1. School of Chemistry and Chemical Engineering, North Minzu University, Yinchuan 750021, P.R.China
2. Department of Chemistry, College of Basic Medicine, Ningxia Medical University, Yinchuan 750004, China
3. School of Materials Science and Engineering, Key Laboratory of Polymer Materials and Manufacturing Technology, North Minzu University, Yinchuan 750021, P.R.China
4. School of Environmental Science and Engineering, Shaanxi University of Science and Technology, Xi'an, 710021, Shanxi, China