Research Articles

Permanent URI for this collection

Browse

Recent Submissions

Now showing 1 - 5 of 10
  • Item
    Attenuation of pollution arising from acid mine drainage by a natural wetland on the Witwatersrand
    (Academy of Science of South Africa (ASSAf), 2017-01) Humphries, M.S.; McCarthy, T.S.; Pillay, L.
    Wetlands are well known to be efficient at sequestering pollutants from contaminated water. We investigated metal accumulation in the peats of the Klip River, a natural wetland that has received contaminated water from gold mining operations in Johannesburg for over 130 years. Previous work conducted in the downstream portion identified the wetland as an important system for sequestering metals. We focused on the upstream section of the wetland, more proximal to the source of acid mine drainage, to provide a better understanding of the pollutant sources and the role of the wetland in pollutant attenuation. Geochemical and mineralogical analyses of peat cores revealed considerable metal enrichments in the peat ash, particularly in Co, Ni, Zn, Pb, Cu and U. Metal concentrations are typically between 4 to 8 times higher than those previously reported for the downstream, more distal portion of the wetland. The distribution of metal accumulation within the peat profiles suggests that contamination arises from a combination of sources and processes. Elevated concentrations in the shallow peat are attributed to the input of contaminated surface water via tributaries that drain the Central Rand Goldfield, whereas enrichments in the deeper peat suggest significant sub-surface inflow of contaminated water through the underlying dolomitic rocks. Metal immobilisation occurs through a combination of mechanisms, which include the precipitation of gypsum, metal sulfides, Fe-Mn oxyhydroxides and phosphates. Our study highlights the environmental and economic importance of natural wetland systems which have the ability to accumulate large quantities of metals and thus remediate polluted waters.
  • Item
    Hierarchical one-dimensional ammonium nickel phosphate microrods for high-performance pseudocapacitors
    (Nature Publishing Group, 2015-12) Raju, K.; Ozoemena, K.I.
    High-performance electrochemical capacitors will drive the next-generation portable, flexible and wearable electronics. Unlike the conventional all-carbon supercapacitors (electric double layer capacitors, EDLC) with high power but poor energy density, pseudocapacitors capitalize the high energy density inherent to reversible redox reactions and provide a facile means to enhancing the energy ratings of supercapacitors. The high length-to-diameter ratio and anisotropic character of 1-D architecture makes them suitable for use in energy storage. For the first time, we report 1-D microrod structures (∼ 36 nm width) of ammonium nickel phosphate hydrate (ANP mr) as a pseudocapacitor with high energy rating and power handling. To confirm the data, the ANP mr -based pseudocapacitor was subjected to various configurations (i.e., half-cell, symmetric, asymmetric, and flexible all-solid-state) and in each case it gave excellent values compared to any accessible literature to date. We clearly demonstrate that a flexible all-solid-state ANP mr -based pseudocapacitor achieved high areal capacitance of 66 mF cm ∼'2 with extra-ordinary energy (21.2 mWh cm ∼'2) and power (12.7 mW cm ∼'2) densities. This work opens doors for a facile, robust and scalable preparation strategy for low-cost, earth-abundant electrode materials for high-performance pseudocapacitors.
  • Item
    A structural study of 4-aminoantipyrine and six of its Schiff base derivatives
    (International Union of Crystallography, 2015-02) Mnguni, M.J.; Lemmerer, A.
    Six derivatives of 4-amino-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-one (4-aminoantipyrine), C11H13N3O, (I), have been synthesized and structurally characterized to investigate the changes in the observed hydrogen-bonding motifs compared to the original 4-aminoantipyrine. The derivatives were synthesized from the reactions of 4-aminoantipyrine with various aldehyde-, ketone- and ester-containing molecules, producing (Z)-methyl 3-[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)amino]but-2-enoate, C16H19N3O3, (II), (Z)-ethyl 3-[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)amino]but-2-enoate, C17H21N3O3, (III), ethyl 2-[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)amino]cyclohex-1-enecarboxylate, C20H25N3O3, (IV), (Z)-ethyl 3-[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)amino]-3-phenylacrylate, C22H23N3O3, (V), 2-cyano-N-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)acetamide, C14H14N4O2, (VI), and (E)-methyl 4-{[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)amino]methyl}benzoate, C20H19N3O3, (VII). The asymmetric units of all these compounds have one molecule on a general position. The hydrogen bonding in (I) forms chains of molecules via intermolecular N-H⋯O hydrogen bonds around a crystallographic sixfold screw axis. In contrast, the formation of enamines for all derived compounds except (VII) favours the formation of a six-membered intramolecular N-H⋯O hydrogen-bonded ring in (II)-(V) and an intermolecular N-H⋯O hydrogen bond in (VI), whereas there is an intramolecular C-H⋯O hydrogen bond in the structure of imine (VII). All the reported compounds, except for (II), feature π-π interactions, while C-H⋯π interactions are observed in (II), C-H⋯O interactions are observed in (I), (III), (V) and (VI), and a C-O⋯π interaction is observed in (II).
  • Item
    Crystal structures of 2,2′-bipyridin-1-ium 1,1,3,3-tetracyano-2-ethoxyprop-2-en-1-ide and bis(2,2′-bipyridin-1-ium) 1,1,3,3-tetracyano-2-(dicyano-methylene) propane-1,3-diide
    (International Union of Crystallography, 2015-05) Setifi, Z.; Valkonen, A.; Fernandes, M.A.; Glidewell, C.; Harrison, W.T.A.; Nummelin, S.; Boughzala, H.; Setifi, F.
    In 2,2′-bipyridin-1-ium 1,1,3,3-tetracyano-2-ethoxyprop-2-en-1-ide, C10H9N2+·-C9H5N4O-, (I), the ethyl group in the anion is disordered over two sets of atomic sites with occupancies 0.634 (9) and 0.366 (9), and the dihedral angle between the ring planes in the cation is 2.11 (7)°. The two independent C(CN)2 groups in the anion make dihedral angles of 10.60 (6) and 12.44 (4)° with the central propenide unit, and the bond distances in the anion provide evidence for extensive electronic delocalization. In bis(2,2′-bipyridin-1-ium) 1,1,3,3-tetra-cyano-2-(dicyanomethylene) propane-1,3-diide [alternative name bis(2,2′-bipyr-idin-1-ium) tris(dicyanomethylene) methanediide], 2C10H9N2+·C10N62- (II), the dihedral angles between the ring planes in the two independent cations are 7.7 (2) and 10.92 (17)°. The anion exhibits approximate C3 symmetry, consistent with extensive electronic delocalization, and the three independent C(CN)2 groups make dihedral angles of 23.8 (2), 27.0 (3) and 27.4 (2)° with the central plane. The ions in (I) are linked by an N - H⋯N hydrogen bond and the resulting ion pairs are linked by two independent C - H⋯N hydrogen bonds, forming a ribbon containing alternating R44(18) and R44(26) rings, where both ring types are centrosymmetric. The ions in (II) are linked by two independent N - H⋯N hydrogen bonds and the resulting ion triplets are linked by a C - H⋯N hydrogen bond, forming a C12(7) chain containing anions and only one type of cation, with the other cation linked to the chain by a further C - H⋯N hydrogen bond.
  • Item
    The effect of structural properties of Cu2Se/polyvinylcarbazole nanocomposites on the performance of hybrid solar cells
    (Hindawi Publishing Corporation, 2016) Govindraju, S.; Ntholeng, N.; Ranganathan, K.; Sikhwivhilu, L.M.; Moloto, N.; Moloto, M.J.
    It has been said that substitution of fullerenes with semiconductor nanocrystals in bulk heterojunction solar cells can potentially increase the power conversion efficiencies (PCE) of these devices far beyond the 10% mark. However new semiconductor nanocrystals other than the potentially toxic CdSe and PbS are necessary. Herein we report on the synthesis of Cu2Se nanocrystals and their incorporation into polyvinylcarbazole (PVK) to form polymer nanocomposites for use as active layers in hybrid solar cells. Nearly monodispersed 4 nm Cu2Se nanocrystals were synthesized using the conventional colloidal synthesis. Varying weight % of these nanocrystals was added to PVK to form polymer nanocomposites. The 10% polymer nanocomposite showed retention of the properties of the pure polymer whilst the 50% resulted in a complete breakdown of the polymeric structure as evident from the FTIR, TGA, and SEM. The lack of transport channels in the 50% polymer nanocomposite solar cell resulted in a device with no photoresponse whilst the 10% polymer nanocomposite resulted in a device with an open circuit voltage of 0.50 V, a short circuit current of 7.34 mA/cm2, and a fill factor of 22.28% resulting in a PCE of 1.02%.