1. Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province, Yancheng Institute of Technology, Yancheng 224051, P. R. China
2. School of Physical and Mathematical Sciences, Nanjing Tech University, Nanjing 210009, P. R. China
3. School of Materials Science and Engineering, Yancheng Institute of Technology, Yancheng 224051, P. R. China
4. School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, P. R. China