1. Department of Applied Chemistry; University of Johannesburg; P.O. Box 17011 Doornfontein Johannesburg 2028 South Africa
2. Department of Chemical Engineering; Vaal University of Technology; Vanderbijlpark 1911 South Africa
3. Inorganic and Physical Chemistry Department; Indian Institute of Science; Bangalore 560 012 Karnataka India
4. College of Science Engineering and Technology; The University of South Africa; P.O. Box P/B X6 Roodepoort South Africa