1. Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077, Hong Kong
2. Hong Kong Institute for Clean Energy, City University of Hong Kong, Kowloon 999077, Hong Kong
3. State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong 999077, China
4. Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom; Department of Physics, EWHA Womans University, Seoul 03760, South Korea
5. Department of Chemistry, City University of Hong Kong, Kowloon 999077, Hong Kong