title: Heteroaggregation of engineered nanoparticles and kaolin clays in aqueous environments.
abstract: The increasing and wide use of nanoparticles (NPs), including TiO2 and Ag NPs, have raised concerns due to their potential toxicity and environmental impacts. Kaolin is a very common mineral in aquatic systems, and there is a very high probability that nanoparticles (NPs) will interact with these clay minerals. We studied the effect of kaolin particles on the aggregation of NPs under different conditions, including the role of pH, ionic strength (IS), and humic acid (HA). We show that kaolin reduces the energy barrier and the Critical Coagulation Concentration (CCC) at pH 4. At pH 8, even though the energy barrier of the system without kaolin increases, kaolin promotes NP aggregation via heteroaggregation. When IS is equal to or greater than the CCC, on the one hand HA promotes aggregation of TiO2 NPs, but on the other hand HA decreases the rate of Ag NP aggregation because the existence of a surface coating may limit the adsorption of HA on these Ag NPs. In addition, the presence of HA increases the energy barrier and the CCC of the binary system (kaolin + NPs). Thus, the complex interactions of clay, NPs, IS, pH, and HA concentration determine the colloidal stability of the NPs. We find that kaolin is a potential coagulant for removal of NPs that behave like Ag and TiO2.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China. Electronic address: hongtao@tongji.edu.cn.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
authors.forename: Ya-nan
authors.initials: YN
authors.lastname: Dong
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
authors.forename: Miao
authors.initials: M
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.affiliation: Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, 93106, United States.
authors.forename: Arturo A
authors.initials: AA
authors.lastname: Keller
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China.
authors.forename: Fengting
authors.initials: F
authors.lastname: Li
mesh_terms: D000327:Adsorption; D000465:Algorithms; D000538:Aluminum Silicates / Q000737:chemistry*; D000077215:Clay; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D007700:Kinetics; D053768:Metal Nanoparticles / Q000737:chemistry / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D009994:Osmolar Concentration; D012834:Silver / Q000737:chemistry; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D006812:Humic Substances; D014874:Water Pollutants, Chemical; D014867:Water; C009495:titanium dioxide; D007616:Kaolin; D012834:Silver; D014025:Titanium; D000077215:Clay
keywords: Aggregation; Critical coagulation concentration; Humic acid; Kaolin; Nanoparticles