1. Department of Chemistry, Vaal University of Technology, Vanderbijlpark, South Africa;
2. Centre for Renewable Energy and Water, Vaal University of Technology, Vanderbijlpark, South Africa;
3. Department of Chemical Engineering, Vaal University of Technology, Vanderbijlpark, South Africa;
4. Botswana International University of Science and Technology, Palapye, Botswana