National Center for Nano structured Materials

Pretoria, South Africa

National Center for Nano structured Materials

Pretoria, South Africa
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Maphoru M.V.,Tshwane University of Technology | Kesavan Pillai S.,National Center for Nano Structured Materials | Heveling J.,Tshwane University of Technology
Journal of Catalysis | Year: 2017

Compositional and morphological studies on supported platinum are important for the improvement and expanded use of catalysts for oxidative coupling reactions. Nanocomposites consisting of 5% Pt supported on activated carbon and promoted with 5% Bi or Sb were prepared by electroless deposition and microwave-assisted (MW) methods. Addition of promoters significantly increases the dispersion of Pt. Bismuth reacts with residual phosphorus of the support to form various phases of BiPO4, while Sb cannot be detected by XRD. However, samples prepared by the MW method are unique in that they contain crystalline PtBi or PtSb alloys as part of the phase matrix. The thermal stability of the samples in air and the TOFs for the oxidation of 2-methyl-1-naphthol correlate with the metal dispersion. Since the oxidation reaction is understood to take place on the surface of metals with high standard electrode potentials, sufficient Pt exposure is one of the key performance parameters. © 2017 Elsevier Inc.

Maphoru M.V.,Tshwane University of Technology | Heveling J.,Tshwane University of Technology | Kesavan Pillai S.,National Center for Nano Structured Materials
Kinetics and Catalysis | Year: 2017

Oxidative coupling of naphthols is a useful method for the formation of new carbon-carbon bonds in organic synthesis. In the presence of hydrogen peroxide, platinum supported on activated carbon catalyses this reaction. The outcome is influenced by the solvent, the reaction temperature and the physical structure of the catalyst. The catalyst structure is determined by the synthesis method and the modifier used (Bi or Sb). Within 40 min 4-methoxy-1-naphthol can be converted to 4,4'-dimethoxy-2,2'-binaphthalenyl-1,1'-diol with a yield of up to 94%, or to 4,4'-dimethoxy-2,2'-binaphthalenylidene-1,1'-dione with a yield of 92%. High amounts of quinoid byproducts (≤22%) are observed in nitromethane as the solvent. © 2017, Pleiades Publishing, Ltd.

Ojijo V.,National Center for Nano Structured Materials | Ojijo V.,Tshwane University of Technology | Sinha Ray S.,National Center for Nano Structured Materials | Sinha Ray S.,University of Johannesburg | Sadiku R.,Tshwane University of Technology
ACS Applied Materials and Interfaces | Year: 2013

Polylactide and poly(butylene succinate-co-adipate) (PLA/PBSA) were melt-blended in the presence of triphenyl phosphite (TPP). An increase in the torque during melt mixing was used to monitor the changes in viscosity as compatibilization of the blends occurred. Scanning electron micrographs showed not only a reduction in the dispersed-phase size with increased TPP content but also fibrillated links between the PLA and PBSA phases, signifying compatibilization. Moreover, optimization of parameters such as the mixing sequence and time, TPP content, and PBSA concentration revealed that blends containing 30 and 10 wt % PBSA and 2 wt % TPP, which were processed for 30 min, were optimal in terms of thermomechanical properties. The impact strength increased from 6 kJ/m2 for PLA to 11 and 16 kJ/m2 for blends containing 30 and 10 wt % PBSA, respectively, whereas the elongation-at-break increased from 6% for PLA to 20 and 37% for blends containing 30 and 10 wt % PBSA, respectively. Upon compatibilization, the failure mode shifted from the brittle fracture of PLA to ductile deformation, effected by the debonding between the two phases. With improved phase adhesion, compatibilized blends not only were toughened but also did not significantly lose tensile strength and thermal stability. © 2013 American Chemical Society.

Malwela T.,National Center for Nano Structured Materials | Sinha Ray S.,National Center for Nano Structured Materials
Polymer | Year: 2011

This communication reports a unique morphology of dispersed clay particles in a polymer nanocomposite. A nanocomposite of poly[butylene succinate)-co-adipate] (PBSA) with 3 wt% of organically modified montmorillonite was prepared by melt-blending in a batch mixer. The focused-ion beam cross-sectioning at 36° to the sample surface, followed by delineation etching with water revealed a unique dispersed morphology of the clay particles in PBSA nanocomposite. The scanning electron microscopy image showed a unique structure, where the vertically embedded stacked silicate layers fall down to the PBSA matrix, forming a corn-flake like structure. This unique structured was called as "nano-flake". © 2010 Elsevier Ltd. All rights reserved.

Maphoru M.V.,Tshwane University of Technology | Heveling J.,Tshwane University of Technology | Pillai S.K.,National Center for Nano Structured Materials
ChemPlusChem | Year: 2014

Bismuth-promoted platinum catalysts were tested for the oxidative coupling of 2- and 4-substituted 1-naphthols at different temperatures and ambient pressure. The principal final products are the 3,3'-substituted 1,1'-binaphthalenylidene-4,4'- diones and the 4,4'-substituted 2,2'-binaphthalenylidene-1,1'- diones, respectively. Hydrogen peroxide was used as the oxidant. Only naphthols with electron-donating substituents reacted. The corresponding binaphthalenyl diols can be considered as reaction intermediates. Yields of up to 99% were obtained from 2-methyl-1-naphthol as the starting material within 20 minutes. Probably for steric reasons, the diol is the final product obtained from 2-ethyl-1-naphthol. For 4-methoxy- 1-naphthol the outcome is determined by the reaction temperature. At 25 8C the expected 1,1'-dione is the major product, whereas at 60 8C 1'-hydroxy-4'-methoxy-2,2'-binaphthalenyl- 1,4-dione is formed; the loss of one methoxy unit and the preservation of the hydroxy group can be explained by the competitive cleavage of one of the two O-Me bonds at higher temperature. Unpromoted platinum and a range of other metallic catalysts, including gold and Raney nickel, were also found to be active. The products obtained are brightly colored solids that could be used as dyes. The method described is truly catalytic and environmentally benign. The potential of the technique justifies further research to expand on the applicability of this novel method. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Motaung D.E.,National Center for Nano structured Materials | Motaung D.E.,University of the Western Cape | Malgas G.F.,National Center for Nano structured Materials | Arendse C.J.,University of the Western Cape
Synthetic Metals | Year: 2010

In this report the effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The polymer blend films spin coated from faster evaporating, non-aromatic solvents demonstrated an improved ordering and optical absorption in P3HT and blended films, indicating that the limited solubility of P3HT:C60 in a marginal solvent can lead directly to optimal morphologies on the films. The PL quenched by a factor of 3 after blending the P3HT with C60 in a 1:1 wt. ratio using CB, xylene, DCB, and toluene as solvents, indicating a partially charge transfer from P3HT to C60. A complete reduction in the PL intensity was observed in the film spin-coated from chloroform. © 2010 Elsevier B.V. All rights reserved.

Folarin O.M.,Tshwane University of Technology | Sadiku E.R.,Tshwane University of Technology | Maity A.,National Center for Nano Structured Materials
International Journal of Physical Sciences | Year: 2011

Polymer-noble metal nanocomposites have been extensively investigated due to their potential ability to provide materials with novel mechanical, electronic or chemical behaviour for technological applications. Many preparative procedures have been proposed and detailed characterizations have been carried out on conducting polymer-noble metal nanocomposites; thanks to the rapid improvement in analytical techniques on surface and nanoscale materials. This review focuses on the preparation, characterization of polymer-noble metal nanocomposites and some potential areas for applications such as sensors, batteries (fuel cells) and capacitors. © 2011 Academic Journals.

Rajendran R.,SRM University | Muralidharan R.,Indira Gandhi Center for Atomic Research | Santhana Gopalakrishnan R.,Indira Gandhi Center for Atomic Research | Chellamuthu M.,SRM University | And 2 more authors.
European Journal of Inorganic Chemistry | Year: 2011

Single-crystalline Fe3O4 nanorice has been prepared by a simple one-pot, surfactant-assisted hydrothermal method using dodecyltrimethylammonium bromide (DTAB) as a surfactant. X-ray powder diffraction, field emission scanning electron microscopy (FESEM), TEM, high-resolution (HR)TEM, micro-Raman spectroscopy and magnetic measurements have been employed to study the properties of the product. The importance of NaAc and ethylene glycol in the formation of the pure magnetite phase has been established. The as-synthesized products have a regular rice-like shape with an average diameter of 150 nm and length of 500 nm and are monodisperse. Shape evolution from cauliflower- to rice-like morphology has been achieved by controlling the DTAB concentration. A possible formation mechanism for the Fe3O4 nanorice is explored. Furthermore, the product showed ferromagnetic properties at room temperature. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Linganiso E.C.,National Center for Nano Structured Materials | Linganiso E.C.,University of Witwatersrand | Mwakikunga B.W.,National Center for Nano Structured Materials | Coville N.J.,University of Witwatersrand | Mhlanga S.D.,University of Johannesburg
Journal of Alloys and Compounds | Year: 2015

Single phase α-NiS nano-compounds with uniformly distributed hierarchical networks were synthesized by a microwave-assisted hydrothermal technique. The materials were evaluated for thermal stability under an oxidative environment and at temperatures between 150 °C and 600 °C. NiS materials showed stability at 300 °C and NiO formation was observed from 350 °C to 600 °C. The annealing effect on the crystalline size and IR absorption of the annealed samples is reported by XRD and FTIR studied. The EPR properties of the annealed materials were studied and compared to the oxidized materials. The transition temperature of 350 °C for the formation of NiO from NiS oxidation was confirmed by calculating the number of spins obtained from the EPR data. Vibrating sample magnetometry (VSM) shows that this pure NiS has both ferromagnetic ordering and paramagnetic domains. Further, the transition temperature of -9 °C of the pure α-NiS nano-compounds was confirmed by performing electrical measurements on the as-synthesized material. © 2014 Elsevier B.V. All rights reserved.

Moodley M.K.,National Center for Nano structured Materials | Moodley M.K.,University of Witwatersrand | Coville N.J.,University of Witwatersrand
Chemical Physics Letters | Year: 2010

In situ optical emission spectroscopy (OES) was used to investigate the spatial and temporal evolution of C2, the electron density (Ne) and the electron temperature (Te) of laser induced plasmas in the laser-furnace method of synthesizing single-walled carbon nanotubes (SWCNTs). The intensities of the spectral maps of C2,Ne and Te showed a strong temperature dependence. The frequency of sharp fluctuations which appear as hot spots in the spectral maps of Ne and Te increased as the furnace temperature was increased from 1073 to 1273 K. We suggest that the appearance of hot spots is a result of the heat of formation of SWCNTs. © 2010 Elsevier B.V. All rights reserved.

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