1. School of Chemisry and Chemical Engineering, North Minzu University, Yinchuan 750021, P. R. China
2. Key Laboratory for Chemical Engineering and Technology, State Ethnic Affairs Commission, North Minzu University, Yinchuan 750021, P. R. China
3. School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, P. R. China