State Key Laboratory of Biogeology & Environmental Geology and School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, 430074, PR China; College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi, 712100, China; The Key Laboratory of Water and Sediment Sciences (Ministry of Education), State Environmental Protection Key Laboratory of All Material Fluxes in River Ecosystems, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China.
Department of Civil & Environmental Engineering, University of Houston, Houston, TX, 77004, United States; Benchmark Lab & Services, Houston, TX, 77092, United States.
Chemosphere. 2023 Apr;319:137992. doi: 10.1016/j.chemosphere.2023.137992. Epub 2023 Jan 28.
The poor colloidal stability of magnetite nanoparticles (MNPs) limits their mobility and application, so various organic coatings (OCs) were applied to MNPs. Here, a comparative study on the colloidal stability of MNPs coated with acetic (HAc) and polyacrylic acids (PAA) was conducted under varied pH (5.0-9.0) in the presence of different concentrations of cations and anions, as well as humic acid (HA). Comparing the effects of various cations and anions, the stability of both HAc/PAA-MNPs followed the order: Na > Caand PO > SO > Cl, which could be explained by their adsorption behaviors onto HAc/PAA-MNPs and the resulting surface charge changes. Under all conditions even with more anion adsorption onto HAc-MNPs (0.14-22.56 mg/g) than onto PAA-MNPs (0.04-18.34 mg/g), PAA-MNPs were more negatively charged than HAc-MNPs, as PAA has a lower pH (2.6 ± 0.1) than that of HAc (3.7 ± 0.1). Neither the HAc nor PAA coatings were displaced by phosphate even at considerably high phosphate concentration. Compared with HAc-MNPs, the stability of PAA-MNPs was greatly improved under all studied conditions, which could be due to both stronger electrostatic and additional steric repulsion forces among PAA-MNPs. Besides, under all conditions, Derjaguin-Landau-Verwey-Overbeek (DLVO) explained well the aggregation kinetic of HAc-MNPs; while extended DLVO (EDLVO) successfully predict that of PAA-MNPs, indicating steric forces among PAA-MNPs. The aggregation of HAc/PAA-MNPs was all inhibited in varied electrolyte solutions by HA (2 mg C/L) addition. This study suggested that carboxyl coatings with higher molecular weights and pK values could stabilize MNPs better due to stronger electrostatic and additional steric repulsion. However, in the presence of HA, these two forces were mainly controlled by adsorbed HA instead of the organic pre-coatings on MNPs.
磁性纳米颗粒 (MNPs) 的胶体稳定性差限制了它们的迁移和应用，因此各种有机涂层 (OCs) 被应用于 MNPs。在这里，我们在不同 pH 值 (5.0-9.0) 下，以及在不同浓度的阳离子和阴离子以及腐殖酸 (HA) 存在的情况下，对醋酸 (HAc) 和聚丙烯酸 (PAA) 涂层的 MNPs 的胶体稳定性进行了比较研究。比较各种阳离子和阴离子的影响，HAc/PAA-MNPs 的稳定性遵循以下顺序：Na>Ca 和 PO>SO>Cl，这可以用它们在 HAc/PAA-MNPs 上的吸附行为以及由此产生的表面电荷变化来解释。在所有条件下，即使 HAc-MNPs 上的阴离子吸附量 (0.14-22.56mg/g) 高于 PAA-MNPs (0.04-18.34mg/g)，PAA-MNPs 的带电量也比 HAc-MNPs 更负，因为 PAA 的 pH 值 (2.6±0.1) 低于 HAc 的 pH 值 (3.7±0.1)。即使在相当高的磷酸盐浓度下，磷酸盐也不会取代 HAc 或 PAA 涂层。与 HAc-MNPs 相比，在所有研究条件下，PAA-MNPs 的稳定性都得到了极大的提高，这可能是由于 PAA-MNPs 之间存在更强的静电和额外的空间排斥力。此外，在所有条件下，DLVO（Derjaguin-Landau-Verwey-Overbeek）都很好地解释了 HAc-MNPs 的聚集动力学；而扩展的 DLVO（EDLVO）成功地预测了 PAA-MNPs 的聚集动力学，这表明了 PAA-MNPs 之间的空间力。在不同的电解质溶液中，HA (2mg C/L) 的添加都抑制了 HAc/PAA-MNPs 的聚集。本研究表明，由于静电和额外的空间排斥力更强，分子量和 pK 值较高的羧基涂层可以更好地稳定 MNPs。然而，在 HA 的存在下，这两种力主要由吸附的 HA 而不是 MNPs 上的有机预涂层控制。
