Production of residue-free nanoparticles by atomization of aqueous solutions

It has been difficult to produce physically and chemically pure nanoparticles from a particle solution in deionized (DI) water by atomization due to residue from impurities in the DI water. In this study, we show that further purification of DI water by reverse osmosis (RO) membrane filtration under high pressure (900 psi) substantially reduces solvent impurities when submicrometer and nanosized particles are atomized. Comparison of size distributions among several types of DI water showed that the production of residual particles significantly decreased by a factor of ∼11 (by number) after the RO filtration of regular DI water from commercially available DI water. Mixing states of aerosolized particles produced from particle solutions were examined by using the hygroscopicity tandem differential mobility analyzer technique and transmission electron microscopy/energy dispersive spectroscopy. We found that residual particles were externally mixed with particles of interest during the aerosolization and drying process and that impurities in DI water can beadded onto the target particles (i.e., internally mixed). By removing impurities in DI water by the RO filtration, the effect of impurities for the production of clean nanoparticles was significantly reduced, suggesting that the atomization method can still be a promising tool to produce pure nanoparticles in a simple and inexpensive way.