1. School of Chemical Engineering and Light Industry Guangdong University of Technology Guangzhou 510006 P. R. China
2. Department of Physics City University of Hong Kong Hong Kong 999077 P. R. China
3. College of Chemistry and Chemical Engineering Xiamen University Xiamen 361005 P. R. China
4. Shenzhen Research Institute City University of Hong Kong Shenzhen 518057 P. R. China