Effects of F-, Cl-, Br-, NO3-, and SO42- on the colloidal stability of Fe3O4 nanoparticles in the aqueous phase

Hao Wang; Xuejiao Han; Yao Chen; Wenjing Guo; Wenli Zheng; Nan Cai; Qingwei Guo; Xiaoli Zhao; Fengchang Wu

doi:10.1016/j.scitotenv.2020.143962

Effects of F^-, Cl^-, Br^-, NO₃^-, and SO₄^2- on the colloidal stability of Fe₃O₄ nanoparticles in the aqueous phase

Sci Total Environ. 2021 Feb 25:757:143962. doi: 10.1016/j.scitotenv.2020.143962. Epub 2020 Dec 8.

Authors

Hao Wang¹, Xuejiao Han², Yao Chen³, Wenjing Guo⁴, Wenli Zheng³, Nan Cai³, Qingwei Guo⁵, Xiaoli Zhao⁶, Fengchang Wu²

Affiliations

¹ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; South China Institute of Environmental Science, Ministry of Ecology and Environment, Guangzhou 510530, China.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
³ South China Institute of Environmental Science, Ministry of Ecology and Environment, Guangzhou 510530, China.
⁴ Institute of Agricultural Resource and Environmental Sciences, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China.
⁵ South China Institute of Environmental Science, Ministry of Ecology and Environment, Guangzhou 510530, China. Electronic address: guoqingwei@scies.org.
⁶ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: zhaoxiaoli_zxl@126.com.

PMID: 33316533
DOI: 10.1016/j.scitotenv.2020.143962

Abstract

The effect of ions on the colloidal behavior of magnetic nanoparticles (MNPs) is an important factor for determining the dispersibility of MNPs. Compared with the effects of cations and organic matter, the effect of anions on MNPs has rarely been studied. Hence, in this study, the effect of anions on the aggregation of Fe₃O₄ MNPs in the aqueous phase was investigated using F^-, Cl^-, Br^-, NO₃^-, and SO₄^2-. The results indicated that the effect of anions on the colloidal behavior of the MNPs varied widely depending on their valence state, concentration, hydration ability, solution pH, and the magnetic force between the MNPs. Specifically, at pH 5.0, the anions were mainly adsorbed on the particle surface by electrostatic attraction, decreasing the electrostatic repulsion between the MNPs and causing an aggregation of the particles in the order of SO₄^2- > F^- > Br^- > Cl^- ≈ NO₃^-. At pH 9.0, anions strengthened the suspension of the MNPs at low ionic strength (IS) (≤5); however, with increasing IS, an aggregation of the MNPs in the following order was formed: NO₃^- > Cl^- > Br^- ≥ F^- > SO₄^2-. This was a result of the combined effects of the IS of solution, hydrability, and polarizability of the anions. Furthermore, the Derjaguin-Landau-Vervey-Overbeek (DLVO) theory can explain the colloidal behavior of MNPs in the presence of magnetic forces, but it fails to differentiate the MNP behaviors between monovalent anions because the effects of ionic hydrability and polarizability are not considered. Distinctively, the secondary minimum between the MNPs particles were induced via magnetic attraction and played a critical role in adjusting the colloidal stability of the MNPs. Overall, these results indicate that specific ionic effects and magnetic attraction are important for interpreting the colloidal stability of MNPs in aqueous conditions.

Keywords: Anions; Aqueous phase; Colloidal stability; DLVO; Magnetic nanoparticles.