1. DSI/Mintek Nanotechnology Innovation Centre, Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, South Africa
2. Department of Chemistry, University of Witwatersrand, Private Bag X3, Braamfontein 2050, South Africa
3. Department of Chemical Sciences, University of Johannesburg, Doornfontein 2028, South Africa
4. Department of Chemistry, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa
5. Next Generation Health, Division 1, CSIR, Meiring Naude Road, Brummeria, Pretoria 0001, South Africa
6. Department of Chemistry, Faculty of Science, Engineering and Agriculture, University of Venda, Private Bag X5050, Thohoyandou 0950, South Africa