Continuous gas-phase synthesis of iron nanoparticles at ambient conditions with controllable size and polydispersity.

HYPOTHESIS

By altering aerosol growth dynamics with unipolar charges, one can obtain aerosols with narrow particles size distributions, a highly desirable feature in applications of functional nanoparticles.

EXPERIMENTS

Unlike liquid colloid systems, aerosol particles in the free molecular regime undergo coarsening due to Brownian coagulation and will eventually attain a self-preserving size distribution with a typical geometric standard deviation of 1.46 - 1.48. We developed a novel continuous one-step aerosol synthesis reactor that produces iron nanoparticles from ferrocene at ambient conditions, which confines the site of precursor breakdown and particle formation in the downstream vicinity of a positive corona discharge.

FINDINGS

We demonstrated that the particle size could be controlled within 3 - 10 nm with a suppressed geometric standard deviation (1.15 - 1.35). The as-produced iron nanoparticles were successfully used as catalyst for the growth of single-walled carbon nanotubes with a narrow diameter range. With a transient aerosol dynamics model, we showed that a fraction (as small as 0.1%) of unipolar-charged particles could have a significant impact on the aerosol growth dynamics, which eventually results in a narrower particle size distribution with smaller size and higher number concentrations.