49 research outputs found
Continuity and change in the South African minibus taxi industry
No full textDissertation presented in fulfilment for the degree of Master of Management to the School of Governance, Faculty of Commerce, Law and Management, University of the Witwatersrand, 2021This dissertation seeks to identify the key features of the South African minibus taxi industry and understand the forces that have shaped it. The author, through qualitative interviews and participant observation, describes and analyses the different layers in the minibus taxi industry, from drivers to the national structures and how the taxi industry interacts with the state and private sector. A pervasive feature of the industry is the centrality of the role of violence, which is also explored as a strategic resource and binding constraint to change in the taxi industry. The dissertation aimed to establish the extent to which there has been continuity and change over the forty years of existence of the minibus taxi industry but concludes that there is an unyielding continuity in how the industry is structured and functions, to the benefit of a relatively few taxi leaders. In contrast, taxi drivers and owners of taxi vehicles continue to be marginalised from achieving decent livelihoods and accumulating wealth. In this context, the prospects of change where the needs of commuters are met, the state can fulfil its public transport mandate, and the taxi industry as a whole can prosper are poor. A prerequisite to change is an improved understanding by policy makers of who holds power in the taxi industry and the ability of the state to introduce measures to shift the balance of power to the majority of owners of taxi vehiclesPC(2023
The influence of the <tex>Ti^{4+}</tex> and Mg/Al-LDHs with photocatalytic properties
No full textAbstract: Herein, we report the formation of TiO2/LDH self-assembled nanocomposite systems using the memory effect property of the layered clay-type materials. Two different synthesis approaches, based on the modification of the initial brucite-like sheets composition, were used in order to investigate the influence of the Ti4+ location on the quality of the final products: the reconstruction of a calcined MgAl-LDH in a TiOSO4 center dot xH(2)O aqueous solution and the reconstruction of a calcined MgAlTi-LDH in aqueous solution. The reconstruction process, monitored using X-ray diffraction, IR spectroscopy, UV-vis diffuse reflectance spectroscopy, SEM and thermal analysis, produced different structural changes strongly related with the brucite-like sheets composition. The photocatalytic activity of the obtained nanocomposite systems was evaluated for the degradation of the methyl-orange (MO) dye. An intimate contact has been created between the anatase and the brucite-like sheets in the nanocomposite systems, which had a direct influence on the HO center dot radical production enhancing thus the photocatalytic performances. When comparing the as-synthesized catalysts, the MgAlTi-LDH solid manifests very powerful photocatalytic effect due to the segregation of small, well defined TiO2 nanoparticles on the highly hydroxilated layered surface. Up to 93% of the dye could be removed by a TiO2/LDH-type nanocomposite system. Controlled thermal treatment of photocatalytic systems allowed us to tailor the quality of the photocatalytic active sites deposited on the layered support. The use of the TiO2/LDHs nanocomposites showed multiple advantages highlighted by the increased activity per mass, higher efficiencies at a decreased solid/liquid ratio, decreased reaction times, reduced agglomeration and easy to separate at the end of the processes. (C) 2013 Elsevier B.V. All rights reserved
Mg-Al and Zn-Fe layered double hydroxides used for organic species storage and controlled release
No full textAbstract: Layered double hydroxides (LDH) containing (Mg and Al) or (Zn and Fe) were prepared by coprecipitation at constant pH, using NaOH and urea as precipitation agents. The most pure LDH phase in the Zn/Fe system was obtained with urea and in Mg/Al system when using NaOH. The incorporation of phenyl-alanine (Phe) anions in the interlayer of the LDH was performed by direct coprecipitation, ionic exchange and structure reconstruction of the mixed oxide obtained by the calcination of the coprecipitated product at 400 degrees C. The reconstruction method and the direct coprecipitation in a medium containing Phe in the initial mixture were less successful in terms of high yields of organic-mineral composite than the ionic exchange method. A spectacular change in sample morphology and yield in exchanged solid was noticed for the Zn3Fe sample obtained by ionic exchange for 6 h with Phe solution. A delivery test in PBS of pH = 7.4 showed the release of the Phe in several steps up to 25 h indicating different host-guest interactions between the Phe and the LDH matrix. This behavior makes the preparation useful to obtain late delivery drugs, by the incorporation of the anion inside the LDH layer. (C) 2013 Elsevier B.V. All rights reserved
Pt-doped semiconductive oxides loaded on mesoporous SBA-15 for gas sensing
No full textAbstract: SBA-15-based solids combining semiconductive oxides (Sn and In) and noble metal (Pt) were prepared by an incipient wet impregnation method in order to obtain materials for gas sensing. The materials were characterized by XRD, BET adsorption, SEM, and TEM. The BET analysis allowed obtaining details about the specific surface areas, pore size, and modifications due to the indium and/or tin oxides followed by the Pt deposition. XRD data revealed that In2O3 did not enter the mesopores of SBA-15, preventing also the entrance of the Pt nanoparticles in the mesopores. On the other hand, SnO2 nanoparticles further doped with Pt could enter the mesoporous network, affording a SBA-15 material loaded with SnO2 and very small Pt nanoparticles with high dispersion. Tablets obtained by pressing the modified SBA-15 were tested as sensitive materials for propene and hydrogen detection
Synthesis and characterization of catalytic metal semiconductor-doped siliceous materials with ordered structure for chemical sensoring
No full textSensing materials based on doped mesoporous silica of SBA-15 type were obtained by repeated wet impregnation of the solid with semiconductive oxides (Sn and In) and noble metal (Pt). The mesoporous structure of SBA was preserved during the doping and calcination of the solid, although slight pore size narrowing occurred as shown by the BET adsorption analysis. The solid was deposited by the casting technique as a thin layer on a finger structure. The modifications of its electrical resistance values in the presence of hydrogen and propene (50–400 ppm), at temperature values of 450 °C was used as sensing parameter, in the presence of propene and hydrogen. The sensitivity to propene was higher than that to hydrogen
Pt-doped semiconductive oxides loaded on mesoporous SBA-15 for gas sensing
No full textSBA-15-based solids combining semiconductive oxides (Sn and In) and noble metal (Pt) were prepared by an incipient wet impregnation method in order to obtain materials for gas sensing. The materials were characterized by XRD, BET adsorption, SEM, and TEM. The BET analysis allowed obtaining details about the specific surface areas, pore size, and modifications due to the indium and/or tin oxides followed by the Pt deposition. XRD data revealed that In2O3 did not enter the mesopores of SBA-15, preventing also the entrance of the Pt nanoparticles in the mesopores. On the other hand, SnO2 nanoparticles further doped with Pt could enter the mesoporous network, affording a SBA-15 material loaded with SnO2 and very small Pt nanoparticles with high dispersion. Tablets obtained by pressing the modified SBA-15 were tested as sensitive materials for propene and hydrogen detection.</p
Fabrication of <tex>CeO_{2}/LDHs$</tex> self-assemblies with enhanced photocatalytic performance : A case study on ZnSn-LDH matrix
No full textAbstract: The study reports the self-organization of CeO2 nanoparticles on highly dispersed ZnO6/SnO6 octahedral units provided by a layered double hydroxide by a simple and environment friendly synthesis procedure. The obtained catalysts were thoroughly investigated by XRD, TG/DTC, chemical analysis, Raman and UV-vis DR spectroscopic techniques in order to obtain information on their crystalline structure and identity, CeO2 content and photoresponsive properties. Furthermore, the controlled thermal treatment allowed us to obtain nano-coupled CeO2/ZnO/SnO2 systems with specific photocatalytic properties and their efficiency was tested for the phenol photodegradation under UV light. The data presented in this study shows that the phenol mineralization efficiency is strongly in relation with the presence of both the support and an optimum amount of CeO2 organized on the layered matrix. This study highlights the positive effect of the combinations of the strategic cations like Zn-Sn or Ce-Zn-Sn in a nano-architectural assembly able to utilize the collective properties of the components for enabling their cumulative photocatalytic properties for "green" removal of dangerous pollutants. (C) 2014 Elsevier B.V. All rights reserved
Infrared and Raman spectroscopic study of Sn-containing Zn/Al-layered double hydroxides
No full textAbstract: Zn/Al- and Zn/Al/Sn-LDHs were prepared by the co-precipitation method at constant pH. The LDH structure and the local environment of the tin cations were investigated using XRD and UV-vis DR methods. Band component analysis of both infrared and Raman spectra has been used for the detailed characterization. Raman spectroscopy proved to be more useful to distinguish between the different metal-OH stretching modes than FT-IR spectroscopy. The carbonate anions were found to be in a lowered symmetry. Changes in the spectral profile were observed when part of Al3 was replaced by Sn4 in the brucite-like structure. The shift of a band and the appearance of a weak shoulder at 498 cm(-1) in the Raman spectrum when the tin cations were involved indicated that small amounts of the tetravalent cations are segregated on the surface of the brucite-like sheets as very small regions of amorphous SnO2
In situ synthesis of <tex>Bi_{2}O_{3}$</tex> nanoparticles on ZincMe (Me = Al or Cr) layered double hydroxide frameworks for photocatalytic oxygen evolution from water under solar-light activation
No full textAbstract: A key target to boost solar-to-chemical conversion processes is to fabricate an efficient solar-light-responsive photocatalyst. Herein, we report the insitu synthesis of nanoparticles (NPs) of Bi2O3 directly on Zn-based layered double hydroxide (LDHs) frameworks. The insitu synthesis of Bi(2)O(3)NPs is done at room temperature, is ligand free and explores the ability of calcined ZnMeLDHs to reconstruct their layered structures in Bi(NO3)(3) aqueous solution. The insitu formation of Bi(2)O(3)NPs on ZnMeLDHs is assessed by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and UV/Vis spectroscopy and compared with the features of a corresponding Bi(2)O(3)NPs/LDH prepared by the conventional impregnation route. The rapid photocatalytic response of the Bi(2)O(3)NPs/ZnMeLDH (Me = Al, Cr) heterostructures is confirmed by O-2 generation from water under solar-light irradiation. The rate of O-2 generation increases by a factor of approximately 2 for the ZnCrLDH based catalysts as compared to that of the family of ZnAlLDH catalysts. Further, the presence of the bismuth phase and its nano-dimension leads to increased efficiency for the insitu prepared Bi(2)O(3)NPs/LDHs as compared to that of impregnated Bi2O3/LDH and the pristine LDHs
