1. School of Chemical and Metallurgical Engineering, University of the Witwatersrand Johannesburg, Private Bag X3 PO Wits 2050, Johannesburg, South Africa
2. School of Chemistry, University of the Witwatersrand Johannesburg, Private Bag X3 PO Wits 2050, Johannesburg, South Africa
3. Department of Natural Science, Manchester Metropolitan University, Chester Street M1 5GD, Manchester, UK