1. School of Mechanics and Photoelectric Physics, Anhui University of Science and Technology, Huainan 232001, P. R. China
2. School of Physics and Materials Science, Anhui University, Hefei 230601, P. R. China
3. School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan 232001, P. R. China
4. Anhui International Joint Research Center for Nano Carbon-based Materials and Environmental Health, Anhui University of Science and Technology, Huainan 232001, P. R. China