Plasma Synthesis of Silver Nanoparticles in Imidazolium-Based Ionic Liquids

Ionic liquids, due to their low vapor pressure and high conductivity, can be combined with low-pressure plasmas to produce metal nanoparticles by reducing dissolved metal salts with the reactive plasma species. In this work, we synthesized 50-nm silver nanoparticles by exposing a solution of AgBF4, dissolved in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), to a DC plasma source. The resulting nanoparticles were extracted and imaged using a field emission scanning electron microscope. Previous studies using ionic liquid electrodes have demonstrated enhanced ionization in the plasma and higher discharge currents compared to metal electrodes. This effect has been attributed to the high secondary electron emission (SEE) yield of ionic liquids. In our study, we measured the SEE yields of three different ionic liquids by bombarding them with electrons and recording the resulting currents. The maximum SEE yield was approximately 2. To better understand this behavior, we conducted molecular orbital calculations, identifying the likely electron donors within each ionic liquid.