Flame-based Aerosol Synthesis of Metal Nanoparticles and Supported-Metal Nanostructures

M. Swihart
University at Buffalo, SUNY,
United States

Keywords: nanomaterial synthesis, High-Temperature Reducing jet, HTRJ, flame

Summary:

This talk will introduce a nanomaterial synthesis method that we call the High-Temperature Reducing Jet (HTRJ) process, describe some of the materials generated by this process, and discuss their applications. Flame-based processes are the dominant commercial approach to the production of large-volume nanomaterials such as carbon black, fumed silica, and titania nanoparticles. However, flame-based synthesis of non-noble metal nanoparticles is not usually possible. In our HTRJ reactor system, the hot combustion products of a fuel-rich hydrogen flame pass through a converging-diverging nozzle to accelerate them to sonic or supersonic velocity. An aqueous metal precursor solution injected at the throat section of the nozzle is atomized by the high velocity gas stream, providing exceptionally rapid heating and mixing of the hot gas and liquid droplets. The droplets evaporate and the precursor decomposes, initiating nucleation of particles in a reducing environment containing excess H2. After the reaction zone, particles are cooled immediately to prevent further particle growth and coalescence. This approach separates combustion chemistry from particle formation chemistry, allowing use of low-cost aqueous solutions of metal nitrates and other salts as precursors. Metals that can be reduced by hydrogen in the presence of water are generated as metallic nanoparticles. Complete conversion of precursors to particles allows precise composition control of alloys and multi-component mixtures. Our recent and current efforts include single-step synthesis of supported metal alloy particles on metal oxides or reduced graphene oxide (RGO), single-step synthesis and surface passivation, and applications of these materials in conductive inks, membranes for hydrogen/CO2 separation, and catalysis.