title: Heteroaggregation of Cerium Oxide Nanoparticles and Nanoparticles of Pyrolyzed Biomass.
abstract: 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 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 alone, and n-PCM is negative and stable alone, 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 core-shell heteraggregate at a size that decreases with n-PCM concentration. The CNCR and CACS mechanisms give fundamental insight into heteroaggregation between oppositely charged, and between neutral and charged nanoparticles.
authors.affiliation: Department of Environmental Sciences, The Connecticut Agricultural Experiment Station , New Haven, Connecticut 06511, United States.|Department of Civil, Environmental and Geomatics Engineering, Florida Atlantic University , Boca Raton, Florida 33431, United States.
authors.forename: Peng
authors.initials: P
authors.lastname: Yi
authors.affiliation: Department of Environmental Sciences, The Connecticut Agricultural Experiment Station , New Haven, Connecticut 06511, United States.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Pignatello
authors.affiliation: Agricultural Research Service, United States Department of Agriculture , 1100 Robert E. Lee Boulevard, New Orleans, Louisiana 70124, United States.
authors.forename: Minori
authors.initials: M
authors.lastname: Uchimiya
authors.affiliation: Department of Analytical Chemistry, The Connecticut Agricultural Experiment Station , New Haven, Connecticut 06511, United States.
authors.forename: Jason C
authors.initials: JC
authors.lastname: White
mesh_terms: D018533:Biomass; D002119:Calcium Carbonate / Q000737:chemistry; D031325:Carya / Q000737:chemistry; D002563:Cerium / Q000737:chemistry*; D002606:Charcoal / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry; D055672:Static Electricity
chemical_list: C540010:biochar; D002606:Charcoal; D002563:Cerium; C030583:ceric oxide; D002119:Calcium Carbonate