1. Department of Chemistry, Cape Peninsula University of Technology, P.O. Box 652, Cape Town 2000, South Africa
2. Department of Chemical Sciences, University of Johannesburg, Doornfontein, P.O. Box 17011, Johannesburg 2028, South Africa
3. Centre for Nanomaterials Science Research, University of Johannesburg, Johannesburg 2028, South Africa
4. Department of Chemistry, University of KwaZulu-Natal, Private Bag X 54001, Durban 4000, South Africa