1. Department of Chemistry, Vaal University of Technology, Private Bag X 021, Vanderbijlpark, 1900, South Africa
2. Institute for Nanotechnology and Water Sustainability, University of South Africa, 28 Pioneer road, Florida Park, Roodeport, 1709, South Africa
3. School of Chemistry, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa