Location: Commodity Utilization ResearchTitle: Heteroaggregation of cerium oxide nanoparticles and nanoparticles of pyrolyzed biomass
|YI, PENG - Connecticut Agricultural Experiment Station
|PIGNATELLO, JOSEPH - Connecticut Agricultural Experiment Station
|WHITE, JASON - Connecticut Agricultural Experiment Station
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2015
Publication Date: 11/17/2015
Citation: Yi, P., Pignatello, J.J., Uchimiya, M., White, J.C. 2015. Heteroaggregation of cerium oxide nanoparticles and nanoparticles of pyrolyzed biomass. Environmental Science and Technology. 49(22):13294-13303.
Interpretive Summary: Nanometer-scale interactions govern the fundamental processes of agricultural soils. Pyrogenic carbonaceous materials (n-PCM, organic carbon produced by heating under air-depleting conditions) are expected to increase in the coming decades by wild fire and intentional amendment of biochar, i.e., pyrolyzed biomass. This study elucidated the fundamental nano-scale interaction mechanisms that nanoparticles will experience on farm. The n-PCM produced from pecan shell biochar was used as the model naturally-occurring nanoparticle. Changes in pH and salt concentration, and the existence of anthropogenic engineered (cerium oxide) nanoparticles were the controlling factors in the environmental fate of natural nanoparticles.
Technical Abstract: Heteroaggregation with indigenous particles is an important process controlling the mobility of engineered nanomaterials in the environment. We studied heteroaggregation of cerium oxide nanoparticles (n-CeO2), which are widely used commercially, with nanoparticles of pyrogenic carbonaceous material (n-PCM) derived from pecan shell biochar. PCM is ubiquitous in soil, and some forms are employed in environmental remediation and agriculture. Images of TEM and STEM indicate that n-PCM carbonaceous particles exist in hard and soft, and amorphous and microcrystalline forms. Calcium carbonate crystals adhering to the particles are abundant. Trace amounts of nanotubes were found in n-PCM through cryo-TEM imaging. Heteroaggregation was evaluated by monitoring hydrodynamic diameter and zeta potential at a constant n-CeO2 concentration and variable n-PCM concentrations, under conditions where nearly all the scattered light intensity originated from n-CeO2 (i.e., n-PCM was ‘invisible’). At pH 5.3, where n-CeO2 is net positively charged and n-PCM is net negatively charged and each is stable to homoaggregation, heteroaggregation is favorable and occurs by a Charge Neutralization-Charge Reversal mechanism (CNCR). According to the CNCR, the heteroaggregate is stable in size at high and low n-CeO2/n-PCM ratios, where it is positively or negatively charged, respectively, while unstable at intermediate ratios. The point of greatest instability occurs when the surface charges of n-CeO2 are fully neutralized by n-PCM particles. Heteroaggregation at that point is irreversible even when the charge on both particles is made negative by raising the pH from 5.3 to 11. At pH 7.1, where n-CeO2 is near neutral and thus undergo favorable homoaggregation, and n-PCM is negative and stable to homoaggregation, adding increasing amounts of n-PCM to a fixed amount of n-CeO2 leads to a decrease in the initial hydrodynamic diameter growth rate (ultimately to zero), an eventual stabilization of the hydrodynamic diameter, and an increasingly negative zeta potential. n-PCM particles form a shell around and stabilize n-CeO2 homoaggregate cores. The size of core-shell heteroaggregate at stabilization is dependent on the n-PCM concentration.