1. School of Material Science and Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, P. R. China
2. Department of Chemistry, University of the Western Cape, Robert Sobukwe Road, Cape Town 7535, South Africa
3. Institute of Environmental Science and Engineering, School of Metallurgy and Environment, Central South University, Changsha 410083, P. R. China