals with the synthesis, characterization and in vitro studies of metal complexes of antimalarial drugs. The synthetic techniques were based on the modification of antimalarial drugs by the introduction of metal ions into the molecular structure of the drugs. Thirty two metal complexes derived from chloroquine, amodiaquine, trimethoprim, sulfadiazine, tetracycline and pyrimethamine have been synthesised using the following metal ions: Co(II), Cu(II), Zn(II), Mn(II), Ni(II), Pt(II), Pd(II), Co(III), Fe(III), Ru(III) and VO(II). The complexes were characterised by melting point / decomposition temperature, solubility, conductivity measurement, elemental analyses, UV-Vis and IR spectroscopy, mass spectrometry, magnetic susceptibility measurement and EPR. Six of the complexes and sulfadiazine ligand were also characterised by single X-ray crystal studies. The complexes were screened in vitro against four isolates of Plasmodium falciparum at various stages of the parasites development The results showed that three of the metal complexes, cobaIt(III)amodiaquine, cobalt(III)quinacrine and iron(III)amodiaquine are more active in vitro against the parasites in comparison to chloroquine the first drug of choice for treatment of chloroquine falciparum malaria in Africa.
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.
The use of metal complexes to deposit metal chalcogenide thin films and nanoparticles
(2006) Musetha, Phumudzo Luvhengo; Revaprasadu, N.; Kolawole, G.A.
This thesis consists of four chapters. The first chapter describes the properties, methods of deposition and applications of semiconductors. The second chapter focuses on the deposition of metal chalcogenides thin films from single molecular precursors of the type [M {N(EPR2)2}2], were M = Pt, Pd, Ni; E = S or Se and R = fPr or Ph. Ligands of the type R2P(E)NP(E)R2, where R = *Pr or Ph were prepared to synthesize these precursors. Single X-ray structures of fP^NfP^PSe^h] and [Pd{N(SPh2)2}2] are reported and discussed. The X-ray structure of the platinum complex shows a square-planar conformation whereas the six membered PtSe2P2N ring adopts a distorted "boat" conformation. The third chapter describes the deposition of metal sulphide thin films from [M(S2COR)2], were M = Pt, Pd, Ni, Cd, Co, Cu and R = Et or dPr. Single X-ray structures of [M(S2COR)2j M = Pt, Pd, and Ni, R = Et are reported and discussed. The NiS thin films are polycrystalline and their 0 values are in good agreement with the literature values. The phases do not seem to be affected by temperature whereas the morphology of the films changes with temperature. The morphology of the films has been found to be greatly influenced by varying the temperature. All the ligands and precursors were characterised by elemental analysis and by using spectroscopic techniques such as infrared (IR), mass spectrometry (MS), proton and carbon nuclear magnetic resonance (*H and !3C NMR). Thin films of PtSea, Pt, PdSe2, PaUSe, Pdi7Sei5, PdS, and PdS2 were deposited by aerosol assisted chemical vapour deposition (AACVD) and low pressure metal-organic vapour deposition (LP-MOCVD) using metal complexes of irninobis(dialkylphosphinato)dichalcogenide ligands. Thin films of NiS, CdS, Pt, PdS, Pdi6S7, and CogSg were deposited by AACVD using the respective metal xanthate complexes. The films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The fourth chapter focuses on the preparation of nanoparticles and nanorods from cadmium complexes. The synthesis of CdS nanoparticles and nanorods are described in detail. The synthetic route used for the synthesis of the CdS nanoparticles is the thermolysis of metal complexes, [Cd(S2CNMe2)2] and [Cd{-SC(=S)OCH(CH3)2}4], in tri-octylphosphine oxide (TOPO) and hexadecylamine (HDA). The optical properties of the nanoparticles were studied by using ultraviolet (UV)-visible and photoluminescence (PL) spectroscopy. There were blue shifts in the band gaps for all CdS samples; however, photoluminescence was very poor. The hexagonal phase of CdS was observed for all CdS samples using XRD measurements. The transmission electron microscopy (TEM) images show that the TOPO capped CdS nanoparticles have a spherical shape whereas the HDA capped particles are rod shaped. Nanoparticles of CdS were characterised by UV-vis, PL, XRD and TEM.
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.
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.
Synthesis and growth dynamics study of silver nanoparticles
(2009) Mdluli, Phumlane Selby; Revaprasadu, N.
The concept of shape-controlled synthesis of metal nanoparticles is investigated by considering the growth mechanism of metal nanoparticles. This thesis is divided into four chapters, chapter one presents a general introduction about various physiochemical aspects of nanornaterials. The different characteristic properties of nanomaterials, their chemically synthesized protocols, characterization techniques, and their applications are discussed in brief. Based on these reviews, the context scope and objective of the present work are outlined. Chapter two deals with the theory of kinetically growth of nanoparticles. The basic optical properties of metal nanoparticles as well as the structural evolution of nanoparticles are also mentioned in this chapter In Chapter three the synthesis of silver nanoparticles with varying morphologies using different synthetic routes are described in detail. Silver nanowires were synthesized by an aqueous route using dimethyl formamide (DMF) as the reducing agent in the presence of poly (iV-vinylpyrrolidone) (PVP) without the addition of seeds. The products were characterized by UV-visible spectroscopy and transmission electron microscopy (TEM). This work was followed by a profound dig-out, to try and comprehend the mechanism for reduction and the kinetics of the reduction of silver nitrate to silver nanoparticles. It was established that in the alkaline medium the reduction of AgNC>3 is enhanced, which resulted to the formation of rod-like silver nanoparticles which were confirmed by TEM and UV-visible spectroscopy. Silver nanodendrites, with an elongated central backbone and distinguished branches were synthesized by die reduction of silver nitrate with formamide using polyvinyl pyrrolidone (PVP) as the surfactant. The drastic evolution of the dendritic nanostructures was due to the variation of the concentration of the reactants. At low PVP concentration isotropic silver nanoparticles are visible in the transmission electron microscopy (TEM) images. The morphological evolution is confirmed by the optical measurements. The growth mechanism for the nanodendrites is discussed in some detail. The use of single molecular precursors is a common route to synthesize nanostructured materials. There have been relatively few reports for the use of sophisticated precursors to synthesize metal nanoparticles at high temperatures. The N-(Diisoproppylthiophosphoryl) thiourea complexes of silver were synthesised using a previously reported literature method. The complexes were then used as single molecule precursors for the synthesis of hexadecylamine (HDA) and tri-octylphosphine oxide (TOPO) capped silver nanoparticles. The absorption spectra of the HDA and TOPO-capped silver nanoparticles exhibit surface plasmon resonance (SPR) absorption in 400-420 nm regions. In chapter four, the morphological evolution of silver nanoparticles prompted the development of a Density Function Theory (DFT) model to understand the adsorption of Pyrrolidinone on the surface of silver and gold nanoparticles. The interaction between PVP and the metal atoms on the surface of silver and gold nanoparticles, was studied using Surface Enhanced Raman Spectroscopy (SERS) and modeled using Density Function Theory (DFT). The SERS analysis was carried out on pyrrolidinone and N-methyl pyrrolidinone in silver and gold colloids, whereas the assignments of bands in the pyrrolidinone molecules were performed by density function theory (DFT) quantum chemical calculations.
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.
Phytochemical analysis and selected biological activity of Phyllanthus parvulus Sond. var garipensis
(2009) Mdlolo, Clerentia Mbali; Oyedeji, O.A.
From the huge family of Euphobiceae stems a large Phyllanthus genus. The Phyllanthus genus has about 800 species world wide of which about 22 species are native to Southern Africa. A number of the Phyllanthus species have been reported to have history hi herbal medicine systems, and studies have been done to support their use. Stemming from the South African species is Phyllanthus parvulus Sond. var garipensis, a shrub that is known botanicaUy but, its medicinal potentials are unknown. This project focuses on the chemical and biological properties of Phyllanthus parvulus Sond. var garipensis. The phytochemical study reveals that the plant possesses some secondary metabolites namely: alkaloids, saponins, flavonoids, tannins and antraquinones. A compound lanosterol-amide linked glycoside was isolated from the ethyl acetate fraction. The hexane, chloroform, ethyl acetate, methanol, ethanol and water extract were tested for antibacterial and antioxidant activities. All the plant extracts showed activity with chloroform extract exhibiting high activity against the reference strains used. It exhibited high sensitivity greater than the standard compound ampicillin. The n-hexane and water extract had the least activities, while in the antioxidant studies the methanol and ethanol extract were the most active. The toxicity of the extract was tested using the brine shrimp lethal test and was found not to be toxic after 12hours since less than 70% of the brime shrimps were still alive.
Synthesis and shape control of functionalized cadmium telluride nanoparticles
(2010) Mntungwa, Nhlakanipho; Revaprasadu, N.
The synthesis of organically and water soluble cadmium telluride nanoparticles by a facile hybrid solution high temperature method is presented. This method involves the reaction by the addition of an aqueous suspension or solution of a cadmium salt (chloride, acetate, nitrate or carbonate) to a freshly prepared NaHTe solution. The nanoparticles were prepared by passivating with organic surfactants such as hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO) for their solubility and stability in organic solvents. To stabilize and make the nanoparticles water soluble, L-cysteine ethyl ester hydrochloride and triethanolamine were used as capping agents. The absorption and photoluminescence spectroscopy, fourier transform infrared spectroscopy, powder X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy techniques were used to confirm the quality of the as-synthesized nanoparticles. All measurements were performed without any post preparative size separation of the nanoparticles. The dissertation comprises of four chapters. The first chapter is a brief description of the properties of nanomaterials and a literature review on some of the principal routes to synthesize nanomaterials. The mechanisms of particle growth and shape control are also discussed. Finally some key applications of CdTe are described. The second chapter deals with the synthesis of HDA and TOPO-capped CdTe nanoparticles. The reaction parameters such as reaction time, reduction time of tellurium, Cd:Te ratio, reaction temperature and cadmium source were varied to investigate their influence on the optical properties and morphology of the particles. Details of the absorption features such as excitonic peaks and band edges are presented. The emission properties are also discussed. The morphology of the particles was investigated by electron microscopy and powder X-ray diffraction techniques. It was found that the cadmium source (chloride, carbonate, acetate and nitrate) had a profound effect on the final morphology of the particles. A detailed mechanism for the particle growth is presented. The synthesis of cysteine and TEA-capped CdTe nanoparticles are described in Chapter three. A systematic study of the effects of the capping group, pH, reaction time and cadmium source was carried out for the water soluble CdTe nanoparticles. The absorption and emission data for the particles are discussed in detail. The electron microscopy images confirm the nanosize and crystalline nature of the particles. In addition fourier transform infrared spectroscopy was used to confirm the capping of the particles by cysteine and TEA. All the cadmium sources were found to be successful in producing high quality water soluble CdTe particles. The final chapter four is a summary of general conclusions of the study.
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.
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.
Synthesis and Cytotoxicity Studies of Gold Nanoparticle Systems
(2010) Sosibo, Ndabenhle Mercury Sosibo; Revaprasadu, N.; Tshikhudo, T.
In this work, the immobilisation of different biomolecules on thioalkylated polyethelene glycol (PEG)-capped gold monolayer protected clusters (MPCs) has been successfully conducted. This followed a series of aqueous and nonaqueous synthetic protocols carried out to synthesize gold nanoparticles and MPCs of sizes ranging between 4 – 200 nm. Hetero-bifunctional PEG ligands possessing functionalities such as carboxyl, hydroxyl, biotin and nitrilotriacetic acid (NTA) were introduced resulting in stable, biocompatible gold MPCs, templates for biomolecular functionalisation reactions. Biomolecular functionalisation strategies such as carbodiimide coupling, biotin-avidin interaction and Ni-NTA-histidine interactions following the introduction of the bivalent hexadentate Ni(II) onto the NTA matrix of the MPCs, were conducted to formulate the biomolecular hybrid systems. A range of biomolecules including the cell-penetrating TAT peptide (YGRKKRRQRRR), mitogen-activated protein kinase (MAP kinase), streptavidin and fluorescent-labelled FAM-TAT peptide were successfully immobilised on the gold MPCs. The simplicity of the synthetic approaches and the stability of the resultant biomolecular systems strengthened their potential applications in targeted drug delivery, molecular recognition tools for diagnostics and in the purification, quantification and beneficiation of tagged fusion biomolecules. The colloidal gold nanoparticles, MPCs and bioconjugates were further investigated for inherent biologic effects through a series of end-point based in vitro assays. The cytotoxicity, namely the causation of necrotic cell death was studied using the neutral red assay on CHO22 cell line. All three system types showed benign cytotoxicity properties; demonstrating minor dose-dependence decline in cell viability through necrotic cell death. Additionally, dose-dependent patterns were also observed in the apoptosis-induction effects of these gold systems on CHO22 and CD4 expressing Jurkat cell lines. Overall, this work demonstrated facile protocols of synthesis for colloidal gold nanoparticles, MPCs and bioconjugates, and subsequently through in vitro cellular interaction assays, demonstrated these systems as useful tools for application in life sciences and related fields.
The synthesis and characterization of gold nanoparticles in water-soluble polymers A
(2010) Chili, Muntuwenkosi M.; Revaprasadu, N.
Nanomaterials with critical dimensions at the nanoscale currently attract considerable attention as they show distinct chemical and physical properties that are dependent on their size and shape. A number of techniques have been used to synthesize metal nanoparticles. This thesis presents modified methods for the synthesis of gold nanoparticles, CdSe and Au-CdSe hybrid nanoparticles, capped with water soluble polymers. Chapter one reviews some basic concepts of nanostructured materials. The electronic structure and properties of gold nanoparticles are discussed. The general synthetic routes of gold nanoparticles are also reviewed with special emphasis on their preparation in water soluble polymers. A few applications of nano-gold including electronics, catalysis and biomedical applications are presented. Finally the characterization techniques used in this study are discussed. Chapter two describes the synthesis of gold nanoparticles from various chemical reduction techniques. These techniques have yielded a combination of both spherical and anisotropic shaped nanoparticles. Different reducing agents, such as sodium borohydride, presence of sodium hydroxide, ascorbic acid, sodium citrate, tri-sodium citrate and hydrogen peroxide have been used in the reduction of Au3+ ions to Au0. Water soluble polymers such as poly vinylpyrrolidone (PVP), poly vinyl alcohol (PVA) and organic ligands tri-n-octylphosphine oxide (TOPO) and octadecylamine (ODA) were used as capping agents for the gold nanoparticles. Seed-mediated and two-phase techniques were also employed to yield anisotropic nanorods of gold. Different structure-directing agents and phase-transfer agents were used in the formation of anisotropic nanoparticles. The optical properties of the gold nanoparticles were studied by UV/Vis spectroscopy. The structure and morphology of the as prepared particles was determined using powder X-ray diffraction (XRD) and electron microscopy, respectively. In Chapter three the anisotropic gold nanoparticles synthesized by a UV-irradiation technique through the interaction of HAuCl4 and a stabilizing agent, poly (vinyl pyrrolidone) (PVP) are presented. The effect of irradiation time on the size and shape of gold nanoparticles was investigated by UV-Visible spectroscopy and Transmission Electron Microscopy (TEM). The other effects that were varied include; capping agent, polymer concentration, precursor concentration, lamp wavelength, solvent, and lastly the presence of citric acid in other reactions. The absorption spectra of all samples show a broad band with the characteristic surface plasmon resonance (SPR) peak visible at around 530 nm. The presence of an additional low intensity absorption peak at a longer wavelength suggests the presence of non-spherical nanoparticles. The TEM measurements show evidence of particle shapes such as spheres, hexagons, decahedrons and truncated triangles as the reaction time was varied. Chapter four describes the synthesis of CdSe semiconductor nanoparticles at room temperature in the presence of PVP as the capping agent. Different cadmium sources were used and the mole ratios of the starting materials were varied in order to obtain monodispersed CdSe nanoparticles. L-cysteine and PVP-capped Au-CdSe hybrid nanostructures were synthesized at room temperature. The UV-Vis of these hybrid materials showed gold absorption features for the PVP-capped Au-CdSe while for cysteine capped hybrid particles very little features were observed on the spectrum. The denser spherical gold particles are distinctly visible in the TEM images. The high resolution TEM clearly showed the lattice fringes that confirm the crystallinity of the PVP capped Au-CdSe hybrid nanoparticles.

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