1. Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, P.O. Box 17011, Doornfontein, Johannesburg 2028, South Africa
2. DSI/Mintek Nanotechnology Innovation Centre, Water Research Node, University of Johannesburg, Doornfontein Campus, P.O. Box 17011, Doornfontein, Johannesburg 2028, South Africa
3. Advanced Materials Division, DSI/Mintek Nanotechnology Innovation Centre, Private Bag X3015, Randburg 2125, South Africa
4. Department of Water and Sanitation, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa