Combustion synthesis of CeO2 nanoparticles for aging and inhalation exposure studies

The continuous production of an aerosol of CeO2 nanoparticles is valuable for nanoparticle aging and inhalation exposure studies, compared with other synthesis processes that require subsequent handling and preparation of the aerosol which can alter nanoparticle properties. This paper describes a new method for producing CeO2 nanoparticles and a novel facility where a combustion synthesis system was integrated in-line with an atmospheric ultraviolet (UV) aging chamber and an inhalation exposure system. Poly-disperse CeO2 nanoparticles were continuously produced to demonstrate the capability of the integrated nanoparticle synthesis and delivery system. The CeO2 nanoparticles were products of combustion of cerium acetate hydrate, a solid-phase precursor, with gas-phase hydrogen, oxygen, and nitrogen reactants. Results for particle size, concentration, crystal structure, and morphology are presented for the CeO2 nanoparticles produced in this study with and without UV exposure in the aging chamber. The setup successfully demonstrated the capability to maintain a steady CeO2 particle number concentration throughout four hours of operation with ~90% of the particles less than 200 nm in size, corresponding to a mass concentration of approximately 500 μg/m3. The CeO2 nanoparticle morphology (including primary particle size and aggregate size) and crystalline phase showed minimal sensitivity to UV aging in the ambient urban environment used in the study. The results indicate other species co-produced in diesel fuel systems (where CeO2 nanoparticles are used as a fuel additive) or found in the urban atmosphere may be required to affect the aging of CeO2 nanoparticles observed in previous studies.