1. School of Mathematics and Physics, China University of Geosciences, Wuhan 430074, P. R. China
2. State Key Laboratory of Biogeology and Environmental Geology, Engineering Research Center of Nano-Geomaterials of Ministry of Education, Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, P. R. China
3. School of Electronic Science and Engineering, Nanjing University, Nanjing 210046, P. R. China