1. Center on Nanoenergy Research School of Physical Science and Technology Guangxi University Nanning 530004 P. R. China
2. Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 P. R. China
3. School of Nanoscience and Technology University of Chinese Academy of Sciences Beijing 100049 P. R. China
4. CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety and CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing 100190 P. R. China