1. Center for Nanochemistry Beijing Science and Engineering Center for Nanocarbons Beijing National Laboratory for Molecular Sciences College of Chemistry and Molecular Engineering Peking University Beijing 100871 P. R. China
2. Beijing Graphene Institute (BGI) Beijing 100095 P. R. China
3. Key Laboratory of Eco-materials Advanced Technology College of Materials Science and Engineering Fuzhou University Fuzhou 350108 P. R. China
4. National Laboratory of Solid State Microstructures Department of Physics Nanjing University Nanjing 210093 P. R. China
5. Department of Chemistry Tsinghua University Beijing 100871 P. R. China
6. School of Materials Science and Engineering Peking University Beijing 100095 P. R. China