Abstract
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−1. The magnitude of interactions and dominant sites of interaction (basal planes versus 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.
Highlights
Nanoparticles (NPs), one of the major classes of nanomaterials, define the particle size class in the range of 1 to 100 nm. Due to their small size, NPs often possess novel physical and chemical properties in comparison to their bulk counterparts, such as higher sorption capacity, greater chemical reactivity, and useful optical signatures. Successful commercialization of their unique properties can be found in various fields, including electronics, cosmetics, biomedical and pharmaceutical sciences, energy technologies, catalytic and material applications, as well as environmental remediation [1,2,3,4,5,6]
The results show that measured ionic Al concentrations in the filtrates ranged from 18 to 33 ppb for the three γ-Al2 O3 NPs, indicating that none of the experimental conditions used for the present study produced a significant concentration of dissolved Al in the solutions
The behavior of three commercial γ-Al2 O3 NPs in aqueous environments was studied in a systematic manner, covering a wide range of natural water conditions
Summary
Nanoparticles (NPs), one of the major classes of nanomaterials, define the particle size class in the range of 1 to 100 nm Due to their small size, NPs often possess novel physical and chemical properties in comparison to their bulk counterparts, such as higher sorption capacity, greater chemical reactivity, and useful optical signatures. Successful commercialization of their unique properties can be found in various fields, including electronics, cosmetics, biomedical and pharmaceutical sciences, energy technologies, catalytic and material applications, as well as environmental remediation [1,2,3,4,5,6]. Γ-Al2 O3 NPs, one of the Al2 O3 NP forms, are very important in high-technology products such as catalysts or catalyst support materials because of their small particle size, high surface area, and, Nanomaterials 2016, 6, 90; doi:10.3390/nano6050090 www.mdpi.com/journal/nanomaterials
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