1. Institute of Coal Chemistry, Chinese Academy of Sciences, 27 Taoyuan South Road, Taiyuan 030001, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing, 100049, P. R. China
3. Engineering Research Center of Ministry of Education for Fine Chemicals, Shanxi University, Taiyuan 030006, P. R. China