Heteroaggregation of Cerium Oxide Nanoparticles and Nanoparticles of Pyrolyzed Biomass.

Heteroaggregation with indigenous particles is critical to the environmental mobility of engineered nanomaterials (ENM). We studied heteroaggregation of ceria nanoparticles (n-CeO2), as a model for metal oxide ENM, with nanoparticles of pyrogenic carbonaceous material (n-PCM) derived from pecan shell biochar, a model for natural chars and human-made chars used in soil remediation and agriculture. The TEM and STEM images of n-PCM identify both hard and soft particles, both C-rich and C,O,Ca-containing particles (with CaCO3 crystals), both amorphous and “onion-skin” C-rich particles, and traces of nanotubes. Heteroaggregation was evaluated at constant n-CeO2, variable n-PCM concentration by monitoring hydrodynamic diameter by dynamic light scattering and ζ-potential 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 r...