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The Development of Palladium(II)-Specific Amine-Functionalized Silica-Based Microparticles: Adsorption and Column Separation Studies
No full textThe adsorption and separation of platinum(IV) and palladium(II) chlorido species ([PtCl6]2− and [PdCl4]2−) on silica-based microparticles functionalized with ammonium centers based on ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetriamine (TETA) and tris-(2-aminoethyl)amine (TAEA) were investigated. The functionalized sorbent materials were characterized using SEM, XPS, BET, and FTIR. The sorbents were used in the batch and column study for adsorption and selective separation of [PtCl62− and PdCl4]2−. The adsorption model for both [PtCl6]2− and [PdCl4]2− on the different sorbent materials fitted the Freundlich isotherm with R2 values > 0.99. The S-TETA sorbent material was palladium(II) specific. Pd(II) loaded on the silica column was recovered using 3% m/v thiourea solution as the eluting agent. Separation of platinum and palladium was achieved by selective stripping of [PtCl6]2− with 0.5 M of NaClO4 in 1.0 M HCl while Pd(II) was eluted with 0.5 M thiourea in 1.0 M HCl. The separation of palladium (Pd) from a mixture containing platinum (Pt), iridium (Ir), and rhodium (Rh) was successful on silica functionalized with triethylenetriamine (TETA) showing specificity for palladium(II) and a loading capacity of 0.27 mg/g. S-TETA showed potential for use in the recovery of palladium from platinum group metals such as from solutions of worn out automobile emission control catalytic convertors and other secondary sources.Original publication is available at http://dx.doi.org/10.1080/01496395.2014.97801
Mercaptopyridine-substituted indium, zinc, and metal-free phthalocyanines: nonlinear optical studies in solution and on polymer matrices
No full textIn this article, the nonlinear optical characterizations and optical limiting properties of metal-free (2), zinc (3), and indium (4) tetra 4-(2-mercaptopyridine) phthalocyanines are discussed. Nonlinear optical properties of the samples were evaluated using Z-scan at 532 nm and 10 ns pulse in CHCl3, and doped on poly(bisphenol A carbonate) (PBC) thin films. Thin films for 2, 3, and 4 are represented as 2-PBC, 3-PBC, and 4-PBC, respectively. We observed two-photon absorption (2PA) and strong reverse saturable absorption as the dominant mechanisms at nanosecond laser excitation in solution and thin films. By virtue of the magnitude of absorption coefficients and other nonlinear optical parameters estimated in this work, sample 4 was found to exhibit strongest nonlinear optical properties followed by 3, while 2 is the weakest nonlinear absorber of the studied samples. Large third-order susceptibility (1.46 × 10−9 esu and 7.74 × 10−10 esu) and hyperpolarizability (2.13 × 10−28 and 8.37 × 10−29 esu) were estimated for 4-PBC and 3-PBC, respectively. Our studies show that these molecules are suitable candidates for practical passive optical limiters.Original publication is available at http://dx.doi.org/10.1080/00958972.2015.107723
Pitied plumage and dying birds : the public mourning of national heroines and post-apartheid foundational mythology construction
No full textThe original contribution of this thesis is the examination of the official construction of a post-apartheid foundation myth through the analysis of the dead body politics of five iconic South African women that spans the three presidencies that have defined South Africa’s democratic era. This thesis examines the death and funeral of Albertina Sisulu, the return and burial of Sara Baartman, and the commemoration of Charlotte Maxeke, Lilian Ngoyi, and Helen Joseph. Sisulu, Baartman, Maxeke, Ngoyi, and Joseph have been constructed as heroines and as foundational figures for the post-apartheid nation in official rhetoric. It will contend that the dead body politics of these women not only informs a new foundational mythology, but also features in the processes of regime legitimation when the ANC-dominated government faces strong societal criticism. Although such official expressions of nationalism may appear exhausted, this thesis will show that nationalism remains a powerful and dangerous force in South Africa that attempts to silence opposition and critical analysis of perceived failing government policies or inaction. This thesis will indicate that as women’s bodies and legacies are appropriated for nationalist projects they are subsumed in discourses of domestic femininity in official rhetoric that dangerously detract from women’s democratic rights and their ability to exercise responsible and productive citizenship in the post-apartheid state. It will argue that women’s historic political activism is contained within the meta-narrative of ‘The Struggle’ and that women are re-subsumed into the patriarchal discourses of the past that are inherited in the present. This thesis approaches this topic by considering a top-to-bottom construction of post-apartheid nationalism through applying feminist critical discourse analysis to official rhetoric articulated at the public mourning and commemorative rituals of these five women
Synthesis, characterization and photophysical properties of an acenaphthalene fused-ring-expanded NIR absorbing aza-BODIPY dye
Get PDFThe synthesis and characterization of an NIR absorbing acenaphthalene fused-ring-expanded aza-BODIPY dye are reported. In contrast with its naphtho-fused analogue, a stable complex is obtained when the corresponding phthalonitrile is used as the precursor. A comparison is made with the photophysical properties of 3,5-diphenyl-aza-dibenzoBODIPY.Original publication is available at http://dx.doi.org/10.1039/C5RA14916
The effect of ascorbic acid on the photophysical properties and photodynamic therapy activities of zinc phthalocyanine-single walled carbon nanotube conjugate on MCF-7 cancer cells
No full textZinc mono carboxy phenoxy phthalocyanine (1) was chemical modified with ascorbic acid via an ester bond to give ZnMCPPc-AA (2). Complexes 2 and 1 were coordinated to single walled carbon nanotubes via π–π interaction to give ZnMCPPc-AA-SWCNT (3) and ZnMCPPc-SWCNT (4) respectively. Complexes 2, 3 and 4 showed better photophysical properties: with improved triplet lifetimes and quantum yields, and singlet oxygen quantum yields when compared to 1 alone. The photodynamic therapy activities of complexes 1, 2, 3 and 4 were tested in vitro on MCF-7 breast cancer cells. Ascorbic acid suppresses the photodynamic therapy effect of 1, due to its ability to reduce oxidative DNA damage as a result of its potent reducing properties. The highest phototoxicity was observed for 4 which resulted in 77% decrease in cell viability, followed by 3 which resulted in 67% decrease in cell viability. This shows the importance of combination therapy, where the phthalocyanines are the photodynamic therapy agents and single walled carbon nanotubes are the photothermal therapy agents.Original publication is available at http://dx.doi.org/10.1016/j.saa.2015.06.06
Photophysical properties gallium octacarboxy phthalocyanines conjugated to CdSe@ZnS quantum dots
No full textl-Glutathione (GSH) capped core CdSe (2.3 nm) and core shell CdSe@ZnS quantum dots (QDs) (3.0 nm and 3.5 nm) were coordinated to gallium octacarboxy phthalocyanine (ClGaPc(COOH)8) to form ClGaPc(COOH)8–QDs conjugates. An efficient transfer of energy from the QDs to the Pcs was demonstrated through Förster resonance energy transfer (FRET), the FRET efficiencies in all cases was above 50%. The photophysical parameters (triplet state and fluorescence quantum yields and lifetimes) were also determined for the conjugates. There was a decrease in the fluorescence lifetimes of ClGaPc(COOH)8 in the presence of all the QDs, due to the heavy atom effect. The triplet quantum yields increased in the conjugates. The lifetimes also became longer for the conjugates compared to Pc alone.Original publication is available at http://dx.doi.org/10.1016/j.saa.2015.06.08
Fluorescence Behaviour and Singlet Oxygen Production of Aluminium Phthalocyanine in the Presence of Upconversion Nanoparticles
No full textNaYF4:Yb/Er/Gd upconversion nanoparticles (UCNP) were synthesised and the photoemission stabilised by embedding them in electrospun fibers. The photophysical behaviour of chloro aluminium tetrasulfo phthalocyanine (ClAlTSPc) was studied in the presence of UCNPs when the two are mixed in solution. The fluorescence quantum yield value of ClAlTSPc decreased in the presence of UCNPs due to the heavy atom effect of UCNPs. This effect also resulted in increase in triplet quantum yields for ClAlTSPc in the presence of UCNPs. The fluorescence lifetimes for UCNPs were shortened at 658 nm in the presence of ClAlTSPc when the former was embedded in fiber and suspended in a dimethyl sulfoxide solution of the latter. A clear singlet oxygen generation by ClAlTSPc though Förster resonance energy transfer was demonstrated using a singlet oxygen quencher, 1,3-diphenylisobenzofuran.Original publication is available at http://dx.doi.org/10.1007/s10895-015-1632-
Investigating the practices of non-isiXhosa-speaking teachers teaching Mathematics to isiXhosa-speaking 3rd Grades through the medium of Afrikaans
No full textThere is a considerable body of literature on the challenges faced by learners who speak an African language at home but who are taught through the medium of English. Less research has focused, however, on contexts where isiXhosa-speaking learners have Afrikaans as their Language of Learning and Teaching (LoLT), especially in Foundation Phase classrooms where teachers may not speak their learners’ home language. Such learners face the triple challenge of simultaneously learning a second language, learning to read in that language, and also learning new content and concepts through it.
Using a multiple case study design, this investigation explores the mathematics teaching practices of Afrikaans-speaking Grade 3 teachers teaching isiXhosa-speaking learners through the medium of Afrikaans. Separate contextual profiles of the teaching practices of the participating teachers at the three schools are presented. Data were derived from school, classroom, and lesson observations (at least five complete mathematics lessons of each teacher), plus interviews with the teachers and with their school principals.
By drawing on Vygotskian sociocultural theory and the interactive model of second language acquisition, this study highlighted the teaching practices of the three teachers as they mediated their learners’ mathematical conceptual development. An inductive data analysis approach was used to isolate recurring themes and patterns. Four main themes were identified: structuring of teaching and learning, facilitating of interaction, language use and implementation of mediating strategies.
Analysis of the data shows that all three teachers’ language use displayed high levels of modified input, and high levels of context-embedded support. The levels of scaffolded learner talk were, however, found to be much lower than the levels of teacher talk, especially as far as academic registers were concerned. The teachers’ mediation strategies also displayed high levels of teacher-directed input which, on the whole, did not provide optimal opportunities for learners to develop independent levels of academic discourse. The study highlights the need for further research to inform teacher education and development with regard to more effective support structures to assist teachers with the sorts of challenges outlined above
An overview of energy minerals in the Springbok Flatsbasin, South Africa : implications for geochemical and geophysical exploration
No full textThis study is informed by the rising demand for power needs in South Africa and aims at
understanding the geophysical and geochemical characteristics of the energy minerals in the
Springbok Flats Basin and relating them to the prevailing geological and structural
setting for improved exploration targeting. The Springbok Flats Basin is part of the Karoo
sediments and host to uranium, coal and coal bed methane (CBM) resources. The lithology
sections in the basin indicate presence of basaltic lavas at the top, underlain by mudrocks,
siltstones, sandstones, conglomerates and diamictite, with interbedded coal beds
occasionally. The coals are uraniferous and shale bounded and of lower Beaufort age at 250
Ma.
The regional radiometric data identifies the regional extent of the Springbok Flats Basin as a
basin with low total count values. This information is useful in exploration as it gives an idea
of the limits of the area where to focus application for prospecting licenses. The reduced to
pole of the total magnetic field, residuals and first vertical derivative maps clearly show the
high magnetic susceptibility nature of the surrounding Bushveld rocks as compared to the
low Karoo sediment susceptibility within the basin. There are distinct ring shaped picks
within the basin possibly due to known Karoo dolerite sills in particular to the central south
western part of the grid.
The regional geochemical mapping program is a cost-effective way of providing an overview
of the relative abundance levels, regional trends and anomalous patterns in the underlying
lithological units. Background values of elements in soils over different lithological units and
the identification of anomalous values relative to these elements can easily be identified. The
geochemical results show an excellent correlation between soil chemistry and underlying
geological formations.
A few distinct gravity highs are clearly shown within the basin. Assuming the effect of the
Letaba basalt to the gravity readings is uniform across the basin; these distinct anomalies
could be due to Karoo dolerite sills as they coincide with areas of distinct high
magnetic signature. A conceptual model was generated assuming that the Karoo sediments’
layering is uniform across the gravity profile but changes in the residual are due to an
increased thickness of the sill supported by the gentle changes on the surface topography.
Satellite imagery has got its challenges especially in areas of vegetation but it does provide a
very useful tool in exploration. A number of spectral analysis techniques and band rations can
be used to differentiate the areas underlain by the Letaba basalts, the Karoo
sandstones/shale and Bushveld granites for mapping purposes. The priority focus will be on
the shallower Karoo sediments because of the potential for cheaper mining.
Exploration targeting needs to be guided by observed geochemical and geophysical
characteristics in order to prioritize areas taking into account the presence of Karoo intrusives
such as the dolerite sills that tend to devolatize the coal hence affecting the quality/rank.
Structures and gravity signatures are very important in delineating areas with thick sediments
that have a potential for CBM. The same understanding in targeting goes a long way in
planning drill holes, resource modelling and pre-feasibility stages for mine planning.
A high resolution airborne geophysical survey is recommended over the basin to better
resolve structures. Geophysical borehole logging is recommended to be part of the
exploration drilling programs in the Springbok Flats Basin in order to define the in-situ
geophysical characteristics. Geophysical logging is useful in particular for the uranium
reserves that cannot be delineated from the surface due to deep intersection
Perceptions of being a learner : an investigation into how first year Journalism students at a South African university construct themselves as learners
No full textThe aim of the research reported in this document was to explore the ways in which first year
Journalism students at a South African University construct themselves as learners. The
research adopted a case study approach of purposively selected first year journalism students.
In exploring this area, focus group and individual in-depth interviewing were employed which
illuminated important aspects of learner identity construction. In order to make sense of these
self-constructions, the research was located in the larger debates on discourse as espoused by
Michel Foucault who argues that discourse constructs subjectivities.
The research demonstrated that there were various discourses at play which influenced how
these learners spoke and behaved. The influence of these discourses on learners' experiences
varied at different times of the year. For example, the awarding of the Duly Performed (DP)
ce1tificate for students who met the minimum attendance and work requirements of a pmticular
course, the giving of tests, exercises and examinations were some of the technologies that
' forced ' students into compliance. In tenns of identity formation, the heterogeneous nature of
'being' a journalism 'student' revealed that the different discourses at play influenced learner
behaviour and that their identities continued to change over the year. Doing additional subjects
such as Sociology, Drama, Art History and others at the same time as Journalism and Media
Studies also meant that the learners had to negotiate the differing role requirements