1. Department of Chemical Sciences, University of Johannesburg, Doornfontein, 2028 Johannesburg, South Africa
2. Centre for Nanostructures and Advanced Materials, DSI-CSIR Nanotechnology Innovation Centre, Council for Scientific and Industrial Research, Pretoria 0001, South Africa
3. Department of Polymer Technology and Engineering, Harare Institute of Technology, Belvedere, Harare, Zimbabwe