[1] Univ Malaya, Dept Chem, Fac Sci, Kuala Lumpur 50603, Malaysia
[2] Univ Malaya, Inst Nanotechnol & Catalysis NanoCat, Kuala Lumpur 50603, Malaysia
[3] Bayero Univ Kano, Dept Pure & Ind Chem, Kano, Nigeria
[4] Univ Malaya, Fac Sci, Dept Phys, Kuala Lumpur 50603, Malaysia