1. Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province; State Key Laboratory of Applied Organic Chemistry and The Research Center of Biomedical Nanotechnology; Lanzhou University; Lanzhou 730000 P. R. China
2. Frontier Institute of Science and Technology; State Key Laboratory for Mechanical Behavior of Materials; Xi'an Jiaotong University; Xi'an 710049 P. R. China