1. School of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, PR China.
2. Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore.
3. School of Science, Chongqing University of Posts and Telecommunications, Chongqing, 400065, PR China.