1. College of Chemistry & Pharmacy, Northwest A&F University, Yangling 712100, P. R. China
2. State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, P. R. China
3. Analysis and Testing Center, Ningxia University, Yinchuan 750021, P. R. China