1. School of Chemistry & Physics, University of KwaZulu-Natal, Pietermaritzburg Campus, Scottsville, Pietermaritzburg 3201, South Africa
2. Applied Photochemistry Group, SPECIFIC, College of Engineering, Swansea University, Bay Campus, Swansea SA1 8EN, U.K.
3. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China