1. College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, P. R. China
2. College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, P. R. China
3. Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province (Taiyuan University of Technology), Taiyuan 030024, P. R. China
4. Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, P.R. China