Mui Julie, Ngo Jennifer, Kim Bojeong
Department of Earth and Environmental Science, College of Science and Technology, Temple University, Philadelphia, PA 19122, USA.
Nanomaterials (Basel). 2016 May 13;6(5):90. doi: 10.3390/nano6050090.
The aggregation and colloidal stability of three, commercially-available, gamma-aluminum oxide nanoparticles (γ-Al₂O₃ NPs) (nominally 5, 10, and 20-30 nm) were systematically examined as a function of pH, ionic strength, humic acid (HA) or clay minerals (e.g., montmorillonite) concentration using dynamic light scattering and transmission electron microscopy techniques. NPs possess pH-dependent surface charges, with a point of zero charge (PZC) of pH 7.5 to 8. When pH < PZC, γ-Al₂O₃ NPs are colloidally stable up to 100 mM NaCl and 30 mM CaCl₂. However, significant aggregation of NPs is pronounced in both electrolytes at high ionic strength. In mixed systems, both HA and montmorillonite enhance NP colloidal stability through electrostatic interactions and steric hindrance when pH ≤ PZC, whereas their surface interactions are quite limited when pH > PZC. Even when pH approximates PZC, NPs became stable at a HA concentration of 1 mg·L. The magnitude of interactions and dominant sites of interaction (basal planes edge sites) are significantly dependent on pH because both NPs and montmorillonite have pH-dependent (conditional) surface charges. Thus, solution pH, ionic strength, and the presence of natural colloids greatly modify the surface conditions of commercial γ-Al₂O₃ NPs, affecting aggregation and colloidal stability significantly in the aqueous environment.
使用动态光散射和透射电子显微镜技术，系统研究了三种市售的γ-氧化铝纳米颗粒（γ-Al₂O₃ NPs）（标称尺寸分别为5、10和20 - 30 nm）的聚集和胶体稳定性与pH值、离子强度、腐殖酸（HA）或粘土矿物（如蒙脱石）浓度之间的关系。纳米颗粒具有pH依赖性表面电荷，零电荷点（PZC）为pH 7.5至8。当pH < PZC时，在高达100 mM NaCl和30 mM CaCl₂的条件下，γ-Al₂O₃ NPs具有胶体稳定性。然而，在高离子强度的两种电解质中，纳米颗粒都会发生显著聚集。在混合体系中，当pH ≤ PZC时，HA和蒙脱石都通过静电相互作用和空间位阻增强纳米颗粒的胶体稳定性，而当pH > PZC时，它们的表面相互作用非常有限。即使pH接近PZC，当HA浓度为1 mg·L时，纳米颗粒也会变得稳定。相互作用的强度和主要作用位点（基面 边缘位点）显著依赖于pH值，因为纳米颗粒和蒙脱石都具有pH依赖性（条件性）表面电荷。因此，溶液pH值、离子强度和天然胶体的存在极大地改变了市售γ-Al₂O₃ NPs的表面条件，在水环境中显著影响其聚集和胶体稳定性。
