1. Faculty of Chemical Engineering, Key Laboratory for Attapulgite Science and Applied Technology of Jiangsu Province, Huaiyin Institute of Technology, Huaian 223003, P. R. China
2. School of Chemistry and Chemical Engineering, Linyi University, Linyi 276005, P. R. China
3. School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, P. R. China