Continuous-flow, atmospheric-pressure microplasmas: a versatile source for metal nanoparticle synthesis in the gas or liquid phase

Continuous-flow, atmospheric-pressure microplamas are a unique class of plasmas that are highly suitable for emerging nanomaterials applications. Here, we present two schemes for the preparation of metal nanoparticles based on these plasma sources. Nanoparticles are synthesized in the gas phase by non-thermal dissociation of vapor precursors in a microplasma reactor. Monometallic Ni and Fe nanoparticles, as well as compositionally controlled NiFe bimetallic nanoparticles, can be grown with tunable mean diameters between 1 and 5 nm and narrow size distributions. Alternatively, colloidal metal nanoparticles are produced directly in aqueous solutions. Metal cations generated from anodic dissolution of a bulk metal or present in the form of metal salt are reduced by the microplasma to form nanoparticles and capped by a stabilizer. Both approaches are low cost, scalable and general and should allow a wide range of nanoparticle materials to be synthesized in the gas or liquid phase.