http://hdl.handle.net/10204/2250 Thu, 20 Jun 2013 08:31:03 GMT 2013-06-20T08:31:03Z http://hdl.handle.net/10204/6769 Title: Scattering tensors and optical transitions in Si and Ge Authors: Kunert, HW; Machatine, AGJ; Niyongabo, P; Govender, M; Mwakikunga, BW Abstract: The selection rules (SR’s) for the Kronecker product (KP) of Si and Ge irreducible representations (irreps) are required to determine the intervalley scattering processes. The SR’s for transitions between the lowest conduction band minima at Γ, X and L high symmetry points and the highest maximum of the valence band (VB) in the Brillouin zone of Oh7 space group symmetry are determined. The elements of El-Ph scattering tensors are linear combinations of the Clebsch-Gordon coefficients (CGC’s). Here we have computed the coupling coefficients relevant to scattering tensors. Our theoretical results confirm the available experimental data. In this work, we focused on utilisation of group theory with regard to matrix elements of scattering tensors which are a linear combination of Clebsch-Gordon coefficients. The required phonon symmetries are determined by irreps contained in KP. We have calculated the U matrix for the LA phonon which diagonalizes the intervalley scattering between the Г2- valley and the four Lvalleys of the same star symmetry. We also have estimated an electron energy loss to X-valley acoustic phonon emission due to L-valleys electron scattering in a quasi-elastic process in agreement with available experimental data. Description: Copyright: 2012. Wiley VCH. This is an ABSTRACT ONLY. The definitive version is published in Physica Status Solidi C, vol. 9(10-11), pp 1974-1977 Wed, 01 Aug 2012 00:00:00 GMT http://hdl.handle.net/10204/6769 2012-08-01T00:00:00Z http://hdl.handle.net/10204/6759 Title: Nanotechnology for potable water and general consumption in developing countries Authors: Hillie, T; Hlophe, M Abstract: This chapter discusses water and its sources; the main focus is put on surface water and ground water. Factors such as water pollution and sewage are also discussed in areas of mining and agriculture. Furthermore the global water challenges that affect people in developing and developed countries. The challenges outlined are; poor governance, water scarcity, sanitation and climate change. Nanotechnology is sufficiently advanced to help provide potable water and water for general assumption in developing countries. The technology to be implemented will depend on the available infrastructure, and in most remote areas in developing countries where potable water is required, these include such rudimentary basics as electricity and accessibility. Water is vital to sustain life in every organism, including human beings. As a basic need for rich and poor alike, water takes on primary importance among public resources, one that we need to better understand and sustain. Description: Copyright: Taylor & Francis, New York, USA. Wed, 01 Aug 2012 00:00:00 GMT http://hdl.handle.net/10204/6759 2012-08-01T00:00:00Z http://hdl.handle.net/10204/6743 Title: Exfoliated polypyrrole-organically modified montmorillonite clay nanocomposite as a potential adsorbent for Cr (VI) removal Authors: Setshedi, KZ; Bhaumik, M; Songwane, S; nyango, MS; Maity, A Abstract: Exfoliated polypyrrole-organically modified montmorillonite clay nanocomposite (PPy OMMT NC), was prepared as a potential adsorbent, via in situ polymerization of pyrrole monomer for adsorption of toxic Cr(VI) from aqueous solution. The WAXD and SAXS results indicated that the clay sheets were exfoliated in the prepared nanocomposite. HR-TEM results showed good dispersion of the clay into the polymer matrix. The presence of the PPy polymer in the nanocomposite and adsorption of Cr(VI) onto the nanocomposite were confirmed using ATR-FTIR. Using the BET method, an improved surface area was observed for the PPy-OMMT NC compared to native clay. Batch adsorption studies whereby the pH, initial Cr(VI) concentration, sorbent dosage and temperature were varied, revealed that Cr(VI) adsorption process was rapid, spontaneous in nature and favoured with increased temperature at pH 2. The kinetic data fitted well to the pseudo second order kinetic model while the equilibrium data was satisfactorily described by the Langmuir isotherm. The Langmuir maximum adsorption capacity of Cr(VI) onto PPy-OMMT NC at pH 2.0 was found to be 112.3, 119.34, 176.2 and 209.6 mg/g at 292 K, 298 K, 308 K and 318 K, respectively. The selective adsorption of Cr(VI) was demonstrated in binary adsorption systems with co-existing ions. Moreover, desorption experiments revealed that the nanocomposite can be reused effectively for two consecutive adsorption–desorption cycles without any loss of its original capacity. Groundwater test results showed that the nanocomposite is a potential adsorbent for Cr(VI) ion removal from contaminated water sources. Description: Copyright: 2013 Elsevier. This is the Pre/Post print version of the work. The definite version is published in Chemical Engineering Journal, vol. 222, pp186-197 Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10204/6743 2013-01-01T00:00:00Z http://hdl.handle.net/10204/6735 Title: Chromium(VI) removal from water using fixed bed column of polypyrrole/Fe3O4 nanocomposite Authors: Bhaumik, M; Setshedi, K; Maity, A; Onyango, M.S Abstract: The adsorption of Cr(VI) using polypyrrole/Fe3O4nanocomposite adsorbent was investigated in a continuous flow fixed-bed column. The effects of composition of the nanocomposite, adsorbent mass, influent Cr(VI) concentration and flow rate on the adsorption characteristics of adsorbent was explored at pH 2. Experimental results confirmed that the breakthrough curves were dependent on bed mass, initial Cr(VI) concentration and flow rate. Three kinetic models; Yoon–Nelson, Thomas, Bohart–Adams were applied to the experimental data to predict the breakthrough curves using linear regression and to determine the characteristic parameters of the column that are useful for process design. The Yoon–Nelson and Thomas models were found appropriate for description of the whole breakthrough curves, whereas the Bohart– Adams model could only predict the initial part of the breakthrough curves. Using environmental water, the PPy/Fe3O4nanocomposite demonstrated its effectiveness in Cr(VI) removal below acceptable level by processing 5.04 L water with initial 76.59 mg/L Cr(VI) concentration using only 2 g of adsorbent mass. It can be concluded therefore that PPy/Fe3O4media provides alternative solution to ameliorate water contaminated with Cr(VI). Description: Copyright: 2013 Elsevier. This is a ABSTRACT ONLY. The definitive version is published in Separation and Purification Technology, Vol.110, pp11-19 Fri, 07 Jun 2013 00:00:00 GMT http://hdl.handle.net/10204/6735 2013-06-07T00:00:00Z