1. Department of Chemistry, Faculty of Applied and Computer Sciences, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900, South Africa
2. Institute of Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Florida Park, Roodepoort 1709, South Africa
3. School of Chemistry, Faculty of Science, Wits University, Private Bag 3, Johannesburg 2050, South Africa
4. Nanotechnology Innovation Centre, Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, South Africa