1. Department of Chemical Engineering, Cape Peninsula University of Technology, Symphony way, P.O. Box 1906, Bellville, Cape Town 7535, South Africa
2. Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla, Missouri 65401, United States
3. Environmental and Nanoscience, Chemistry Department, Faculty of Natural Science, University of the Western Cape, Cape Town 8000, South Africa