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.