Effects of monovalent and divalent metal cations on the aggregation and suspension of Fe3O4 magnetic nanoparticles in aqueous solution

Hao Wang; Xiaoli Zhao; Xuejiao Han; Zhi Tang; Shasha Liu; Wenjing Guo; Chaobing Deng; Qingwei Guo; Huanhua Wang; Fengchang Wu; Xiaoguang Meng; John P Giesy

doi:10.1016/j.scitotenv.2017.02.060

Effects of monovalent and divalent metal cations on the aggregation and suspension of Fe₃O₄ magnetic nanoparticles in aqueous solution

Sci Total Environ. 2017 May 15:586:817-826. doi: 10.1016/j.scitotenv.2017.02.060. Epub 2017 Feb 12.

Authors

Hao Wang¹, Xiaoli Zhao², Xuejiao Han³, Zhi Tang³, Shasha Liu¹, Wenjing Guo¹, Chaobing Deng⁴, Qingwei Guo⁵, Huanhua Wang³, Fengchang Wu³, Xiaoguang Meng⁶, John P Giesy⁷

Affiliations

¹ 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.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: zhaoxiaoli_zxl@126.com.
³ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
⁴ Environmental Monitoring Center of Guangxi Zhuang Autonomous Region, Guangxi 530028, China.
⁵ South China Institute of Environmental Science, MEP, Guangzhou 510655, China.
⁶ 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.
⁷ 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.

PMID: 28202242
DOI: 10.1016/j.scitotenv.2017.02.060

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 Fe₃O₄ MNPs. 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 Fe₃O₄ MNPs were linearly proportional to the hydrodynamic diameter (HDD) of Fe₃O₄ MNPs 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 Fe₃O₄ MNPs based on the excellent linear relationships of the HDD of Fe₃O₄ MNPs 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.

Keywords: Aggregation and suspension; Aquatic environment; Fe(3)O(4) MNPs; Metal cations; Specific ion effects.