[1] Council Sci & Ind Res CSIR, Ctr Nanostruct & Adv Mat CeNAM, HySA Infrastruct Ctr Competence, Chem Cluster, Pretoria, South Africa
[2] Univ Pretoria, Dept Phys, Inst Appl Mat, SARCHI Chair Carbon Technol & Mat, Pretoria, South Africa
[3] Obafemi Awolowo Univ, Dept Phys & Engn Phys, Ife 220005, Nigeria