1. Laboratory of Nanomaterials for Sensors and Energy Faculty of Science University of Yaounde I, P.O.Box. 812 Yaounde Cameroon
2. Department of Chemistry University of Pretoria Private Bag X20 Pretoria, Hatfield 0028 South Africa
3. Nanostructures and Advanced Materials (CeNAM) Chemicals Cluster Council for Scientific and Industrial Research (CSIR) Meiring Naude Road, Brummeria Pretoria 0001 South Africa
4. School of Chemistry University Park University of Nottingham Nottingham NG7 2RD United Kingdom