1. School of Chemistry and Material Science, Shanxi Normal University, Linfen 041004, P. R. China
2. College of Chemistry and Environmental Engineering, Shanxi Datong University, Datong 037009, P. R. China
3. Hunan Provincial Key Laboratory of Cytochemistry, School of Chemistry and Food Engineering, Changsha University of Science and Technology, Changsha 410114, P. R. China