1. Key Laboratory of Eco-Environment-Related Polymer Materials; Ministry of Education of China; College of Chemistry and Chemical Engineering; Northwest Normal University; Lanzhou 730070 P. R. China
2. State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals; Key Laboratory of Nonferrous Metal alloys and Processing; Ministry of Education; School of Materials Science & Engineering; Lanzhou University of Technology; Lanzhou 730050 P. R. China