1. 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
2. Division of Chemistry and Biological Chemistry; School of Physical and Mathematical Sciences; Nanyang Technological University; 21 Nanyang Link 637371 Singapore Singapore
3. State Key Laboratory of Coal Combustion; School of Energy and Power Engineering; Huazhong University of Science & Technology; Wuhan 430074 P. R. China