1. Department of Science and Environmental Studies The Education University of Hong Kong Tai Po, New Territories Hong Kong P. R. China
2. Department of Chemistry Tsinghua University Beijing 100084 P. R. China
3. State Key Laboratory of Photocatalysis on Energy and Environment College of Chemistry Fuzhou University Fuzhou 350116 P. R. China
4. Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hong Kong P. R. China