Repository logo

Doctoral Degrees (Chemistry)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6596

Browse

Browsing Doctoral Degrees (Chemistry) by Author "Ajibade, Peter Adewale."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Synthesis structural and optical studies of copper sulphide and silfide nanoparticles from Cu(II) and Ag(I) dithiocarbamate single source precursors.
    (2018) Botha, Nandipha Loveness.; Ajibade, Peter Adewale.
    Eight dithiocarbamate ligands were synthesized from butylamine, diallylamine, N-ethyl aniline, N-methyl benzyl amine, piperidine, morpholine, dibenzyl amine and phenyl piperizine. Eight copper(II) dithiocarbamate complexes and Eight silver(I) dithiocarbamate complexes were synthesized. Spectroscopy techniques were used to characterise the obtained compounds. The structure of the synthesized dithiocarbamate ligands was confirmed using NMR spectroscopy. Proton NMR showed all the expected peaks and showed the ligands to be pure with no extra peaks for contaminations. 13C NMR showed the peak corresponding to the carbon in the carbon disulphide resonation at around 200 to 220 ppm in all the ligands confirming their formation. FTIR was carried out for all the compounds, ligands and their corresponding metal complexes. In the ligands the C – S, C = S and C – N vibrations were observed corresponding to the dithio- moiety. In the copper complexes the C – S and C = S frequency merged and gave one vibration which confirmed the coordination of the metal to the ligands. UV-Visible was also used to confirm the geometry of the complexes. The ligands gave the bands corresponding to π – π* and n – π* due to N–C=S and S–C=S groups. The copper complexes showed the intra-ligand transitions and two extra bands in the visible region corresponding to the d-d transition of the square planar geometry of copper(II) complexes. Crystal structures of four complexes were isolated, two copper(II)complexes which confirmed the square planar geometry given by the UV-Vis data and two Silver(I) complexes. However, it turned out that silver complexes obtained are the metal clusters. The sixteen metal dithiocarbamate complexes were used as single source precursors to synthesize thirty-two metal sulphide nanoparticles. Four single source precursors, from each metal ion were thermolyzed at 220°C to study the effect of the precursor on the nanoparticle structural and optical properties. The other four precursors for each metal ion were further thermolyzed at three different temperatures, 220°C, 180°C and 120°C, to study the influence of the temperature on the structural and optical properties of the nanoparticles. The obtained nanoparticles were further studied using p-XRD. The X-ray data showed the copper sulphide nanoparticles to have Cu1.8S digenite phase. Silver sulphide nanoparticles have α-Ag2S phase that is usually obtained at lower temperature. The shape and crystallite sizes of the nanoparticles were determined using TEM/HRTEM. TEM images showed the silver nanoparticles synthesized at 220°C all adapted the same spherical shape that are monodispersed. Their size ranged from 8 nm to 78 nm. When the thermolysis was done at 180°C the sizes ranged from 5 to 71 nm and 2-23 nm when thermolyzed at 120°C. For the copper sulphide nanoparticles synthesized at 220°C the size ranged from 5 to 125 nm. 180°C and 120°C gave size ranges of 10 to 55 nm and 4 to 40 nm respectively. The copper sulphide nanoparticles showed some effect of agglomeration and a mixture of shapes from spherical to hexagonal shapes. Their surface morphology was examined with SEM and they changed with different temperature and precursors. EDX was used to confirm the metals and sulphur present in the particles. The interaction of the capping agents and nanoparticles was studied by FTIR. Their optical properties were studied using photoluminescence and UV-Visible spectroscopy. The nanoparticles were found to be quantum confined as the estimated band gap energies showed blue shift when compared to that of the bulk.
  • Thumbnail Image
    Item
    Synthesis, characterization and evaluation of ionic liquids and polymeric ionic liquids/functionalized multiwalled carbon nanotubes for Cr(VI) adsorption.
    (2019) Matandabuzo, Mzukisi.; Ajibade, Peter Adewale.
    In this study, a series of imidazolium and pyridinium-based ionic liquids (ILs), polymeric ionic liquids (PILs), and their carbon nanotubes-functionalized composites were synthesized, characterized and applied as potential adsorbents for hexavalent Cr(VI). Polymeric ionic liquids of different polymerizable moieties (vinyl and styrenic moieties) were studied. Furthermore, multi-walled carbon nanotubes (MWCNTs) were synthesized, characterized and dispersed on both imidazolium and pyridinium-based ILs and PILs, respectively. Thermal studies revealed that vinyl pyridinium PILs possess good thermal stability than the vinyl imidazolium counterparts. The size of the counter-anions bromide (Br-), hexafluorophosphate (PF6-), and bis(trifluoromethanesulfonyl) imide (TFSI-) and the charge delocalization in cationic rings greatly influenced the glass transition temperatures of PILs. Expectedly, pyridinium and imidazolium-based PILs with hexafluorophosphate ions showed poor solubility in polar protic solvents (water, methanol) and good solubility in polar aprotic solvents (DMSO, DMF, THF) except acetone (a dipolar aprotic solvent). The as-synthesized ILs/MWCNT composites were characterized using FTIR spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermal analysis. The results obtained indicate that the pyridinium-based ILs exhibited higher decomposition temperatures (above 400 °C) compared to imidazolium-based ILs counterparts (onset decomposition at 250 °C) with poor water-solubility and their glass transition temperatures were dependent on ion mobility. The effect of the alkyl lateral chain (propyl and isopropyl) at the first and third position of imidazolium and N-position of pyridinium cationic rings towards their thermal stability, conductivity, and solubility of the ionic liquids was investigated. Their solubilities in different polar and non-polar solvents were also investigated. Spectroscopic and microscopic analyses confirmed the formation of the ILs/MWCNT composites with new functionalities and unaltered surface morphology of carbon nanotubes. Pyridinium and imidazolium-based PILs/MWCNT composites were characterized by thermal, spectroscopic, and electron microscopy techniques. It was observed that the composites were thermally stable compared to the corresponding precursors and were insoluble in polar aprotic solvents. For application, solid-liquid adsorption process was used in the adsorption of Cr(VI) from aqueous solution using the as-synthesized ILs/MWCNT and PILs/MWCNT composites as adsorbents. Under batch adsorption experiments, the effect of solution pH, contact time and initial concentration of Cr(VI) were investigated. It was established that the adsorption of Cr(VI) took place under acidic conditions (pH=2-3), thereby confirming significant adsorption of dichromate (Cr2O7-) and hydrochromate (HCrO4-) anions. At lower pH values, the ionic and π-anionic electrostatic interactions between the positively-charged regions of the composites and Cr(VI) were believed to have facilitated the adsorption of anionic (Cr2O7-) and (HCrO4-). Adsorption results obtained based on contact time showed that increase in contact time gradually increases the adsorption of Cr(VI) within 2 h. However, further increase in experimental contact time above 2 h insignificantly affected the adsorption of Cr(VI) due to early or quick oversaturation of the surface active sites on the adsorbents. The adsorption of Cr(VI) onto ILs/MWCNT and PILs/MWCNT composites fitted well into both Langmuir and Freundlich adsorption isotherms. However, the homogeneity/heterogeneity nature of the adsorbents relied on the diversified nature of the composites, which includes bulky pyridinium and imidazolium organic cations with delocalized charges, some large counter anions and the graphitic functional carbon groups. In order to understand the mechanisms of the adsorption of Cr(VI) onto ILs/MWCNT and PILs/MWCNT composites, pseudo-second-order kinetic model was employed. The results obtained showed that the calculated maximum adsorption capacities (qecal) and experimental maximum adsorption capacities (qe.exp) depict high correlation co-efficiencies (R2>0.99) confirming the applicability and feasibility of pseudo-second-order model on the adsorption of Cr(VI) in this study.