Preparation of metal nanoparticles by salt-assisted spray pyrolysis

Abstract

Metal nanoparticles which exhibit size dependent optical, magnetic, electronic and catalytic properties have been a subject of considerable interest because of potential applications for novel nanostructures. In this thesis, submicron-sized metal particles including silver, tungsten and nickel were prepared by conventional spray pyrolysis by varying operating conditions such as processing temperatures and types of carrier gas. The processing temperature affected the crystallinity and particle size. The crystal size of particles increased with increasing processing temperature. When the Ni particles were prepared, particle size obtained from scanning electron microscope (SEM) was decreased with increasing reaction temperature. These results are explained by the fact that hollow particles melt and become dense particles at low temperature. In the effect of types of carrier gas, hydrogen gas accelerated the decomposition of precursor at low temperature and acted as a reductive agent. Ni metal nanoparticles were prepared by salt-assisted spray pyrolysis (SASP) at various operating conditions such as types and molar concentration of salt and processing temperature. The particle size was decreased with the increase of the salt/Ni molar ratio, and the particle size was increased with the increase of the reaction temperature. Furthermore, the crystallite size obtained from XRD was almost same as the diameter obtained from the BET surface area measurement. The types of salt affect the shape and size of Ni particles. Ni particles were faceted and agglomerated when nitrate salts were used. When NaCl was used as matrix, Ni particles were separated into nano-sized particles more easily than when nitrate salts were used. These results are explained by the relation between melting points of slat and processing temperature. Therefore, in this study, NaCl was found to be better controlling agent than nitrate salts for the preparation of Ni particles. The compositional hom...