1. State Key Laboratory of Urban Water Resource and Environment (SKLUWRE), Harbin Institute of Technology, 73 Huanghe Road, Nangang District, Harbin, 150090, P.R. China
2. Department of Civil and Environmental Engineering, Duke University, Durham, North Carolina 27708, United States
3. Center for the Environmental Implications of NanoTechnology (CEINT), Duke University, Durham, North Carolina 27708, United States