title: Effects of monovalent and divalent metal cations on the aggregation and suspension of Fe3O4magnetic nanoparticles in aqueous solution.
abstract: There has been limited research investigating how the mechanisms of aggregation of magnetic nanoparticles (MNPs) are affected by inorganic ions. In this study, Na+, Mg2+, Ca2+, Sr2+and Ba2+were selected to systematically study the aggregation mechanisms of Fe3O4MNPs. The results indicated that divalent cations more significantly affected the stabilities of MNPs than Na+at low concentrations (e.g., 0.1mM) in a decreasing order of Ba2+>Sr2+>Ca2+>Mg2+>Na+. Extended DLVO theory did not offer a satisfactory explanation for the above difference due because it ignores specific ion effects. It was also found that the initial adsorption ratios of these metals by Fe3O4MNPs were linearly proportional to the hydrodynamic diameter (HDD) of Fe3O4MNPs before aggregation occurred. In addition to the valence states, the hydration forces and ionic radii of the metal cations were proposed to be other factors that significantly affected the interactions of metal cations with Fe3O4MNPs based on the excellent linear relationships of the HDD of Fe3O4MNPs and these three factors. Moreover, a bridging function of divalent cations might develop after aggregation occurred based on the increases in their adsorption amounts and intensities for binding oxygen-containing functional groups. In addition, an increase in the positive ζ potential of MNPs was observed with the addition of divalent cations until 10.0mM at a pH of 5.0, which potentially enhances the resistance of MNPs to aggregation in aquatic systems compared with Na+. Consequentially, the effects of metal cations on the aggregation of MNPs are determined by the hydration forces, valance states, ionic radii and bond types formed on the MNPs. Thus, the specific ion effects of these cations should be considered in predicting the environmental behaviors of specific nanomaterials.
authors.affiliation: College of Water Sciences, Beijing Normal University, Beijing 100875, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: zhaoxiaoli_zxl@126.com.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Xuejiao
authors.initials: X
authors.lastname: Han
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Tang
authors.affiliation: College of Water Sciences, Beijing Normal University, Beijing 100875, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Shasha
authors.initials: S
authors.lastname: Liu
authors.affiliation: College of Water Sciences, Beijing Normal University, Beijing 100875, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Guo
authors.affiliation: Environmental Monitoring Center of Guangxi Zhuang Autonomous Region, Guangxi 530028, China.
authors.forename: Chaobing
authors.initials: C
authors.lastname: Deng
authors.affiliation: South China Institute of Environmental Science, MEP, Guangzhou 510655, China.
authors.forename: Qingwei
authors.initials: Q
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Huanhua
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors.forename: Fengchang
authors.initials: F
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, United States.
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Meng
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Department of Biomedical and Veterinary Biosciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: John P
authors.initials: JP
authors.lastname: Giesy
keywords: Aggregation and suspension; Aquatic environment; Fe(3)O(4) MNPs; Metal cations; Specific ion effects