1. School of Chemistry and Chemical Engineering, Jiangsu Univers ity, Zhenjiang 212013, P. R. China
2. Baotou Research Institute of Rare Earths, Baotou 014030, P. R. China
3. College of Chemistry, Jilin University, Changchun 130012, P. R. China
4. College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, Guangdong, P. R. China