1. Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
2. Department of Chemical Engineering, Stellenbosch University, Stellenbosch 7604, South Africa
3. Department of Chemistry, Debre Berhan University, P.O. Box 405, Debre Berhan, Ethiopia
4. Department of Chemistry, Addis Ababa University, P.O. Box 33658, Addis Ababa, Ethiopia
5. Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE412 96, Gothenburg, Sweden