1. Anhui Province Key Laboratory of Pollutant Sensitive Materials and Environmental Remediation, Key Laboratory of Green and Precise Synthetic Chemistry and Applications, Ministry of Education, School of Physics and Electronic Information, Huaibei Normal University, Huaibei, Anhui 235000, P. R. China
2. Department of Materials Science, Fudan University, Shanghai 200433, P. R. China
3. Key Laboratory of Materials Physics and Anhui Key Laboratory of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, P. R. China