Due to the wide application and reported toxicity of cerium oxide nanoparticles (n-CeO2), it is important to predict their fate and transport once released to the environment. Pyrogenic carbonaceous material (PCM) from incidental sources, such as biomass burning and fuel combustion, as well as human made biochar is widespread in soil. Nanoparticulate forms of natural chars and biochars have been reported and are expected to have considerable effects on the fate and transport of many contaminants, including engineered nanoparticles. In this study, the influence of PCM nanoparticles (n-PCM) on the colloidal stability of n-CeO2 is investigated. The shape, elemental composition, atomic arrangement, and colloidal stability of n-PCM derived from pecan shell biochar are characterized. Heteroaggregation of n-CeO2 with n-PCM is induced by adding variable concentrations of n-PCM to 7.26 mg/L n-CeO2. Hydrodynamic diameter and zeta potential of n-CeO2 were monitored by dynamic light scattering under conditions where n-PCM is “invisible”. At pH 5.3, where n-CeO2 and n-PCM are positively and negatively charged, respectively, and each stable to homoaggregation, heteroaggregation is favorable and occurs by a Charge Neutralization-Charge Reversal mechanism (CNCR): in this mechanism, primary heteroaggregates that form in the initial stage are stable at low or high n-PCM concentration due to electrostatic repulsion, but unstable at intermediate n-PCM concentration, leading to secondary heteroaggregation. The greatest instability coincides with full charge neutralization. At pH 7.1, where n-CeO2 is neutral and unstable, and n-PCM is negative and stable to homoaggregation, heteroaggregation occurs by a Charge-Accumulation, Core-shell Stabilization (CACS) mechanism: n-PCM binds to and forms a negatively charged shell on the neutral surface of the nascent n-CeO2 core, stabilizing the n-CeO2 core at a hydrodynamic diameter that decreases with n-PCM concentration. In addition, the reversibility of the heteroaggregation is examined by raising pH.

Influence of nanoparticles of pyrogenic carbonaceous material on the colloidal stability of cerium oxide nanoparticles

252nd National Meeting (2016)

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