1. School of Chemistry and Chemical Engineering Guangxi University Nanning Guangxi 530004 P. R. China
2. School of Chemical and Environmental Engineering China University of Mining & Technology (Beijing) Beijing 100083 China
3. CAS Center for Excellence in Nanoscience Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100083 China
4. School of Nanoscience and Technology University of Chinese Academy of Sciences Beijing 100049 China