1. a DST/NRF Centre of Excellence in Strong Materials , University of the Witwatersrand , Johannesburg , South Africa
2. b Molecular Sciences Institute, School of Chemistry , University of the Witwatersrand , Johannesburg , South Africa
3. c Laboratório de Nanotecnologia e Energia Solar , (Institute of Chemistry, University of Campinas–UNICAMP) , Campinas , Brazil
4. d Department of Chemistry and Polymer Sciences , Stellenbosch University , Stellenbosch , Western Cape , South Africa