1. School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, 637459 Singapore
2. State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing 210023, P. R. China
3. Research Center for Environmental Nanotechnology (ReCENT), Nanjing University, Nanjing 210023, China