1. Laboratory of Porous Materials for Sensors and Energy, Faculty of Science, University of Yaounde 1, P.O. Box 812, Yaounde, Cameroon
2. Department of Chemistry, High Teacher Training College, University of Yaounde 1, P.O. Box 49, Yaounde, Cameroon
3. Universidade de São Paulo, Instituto de Química, Av. Professor Lineu Prestes, 748, CEP: 05508-000-São Paulo, Brazil