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Nanomaterials 2016, 6(5), 90; doi:10.3390/nano6050090

Aggregation and Colloidal Stability of Commercially Available Al2O3 Nanoparticles in Aqueous Environments

Department of Earth and Environmental Science, College of Science and Technology, Temple University, Philadelphia, PA 19122, USA
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Author to whom correspondence should be addressed.
Academic Editor: Yoshihiro Ito
Received: 2 February 2016 / Revised: 28 April 2016 / Accepted: 3 May 2016 / Published: 13 May 2016
(This article belongs to the Special Issue Engineered Nanomaterials in the Environment)
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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. View Full-Text
Keywords: aluminum oxide; nanoparticles; humic acid; montmorillonite; aggregation aluminum oxide; nanoparticles; humic acid; montmorillonite; aggregation
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MDPI and ACS Style

Mui, J.; Ngo, J.; Kim, B. Aggregation and Colloidal Stability of Commercially Available Al2O3 Nanoparticles in Aqueous Environments. Nanomaterials 2016, 6, 90.

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