1. DSI/Mintek-Nanotechnology Innovation Centre, Advanced Materials, Mintek, Randburg 2125, South Africa
2. Centre for Nanostructures and Advanced Materials, Chemicals Cluster, CSIR, Pretoria 0001, South Africa
3. Department of Chemistry, Durban University of Technology, Durban 4000, South Africa
4. Department of Life Sciences, Central University of Technology Free State, Bloemfontein 9301, South Africa
5. Department of Chemistry, Nelson Mandela University, Port Elizabeth 6001, South Africa